Synthesis and Reactivity of Coordinatively Unsaturated Dinuclear

ARTICLE pubs.acs.org/Organometallics

Synthesis and Reactivity of Coordinatively Unsaturated Dinuclear Ruthenium Bridging Imido Complexes Shin Takemoto,* Tomoharu Kobayashi, Takahiro Ito, Akira Inui, Kenji Karitani, Sayuri Katagiri, Yusaku Masuhara, and Hiroyuki Matsuzaka* Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, Osaka 599-8531, Japan

bS Supporting Information ABSTRACT: [Cp*Ru(μ-NHPh)]2 (Cp* = η5-C5Me5) reacted with CO, t-BuNC, Ph2SdCH2, or Me3SiCtCH to give the dinuclear ruthenium bridging imido complexes [(Cp*Ru)2(μNPh)(μ-L)] (2a, L = CO; 2b, L = t-BuNC; 2c, L = CH2; 2d, L = CCHSiMe3). Protonolysis of 2d with t-BuOH produced the parent vinylidene complex [(Cp*Ru)2(μ-NPh)(μ-CCH2)] (2e). Treatment of 2e with HOTf or MeOTf afforded the cationic alkylidyne complexes [(Cp*Ru)2(μ-NPh)(μ-CR)]OTf (2f, R = Me; 2g, R = Et). Hydride abstraction from 2c with Ph3CBF4 gave the methylidyne complex [(Cp*Ru)2(μ-NPh)(μ-CH)]BF4 (2h). X-ray structures of 2ac and 2f revealed short RuN distances (1.8761.894 Å) consistent with RuN multiple bonds, and the μalkylidyne 2f also featured short RuC bonds (1.929(7) and 1.914(7) Å). In addition to giving simple Lewis base adducts such as [(Cp*Ru)2(μ-NPh)(μ-CO)(PMe3)] and [(Cp*Ru)2(μ-NPh)(μ-CH2)(t-BuNC)2], these imido complexes provided an array of novel ligand coupling reactions. Thus, 2b underwent a tandem imidoisocyanide coupling and CH activation reaction to give an amidinate complex. Complexes 2c and 2e mediated imidoCOmethylene and imidoCOvinylidene coupling to give [{Cp*Ru(CO)2}2(μ-PhNCOCH2)] (6) and [{Cp*Ru(CO)}2(μ-PhNCOCdCH2)] (7), respectively. Complex 2c also underwent a selective coupling reaction with 2 equiv of Me3SiCtCH to give the μ-allenylimine complex [(Cp*Ru)2{μ-Me3SiCHdCdC(SiMe3)C(Me)dNPh}] (8). The imido methylidyne complex coupled with 2 equiv of alkynes to give [(Cp*Ru)2{μ-HC(R1CCR2)(R2CCR1)NPh}]OTf (9ac), a product of double alkyne cycloaddition to the RuN and RuC multiple bonds and CC coupling of the resulting ruthena- and azaruthenacyclobutene moieties.

’ INTRODUCTION Transition metal imido complexes are an important class of metalnitrogen multiply bonded compounds18 that have found many applications in organic synthesis, such as hydroamination of alkynes,9,10 aziridination of olefins,11 and nitrene insertion into CH bonds.11,12 Transition metal imido complexes are also widely used as catalysts for the metathesis13 and polymerization14 of olefins, where the MdNR multiple bond is an effective ancillary unit that supports electron-deficient metal alkylidene and alkyl species. Recently, considerable attention has been focused on the chemistry of dinuclear bridging imido complexes, which provide unique dinuclear platforms with coordinatively unsaturated metal centers and potentially reactive metalnitrogen bonds.1541 Early studies by the Bergman and Sharp groups have demonstrated that bridging imido complexes of low-oxidation-state late transition metals display remarkable reactivity, such as the facile single and double insertion of CO into metalnitrogen bonds,23 transfer of a μ-imido ligand to PMe3,24 and interconversion between μ-imido and μ-oxo complexes.24 Recent efforts by us and others have extended the scope of the imido reactivity in dinuclear systems, such as the alkyne insertion reactions on diruthenium and r 2011 American Chemical Society

dirhodium μ-imido complexes,29,36 CO diamination and redoxcoupled H2 activation on [Cp*Rh(μ-NTs)]2,37,38 catalytic carbodiimide formation via dinickel μ-imido complexes,39 and the use of dicopper μ-imido complexes in catalytic CH amination reactions.35 Additionally, bridging imido complexes have also received interest for their relevance to dinitrogen reduction4244 and ammonia activation systems.45,46 In a previous communication, we described the reactions of the diruthenium bridging amido complex [Cp*Ru(μ-NHPh)]2 (1)47 with several π-acceptor ligands (i.e., CO, t-BuNC, and CH2).29 In contrast to the reaction of 1 with PMe3, which produces the monomeric amido complex [Cp*Ru(NHPh)(PMe3)2],47 the reactions of 1 with the above π-acceptor ligands produced the dinuclear bridging imido complexes [(Cp*Ru)2(μ-NPh)(μ-L)] (Scheme 1; 2a, L = CO; 2b, L = t-BuNC; 2c, L = CH2).29 Spectroscopic monitoring of the reaction of 1 with CO revealed that the μ-CO adduct [(Cp*Ru)2(μ-NHPh)2(μ-CO)] (1a) is rapidly generated upon addition of CO to 1 and cleanly converted into 2a and aniline (Scheme 1), indicating that the imido complex Received: November 30, 2010 Published: January 25, 2011 2160

dx.doi.org/10.1021/om1011227 | Organometallics 2011, 30, 2160–2172

Organometallics Scheme 1

2a was formed by bridging coordination of CO to the unsaturated ruthenium centers in 1 followed by R-elimination of aniline from the saturated adduct 1a.29 X-ray studies for 2ac revealed short RuN (1.881.89 Å) distances consistent with the delocalized multiple bond over the RuNRu linkage. The RuRu distances are also short (2.572.66 Å), and DFT studies supported the existence of a net RuRu bonding character, although there is uncertainty about actual RuRu bond order because RuRu bonding and antibonding orbitals are not purely metal-centered but delocalized into bridging ligand fragments.29 A plausible resonance description for 2ac is shown in Chart 1, which can explain the delocalized RuN multiple bonds, the existence of RuRu bonding interaction, and the unsaturated nature of the ruthenium centers (18e and 16e in each structure). The imido complexes 2ac constitute a new family of πstabilized 16-electron Cp*Ru complexes, whose chemistry has received considerable attention.4864 The key feature of the imido complexes 2ac is the assembly of potentially reactive RuN, RuC, and RuRu bonds on a coordinatively unsaturated bimetallic site. We have investigated the reactivity of these imido complexes, and two specific examples, namely, phosphine PH bond addition across the RuN bond and heteronuclear cluster formation with a Pt(0) fragment, have recently been reported.32,34,40 In the present study we have synthesized a new series of diruthenium imido complexes containing μ-vinylidene and μ-alkylidyne functionalities, 2dh. We have also investigated the reactivity of the whole series of the imido complexes 2ah toward unsaturated small molecules and revealed an array of ligand coupling reactions that are unprecedented in transition metal imido chemistry. Details of these findings are reported herein.

’ RESULTS AND DISCUSSION

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Chart 1

Figure 1. ORTEP drawing of 2f, showing 35% thermal ellipsoids. The triflate anion and hydrogen atoms are omitted. Selected bond lengths (Å) and angles (deg): Ru1Ru2 = 2.5319(8); Ru1N1 = 1.879(5); Ru2N1 = 1.881(5); Ru1C1 = 1.929(7); Ru2C1 = 1.914(7); C1C2 = 1.480(10); N1C3 = 1.421(8); Ru1N1Ru2 = 84.7(2); Ru1C1Ru2 = 82.4(3); N1Ru1C1 = 96.2(3); N1Ru2C1 = 96.7(3); Ru1N1C3 = 140.1(4); Ru2N1C3 = 135.2(4); Ru1C1C2 = 139.1(5); Ru2C1C2 = 138.5(5).

The trimethylsilylvinylidene complex 2d was found to be highly moisture sensitive. A trace of moisture caused hydrolysis of 2d to give the parent vinylidene complex [(Cp*Ru)2(μNPh)(μ-CdCH2)] (2e), probably via protonation at the vinylidene β carbon atom. For preparative purpose, complex 2e was best prepared by the treatment of 2d with excess t-BuOH in toluene (eq 2) and isolated in ca. 60% yield as a gray-violet microcrystalline solid.

