Anionic Trinuclear Iridium(I) Oxo Complex: Synthesis and Reactivity as

4 hours ago - *E-mail: [email protected]., *E-mail: [email protected]. Cite this:Organometallics XXXX, XXX, XXX-XXX ...
2 downloads 4 Views 2MB Size
Download PDF
Article Cite This: Organometallics XXXX, XXX, XXX−XXX

Anionic Trinuclear Iridium(I) Oxo Complex: Synthesis and Reactivity as a Metal-Centered σ‑Donor Ligand to Gold(I) and Silver(I) Shin Takemoto,* Takayuki Tsujimoto, and Hiroyuki Matsuzaka* Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan S Supporting Information *

ABSTRACT: The diiridium(I) μ-hydroxo complex [Ir(μ-OH)(cod)]2 (1; cod = 1,5-cyclooctadiene) readily reacted with aqueous NaOH in DMSO-d6 or NaN(SiMe3)2 in THF to give the anionic trinuclear iridium oxo complex Na[{Ir(cod)}3(μ3-O)2] (2) in high yield. Complex 2 crystallized in the form of the contact ion pair [{Na(thf)2(H2O)}(μ4O){Ir(cod)}3(μ3-O)] (2·(THF)2(H2O)) upon recrystallization from THF−hexane. Reactions of 2 with group 11 metal electrophiles (AuCl(PPh3), AgCl(PPh3), and AgCl) afforded iridium−gold and −silver mixed-metal cluster complexes [{Ir(cod)}3(μ3-O)2M(PPh3)] (3a: M = Au; 3b: M = Ag) and [Na(dmso)3(μ-dmso)]2[{Ir(cod)}3(μ3-O)2Ag(μCl)]2 (4) containing Ir(I) → Au(I)/Ag(I) dative interactions as revealed by DFT and NBO analysis. These results demonstrate the ability of 2 to act as an iridium(I)-centered σ-donor ligands to the group 11 metal centers. Single-crystal X-ray structures of 2·(THF)2(H2O), 3a, 3b, and 4 are presented.

■

of iridium(III) hydride complexes.13 Also, an imido-bridged Ir2Au2 aggregate was synthesized by a reaction of a dimeric iridium(I) μ-imido dianion with AuCl(PPh3).14 Our group has recently reported the synthesis of ruthenium− platinum, −palladium, −gold, and −silver mixed noble metal clusters using diruthenium imido and carbido complexes as building blocks.15 We have now synthesized iridium−gold and iridium−silver mixed noble metal clusters using an anionic trinuclear iridium(I) oxo complex Na[{Ir(cod)}3(μ3-O)2] (2) as a building block. Complex 2 is synthesized surprisingly easily from the reaction of 1 with NaOH or NaN(SiMe3)2 and exhibits considerable basicity at iridium(I), acting as a bidentate metal-centered σ-donor ligand to gold(I) and silver(I) to give clusters containing unsupported metal−metal dative bonds.16 Years ago, Ciriano and Oro et al. demonstrated the intriguing reactivity of the trirhodium(I) bis(imido) anions [{Rh(L)2}3(μ3-NR)2]− (L = 1/2 diene or CO) as versatile metalcentered σ-donor ligands to gold(I), palladium(II), and mercury(II).17 These trirhodium anions could be isolated in the form of complex salts such as [Rh(CNtBu)4][{Rh(diene)}3(μ3-NR)2] but nonetheless must be derived from tetrarhodium precursors via expulsion of a {Rh(diene)}+ fragment.17 The present study serves to extend the work by Oro and Ciriano et al. to an iso(valence)electronic iridium oxo system, using an isolable and readily accessible triiridium(I) dioxo anion.

INTRODUCTION Iridium oxo complexes have attracted considerable attention due to their applications in oxygen atom transfer reactions.1−3 The formation of iridium oxo complexes from their hydroxo or aquo precursors is of relevance to the iridium-catalyzed water oxidation4 but has limited experimental precedents.1,5−8 The dimeric iridium(I) hydroxo complex [Ir(μ-OH)(cod)]2 (1)9 is a readily accessible starting material in organoiridium chemistry and is expected to give iridium oxo complexes via O−H bond scission. Earlier reports concerning the synthesis of iridium oxo complexes from 1 involved its reaction with titanium and tantalum alkyls, which afforded μ3-oxo-bridged early late heterobimetallic complexes.5 More recently, complex 1 was shown to undergo a spontaneous dehydrative condensation to afford a pentanuclear iridium oxo complex:6

Our interest in iridium oxo complexes stems from their use as precursors of iridium−gold mixed-metal clusters. Mixedmetal clusters can serve as precursors of supported bimetallic nanoparticles.10 Iridium−gold nanoparticles have been shown to exhibit significant catalytic activity in exhaust gas treatment (i.e., the conversion of CO to CO2 and NOx to N2).11 Existing methods for the synthesis of iridium−gold cluster complexes involve the redox condensation between anionic iridium carbonyl clusters with gold(I) electrophiles12 and the auration © XXXX American Chemical Society

Received: March 17, 2018

A

DOI: 10.1021/acs.organomet.8b00159 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

■

RESULTS AND DISCUSSION Synthesis, Characterization, and Properties of 2. The oxo complex Na[{Ir(cod)}3(μ3-O)2] (2) was readily synthesized by base-induced dehydration of the μ-hydroxo dimer [(cod)Ir(μ-OH)]2 (1). As shown in Scheme 1, treatment of the Scheme 1. Synthesis of 2

