Reactivity of Phosphine- and Thioether-Tethered N-Heterocyclic

Article pubs.acs.org/Organometallics

Reactivity of Phosphine- and Thioether-Tethered N-Heterocyclic Carbenes with Ruthenium Carbonyl Javier A. Cabeza,*,† Marina Damonte,† Pablo García-Á lvarez,† M. Guadalupe Hernández-Cruz,† and Alan R. Kennedy‡ †

Departamento de Química Orgánica e Inorgánica-IUQOEM, Universidad de Oviedo−-CSIC, E-33071 Oviedo, Spain WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, U.K.

‡

S Supporting Information *

ABSTRACT: The reactions of the NHC-functionalized phosphines 1[{2-(diphenylphosphino)phenyl}methyl]-3-methylimidazol-2-ylidene (Ph 2PC 6H 4CH 2ImMe) and 1-[{2-(dicyclohexylphosphino)phenyl}methyl]-3-methylimidazol-2-ylidene (Cy 2PC 6H4CH 2ImMe) and the NHC-functionalized thioether 1-{(2-methylsulfide)ethyl}-3-methylimidazol-2-ylidene (MeSCH2CH2ImMe) with [Ru3(CO)12] have been studied. Both NHC-phosphines react with equimolar amounts of [Ru3(CO)12], in THF at room temperature, to give the edge-bridged disubstituted products [Ru3(μ-κ2P,CNHC-R2PC6H4CH2ImMe)(CO)10], R = Ph (1), Cy (2), which selectively undergo a double C−H bond activation of their CH2 group upon gentle warming (R = Ph) or at room temperature (R = Cy) to give the dihydrido derivatives [Ru3(μ-H)2(μ3-κ3P,C,CNHC-R2PC6H4CImMe)(CO)8], R = Ph (3) and Cy (4), respectively. These products contain novel facecapping ligands that arise from the oxidative addition of both C−H bonds of the corresponding NHC-phosphine ligand CH2 group. This double-metalation process is facilitated by the rigidity of the C6H4CH2 linker of these ligands. The treatment of [Ru3(CO)12] with 3 equivalents of Ph2PC6H4CH2ImMe leads to the mononuclear ruthenium(0) complex [Ru(κ2P,CNHCPh2PC6H4CH2ImMe)(CO)3] (5). No trinuclear derivatives were obtained from reactions of [Ru3(CO)12] with MeSCH2CH2ImMe, the tetranuclear derivative [Ru4(μ-κ2S,CNHC-MeSCH2CH2ImMe)(μ-CO)2(CO)10] (6) being the only product that could be isolated. Compound 6 contains a butterfly arrangement of the metal atoms with the wing tips bridged by the ligand sulfur atom, while the NHC fragment is attached to one wing tip.

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by ours6 and Wang’s groups,17 of C−H bond activation processes involving triruthenium clusters and NHCs of the type 1-hydrocarbyl-3-methylimidazol-2-ylidene (RImMe). On the other hand, although the coordination chemistry of bi-, tri-, or polydentate ligands constituted by at least one NHC moiety has already been extensively studied,20 only a few works have hitherto been published involving such ligands and ruthenium carbonyl clusters. They implicate NHC-functionalized pyridine,11 phosphine,12 indene,16 alkene,17 and thiolato21 ligands. Due to their close relationship with the results described in the present article, the reported12 reactivity of [Ru3(CO)12] with the NHC-functionalized phosphine Ph2PCH2CH2ImMe is summarized in Scheme 2. We now describe the reactivity of [Ru3(CO)12] with two NHC-tethered phosphines, namely, 1-[{2-(diphenylphosphino)phenyl}methyl]-3-methylimidazol-2-ylidene (Ph2PC6H4CH2ImMe) and 1-[{2-(dicyclohexylphosphino)phenyl}methyl]-3-methylimidazol-2-ylidene (Cy2PC6H4CH2ImMe),22 and an NHC-tethered thioether, 1-{(2-methylsulfide)ethyl}-3methylimidazol-2-ylidene (MeSCH2CH2ImMe).23 Both NHC-phosphine ligands diverge in the basicity and volume of the phosphine fragment, have their phosphine and

INTRODUCTION In the past decade, chemists have dedicated many efforts to investigate the coordination chemistry of N-heterocyclic carbenes (NHCs).1−3 Although most of their findings deal with mononuclear complexes,1,2 transition metal carbonyl clusters have not escaped from these investigations.3 In this field, the pioneering work of Lappert and Pye, who reported the synthesis of [Ru3(CO)11(Et2H2Im)] (Et2H2Im = 1,3-diethylimidazolin-2-ylidene),4 has been recently continued by us5−12 and by the research groups of Whittlesey,13,14 Cole,15 and Wang,16,17 who have reported studies involving triruthenium clusters derived from 1,3-disubstituted imidazol-2-ylidenes4−8,11−17 (R2Im), pyrid-2ylidenes,9 and pyrimid-2-ylidenes.10 The reactions of some NHCs with [Ru4(μ-H)4(CO)12] have also been communicated.18,19 Those studies have shown that, as a consequence of the high basicity of the NHC ligands, the clusters [Ru3(NHC)(CO)11], which are the initial products of the reactions of NHCs with [Ru3(CO)12] in 1:1 mol ratio,5,13,17 undergo easy C−H bond cleavage processes upon thermal activation to give hydrido derivatives that contain NHC-derived bridging ligands.6−9,13,16,17 The use of NHC to [Ru3(CO)12] ratios greater than 3 gives rise to mononuclear ruthenium(0) derivatives of the types [Ru(R2Im)2(CO)3]14 and [Ru(R2Im)(CO)4]15 or ruthenium(II) complexes that arise from subsequent C−H bond activation processes.17 Scheme 1 shows some representative examples, reported © 2011 American Chemical Society

