Synthesis of a Heterometallic Trinuclear Cluster of Ruthenium and

Article pubs.acs.org/Organometallics

Synthesis of a Heterometallic Trinuclear Cluster of Ruthenium and Platinum with a Linear Alignment Takuya Kuzutani,† Yushi Torihata,† Hiroharu Suzuki,† and Toshiro Takao*,†,‡ †

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan ‡ JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 3332-0012, Japan S Supporting Information *

ABSTRACT: A heterobimetallic trinuclear complex of Ru and Pt in a linear alignment, {Cp*Ru(H)2}2(Pt)(μ-PtBu2)2(μ-H)2 (2; Cp* = η5-C5Me5), was synthesized via P−C bond scission upon the photolysis of Cp*Ru(μ-H)4RuCp* (1) in the presence of Pt(PtBu3)2. Complex 2 was alternatively synthesized by the reaction of 1 with Pt(PtBu2H)3, together with the formation of a triangular Ru2Pt complex, (Cp*Ru)2{Pt(PtBu2H)}(μ-PtBu2)(μ-H)3(H)2 (4). X-ray diffraction experiments showed that the structure of 2 could be regarded as a dimer of [Cp*RuH3(PtBu2)]− fragments linked by a Pt2+ ion. In contrast to the relevant monometallic trihydrido complex of ruthenium, Cp*RuH3(PtR3), terminal hydrides of 2 were readily substituted by CO and ethylene, leading to the formation of {Cp*Ru(L)}2(Pt)(μ-PtBu2)2(μ-H)2 (5; L = CO, 6; L = C2H4). Such high reactivity could be attributed to the facile formation of a coordinatively unsaturated intermediate owing to stabilization by bulky μ-PtBu2 moieties as well as electronic influence of the central Pt atom. In fact, terminal hydrides of 2 were readily removed upon evacuation, leading to the formation of tetra- and dihydrido complexes (Cp*Ru){Cp*Ru(H)2}Pt(μ-PtBu2)2(μ-H)2 (3) and (Cp*Ru)2Pt(μ-PtBu2)2(μ-H)2 (8), consecutively. Upon hydrogenation, 3 and 8 were smoothly transformed into 2. In contrast with the reactions of 2 with 2e donors, substitution at the Pt atom occurred in reactions with Ph2SiH2 and Et2SiH2, resulting in μsilylene and μ-silyl complexes {Cp*Ru(H)}{Cp*Ru(PtBu2H)}Pt(μ-PtBu2)(μ-SiPh2)(μ-H)2 (9) and {Cp*Ru(H)2}{Cp*Ru(PtBu2H)}Pt(μ-PtBu2)(μ-η2-SiEt2)(μ-H)2 (10), respectively. In these reactions, the μ-phosphido ligand bridging the Ru and Pt atoms was transformed into a terminal phosphine ligand at the peripheral Ru atom, alongside the formation of μ-silylene and μsilyl ligands via reductive P−H bond formation.

■

INTRODUCTION Bimetallic catalysts are widely utilized in chemical processes because they often show superior selectivity and activity to the catalyst of their parent metals.1 Mixed-metal clusters are good precursors for supported bimetallic nanoparticles due to the guarantee of their stoichiometry. Thus, various novel nanocatalysts have been prepared from structurally well-defined mixed-metal clusters.2 In particular, bimetallic catalysts composed of platinum and other metals have attracted considerable attention due to their wide use in petroleum reforming processes.3 Among various platinum-based bimetallic catalysts, interest in the combination of Pt and Ru has significantly increased due to their remarkable activity in the hydrogenation of benzoic acid, naphthalene, and dimethyl terephthalate,4 catalytic partial oxidation of methane,5 and catalytic hydrogenolysis of alkanes6 as well as their application in hydrogen fuel cells.7 As an anisotropic Ru−Pt bond would be responsible for the enhanced reactivity and selectivity, the reactivity of Ru/Pt clusters themselves has been intensively studied in order to evaluate the influence of the heterometallic bond.8,9 Adams and co-workers elucidated that a heterometallic Ru/Pt cluster, © XXXX American Chemical Society

Pt3Ru6(CO)20(μ3-PhCCPh)(μ3-H)(μ-H), is a more effective catalyst for hydrogenation and hydrosilylation of diarylalkynes than its homometallic analogues.8 Heterometallic Ru/Pt clusters are commonly prepared by the reaction of a carbonyl-cluster-derived Ru species with Pt complexes.10 One such successful method to obtain a heterometallic Ru−Pt bond is by the addition of “Pt(PtBu3)” groups, which are generated from Pt(PtBu3)2, to the metal− metal bond of a coordinatively saturated carbonyl cluster.11 More importantly, the sterically demanding nature of the “Pt(PtBu3)” unit enables it to stabilize an unsaturated cluster skeleton. Although Re2(CO)10 does not afford an adduct with “Pt(PtBu3)”, Re2(CO)10 reacts with Pt(PtBu3)2 with the loss of CO to yield a trigonal bipyramidal pentanuclear cluster, Re2Pt3(CO)6(PtBu3)3.12 This Re2Pt3 cluster contains only 62 valence electrons, which is fewer than the 72 electrons expected for a saturated pentanuclear cluster in tbp form. Owing to its unsaturated nature, the Pt3Re2 cluster readily reacts with three molecules of hydrogen to form a series of hydrido clusters, Received: June 3, 2016

A

DOI: 10.1021/acs.organomet.6b00449 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Re2Pt3(CO)6(PtBu3)3(H)n (n = 2, 4, 6). Adams et al. also demonstrated the reversibility of these hydrido clusters, which smoothly eliminate dihydrogen from the cluster core upon irradiation. We have investigated the various transformations of hydrocarbyl ligands on a triruthenium cluster derived from {Cp*Ru(μ-H)}3(μ3-H)2 and showed that liberation of hydrogen from the cluster is crucial not only for the generation of a vacant site but also for the promotion of the skeletal rearrangement of hydrocarbyl ligands located on the cluster surface.13 As shown for Re2Pt3 clusters, the introduction of the “Pt(PtBu3)” unit into the polyhydrido cluster skeleton is a promising approach to increase mobility of a hydrido ligand, hence providing reactive polyhydrido clusters. As mentioned above, many methods for obtaining heterometallic Ru/Pt clusters using coordinatively saturated Ru clusters have been well documented.10 However, the reaction of unsaturated Ru clusters with Pt species has scarcely been investigated, even though their unsaturated nature is expected to permit the selective formation of a bimetallic core. Takemoto et al. succeeded in synthesizing a Ru2Pt cluster with a μ3-imido ligand in a selective manner by the reaction of coordinatively unsaturated diruthenium complex (Cp*Ru)2(μCH2)(μ-NPh) with Pt(C2H4)(PMe3)2 (Cp* = η5-C5Me5).14 We reported the syntheses of heterometallic clusters (Cp*Ru) 2 (Cp*Ir)(H) 4 , 1 5 (Cp*Ru) 2 (Cp*Co)(H) 4 , 1 6 (Cp*Ru)2(Cp*Os)(H)5,17 and (Cp*Ru)2(Cp*Re)(H)4,18 from Cp*Ru(μ-H)4RuCp* (1). In these reactions, the unsaturated nature of 1 effectively drove the formation of a heterometallic architecture. Thus, 1 was anticipated to readily form a heterometallic adduct upon treatment with Pt(PtBu3)2. However, unlike the reaction of [Ru5(CO)15(C)] with Pt(PtBu3)2,11a this reaction did not provide a simple “Pt(PtBu3)” adduct. Instead, a trinuclear bimetallic complex with a linear arrangement was obtained as a consequence of P−C bond cleavage. In this article, we discuss the reaction of 1 with Pt(PtBu3)2 and Pt(PtBu2H)3 leading to the formation of novel heterometallic Ru2Pt clusters.

Figure 1. Molecular structure and labeling scheme of 2 with thermal ellipsoids at the 30% probability level: (a) top view and (b) side view. Selected bond lengths (Å) and angles (deg): Pt(1)−Ru(1) = 2.8701(3), Pt(1)−P(1) = 2.2781(7), Pt(1)−H(3) = 1.63(4), Ru(1)−P(1) = 2.3279(7), Ru(1)−H(1) = 1.54(5), Ru(1)−H(2) = 1.64(5), Ru(1)−H(3) = 1.74(5), Ru(1)−Pt(1)−Ru(1#) = 180, Ru(1)−Pt(1)−P(1) = 52.236(18), Ru(1)−Pt(1)−P(1#) = 127.763(18), Ru(1)−Pt(1)−H(3) = 32.9(15), Ru(1)−Pt(1)−H(3#) = 147.1(15), P(1)−Pt(1)−P(1#) = 180, P(1)−Pt(1)−H(3) = 84.4(15), P(1)−Pt(1)−H(3#) = 95.6(15), Pt(1)−Ru(1)−P(1) = 50.683(19), Pt(1)−Ru(1)−H(3) = 30.6(13), P(1)−Ru(1)−H(3) = 80.6(13), Pt(1)−P(1)−Ru(1) = 77.08(2).

■

RESULTS AND DISCUSSION Preparation of a Ru2Pt Complex with a Linear Alignment. In order to obtain a “Pt(PtBu3)” adduct of a diruthenium complex, Cp*Ru(μ-H)4RuCp* (1) was subjected to react with Pt(PtBu3)2. While no bimetallic complex was formed upon heating at 100 °C,19 a mixture containing a trinuclear bimetallic Ru2Pt complex was formed upon photolysis. Irradiation of the THF solution of 1 in the presence of an equimolar amount of Pt(PtBu3)2 at 0 °C gave a trinuclear bimetallic complex, {Cp*Ru(H)2}2Pt(μ-PtBu2)2(μ-H)2 (2), with a linear Ru−Pt−Ru alignment (eq 1). Complex 2 was

Pt(1)−P(1#) were shown to be 180°, respectively. Two of the six hydrides, H(3) and H(3#), bridged the Ru and Pt atoms, while the other four hydrides were coordinated to Ru atoms as terminal hydrides. The terminal coordination of hydrides was also confirmed by the strong ν(Ru−H) absorption at 1991 cm−1 in the IR spectrum. Owing to the presence of the terminal hydrides, Cp* groups were bent away from the Ru−Pt−Ru vector by 34° in a mutually transoid fashion. The Ru−Pt distance (2.8701(3) Å) lay within the reported range for Ru−Pt bonds (2.61−3.26 Å),20 but might not be indicative of direct Ru−Pt bonding. The geometry at the Pt atom was shown to be planar, with the sum of bond angles around the Pt(1) atom, Ru(1)−Pt(1)−P(1), Ru(1)−Pt(1)− P(1#), Ru(1#)−Pt(1)−P(1), and Ru(1#)−Pt(1)−P(1#), being 360°. The bridging hydrides were also located on the same plane as the Ru, Pt, and P atoms. Whereas the positional data for hydride are intrinsically inaccurate in an X-ray diffraction study, the structure is also supported by DFT calculation on 2 (Figure S-52 in the Supporting Information). On the basis of the values for P(1)−Pt(1)−H(3) (84.4(15)°) and P(1)− Pt(1)−H(1#) (95.6(15)°), the geometry at the central platinum atom was described as a square planar conformation

isolated from the crude mixture in 25% yield by recrystallization. The linear Ru−Pt−Ru skeleton was unambiguously confirmed by X-ray diffraction, as shown in Figure 1. The central platinum atom was located at the center of inversion, and the angles Ru(1)−Pt(1)−Ru(1#) and P(1)− B


Article

Organometallics

In addition to the Cp* flipping motion, rapid site exchange of the hydrido ligands also occurred in 2. The 1H NMR spectrum recorded at 25 °C exhibited a time-averaged signal in the hydrido region: a triplet observed at δ −11.57 ppm (JP−H = 6.0 Hz) with satellite signals due to spin−spin coupling with the 195Pt nucleus (JPt−H = 264 Hz) (Figure 2). This signal broadened as the temperature decreased, becoming buried under the baseline at −90 °C.

ligated by two H and two P atoms, which strongly suggested that the formal oxidation state of the Pt atom was +2. This implied that electron transfer from Pt(0) to Ru(III) took place at the initial stage of the reaction. Subsequent C−H oxidative addition of a t-Bu group, which was followed by the elimination of isobutene, took place at each Ru center. Thereby, the formal oxidation state of the Ru center in 2 was estimated to be +4. While several triangular Ru2Pt clusters are known,9b,11d,f,21 linear Ru2Pt complexes are less common;22 Goh and coworkers synthesized a linear Ru2Pt complex, [{Cp*Ru(μ-η2:η3tpdt)}2Pt]2+ (tpdt = 3-thiapentane-1,5-dithiolate), by the reaction of Cp*Ru(η3-tpdt) with PtCl2. In contrast, the Pt atom in Pt{Ru3(CO)9(μ-H)(μ3-CCtBu)}2, which was synthesized by the reaction of Ru3(CO)9(μ-H)(μ3-CCtBu)} with Pt(C2H4)3 by Farrugia and co-workers, adopted a distorted tetrahedral geometry, in which the value of Ru−Pt−Ru was shown to be 144.3(1)°.23 This was likely owing to the nature of the central Pt(0) atom. In the 1H NMR spectrum of 2 recorded at 25 °C, a sharp singlet, assigned to the Cp*, was observed at δ 2.01, which agreed with the Ci structure of 2. While a triplet-like signal derived from the t-Bu groups was observed at δ 1.45 at 25 °C,24 it became broad as temperature decreased, becoming buried beneath the baseline at −90 °C (Figure S-6 in the Supporting Information). This dynamic behavior was rationalized by the flipping motion of the Cp* groups, leading to site exchange of the syn and anti t-Bu groups with respect to the Cp* groups (Scheme 1), but the motion was not frozen within the NMR time scale even at −100 °C.