μ-hydroxo complex 1 with 2/3 equiv of aqueous NaOH in DMSO-d6 produced 2 in 90% NMR yield. The reaction appeared to occur instantly as indicated by 1H NMR spectroscopy. For the isolation of 2, it was convenient to conduct the reaction in THF using NaN(SiMe3)2 as the base. Then, complex 2 was isolated in 88% yield as an air-sensitive yellow solid after precipitation from THF−hexane and drying in vacuo. To the best of our knowledge, complex 2 is the first example of an anionic iridium(I) oxo complex. Complex 2 was characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray analysis. The 1H NMR spectrum of 2 in DMSO-d6 showed a single olefinic resonance at 3.23 ppm, along with two multiplets at 2.17 and 1.73 ppm assignable to the diastereotopic methylene protons of the COD ligands. Accordingly, the 13C{1H} NMR spectrum of 2 in DMSO-d6 showed two signals at 50.77 and 33.38 ppm due to the olefinic and methylene COD carbons, respectively. These spectral data are consistent with the D3h symmetry of the [{Ir(cod)}3(μ3-O)2]− anion in DMSO-d6 solution. Although coordination of this anion to the sodium cation through μ4-oxo bridge was observed in the crystal structure of 2·(THF)2(H2O) (see below), the NMR data indicate that such coordination is absent or highly labile in solution. Single crystals of 2·(THF)2(H2O) were obtained by slow diffusion of hexane into a THF solution of 2. A thermal ellipsoid plot for 2·(THF)2(H2O) is depicted in Figure 1. The molecule can be viewed as a contact ion pair of the anion [{Ir(cod)}3(μ3-O)2]− and the cation [Na(thf)2(H2O)]+ linked through a μ4-oxo bridge. In the anionic part, each of the three iridium atoms is coordinated by a COD and two oxo ligands to adopt a distorted square-planar geometry. The Ir−Ir distances are 2.7507(3)−2.8737(4) Å. These Ir−Ir distances are comparable to those reported for [(cod)Ir(μ-NH 2 )] 2 (2.8146(3) Å)18 and [(cod)Ir(μ-OEt)]2 (2.8958(11) Å).19 The Ir−O bond lengths (2.055(3)−2.086(3) Å) are at the longer side among the known Ir-oxo bond lengths (1.73−2.14 Å),1,6−8,20 reflecting the low metal oxidation state and small Ir− O multiple bond nature in 2. The sodium cation in 2·(THF)2(H2O) adopts a distorted tetrahedral geometry, coordinated by the oxo, two THF, and an aqua ligand. Although the hydrogen atoms on the aqua ligand could not be found in the difference Fourier map, an intermolecular hydrogen bond between the aqua ligand and a μ3-oxo ligand of an adjacent molecule in the crystal lattice was

Figure 1. Thermal ellipsoid plot for 2·(THF)2(H2O) at 50% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic distances (Å) and angles (deg): Ir1−Ir2 2.8737(4), Ir2− Ir3 2.8389(3), Ir1−Ir3 2.7507(3), Ir1−O1 2.071(3), Ir1−O2 2.075(3), Ir2−O1 2.064(3), Ir2−O2 2.055(3), Ir3−O1 2.086(3), Ir3−O2 2.071(3), Na1−O1 2.251(3), Na1−O3 2.277(4), Na1−O4 2.414(4), Na1−O5 2.414(4), O1−Ir1−O2 75.99(11), O1−Ir2−O2 76.60(11), O1−Ir3−O2 75.76 (11), Ir1−O1−Ir2 88.06(11), Ir2−O1−Ir3 86.34(10), Ir1−O1−Ir3 82.86(10), Ir1−O2−Ir2 88.19(11), Ir2− O2−Ir3 86.97(10), Ir1−O2−Ir3 83.13(10).

indicated by a short O···O contact (2.564 Å). Reflecting this hydrogen bond, the difference in the Ir−O bond lengths between the μ 3 -O (2.055(3)−2.075(3) Å) and μ 4 -O (2.064(3)−2.086(3) Å) ligands is relatively small despite the difference in their coordination number. Synthesis of Ir−Au/Ag Clusters 3a, 3b, and 4. Having established the facile access to anionic triiridium(I) oxo complex 2, we next examined the use of this complex as a building block for the synthesis of iridium−gold and −silver mixed-metal clusters. As shown in Scheme 2, the reaction of 2 with MCl(PPh3) (M = Au, Ag) afforded the neutral Ir3M (M = Au, Ag) mixed-metal oxo clusters 3a and 3b in 94 and 73% yield, respectively. When AgCl was used as a metal electrophile, a higher nuclear Ir6Ag2 cluster aggregate 4 was obtained in 92% yield. These reactions characterize [{Ir(cod)}3(μ3-O)2]− as a metal-centered anionic σ-donor ligand to the group 11 metal electrophiles. The synthesis of 4 also demonstrates that the formation of Ir−Au and Ir−Ag bonds is not necessarily driven by the elimination of NaCl. The clusters 3a, 3b, and 4 were characterized by a combination of elemental analysis, NMR spectroscopy, and single-crystal X-ray analysis. The 1H NMR spectrum of 3a indicated three olefinic and six methylene proton environments in equal integrals, and the 13C{1H} NMR spectrum of 3a contained three olefinic and three methylene carbon resonances. These data are in agreement with the addition of a gold(I) fragment to one of the Ir−Ir edges of the triiridium B