Synthesis of the Imido Vinylidene and Imido Alkylidyne Complexes 2dh. We previously reported the reaction of 1

with diphenylacetylene, which gave [(Cp*Ru)2(μ-PhCCPhNPh)], a product of alkyne insertion into RuN(imido) bonds.29 As an extension of this study, we examined a reaction of 1 with Me3SiCtCH (eq 1).64 Interestingly, the reaction produced a new imido complex containing a μ-vinylidene ligand, [(Cp*Ru)2(μ-NPh)(μ-CdCHSiMe3)] (2d), rather than the expected alkyne insertion product. Complex 2d, isolated quantitatively as a maroon solid, showed 13C NMR resonances characteristic of the μ-vinylidene R and β carbons at 314.8 and 117.7 ppm, respectively.65

The facile protonolysis of the CSi bond in 2d suggested that the μ-vinylidene ligands in these imido complexes could be protonated at the vinylidene β carbon atom. This was partly supported by an H/D exchange reaction between 2e and excess D2O in benzene-d6, which caused the disappearance of the 2161

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Table 1. Selected Bond Distances (Å) in 2a, 2b, 2c, and 2f 2a

2b

2c

2f

Ru1Ru2

2.6013(4)

2.6594(5)

2.5728(11)

2.5319(8)

Ru1N1

1.876(6)

1.890(4)

1.891(5)

1.879(5)

Ru2N1 Ru1C1

1.880(6) 2.002(8)

1.885(4) 2.090(5)

1.894(5) 2.057(6)

1.881(5) 1.929(7)

Ru2C1

1.993(8)

2.082(5)

2.061(6)

1.914(7)

N1C3

1.423(9)

1.402(7)

1.415(7)

1.421(8)

μ-vinylidene 1H NMR signal (δ 6.55), suggesting the formation of [(Cp*Ru)2(μ-NPh)(μ-CdCD2)] (2e-d2). Most significantly, we were able to isolate the cationic imido alkylidyne complex [(Cp*Ru)2(μ-NPh)(μ-CMe)]OTf (2f) in 93% yield by protonation of 2e with HOTf (eq 3). Although protonation of a μ-vinylidene ligand is an established organometallic reaction,65 it is rather surprising that this occurs in preference to protonation at imido nitrogen. Probably, π-donation from the imido ligand would play an important role in the stability of complex 2f. The X-ray structure and bonding of 2f are discussed in a later section. The 13C NMR spectrum of 2f showed a signal attributable to the alkylidyne R carbon at 384.4 ppm. The propylidyne analogue [(Cp*Ru)2(μ-NPh)(μ-CEt)]OTf (2g) was also prepared in 94% yield by alkylation of 2e with MeOTf (eq 3).

The successful isolation of the cationic μ-alkylidyne complexes 2f and 2g prompted us to prepare a μ-methylidyne analogue by hydride abstraction from the μ-methylene complex 2c, an approach taken to synthesize [(CpFe)2(CO)3(μ-CH)]PF6 from [(CpFe)2(CO)3(μ-CH2)].66 Thus treatment of 2c with 1 equiv of Ph3CBF4 at low temperature cleanly afforded the brown crystalline [(Cp*Ru)2(μ-NPh)(μ-CH)]BF4 (2h), isolated in 70% yield after recrystallization from THF (eq 4). The 1H NMR spectrum of 2h contained a resonance for the μ-CH proton at 18.15 ppm. The 13C NMR signal for the μ-CH carbon in 2h was observed at 377.1 ppm. Although these μ-CH resonances are not as deshielded as those of [(CpFe)2(CO)3(μ-CH)]PF6 (δH 22.8, δC 490.2),66 they are easily distinguished from the μ-CH2 resonances of 2c (δH 12.79, δC 186.6).

Structure and Bonding of the Imido Alkylidyne Complex 2f. The X-ray structure of 2f is shown in Figure 1. Selected bond

distances are listed in Table 1 with the corresponding distances in 2ac. The imido alkylidyne 2f has a planar central Ru2NC core

Figure 2. Selected molecular orbitals of [(CpRu)2(μ-NH)(μ-CH)]þ with their energy (eV) and prevalent bonding character.

similar to those in 2ac. The μ-imido and μ-ethylidyne ligands are both trigonal planar (angle sums 360°) and exhibit short RuN (1.879(5) and 1.881(5) Å) and RuC (1.929(7) and 1.914(7) Å) distances indicative of RuN and RuC multiple bonds delocalized over the Ru2N and Ru2C units, respectively. The RuN distances are similar to those in 2ac,29 and the RuCalkylidyne distances are comparable to those in [Cp*Ru(μCMe)2OsCp*].67 The RuRu distance in 2f is 2.5319(8) Å, which is the shortest among 2af. The nature of bonding in 2f was investigated by DFT calculations. The structure optimization was performed for the simplified model [(CpRu)2(μ-NH)(μ-CH)]þ and for the full molecule [(Cp*Ru)2(μ-NPh)(μ-CMe)]þ. The former was used for qualitative evaluation of bonding in the central Ru2NC core. The relevant molecular orbitals are presented in Figure 2. The MO58 (HOMO) and MO57 can be characterized as δ-type RuRu antibonding and bonding interactions, respectively.68 The MO56 and MO50 represent another pair of RuRu δ antibonding and bonding combinations. The MO50 also displays π-bonding interactions in both RuNRu and RuCRu linkages, indicating the π-conjugated nature of the RuN and RuC multiple bonds. The MO52 and MO49 can be viewed as the RuRu σ-bonding and σ-antibonding orbitals, respectively. The latter has a significant contribution from the methylidyne 2p orbital and hence has a diminished RuRu σ-antibonding character. The MO48 shows a π-type interaction within the Ru2N moiety with a considerable RuRu π-bonding character. These seven occupied orbitals constitute a formal π2σ*2δ2σ2δ*2δ2δ*2 configuration with respect to the RuRu bond. Although these orbitals are not purely metal-centered, a net RuRu bonding character would be produced by the π-bonding MO that spreads over the Ru2N unit (MO48) and the diminished RuRu σ-antibonding character in MO49, which leaves a net RuRu σ-bonding interaction. 2162


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Table 2. DFT-Calculated RuRu Distances (Å) and Bond Orders (Mayer and Wiberg)a 2a

2b

2c

2f

RuRu

2.6293

2.6966

2.6024

2.5766

Mayer Wiberg

0.5019 0.4744

0.4699 0.4516

0.5526 0.5090

0.5539 0.5250

a

Calculated for the full structures [(Cp*Ru)2(μ-NPh)(μ-L)] (L = CO, t-BuNC, CH2, CMeþ).

We further consider the effect of the contribution of ligandbased orbitals in MO50 and MO49 on the RuRu bonding. These MOs can be considered as representing the back-bonding from the occupied RuRu δ and σ* orbitals into the corresponding empty 2p orbitals of the methylidyne ligand, CHþ. The backdonation from the RuRu σ* orbital would be more significant than that from the RuRu δ orbital, since the former is a RuC σ interaction while the latter is a RuC π interaction. These types of back-bonding interactions should exist in the whole series of the imido complexes 2ah, and the difference in the extent of back-bonding would be reflected in the variation in RuRu distances. Indeed, the observed RuRu distances in 2af become shorter (2b > 2a > 2c > 2f) as the acceptor strength of the bridging carbon ligands increases (CNBut < CO < CH2 < CMeþ). This also supports our view that back-bonding from the filled RuRu σ* orbital plays an important role in the formation of the RuRu bonding interaction. To further confirm the above trend in RuRu distances, we carried out full structure optimization for 2af and computed bond orders (Mayer69 and Wiberg70 bond indices) for these structures (Table 2). The calculated RuRu distances well reproduced the experimentally observed trend (2f < 2c < 2a < 2b), and the bond order indices are also consistent with this trend. The relatively small bond order values are probably due to the delocalization of RuRu bonding electrons into ligand-centered orbitals, which is often encountered in bridged dinuclear systems.7173 Reactivity of Imido Complexes 2ah. Formation and Structures of PMe3 and t-BuNC Adducts. The coordinatively unsaturated nature of these imido complexes was exemplified by their reaction with PMe3. Treatment of 2ac with 2.5 equiv of PMe3 in THF cleanly afforded the corresponding mono-PMe3 adducts [(Cp*Ru)2(μ-NPh)(μ-L)(PMe3)] (3a, L = CO; 3b, L = t-BuNC; 3c, L = CH2) in ca. 60% yield (eq 5). The 1H NMR spectra of these products in C6D6 contained two inequivalent Cp* signals, one of which appeared as a doublet due to coupling with the 31P nucleus (4JPH = 1.01.5 Hz).

Complex 3a was structurally characterized by X-ray diffraction. An ORTEP diagram is shown in Figure 3. The molecule features unsymmetrical dinuclear structure with one PMe3, and the phosphine-containing ruthenium (Ru2) has a much longer

Figure 3. ORTEP drawing of 3a, showing 35% thermal ellipsoids. Hydrogen atoms are omitted. Selected bond lengths (Å) and angles (deg): Ru1Ru2 = 2.6696(6); Ru1N1 = 1.884(4); Ru2N1 = 2.056(4); Ru1C1 = 2.024(5); Ru2C1 = 1.997(6); Ru2P1 = 2.3012(18); N1C2 = 1.385(6); Ru1N1Ru2 = 85.20(15); Ru1C1Ru2 = 83.2(2); N1Ru1C1 = 95.5(2); N1Ru2C1 = 91.17(19); Ru1N1C2 = 142.2(3); Ru2N1C2 = 132.2(3).

RuN distance (2.056(4) Å) than the other (1.884(4) Å). The latter short RuN distance and the planarity of the imido nitrogen (angle sum 359.6°) indicate the presence of π donation from the imido nitrogen to the 16-electron Ru1. The RuRu distance of 2.6696(6) Å is consistent with a RuRu single bond, which is also expected from electron counting.