Received: October 10, 2011 Published: December 14, 2011 327

dx.doi.org/10.1021/om200954w | Organometallics 2012, 31, 327−334

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room temperature led to the trinuclear cluster [Ru3(μ−κ2P,CNHCPh2PC6H4CH2ImMe)(CO)10] (1), which was isolated as a red solid after a chromatographic workup (Scheme 3).

Scheme 1

Scheme 3

The X-ray structure of compound 1 is shown in Figure 1. A selection of bond distances is given in Table 1. The structure

Scheme 2

Figure 1. Molecular structure of compound 1 (ellipsoids set at 30% probability). Hydrogen atoms (except those of the CH2 group) are omitted for clarity.

Table 1. Selected Interatomic Distances (Å) in Compound 1

NHC fragments separated by a C6H4CH2 group, being therefore more rigid than 1-[2-(diphenylphosphino)ethyl]3-methylimidazol-2-ylidene (Ph2PCH2CH2ImMe, Scheme 2), and have an already demonstrated behavior as excellent chelating ligands in mononuclear palladium(II) complexes.22 The coordination chemistry of phosphine-functionalized imidazol-2ylidenes has already been studied to a significant extent.12,22,24 However, nearly all those works deal with mononuclear complexes, the only exception being that summarized in Scheme 2.12 Many studies on the coordination chemistry of thioetherfunctionalized imidazol-2-ylidenes have also been reported, but they do not deal with tri- or polynuclear complexes.25 It has been observed that NHC-thioethers of the type RSCH2CH2ImR′ can behave as CNHC-terminal,26,27 κ2S,CNHC-chelating,23,26,27 and κ2S,CNHC-bridging26 ligands.

Ru1−Ru2 Ru1−Ru3 Ru2−Ru3 C1−Ru1 C1−N1 C1−N2 C2−C3 C2−N1

2.8499(3) 2.9028(3) 2.8344(3) 2.112(3) 1.362(4) 1.368(4) 1.338(5) 1.383(4)

C3−N2 C4−N2 C5−N1 C5−C6 P1−Ru3 C−O (av.) C(CO)−Ru (av)

1.382(5) 1.456(5) 1.459(4) 1.512(4) 2.3376(8) 1.14(1) 1.93(3)

can be described as resulting from the substitution of a Ph2PC6H4CH2ImMe ligand for two equatorial CO groups of different Ru atoms of [Ru3(CO)12], thus spanning an Ru−Ru edge. When compared with the structure of [Ru3(μ-κ2P,CNHCPh2PCH2CH2ImMe)(CO)10] (Scheme 2),12 it can be observed that, while the P and CNHC atoms of the latter are coplanar with the Ru3 triangle, those of compound 1 are 0.4582(8) and 0.387(3) Å, respectively, away from the Ru3 plane. Such a distortion also imposes a significant deviation of the CO ligands of 1 from their ideal axial or equatorial arrangements. No doubt, the structural differences between these two clusters

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RESULTS AND DISCUSSION Reactions of [Ru3(CO)12] with Ph2PC6H4CH2ImMe. The treatment of [Ru3(CO)12] with an equimolar amount of Ph2PC 6 H 4 CH 2 ImMe (prepared in situ by deprotonating [Ph2PC6H4CH2ImHMe][BF4] with K[N(SiMe3)2]) in THF at 328


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have to be associated with the more rigid character and longer length of the C6H4CH2 linker of 1, which, in addition to forcing a hydrogen atom of the CH2 group to be close to two metal atoms (H5b−Ru1 3.2605(2) Å, H5b−Ru3 3.1297(2) Å), maintains the phosphine and the NHC fragments more separated (P···CNHC = 4.787(3) Å) than the CH2CH2 linker of [Ru3(μ-κ2P,CNHC-Ph2PCH2CH2ImMe)(CO)10] (P···CNHC = 3.620(4) Å). Despite these structural differences, both complexes have very similar Ru−Ru, Ru−P, and Ru−Ccarbene distances, being also comparable to the respective bond distances found in [Ru3(CO)12],28 [Ru3(Me2Im)(CO)11],4 [Ru3(PPh3)(CO)11],29 and [Ru3(μ-κ2P2-dppe)(CO)10] (dppe = 1,2-bis(diphenylphosphino)ethane).30 The solution IR and NMR spectroscopic data of compound 1 are in harmony with its solid-state structure. The absorptions of terminal CO ligands are the only signals observed in the stretching carbonyl region of its IR spectrum. The 13C and 31P NMR spectra of 1 show the resonances of the Ccarbene and P atoms at 173.9 and 39.1 ppm, respectively. With the aim of further comparing the reactivity of [Ru3(CO)12] with Ph2PC6H4CH2ImMe with that reported for Ph2PCH2CH2ImMe (Scheme 2),12 we also studied the reaction [Ru3(CO)12] with 3 equivalents of Ph2PC6H4CH2ImMe in THF at room temperature. The mononuclear ruthenium(0) derivative [Ru(κ2P,CNHC-Ph2PC6H4CH2ImMe)(CO)3] (5) was the only product of this reaction (Scheme 4). Its νCO

Figure 2. Molecular structure of compound 3 (ellipsoids set at 30% probability). Hydrogen atoms (except hydrides) are omitted for clarity.