DOI: 10.1021/acs.organomet.8b00159 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

distance relative to the Ir2−Au1 in 3a suggests a stronger Ir(I) → Au(I) dative interaction from Ir1 than from Ir2. The molecular structure of 3b (Figure 3), being roughly isostructural to 3a, contains an Ir−Ag−Ir bridge more

Scheme 2. Synthesis of Ir−Au/Ag Clusters 3a, 3b, and 4

core of 2 and the retention of this structure in solution. Complexes 3b and 4 showed similar spectral patterns. A thermal ellipsoid plot for 3a is shown in Figure 2. The Ir3Au core is almost flat, and the phosphorus atom on gold also

Figure 3. Thermal ellipsoid plot for 3b at 50% probability level. Hydrogen atoms are omitted for clarity. Selected interatomic distances (Å) and angles (deg): Ir1−Ag1 2.7788(5), Ir2−Ag1 2.7849(5), Ir1− Ir2 2.8919(4), Ir2−Ir3 2.7490(4), Ir1−Ir3 2.7095(4), Ir1−O1 2.047(4), Ir1−O2 2.051(4), Ir2−O1 2.047(4), Ir2−O2 2.059(4), Ir3−O1 2.053(4), Ir3−O2 2.058(4), Ag1−P1 2.4237(14), Ir1−Ag1− Ir2 62.634(13), Ir1−Ag1−P1 145.63(4), Ir2−Ag1−P1 143.66(4).

symmetrical than the Ir−Au−Ir one in 3a. The two Ir−Ag bond lengths are almost identical (2.7788(5) and 2.7849(5) Å), as are the two Ir−Ag−P bond angles (145.63(4) and 143.66(4)°). The Ir−Ir distances in the triiridium unit in 3b are comparable to those found in 3a, with the silver-bridged iridium atoms exhibiting a longer Ir−Ir distance (2.8919(4) Å) than the other two (2.7490(4) and 2.7095(4) Å). The X-ray structure of 4 is depicted in Figure 4. The compound consists of a dianionic Ir6Ag2 octanuclear cluster and a dicationic disodium complex. The Ir6Ag2 dianion consists of two Ir3Ag clusters doubly bridged by the chloride ligands and related to each other by a crystallographic center of symmetry. The silver atoms adopt a distorted tetrahedral geometry coordinated by two iridium and two chloride ligands with slightly dissimilar Ag−Cl distances (Ag1−Cl1 = 2.557(2), Ag1−Cl1* = 2.652(2) Å). The Ir−Ag and Ir−Ir distances in the Ir3Ag units of 4 are very similar to those in 3b, despite the difference in coordination number at silver. The cationic part, which also has a centrosymmetric dimeric structure, is a dicationic disodium complex with two bridging DMSO ligands. Each sodium center adopts distorted square pyramidal geometry with five DMSO ligands bound through the oxygen atoms. It is of interest to compare the structures of 3a, 3b, and 4 with that of the known iodo derivative [{Ir(cod)}3(μ3-O)2(μI)] (5).23 This compound was previously synthesized in low yield (5%) from [Ir(cod)I(μ-I)]2 and AgOAc.23 It can now be readily obtained from 2 and I2 in 93% yield:

Figure 2. Thermal ellipsoid plot for 3a at 50% probability level. One of the two crystallographically independent molecules is shown. Hydrogen atoms are omitted for clarity. Selected interatomic distances (Å) and angles (deg): Ir1−Au1 2.7240(5), Ir2−Au1 2.8522(5), Ir1−Ir2 2.8580(5), Ir2−Ir3 2.7298(5), Ir1−Ir3 2.7206(5), Ir1−O1 2.043(6), Ir1−O2 2.042(5), Ir2−O1 2.051(5), Ir2−O2 2.051(6), Ir3−O1 2.059(5), Ir3−O2 2.049(5), Au1−P1 2.276(2), Ir1−Au1−Ir2 61.615(13), Ir1−Au1−P1 159.73(6), Ir2−Au1−P1 137.44(6).

lies in the same plane. The Ir−Ir distances in 3a are Ir1−Ir2 = 2.8580(5), Ir2−Ir3 = 2.7298(5), and Ir1−Ir3 = 2.7206(5) Å. These distances are similar to those found in 2 (2.7507(3)− 2.8737(4) Å) and can be considered as nonbonding distances between iridium(I) centers. The longer Ir−Ir distance for the gold-bridged iridium atoms relative to the other two is probably due to the steric crowding caused by the presence of the bridging Au(PPh3)+ unit. The Ir−Au bonds can be considered as Ir(I) → Au(I) dative bonds. The Ir−Au bond lengths in 3a are Ir1−Au1 = 2.7240(5) and Ir2−Au1 = 2.8522(5) Å. These are longer than those found in [(dppe)2IrAu(PPh)3]2+ (2.625 Å)21 and [{Ir2(PPh3)2(μ-L)2}Au(PPh3)]3+ (2.607 Å; L = 1,8diisocyano-p-menthan),22 both of which contain an unsupported Ir(I) → Au(I) dative bond from a single iridium(I) center to a Au(PPh3)+ unit. The longer Ir−Au distances in 3a relative to those in these compounds would be due, in part, to the electronic saturation of the gold(I) center with one Ir(I) → Au(I) dative bond per Au(PPh3)+ unit. The shorter Ir1−Au1