Figure 2. Variable-temperature 1H NMR spectra of 2 showing the hydrido region (400 MHz, THF-d8:toluene-d8 = 4:1).

As the structure of 2 can be regarded as a dimer of [Cp*RuH3(PtBu2)]− fragments linked by a Pt2+ ion, 2 was expected to have properties similar to a monometallic trihydrido complex of ruthenium, Cp*RuH3(PR3).25 Chaudret and co-workers synthesized related heterometallic clusters derived from Cp*RuH3(PCy3) and copper salts, [{Cp*RuH(PCy3)}2Cu(μ-H)4]+ and [{Cp*RuH(PCy3)}2{Cu(μ-Cl)}2(μH)4]+, which demonstrated similar dynamic behavior, namely, site exchange between the terminal and bridging hydrides.26 It is well-known that the three hydrides in Cp*RuH3(PR3) exhibit quantum-mechanical exchange couplings, which provide extremely large spin−spin couplings between hydrides.25 Although a detailed discussion of the distance relating to a hydrido ligand is impeded, relatively short H−H distances (H(1)−H(2) = 1.54 Å, H(1)−H(3) = 1.97 Å) seem similar to those found for Cp*RuH3(PR3) (1.48−1.70 Å). Therefore, the severe broadening of hydrido signals partly arose from quantum-mechanical exchange couplings as seen in the monometallic trihydrido complexes. The molecular structure of 2 unambiguously showed the loss of one t-Bu group from a PtBu3 fragment. Adams et al. also reported P−C bond cleavage in the reaction of Os3(CO)12 with Pt(PtBu3)2. When the reaction was performed at 97 °C, a μ3vinylidene complex, Pt2Os3(CO)9(PtBu3)(μ-PtBu2)(μ-H)(μ3η2-CCMe2), with a μ-di-tert-butylphosphido group was formed via a cyclometalated intermediate, Pt2Os3(CO)10(PtBu3)(PtBu2CMe2CH2)(μ-H).27 This sequence implied that the μ-phosphido group was formed via an initial C−H bond cleavage in the Me group, and subsequent C−H bond cleavage followed by P−C bond scission led to the formation of the μ3CCMe2 group. In our case, a vinylidene fragment was not formed in the Ru2Pt skeleton. Instead, isobutene was liberated, as confirmed using 1H NMR spectroscopy.28 This fact strongly suggests that two of the six hydrides were derived from the t-Bu groups, while the other four hydrides originated from 1.

Scheme 1. Plausible Mechanism for Site Exchange between the syn and anti t-Bu Groups in 2

It is reasonable to assume that site exchange proceeds via the formation of an isomeric cisoid intermediate, cis-2, where the two Cp* groups are directed to the same side with respect to the Ru−Pt−Ru vector. As mentioned later, we found an equilibrium between the cisoid and transoid isomers of linear Ru2Pt complex 5, in which CO replaced the terminal hydrides. The ratio of cis- and trans-5 was estimated to be 42/58 in solution. This indicated that the energy difference between cis-5 and trans-5 was not significant. Thus, a considerable amount of cis-2 would be also populated in the solution prepared from a single crystal of trans-2, although the formation of cis-2 was not detected in the VT-NMR spectra. This might arise from the rapid isomerization between them, leading to the production of a time-averaged spectrum. C


Article

Organometallics The formation of μ-di-tert-butylphosphido groups in 2 prompted us to examine the reaction using PtBu2H, in which complex 2 would be directly formed from the reaction of 1 with Pt(PtBu2H)3.29 Pt(PtBu2H)3 was shown to equilibrate with Pt(PtBu2H)2 in solution via elimination of a phosphine ligand. In fact, 1 spontaneously reacted with Pt(PtBu2H)3 at 0 °C to yield 2 in 66% yield (eq 2). A dehydrogenated trinuclear

Figure 3. Molecular structure and labeling scheme of 4 with thermal ellipsoids at 30% probability level. Selected bond lengths (Å) and angles (deg): Pt(1)−Ru(1) = 2.7483(3), Pt(1)−Ru(2) = 2.9163(3), Ru(1)−Ru(2) = 2.9692(3), Pt(1)−P(1) = 2.2158(8), Pt(1)−H(1) = 1.43(4), Pt(1)−H(2) = 1.90(4), Pt(1)−H(3) = 1.78(4), Ru(1)−P(2) = 2.2844(7), Ru(1)−H(2) = 1.60(4), Ru(1)−H(4) = 1.61(4), Ru(2)−P(2) = 2.3614(7), Ru(2)−H(3) = 1.69(4), Ru(2)−H(4) = 1.87(4), Ru(2)−H(5) = 1.49(3), Ru(1)−Pt(1)−Ru(2) = 63.142(7), Ru(1)−Pt(1)−P(1) = 165.440(19), Ru(2)−Pt(1)−P(1) = 114.84(2), Pt(1)−Ru(1)−Ru(2) = 61.193(7), Pt(1)−Ru(1)−P(2) = 89.12(2), Ru(2)−Ru(1)−P(2) = 51.429(19), Pt(1)−Ru(2)−Ru(1) = 55.665(7), Pt(1)−Ru(2)−P(2) = 83.737(18), Ru(1)−Ru(2)−P(2) = 49.140(18), Ru(1)−P(2)−Ru(2) = 79.43(2).

complex, (Cp*Ru){Cp*Ru(H) 2}Pt(μ-P tBu 2) 2(μ-H)2 (3), which was alternatively prepared via dehydrogenation of 2 under reduced pressure (vide inf ra), was also produced in 19% yield. As 3 was readily transformed to 2 upon treatment with 1 atm of H2, 2 was isolated in 72% yield by treatment of the mixture with 1 atm of H2. In contrast to the reaction with Pt(PtBu3)2, an isomeric triangular Ru2Pt complex, (Cp*Ru)2{Pt(PtBu2H)}(μ-PtBu2)(μH)3(H)2 (4), was formed in 13% yield, alongside 2.30 Thermolysis of 4 resulted in its conversion to 2, but the reaction took 14 h at 50 °C. Thermolysis of 2 resulted in the formation of 3, along with decomposition into unidentified products, and did not afford 4 at all. These facts suggested that 2 was not generated via the formation of 4 as an intermediate, or in equilibrium with 4, but that these isomers were formed independently. In order to gain mechanistic insight into the formation of 2, the reaction of a mixture of 1 and EtCpRu(μ-H)4RuEtCp (1′) (EtCp = η5-C5Me4Et) with Pt(PtBu2H)3 was examined. Similar to the reaction shown in eq 2, complexes 2, 3, and 4 were formed, together with their corresponding EtCp analogues, 2′, 3′, and 4′. However, crossover products containing both Cp*Ru and EtCpRu fragments were not produced. This strongly indicated that 1 maintains its diruthenium skeleton when reacting with “Pt(PtBu2H)2”. Preparation of the Triangular Ru2Pt Complex 4. When 1 and Pt(PtBu2H)3 were premixed in the solid state in a 2:1 ratio, then dissolved in toluene at 25 °C, the selectivity for the triangular complex 4 increased to 47%, which was determined by the 1H NMR spectrum of the crude product. Although the reason for this change in selectivity was not clear, a possible explanation was that premixing in the solid state might enable the reaction of 1 with Pt(PtBu2H)3 and not with “Pt(PtBu2H)2” formed in the equilibrium. Under these conditions, 1 was able to react with Pt(PtBu2H)3 before most Pt(PtBu2H)3 was converted into Pt(PtBu2H)2. Complex 4 was isolated using column chromatography on alumina, and the molecular structure of 4 was determined by X-ray diffraction, as shown in Figure 3. The ORTEP diagram clearly shows the triangular Ru2Pt skeleton of 4. Whereas the examples of bimetallic trinuclear Ru2Pt complexes with linear skeletons are quite limited, several examples of triangular Ru 2 Pt complexes have been known.9b,11d,f,21 The sum of the bond angles around the Pt

atom with P(1), H(1), H(2), and H(3) atoms is 356.9°. Although the environment of the Pt center in 4 is slightly distorted from square planar geometry, the formal oxidation state of the Pt center was also considered to be +2. While one PtBu2H group remained in contact with the Pt atom, the other was coordinated to two Ru atoms as a μ-phosphido group. The locations of the phosphine and μ-phosphido groups are the same as those found for the triangular complex {Ru(CO)3}2{Pt(CO)(PCy3)}(μ-PPh2)(μ-H), reported by Powell et al., which also possessed a terminal phosphine ligand at the Pt center and a μ-PPh2 group at the Ru−Ru edge.21a The length of Ru(2)−Pt(1) (2.9163(3) Å) was considerably greater than that of Ru(1)−Pt(1) (2.7483(3) Å), which was likely due to steric repulsion between the PtBu2H and the Cp* groups on Ru(2). The trans influence arising from the terminal hydride, H(1), which was trans to Ru(2), seemed to also be responsible for elongation of the Ru(2)−Pt(1) bond. The positions of the hydrido ligands were successfully determined by diffraction study; two terminal hydrides, H(1) and H(5), were respectively located at the Pt(1) and Ru(2) atoms, while the other three hydrides were located at each M− M edge. In the 1H NMR spectrum recorded at −30 °C, five hydrido signals were observed at δ −18.77 (m, 1H, JPt−H = 478 Hz), −18.75 (dd, 1H, JP−H = 68.6, 17.2 Hz, JPt−H = 317 Hz), −10.94 (s, 1H), −9.19 (d, 1H, JP−H = 28.8 Hz, JPt−H = 1254 Hz), and −7.52 (dd, 1H, JP−H = 12.7, 12.7 Hz, JPt−H = 337 Hz). Among them, the signal resonating at δ −9.19 was assigned to the terminal Pt−H(1), based on the large JPt−H value (1254 Hz), and the singlet signal at δ −10.94 was assigned to the terminal hydride, H(5), on the Ru(2) atom. The two highshielded signals are likely attributed to the bridging hydrido ligands at the Ru(1)−Pt(1) and Ru(2)−Pt(1) edges (H(2) and D


Article

Organometallics H(3), respectively). Due to the large 2JP−H value (68.6 Hz), the signal at δ −18.75 was assigned to H(2), which was trans to P(1). The hydrido signal resonating at δ −7.52 was therefore assigned to the μ-hydride positioned at the Ru−Ru edge, H(4). Whereas the distance between the H(4) and Pt(1) atoms (2.2 Å) seemed to be slightly larger than the direct Pt−H interaction, the small JPt−H value of 337 Hz implied that there could be a weak interaction between H(4) and Pt(1). The IR spectrum of 4 showed strong absorptions arising from ν(Pt−H) and ν(P−H) at 2132 and 2272 cm−1, respectively. In contrast, the ν(Ru−H) appeared as a very weak absorption at 1996 cm−1. The reason for significant weakening of the ν(Ru−H) was unclear, but the weak intensity of ν(Ru−H) compared with that of ν(Pt−H) was reasonably reproduced by DFT calculations (Figure S-14 in the Supporting Information). These hydrido signals were observed to be broad as a consequence of site exchange above room temperature (Figure S-11 in the Supporting Information). Since the time-averaged spectrum was not obtained up to 65 °C, the motion of the hydrido ligands in 4 is not currently clear. Instead, the spectral change in the Cp* signals revealed the twisting motion of the Pt center, which resulted in the positions of the PtBu2H and the terminal hydride, H(1), at the Pt(1) atom exchanging as shown in Scheme 2. Consequently, the Cp* signals resonating at δ 1.93 and 2.02 ppm at 0 °C became broad at elevated temperature and coalesced at 40 °C, as shown in Figure 4.

Figure 4. Variable-temperature 1H NMR spectra of 4 showing the Cp* region (400 MHz, THF-d8:toluene-d8 = 4:1). The signal marked with ● was the Cp* signal derived from contaminated 2.