Table 2. Selected Interatomic Distances (Å) in Compound 3 Ru1−Ru2 Ru1−Ru3 Ru2−Ru3 C1−Ru1 C1−N1 C1−N2 C2−C3 C2−N1 C3−N2

Scheme 4

2.7962(5) 3.0320(5) 2.8171(5) 2.103(4) 1.339(6) 1.360(5) 1.347(7) 1.393(5) 1.377(7)

C4−N2 C5−N1 C5−C6 C5−Ru2 C5−Ru3 P1−Ru3 C−O (av) C(CO)−Ru (av)

1.441(6) 1.473(5) 1.499(6) 2.153(4) 2.116(4) 2.301(1) 1.138(7) 1.92(2)

Ru2−Ru3 2.8171(5) Å. The cluster shell is completed by eight carbonyl ligands. The solution IR and NMR spectra of 3 are in complete agreement with its solid-state structure. The IR spectrum clearly shows that this complex has only terminal CO ligands. The NMR resonances of the Ccarbene and P atoms of 3 are observed at 170.2 and 60.3 ppm in their respective spectra. In addition to the resonances of the Ph2PC6H4CImMe ligand, the 1H NMR spectrum of 3 also contains the resonances of two hydrides (at −12.54 and −16.76 ppm), whose JH−P coupling constants (9.9 and 27.1 Hz, respectively) indicate that they are attached to the same Ru atom as the phosphine fragment in cis (JH−P = 9.9 Hz) and trans (JH−P = 27.1 Hz) arrangements31 with respect to the P atom. It has been previously shown that for reactions of [Ru3(CO)12] with asymmetric NHC ligands of the type MeImR in which the R group is flexible (viz., those depicted in Schemes 1 and 2), the NHC N-methyl group is generally preferred over the N-R group to become involved in C−H bond activation reactions.12,17 However, this is not the case for Ph2PC6H4CH2ImMe. Although the mechanism of the reaction that leads to compound 3 from 1 has not been established, the structure of compound 1 (Figure 1) explains why the product of its thermal activation (3) arises from the oxidative addition of C−H bonds of its internal CH2 group. The rigidity and the edge-bridging attachment of the Ph2PC6H4CH2ImMe ligand of 1 impose one of the CH2 hydrogen atoms to be in close proximity to two metal atoms, thus favoring its participation in C−H bond activation processes that, in addition, are facilitated by the high basicity of the NHC ligand. The mechanism of the reaction that transforms [Ru3(Me2Im)(CO)11] into [Ru3(μ-H)2(μ3-κ2C, CNHC-CHImMe)(CO)9] (Scheme 1, top reaction) has been modeled by DFT calculations.8c Reactions of [Ru3(CO)12] with Cy2PC6H4CH2ImMe. As this NHC-phosphine ligand is bulkier and more basic than Ph2PC6H4CH2ImMe, we decided to study its reactivity with

absorptions (3 bands in the range 1996−1885 cm−1) are very similar to those reported for [Ru(κ2P,CNHC-Ph2PCH2CH2ImMe)(CO)3], which has a trigonal-bypyramidal ligand arrangementwith an axial−equatorial coordination of the NHC-phosphine ligand (Scheme 2).12 The resonances of the Ccarbene and P atoms of 5 are observed at 179.6 and 25.8 ppm in the appropriate spectra. Only one additional work describing the synthesis of ruthenium(0) complexes having a bidentate NHC-phosphine ligand has hitherto been published. It describes the preparation of [Ru(κ2P,CNHC-Ph2PCH2CH2ImR)(PPh3)(CO)2] (R = Mes, Dipp) from Ph2PCH2CH2ImR and the mononuclear complex [Ru(PPh3)3(CO)2].24b Thermolysis of Compound 1. Heating to reflux a THF solution of complex 1 for only 10 min led to the quantitative formation of the face-capped C−H-activated trinuclear derivative [Ru3(μ-H)2(μ3-κ3P,C,CNHC-Ph2PC6H4CImMe)(CO)8] (3), which was isolated as a yellow solid (Scheme 3). The molecular structure of 3 was determined by X-ray diffraction (Figure 2, Table 2). The molecule contains a Ph2PC6H4CImMe ligand capping a face of the ruthenium triangle in such a way that the Ru1 atom is attached to the carbene C atom while the Ru2−Ru3 edge is spanned by the C atom that links the NHC and C6H4PPh2 fragments. The Ru3 metal atom is also bound to the phosphine fragment P atom. Two edges of the metal triangle, Ru1−Ru3 and Ru2−Ru3, are also spanned by hydride ligands. The Ru1−Ru2 edge, 2.7962(5) Å, is shorter than the hydride-bridged edges, Ru1−Ru3 3.0320(5) Å and 329


