Article pubs.acs.org/Organometallics
Reactivity of a Quinoline-Tethered N‑Heterocyclic Carbene with Polynuclear Ruthenium Carbonyls Javier A. Cabeza,*,† Marina Damonte,† and Enrique Pérez-Carreño‡ †
Departamento de Química Orgánica e Inorgánica-IUQOEM, Universidad de Oviedo-CSIC, E-33071 Oviedo, Spain Departamento de Química Física y Analítica, Universidad de Oviedo, E-33071 Oviedo, Spain
‡
S Supporting Information *
ABSTRACT: The quinoline-functionalized N-heterocyclic carbene 1-(8-quinolyl)methyl-3-methylimidazol-2-ylidene (QuinCH2ImMe) reacted with [Ru3(CO)12] at room temperature to give the monosubstituted derivative [Ru3(κCNHCQuinCH2ImMe)(CO)11] (1), which, upon heating in refluxing THF, underwent a thermally induced double C(sp3)−H bond activation to give the dihydrido derivative [Ru3(μ-H)2(μ3κ3N,C,CNHC-QuinCImMe)(CO)8] (2). The mechanism of this transformation has been studied by DFT calculations. The room-temperature reaction of QuinCH2ImMe with [Ru4(μ-H)4(CO)12] initially gave the imidazolium salt [QuinCH2ImHMe][Ru4(μ-H)3(CO)12], but it evolved to the monosubstituted tetranuclear derivative [Ru4(μ-H)4(κCNHC-QuinCH2ImMe)(CO)11] (3) when it was heated in refluxing toluene.
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INTRODUCTION The past decade has witnessed a tremendous advance in the Nheterocyclic carbene (NHC) chemistry of transition-metal cluster complexes.1 This research field, which was initiated in 1977 with Lappert’s synthesis of [Ru3(CO)11(Et2H2Im)] (Et2H2Im = 1,3-diethylimidazolin-2-ylidene),2 has been mostly developed by the research groups of Whittlesey,3,4 Cole,5 and Wang,6,7 and also by our group,8−15 who have reported studies involving triruthenium and triosmium clusters derived from 1,3disubstituted imidazol-2-ylidenes3−11,14,15 (R2Im), pyrid-2ylidenes,12 and pyrimid-2-ylidenes.13 The reactions of some NHCs with [Ru4(μ-H)4(CO)12] have also been communicated.16,17 These 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 a 1:1 mol ratio,3,7,8 are prone to undergo easy C−H bond cleavage processes upon thermal activation to give hydrido derivatives that contain NHC-derived cyclometalated bridging ligands.3,6,7,9−12 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,18 only a few works have hitherto been published involving such ligands and ruthenium carbonyl clusters. They implicate NHC-functionalized pyridine,14,16b phosphine,15,16b indene,6 alkene,7 thioether,15b,16b and thiolato19 ligands. The very interesting C(sp2)−H and C(sp3)−H bond activation processes observed in reactions of [Ru3(CO)12] with pyridine-functionalized NHC ligands (Scheme 1)14 prompted us to extend our investigations to the quinolinefunctionalized NHC 1-(8-quinolyl)methyl-3-methylimidazol-2ylidene (QuinCH2ImMe), expecting that the greater separation © 2012 American Chemical Society
Scheme 1
of the N and CNHC atoms in QuinCH2ImMe would lead to a reactivity pattern different from that observed for the pyridinefunctionalized NHC ligands, yet involving C−H bond activation processes because these two types of NHC ligands have comparable basicities. We now report that this has indeed been the case, describing in this paper the incorporation of Received: July 11, 2012 Published: November 7, 2012 8114
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ligand, at least under mild reaction conditions, although the chelating behavior of related quinoline-NHC ligands has been previously observed in mononuclear rhodium and iridium complexes.20 Thermolysis of Compound 1. Heating to reflux a THF solution of complex 1 slowly (2.5 h) led to the quantitative formation of the face-capped doubly C−H-activated trinuclear derivative [Ru3(μ-H)2(μ3-κ3N,C,CNHC-QuinCImMe)(CO)8] (2), which was isolated as a yellow solid (Scheme 2). The molecular structure of 2 was determined by X-ray diffraction (Figure 1, Table 1). This complex contains a
QuinCH2ImMe to tri- and tetraruthenium carbonyl clusters (using [Ru3(CO)12] and [Ru4(μ-H)4(CO)12] as starting complexes) and an unusual thermally induced transformation of a simple triruthenium complex containing a terminal κCNHCQuinCH2ImMe ligand into a derivative that results from the activation of both C−H bonds of the CH2 group that links the quinolyl and NHC fragments in the original ligand. The mechanism of this transformation has been modeled with the help of DFT calculations. Quinoline-tethered NHCs have previously been used as ligands only in mononuclear complexes of rhodium and iridium.20
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RESULTS AND DISCUSSION Reaction of [Ru3(CO)12] with QuinCH2ImMe. The treatment of [Ru3(CO)12] with an equimolar amount of QuinCH2ImMe (prepared in situ by deprotonating the imidazolium salt [QuinCH2ImHMe]Br with K[N(SiMe3)2]) in THF at room temperature led to the trinuclear cluster [Ru3(κCNHC-QuinCH2ImMe)(CO)11] (1), which was isolated as a red solid after a chromatographic workup (Scheme 2). Scheme 2
Figure 1. Molecular structure of compound 2 (ellipsoids set at 40% probability).