Although reactions of the imido complexes 2ah with other potential two-electron donors such as CO led mostly to ligand coupling reactions (vide infra), treatment of the μ-methylene and μ-vinylidene imido complexes 2c and 2e with excess t-BuNC afforded the stable bis-isocyanide adducts [{Cp*Ru(t-BuNC)}2(μ-NPh)(μ-L)] (4c, L = CH2; 4e, L = CCH2; eq 6), which were isolated in ca. 60% yield as dark yellow crystals. The infrared spectra of 4c and 4e showed two isocyanide CtN stretching bands at around 2100 and 2040 cm1. The 1H NMR spectra of these complexes contained Cp* and t-Bu signals in 30:18 intensity ratio, and complex 4c displayed two diastereotopic μmethylene resonances at 8.56 and 7.77 ppm consistent with the cis coordination of the two isocyanide ligands. The structures of 4c and 4e were determined by X-ray crystallography. An ORTEP drawing of 4c is shown in Figure 4. Most notable features are the pyramidal geometry at the imido nitrogen (angle sum 334.3°) and the elongated RuN bond distances (2.050(2), 2.029(2) Å) compared to those in 2c (1.893(av) Å). These features indicate that the RuN multiple bond is essentially absent in these complexes, and a nonbonding pair of electrons is localized on the imido nitrogen atom. The pyramidalization of imido nitrogen on going from 2c to 4c is consistent with the theory of dπpπ repulsion,74 demonstrating that the achievement of an 18-electron configuration at both of the two ruthenium centers considerably reduces the RuN πbonding interaction and causes the localization of the imido lone 2163


Organometallics

Figure 4. ORTEP drawing of 4c, showing 35% thermal ellipsoids. Hydrogen atoms are omitted. Selected bond lengths (Å) and angles (deg): Ru1Ru2 = 2.6760(3); Ru1N1 = 2.050(2); Ru2N1 = 2.029(2); Ru1C1 = 2.062(3); Ru2C1 = 2.066(3); Ru1C8 = 1.883(3); Ru2C9 = 1.880(3); N1C2 = 1.369(3); Ru1N1Ru2 = 82.00(8); Ru1C1Ru2 = 80.82(11); N1Ru1C1 = 97.62(10); N1Ru2C1 = 98.14(10); Ru1N1C2 = 125.51(17); Ru2N1 C2 = 126.80(18).

pair electrons on the nitrogen atom. Similar structural features were also observed for 4e (see Supporting Information). ImidoCO Coupling Reactivity. CO is among the most prevalent substrates in imido group transfer reactions.23,7582 Treatment of the imido complex 2a with excess CO (1 atm) in C6D6 at room temperature resulted in the formation of [Cp*Ru(CO)2]2 (90%) and PhNCO (20%) (eq 7). These products were identified by 1H NMR and GC-MS analyses, and yields were determined by integration of 1H NMR signals against an internal standard. Organic products other than phenyl isocyanate were also observed by 1H NMR, but they could not be identified. Although the yield of PhNCO was low, the above results demonstrate the imido transfer ability of the diruthenium complex 2a. The reaction probably proceeded via coordination of CO to the 16-electron ruthenium centers in 2a. This would give a bis-carbonyl adduct containing a pyramidal imido ligand analogous to that observed in the bis-isocyanide adduct 4c. Such a pyramidal imido ligand would be nucleophilic enough to attack a coordinated CO to give a PhNCO ligand, which would be released from the metal centers in the presence of excess CO.

Amidinate Formation via ImidoIsocyanide Coupling. Isocyanides are isoelectronic with CO, and we examined imidoisocyanide coupling reactivity by using 2b. This complex reacted with excess t-BuNC to give the orthometalated amidinate complex [(Cp*Ru)2(μ-t-BuNCHNC6H4)(t-BuNC)3] (5), a product of tandem imidoisocyanide coupling and phenyl CH bond activation (eq 8). Complex 5 was produced as a 2:1 mixture of two stereoisomers that differ in the relative orientation of the two Cp* groups. Recrystallization from hexane afforded 5 as a yellow crystalline solid, which also contained the two isomers in 2:1 molar ratio. The yield was typically 70%.

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Figure 5. ORTEP drawing of an isomer of 5. Ellipsoids are drawn at the 35% probability level. Hydrogen atoms are omitted. Selected bond lengths (Å): Ru1N1 = 2.157(3); Ru1N2 = 2.177(3); Ru1C12 = 1.901(4); Ru2C7 = 2.155(4); Ru2C17 = 1.914(5); Ru2C22 = 1.887(4); N1C1 = 1.326(5); N2C1 = 1.311(5).

Characterization of 5 was based on 1H NMR, FAB-MS, and elemental analysis. The structure of one isomer was confirmed by single-crystal X-ray diffraction (vide infra). The 1H NMR spectrum of 5 contained signals attributable to the amidinate CH protons at 9.97 (major isomer) and 8.95 (minor isomer) ppm. Each isomer showed three t-Bu resonances in 1:1:2 intensity ratio, which can be rationalized by assuming a rapid exchange of diastereotopic t-BuNC ligands on the Cp*Ru(t-BuNC)2 fragment. The FAB-MS spectrum of 5 showed a molecular ion peak at m/z 897 and a series of fragment peaks at m/z 814, 731, and 648 due to the successive loss of t-BuNC ligands. The solid sample of 5 contained some large crystals suitable for X-ray study, which revealed the structure of one isomer of 5 (Figure 5). The orthometalated amidinate ligand is κ2-bonded to the Cp*Ru(t-BuNC) fragment by the amidinate nitrogen atoms and is η1-bonded to the Cp*Ru(t-BuNC)2 fragment with the ortho phenyl carbon atom, C7. The RuN and CN bond distances for the amidinate moiety are similar to those found in [Cp*Ru(L)(amidinate)].59 The least-squares plane defined by the amidinate moiety (i.e., Ru1, N1, C1, N2 atoms) is roughly coplanar with the phenylene ring, and the two Cp* groups are mutually cis with respect to this approximate plane. Restricted rotation about the Ru2C7 bond is suggested by the steric crowding around Ru2, which prevents interconversion between the cis and trans isomers. The imidoisocyanide coupling usually gives carbodiimide complexes.30,76,78 Sometimes, unusual multiple isocyanide insertion and cyclometalation products are observed.26,84 As to the reaction of 2b with t-BuNC, the structure of the product 5 suggests that the reaction involves imidoisocyanide coupling, phenyl CH activation, and amidinate CH bond formation. A possible mechanism that includes these processes is shown in Scheme 2. The initial step would be the coordination of isocyanide molecules to give the saturated bis-isocyanide adduct 2164


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Scheme 2

A, the formation of which was indirectly supported by the isolation and characterization of 4c (vide infra). Then, imido isocyanide coupling would proceed via nucleophilic attack of imido nitrogen on a coordinated isocyanide to give the μ-κ1:η1carbodiimide intermediate B. The next step would be the rearrangement of B to the μ-κ2:η1-bonded complex C with an amidinate-like four-membered metallacycle. Subsequent CH activation by the 16-electron Ru center could give D, which would be followed by CH reductive elimination and isocyanide coordination to furnish the observed product 5. ImidoCOMethylene and ImidoCOVinylidene Coupling Reactions. The imido methylene complex 2c provided an example of highly selective multiligand coupling reaction involving both the μ-imido and μ-methylene moieties. Thus, treatment of 2c with excess CO (1 atm) in THF at room temperature afforded the dinuclear acetanilido(2) complex [{Cp*Ru(CO)2}2(μ-PhNCOCH2)] (6) in 73% yield as a result of imidoCOmethylene coupling (eq 9). The 1H NMR spectrum of 6 showed a singlet for the R-ketonyl proton at δ 2.13 ppm, similar to that in [{Cp*Ru(CO)2}2(μ-COCH2)] (2.41 ppm).85 The FAB-MS spectrum of 6 contained a molecular ion peak at m/z 719 and a series of fragment peaks due to successive loss of four CO ligands (m/z 691, 663, 635, 607).

The imido vinylidene complex 2d also underwent coupling reaction with CO (eq 10). The product, isolated in 69% yield as red plates, was the μ-acrylanilido(2) complex 7, which features a novel imidoCOvinylidene coupling sequence. The presence of coordinated CdCH2 group was evident from the 1H NMR signals at 4.07 and 4.01 ppm (d, 1H, J = 2.0 Hz). The 13C NMR spectrum of 7 showed two terminal CO resonances at 220.5 and 207.3 ppm. The carbon resonances for the CdCH2 group at δ 48.8 (CH2) and 175 (quaternary) were consistent with the μ-η1:η2-vinylic structure.86,87 The structure of 7 was further elucidated by X-ray analysis of the NAr analogue [{Cp*Ru(CO)}2(μ-CH2dCCONAr)] (70 , Ar = p-tolyl, Figure 6). The compound contains a RuRu single bond (RuRu = 2.8521(5) Å), which contrasts to the non metalmetal bonded structure of 6. The μ-η1:η2 coordination of the CdCH2 group is confirmed, and the amidato nitrogen atom is terminally bound with a RuN distance of 2.121(2) Å.

Figure 6. ORTEP drawing of 70 , showing 35% thermal ellipsoids. Hydrogen atoms are omitted. Selected bond lengths (Å) and angles (deg): Ru1Ru2 = 2.8521(5); Ru1N1 = 2.121(2); Ru1C1 = 2.036(3); Ru1C4 = 1.866(3); Ru2C1 = 2.104(3); Ru2C2 = 2.239(3); Ru2C5 = 1.853(3); C1C2 = 1.388(4); C1C3 = 1.497(4); C3N1 = 1.349(4); C3O1 = 1.225(3); C2C1C3 = 130.4(3).

Formation of μ-Allenylimine Ligand via Imido AlkyneMethylene Coupling. The reactivity of bridging imido

complexes toward alkynes has been studied extensively.29,36,45,88,89 ImidoCOalkyne coupling reactions have been observed for some imido carbonyl clusters,88,89 while direct imidoalkyne coupling is rare in bridging imido systems.29,36 We now found that the imido methylene complex 2c undergoes a selective multiligand coupling reaction with an alkyne. Thus, treatment of 2c with a slight excess of Me3SiCtCH (5 equiv) in THF at room temperature afforded the product formulated as the μ-allenylimine complex [(Cp*Ru)2{μ-Me3SiCHdCdC(SiMe3)C(Me)d NPh}] (8) in 88% yield (eq11). The newly formed ligand featured an acyclic vinylidenealkyneimido linkage, with the central alkyne unit {Me3SiCCMe} indicating a formal methylene insertion into the alkyne CH bond. The 1H NMR spectrum of 8 contained signals attributable to the terminal allenic proton (δ 4.22) and the imine methyl substituent (δ 1.99). The 13C NMR spectrum of 8 showed the central allenic carbon resonance at 183.5 ppm, a shift indicative of considerable μ-carbenic character.