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[Ru3(CO)12] in order to compare it with that described above for Ph2PC6H4CH2ImMe. The treatment of [Ru3(CO)12] with an equimolar amount of Cy2PC6H4CH2ImMe (prepared in situ by deprotonating [Cy2PC6H4CH2ImHMe]I with K[N(SiMe3)2]) in THF at room temperature led, initially, to the red-brown edge-bridged trinuclear cluster [Ru3(μ-κ2P,CNHC-Cy2PC6H4CH2ImMe)(CO)10] (2), but, in solution at room temperature, this compound slowly led to the cyclometalated derivative [Ru3(μ-H)2(μ3-κ3P,C,CNHCCy2PC6H4CImMe)(CO)8] (4) (Scheme 3). Using this synthetic method, compound 2 could not be obtained pure, being always contaminated by some [Ru3(CO)12] and/or compound 4, from which it could not be separated. Fortunately, the use of the activated cluster [Ru3(MeCN)2(CO)10]32 as starting complex reduced the reaction time to only a few minutes, thus allowing the isolation of pure 2 without needing any chromatographic process. Heating compound 2 in THF at reflux temperature for a few minutes led to its quantitative transformation into compound 4, which was isolated as a yellow solid. An intractable mixture of compounds was obtained when [Ru3(CO)12] was treated with Cy2PC6H4CH2ImMe in a 1:3 mol ratio. The analytical and spectroscopic data of 2 and 4 confirm that their molecular structures are similar to those of the phenyl derivatives 1 and 3, respectively, the only remarkable difference being that the IR νCO absorptions of the cyclohexyl derivatives are displaced to lower wavenumbers than those of the phenyl derivatives, reflecting the higher basicity of the NHC-phosphine ligands of 2 and 4. The high basicity of Cy2PC6H4CH2ImMe is in fact responsible for the lower thermal stability of 2 with respect to that of 1, because the higher the basicity of the ligands, the higher the tendency of the metal atoms to which they are attached to get involved in oxidative addition processes. The different volume of the phosphine fragment substituents of Ph2PC6H4CH2ImMe and Cy2PC6H4CH2ImMe does not seem to have any influence on their reactions with [Ru3(CO)12]. Reaction of [Ru3(CO)12] with Me2SCH2CH2ImMe. The thioether-tethered NHC MeSCH2CH2ImMe (prepared in situ by treating [MeSCH2CH2ImHMe][BF4] with KOtBu) reacted very slowly with an equimolar amount of [Ru3(CO)12] in THF at room temperature. Heating the reaction mixture at reflux temperature for 2 h allowed the isolation of [Ru4(μ-κ2S,CNHCMeSCH2CH2ImMe)(μ-CO)2(CO)10] (6) (Scheme 5), which was obtained as a red solid after a chromatographic workup.

Figure 3. Molecular structure of compound 6 (ellipsoids set at 30% probability).

Table 3. Selected Interatomic Distances (Å) in Compound 6 Ru1−Ru2 Ru1−Ru4 Ru2−Ru3 Ru2−Ru4 Ru3−Ru4 C1−Ru1 C1−N1 C1−N2 C2−C3 C2−N1

2.932(1) 2.843(1) 2.834(1) 2.732(1) 2.863(1) 2.11(1) 1.34(2) 1.33(2) 1.34(2) 1.41(2)

C3−N2 C4−N2 C5−N1 C5−C6 C6−S1 C7−S1 S1−Ru1 S1−Ru3 C−O(av) C(CO)−Ru (av)

1.41(2) 1.46(2) 1.47(1) 1.53(2) 1.81(1) 1.80(1) 2.357(3) 2.345(3) 1.15(2) 1.91(4)

[Ru4(μ-H)2(μ-κS-R2S)(CO)12],33b,c,34 which also have a thiother ligand bridging the butterfly wing tips. Although some triosmium and triruthenium carbonyl clusters containing ditopic NHC-thiolate ligands have been reported,35 compound 6 represents the first polynuclear derivative of an NHCthioether ditopic ligand. The IR and NMR spectroscopic data of compound 6 provide little structural information, since they only confirm the existence of terminal and bridging CO ligands (IR) and the presence of an intact MeSCH2CH2ImMe ligand (1H and 13C NMR). The NMR resonance of the Ccarbene atom is observed at 166.0 ppm. It is noteworthy that MeSCH2CH2ImMe is not able to form stable trinuclear CO-substitution derivatives, analogous to 1, 3, or [Ru3(μ-κ2P,CNHC-Ph2PCH2CH2ImMe)(CO)10],12 and that no product arising from C−H activation processes has been observed. This fact clearly indicates that the electronic features of the thioether fragment of MeSCH2CH2ImMe determine the reactivity of the ligand. In fact, the thioether fragment is a poor π-acceptor four-electron donor, whereas the phosphine fragments of R2PC6H4CH2ImMe are two-electron donors of higher basicity and stronger π-accepting character.