Table 1. Selected Interatomic Distances (Å) in Compound 2a Ru1−Ru2 Ru1−Ru3 Ru2−Ru3 C1−Ru3 C1−N1 C1−N2 C2−C3 C2−N1 C3−N2 C4−N1 C5−Ru1 C5−Ru2 C5−C6
The structure of compound 1 was suggested by its FAB mass spectrum, which confirmed its formulation as a triruthenium species with 1 QuinCH2ImMe ligand and 11 CO groups, and was established by its IR spectrum, whose νCO region contained an absorption pattern similar to that of the X-ray diffractioncharacterized compound [Ru 3(κCNHC-MeImMe)(CO) 11], which has the NHC ligand in an equatorial position.8 This result contrasts with those previously reported for reactions of [Ru3(CO)12] with other ditopic NHC ligands, such as 1-(2-diphenylphosphino)ethyl-3-methylimidazol-2-ylidene (Ph2PCH2CH2ImMe),15a 1-{2-(diphenylphosphino)phenyl}methyl-3-methylimidazol-2-ylidene (Ph2PC6H4CH2ImMe),15b and 1-(pyrid-2-yl)methyl-3-methylimidazol-2-ylidene (HpyCH2ImMe, Scheme 1),14 since they all are able to replace more than one CO ligand of [Ru3(CO)12] at room temperature, leading to ligand-bridged derivatives. A monosubstituted trinuclear product has also been obtained from an analogous reaction with 1-(6-picol-2-yl)methyl-3-methylimidazol-2-ylidene (MepyCH2ImMe, Scheme 1), which has the coordination of the pyridine N atom sterically impeded by the adjacent methyl group.14 Therefore, it seems that the particular structure of QuinCH2ImMe, which is bulky and rather rigid, does not favor its coordination either as a bridging or as a chelating
a
2.8142(4) 2.9970(4) 2.8004(5) 2.083(4) 1.372(5) 1.353(6) 1.349(7) 1.369(6) 1.390(6) 1.463(6) 2.088(4) 2.170(4) 1.477(6)
C5−N2 C6−C7 C6−C14 C7−C8 C8−C9 C9−C10 C10−C11 C10−C14 C11−C12 C12−C13 C13−N3 C14−N3 N3−Ru1
1.467(5) 1.395(6) 1.423(6) 1.410(7) 1.359(7) 1.427(7) 1.405(7) 1.396(7) 1.356(7) 1.404(6) 1.328(6) 1.389(6) 2.111(4)
Atom labels are those used in Figure 1.
QuinCImMe ligand capping a face of the ruthenium triangle in such a way that the Ru3 atom is attached to the carbenic C1 atom while the Ru1−Ru2 edge is spanned by the C atom that links the quinoline and NHC fragments, C5. The Ru1 metal atom is also bound to the quinoline fragment N3 atom. Two edges of the metal triangle, Ru1−Ru2 and Ru1−Ru3, are spanned by hydride ligands. The Ru2−Ru3 edge, 2.8004(5) Å, is shorter than the hydride-bridged edges, Ru1−Ru2 2.8142(4) Å and Ru1−Ru3 2.9970(4) Å. The cluster shell is completed by eight terminal carbonyl ligands. The solution IR and NMR spectra of 2 are in complete agreement with its solid-state structure. The IR spectrum clearly shows that this complex only has terminal CO ligands. The 13C NMR resonances of the Ccarbene and Cbridging atoms of 2 are observed at 177.9 and 130.0 ppm. In addition to the resonances expected for the QuinCImMe ligand, the 1H NMR 8115
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Figure 2. DFT-calculated mechanism for the thermal transformation of 1 into 2 + 3CO. Part 1: From 1 to i2·CO. The energy given for each stationary point (ΔE, kcal mol−1) is relative to that of compound 1.