Reactions of 2 with 2e Donors. Chaudret and co-workers reported the reaction of ruthenium trihydrido complex Cp*RuH3(Ppyl3) (pyl = pyrrolyl) with CO, yielding Cp*RuH(CO)(Ppyl3).31 Since the environment of the peripheral Ru atoms in 2 resembled that of Cp*RuH3(PR3), we decided to examine the reaction of 2 with CO. While the reaction of Cp*RuH3(PR3) with CO required reflux conditions in toluene, 2 readily reacted with 1 atm of CO at ambient temperature to yield a mixture of bis(carbonyl) complexes {Cp*Ru(CO)}2Pt(μ-PtBu2)2(μ-H)2 (cis- and trans5) (Scheme 3). Among the isomers, only trans-5 was recrystallized from the mixture.

Scheme 2. Dynamic Behavior of the Pt(PtBu2H) and μPhosphido Moieties in 4

Scheme 3. Reactivity of 2 with CO and Ethylene

The Cp* signals also started to broaden as the temperature decreased below 0 °C. The hydride signals also became broad with decreasing temperature. Such spectral changes can be explained by an isomeric equilibrium. As mentioned above, 4 gradually isomerized to 2 upon heating at 50 °C, but 4 was stable below 0 °C. This implied that 4 equilibrated with a different isomer, A, from 2. We tentatively propose that A is the isomer possessing a μ-phosphido ligand at the Ru−Pt edge trans to the terminal PtBu2H group at Pt(1), which can be regarded as an intermediate for the isomerization to 2, although experimental evidence is missing. The structure of A is proposed based on the DFT calculation that suggested that A was less stable than 4 by 8.6 kcal mol−1 (Figure S-54 in the Supporting Information).

X-ray diffraction studies clearly showed that CO had replaced the terminal hydrides of 2 at each Ru center (Figure 5). Two CO ligands were coordinated to the peripheral Ru centers in a terminal fashion with a mutually transoid geometry with respect to the Ru−Pt−Ru vector. The central platinum atom was also located at the center of inversion, as found in 2. Except for the presence of two CO ligands instead of four hydrides, the structural parameters of the Ru2PtP2 core of trans-5 were very similar to those of 2. The positions of the hydrides were successfully determined as being between the Ru and Pt atoms by diffraction studies, and they E


Article

Organometallics

Figure 6. Molecular structure and labeling scheme of trans-6 with thermal ellipsoids at the 30% probability level: top view (left) and side view (right). Selected bond lengths (Å) and angles (deg): Pt(1)− Ru(1) = 2.9286(3), Pt(1)−P(1) = 2.2975(7), Ru(1)−P(1) = 2.3778(8), Ru(1)−C(1) = 2.169(3), Ru(1)−C(2) = 2.179(3), C(1)−C(2) = 1.398(5), Ru(1)−Pt(1)−Ru(1#) = 180, Ru(1)− Pt(1)−P(1) = 52.452(18), Ru(1)−Pt(1)−P(1#) = 127.548(18), P(1)−Pt(1)−P(1#) = 180, Pt(1)−Ru(1)−P(1) = 50.000(18), C(1)−Ru(1)−C(2) = 37.51(13), Pt(1)−P(1)−Ru(1) = 77.55(2).

Figure 5. Molecular structure and labeling scheme of trans-5 with thermal ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Pt(1)−Ru(1) = 2.8621(3), Pt(1)−P(1) = 2.2827(9), Pt(1)−H(1) = 1.64(4), Ru(1)−P(1) = 2.3599(9), Ru(1)− C(19) = 1.827(4), Ru(1)−H(1) = 1.66(4),C(19)−O(1) = 1.156(5), Ru(1)−Pt(1)−Ru(1#) = 180, Ru(1)−Pt(1)−P(1) = 53.17(2), Ru(1)−Pt(1)−P(1#) = 126.83(2), P(1)−Pt(1)−P(1#) = 180, P(1)−Pt(1)−H(1) = 83.1(13), P(1)−Pt(1)−H(1#) = 96.9(13), Pt(1)−Ru(1)−P(1) = 50.73(2), Pt(1)−Ru(1)−C(19) = 89.92(14), P(1)−Ru(1)−C(19) = 91.71(13), Pt(1)−P(1)−Ru(1) = 76.10(3), Ru(1)−C(19)−O(1) = 168.6(4).

size of ethylene than hydrides and CO, the Ru−Pt distance of trans-6 (2.9286(3) Å) was slightly longer compared with those of 2 (2.8701(3) Å) and trans-5 (2.8621(3) Å). While no intermediate was observed in the reaction with CO, formation of a mono(ethylene) complex, {Cp*Ru(H)2}{Cp*Ru(C2H4)}Pt(μ-PtBu2)2(μ-H)2 (7), was observed when the reaction was carried out in a sealed NMR tube. After 10 min, 78% of 2 was converted into a mixture of 7 and cis/trans6, with a ratio of 7 and 6 estimated at ca. 3:1. The 1H NMR spectrum of 7 showed two Cp* signals at δ 1.64 and 2.00, which strongly supported its asymmetric structure. In the hydrido region, two signals with an intensity ratio of 3:1 were observed at δ −11.93 and −9.39 ppm, respectively. Prolonged reaction led to the complete conversion of 7 into a mixture of cis and trans-6. During the reaction, ethane formation was detected, as confirmed by the singlet resonance at δ 0.795 ppm in the 1H NMR spectrum. This indicated that two hydrido ligands in 7 were removed via hydrogenation of πbonded ethylene. Liberation of ethane led to the formation of an unsaturated intermediate, (Cp*Ru)2Pt(μ-PtBu2)2(μ-H)2 (8), which contains 44 valence electrons, according to the EAN rule. This was four less than 48 electrons in 2, and this electron deficiency would allow the facile incorporation of ethylene molecules to form bis(ethylene) complex 6. Adams et al. demonstrated the reversible addition of dihydrogen to a Re2Pt2 cluster; thermolysis of Re2Pt2(CO)7(PtBu3)2(μ-H)2(μ3-H)(H) in refluxing heptane resulted in the loss of H2 and formation of Re2Pt2(CO)7(PtBu3)2(μ-H)2.12 The unsaturated Re2Pt2 dihydrido cluster has been shown to readily react with H2 to regenerate the tetrahydrido cluster, and the authors note that bulky PtBu3 ligands effectively stabilize the coordinatively unsaturated cluster, enabling the reversible addition of dihydrogen. Thus, it was anticipated that the di-tertbutylphosphido groups in 6 could also promote facile liberation of π-coordinated ethylene and stabilize the resulting unsaturated species. In fact, unsaturated complex 8 was formed by repeated evacuation (eq 3). The lack of terminal hydrides was confirmed by the absence of the sharp absorption around 2000 cm−1 in the IR spectrum. A remarkable upfield shift of the 31P signal arising from the μ-phosphido group (δ 164.6) compared

resonated at δ −9.99 (t, JP−H = 9.2 Hz) with satellite signals (JPt−H = 761 Hz) in the 1H NMR spectrum. The 13C signal derived from the terminal CO was not detected by means of 13C{1H} NMR spectroscopy, probably due to the equilibrium between trans-5 and cis-5 in solution mentioned below. However, terminal coordination of the CO ligand was confirmed by the IR spectrum, showing an asymmetric stretching vibration at 1907 cm−1. Although trans-5 was stable in the solid state, cis-5 was gradually generated in solution. The cis/trans ratio reached 42/ 58 within 48 h in C6D6 at room temperature. While the Cp* signal of cis-5 appeared at the same frequency as that of trans-5 (δ 1.94 ppm), the hydride resonated at a noticeably higher magnetic field (δ −10.21 ppm) than in trans-5 (δ −9.99 ppm). Irradiation of the hydrido signal of cis-5 at 70 °C resulted in a decrease in the hydride signal intensity of trans-5 by 47%. The fact that spin-saturation transfer was observed between the hydrido signals of cis- and trans-5 indicated that isomerization occurred within the NMR time scale. In the IR spectrum of the mixture of cis- and trans-5, an absorption derived from a symmetric stretching vibration was observed at 1923 cm−1 in addition to the ν(CO) asym of trans-5. Complex 2 also reacted with ethylene, and a mixture of cisand trans-bis(ethylene) complexes, {Cp*Ru(C2H4)}2Pt(μPtBu2)2(μ-H)2 (cis- and trans-6), was obtained in a similar fashion to the reaction of 2 with CO. The ratio of cis- and trans-6, deduced from the 1H NMR spectrum recorded at 25 °C, was 45:55. Unlike the CO complex 5, an equilibrium of cisand trans-isomers of the ethylene complex was obtained spontaneously in solution. As mentioned below, the ethylene ligand readily eliminates from the Ru center. Recoordination of liberated ethylene from the opposite face would facilitate cis/ trans isomerization. Thus, we tentatively assigned the major isomer as trans-6. The molecular structure of trans-6 was determined by an Xray diffraction study, as shown in Figure 6. The ethylene molecules were π-bonded to different ruthenium atoms from the opposing faces of the Ru2PtP2 plane. Owing to the larger F


Article

Organometallics

distance between the Ru atom and the centroid of the EtCp group (CEN) was remarkably shorter in 8′ (Ru−CEN: 8′, 1.801 Å; 2: 1.871 Å). Girolami and co-workers reported significant difference in the Ru−CEN distances in (Cp*Ru)2(μCH2)(μ-Cl)(SiMe3), which possesses two ruthenium nuclei with different coordination numbers, and they noted that the Ru−CEN distance of the lower coordination number is shorter than the other by 0.1 Å.32 Thus, the shortening of the Ru− CEN distance in 8′ compared to that of 2 strongly indicated the absence of terminal hydrides. Another possible explanation for the Ru−CEN shortening is due to enhanced back-donation from the reduced Ru center in 8. Treatment of 8 with 1 atm of H2 resulted in immediate conversion to 2 by the oxidative addition of H2 at each Ru center (Scheme 4). This was in contrast with the case of

with that of 2 (δ 239.1) was found in the 31P{1H} NMR spectrum. In the 1H NMR spectrum, a doublet for the hydride was observed at δ −11.25 (JP−H = 13.1 Hz) with satellite signals (JPt−H = 207 Hz). The JPt−H value of 8 was remarkably smaller than those observed for trans-5 (JPt−H = 761 Hz) and trans-6 (JPt−H = 763 Hz). While the JPt−H value of 264 Hz was observed for 2, this was the average of four terminal Ru−H and two Ru− H−Pt bonds. The reduction in the JPt−H value of 8 may indicate that the Pt−H interaction is considerably weakened by the unsaturated Ru centers. In other words, this would represent that the unsaturated Ru center in 8 is effectively stabilized by the Pt−H bond. A single crystal suitable for X-ray diffraction was obtained using EtCp analogue 8′, with the molecular structure of 8′ shown in Figure 7 with relevant bond lengths and angles. The

Scheme 4. Interconversion among 2, 3, and 8 via Reversible H2 Addition and Elimination

Os 3 Pt(CO) 7 (P t Bu 3 )(μ-P t Bu 2 )(μ 4 -CHCMeCH)(μ-H)(H), where the Pt center acted as the activation site for H2.33 Unlike the Os3Pt cluster, 8 contains a divalent Pt atom, and so dihydrogen preferred to add at the low-valent peripheral Ru(II) centers. As mentioned above, hexahydrido complex 2 readily released dihydrogen to yield tetrahydrido complex 3 under reduced pressure. Repeated evacuation resulted in removal of the hydrido ligands and led to the formation of 3 in 61% yield, together with the formation of 8 in 8% yield. Although complex 3 was not isolated from the mixture, the 1H NMR spectrum of the mixture clearly showed that the two Cp*Ru moieties in 3 were not equivalent; two sharp Cp* signals were observed at δ 1.77 and 2.01 ppm. The asymmetric structure of 3 was also supported by the 31P{1H} NMR spectrum, which showed two doublet signals at δ 237.0 (d, JP−P = 186.3 Hz, JPt−P = 2160 Hz) and δ 154.8 (d, JP−P = 186.3 Hz, JPt−P = 1858 Hz). It is noteworthy that each chemical shift is close to that of the μphosphido group in 2 (δ 237.9) and 8 (δ 164.6). This implied that reductive elimination of dihydrogen occurred consecutively at each Ru center. Thus, the structure of 3 was tentatively proposed, as shown in Scheme 4, in which two terminal hydrides were bonded to one peripheral Ru atom. The lowered symmetry of 3 would also cause the four hydrides to be nonequivalent. Nevertheless, only one sharp signal was observed in the hydrido region in the 1H NMR spectrum of 3 recorded at 25 °C (δ −11.25). This meant that rapid site exchange of hydrides also occurred in 3, and, more importantly, hydrides migrate between the two nonequivalent Ru centers. Although the mechanism for site exchange between