Scheme 5

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CONCLUDING REMARKS The NHC-tethered phosphines R2PC6H4CH2ImMe, R = Ph, Cy, react with equimolar amounts of [Ru3(CO)12] to stepwise give the edge-bridged disubstituted products [Ru3(μ-κ2P,CNHCR2PC6H4CH2ImMe)(CO)10], R = Ph (1), Cy (2), and the dihydrido derivatives [Ru3(μ-H)2(μ3-κ3P,C,CNHC-R2PC6H4CImMe)(CO)8], R = Ph (3) and Cy (4), respectively. Compounds 3 and 4 contain novel face-capping ligands that arise from the oxidative addition of both C−H bonds of

The X-ray structure of compound 6 (Figure 3, Table 3) shows that it is a tetranuclear species in which the metal atoms adopt a butterfly arrangement, the hinge Ru−Ru edge being 0.1−0.2 Å shorted than the remaining Ru−Ru edges. While the sulfur atom of an intact MeSCH2CH2ImMe ligand symmetrically spans both wing tips, the NHC fragment is attached to one of them. The cluster shell is completed by two edgebridging and 10 terminal CO ligands. The structure can be compared with those of [Ru4(μ-κS-R2S)(μ-CO)(CO)12]33 and 330


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(d, J = 16 Hz, C), 134.0 (s, J = 2 Hz, C), 132.7 (s, CH), 132.6 (s, CH), 132.1 (d, J = 7 Hz, CH), 131.3 (d, J = 10 Hz, CH), 130.9 (s, CH), 129.5 (d, J = 10 Hz, CH), 129.2 (d, J = 10 Hz, CH), 128.5 (s, CH), 128.0 (d, J = 10 Hz, CH), 125.8 (d, J = 13 Hz, C), 124.5 (s, CH), 124.1 (s, CH), 54.5 (d, J = 15 Hz, CH2), 40.9 (s, CH3). Synthesis of [Ru3(μ-κ2P,CNHC-Cy2PC6H4CH2ImMe)(CO)10] (2). A toluene solution of K[N(SiMe3)2] (330 μL, 0.5 M, 0.165 mmol) was added to a suspension of [Cy2PC6H4CH2ImHMe]I (87 mg, 0.227 mmol) in THF (30 mL). After stirring for 30 min, this solution was transferred to an acetonitrile (10 mL) solution of [Ru3(MeCN)2(CO)10] (0.155 mmol) (recently prepared from [Ru3(CO)12] and Me3NO in acetonitrile33). The color changed from orange to red. The mixture was stirred for 15 min. The solvent was removed under reduced pressure, and the solid residue was washed with hexane (2 × 5 mL) to render compound 2 as a red-brown solid (96 mg, 65%). This cluster slowly leads to compound 4 when it is left in solution at room temperature. Anal. Calcd for C33H33N2O10PRu3 (951.8): C, 41.64; H, 3.50; N, 2.94. Found: C, 41.85; H, 3.39; N, 2.87. (+)-FAB MS: no satisfactory spectrum could be obtained. IR (THF): νCO 2034 (m), 2016 (m), 1991 (vs). 1H NMR (CD2Cl2, 293 K): δ 7.64−7.44 (m, 2 H), 7.43−7.24 (m, 2 H), 6.96 (d, J = 1.8 Hz, 1 H), 6.84 (d, J = 1.8 Hz, 1 H), 4.07−3.80 (m, 2 H), 3.80 (s, 3 H), 1.87−1.16 (m, 14 H), 1.07−0.74 (m, 8 H). 31P{1H} NMR (CD2Cl2, 293 K): δ 17.7 (s). Synthesis of [Ru3(μ-H)2(μ3-κ3P,C,CNHC-Ph2PC6H4CImMe)(CO)8] (3). A THF solution (30 mL) of compound 1 (43 mg, 0.045 mmol) was stirred at reflux temperature for 10 min. The color changed from red to yellow. The solvent was removed under reduced pressure, and the solid residue was washed with hexane (2 × 10 mL) to give compound 3 as a yellow solid (32 mg, 81%). Anal. Calcd for C31H21N2O8PRu3 (883.70): C, 42.13; H, 2.40; N, 3.17. Found: C, 42.26; H, 2.53; N, 3.09. (+)-FAB MS: m/z 885 [M]+. IR (THF): νCO 2064 (s), 2028 (vs), 2019 (s), 1991 (s), 1980 (w), 1966 (w). 1H NMR (CD2Cl2, 293 K): δ 7.92−7.80 (m, 2 H), 7.58−7.30 (m, 12 H), 7.20 (d, J = 1.9 Hz, 1 H), 6.60 (d, J = 1.9 Hz, 1 H), 3.65 (s, 3 H), −12.54 (dd, J = 9.9, 1.7 Hz, 1 H), −16.76 (dd, J = 27.1, 1.7 Hz, 1 H). 31P{1H} NMR (CD2Cl2, 293 K): δ 60.3 (s). 13C{1H} and DEPT NMR (CD2Cl2, 293 K): δ 202.1 (s, C); 200.2 (s, C), 192.9 (s, C), 187.0 (s, C); 170.2 (s, C), 138.2 (s, C); 135.1 (d, J = 11 Hz, CH), 132.7 (d, J = 20 Hz, C), 132.4 (s, CH), 131.6 (d, J = 11 Hz, CH), 131.5 (s, CH), 130.8 (s, CH), 130.4 (s, CH), 129.1 (d, J = 10 Hz, C), 129.0 (d, J = 10 Hz, CH), 128.7 (d, J = 12 Hz, CH), 125.7 (d, J = 15 Hz, CH), 124.2 (s, CH), 119.6 (s, CH), 119.1 (s, CH), 38.5 (s, CH3). Synthesis of [Ru3(μ-H)2(μ3-κ3P,C,CNHC-Cy2PC6H4CImMe)(CO)8] (4). A toluene solution of K[N(SiMe3)2] (210 μL, 0.5 M, 0.105 mmol) was added to a suspension of [Cy2PC6H4CH2ImHMe]I (50 mg, 0.101 mmol) in THF (30 mL). After stirring for 20 min, finely powdered [Ru3(CO)12] (65 mg, 0.102 mmol) was added. The mixture was stirred for 21 h and then was heated to reflux for 10 min. The color gradually changed from orange to red, to orange, and finally to yellow. The solvent was removed under reduced pressure, and the crude reaction mixture was separated by column chromatography on silica gel (2 × 15 cm). Hexane eluted compound 4, which was isolated as a yellow solid (73 mg, 80%). Anal. Calcd for C31H33N2O8PRu3 (895.8): C, 41.57; H, 3.71; N, 3.13. Found: C, 41.62; H, 3.76; N, 3.05. (+)-FAB MS: no satisfactory spectrum could be obtained. IR (THF): νCO 2063 (m), 2048 (w), 2023 (ws), 2009 (s), 1992 (vs), 1955 (m). 1 H NMR (CD2Cl2, 293 K): δ 7.50 (dd, J = 7.8, 2.8 Hz 1 H), 7.31 (m, 2 H), 7.14 (d, J = 1.9 Hz, 1 H), 6.99 (t, J = 7.4 Hz, 1 H), 6.62 (d, J = 1.9 Hz, 1 H), 3.70 (s, 3 H), −12.99 (dd, J = 10.3, 1.4 Hz 1 H), −15.72 (dd, J = 25.3, 1.4 Hz, 1 H). 31P{1H} NMR (CD2Cl2, 293 K): δ 76.8 (s). 13C{1H} and DEPT NMR (CD2Cl2, 293 K): δ 202.2 (s, C), 201.8 (s, C), 200.1 (s, C), 192.5 (s, C), 188.3 (s, C), 178.4 (s, C), 153.6 (d, J = 3 Hz, C), 131.2 (s, CH), 129.7 (s, CH), 125.2 (s, CH), 122.8 (d, J = 6 Hz, CH), 119.1 (s, CH), 118.4 (s, CH), 41.0 (d, J = 24 Hz, CH), 38.0 (s, CH3), 31.2−25.7 (m, CH2). Synthesis of [Ru(κ2P,CNHC-Ph2PC6H4CH2ImMe)(CO)3] (5). A toluene solution of K[N(SiMe3)2] (1.4 mL, 0.5 M, 0.700 mmol) was added to a suspension of [Ph2PC6H4CH2ImHMe][BF4] (277 mg, 0.624 mmol) in THF (25 mL). After stirring for 20 min, finely powdered [Ru3(CO)12] (133 mg, 0.210 mmol) was added. The mixture