As reported earlier, complex 5 has a relatively long Ir−Ir distance for the iodo-bridged nonbonded iridium atoms (3.002(1) Å) and two short Ir−Ir distances (2.660(1) and C

DOI: 10.1021/acs.organomet.8b00159 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

Figure 4. Thermal ellipsoid plot for the anionic (left) and cationic (right) parts of 4 with probability level set at 50 and 30%, respectively. Hydrogen atoms are omitted and only one conformation of the disordered DMSO (the one containing O6) is shown for clarity. Selected interatomic distances (Å) and angles (deg): Ir1−Ag1 2.7982(6), Ir2−Ag1 2.8379(6), Ir1−Ir2 2.8923(4), Ir2−Ir3 2.7878(4), Ir1−Ir3 2.7198(4), Ir1−O1 2.052(4), Ir1−O2 2.064(5), Ir2−O1 2.051(4), Ir2−O2 2.044(4), Ir3−O1 2.044(5), Ir3−O2 2.063(4), Ag1−Cl1 2.557(2), Ag1−Cl1* 2.652(2), Ag1−Ag1* 3.528, Na1−O3 2.340(6), Na1−O3* 2.320(6), Na1−O4 2.285(7), Na1−O5 2.324(7), Na1−O6 2.309(10), Cl1−Ag1−Cl1* 94.76(7), Ir1−Ag1−Cl1 131.77(6), Ir1−Ag1−Cl1* 119.82(5), Ir2−Ag1−Cl1 129.63(6), Ir2−Ag1−Cl1* 120.45(6).

2.663(1) Å) that can be attributed to metal−metal bonds.23 The formal oxidation states for the iridium centers in 5 were assigned as Ir(II)2Ir(I). The longer Ir−Ir distances in 3a, 3b, and 4 relative to the Ir−Ir bonding distances in 5 would provide an additional support for the assignment of the formal oxidation state of Ir(I)3 with no direct Ir−Ir bond and with Ir(I) → Au(I)/Ag(I) dative bonds in 3a, 3b, and 4. To shed light on the nature of the metal−metal bonds in clusters 3a and 3b, the structures of these clusters were optimized by density functional theory (DFT) calculations and subjected to natural bond orbital (NBO) analyses. The optimized geometries of 3a and 3b at the B97-D/6-31G(d) &SDD level in the gas phase are in excellent agreement with the crystallographically determined structures (Table 1). Table 1. Comparison of Selected Interatomic Distances (Å) and Bond Indices in 3a and 3b 3a (M = Au) Ir1−M1b Ir2−M1b Ir1−Ir2b Ir2−Ir3b Ir1−Ir3b M1−P1b

Figure 5. (a) Natural localized molecular orbitals (NLMOs) corresponding to the Ir → Au dative bonds in 3a. (b) Superposition of the donor and acceptor NBOs for the Ir → Au dative interaction in 3a and the second-order perturbation theory stabilizing energies ΔE(2) for Ir → Au electron donation.

3b (M = Ag)

calcd

exptl

WBIa

calcd

exptl

WBIa

2.776 2.849 2.954 2.755 2.719 2.301

2.724 2.852 2.858 2.730 2.721 2.276

0.230 0.174 0.089 0.114 0.118 0.471

2.773 2.809 2.972 2.736 2.751 2.404

2.779 2.785 2.892 2.749 2.710 2.424

0.188 0.160 0.087 0.110 0.110 0.320

(Table 1). Conceptually similar but somewhat weaker donor− acceptor interactions were found for the Ir−Ag bonds in 3b (ΔE(2) = 85 and 71 kcal/mol for Ir1−Ag1 and Ir2−Ag2 bonds, respectively).

■

CONCLUSION We have synthesized novel anionic triiridium(I) oxo complex 2 in high yield from the reaction of familiar organoiridium(I) hydroxo complex 1 with NaN(SiMe3)2. While the triiridium(I) dioxo anion [{Ir(cod)}3(μ3-O)2]− acts as an oxygen-donor Lewis base to the hard sodium cation in the crystals of 2· (THF)2(H2O), it serves as an iridium(I)-centered Lewis base to the soft electrophiles, M(PPh3)+ (M = Au, Ag) and I+. The reaction with I+ afforded known iodo cluster 5 with formal oxidation of two iridium(I) centers to iridium(II). In contrast, the reaction with the M(PPh3)+ fragments produced Ir3M clusters 3a and 3b through the formation of two Ir(I) → M(I) dative bonds, as supported by X-ray structural and DFT-NBO analyses. When AgCl was employed as an electrophile, higher nuclear Ir6Ag2 cluster aggregate 4 was obtained. These results demonstrate that complex 2 can serve as a readily accessible and versatile building block for the synthesis of iridium-

a

Wiberg bond indices. bAtom labels are the same as those used in Figures 2 and 3.