Figure 3. DFT-calculated mechanism for the thermal transformation of 1 into 2 + 3CO. Part 2: From i2 to i5·CO. The energy given for each stationary point (ΔE, kcal mol−1) is relative to that of compound 1 and corresponds to its energy plus that of one CO molecule.
C−H bonds of the CH2 group of the Ph2PC6H4CH2ImMe ligand,15b and the bidentate pyridine-NHC ligands MepyCH2ImMe and HpyCH2ImMe do not activate any C−H bond of the groups that are directly attached to their NHC fragment when they react with [Ru3(CO)12] at elevated temperatures (Scheme 1).14 The thermal decarbonylation of 1 into 2 (3 mol of CO are released per mole of 1) is accompanied by an easy (it occurs in THF at reflux temperature) and selective double C(sp3)−H activation process (it involves only the methylene C−H bonds of the QuinCH2ImMe ligand). As this result contrasts with those commented in the above paragraph for related pyridineNHC and other functionalized NHC ligands, we decided to
spectrum of 2 also contains the resonances of two hydrides (at −11.03 and −21.33 ppm). It has been previously shown that, for triruthenium clusters containing monodentate asymmetric NHC ligands of the type RImMe, the NHC N-methyl group is generally preferred over the N-R group to become involved in C−H bond activation reactions.7,9 An analogous behavior has also been observed for the bidentate phosphine-NHC ligand Ph2PCH2CH2ImMe, which reacts with [Ru3(CO)12] to give [Ru3(μ-H)2(μ3κ3P,CNHC,C-Ph2PCH2CH2ImCH)(CO)8] under appropriate thermal conditions (THF, 70 °C).15a However, the phosphine-NHC cluster [Ru3(μ-H)2(μ3-κ3P,C,CNHCPh2PC6H4CImMe)(CO)8] arises from the activation of the 8116
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Figure 4. DFT-calculated mechanism for the thermal transformation of 1 into 2 + 3CO. Part 3: From i5 to i8·CO. The energy given for each stationary point (ΔE, kcal mol−1) is relative to that of compound 1 and corresponds to its energy plus that of two CO molecules.
2.044 Å in i5). The oxidative addition of the C2−H1 bond to the Ru1 atom of i5 (Figure 4), to give i6, in which the Ru1 atom is attached to C2 and H1 (Ru1−C2 2.319 Å, Ru1−H1 1.613 Å), is the step that has the highest energy barrier of the overall process (38.2 kcal mol−1). Once hydride H1 is placed over the Ru1−Ru2 edge (i7), a rotation of the quinolyl fragment toward Ru1 induces the release of a CO ligand and the coordination of the quinolinic N1 atom to Ru1 (Ru1−N1 2.177 Å in i8). Finally, an easy (energy barrier = 10.6 kcal mol−1) edge migration of hydride H2 (from Ru2−Ru3 to Ru1− Ru3) renders compound 2 (Figure 5). The energy balance for the overall process (1 → 2 + 3CO) is unfavorable by 54.6 kcal mol−1. However, it involves three COelimination steps that experimentally drive the reaction to the end (as the reaction is performed in an open system, the COelimination steps are irreversible), and the energy balance for the transformation of i8 (that is formed after the last COrelease step, Figure 5) into the final product 2 liberates 6.1 kcal mol−1. The highest energy barrier of the whole process, 38.2 kcal mol−1 (transformation of i5 into i6), explains the experimental fact that the reaction takes 2.5 h to be completed in refluxing THF (boiling temperature 66 °C). The only previously reported DFT-studied mechanism related to that described in this work is the conversion of [Ru3(κCNHC-MeImMe)(CO)11] into [Ru3(μ-H)2(μ3-κ2CNHC,CMeImCH)(CO)9] + 2CO, which proceeds via the activation of two C−H bonds of an N-methyl group.21 In that reaction, as well as in the transformation of 1 into 2, the C−H bond activation processes are, no doubt, facilitated by the great basicity of NHC ligands, which enhances the tendency of the metal systems to which they are bonded to participate in oxidative addition reactions.1 Reaction of [Ru4(μ-H)4(CO)12] with QuinCH2ImMe. The treatment of [Ru4(μ-H)4(CO)12] with an equimolar amount of QuinCH2ImMe (previously prepared in situ by deprotonating the imidazolium salt [QuinCH 2 ImHMe]Br with K[N-