the corresponding NHC-phosphine ligand CH2 group. This double-metalation process, which seems to be facilitated by the rigidity of the C6H4CH2 linker of these ligands, is easier for R = Cy because the greater basicity of Cy2PC6H4CH2ImMe enhances the tendency of the metal atoms to which this ligand is attached to become involved in oxidative addition processes. The different volume of the phosphine fragment of Ph2PC6H4CH2ImMe and Cy2PC6H4CH2ImMe does not seem to have any influence on their reactions with [Ru3(CO)12]. The treatment of [Ru3(CO)12] with 3 equivalents of Ph2PC6H4CH2ImMe does not lead to any trinuclear product, but to the mononuclear ruthenium(0) complex [Ru(κ2P,CNHC-Ph2PC6H4CH2ImMe)(CO)3] (5). No trinuclear derivatives were obtained from reactions of [Ru3(CO)12] with MeSCH2CH2ImMe, the only product that could be isolated being the tetranuclear derivative [Ru4(μ-κ2S, CNHC-MeSCH2CH2ImMe)(μ-CO)2CO)10] (6), which has a butterfly arrangement of the metal atoms. This compound is the first polynuclear derivative of an NHC-thioether ligand. The very different reactivity found for MeSCH2CH2ImMe with respect to those of the NHC-phosphine ligands R2PC6H4CH2ImMe (this work) and Ph2PCH2CH2ImMe12 in their reactions with [Ru3(CO)12] has to be associated with the very different electronic features of the thioether and phosphine fragments.