Inspection of natural localized molecular orbitals (NLMOs) revealed that the Ir−Au bonding orbitals in 3a are significantly polarized toward the iridium centers (Figure 5a, 85% Ir and 5% Au for both NLMOs), indicating that the Ir−Au bonds are best considered as donor−acceptor bonds from iridium(I) Lewis bases to a gold(I) Lewis acid. Accordingly, the second-order perturbation theory analysis revealed a remarkable two-electron delocalization from a filled 5d orbital of each iridium center to a vacant 6s orbital of gold atom with large stabilization energies ΔE(2) of ca. 227 and 127 kcal/mol for Ir1−Au1 and Ir2−Au1 bonds, respectively (Figure 5b). The greater ΔE(2) for the Ir1− Au1 interaction relative to Ir2−Au1 parallels the trends in bond lengths and Wiberg bond indices (WBI) for these Ir−Au bonds D

DOI: 10.1021/acs.organomet.8b00159 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

J(31P−109Ag) = 497.9 Hz). 13C{1H} NMR (CH2Cl2, 100 MHz): δ 133.85 (d, 2JPC = 15.8 Hz, o-Ph), 131.09 (d, 1JPC = 30.7 Hz, ipso-Ph), 131.06 (s, p-Ph), 129.28 (d, 3JPC = 10.0 Hz, m-Ph), 64.63, 58.41, 53.10 (s, cod CH), 34.48, 33.55, 33.45 (s, cod CH2). Single crystals of 3b used for the X-ray study were grown from THF−hexane as described above and contained one THF molecule per molecule of 3b. [Na(dmso)3(μ-dmso)]2[{Ir(cod)}3(μ3-O)2Ag(μ-Cl)]2 (4). A stirred suspension of 1 (95 mg, 0.15 mmol) in DMSO (1 mL) was treated with a solution of NaN(SiMe3)2 in THF (1.0 M, 0.10 mL, 0.10 mmol) at room temperature. After a few minutes of stirring, THF was distilled off under reduced pressure. To the resulting solution was added AgCl (14 mg, 0.10 mmol), and the mixture was stirred in the dark for 2.5 h. The solution was then diluted with THF (2 mL) and filtered, and the filter chip was washed with 2 mL of THF. The combined filtrate was layered with diethyl ether (30 mL) and allowed to stand for 5 days. Yellow crystals of 4 that deposited were collected by filtration and dried in vacuo. Yield 0.129 g (0.046 mmol, 92%). Anal. Calcd for C64H120Ag2Cl2Ir6Na2O12S8: C, 27.22; H, 4.28. Found: C, 27.02; H, 4.20. 1H NMR (DMSO-d6, 400 MHz): δ 3.58 (br m, 16H, cod CH), 3.32 (br m, 8H, cod CH), 2.66−2.46 (br m, 24H, cod CH2), 2.54 (s, 48H, DMSO), 2.06 (br m, 24H, cod CH2). 13C{1H} NMR (DMSOd6, 100 MHz): δ 63.54 (br s, cod CH), 58.19 (br s, cod CH), 54.84 (br s, cod CH), 36.72 (br s, cod CH2), 36.00 (br s, cod CH2), 35.76 (br s, cod CH2). Single crystals of 4 were grown from a DMSO−THF−Et2O mixture as described above. [{Ir(cod)}3(μ3-O)2(μ-I)] (5). Complex 2 was prepared in situ as described above from 1 (76 mg, 0.12 mmol) and NaN(SiMe3)2 (0.090 mmol) in THF (20 mL). Then, I2 (23 mg, 0.090 mmol) dissolved in THF (3 mL) was added. The mixture was stirred for a few minutes and evaporated to dryness. The residue was extracted with toluene (20 mL) and filtered, and acetonitrile (60 mL) was layered onto the filtrate. After 7 days, black crystals that deposited were collected with filtration, washed with hexane (2 mL × 2) and dried in vacuo. Yield 88.9 mg (0.077 mmol, 96%). Anal. Calcd for C24H36Ir3O2I: C, 27.19; H, 3.42. Found: C, 27.24; H, 2.30. Although the hydrogen analysis is outside the range viewed as establishing analytical purity, clean NMR spectra are provided in the Supporting Information as evidence of bulk purity. 1H NMR (CDCl3, 400 MHz): δ 5.73, 4.90, 4.37 (m, 4H each, cod CH) 3.04, 2.70, 2.62, 2.51, 2.38, 2.24 (m, 4H each, cod CH2). 13 C{1H} NMR (CH2Cl2, 100 MHz): δ 75.10, 69.37, 67.75 (s, cod CH), 34.59, 34.04, 31.54 (s, cod CH2). Single crystals of 5 used for Xray analysis were grown from toluene−acetonitrile and contained one toluene molecule per molecule of 5. X-ray Crystallography. Single crystals of each compound were prepared as described in the synthetic procedures. All measurements were performed on a Rigaku R-AXIS Rapid imaging plate detector with graphite monochromated Mo Kα radiation (λ = 0.71069 Å) at 173 K. The frame data were processed using Rigaku PROCESSAUTO,26 and the reflection data were corrected for absorption with ABSCOR.27 The structures were solved by SHELXS-97 and refined by SHELXL-97.28 All non-hydrogen atoms were refined with anisotropic displacement parameters unless otherwise mentioned. Hydrogen atoms were placed at calculated positions and treated as riding models unless otherwise mentioned. Hydrogen atoms on the aqua ligand of 2·(THF)2(H2O) were not found in the difference Fourier map and were not included in the structure refinement. The asymmetric unit of the crystal of 3a contained two crystallographically independent molecules and a solvent molecule that could be a disordered cyclohexane or THF. The solvent moiety was modeled with six carbon atoms and refined with isotropic displacement factors without any hydrogen atoms being added. Two of the DMSO ligands (those containing O6 and O6*) in the cationic part of 4 were highly disordered and treated with split atoms. These atoms were refined isotropically with no hydrogen atoms being added. The final structure of 4 showed minor residual peaks attributable to an unidentified solvent molecule, most likely diethyl ether. Four carbon atoms were tentatively placed to model this solvent residue. Further details are provided in the crystallographic information file (CIF). Computational Details. All calculations were done with Gaussian 0929 and NBO 6.030 using the B97-D dispersion corrected 1