The X-ray structure of 8 is shown in Figure 7. The μallenylimine ligand forms three- and five-membered metallacycles with the Ru1 atom. The latter is almost planar and is η5-bonded to Ru2. Considerable back-bonding to the μ-allenylimine ligand is indicated by the bent C1C2C3 linkage (140.9(4)°) as well as the bond lengths in the C1C2C3C4N1 chain 2165


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Scheme 3

Figure 7. ORTEP drawing of 8, showing 35% thermal ellipsoids. Hydrogen atoms except for H1 are omitted. Selected bond lengths (Å) and angles (deg): Ru1Ru2 = 2.8469(7); Ru1N1 = 2.093(3); Ru1C1 = 2.306(4); Ru1C2 = 2.098(4); Ru2N1 = 2.242(3); Ru2C2 = 2.098(4); Ru2C3 = 2.182(5); Ru2C4 = 2.129(5); C1C2 = 1.386(6); C2C3 = 1.441(6); C3C4 = 1.400(6); C4N1 = 1.384(5); N1C6 = 1.427(5); C1C2C3 = 140.9(4).

Figure 8. ORTEP drawing of the cationic part of 9a, showing 35% thermal ellipsoids. Hydrogen atoms are omitted. Selected bond lengths (Å): Ru1Ru2 = 2.7394(7); Ru1N1 = 2.103(4); Ru1C1 = 2.107(5); Ru1C2 = 2.228(5); Ru1C3 = 2.168(5); Ru2N1 = 2.126(4); Ru2C1 = 2.036(5); Ru2C4 = 2.168(5); Ru2C5 = 2.174(5); C1C2 = 1.417(6); C2C3 = 1.412(6); C3C4 = 1.484(6); C4C5 = 1.407(7); C5N1 = 1.410(6); N1C6 = 1.427(6).

(1.384(5)1.441(6) Å) that are intermediate between singleand double-bond distances. Alkyne Coupling Reactivity Involving Both RuN and Ru C Multiple Bonds. It has been known that MN multiple bonds of μ-imido complexes36 and MC multiple bonds of μ-alkylidyne complexes90 undergo cycloaddition reactions with

alkynes. The imido methylidyne complex 2h has both RuN and RuC multiple bonds, and it is found that this integrated multiplebond system reacts with alkynes to give products of tandem double alkyne cycloaddition and ruthenacyclobuteneazaruthenacyclobutene coupling. Thus, heating a mixture of [(Cp*Ru)2(μ-NPh)(μ-CH)]OTf (2h0 )91 and a 5-fold excess of p-tolylacetylene in THF at 60 °C for 4 h produced the 6-phenyl-2,5-di(p-tolyl)-6-aza-1,3,5hexatrien-1-yl complex [(Cp*Ru)2(μ-HC(R1CCR2)(R2CCR1)NPh)]OTf (9a, R1 = p-tolyl, R2 = H) in 70% yield as reddishpurple block crystals (eq 12). Complex 2h0 also reacted with 1-hexyne and diphenylacetylene under slightly forcing conditions to give the corresponding products 9b (47%) and 9c (50%), respectively. These products were characterized by elemental analysis and NMR spectroscopy, and complexes 9a and 9b were structurally characterized by single-crystal X-ray diffraction. The 1H NMR spectra of 9ac showed two distinct Cp* signals. The presence of a μ-CH terminus in the azahexatrienyl linkage was evidenced by characteristic downfield signals in the 1H and 13C NMR spectra (e.g., δH = 11.54 and δC = 184.8 for 9a). The 1H NMR spectra of 9a and 9b showed signals for the internal alkenyl protons in a region consistent with the π-allyl-like bonding (e.g., δ 4.67 and 3.32 for 9a).

The X-ray structure of the cationic part of 9a is shown in Figure 8. The μ-azahexatrienyl ligand forms an S-shaped structure comprised of a π-allyl-like C1C2C3 unit and an aza-π-allyllike C4C5N1 unit. The CC and CN bond lengths (1.407(7)1.417(6) Å) within these allylic units are intermediate between single- and double-bond distances. In contrast, the C3C4 bond that connects the two allylic units is long (1.484(6) Å) and can be formulated as a CC single bond. The RuRu distance of 2.7394(7) Å is consistent with a RuRu single bond. Complex 9b also has similar structural features (see Supporting Information). Although efforts to detect intermediates such as a monoalkyne adduct were unsuccessful, the structures of the products 9ac 2166


Organometallics are informative enough to suggest a possible reaction mechanism, which is shown in Scheme 3. The presence of π-allyl- and aza-π-allyl-type structures in the products suggests that the initial steps of the reaction would be the cycloaddition of alkynes to the RuC and RuN multiple bonds to give the intermediate E, containing the ruthenacyclobutene and azaruthenacyclobutene structures. The Markovnikov regiochemistry in these cycloaddition steps would be sterically favored, as it could avoid repulsion between the alkyne substituents and the Cp* ligands. The CC coupling between the resulting metallacycle moieties and subsequent π coordination of alkyne-derived carbon atoms would furnish the observed products.

’ CONCLUSION We have synthesized and characterized a series of dinuclear ruthenium bridging imido complexes [(Cp*Ru)2(μ-NPh)(μL)]nþ (n = 0 or 1) containing a variety of organometallic functionalities (i.e., CO, t-BuNC, CH2, vinylidene, alkylidyne). The synthesis of these imido complexes is based on the addition of π-acceptor ligands to the bis-amido complex 1, which induces disproportionation of the two amido ligands into free aniline and the imido ligand. In addition, modification of the μ-methylene and μ-vinylidene ligands turned out to be an effective way to synthesize the imidoalkylidyne derivatives. All of these complexes feature the delocalized multiple bonds over the RuNRu unit, which should contribute to make these coordinatively unsaturated complexes sufficiently stable to be isolated. The imidoalkylidyne complexes also possess the multiply bonded RuC linkage. The presence of a net RuRu bonding character has been suggested by DFT calculations; the major bonding contributions characterized are the formation of a π-bonding molecular orbital that spreads over the Ru2N unit and the back-donation of RuRu σ* electrons into the bridging carbon moiety, which leaves a net RuRu σ-bonding interaction. The latter role of π-acceptor ligands in RuRu bonding may explain the absence of RuRu bond formation in the reaction of 1 with the σ-donor PMe3, which gives the monomeric adduct [Cp*Ru(NHPh)(PMe3)2].47 Owing to the coordinatively unsaturated nature of the ruthenium centers, these imido complexes are highly reactive toward incoming substrates. The diverse combination of the imidodiruthenium fragment (Cp*Ru)2(μ-NPh) with an additional organometallic functional group allows us to observe a number of ligand coupling reactions that are unprecedented in transition metal imido chemistry. These include the imidoCO methylene and imidoCOvinylidene coupling reactions observed for 2c and 2e, the formation of allenylimine ligand in the reaction of 2c with Me3SiCtCH, and the imidoalkyne alkynemethylidyne coupling reaction observed for the imido methylidyne complex 2h0 . The last example is quite characteristic to this RuN and RuC multiply bonded system, as the reaction appears to proceed via double alkyne cycloaddition to these multiple bonds followed by dinuclear CC coupling of the ruthenacyclobuteneazaruthenacyclobutene moieties. ’ EXPERIMENTAL SECTION General Remarks. All manipulations were performed under an atmosphere of nitrogen using standard Schlenk techniques. Anhydrous solvents (toluene, hexanes, THF, acetonitrile, and 2-propanol) were purchased from Kanto Chemical Co., Inc. and degassed before use.