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EXPERIMENTAL SECTION

General Data. Solvents were dried over sodium diphenyl ketyl (hydrocarbons, diethyl ether, THF) or CaH2 (dichloromethane) and distilled under nitrogen before use. The reactions were carried out under nitrogen, using Schlenk-vacuum line techniques, and were routinely monitored by solution IR spectroscopy (carbonyl stretching region) and spot TLC on silica gel. The salts [R2PC6H4CH2ImHMe]I (R = Ph, Cy)22 and [MeSCH2CH2ImHMe]Cl23 were prepared as described elsewhere. Their treatment with an aqueous solution of Na[BF4] led to the corresponding tetrafluoroborate salts. All remaining starting reagents were purchased from commercial sources. All reaction products were vacuum-dried for several hours prior to being weighed and analyzed. IR spectra were recorded in solution on a Perkin-Elmer Paragon 1000 FT spectrophotometer. NMR spectra were run on a Bruker DPX-300 instrument. Microanalyses were obtained from the University of Oviedo Analytical Service. FAB mass spectra were obtained from the University of A Coruñ a Mass Spectrometric Service; data given refer to the most abundant molecular ion isotopomer. Synthesis of [Ru3(μ-κ2P,CNHC-Ph2PC6H4CH2ImMe)(CO)10] (1). A toluene solution of K[N(SiMe3)2] (425 μL, 0.5 M, 0.212 mmol) was added to a suspension of [Ph2PC6H4CH2ImHMe][BF4] (87 mg, 0.227 mmol) in THF (30 mL). After stirring for 20 min, finely powdered [Ru3(CO)12] (133 mg, 0.207 mmol) was added. The color changed from orange to red. The mixture was stirred for 1 h. The solvent was removed under reduced pressure, and the crude reaction mixture was separated by column chromatography on silica gel (2 × 15 cm). Hexane eluted a small amount of [Ru3(CO)12]. Hexane− dichloromethane (35:15) eluted a weak band containing a mixture of compounds. Hexane−dichloromethane (15:35) eluted compound 1, which was isolated as a red solid (74 mg, 38%). Anal. Calcd for C33H21N2O10PRu3 (939.72): 42.18; H, 2.25; N, 2.98. Found: C, 42.54; H, 2.36; N, 2.74. (+)-FAB MS: m/z 941 [M]+. IR (THF): νCO 2070 (m), 2008 (w), 1991 (vs). 1H NMR (CD2Cl2, 293 K): δ 7.87−7.77 (m, 2 H), 7.76−7.56 (m, 3 H), 7.56−7.49 (m, 6 H), 7.40 (m, 1 H), 7.28 (d, J = 1.9 Hz, 1 H), 7.16 (d, J = 1.9 Hz, 1 H), 7.07 (dd, J = 7.7, 4.3 Hz, 1 H), 6.96 (dd, J = 11.0, 7.8 Hz, 1 H), 5.24 (dd, J = 16.0, 3.2 Hz, 1 H), 4.15 (dd, J = 16.0, 1.4 Hz, 1 H), 3.92 (s, 3 H). 31P{1H} NMR (CD2Cl2, 293 K): δ 39.1 (s). 13C{1H} and DEPT NMR (CD2Cl2, 293 K): δ 212.1 (s, br, C), 210.7 (d, J = 25 Hz, C), 173.9 (s, C), 139.3 (d, J = 12 Hz, C), 135.6 (d, J = 12 Hz, CH), 134.4 331


Organometallics

Article

Table 4. Crystal, Measurement, and Refinement Data for the Compounds Studied by X-ray Diffraction formula fw cryst syst space group a, Å b, Å c, Å α, β, γ, deg V, Å3 Z F(000) Dcalcd, g cm−3 μ(Cu Kα), mm−1 cryst size, mm T, K θ range, deg min./max. h, k, l no. collected reflns no. unique reflns no. reflns with I > 2σ(I) no. params/restraints GOF on F2 R1 (on F, I > 2σ(I)) wR2 (on F2, all data) min./max. Δρ, e Å−3

1

3·(C6H14)0.5

6

C33H21N2O10PRu3 939.70 monoclinic P21/n 9.4156(1) 20.3831(2) 17.0300(2) 90, 95.538(1), 90 3253.13(6) 4 1840 1.919 12.142 0.04 × 0.02 × 0.01 150(2) 3.39 to 70.00 −8/11, −24/24, −20/20 18 076 6130 5476 442/0 1.033 0.026 0.070 −0.736/0.773

C31H21N2O8PRu3·0.5C6H14 926.76 triclinic P1̅ 9.3896(4) 11.3196(4) 17.2165(7) 92.367(3), 94.861(3), 110.272(4) 1705.5(1) 2 914 1.805 11.520 0.14 × 0.06 × 0.06 150(2) 4.18 to 74.59 −7/11, −14/12, −20/21 10 693 6646 5873 453/38 1.044 0.037 0.104 −1.058/1.063

C19H12N2O12Ru4S 896.7 monoclinic P21/c 9.7239(1) 16.8627(2) 15.6488(2) 90, 94.056(1), 90 2559.53(5) 4 1712 2.327 20.110 0.10 × 0.04 × 0.01 123(2) 3.86 to 62.50 −11/11, 0/19, 0/18 3934 3934 3192 325/0 1.124 0.055 0.212 −2.393/2.119