containing mixed-metal oxo clusters. Further studies will be directed to the applications of clusters 3a, 3b, and 4 to heterogeneous or homogeneous oxidation catalysis as well as the synthesis of new mixed-metal clusters using 2 as a building block.

■

EXPERIMENTAL SECTION

General Remarks. All operations were performed under a nitrogen atmosphere using standard Schlenk techniques, employing dry solvents and glassware unless otherwise noted. NMR spectra were obtained on a JEOL JMN-AL400 or a Varian VNMR400 spectrometers. 1H NMR chemical shifts are reported in parts per million (ppm) relative to residual solvent peaks (7.26 ppm for CDCl3, 7.16 ppm for C6D6, 5.31 ppm for CD2Cl2, and 2.50 ppm for DMSOd6). 13C{1H} NMR chemical shifts were also reported relative to the solvent peak (39.52 ppm for DMSO-d6 and 53.84 ppm for CH2Cl2). 31 1 P{ H} NMR chemical shifts were reported relative to H3PO4. Elemental analyses were performed on a PerkinElmer 2400 Series II analyzer or by A Rabbit Science Microanalysis Laboratory. Compounds 1,9 [AuCl(PPh3)],24 and [AgCl(PPh3)]25 were prepared by the literature methods. Other reagents were purchased from commercial venders and used as received. Na[{Ir(cod)}3(μ3-O)2] (2). Complex 1 (76 mg, 0.12 mmol) was dissolved in THF (12 mL). A solution of NaN(SiMe3)2 in THF (1.0 M, 80 μL, 0.080 mmol) was added. After stirring for a few minutes, hexane (40 mL) was layered. After 13 days, the supernatant was filtered off, and the yellow crystalline solid collected was dried in vacuo. Yield 67 mg (0.070 mmol, 88%). Anal. Calcd for C24H36Ir3NaO2: C, 30.15; H, 3.80. Found: C, 30.06; H, 3.81. 1H NMR (DMSO-d6, 400 MHz): δ 3.23 (m, 12H, cod CH), 2.17 (m, 12H, cod CH2), 1.73 (m, 12H, cod CH2). 13C{1H} NMR (DMSO-d6, 100 MHz): δ 50.77 (cod CH), 33.38 (cod CH2). Single-crystals of [{Na(thf)2(H2O)}(μ4-O){Ir(cod)}3(μ3-O)] (2·(THF)2(H2O)) suitable for X-ray analysis were grown from THF−hexane. Na[{Ir(cod)}3(μ3-O)2] (2) from 1 and NaOH. Complex 1 (19 mg, 0.030 mmol) was dissolved in DMSO-d6 (1 mL). An aqueous solution of NaOH (1.0 M, 20 μL, 0.020 mmol) was added. The solution was then evacuated to remove excess of water. After addition of 1,4dioxane (3.8 mg, 0.044 mmol) as an internal standard, the solution was analyzed by 1H NMR, which showed the formation of 2 in 90% yield. [{Ir(cod)}3(μ3-O)2Au(PPh3)] (3a). A stirred suspension of 1 (0.38 g, 0.60 mmol) in THF (20 mL) was treated with a solution of NaN(SiMe3)2 in THF (1.0 M, 0.40 mL, 0.40 mmol) at room temperature. After a few minutes of stirring, a solution of [AuCl(PPh3)] (0.20 g, 0.40 mmol) in THF (20 mL) was added to give a deep red solution. The solvent was then removed in vacuo, the residue extracted with CH2Cl2 (30 mL), and the extract evaporated to dryness. The orange solid that remained was washed with hexane and dried in vacuo. Yield 0.525 g (0.378 mmol, 94%). Anal. Calcd for C42H51AuIr3O2P: C, 36.23; H, 3.69. Found: C, 36.22; H, 3.76. 1H NMR (C6D6, 400 MHz): δ 7.68 (m, 6H, Ph), 7.02 (m, 9H, Ph), 4.35, 4.33 (m, 4H each, partially overlapping, cod CH) 4.09 (m, 4H, cod CH), 2.63, 2.61 (m, 4H each, partially overlapping, cod CH2), 2.43 (m, 4H, cod CH2), 2.17, 2.12 (m, 4H each, partially overlapping, cod CH2), 1.91 (m, 4H, cod CH2). 31P{1H} NMR (CH2Cl2, 162 MHz): δ 26.2 (s). 13C{1H} NMR (CH2Cl2, 100 MHz): δ 133.93 (d, 2JPC = 14.2 Hz, o-Ph), 131.72 (d, 1JPC = 47.5 Hz, ipso-Ph), 131.10 (d, 4JPC = 2.3 Hz, p-Ph), 129.47 (d, 3JPC = 10.9 Hz, m-Ph), 67.77, 59.56, 56.62 (s, cod CH), 33.55, 33.48, 33.42 (s, cod CH2). Single crystals of 3a used for the X-ray study were grown from THF−hexane. [{Ir(cod)}3(μ3-O)2Ag(PPh3)] (3b). Compound 3b was prepared in a manner similar to that described for 3a from 0.19 g (0.30 mmol) of 1 and 81 mg (0.20 mmol) of [AgCl(PPh3)] and purified by recrystallization from THF−hexane. Yield 0.190 g (0.146 mmol, 73%). Anal. Calcd for C42H51AgIr3O2P·(THF)0.5: C, 39.46; H, 4.14. Found: C, 39.80; H, 4.26. 1H NMR (CD2Cl2, 400 MHz): δ 7.66 (m, 6H, Ph), 7.52 (m, 9H, Ph), 3.80, 3.74, 3.52 (m, 4H, cod CH), 2.50, 2.42, 2.18, 2.06 (m, 4H, cod CH2), 1.84 (m, 8H, cod CH2). 31P{1H} NMR (CH2Cl2, 162 MHz): δ 5.3 (dd, 1J(31P−107Ag) = 431.3 Hz, E