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Deuterated solvents were obtained from Cambridge Isotope Laboratories, Inc., degassed, and stored over activated 4A molecular sieves. [Cp*Ru(μNHPh)]2 was prepared from [Cp*Ru(μ3-Cl)]4 by a modification of the literature method;47 LiNHPh (prepared from n-BuLi and NH2Ph) was used instead of NaNHPh 3 0.3THF, and the product was crystallized from a layered solution of toluene/hexanes in 6070% yield as dark blue block crystals. Other reagents were purchased from commercial vendors and used without further purification unless otherwise noted. 1H and 31P{1H} NMR spectra were recorded on a JEOL ECP500 spectrometer at the field strength of 500.16 and 202.48 MHz, respectively. 13C{1H} NMR spectra were obtained on a Varian VNMR400 spectrometer at the field strength of 100.55 MHz. Infrared spectra were obtained using a JASCO FT-IR 4100 spectrometer. FAB-MS spectra were recorded on a JEOL JMS700 spectrometer. Elemental analyses were performed on a Perkin-Elmer 2400 Series II CHNS/O analyzer. [(Cp*Ru)2(μ-NPh)(μ-CO)] (2a). To a solution of 1 (210 mg, 0.320 mmol) in THF (15 mL) was added CO (11 mL) at room temperature. The color of the solution instantly changed from blue to yellow and then gradually to dark orange. After stirring overnight at room temperature, the solvent was removed in vacuo, and the remaining solid was extracted with hexanes (total 30 mL). The extract was concentrated to 10 mL and set aside for 1 day. Red crystals of 2a were collected by filtration and dried under vacuum. Yield: 120 mg, 63%. Anal. Calcd for C27H35NORu2: C, 54.81; H, 5.96; N, 2.37. Found: C, 54.87; H, 5.95; N, 2.33. 1H NMR (C6D6): δ 7.38 (t, 2H, Ph), 7.16 (t, 1H, Ph), 7.12 (d, 2H, Ph), 1.63 (s, 30H, Cp*). 13C{1H} NMR (toluene-d8, 22 °C): δ 258.7 (μ-CO), 168.5, 122.1, 117.6 (Ph), 91.0 (C5Me5), 9.8 (C5Me5). IR (KBr): 1744 cm1 (ν(CO)). [(Cp*Ru)2(μ-t-BuNC)(μ-NPh)] (2b). To a solution of 1 (687 mg, 1.05 mmol) in THF (25 mL) was added a solution of t-BuNC (110 μL, 1.05 mmol) in 5 mL of THF at 80 °C. The dark violet solution was allowed to warm slowly to room temperature and stirred for 4 h. The solvent was removed in vacuo, and the residue was recrystallized from cold tolueneacetonitrile to afford 2b as dark red crystals. Yield: 561 mg, 83%. Anal. Calcd for C31H44N2Ru2: C, 57.56; H, 6.86; N, 4.33. Found: C, 57.76; H, 6.97; N, 4.39. 1H NMR (C6D6): δ 7.38 (t, 2H, Ph), 7.13 (t, 2H, Ph), 7.01 (d, 1H, Ph), 1.97 (s, 9H, t-Bu), 1.56 (s, 30H, Cp*). 13 C{1H} NMR (C6D6): δ 212.9 (CN), 170.7, 122.4, 118.5 (Ph), 88.3 (C5Me5), 59.1 (CMe3), 32.2 (CMe3), 10.8 (C5Me5). IR (KBr): 1809 cm1 (ν(CN)). [(Cp*Ru)2(μ-CH2)(μ-NPh)] (2c). To a stirred suspension of [Ph2SMe][BF4] (1.09 g, 3.78 mmol) in THF (10 mL) was added dropwise a solution of NaN(SiMe3)2 in THF (1.09 M, 3.81 mL, 4.16 mmol) at 80 °C. The mixture was slowly warmed to 10 °C to form a clear yellow solution. The solution was cooled again to 80 °C and transferred via cannula to a cooled (80 °C) stirred solution of 1 (2.60 g, 3.78 mmol) in 20 mL of THF. The combined solution was allowed to warm slowly to room temperature and stirred for 12 h. The solvent was removed in vacuo, and the residue was extracted with toluene (total 80 mL). The extract was concentrated (ca. 20 mL), layered with acetonitrile (40 mL), and stood for 2 days to give 2c as dark red needles. Yield: 1.58 g, 71%. Anal. Calcd for C27H37NRu2: C, 56.13; H, 6.46; N, 2.42. Found: C, 55.97; H, 6.36; N, 2.84. 1H NMR (C6D6): δ 12.79 (s, 2H, CH2), 7.36 (t, 2H), 7.19 (d, 2H), 7.14 (t, 1H, Ph), 1.63 (s, 30H, Cp*). 13C{1H} NMR (C6D6): δ 186.6 (CH2), 168.9, 136.42, 131.35, 120.3 (Ph), 86.1 (C5Me5), 10.7 (C5Me5). [(Cp*Ru)2(μ-NPh)(μ-CdCHSiMe3)] (2d). To a solution of 1 (0.40 g, 0.61 mmol) in THF (15 mL) was added at 80 °C a solution of Me3SiCtCH (85 μL, 0.61 mmol) in THF (5 mL). The mixture was allowed to warm slowly to room temperature and stirred for 12 h. Evaporation of the solution afforded 2d as a maroon solid. Yield: 0.40 g, 99%. Anal. Calcd for C31H45NSiRu2: C, 56.25; H, 6.85; N, 2.12. Found: C, 56.08; H, 6.77; N, 2.54. 1H NMR (C6D6): δ 7.32 (t, 2H, Ph), 7.14 (t, 1H, Ph), 6.99 (d, 2H, Ph), 6.97 (s, 1H, CdCHSiMe3), 1.49 (s, 30H, 2167


Organometallics Cp*), 0.86 (s, 9H, SiMe3). 13C{1H} NMR (C6D6): δ 314.8 (CCHSiMe3), 168.6, 129.4, 123.2, 119.4 (Ph), 117.7 (CCHSiMe3), 90.7 (C5Me5), 10.0 (C5Me5), 5.06 (SiMe3). [(Cp*Ru)2(μ-NPh)(μ-CdCH2)] (2e). To a solution of 1 (0.40 g, 0.61 mmol) in toluene (10 mL) was added Me3SiCtCH (86 μL, 0.61 mmol) at room temperature. After 20 min, t-BuOH (1 mL) was added. The mixture was stirred for 2.5 h and evaporated to dryness. The residue was washed with diethyl ether (10 mL) to give 2e as a gray-violet microcrystalline solid. Yield: 0.23 g, 64%. Anal. Calcd for C28H37NRu2: C, 57.03; H, 6.32; N, 2.38. Found: C, 56.91; H, 6.52; N, 2.50. 1H NMR (C6D6): δ 7.35 (t, 2H, Ph), 7.15 (t, 1H, Ph), 7.05 (d, 2H, Ph), 6.55 (s, 2H, CdCH2), 1.51 (s, 30H, Cp*). 13C{1H} NMR (C6D6): δ 304.0 (CCH2), 168.3, 128.2, 122.7, 119.3 (Ph), 105.6 (CCH2), 89.3 (C5Me5), 9.5 (C5Me5). [(Cp*Ru)2(μ-NPh)(μ-CMe)]OTf (2f). To a solution of 2e (0.139 g, 0.236 mmol) in toluene (5 mL) was added HOTf (21 μL, 0.236 mmol) at room temperature. The mixture was stirred for 10 min and evaporated to dryness. Recrystallization of the residue from CH2Cl2/ hexanes afforded 2f as red needles. Yield: 0.163 g, 93%. Anal. Calcd for C29H38NO3F3SRu2: C, 47.08; H, 5.18; N, 1.89. Found: C, 46.87; H, 5.27; N, 1.85. 1H NMR (CD2Cl2): δ 7.46 (t, 2H, Ph), 7.39 (t, 1H, Ph), 6.68 (d, 2H, Ph), 3.87 (s, 3H, CMe), 1.63 (s, 30H, Cp*). 13C{1H} NMR (CD2Cl2): δ 384.4 (CMe), 164.3, 129.2, 126.7, 117.3 (Ph), 121.3 (q, J = 319 Hz, CF3SO3), 102.3 (C5Me5), 45.5 (CMe), 9.8 (C5Me5). [(Cp*Ru)2(μ-NPh)(μ-CEt)]OTf (2g). To a solution of 2e (60 mg, 0.10 mmol) in toluene (8 mL) was added MeOTf (12 μL, 0.11 mmol) at room temperature. The mixture was stirred for 12 h and evaporated to dryness. Recrystallization of the residue from THF/hexanes afforded 2g as red needles. Yield: 71 mg, 94%. Anal. Calcd for C30H40NO3F3SRu2: C, 47.80; H, 5.35; N, 1.86. Found: C, 47.77; H, 4.94; N, 1.64. 1H NMR (CD2Cl2): δ 7.49 (t, 2H, Ph), 7.43 (t, 1H, Ph), 6.66 (d, 2H, Ph), 4.46 (q, J = 7.6 Hz, 2H, CH2CH3), 1.64 (s, 30H, Cp*), 1.60 (t, J = 7.6 Hz, 3H, CH2CH3). 13C{1H} NMR (CD2Cl2): δ 391.5 (CCH2CH3), 164.1, 129.3, 126.9, 117.1 (Ph), 121.3 (q, J = 319 Hz, CF3SO3), 102.6 (C5Me5), 49.8 (CCH2CH3), 11.7 (CCH2CH3), 9.9 (C5Me5). [(Cp*Ru)2(μ-NPh)(μ-CH)]BF4 (2h). A stirred solution of 2c (470 mg, 0.814 mmol) in toluene (15 mL) was cooled to 80 °C and treated with Ph3CBF4 in CH2Cl2 (1.0 mol/L, 0.81 mL). The mixture was allowed to warm to room temperature with stirring over 3 h and then evaporated to dryness. The residue was washed twice with 5 mL of diethyl ether, and the remaining solid was recrystallized from THF at 30 °C to give 2h as a brown crystalline solid. Yield: 380 mg, 70%. Anal. Calcd for C27H36BNF4Ru2: C, 48.87; H, 5.47; N, 2.11. Found: C, 49.10; H, 5.46; N, 1.98. 1H NMR (CD2Cl2): δ 18.15 (s, 1H, μ-CH), 7.47 (m, 3H, Ph), 6.76 (d, 2H, Ph), 1.77 (s, 30H, Cp*). 13C{1H} NMR (CD2Cl2): δ 377.1 (μ-CH), 165.0, 129.6, 126.8, 117.0 (Ph), 103.5 (C5Me5), 10.7 (C5Me5). The μ-CH signal was observed by using a 13C-enriched sample of 2h. The 13 C-enriched 2h was prepared from 13C-enriched 2c. The 13C-enriched 2c was prepared using the sulfonium salt [Ph2S13CH3][OTf]. This sulfonium salt was prepared from the commercially available 13CH3OTf and Ph2S according to the literature method.92 [(Cp*Ru)2(μ-NPh)(μ-CH)]OTf (2h0 ). 2h (471 mg, 0.710 mmol) and NaOTf (6.11 g, 35.5 mmol) were dissolved in 50 mL of acetone, and the solution was stirred at room temperature for 1 h. After removal of the solvent under reduced pressure, the residue was extracted with CH2Cl2 (total 70 mL). The extract was concentrated to ca. 4 mL and layered with diethyl ether (20 mL) to give 2h0 as brown crystals. Yield: 439 mg, 85%. Anal. Calcd for C28H36NO3F3SRu2: C, 46.34; H, 5.00; N, 1.93. Found: C, 46.47; H, 4.71; N, 1.80. 1H NMR (acetone-d6): δ 18.60 (s, 1H, μCH), 7.55 (t, 2H, Ph), 7.46 (t, 1H, Ph), 6.96 (d, 2H, Ph), 1.85 (s, 30H, Cp*). 13C{1H} NMR (acetone-d6): δ 165.7, 130.1, 127.3, 118.1 (Ph), 122.2 (q, J = 320 Hz, CF3SO3), 104.0 (C5Me5), 10.7 (C5Me5). [(Cp*Ru)2(μ-NPh)(μ-CO)(PMe3)] (3a). To a solution of 2a (129 mg, 0.218 mmol) in THF (10 mL) was added a THF solution of PMe3