Figure 7. Molecular structure and labeling scheme of 8′ with thermal ellipsoids at the 30% probability level: top view (left) and side view (right). Selected bond lengths (Å) and angles (deg): Pt(1)−Ru(1) = 2.8552(3), Pt(1)−P(1) = 2.2906(8), Pt(1)−H(1) = 1.70(4), Ru(1)− P(1) = 2.3350(9), Ru(1)−H(1) = 1.71(3), Ru(1)−Pt(1)−Ru(1#) = 179.999(11), Ru(1)−Pt(1)−P(1) = 52.59(2), Ru(1)−Pt(1)−P(1#) = 127.41(2), P(1)−Pt(1)−P(1#) = 180, P(1)−Pt(1)−H(1) = 85.7(12), P(1)−Pt(1)−H(1#) = 94.3(12), Pt(1)−Ru(1)−P(1) = 51.19(2), P(1)−Ru(1)−H(1) = 84.1(12), Pt(1)−P(1)−Ru(1) = 76.23(3).

planar geometry around the central Pt atom indicated that the formal oxidation state of the Pt atom was +2, as also seen in 2. Although the terminal hydrides were absent in 8′, the EtCp groups were also bent away from the Ru−Pt−Ru vector, in the opposite direction. However, the Pt−Ru−CEN angle in 8′ (150.89°) was marginally larger than that of 2 (141.96°), likely owing to the lack of terminal hydrides. Whereas the structural parameters around the Ru2PtP2 core of 8′ were almost the same as those of 2, despite the lack of terminal hydrides, the G


Article

Organometallics

Since cis-9 and trans-9 had similar 1H and 31P{1H} NMR data, we assigned them as conformational isomers regarding the orientation of the two Cp* ligands. One of the isomers, cis-9, was recrystallized from the mixture as a deep blue single crystal and subjected to diffraction studies (Figure 8). Crystallo-

two μ-hydrides located in a mutually trans geometry with respect to the Pt center is unclear at present, the smooth migration of the hydrides between the two Ru centers separated by the central Pt atom could be a model for facile hydrogen diffusion in Ru/Pt bimetallic catalysts, leading to their high hydrogenation activity. As the number of valence electrons of Cp*RuH3(PR3) is 18, it must generate unsaturated species for substitution reaction, i.e., the reductive elimination of dihydrogen or ring slippage of the Cp* group. However, substitution reactions do not readily occur, as shown in the literature,31 probably owing to the instability of the assumed intermediate. In contrast, the substitution reaction at the Ru centers in 2 occurred smoothly at ambient temperature. This was most likely ascribed to the presence of the bulky Pt(μ-PtBu2)2 moiety, which effectively stabilized the coordinatively unsaturated species 3 and 8. However, a monometallic trihydrido complex containing a relatively bulky phosphine group, Cp*RuH3(PiPr3), was also shown to be unreactive toward substitution reaction.34 In contrast, Caulton and co-workers demonstrated that Cp*Ru(PiPr2Ph)(H)2X (X = Cl, Br, I) readily releases dihydrogen to form a 16e complex, Cp*Ru(PiPr2Ph) X.35 This means that (σ + π) donation of the halide stabilizes the unsaturated Ru center effectively. Thus, it is implied that the central Pt atom also brings about a substantial electronic effect on the Ru center, leading to stabilization of the unsaturated Ru centers, likely through the bridging hydride. This seems to cause the decrease in the JPt−H value of 8. Reactions of 2 with Secondary Silanes. In addition to the reaction of 2 with 2e donors, reactions with secondary silanes, Ph2SiH2 and Et2SiH2, were also investigated. The reactions of Cp*RuH3(PR3) with tertiary silanes, leading to silyl complexes, as studied by Chaudret’s31 and Nikonov’s group,35 have been shown to require heating above 90 °C. In contrast, the reaction of 2 with Ph2SiH2 proceeded cleanly at ambient temperature and yielded a mixture of μ-silylene complexes, cis9 and trans-9, resulting from the successive oxidative addition of two Si−H bonds (Scheme 5). Unlike the reactions with L-

Figure 8. Molecular structure and labeling scheme of cis-9 with thermal ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Pt(1)−Ru(1) = 2.66806(19), Pt(1)−Ru(2) = 2.92690(18), Pt(1)−P(2) = 2.2656(6), Pt(1)−Si(1) = 2.3414(6), Ru(1)−P(1) = 2.3149(6), Ru(2)−Si(1) = 2.3231(6), Ru(2)−P(2) = 2.2588(6), Ru(2)−Pt(1)−Ru(2) = 170.154(6), Ru(1)−Pt(1)−P(2) = 138.363(15), Ru(1)−Pt(1)−Si(1) = 50.856(15), Ru(2)−Pt(1)−P(2) = 49.590(14), Ru(2)−Pt(1)−Si(1) = 50.856(15), Si(1)−Pt(1)−P(2) = 99.90(2), Pt(1)−Ru(1)−P(1) = 105.176(16), Pt(1)−Ru(2)−Si(1) = 51.416(15), Pt(1)−Ru(2)−P(2) = 49.793(15), Si(1)−Ru(2)−P(2) = 100.66(2), Pt(1)−Si(1)−Ru(2) = 77.728(19), Pt(1)−P(2)−Ru(2) = 80.617(19).

graphical analysis on cis-9 revealed that a silylene moiety bridges the Ru(2) and Pt(1) atoms, forming a Ru(2)Pt(1)P(2)Si(1) four-membered ring. The other μ-phosphido group was converted to a terminal phosphine ligand via reductive P− H bond formation and was bonded to the Ru(1) atom. Consequently, the Ru(1) and Pt(1) atoms were linked by two hydrido ligands, H(14) and H(15). Reductive P−H bond formation in a μ-phosphido group has been documented for a cationic diplatinum complex, [Pt2(μPtBu2)2(H)(CO)(PtBu2H)]+, in which one of the μ-phosphido groups is transformed into a PtBu2H group in [Pt2(μPtBu2)(CO)2(PtBu2H)2]+ upon treatment with CO.37 Formation of the PtBu2H group in cis-9 was also confirmed by the 1 H and 31P{1H} NMR spectra, as well as IR spectrum, showing a sharp absorption at 2284 cm−1. The P−H signal appeared at δ 5.42, showing a large 1JP−H coupling in the 1H NMR spectrum (1JP−H = 301.0 Hz), and two distinctive 31P signals were observed at δ 100.2 (JPt−P = 53 Hz) and 270.5 (JPt−P = 1822 Hz). Among them, the former was unambiguously assigned to the phosphine group due to its chemical shift and the smaller JPt−P value (53 Hz). The Ru(2)−Pt(1) distance (2.926 90(18) Å), which is linked by the μ-phosphido and μ-silylene ligands, is slightly larger than the Ru−Pt distance in 2 (2.8701(3) Å), probably owing to the bulk of the silylene bridge. On the other hand, the Ru(1)− Pt(1) distance (2.668 06(19) Å) was much shorter, perhaps due to the small size of the hydride bridges. The asymmetric structure caused a slight bending of the Ru(1)−Pt(1)−Ru(2)

Scheme 5. Reactions of 2 with R2SiH2 (R = Ph and Et)

type ligands, which result only in substitution at the Ru centers, participation of the central Pt atom was observed in this reaction. While several multinuclear bimetallic Ru/Pt complexes containing a bridging ER2 group (E = Sn, Ge, and Pb) at the Ru−Pt edge are known,11f,36 to the best of our knowledge, this is the first example of a heterometallic Ru/Pt complex containing a μ-silylene bridge. H


Article

Organometallics vector (170.154(6)°) compared to the linear skeleton in 2. Nevertheless, the sum of bond angles around the Pt(1) atom was still close to 360° (359.75°), which indicated that the formal oxidation state of the Pt atom remained +2. In the 1H NMR spectrum of cis-9 recorded at 25 °C, three well-resolved hydride signals with the same intensities were observed at δ −15.58 (d, JP−H = 30.3 Hz, JPt−H = 29 Hz), −7.98 (dd, JP−H = 55.2, 7.7 Hz, JPt−H = 914 Hz), and −7.24 ppm (d, JP−H = 13.6 Hz, JPt−H = 986 Hz). The most shielded signal, resonating at δ −15.58 ppm, was assigned to the terminal hydride, H(16), bonded to Ru(2), due to the small JPt−H value, while the signals at δ −7.98 and −7.24 ppm were assigned to H(14) and H(15), respectively, based on their JP−H values. Unlike 2 and 3, which showed rapid site exchange of the hydrides, the lack of spin-saturation transfer among the hydrido signals indicated that the hydride ligands in cis-9 were not fluxional, at least within the NMR time scale. Even when isolated cis-9 crystals were dissolved in C6D6, the signals derived from trans-9 gradually appeared, with the amount of trans-9 stabilizing after 10 h at 25 °C, where the cis9/trans-9 ratio was 3:1. The NMR data of trans-9 were very similar to those of cis-9, although some coupling data were not well identified owing to its low population. The hydride signals of trans-9 were observed at δ −14.80 (d, JP−H = 29.0 Hz), −8.34 (dd, JP−H = 55.6, 7.6 Hz, JPt−H = 918 Hz), and −6.65 ppm (d, JP−H = 10.4 Hz, JPt−H = 978 Hz), while the 31P signals resonated at δ 103.0 and 261.4 ppm. Considering the reactivity of 2, it seemed reasonable to assume that 3 was generated first, and subsequent oxidative addition of Ph2SiH2 occurs at the unsaturated Ru center to form intermediate B in Scheme 5. Intramolecular oxidative addition of the SiPh2H moiety on Ru(2), according to the numbering scheme in Figure 8, would take place subsequently at Pt(1), which was followed by reductive P−H bond formation. Liberation of the second dihydrogen from the other Ru center, Ru(1), would lead to formation of the PtBu2H ligand at the Ru(1) center. In contrast to the formation of a μ-silylene ligand, the reaction of 2 with Et2SiH2 produced μ-silyl complex 10, possessing 3c-2e Ru−H−Si interactions. A diffraction study unambiguously determined that the bridging silicon atom is bonded to Ru(1) through the Si−H bond and σ-bonded to Pt(1) (Figure 9); the Ru(1)−Si(1) distance (2.5739(8) Å) was much longer than that of cis-9 (2.3231(6) Å), while the Pt(1)− Si(1) distance (2.2623(9) Å) was considerably shorter than that of cis-9 (2.3414(6) Å). Owing to the asymmetric coordination of the bridging silicon moiety, the Ru−Pt−Ru skeleton in 10 was folded further than cis-9, producing a Ru(1)−Pt(1)−Ru(2) angle of 132.099(10)°. It was also notable that the Pt center still kept a square planar geometry, despite such distortion. The sum of bond angles around the Pt(1) atom was 359.97°. The reason for σ-coordination of the Si−H bond was likely due to the higher energy level of the σ*(Si−H) orbital of Et2SiH2 compared with that of Ph2SiH2.38 Similar observations were made for the reactions of 1 with Ph2SiH2 and Et2SiH2, where only a bis(μ-silylene) complex was obtained by the reaction with Ph2SiH2.39 Due to the absence of the second Si− H bond scission of Et2SiH2, the oxidation state of the Ru2Pt cluster was lower, which impeded the reductive elimination of dihydrogen from the Ru(2) atom. This also inhibited the formation of a PtBu2H group on the Ru(2) atom, unlike that seen for 9. Consequently, a PtBu2H group should be formed on

Figure 9. Molecular structure and labeling scheme of 10 with thermal ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Pt(1)−Ru(1) = 2.9373(3), Pt(1)−Ru(2) = 2.9520(4), Pt(1)−Si(1) = 2.2623(9), Pt(1)−P(2) = 2.2464(7), Pt(1)−H(3) = 1.73(3), Pt(1)−H(4) = 1.85(3), Ru(1)−Si(1) = 2.5739(8), Ru(1)− P(1) = 2.3009(9), Ru(1)−H(2) = 1.61(3), Ru(1)−H(3) = 1.70(3), Ru(2)−P(2) = 2.3378(9), Ru(2)−H(4) = 1.64(3), Ru(2)−H(5) = 1.52(3), Si(1)−H(2) = 1.69(3), Ru(1)−Pt(1)−Ru(2) = 132.099(10), Ru(1)−Pt(1)−P(2) = 168.45(2), Ru(1)−Pt(1)−Si(1) = 57.60(2), Ru(2)−Pt(1)−P(2) = 51.28(2), Ru(2)−Pt(1)−Si(1) = 166.00(2), P(2)−Pt(1)−Si(1) = 116.98(3), Pt(1)−Ru(1)−Si(1) = 47.914(18), Pt(1)−Ru(1)−P(1) = 106.20(2), Si(1)−Ru(1)−P(1) = 104.33(3), Pt(1)−Ru(2)−P(2) = 48.571(18), Pt(1)−Si(1)−Ru(1) = 74.48(3), Pt(1)−P(2)−Ru(2) = 80.15(3).

the Ru(1) atom in 10, to which the Si−H bond is η2coordinated. In the 1H NMR spectrum of 10 recorded at 25 °C, three hydride signals were observed at δ −11.87 (d, JP−H = 16.6 Hz, JPt−H = 115 Hz), −11.58 (d, JP−H = 17.0 Hz, JPt−H = 54 Hz), and −10.12 (dd, JP−H = 37.3, 16.7 Hz, JPt−H = 448 Hz) with an intensity ratio of 3:1:1. Among them, the signal resonating at δ −11.87 was attributed to the averaged signal of the three hydrides attached to the Ru(2) atom, while the peak at δ −10.12 was attributed to hydride bridging between Ru(1) and Pt(1) because of the spin−spin coupling with the two 31P nuclei. The signal of the η2-Si−H was hence assigned to the signal appearing at δ −11.58, although satellite signals with the 29 Si nucleus were not detected due to being obstructed by the 195 Pt satellites. The formation of a 3c-2e interaction was confirmed by broad absorption observed around 1782 cm−1 in the IR spectrum.