DOI: 10.1021/acs.organomet.8b00159 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics functional.31 Iridium, gold, and silver atoms were described with SDD effective core potentials and the associated basis sets,32 while the 631G(d) basis set33 was used for all other atoms. Geometry optimizations were performed without any symmetry constraints in the gas phase, and the stationary points were checked by frequency calculations to confirm all positive frequencies.

■

(10) Braunstein, P.; Rosé, J. Heterometallic Clusters for Heterogeneous Catalysis. In Catalysis by Di- and Polynuclear Metal Cluster Complexes; Adams, R. D., Cotton, F. A., Eds.; Wiley-VCH: New York, 1998; pp 443−508. (11) (a) Hirata, H.; Tsuji, S.; Takeuchi, M. Exhaust gas treatment catalysts for effective purification of nitrogen oxides under oxidizing atmosphere and their manufacture. Jpn. Kokai Tokkyo Koho, JP 2002210369, 2002. (b) Bokhimi, X.; Zanella, R.; Angeles-Chavez, C. J. Phys. Chem. C 2010, 114, 14101−14109. (12) (a) Adams, R. D.; Chen, M.; Yang, X. Organometallics 2012, 31, 3588−3598. (b) Adams, R. D.; Chen, M. Organometallics 2012, 31, 6457−6465. (c) Adams, R. D.; Chen, M.; Elpitiya, G.; Yang, X.; Zhang, Q. Organometallics 2013, 32, 2416−2426. (13) (a) Casalnuovo, A. L.; Pignolet, L. H.; van der Velden, J. W. A.; Bour, J. J.; Steggerda, J. J. J. Am. Chem. Soc. 1983, 105, 5957−5958. (b) Albinati, A.; Demartin, F.; Janser, P.; Rhodes, L. F.; Venanzi, L. M. J. Am. Chem. Soc. 1989, 111, 2115−2125. (14) Kolel-Veetil, M. K.; Ahmed, K. J. Inorg. Chem. 1994, 33, 4945− 4949. (15) (a) Takemoto, S.; Morita, H.; Kamikawa, K.; Matsuzaka, H. Chem. Commun. 2006, 1328−1330. (b) Takemoto, S.; Morita, H.; Karitani, K.; Fujiwara, H.; Matsuzaka, H. J. Am. Chem. Soc. 2009, 131, 18026−18027. (c) Takemoto, S.; Ohata, J.; Umetani, K.; Yamaguchi, M.; Matsuzaka, H. J. Am. Chem. Soc. 2014, 136, 15889−15892. (d) Takemoto, S.; Tsujita, M.; Matsuzaka, H. Organometallics 2017, 36, 3686−3691. (16) (a) Bauer, J.; Braunschweig, H.; Dewhurst, R. D. Chem. Rev. 2012, 112, 4329−4346. (b) Amgoune, A.; Bourissou, D. Chem. Commun. 2011, 47, 859−871. (17) (a) Tejel, C.; Shi, Y.-M.; Ciriano, M. A.; Edwards, A. J.; Lahoz, F. J.; Modrego, J.; Oro, L. A. J. Am. Chem. Soc. 1997, 119, 6678−6679. (b) Oro, L. A.; Ciriano, M. A.; Tejel, C.; Shi, Y.-M.; Modrego, J. Novel Imido Rhodium Clusters: Synthesis and Perspectives. In Metal Clusters in Chemistry; Braunstein, P.; Oro, L. A.; Raithby, P. R., Eds.; WileyVCH: New York, 1999; Vol. 1, pp 381−398. (18) Mena, I.; Jaseer, E. A.; Casado, M. A.; García-Orduna, P.; Lahoz, F. J.; Oro, L. A. Chem. - Eur. J. 2013, 19, 5665−5675. (19) Kownacki, I.; Marciniec, B.; Kubicki, M. Chem. Commun. 2003, 76−77. (20) (a) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain-Bates, B.; Hursthouse, M. B. Polyhedron 1993, 12, 2009−2012. (b) Almog, O.; Bino, A.; Garfinkel-Shweky, D. Inorg. Chim. Acta 1993, 213, 99−102. (c) Fandos, R.; Hernández, C.; Otero, A.; Rodríguez, A.; Ruiz, M. J.; Terreros, P. Chem. - Eur. J. 2003, 9, 671−677. (d) Sharninghausen, L. S.; Sinha, S. B.; Shopov, D. Y.; Choi, B.; Mercado, B. Q.; Roy, X.; Balcells, D.; Brudvig, G. W.; Crabtree, R. H. J. Am. Chem. Soc. 2016, 138, 15917−15926. (e) Sinha, S. B.; Shopov, D. Y.; Sharninghausen, L. S.; Stein, C. J.; Mercado, B. Q.; Balcells, D.; Pedersen, T. B.; Reiher, M.; Brudvig, G. W.; Crabtree, R. H. J. Am. Chem. Soc. 2017, 139, 9672−9683. (21) Casalnuovo, A. L.; Laska, T.; Nilsson, P. V.; Olofson, J.; Pignolet, L. H. Inorg. Chem. 1985, 24, 233−235. (22) Sykes, A. G.; Mann, K. R. J. Am. Chem. Soc. 1990, 112, 7247− 7254. (23) Cotton, F. A.; Lahuerta, P.; Sanau, M.; Schwotzer, W. J. Am. Chem. Soc. 1985, 107, 8284−8285. (24) McAuliffe, C. A.; Parish, R. V.; Randall, P. D. J. Chem. Soc., Dalton Trans. 1979, 1730−1735. (25) Stein, R. A.; Knobler, C. Inorg. Chem. 1977, 16, 242−245. (26) PROCESS AUTO, Automatic Data Acquisition and Processing Package for Imaging Plate Diffractometer; Rigaku Corporation: Tokyo, Japan, 1998. (27) Higashi, T. ABSCOR, Empirical Absorption Correction Based on Fourier Series Approximation; Rigaku Corporation: Tokyo, Japan, 1995. (28) Sheldrick, G. M. SHELX97, Program for Crystal Structure Determination; University of Göttingen: Göttingen, Germany, 1997. (29) 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.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00159. NMR spectra and crystallographic data (PDF) Cartesian coordinates for calculated structures (XYZ) Accession Codes