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(1.0 M, 0.545 mL, 0.545 mmol). After stirring overnight at room temperature, the solution was evaporated to dryness, and the remaining solid was extracted with hexanes (10 mL). The extract was concentrated to 1 mL and set aside for 1 day. Dark orange crystals of 3a were collected by filtration and dried in vacuo. Yield: 87 mg (60%). Anal. Calcd for C30H44NOPRu2: C, 53.96; H, 6.64; N, 2.10. Found: C, 53.60; H, 6.53; N, 2.31. 1H NMR (C6D6): δ 7.54 (d, 2H, Ph), 7.34 (t, 2H, Ph), 6.99 (t, 1H, Ph), 1.85 (s, 15H, Cp*), 1.70 (d, 4JPH = 1.4 Hz, 15H, Cp*), 0.76 (d, 2 JPH = 9.0 Hz, 9H, PMe3). 13C{1H} NMR (C6D6): δ 260.2 (μ-CO), 165.7, 128.5, 128.3, 123.4 (Ph), 94.1, 89.3 (C5Me5), 17.5 (d, 1JPC = 28.8 Hz, PMe3), 10.9, 10.8 (C5Me5). 31P{1H} NMR (C6D6): δ 7.8 (s). IR (KBr): 1731 cm1 (ν(CO)). [(Cp*Ru)2(μ-NPh)(μ-t-BuNC)(PMe3)] (3b). To a solution of 2b (148 mg, 0.229 mmol) in hexanes (15 mL) was added a THF solution of PMe3 (1.0 M, 570 μL, 0.57 mmol). After stirring overnight at room temperature, the solution was concentrated to ca. 1 mL and set aside for 1 day at 30 °C to give dark brown crystals of 3b, which were collected by filtration and dried in vacuo. Yield: 98 mg, 59%. Anal. Calcd for C34H53N2PRu2: C, 56.49; H, 7.39; N, 3.88. Found: C, 56.40; H, 7.58; N, 3.76. 1H NMR (C6D6): δ 7.59 (d, 2H, Ph), 7.33 (t, 2H, Ph), 7.00 (t, 1H, Ph), 1.81 (s, 15H, Cp*), 1.75 (d, 4JPH = 1.5 Hz, 15H, Cp*), 1.63 (s, 9H, tBu), 0.75 (d, 2JPH = 9.0 Hz, 9H, PMe3). 13C{1H} NMR (C6D6): δ 215.4 (t-BuNC), 164.8, 124.5, 123.7, 117.2 (Ph), 92.5 (d, 2JPC = 3.1 Hz, C5Me5), 86.4 (C5Me5), 58.3 (CMe3), 32.1 (CMe3), 19.3 (d, 1JPC = 28.8 Hz, PMe3), 12.1, 11.3 (C5Me5). 31P{1H} NMR (C6D6): δ 1.3 (s). IR (KBr): 1759 cm1 (ν(CN)). [(Cp*Ru)2(μ-NPh)(μ-CH2)(PMe3)] (3c). To a solution of 2c (126 mg, 0.218 mmol) in THF (10 mL) was added a THF solution of PMe3 (1.0 M, 0.545 mL, 0.545 mmol). After stirring overnight at room temperature, the solution was evaporated to dryness, and the remaining solid was extracted with hexanes (10 mL). The extract was concentrated to 1 mL and set aside for 1 day to give 3c as dark blue crystals. Yield: 85 mg, 60%. Anal. Calcd for C30H46NPRu2: C, 55.11; H, 7.09; N, 2.14. Found: C, 55.21; H, 7.57; N, 2.37. 1H NMR (C6D6): δ 10.23 (d, 2JHH = 2.0 Hz, 1H, CH2), 8.83 (dd, 2JHH = 2.0 Hz, 3JPH = 15.1 Hz, 1H, CH2), 7.52 (d, 2H, Ph), 7.34 (t, 2H, Ph), 6.93 (t, 1H, Ph), 1.77 (s, 15H, Cp*), 1.68 (d, 4JPH = 1.0 Hz, 15H, Cp*), 0.82 (d, 2JPH = 8.3 Hz, 9H, PMe3). 13 C{1H} NMR (C6D6): δ 165.8 (Ph), 161.5 (d, 2JPC = 9.6 Hz, CH2), 128.3, 123.3, 115.8 (Ph), 94.3, 84.0 (C5Me5), 18.2 (d, 1JPC = 26.9 Hz, PMe3), 11.6, 11.0 (C5Me5). 31P{1H} NMR (C6D6): δ 13.1 (s). [(Cp*Ru)2(μ-NPh)(μ-CH2)(t-BuNC)2] (4c). To a solution of 2c (291 mg, 0.504 mmol) in THF (15 mL) was added t-BuNC (0.590 mL, 5.03 mmol), and the mixture was stirred overnight at room temperature. The solution was evaporated to dryness, and the residue was extracted with hexanes (15 mL). The extract was concentrated to 1 mL and set aside for 1 day to give 4c as dark yellow crystals. Yield: 232 mg, 62%. Anal. Calcd for C37H55N3Ru2: C, 59.73; H, 7.45; N, 5.65. Found: C, 59.99; H, 7.77; N, 6.15. 1H NMR (C6D6): δ 8.56, 7.77 (s, 1H each, CH2), 7.20 (t, 2H, Ph), 7.13 (d, 2H, Ph), 6.68 (t, 1H, Ph), 1.89 (s, 30 H, Cp*), 1.07 (s, 18 H, t-Bu). 13C{1H} NMR (C6D6): δ 180.6 (t-BuNC), 172.8 (μ-CH2), 135.2, 127.2, 118.6, 112.4 (Ph), 97.5 (C5Me5), 55.6 (CMe3), 31.9 (CMe3), 11.2 (C5Me5). IR (KBr): 2102, 2040 cm1 (ν(CN)). [(Cp*Ru)2(μ-NPh)(μ-CdCH2)(t-BuNC)2] (4e). To a solution of 2e (0.10 g, 0.17 mmol) in toluene (12.5 mL) was added t-BuNC (86 μL, 0.76 mmol), and the mixture was stirred for 30 min at room temperature. The solution was evaporated to dryness, and the residue was extracted with hexanes (10 mL). The extract was concentrated to 1 mL and set aside for 1 day to give 4e as dark yellow crystals. Yield: 73 mg, 57%. Anal. Calcd for C38H55N3Ru2: C, 60.37; H, 7.33; N, 5.56. Found: C, 60.43; H, 7.71; N, 5.36. 1H NMR (C6D6): δ 7.20 (t, 2H, Ph), 7.06 (d, 2H, Ph), 6.67 (t, 1H, Ph), 5.74 (s, 2H, CdCH2), 1.91 (s, 30 H, Cp*), 1.06 (s, 18 H, t-Bu). 13C{1H} NMR (C6D6): δ 268.5 (CCH2), 180.2 (CN), 167.8, 127.3, 117.9, 112.6 (Ph), 109.2 (CCH2), 98.0 (C5Me5), 55.6 (CMe3), 31.7 (CMe3), 10.9 (C5Me5). IR (KBr): 2091, 2044 cm1 (ν(CN)). 2168