■

CONCLUSION A novel trinuclear bimetallic complex of Ru and Pt in a linear Ru−Pt−Ru arrangement, {Cp*Ru(H)2}2Pt(μ-PtBu2)2(μ-H)2 (2), was prepared by the reaction of diruthenium tetrahydrido complex Cp*Ru(μ-H)4RuCp* (1) with Pt(PtBu3)2 or Pt(PtBu2H)3. VT-NMR studies on 2 showed that the flexibility of the Ru−Pt−Ru framework led to cis/trans isomerization. In addition, the hydride ligands in 2 underwent rapid site exchange between the terminal and bridging positions. This resembled the properties of hydrides in the monometallic trihydrido complex of ruthenium, Cp*Ru(PR3)(H)3, which exhibited quantum-mechanical exchange coupling. Unlike Cp*Ru(PR3)(H)3, complex 2 reacted with CO and ethylene readily at ambient temperature to yield cis/trans mixtures of I


Article

Organometallics {Cp*Ru(CO)}2Pt(μ-PtBu2)2(μ-H)2 (5) and {Cp*Ru(C2H4)}2Pt(μ-PtBu2)2(μ-H)2 (6), respectively. The reaction possibly proceeds in a dissociative manner, via the formation of coordinatively unsaturated {Cp*Ru(H)2}(Cp*Ru)Pt(μ-PtBu2)2(μ-H)2 (3). Formation of a vacant site at the peripheral Ru center would be promoted by the combination of the steric bulk of the “Pt(μ-PtBu2)2” moiety and the electronic effect of the central Pt atom, in contrast with Cp*Ru(PR3)(H)3. The reactions of 2 with dihydrosilanes were also investigated, showing Pt−Si bond formation accompanied by decoordination of one of the μ-phosphido ligands on the Pt atom. According to the nature of the Si−H bond, two kinds of products were obtained. Namely, the more activated Ph2SiH2 provided a mixture of μ-silylene complexes, cis- and trans-9, while μ-silyl complex 10, with a Ru−H−Si interaction, was formed in the reaction of 2 with Et2SiH2. These reactions demonstrated that the central Pt atom acted not only as a clump, binding two Cp*Ru fragments, but also as an activation site. In this regard, the fact that CO coordination occurred only at the Ru centers perhaps demonstrated the preference of CO binding to the Ru atoms rather than the Pt atom in 2. Although, at present, it is uncertain whether the formation of 5 was determined kinetically or thermodynamically, the observed preference could be a model for the CO tolerance of Ru/Pt bimetallic catalysts.

■

anisotropically. The refinements were carried out by least-squares methods based on F2 with all measured reflections. The metal-bound hydrogen atoms were located in the difference Fourier map and refined isotropically. Crystal data and results of the analyses are listed in Table S-4 in the Supporting Information. NMR Simulations. NMR simulations for the t-Bu groups of 2, 3, and 8 were performed using the gNMR v4.1.0. software package (Ivory Soft, 1995−1999). Final simulated line shapes were obtained via an iterative parameter search upon the coupling constants among the hydride ligands and the phosphorus nucleus. Complete details of the fitting procedure and results are shown in the Supporting Information. Computational Details. Density functional theory (DFT) calculations on 2, 4, and the possible isomer of 4 (A in Scheme 4) were carried out at the ωB97X level44 in conjunction with the Stuttgart/Dresden ECP45 and associated with triple-ζ SDD basis sets for the transition metals. The 6-31G(d) basis set was employed for the hydrogen, carbon, and phosphorus atoms. No simplified model compounds were used for the calculations. Initial geometries for the optimization were based on crystallographically determined structures for 2 and 4. Frequency calculations at the same level of theory as geometry optimizations were performed on the optimized structure to ensure that minima exhibit only positive frequency. All Gibbs energies were computed in the gas phase at 298 K from the corresponding zero-point-corrected electronic energies. All calculations were carried out without symmetry constraints utilizing the Gaussian 09 program (revision D.01).46 The molecular structure was drawn by using the GaussView version 5.0 program.47 Information on the atom coordinates (xyz files) for all optimized structures, important geometrical parameters, and the optimized structures are collected in the Supporting Information. Reaction of 1 with Pt(PtBu3)2: Preparation of {Cp*Ru(H)2}2Pt(μ-PtBu2)2(μ-H)2 (2). A 50 mL Schlenk tube equipped with a JYoung valve was charged with 1 (36.8 mg, 77.2 μmol), Pt(PtBu3)2 (51.2 mg, 85.4 μmol), and THF (5 mL). The reaction vessel was put in an ice bath and kept at 0 °C during the reaction. The solution was then irradiated by a high-pressure mercury lamp for 14 h with vigorous stirring. The color of the solution turned from orange to dark green. The solvent was then removed under reduced pressure. The 1H NMR spectrum of the residual black solid showed formation of 2 with several unidentified products, in which the yield of 2 was roughly estimated at 35% on the basis of the signal intensity of 2 in the Cp* signal region. Recrystallization from the THF solution of the crude mixture stored at −30 °C afforded green single crystals of 2. Decantation followed by drying under vacuum gave a 19.2 mg amount of 2 (25% yield). 1H NMR (400 MHz, C6D6, 25 °C): δ −11.57 (t, 6H, JPt−H = 264 Hz, JP−H = 6.0 Hz, Ru−H and Ru−H−Pt), 1.45 (m, 36H, JP−H = 12.0, 1.0 Hz, t Bu)*, 2.01 ppm (s, 30H, Cp*). *The JP−H values were obtained from the NMR simulation. 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ 12.8 (s, C5Me5), 33.4 (dd, JP−C = 3.7, 3.7 Hz, C(CH3)3), 37.0 (dd, JP−C = 4.8, 4.8 Hz, C(CH3)3), 95.9 ppm (s, C5Me5). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 239.1 ppm (s, JPt−P = 2161 Hz, PtBu2). The JP−P′ value was estimated at 100.0 Hz based on the simulation of the tBu signal in the 1H NMR spectrum. IR (ATR, cm−1): 2940, 2898, 1991 ν(RuH), 1471, 1456, 1379, 1354, 1172, 1068, 1016. Anal. Calcd for C36H72P2PtRu2: C, 44.85; H, 7.53. Found: C, 44.96; H, 7.59. Preparation of {Cp*Ru(H)2}2Pt(μ-PtBu2)2(μ-H)2 (2) by the Reaction of 1 with Pt(PtBu2H)3. A 200 mL Schlenk tube equipped with a dropping funnel was charged with Pt(PtBu2H)3 (215.0 mg, 0.340 mmol) and toluene (42 mL). The flask was kept at 0 °C with an ice bath. A 126.1 mg amount of 1 (0.264 mmol) was introduced into a 50 mL Schlenk tube and dissolved in toluene (14 mL). The whole toluene solution of 1 was then introduced into the dropping funnel and gradually added to the solution of Pt(PtBu2H)3 for 0.5 h. After the solution of 1 was introduced, the solution was stirred for 40 min at 0 °C, and the color of the solution turned from yellow to dark green. A dark green residue was obtained by the removal of the solvent under reduced pressure. The 1H NMR spectrum of the crude mixture showed that complexes 2, 3, and 4 were formed in a ratio of 66:19:13 with a small amount of byproducts (2%).30 The residual solid was

EXPERIMENTAL SECTION

General Procedures. All air- and moisture-sensitive compounds were manipulated using standard Schlenk and high-vacuum line techniques under an argon atmosphere. Dehydrated toluene, tetrahydrofuran (THF), hexane, and pentane were purchased from Kanto Chemicals and stored under an argon atmosphere. [D6]benzene and [D8]THF were distilled from sodium benzophenone ketyl and stored under an argon atmosphere. The starting diruthenium complex, Cp*Ru(μ-H)4RuCp* (1), was prepared according to the previously published method,40 and the (C5Me4Et) analogue, EtCpRu(μH)4RuEtCp (1′) (EtCp = η5-C5Me4Et), was prepared in a similar manner using [EtCpRuCl2]2 as a starting material. Platinum complexes, Pt(PtBu3)241 and Pt(PtBu2H)3,29 were synthesized according to the literature. 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded on Varian 400MR and INOVA400 spectrometers. 1H NMR spectra were referenced to tetramethylsilane as an internal standard. 13C{1H} NMR spectra were referenced to the natural-abundant carbon signal of the solvent employed. 31P{1H} NMR spectra were recorded with an 85% aqueous solution of phosphoric acid as an external standard (referenced to δ = 0 ppm). IR spectra were recorded on a JASCO FT/IR-4200 spectrophotometer by the diffuse reflection method using KBr and by an ATR cell (ZnSe). Elemental analysis was performed on a PerkinElmer 2400II series CHN analyzer. Photoirradiation experiments were performed using an Asahi Spectra REX-250 high-power mercury light source without any band-pass filter. X-ray Diffraction Studies. Single crystals of 2, 4, trans-5, trans-6, 8′, cis-9, and 10 for the X-ray analyses were obtained directly from the preparations described below and mounted on nylon Cryoloops with Paratone-N (Hampton Research Corp.). Diffraction experiments were performed on a Rigaku R-AXIS RAPID imaging plate diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.710 69 Å). Cell refinement and data reduction were performed using the PROCESSAUTO program.42 Intensity data were corrected for Lorentz− polarization effects and empirical absorption. The structures of 6 and cis-9 were solved by the direct and Patterson methods using the SHELX-97 program package, respectively.41 The structures of 2, 4, cis5, and 10 were solved by the direct method, and the structure of 8′ was solved by the Patterson method by using SHELX-2014/5 and SHELX-2014/7 program packages.43 All non-hydrogen atoms were found by the difference Fourier synthesis and were refined J