CCDC 1830366−1830370 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Shin Takemoto: 0000-0001-7367-4733 Hiroyuki Matsuzaka: 0000-0001-6494-034X Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank Prof. Hajime Kameo for fruitful discussion. This work was supported by JSPS KAKENHI Grant Nos. JP16H01038, JP15K05457, JP15H00958, and JP15K05459. We also thank Toyota Motor Corporation and Osaka Prefecture University for financial support.

■

REFERENCES

(1) McGhee, W. D.; Foo, T.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 8543−8545. (2) Dobbs, D. A.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 3836− 3837. (3) Jacobi, B. G.; Laitar, D. S.; Pu, L.; Wargocki, M. F.; DiPasquale, A. G.; Fortner, K. C.; Schuck, S. M.; Brown, S. N. Inorg. Chem. 2002, 41, 4815−4823. (4) (a) McDaniel, N. D.; Coughlin, F. J.; Tinker, L. L.; Bernhard, S. J. Am. Chem. Soc. 2008, 130, 210−217. (b) Hull, J. F.; Balcells, D.; Blakemore, J. D.; Incarvito, C. D.; Eisenstein, O.; Brudvig, G. W.; Crabtree, R. H. J. Am. Chem. Soc. 2009, 131, 8730−8731. (c) Nakagawa, T.; Beasley, C. A.; Murray, R. W. J. Phys. Chem. C 2009, 113, 12958−12961. (d) Blakemore, J. D.; Schley, N. D.; Olack, G. W.; Incarvito, C. D.; Brudvig, G. W.; Crabtree, R. H. Chem. Sci. 2011, 2, 94−98. (5) Fandos, R.; Hernández, C.; Otero, A.; Rodríguez, A.; Ruiz, M. J.; García Fierro, J. L.; Terreros, P. Organometallics 1999, 18, 2718−2723. (6) Ahmed, T. S.; Tonks, I. A.; Labinger, J. A.; Bercaw, J. E. Organometallics 2013, 32, 3322−3326. (7) Burford, R. J.; Piers, W. E.; Ess, D. H.; Parvez, M. J. Am. Chem. Soc. 2014, 136, 3256−3263. (8) Schau-Magnussen, M.; Malcho, P.; Herbst, K.; Brorson, M.; Bendix, J. Dalton Trans. 2011, 40, 4212−4216. (9) Green, L. M.; Meek, D. W. Organometallics 1989, 8, 659−666. F

DOI: 10.1021/acs.organomet.8b00159 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics 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, revision C.01; Gaussian, Inc.: Wallingford, CT, 2009. (30) NBO 6.0; Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.; Bohmann, J. A.; Morales, C. M.; Landis, C. R.; Weinhold, F. Theoretical Chemistry Institute, University of Wisconsin: Madison, WI, 2013. (31) Grimme, S. J. Comput. Chem. 2006, 27, 1787−1799. (32) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (33) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213− 222.

G

DOI: 10.1021/acs.organomet.8b00159 Organometallics XXXX, XXX, XXX−XXX