X-ray Diffraction Analyses. Crystals of 1, 3·(C6H14)0.5, and 6 were analyzed by X-ray diffraction methods. A selection of crystal, measurement, and refinement data is given in the Table 4. Diffraction data were collected on an Oxford Diffraction Xcalibur Onyx Nova single-crystal diffractometer, using Cu Kα radiation. Empirical absorption corrections for 1 and 3·(C6H14)0.5 were applied using the SCALE3 ABSPACK algorithm as implemented in the program CrysAlisPro RED.36 The XABS237 empirical absorption correction was applied for 6. The structures were solved using the programs SIR200438 (1), DIRDIF39 (3·(C6H14)0.5), and SIR-9740 (6). Isotropic and full-matrix anisotropic least-squares refinements were carried out using SHELXL.41 All non-H atoms were refined anisotropically except four CO carbon atoms of 6, which were kept isotropic due to their tendency to give nonpositive definite ellipsoids. The solvent molecules of 3·(C6H14)0.5 were disordered about centers of symmetry and required restraints on their geometrical and thermal parameters. The positions of the hydride ligands of 3·(C6H14)0.5 were calculated with XHYDEX.42 The remaining hydrogen atoms were set in calculated positions and refined riding on their parent atoms. The molecular plots were made with the PLATON program package.43 The WINGX program system44 was used throughout the structure determinations. CCDC deposition numbers: 844980 (1), 844981 (3·(C6H14)0.5), and 847015 (6).

was stirred for 1 h, the solid was filtered off, and the resulting solution was evaporated to dryness. The residue was washed with cold hexane (5 mL) to give compound 5 as a red-brown solid (297 mg, 88%). Anal. Calcd for C26H21N2O3PRu (541.55): C, 57.51; H, 3.91; N, 5.17. Found: C, 58.01; H, 4.06; N, 5.09. IR (toluene): νCO 1996 (s), 1913 (s), 1885 (vs). 1H NMR (toluene-d8, 293 K): δ 7.14−6.94 (m, 14 H), 6.88 (t, J = 7.2 Hz, 1 H), 6.77 (t, J = 7.6 Hz, 1 H), 6.68 (ddd, J = 7.6, 4.4, 1.1 Hz, 1 H), 6.14 (d, J = 1.8 Hz, 1 H), 5.95 (d, J = 1.8 Hz, 1 H), 5.63 (m, 1 H), 3.52 (s, 3 H). 31P{1H} NMR (toluene-d8, 293 K): δ 25.8 (s). 13C{1H} and DEPT NMR (toluene-d8, 293 K): δ 213.9 (d, J = 11 Hz, C,), 179.6 (d, J = 12 Hz, C), 139.7 (d, J = 16 Hz, C), 138.5 (d, J = 21 Hz, C), 137.8 (s, C), 134.8 (d, J = 18 Hz, CH), 133.6 (d, J = 11 Hz, CH), 132.0 (s, CH), 129.9 (d, J = 6.Hz, CH), 129.6 (s, CH), 129.3 (s, CH), 129.1 (d, J = 4 Hz, CH), 128.5 (s, CH), 128.3 (d, J = 7 Hz, CH), 125.6 (s, CH), 122.5 (s, CH), 120.41 (s, CH), 53.5 (d, J = 18 Hz, CH2), 39.7 (s, CH3). Synthesis of [Ru 4(μ-κ 2S,CNHC -MeSCH 2CH 2 ImMe)(μ-CO) 2(CO)10] (6). A dichloromethane solution of [MeSCH2CH2ImHMe][BF4] (0.4 mL, 0.45 M, 0.160 mmol) was added to a solution of KOtBu (20 mg, 0.160 mmol) in THF (20 mL). After stirring for 2 h, finely powdered [Ru3(CO)12] (100 mg, 0.160 mmol) was added, and the mixture was heated to reflux for 2 h. The color changed from orange to brown. The solvent was removed under reduced pressure, and the crude reaction mixture was separated by column chromatography on silica gel (2 × 15 cm). Hexane−dichloromethane (1:4) eluted compound 6, which was isolated as a red solid (22 mg, 15%). Anal. Calcd for C19H12N2O12Ru4S (896.65): C, 25.45; H, 1.35; N, 3.12. Found: C, 25.58; H, 1.41; N, 3.07. (+)-FAB MS: 898 [M]+. IR (THF): νCO 2057 (m), 2016 (vs), 2008 (s), 1991 (m), 1966 (m), 1950 (w, sh), 1930 (w, sh), 1829 (w, br). 1H NMR (acetone-d6, 293 K): δ 7.46 (d, J = 2.0 Hz, 1 H), 7.43 (d, J = 2.0 Hz, 1 H), 5.08 (ddd, J = 15.9, 4.2, 2.0 Hz, 1 H), 4.67 (ddd, J = 15.9, 12.0, 1.0 Hz, 1 H), 4.22 (ddd, J = 13.7, 4.2, 1.0 Hz, 1 H), 3.71 (s, 3 H), 3.89 (s, 3 H), 2.87 (ddd, J = 13.7, 12.0, 2.0 Hz, 1 H). 13C{1H} and DEPT NMR (acetoned6, 293 K): δ 213.8 (s, C), 208.2 (s, C), 205.9 (s, C), 192.7 (s, C), 166.0 (s, C), 125.5 (s, CH), 125.3 (s, CH), 50.2 (s, CH2), 47.3 (s, CH2), 41.7 (s, CH3), 39.8 (s, CH3).

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ASSOCIATED CONTENT S Supporting Information * Crystallographic data in CIF format for the compounds studied by X-ray diffraction. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. ACKNOWLEDGMENTS This work has been supported by the European Union (FEDER grants and Marie Curie action FP7-2010-RG-268329) and the 332


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Spanish MICINN (projects CTQ2010-14933 and DELACIERVA-09-05). M.G.H.-C. is grateful to the Mexican CONACYT for granting her a research period in Oviedo.

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REFERENCES

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