Article

Organometallics

°C with an ice bath. Complexes 1 (5.2 mg, 11 μmol) and 1′ (5.5 mg, 11 μmol) were introduced into another 50 mL Schlenk tube and dissolved in toluene (2 mL). The whole toluene solution of 1 and 1′ was then introduced into the dropping funnel and gradually added to the solution of Pt(PtBu2H)3 for 20 min. After the solution of 1 and 1′ was introduced, the solution was stirred for 10 min at 0 °C. Removal of the solvent gave a 31.4 mg amount of dark green residue. An NMR tube equipped with a Teflon valve was charged with the residual solid (1.5 mg) and C6D6 (0.4 mL). After the tube was degassed, 1 atm of dihydrogen was introduced in order to convert 3 and 3′ into 2 and 2′. The 1H NMR spectrum was recorded in the presence of H2, and the ratio among 2, 2′, and (4 + 4′) was estimated at 46:45:9 on the basis of the signal intensities of Cp* and EtCp groups. Formation of another product possessing both Cp* and EtCp groups was not observed. Formation of 2 and 2′ was identified with their Cp*, t-Bu, and hydride signals compared to their authentic samples. Reaction of 2 with CO. Preparation of {Cp*Ru(CO)}2Pt(μPtBu2)2(μ-H)2 (cis- and trans-5). A 50 mL Schlenk was charged with 2 (30.4 mg, 31.5 μmol) and toluene (8 mL). After the flask was cooled at −78 °C with a dry ice/methanol bath, the flask was evacuated. The solution was then warmed to 25 °C, and 1 atm of CO was introduced into the flask with vigorous stirring. The solution was reacted for 1 h, and the color of the solution immediately turned from greenish-yellow to orange. After the solution was condensed under reduced pressure, the solution was stored at −30 °C. A 13.3 mg amount of trans-5 was obtained as an orange single crystal upon decantation followed by drying under vacuum (13.1 μmol, 42%). The C6D6 solution was prepared using the obtained single crystals of trans-5, and the 1H NMR spectrum was recorded. After 48 h, the spectrum showed the formation of cis-5 in the solution, in which the cis/trans ratio reached 42/58 at 25 °C. trans-5: 1H NMR (400 MHz, C6D6, 25 °C): δ −9.99 (t, 2H, JP−H = 9.2 Hz, JPt−H = 761 Hz, Ru−H−Pt), 1.29 (br, 18H, tBu), 1.61 (m, 18H, JP−H = 6.6 Hz, tBu), 1.94 ppm (s, 30H, Cp*). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ 12.0 (s, C5Me5), 33.2 (br, CMe3), 34.1 (br, CMe3), 36.9 (d, JP−C = 36.1 Hz, CMe3), 95.5 ppm (s, C5Me5). * The 13C signals for one of the quaternary carbons of the t-Bu group and CO groups were not detected because of the broadening of the signals due to equilibrium between trans-5 and cis-5. 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 200.9 ppm (s, JPt−P = 1865 Hz, μ-PtBu2). IR (ATR, cm−1): 2948, 2905, 1907 ν(CO), 1857, 1475, 1451, 1380, 1357, 1172, 1024. Anal. Calcd for C38H68O2P2PtRu2: C, 44.92; H, 6.75. Found: C, 44.85; H, 6.46. cis-5: 1H NMR (400 MHz, C6D6, 25 °C): δ −10.21 (t like dd, 2H, JP−H = 9.8 Hz, JPt−H = 757 Hz, Ru−H− Pt), 1.29* (br, 18H, tBu), 1.61* (m, 18H, JP−H = 6.6 Hz, tBu), 1.94* ppm (s, 30H, Cp*). The asterisked 1H signals derived from t-Bu and Cp* groups of cis-5 superimposed on the signals derived from those of trans-5. 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 195.7 ppm (s, JPt−P = 1844 Hz, μ-PtBu2). IR (ATR, cm−1): 1923 ν(CO). Reaction of 4 with Ethylene. Preparation of {Cp*Ru(C2H4)}2Pt(μ-PtBu2)2(μ-H)2 (cis- and trans-6). A 50 mL Schlenk was charged with 2 (30.4 mg, 31.5 μmol) and THF (8 mL). After the flask was cooled at −78 °C with a dry ice/methanol bath, the flask was evacuated. The solution was then warmed to 25 °C, and 1 atm of ethylene was introduced into the flask with vigorous stirring. The solution was reacted for 1 h, and the color of the solution immediately turned from greenish-yellow to reddish-orange. After the solution was condensed under reduced pressure, the solution was stored at 25 °C. Analytically pure trans-6 was obtained from a THF solution stored at 25 °C (6.9 mg, 6.79 μmol, 81%). The C6D6 solution was prepared using the obtained single crystals of trans-6, and the 1H NMR spectrum was recorded. The spectrum showed the formation of cis-6 in the solution, in which the cis/trans ratio reached 45/55 at 25 °C. Since each isomer was not isolated, the assignment of the signals was carried out on the mixture of cis- and trans-6. We tentatively assigned the major isomer to trans-6. trans-6: 1H NMR (400 MHz, C6D6, 25 °C): δ −10.39 (t, 2H, JP−H = 9.9 Hz, JPt−H = 763 Hz, Ru−H−Pt), 1.16 (dd, 2H, JH−H = 10.1, 10.1 Hz, C2H4), 1.53 (m, 18H, tBu), 1.63 (s, 30H, Cp*), 2.23 ppm (m, 2H, C2H4). *The other t-Bu signal and the rest of the C2H4 signals were obscured by the Cp* and t-Bu signals. 31 1 P{ H} NMR (162 MHz, C6D6, 25 °C): δ 210.4 ppm (s, JPt−P = 1880

washed two times with 5 mL of hexane at 0 °C in order to remove 4 and the remaining Pt(PtBu2H)3. After the solid was dissolved into THF (5 mL), the flask was cooled at −78 °C with a dry ice/methanol bath. The flask was then evacuated, and 1 atm of dihydrogen was introduced into the flask. The solution was then warmed to 25 °C and stirred for 10 min. The color of the solution turned from dark green to greenish-yellow. Removal of the solvent under reduced pressure gave 2 as a greenish-yellow solid in 72% yield (183.3 mg, 0.190 mmol). A single crystal suitable for the XRD study was obtained from the toluene solution of 2 stored at 0 °C. Preparation of {EtCpRu(H)2}2Pt(μ-PtBu2)2(μ-H)2 (2′). The EtCp analogue of 2 was synthesized in a similar manner to the preparation of 2 using EtCpRu(μ-H)4RuEtCp (1′) instead of 1. Complex 2′ was obtained as a greenish-yellow solid in 69% yield. 1H NMR (400 MHz, C6D6, 25 °C): δ −11.59 (t, 6H, JP−H = 6.6 Hz, JPt−H = 246 Hz, Ru−H and Ru−H−Pt), 1.01 (t, 6H, JH−H = 7.6 Hz, C5Me4CH2CH3), 1.45 (m, 36H, tBu), 1.99 (s, 12H, C5Me4Et), 2.07 (s, 12H, C5Me4Et), 2.54 ppm (q, 4H, C5Me4CH2CH3). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 238.3 ppm (s, JPt−P = 2169 Hz, PtBu2). Preparation of (Cp*Ru)2{Pt(PtBu2H)}(μ-PtBu2)(μ-H)3(H)2 (4). A 50 mL Schlenk was charged with 1 (54.0 mg, 0.113 mmol) and Pt(PtBu2H)3 (35.0 mg, 55.3 μmol). The solids were stirred and homogenized by a magnetic stirrer bar for 0.5 h. Then, a 4.5 mL amount of toluene was introduced into the flask with vigorous stirring at 25 °C. The solution was reacted for 0.5 h. The color of the solution turned from orange to dark green. A dark green residue was obtained by the removal of the solvent under reduced pressure. The 1H NMR spectrum of the residual solid showed the formation of 2, 3, and 4, in which the selectivity for 4 was estimated at 47%. The residual solid was then extracted three times with 10 mL of hexane. After the volume of the combined extracts was reduced to 5 mL under reduced pressure, the product was purified by the use of column chromatography on alumina (Merck, Art. No. 1097) eluted with hexane. The first purple band including 4 was collected, and 4 was obtained as a dark green solid by the removal of solvent under reduced pressure. Analytically pure 4 was obtained from the cold pentane solution stored at −30 °C as dark green crystals (15.6 mg, 16.2 μmol, 29%). 1H NMR (400 MHz, THF-d8/toluene-d8, 4:1, −30 °C): δ −18.77 (m, 1H, JPt−H = 478 Hz, Ru−H−Pt), −18.75 (dd, 1H, JP−H = 68.6, 17.2 Hz, JPt−H = 317 Hz, Ru−H−Pt), −10.94 (s, 1H, Ru−H), −9.19 (d, 1H, JP−H = 28.8 Hz, JPt−H = 1254 Hz, Pt−H), −7.52 (dd, 1H, JP−H = 12.7, 12.7 Hz, JPt−H = 337 Hz, Ru−H−Ru), 0.75 (d, 3H, JP−H = 19.6 Hz, μ-PtBu2), 1.01 (d, 9H, JP−H = 12.4 Hz, PtPtBu2H), 1.13 (d, 9H, JP−H = 14.0 Hz, μ-PtBu2), 1.35 (d, 9H, JP−H = 14.0 Hz, PtPtBu2H), 1.53 (d, 3H, JP−H = 8.4 Hz, μPtBu2), 1.62 (d, 3H, JP−H = 9.2 Hz, μ-PtBu2), 1.93 (s, 15H, Cp*), 2.02 (s, 15H, Cp*), 4.15 ppm (d, 1H, JP−H = 310.0 Hz, PtPtBu2H). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ 13.1 (s, C5Me5), 14.4 (s, C5Me5), 29.7 (br, μ-PtBu(CMe3)), 30.4 (br, P(CMe3)2H), 30.9 (br, P(CMe3)2H), 32.8 (br d, JP−C = 30.4 Hz, P(CMe3)2H), 33.0 (br, μPtBu(CMe3)), 33.7 (d, JP−C = 3.6 Hz, μ-P(CMe3)tBu), 34.7 (br d, JP−C = 25.6 Hz, P(CMe3)2H), 36.2 (d, JP−C = 17.1 Hz, μ-PtBu(CMe3)), 36.5 (br d, JP−C = 22.1 Hz, μ-P (CMe3)tBu)), 40.1 (s, μ-PtBu(CMe3)), 90.9 (s, C5Me5), 93.6 ppm (s, C5Me5). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 67.1 (s, JPt−P = 3685 Hz, PtPtBu2H), 259.8 ppm (s, μPtBu2). IR (KBr, cm−1): 2953, 2897, 2272 ν(PH), 2132 ν(PtH), 1996 ν(RuH), 1604, 1476, 1372, 1175, 1023. Anal. Calcd for C36H72P2PtRu2: C, 44.85; H, 7.53. Found: C, 45.08; H, 7.70. Isomerization of 4 to 2. An NMR tube equipped with a Teflon valve was charged with 4 (1.0 mg, 1.0 μmol), C6D6 (0.4 mL), and ferrocene as an internal standard. The tube was then heated at 50 °C with an oil bath. The reaction was periodically monitored by means of 1 H NMR spectroscopy. The spectrum recorded after 14 h showed that 4 was completely consumed, and complexes 2 and 3 were formed at 64% and 24%, respectively. The spectrum also showed the formation of a unidentified product in 12% yield. This side product was alternatively obtained upon thermolysis of 2 at 50 °C. Reaction of a Mixture of Cp*Ru(μ-H)4RuCp* (1) and EtCpRu(μ-H)4RuEtCp (1′) with Pt(PtBu2H)3. A 50 mL Schlenk tube equipped with a dropping funnel was charged with Pt(PtBu2H)3 (19.9 mg, 31.4 μmol) and toluene (5 mL). The flask was kept at 0 K


Article

Organometallics Hz, μ-PtBu2). IR (KBr, cm−1): 2952, 2903, 1473, 1384, 1199, 1020. Anal. Calcd for C40H76P2PtRu2: C, 47.28; H, 7.54. Found: C, 47.20; H, 7.71. cis-6: 1H NMR (400 MHz, C6D6, 25 °C): δ −10.12 (t, 2H, JP−H = 9.9 Hz, JPt−H = 758 Hz, Ru−H−Pt), 1.03 (dd, JH−H = 10.4, 10.4 Hz, 2H, C2H4), 1.16 (dd, JH−H = 10.4, 10.4 Hz, 2H, C2H4), 1.39 (m, 18H, t Bu), 1.62 (s, 30H, Cp*), 2.51 ppm (m, 2H, C2H4). *The other t-Bu signal and the rest of the C2H4 signals were obscured by the Cp* and t-Bu signals. 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 212.1 ppm (s, JPt−P = 1883 Hz, μ-PtBu2). Reaction of 2 with Ethylene in a Sealed NMR Tube. Observation of {Cp*Ru(H)2}{Cp*Ru(C2H4)}Pt(μ-PtBu2)2(μ-H)2 (7). An NMR tube equipped with a Teflon valve was charged with 2 (1.0 mg, 1.0 μmol) and C6D6 (0.4 mL). After the solution was frozen with a dry ice/methanol bath, the tube was degassed. The solution was then warmed to 25 °C, and 1 atm of ethylene was introduced. The color of solution immediately turned from dark green to orange. The 1 H NMR spectrum recorded after 10 min showed that 78% of 2 was converted into the mixture of cis- and trans-6 (19%) and {Cp*Ru(H)2}{Cp*Ru(C2H4)}Pt(μ-PtBu2)2(μ-H)2 (7; 59%). 1H NMR (400 MHz, C6D6, 25 °C): δ −11.93 (d, 3H, JP−H = 12.8 Hz, JPt−H = 285 Hz, Ru−H−Pt and Ru−H), −9.39* (d, 1H, JP−H = 17.6 Hz, Ru−H−Pt), 1.56 (d, 9H, JP−H = 13.4 Hz, tBu), 1.64 (s, 15H, Cp*), 2.00 ppm (s, 15H, Cp*). *Satellite peaks were not detected due to the low intensity of the hydrido signal at δ −9.39 ppm. The three remaining t-Bu signals and signals derived from the ethylene ligand were not observed because they were obscured by the signals stemming from 2 and cis- and trans-6. Preparation of (Cp*Ru)2Pt(μ-PtBu2)2(μ-H)2 (8). A 100 mL Schlenk was charged with 2 (70.1 mg, 72.7 μmol) and toluene (20 mL). After the flask was cooled at −78 °C with a dry ice/methanol bath, the flask was evacuated. The solution was then warmed to 25 °C, and 1 atm of ethylene was introduced into the flask with vigorous stirring. The solution was reacted for 24 h, and the color of the solution turned from greenish-yellow to reddish-orange. The flask was then cooled at −78 °C with a dry ice/methanol bath, and the flask was evacuated at ca. 20 Pa. After the solution was warmed to 25 °C, it was stirred for 5 min. These operations were repeated five times to remove the coordinated ethylene. Finally, the color of the solution turned from reddish-orange to dark green. Removal of the solvent under reduced pressure gave a dark green solid. The residual solid was dissolved in toluene (11 mL) and stored at 0 °C. A 33.5 mg amount of analytically pure 8 was obtained as a black single crystal (34.9 μmol, 48%). 1H NMR (400 MHz, C6D6, 25 °C): δ −11.25 (d, 2H, JP−H = 13.1 Hz, JPt−H = 207 Hz, Ru−H−Pt), 1.36 (m, 36H, JP−H = 12.5, 1.20 Hz, tBu), 1.78 ppm (s, 30H, Cp*). *The JP−H values were obtained from the NMR simulation. 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ 13.1 (s, C5Me5), 32.1 (t, JP−C = 4.5 Hz, CMe3), 38.2 (m, CMe3), 75.8 ppm (s, C5Me5). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 164.6 ppm (s, JPt−P = 1700 Hz, μ-PtBu2). The JP−P′ value was estimated at 90.0 Hz based on the simulation of the t-Bu signal in the 1H NMR spectrum. IR (ATR, cm−1): 2894, 1455, 1375, 1172, 1017. Anal. Calcd for C36H68P2PtRu2: C, 45.04; H, 7.14. Found: C, 44.93; H, 7.42. Observation of {Cp*Ru(H)2}(Cp*Ru)Pt(μ-PtBu2)2(μ-H)2 (3). A 50 mL Schlenk was charged with 2 (37.4 mg, 38.9 μmol). After 2 was dissolved in toluene (12 mL) at 25 °C, the solution was removed under reduced pressure to remove dihydrogen. Dissolution and evacuation were repeated four times, and a dark green residual solid was obtained. The 1H NMR spectrum of the residual solid showed that 69% of 2 was converted into 3 (61%) and 8 (8%). A 1.1 mg amount of the residual solid and C6D6 (0.4 mL) were introduced into an NMR tube equipped with a Teflon valve with hexamethylbenzene as an internal standard. After the solution was frozen with a dry ice/ methanol bath, the NMR tube was evacuated. The solution was then warmed to 25 °C, and 1 atm of H2 was introduced into the tube. The color of the solution immediately turned from dark green to greenishyellow. The 1H NMR spectrum showed that both 3 and 8 were converted into 2 quantitatively. 1H NMR of 3 (400 MHz, C6D6, 25 °C): δ −11.25 (d, 4H, JP−H = 13.2 Hz, JPt−H = 216 Hz, Ru−H−Pt and Ru−H), 1.32 (d, 18H, JP−H = 13.3 Hz, tBu), 1.55 (d, 18H, JP−H = 13.0 Hz, tBu), 1.77 (s, 15H, Cp*), 2.01 ppm (s, 15H, Cp*). One of the