Organometallics Reaction of 2a with CO: Formation of [Cp*Ru(CO)2]2 and PhNCO. In a 25 mL Schlenk flask, the imido complex 2a (23.3 mg, 0.0394 mmol) and 1,3,5-trimethoxybenzene (an internal standard, 3.3 mg, 0.0197 mmol) were dissolved in C6D6 (1 mL). The solution was frozen, evacuated, and thawed. Then, CO was introduced into the flask, and the mixture was stirred under a CO atmosphere for 14 h. The 1H NMR spectrum showed the formation of [Cp*Ru(CO)2]2 (90%, δ 1.71) and PhNCO (20%). The existence of PhNCO was also confirmed by a GC-MS analysis. Data for PhNCO: 1H NMR (C6D6) δ 6.82 (m, 2H), 6.76 (m, 1H), 6.57 (m, 2H); MS(EI) m/z 119, 91, 64. The 1H NMR spectrum also contained unidentified signals in the aromatic region: δ 7.76 (m), 7.48 (m), 7.35 (m), 7.30 (m), 7.23 (m), 7.15 (m), 7.09 (m). [(Cp*Ru)2(μ-t-BuNCHNC6H4)(t-BuNC)3] (5). To a solution of 2b (67 mg, 0.10 mmol) in THF (10 mL) was added t-BuNC (0.11 mL, 1.0 mmol). The mixture was stirred for 2 days at room temperature to give a yellow solution. The solution was evaporated to dryness, and the residue was extracted with hexanes (10 mL). The extract was concentrated to 1 mL and set aside for 1 day to give 5 as a yellow crystalline solid. Yield: 64 mg, 69%. The product was obtained as a 2:1 mixture of two isomers. Anal. Calcd for C46H71N5Ru2: C, 61.65; H, 7.98; N, 7.81. Found: C, 61.70; H, 8.01; N, 7.70. 1H NMR (C6D6): major isomer, δ 9.97 (s, 1H, NCHN), 7.95 (d, 1H, C6H4), 7.37.2 (m, 2H, C6H4), 6.86 (m, 1H, C6H4), 2.00 (s, 15H, Cp*), 1.95 (s, 15H, Cp*), 1.60 (s, 18H, tBu), 1.28 (s, 9H, t-Bu), 1.16 (s, 9H, t-Bu); minor isomer, δ 8.95 (s, 1H, NCHN), 7.60 (d, 1H, C6H4), 7.37.2 (m, 2H, C6H4), 6.88 (m, 1H, C6H4), 1.96 (s, 15H, Cp*), 1.81 (s, 15H, Cp*), 1.44 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.15 (s, 18H, t-Bu). MS (FAB): m/z 897 [M]þ, 814 [M(tBuNC)]þ, 731 [M 2(t-BuNC)]þ, 648 [M 3(t-BuNC)]þ. [{Cp*Ru(CO)2}2(μ-PhNCOCH2)] (6). A solution of 2c (108 mg, 0.187 mmol) in 10 mL of THF was placed in a 25 mL Schlenk flask, and the solution was frozen, evacuated, and thawed. CO was introduced to the flask, and the mixture was stirred for 2 days. The solvent was removed in vacuo, and the residue was extracted with hexanes (10 mL). The extract was concentrated to 1 mL and set aside for 1 day under a CO atmosphere. The yellow crystals of 6 deposited were collected by filtration and dried in vacuo. Yield: 98 mg, 73%. Anal. Calcd for C32H37NO5Ru2: C, 53.55; H, 5.20; N, 1.95. Found: C, 53.90; H, 5.05; N, 2.11. 1H NMR (C6D6): δ 7.45 (d, 2H, Ph), 7.29 (t, 2H, Ph), 7.00 (t, 1H, Ph), 2.13 (s, 2H, CH2), 1.61 (s, 15H, Cp*), 1.48 (s, 15H, Cp*). 13C{1H} NMR (C6D6): δ 204.7, 202.5 (Ru-CO), 185.2 (PhNCOCH2), 158.4, 128.9, 128.3, 122.6 (Ph), 99.8, 98.4 (C5Me5), 9.8, 9.5 (C5Me5), 6.9 (CH2). MS (FAB): m/z 719 [M]þ, 691 [M 2CO]þ, 663 [M3CO]þ, 635 [M3CO]þ, 607 [M4CO]þ. IR (KBr): 2020, 1998, 1945 cm1 (ν(CO)). [{Cp*Ru(CO)}2(μ-CH2dCCONPh)] (7). Complex 2e (0.14 g, 0.24 mmol) was dissolved in 20 mL of toluene in a 25 mL Schlenk flask under nitrogen. The flask was evacuated, and CO was introduced to the flask at room temperature. After stirring for 30 min, the solvent was removed in vacuo, and the residue was recrystallized from toluene/ hexanes to give 7 as red plate crystals. Yield: 0.11 g, 69%. Anal. Calcd for C31H37NO3Ru2: C, 55.26; H, 5.54; N, 2.08. Found: C, 55.66; H, 5.75; N, 2.10. 1H NMR (C6D6): δ 8.00 (br, 2H, Ph), 7.31 (t, 2H, Ph), 6.89 (t, 1H, Ph), 4.07, 4.01 (d, J = 2.0 Hz, 1H each, CdCH2), 1.54, 1.50 (s, 15H each, Cp*). 13C{1H} NMR (C6D6): δ 220.5, 207.3 (Ru-CO), 174.6, 174.0 (s, CH2dCCONPh), 147.3, 128.5, 123.6, 120.2 (Ph), 99.7, 97.0 (C5Me5), 48.8 (s, CH2dCCONPh), 9.5, 9.3 (C5Me5). IR (Nujol): 2723 (w), 2524 (w), 2503 (w), 2445 (w), 2341 (w), 2205 (w), 2059 (w), 1940 (s), 1848 (s), 1614 (s), 1578 (s), 1462 (s), 1342 (s), 1318 (s), 1303 (s), 1283 (m), 1182 (w), 1156 (m), 1067 (m), 1024 (m), 993 (m), 968 (w), 911 (w), 862 (w), 799 (w), 768 (s), 754 (s), 624 (w), 565 (s) cm1. [{Cp*Ru(CO)}2(μ-CH2dCCONAr)] (70 , Ar = p-tolyl). This compound was obtained in 62% yield from [(Cp*Ru)2(μ-NAr)(μCdCH2)] in a manner similar to that described for 7. Anal. Calcd for

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C32H39NO3Ru2: C, 55.88; H, 5.72; N, 2.04. Found: C, 56.17; H, 5.72; N, 2.04. 1H NMR (C6D6): δ 7.94 (br, 2H, aryl), 7.13 (d, 2H, aryl), 4.08, 4.02 (d, J = 2.0 Hz, 1H each, CdCH2), 2.24 (s, 3H, C6H4Me), 1.56, 1.51 (s, 15H each, Cp*). 13C{1H} NMR (C6D6): δ 220.6, 207.4 (Ru-CO), 174.3, 174.2 (s, CH2dCCONAr), 144.8, 129.2, 128.9, 123.6 (aryl), 99.6, 97.0 (C5Me5), 48.6 (s, CH2dCCONAr), 21.0 (s, C6H4Me), 9.6, 9.4 (C5Me5). IR (Nujol): 2723 (w), 1937 (s), 1857 (s), 1614 (s), 1600 (s), 1501 (s), 1344 (s), 1304 (w), 1275 (w), 1184 (w), 1162 (w), 1109 (w), 1030 (m), 910 (w), 829 (m), 755 (w), 723 (w), 705 (w), 563 (m) cm1. [(Cp*Ru)2{μ-Me3SiCHdCdC(SiMe3)C(Me)dNPh}] (8). To a solution of 2c (154 mg, 0.267 mmol) in THF (7.5 mL) was added trimethylsilylacetylene (184 μL, 1.33 mmol) at room temperature. After stirring for 14 h, the solution was evaporated to dryness. Recrystallization of the residue from THF/acetonitrile afforded 8 as dark red crystals. Yield: 182 mg, 88%. Anal. Calcd for C37H57N2Si2Ru2: C, 57.40; H, 7.42; N, 1.81. Found: C, 57.22; H, 7.29; N, 1.89. 1H NMR (C6D6): δ 7.16 (m, 1H, Ph), 7.04 (m, 1H, Ph), 6.99 (m, 1H, Ph), 6.88 (m, 1H, Ph), 6.85 (m, 1H, Ph), 4.22 (s, 1H, CHSiMe3), 1.99 (s, 3H, Me), 1.84, 1.15 (s, 15H each, Cp*), 0.50, 0.36 (s, 9H each SiMe3). 13C{1H} NMR (C6D6): δ 183.5 (Me3SiCHdCdC(SiMe3)C(Me)dNPh), 153.3, 128.5, 126.9, 126.2, 125.7, 125.3 (Ph), 114.0 (Me3SiCHdCdC(SiMe3)C(Me)dNPh), 84.7, 82.0 (C5Me5), 58.7 (Me3SiCHdCdC(SiMe3)C(Me)dNPh), 50.9 (Me3SiCHdCdC(SiMe3)C(Me)dNPh), 16.1 (Me3SiCHdC dC(SiMe3)C(Me)dNPh), 11.4, 10.4 (C5Me5), 2.4, 2.2 (SiMe3). [(Cp*Ru)2{μ-HC(RCCH)(HCCR)NPh}]OTf (9a, R = p-tolyl). To a solution of 2h0 (112 mg, 0.154 mmol) in 10 mL of THF was added ptolylacetylene (195 μL, 1.54 mmol), and the solution was stirred at 60 °C for 4 h. Volatiles were removed under reduced pressure, and the residue was washed with hexanes. The remaining solid was recrystallized from THF/Et2O to give 9a as reddish-purple block crystals. Yield: 88.4 mg, 70%. Anal. Calcd for C46H52NO3F3SRu2: C, 57.66; H, 5.47; N, 1.46. Found: C, 57.57; H, 5.48; N, 1.42. 1H NMR (acetone-d6): δ 11.54 (d, J = 2.6 Hz, 1H, HC(RCCH)(HCCR)NPh), 7.716.81 (m, 13H, aryl), 4.67 (dd, J = 2.6 and 2.0 Hz, 1H, HC(RCCH)(HCCR)NPh), 3.32 (d, J = 2.0 Hz, 1H, HC(RCCH)(HCCR)NPh), 2.38, 2.27 (s, 3H each, C6H4Me), 1.70, 1.11 (s, 15H each, C5Me5). 13C{1H} NMR (acetone-d6): δ 184.8 (HC(RCCH)(HCCR)NPh), 152.8, 141.2, 140.6, 132.9, 130.4, 130.0, 129.6, 129.0, 128.7, 128.4, 128.0, 126.5 (aryl), 122.2 (q, J = 320 Hz, CF3SO3), 126.4 (HC(RCCH)(HCCR)NPh), 117.8 (HC(RCCH) (HCCR)NPh), 99.8, 98.7 (C5Me5), 71.8 (HC(RCCH)(HCCR)NPh), 70.0 (HC(RCCH)(HCCR)NPh), 21.3, 21.3 (C6H4Me), 10.6, 9.3 (C5Me5). FAB-MS: m/z 809 [M]þ. [(Cp*Ru)2{μ-HC(RCCH)(HCCR)NPh}]OTf (9b, R = n-Bu). To a solution of 2h0 (184 mg, 0.254 mmol) in 10 mL of THF was added 1-hexyne (292 μL, 2.50 mmol), and the solution was stirred at 60 °C for 7 h. Volatiles were removed under reduced pressure, and the residue was washed with hexanes. The remaining solid was recrystallized from THF/ Et2O to give 9b as reddish-purple block crystals. Yield: 107.5 mg, 47%. Anal. Calcd for C40H56NO3F3SRu2: C, 53.98; H, 6.34; N, 1.57. Found: C, 54.25; H, 6.59; N, 1.36. 1H NMR (acetone-d6): δ 10.90 (d, J = 1.9 Hz, 1H, HC(RCCH)(HCCR)NPh), 7.77, 7.64, 7.61, 7.46, 6.73 (m, 1H, Ph), 3.81 (pseudo t, J = 1.9 Hz, HC(RCCH)(HCCR)NPh), 2.80 (d, J = 1.9 Hz, HC(RCCH)(HCCR)NPh), 2.181.44 (m, 12H, n-Bu), 1.90, 1.42 (s, 15H each, Cp*), 0.97, 0.82 (t, 3H each, n-Bu). 13C{1H} NMR (acetone-d6): δ 193.1 (HC(RCCH)(HCCR)NPh), 151.5, 130.3, 130.2, 129.7, 128.5, 126.6 (Ph), 123.8 (HC(RCCH)(HCCR)NPh), 122.3 (q, J = 320 Hz, CF3SO3), 98.9, 98.1 (C5Me5), 77.8 (HC(RCCH) (HCCR)NPh), 71.4 (HC(RCCH)(HCCR)NPh), 68.2 (HC(RCCH) (HCCR)NPh), 34.9, 32.5 (CH2CH2CH2CH3), 30.2, 26.3 (CH2CH2 CH2CH3), 23.5, 23.3 (CH2CH2CH2CH3), 14.4, 13.9 (CH2CH2CH2 CH3), 10.6, 9.3 (C5Me5). FAB-MS: m/z 741 [M]þ. [(Cp*Ru)2{μ-HC(PhCCPh)(PhCCPh)NPh}]OTf (9c). Complex 2h0 (75.2 mg, 0.104 mmol) and diphenylacetylene (187 mg, 1.05 mmol) were dissolved in 6 mL of CH2Cl2, and the solution was stirred at 80 °C 2169