Cp* signals of 3 appeared at the same chemical shift as that of 2 (δ 2.01 ppm). 31P{1H} NMR of 3 (162 MHz, C6D6, 25 °C): δ 154.8 (s, JP−P = 186.3 Hz, JPt−P = 1858 Hz, μ-PtBu2), 237.0 ppm (s, JP−P = 186.3 Hz, JPt−P = 2160 Hz, μ-PtBu2). Preparation of {Cp*Ru(H)}{Cp*Ru(PtBu2H)}Pt(μ-PtBu2)(μSiPh2)(μ-H)2 (cis- and trans-9). A 50 mL Schlenk was charged with 2 (45.3 mg, 47.0 μmol) and THF (3 mL). A 8.7 μL amount of diphenylsilane (46.9 μmol) was then added to the solution at 25 °C and stirred for 37 h. The color of the solution turned from dark green to deep blue. After the solvent was removed under reduced pressure, the residual dark purple solid was dissolved in hexane. The product was purified by the use of column chromatography on alumina (Merck, Art. No. 1097) eluted with hexane. The first purple band including a cis/trans mixture of 9 was collected. Removal of the solvent under reduced pressure gave a cis/trans mixture of 9 as a dark purple solid. The 1H NMR spectrum of the residual solid showed that the cis/ trans ratio was 3:1. A single crystal of cis-9 was obtained from the cold hexane solution stored at −30 °C as dark purple crystals (10.4 mg, 9.1 μmol, 19%). cis-9: 1H NMR (400 MHz, C6D6, 25 °C): δ −15.58 (d, 1H, JP−H = 30.3 Hz, JPt−H = 29 Hz, Ru−H), −7.98 (dd, 1H, JP−H = 55.2, 7.7 Hz, JPt−H = 914 Hz, Ru−H−Pt trans to μ-PtBu2), −7.24 (d, 1H, JP−H = 13.6 Hz, JPt−H = 986 Hz, Ru−H−Pt cis to μ-PtBu2), 0.83 (d, 9H, JP−H = 13.1 Hz, tBu), 1.20 (d, 9H, JP−H = 12.4 Hz, tBu), 1.43 (d, 9H, JP−H = 13.3 Hz, tBu), 1.52 (d, 15H, JP−H = 1.9 Hz, Cp*), 1.762 (s, 15H, Cp*), 1.764 (d, 9H, JP−H = 13.1 Hz, tBu), 5.42 (d, 1H, JP−H = 301.0 Hz, PtBu2H), 7.22−7.25 (m, 2H, p-Ph), 7.32 (m, 4H, m-Ph), 8.14 ppm (m, 4H, o-Ph). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 100.2 (d, JP−P = 3.2 Hz, JPt−P = 53 Hz, PtBu2H), 270.5 ppm (m, JPt−P = 1822 Hz, μ-PtBu2). IR (ATR, cm−1): 2958, 2893, 2284 ν(PH), 2026 ν(RuH), 1597, 1474, 1426, 1378, 1177, 1025, 1008. Anal. Calcd for C48H80P2SiPtRu2: C, 50.38; H, 7.05. Found: C, 50.52; H, 7.30. trans-9: 1 H NMR (400 MHz, C6D6, 25 °C): δ −14.80 (d, 1H, JP−H = 29.0 Hz, Ru−H), −8.34 (dd, 1H, JP−H = 55.6, 7.6 Hz, JPt−H = 918 Hz, Ru−H− Pt trans to μ-PtBu2), −6.65 (d, 1H, JP−H = 10.4 Hz, JPt−H = 978 Hz, Ru−H−Pt cis to μ-PtBu2), 1.23 (d, 18H, JP−H = 12.7 Hz, tBu), 1.34 (d, 18H, JP−H = 12.5 Hz, tBu), 1.43 (d, 15H, JP−H = 2.0 Hz, Cp*), 1.52 (d, 9H, JP−H = 13.1 Hz, tBu), 1.64 (d, 9H, JP−H = 13.3 Hz, tBu), 1.74 (s, 15H, Cp*), 5.60 (d, 1H, JP−H = 301.3 Hz, PtBu2H), 7.86−7.88 (m, 2H, p-Ph), 7.43 (dd, 4H, JH−H = 7.4, 7.0 Hz, m-Ph), 8.35 ppm (d, 4H, JH−H = 7.0 Hz, o-Ph). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 103.0 (d, JP−P = 4.6 Hz, PtBu2H), 261.4 ppm (m, JP−P = 4.6 Hz, μ-PtBu2). Preparation of {Cp*Ru(H)2}{Cp*Ru(PtBu2H)}Pt(μ-PtBu2)(μ-η2SiEt2)(μ-H)2 (10). A 50 mL Schlenk was charged with 2 (39.5 mg, 41.0 μmol) and toluene (5 mL). A 0.77 M toluene solution of diethylsilane (74 μL, 57.0 μmol) was then added to the solution at 25 °C and stirred for 24 h. The color of the solution turned from dark green to reddish-orange. Removal of the solvent under reduced pressure gave a red solid including 10 and several unidentified products. The yield of 10 was roughly estimated to be 85% on the basis of the 1H NMR spectrum of the residual solid. Analytically pure 10 was obtained from a THF solution of the residual solid stored at −30 °C (15.7 mg, 13.6 μmol, 39%). 10: 1H NMR (400 MHz, C6D6, 25 °C): δ −11.87 (d, 3H, JP−H = 16.6 Hz, JPt−H = 115 Hz, Ru−H and Ru−H−Pt), −11.58 (d, 1H, JP−H = 17.0 Hz, JPt−H = 54 Hz, Ru−H−Si), −10.12 (dd, 1H, JP−H = 37.3, 16.7 Hz, JPt−H = 448 Hz, Ru−H−Pt), 1.22 (d, 9H, JP−H = 12.7 Hz, tBu), 1.23 (d, 9H, JP−H = 13.1 Hz, tBu), 1.43 (t, 6H, JC−H = 7.7 Hz, SiCH2CH3), 1.47 (d, 9H, JP−H = 13.3 Hz, tBu), 1.51 (d, 9H, JP−H = 13.4 Hz, tBu), 1.55−1.63 (m, 4H, SiCH2CH3), 1.74 (d, 15H, JP−H = 2.1 Hz, Cp*), 2.08 (s, 15H, Cp*), 4.57 ppm (d, 1H, JP−H = 305.8 Hz, PtBu2H). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ 11.6 (s, C5Me5), 12.30 (s, SiCH2CH3), 13.0 (s, C5Me5), 17.9 (s, SiCH2CH3), 30.8 (s, CMe3), 31.9 (d, JP−C = 14.3 Hz, CMe3), 32.9 (d, JP−C = 4.3 Hz,CMe3), 33.2 (d, JP−C = 6.1 Hz, CMe3), 33.8 (d, JP−C = 6.5 Hz, CMe3), 34.8 (d, JP−C = 15.6 Hz, CMe3), 35.9 (d, JP−C = 12.1 Hz, CMe3), 89.6 (s, C5Me5), 95.0 ppm (s, C5Me5). One of the CMe3 signals was not observed probably due to the obstruction by the CMe3 signals appearing at δ 33−34 ppm. 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 97.9 (s, PtBu2H), 222.5 ppm (s, JPt−P = 3276 Hz, μ-PtBu2). IR (ATR, cm−1): 2952, 2902, 2297 ν(PH), 2000 ν(RuH), 1782 ν(RuHSi), 1473, L


Article

Organometallics

Gates, B. C. Catal. Lett. 2007, 115, 99−107. (d) Chotisuwan, S.; Wittayakun, J.; Gates, B. C. J. Phys. Chem. B 2006, 110, 12459−12469. (7) (a) Zhang, L.; Kim, J.; Zhang, J.; Nan, F.; Gauquelin, N.; Botton, G. A.; He, P.; Bashyam, R.; Knights, S. Appl. Energy 2013, 103, 507− 513. (b) Zhang, L.; Kim, J.; Chen, H. M.; Nan, F.; Dudeck, K.; Liu, R.S.; Borron, G. A.; Zhang, J. J. Power Sources 2011, 196, 9117−9123. (c) Alayoglu, S.; Lai, L.-C.; Chiou, W.-A.; Eichhorn, B. Microsc. Microanal. 2009, 15, 1206−1207. (d) Alayoglu, S.; Nilekar, A. U.; Mavrikakis, M.; Eichhorn, B. Nat. Mater. 2008, 7, 333−338. (8) (a) Adams, R. D.; Li, Z.; Wu, W.; Swepston, P.; Yamamoto, J. J. Am. Chem. Soc. 1992, 114, 10657−10658. (b) Adams, R. D.; Barnard, T. S.; Li, Z.; Wu, W.; Yamamoto, J. H. J. Am. Chem. Soc. 1994, 116, 9103−9113. (c) Adams, R. D.; Barnard, T. S.; Li, Z.; Wu, W.; Yamamoto, J. Organometallics 1994, 13, 2357−2364. (d) Adams, R. D.; Barnard, T. S. Organometallics 1998, 17, 2567−2573. (e) Adams, R. D.; Barnard, T. S. Organometallics 1998, 17, 2885−2890. (f) Adams, R. D. J. Organomet. Chem. 2000, 600, 1−6. (g) Adams, R. D.; Captain, B. J. Organomet. Chem. 2004, 689, 4521−4529. (9) (a) Adams, R. D.; Chen, G.; Wang, J.-G.; Wu, W. Organometallics 1990, 9, 1339−1341. (b) Adams, R. D.; Bunz, U.; Captain, B.; Fu, W.; Steffen, W. J. Organomet. Chem. 2000, 614−615, 75−82. (c) Adams, R. D.; Captain, B.; Zhu, L. J. Am. Chem. Soc. 2004, 126, 3042−3043. (d) Adams, R. D.; Captain, B.; Zhu, L. Inorg. Chem. 2005, 44, 6623− 6631. (e) Adams, R. D.; Captain, B.; Zhu, L. J. Organomet. Chem. 2006, 691, 3122−3128. (f) Takemoto, S.; Morita, H.; Karitani, K.; Fujiwara, H.; Matsuzaka, H. J. Am. Chem. Soc. 2009, 131, 18026−18027. (10) Sivaramakrishna, A.; Clayton, H. S.; Makhubela, B. C. E.; Moss, J. R. Coord. Chem. Rev. 2008, 252, 1460−1485. (11) (a) Adams, R. D.; Captain, B.; Fu, W.; Pellechia, P. J.; Smith, M. D. Angew. Chem., Int. Ed. 2002, 41, 1951−1953. (b) Adams, R. D.; Captain, B.; Fu, W.; Pellechia, P. J.; Smith, M. D. Inorg. Chem. 2003, 42, 2094−2101. (c) Adams, R. D.; Captain, B.; Fu, W.; Smith, M. D. J. Organomet. Chem. 2003, 682, 113−118. (d) Adams, R. D.; Captain, B.; Fu, W.; Hall, M. B.; Smith, M. D.; Webster, C. E. Inorg. Chem. 2004, 43, 3921−3929. (e) Adams, R. D.; Captain, B.; Fu, W.; Smith, J. L., Jr.; Smith, M. D. Organometallics 2004, 23, 589−594. (f) Adams, R. D.; Trufan, E. Organometallics 2008, 27, 4108−4115. (12) (a) Adams, R. D.; Captain, B.; Smith, M. D. Angew. Chem., Int. Ed. 2006, 45, 1109−1112. (b) Adams, R. D.; Captain, B.; Beddie, C.; Hall, M. B. J. Am. Chem. Soc. 2007, 129, 986−1000. (c) Adams, R. D.; Captain, B.; Smith, M. D.; Beddie, C.; Hall, M. B. J. Am. Chem. Soc. 2007, 129, 5981−5991. (d) Adams, R. D.; Captain, B. Acc. Chem. Res. 2009, 42, 409−418. (13) Takao, T.; Suzuki, H. Bull. Chem. Soc. Jpn. 2014, 87, 443−458. (14) Takemoto, S.; Morita, H.; Kamikawa, K.; Matsuzaka, H. Chem. Commun. 2006, 1328−1330. (15) Shima, T.; Sugimura, Y.; Suzuki, H. Organometallics 2009, 28, 871−881. (16) Nagaoka, N.; Takao, T.; Suzuki, H. Organometallics 2012, 31, 6547−6554. (17) Kameo, H.; Shima, T.; Nakajima, Y.; Suzuki, H. Organometallics 2009, 28, 2535−2545. (18) Ito, J.; Shima, T.; Suzuki, H. Organometallics 2004, 23, 2447− 2460. (19) Only thermal decomposition of 1 leading to the formation of a mixture involving {Cp*Ru(μ-H)}3(μ3-H) and (Cp*Ru)4(H)6 occurred upon heating at 100 °C. (20) Structural data for 201 complexes having Ru−Pt interaction were obtained from Cambridge Structural Database System version 5.37 (Nov 2015 update): Allen, F. A. Acta Crystallogr., Sect. B: Struct. Sci. 2002, B58, 380−388. (21) (a) Powell, J.; Brewer, J. C.; Gulia, G.; Sawyer, J. F. Inorg. Chem. 1989, 28, 4470−4476. (b) Davies, D. L.; Jeffery, J. C.; Miguel, D.; Sherwood, P.; Stone, F. G. A. J. Organomet. Chem. 1990, 383, 463− 480. (c) Adams, R. D.; Chen, G.; Wu, W. J. Cluster Sci. 1993, 4, 119− 132. (d) Adams, R. D.; Wu, W. Organometallics 1993, 12, 1248−1256. (e) Sterenberg, B. T.; Jennings, M. C.; Puddephatt, R. J. Organometallics 1999, 18, 2162−2167. (f) Sravani, C.; Venkatesh, S.; Sivaramakrishna, A.; Vijayakrishna, K.; Clayton, H. S.; Moss, J. R.;

1378, 1363, 1175, 1071, 1026. Anal. Calcd for C40H82P2SiPtRu2: C, 45.74; H, 7.87. Found: C, 45.81; H, 7.97.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00449. NMR and IR spectra of 2−10 as well as VT-1H NMR spectra of 2 and 4, crystallographic data for 2, 4, trans-5, trans-6, 8′, cis-9, and 10, and results of the DFT calculation on 2, 4, and possible isomer of 4 (A in Scheme 2) (PDF) X-ray crystallographic data for 2, 4, trans-5, trans-6, 8′, cis-9, and 10 (CIF) Optimized Cartesian coordinates (XYZ) (XYZ) (XYZ)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail (T. Takao): [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was partly supported by a Grant-in-Aid for Scientific Research on Innovative Areas “Stimuli-responsive Chemical Species for the Creation of Functional Molecules (No. 2408)” (JSPS KAKENHI Grant Number JP15H00924). The authors also thank Dr. Kyo Namura for fruitful discussions.

■

REFERENCES

(1) (a) Buchwalter, P.; Rosé, J.; Braunstein, P. Chem. Rev. 2015, 115, 28−126. (b) Braunstein, P.; Rosé, J. Heterometallic clusters in catalysis. In Metal Clusters in Chemistry; Braunstein, P.; Oro, L. A.; Raithby, P. R., Eds.; Wiley-VCH: Weinheim, 1999; Vol. 2, pp 616− 617. (c) Xiao, J.; Puddephatt, R. J. Coord. Chem. Rev. 1995, 143, 457− 500. (d) Farrugia, L. J. Adv. Organomet. Chem. 1990, 31, 301−391. (e) Guczi, L. J. Mol. Catal. 1984, 25, 13−29. (f) Sinfelt, J. H. Acc. Chem. Res. 1977, 10, 15−20. (2) (a) Braunstein, P.; Bender, R.; Kervennal, J. Organometallics 1982, 1, 1236−1238. (b) Zacchini, S. Eur. J. Inorg. Chem. 2011, 2011, 4125−4145. (c) Raja, R.; Sankar, G.; Hermans, S.; Shephard, D. S.; Bromeley, S.; Thomas, J. M.; Johnson, B. F. G. Chem. Commun. 1999, 1571−1572. (d) Grosshans-Vièles, S.; Croizat, P.; Paillaud, J.-L.; Braunstein, P.; Ersen, O.; Rosé, J.; Lebeau, B.; Rabu, P.; Estournès, C. J. Cluster Sci. 2008, 19, 73−88. (e) Alexeev, O.; Gates, B. C. Top. Catal. 2000, 10, 273−293. (f) Siani, A.; Captain, B.; Alexeev, O. S.; Stafyla, E.; Hungria, A. B.; Midgley, P. A.; Thomas, J. M.; Adams, R. D.; Amiridis, M. D. Langmuir 2006, 22, 5160−5167. (3) (a) Sinfelt, J. H. Bimetallic Catalysts: Discoveries, Concepts and Applications; John Wiley and Sons: New York, 1983. (b) Yu, W.; Porosoff, M. D.; Chen, J. G. Chem. Rev. 2012, 112, 5780−5817. (4) (a) Thomas, J. M.; Johnson, B. F. G.; Raja, R.; Sankar, G.; Midgley, P. A. Acc. Chem. Res. 2003, 36, 20−30. (b) Raja, R.; Khimyak, T.; Thomas, J. M.; Hermans, S.; Johnson, B.F. G. Angew. Chem., Int. Ed. 2001, 40, 4638−4642. (5) (a) Lanza, R.; Canu, P.; Järås, S. G. Appl. Catal., A 2008, 348, 221−228. (b) Dossumov, K.; Salakhova, R. Kh.; Popova, N. M.; Tungatarova, S. A.; Grigorieva, V. P.; Komashko, L. V.; Sass, A. S. J. Alloys Compd. 2007, 434−435, 796−798. (6) (a) McVicker, G. B.; Westfield, N. J. U.S. Patent, 4,187,168, Feb 5, 1980. (b) McVicker, G. B.; Westfield, N. J. U.S. Patent, 4,302,400, Nov 24, 1981. (c) Chotisuwan, S.; Wittayakun, J.; Lobo-Lapidus, R. J.; M


Article

Organometallics Moberg, V.; Su, H. Polyhedron 2013, 62, 169−178. (g) Saha, S.; Captain, B. Inorg. Chem. 2014, 53, 1210−1216. (h) Mathur, P.; Rai, D. K.; Joshi, R. K.; Jha, B.; Mobin, S. M. Organometallics 2014, 33, 3857− 3866. (22) Shin, R. Y. C.; Tan, G. K.; Koh, L. L.; Goh, L. Y.; Webster, R. D. Organometallics 2004, 23, 6108−6115. (23) Farrugia, L. J. Organometallics 1990, 9, 105−110. (24) The virtual coupling in the P(t-Bu) proton resonance in 2 was analyzed by the line shape analysis, which revealed that the 2JP−H, 4 JP−H, and 2JP−P′ values are 12.0, 1.0, and 100.0 Hz, respectively. (25) Sabo-Etienne, S.; Chaudret, B. Chem. Rev. 1998, 98, 2077−2091. (26) Arliguie, T.; Chaudret, B.; Jalon, F. A.; Otero, A.; Lopez, J. A.; Lahoz, F. J. Organometallics 1991, 10, 1888−1896. (27) Adams, D. A.; Boswell, E. Organometallics 2008, 27, 2021−2029. (28) The photoreaction of 1 with Pt(PtBu3)2 performed in a sealed NMR tube with C6D6 was monitored by means of 1H NMR spectroscopy. Along with the formation of 2, a signal derived from the methylene group of isobutene was observed at δ 4.74, while the methyl signal (δ 1.58) was not confirmed due to the obstruction by the Cp* and t-Bu signals. (29) Leopni, P.; Chiaradonna, G.; Pasquali, M.; Marchetti, F.; Fortunelli, A.; Germano, G. Inorg. Chim. Acta 1997, 264, 185−191. (30) In addition to 2, 3, and 4, a mixture of diruthenium complexes was formed in 2% yield. These species were obtained by the reaction of 1 with PtBu2H. This fact indicates that these side products would be formed by the reaction of 1 with liberated PtBu2H from Pt(PtBu2H)3. Characterization of the diruthenium complexes are now under way and will be published in the future. (31) Rodriguez, V.; Donnadieu, B.; Sabo-Etienne, S.; Chaudret, B. Organometallics 1998, 17, 3809−3814. (32) Lin, W.; Wilson, S. R.; Girolami, G. S. Organometallics 1994, 13, 2309−2319. (33) Adams, R. D.; Boswell, E. M.; Hall, M. B.; Yang, X. Organometallics 2008, 27, 4938−4947. (34) Johnson, T. J.; Coan, P. S.; Caulton, K. G. Inorg. Chem. 1993, 32, 4594−4599. (35) Osipov, A. L.; Gerdov, S. M.; Kuzmina, L. G.; Howard, J. A. K.; Nikonov, G. I. Organometallics 2005, 24, 587−602. (36) (a) Adams, R. D.; Captain, B.; Fu, W. J. Organomet. Chem. 2003, 671, 158−165. (b) Adams, R. D.; Captain, B.; Hall, M. B.; Trufan, E.; Yang, X. J. Am. Chem. Soc. 2007, 129, 12328−12340. (c) Adams, R. D.; Captain, B.; Trufan, E. J. Organomet. Chem. 2008, 693, 3593−3602. (37) Cittadini, V.; Leoni, P.; Marchetti, L.; Pasquali, M.; Albinati, A. Inorg. Chim. Acta 2002, 330, 25−32. (38) (a) Lichtenberger, D. L.; Rai-Chaudhuri, A. J. Am. Chem. Soc. 1989, 111, 3583−3591. (b) Lichtenberger, D. L.; Rai-Chaudhuri, A. Inorg. Chem. 1990, 29, 975−981. (c) Lichtenberger, D. L.; RaiChaudhuri, A. J. Am. Chem. Soc. 1990, 112, 2492−2497. (39) Suzuki, H.; Takao, T.; Tanaka, M.; Moro-oka, Y. J. Chem. Soc., Chem. Commun. 1992, 476−478. (40) Suzuki, H.; Omori, H.; Lee, D. H.; Yoshida, Y.; Moro-oka, Y. Organometallics 1988, 7, 2243−2245. (41) Jaw, H.-R. C.; Mason, W. R. Inorg. Chem. 1989, 28, 4370−4373. (42) PROCESS-AUTO, Automatic Data Acquisition and Processing Package for Imaging Plate Diffractometer; Rigaku Corporation: Tokyo (Japan), 1998. (43) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−8. (b) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (44) Chai, J.-D.; Head-Gordon, M. J. Chem. Phys. 2008, 128, 084106/ 1−084106/15. (45) Andrae, D.; Häußermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (46) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;

Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.Gaussian 09; Gaussian, Inc.: Wallingford, CT, 2009. (47) Dennington, R.; Keith, T.; Millam, J. GaussView version 5.0; Semichem Inc.: Shawnee Mission, KS, 2009.

N


Synthesis of a Heterometallic Trinuclear Cluster of Ruthenium and

Recommend Documents