Organometallics

ARTICLE

Table 3. Crystal Data and Structure Refinement Parameters for 2f, 3a, 4c, and 4e 3a

4c

4e

formula

C30H40NO3F3SCl2Ru2

C30H44NOPRu2

C37H55N3Ru2

C38H55N3Ru2

fw

824.73

667.77

743.98

755.99

T (°C)

23

23

23

23

cryst syst

monoclinic

monoclinic

orthorhombic

monoclinic

space group

P21/n (#14)

P21/c (#14)

Pbca (#61)

P21/c (#14)

a (Å)

11.917(3)

11.9490(10)

19.7902(10)

10.463(3)

b (Å)

24.975(8)

12.1985(13)

16.1809(7)

18.375(5)

c (Å) R (deg)

12.050(3) 90

20.7663(16) 90

23.1204(8) 90

19.380(5) 90

β (deg)

107.903(10)

97.019(4)

90

93.921(12)

γ (deg)

90

90

90

90

V (Å3)

3412.5(15)

3004.2(5)

7403.7(6)

3717.1(16)

Z

4

4

8

4

Dcalc (g/cm3)

1.605

1.476

1.335

1.351

μ (mm1)

1.150

1.080

0.843

0.840

R1 [I > 2σ(I)]a wR2 (all data)b

0.0582 0.1486

0.0537 0.1374

0.0365 0.0983

0.0328 0.0890

GOF on F2

0.962

1.021

0.963

1.035

)

R1 = ∑ Fo| |Fc /∑|Fo|. b wR2 = [∑(w(Fo2 Fc2)2/∑w(Fo2)2]1/2. )

a

2f 3 CH2Cl2

Table 4. Crystal Data and Structure Refinement Parameters for 5, 70 , 8, 9a, and 9b 70

8

9a

9b

formula

C46H71N5Ru2

C32H39NO3Ru2

C37H57NSi2Ru2

C28H38NO3F3S2Ru2

C40H56NO3F3O2SRu2

fw

896.22

687.78

774.16

727.79

890.06

T (°C)

23

23

23

23

23

cryst syst

monoclinic

monoclinic

monoclinic

monoclinic

triclinic

space group

P21/c (#14)

P21/a (#14)

P21/c (#14)

P21/n (#14)

P1 (#2)

a (Å)

13.590(4)

18.720(4)

13.738(4)

16.583(8)

9.499(3)

b (Å) c (Å)

20.820(4) 16.966(4)

8.585(2) 19.149(4)

11.626(3) 23.086(8)

16.590(7) 11.075(5)

12.149(5) 18.523(9)

R (deg)

90

90

90

90

71.544(17)

β (deg)

91.196(11)

105.616(9)

91.268(12)

90.39(2)

81.347(17)

γ (deg)

90

90

90

90

88.356(14)

V (Å3)

4800(2)

2963.9(11)

3686.6(18)

3047(2)

2004.2(15)

Z

4

4

4

4

2

Dcalc (g/cm3)

1.240

1.541

1.395

1.587

1.475

μ (mm1) R1 [I > 2σ(I)]a

0.663 0.0474

1.051 0.0338

0.909 0.0479

1.107 0.0859

0.856 0.0456

wR2 (all data)b

0.1300

0.0879

0.1331

0.2436

0.1187

GOF on F2

0.994

1.065

1.028

0.963

1.016

)

R1 = ∑ Fo| |Fc /∑|Fo|. b wR2 = [∑(w(Fo2 Fc2)2/∑w(Fo2)2]1/2. )

a

5

in a pressure-resistant Teflon-sealed Schlenk tube for 7 h. Then the solvent was removed under reduced pressure, and the residue was washed with diethyl ether. The remaining solid was recrystallized from THF/Et2O to give 9c as a red crystalline solid. Yield: 58.2 mg, 50%. Anal. Calcd for C56H56NO3F3SRu2: C, 62.15; H, 5.22; N, 1.29. Found: C, 62.22; H, 5.05; N, 1.12. 1H NMR (acetone-d6): δ 11.62 (s, 1H, HC(PhCCPh)(PhCCPh)NPh), 7.686.17 (m, 25H, Ph), 1.66, 1.10 (s, 15H each, Cp*). 13C{1H} NMR (acetone-d6): δ 186.8 (HC(PhCCPh)(PhCCPh)NPh), 150.2, 139.7, 137.0, 134.7, 133.2, 132.9, 130.9, 130.8, 130.7, 130.6, 129.9, 129.8, 128.9, 128.7, 127.2, 126.8, 126.2 (Ph), 122.5 (q, J = 320 Hz, CF3SO3), 100.4, 102.4 (C5Me5), 114.9, 98.3,

90.6, 88.7 (HC(PhCCPh)(PhCCPh)NPh), 10.6, 9.3 (C5Me5). FABMS: m/z 934 [M]þ. X-ray Crystallography. In all cases, crystals were taken from asisolated products. A single crystal of each sample was coated with Paratone-N hydrocarbon oil and mounted on a glass capillary. All measurements were performed on a Rigaku R-AXIS Rapid imaging plate detector with graphite-monochromated Mo KR radiation (λ = 0.71069 Å). The frame data were processed using the Rigaku PROCESS-AUTO program,93 and the reflection data were corrected for absorption with an ABSCOR program.94 The structures were solved by a direct method (SHELXS 97) and refined on F2 by full-matrix least2170


Organometallics squares methods by using SHELX97.95 Anisotropic refinement was applied to all non-hydrogen atoms. The vinylic hydrogen atoms in 4e, 8, and 9b were located by the Fourier method and isotropically refined. Other hydrogen atoms were placed at calculated positions and treated as riding models. Thermal ellipsoid plots were drawn with the ORTEP-3 program96 and presented at the 35% probability level. The checkcif reports for 3a, 4c, 4e, 5, 70 , and 9b feature level-A alerts, which are based on large variations of U(eq) values for carbon atoms in each structure. Although these alerts suggest incorrect identification of atomic species, these are in fact due to large thermal motion of some of the Cp* and t-Bu groups in the structures and do not affect the results of structure determinations. Computational Details. Geometry optimization was performed with the Gaussian 03 program package97 by density functional theory with B3PW9198 hybrid functional and LANL2DZ99 basis set. Initial geometry was constructed by modification of the X-ray structures. No symmetry constraints were applied in the optimization, and the local minima for the optimized structures were checked by frequency calculations. Mayer bond orders were calculated using the program BORDER.100 Wiberg bond orders were calculated using the NBO code included in the Gaussian 03 program.

’ ASSOCIATED CONTENT

bS

Supporting Information. Crystallographic information files (CIF) for 2f, 3a, 4c, 4e, 5 (cis isomer), 70 , 8, 9a, and 9b; thermal ellipsoid plots for 4e and 9b; optimized structures and atomic coordinates. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; [email protected]. ac.jp.

’ ACKNOWLEDGMENT This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan (No. 21550064 and No. 18033046 Research on Priority Area “Chemistry of Coordination Space”). We also acknowledge financial support from Mitsubishi Foundation, Ube Foundation, and Toyota Motor Corporation. ’ REFERENCES (1) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds; Wiley Interscience: New York, 1988. (2) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239. (3) Sharp., P. R. J. Chem. Soc., Dalton Trans. 2000, 2647. (4) Duncan, A. P.; Bergman, R. G. Chem. Rec. 2002, 2, 431. (5) Leung, W.-H. Eur. J. Inorg. Chem. 2003, 583. (6) Eikey, R. A.; Abu-Omar, M. M. Coord. Chem. Rev. 2003, 243, 83. (7) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005, 38, 839. (8) Hayton, T. W. Dalton Trans. 2010, 39, 1145. (9) Severin, R.; Doye, S. Chem. Soc. Rev. 2007, 36, 1407. (10) M€uller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, 3795. (11) Fruit, C.; M€uller, P. Chem. Rev. 2003, 103, 2905. (12) Davis, H. M. L.; Manning, J. R. Nature 2008, 451, 417. (13) Schrock, R. R. Chem. Rev. 2009, 109, 3211. (14) Bolton, P. D.; Mountford, P. Adv. Synth. Catal. 2005, 347, 355. (15) Kee, T. P.; Park, L. Y.; Robbins, J.; Schrock, R. R. J. Chem. Soc., Chem. Commun. 1991, 121.

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