undertake a theoretical (DFT) study of the reaction that transforms 1 into 2 + 3CO in order to shed some light on its mechanism. The results of this theoretical study are summarized in Figures 2−5, which show the energy profile (potential energy surface) of the process and the structures of all intermediate species and transition states, and in Table S1 of the Supporting Information, which shows the evolution of selected interatomic distances along the reaction coordinate. All calculations were computed in the gas phase. Therefore, the calculated energies should be slightly different from those of the experimental reaction. To compare the energies of all stationary points with that of compound 1, the energy of the liberated CO molecules has been included in the construction of potential energy surfaces (Figures 2−5). The reaction that leads to complex 2 from 1 is a multistep process that begins with a ligand rearrangement over the Ru3 triangle that places three CO ligands in edge-bridging positions and moves the QuinCH2ImMe ligand from an equatorial (1) to an axial coordination site on the Ru3 atom (i1; Figure 2). The release of an axial CO ligand from the Ru2 atom of i1 originates a coordination vacancy that is alleviated by an agostic interaction between Ru2 and the nearby H2 atom (Ru2−H2 2.775 Å in i2). The energy barrier of this step is 1.0 kcal mol−1 lower than that computed for an alternative pathway in which an axial CO is released from Ru1 (that would subsequently lead to the activation of a methyl C−H bond instead of a methylene C−H bond; see below). We also explored the coordination of the quinoline N atom to the unsaturated Ru center of i2 (after the loss of the first CO ligand), but we found that this is not possible. A subsequent oxidative addition of the C2−H2 bond to Ru2 generates i3 (Figure 3), in which the Ru2 atom is attached to C2 and H2 (Ru2−C2 2.349 Å, Ru2−H2 1.609 Å). After a facile movement of hydride H2 (terminal in i3) to a bridging position (i4), an approach of the H1 atom to Ru1 provokes the release of the second CO molecule (Ru1−H1 8117
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and rigidity of QuinCH2ImMe do not facilitate its coordination as a bidentate ligand to the tetraruthenium framework.
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CONCLUDING REMARKS The NHC-tethered quinoline ligand QuinCH2ImMe behaves as a simple NHC in its room-temperature reactions with [Ru3(CO)12] and [Ru4(μ-H)4(CO)12]. With the former, it gives the monosubstituted derivative 1, whereas with the latter, it gives the imidazolium salt [QuinCH2ImHMe][Ru4(μH)3(CO)12]. Upon heating in refluxing THF, compound 1 evolves toward 2 + 3CO through a multistep reaction pathway that involves the activation of both C−H bonds of the methylene group that links the quinolyl and the NHC fragments of the ligand. The mechanism of this reaction has been modeled by means of theoretical calculations. Upon heating in refluxing toluene, the imidazolium salt [QuinCH2ImHMe][Ru4(μ-H)3(CO)12] evolves toward the tetranuclear monosubstituted complex 3, which contains a QuinCH2ImMe ligand coordinated only through its NHC fragment. No doubt, the reactivity observed for the potentially bidentate QuinCH 2 ImMe ligand in its reactions with [Ru3(CO)12] and [Ru4(μ-H)4(CO)12] is a consequence of two factors: (a) the high basicity of the NHC fragment, which favors its coordination under mild reaction conditions and that enhances the tendency of the metal atoms to which it is attached to get involved in oxidative addition processes, and (b) the particular structure and rigidity of the QuinCH2ImMe ligand, which disfavor its coordination as a bidentate ligand.
Figure 5. DFT-calculated mechanism for the thermal transformation of 1 into 2 + 3CO. Part 4: From i8 to 2. The energy given for each stationary point (ΔE, kcal mol−1) is relative to that of compound 1 and corresponds to its energy plus that of three CO molecules.
(SiMe3)2]) in THF at room temperature led to instantaneous formation of the salt [QuinCH2ImHMe][Ru4(μ-H)3(CO)12] (Scheme 3). Similar proton-transfer processes, induced by the Scheme 3
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EXPERIMENTAL SECTION
General Procedures. Solvents were dried over sodium diphenyl ketyl (hydrocarbons, THF), CaH2 (dichloromethane), or Na2SO4 (acetonitrile) 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 carbonyl cluster [Ru4(μ-H)4(CO)12]22 was prepared as described elsewhere. 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 Bruker DPX-300 or AV-400 instruments. Microanalyses were obtained from the University of Oviedo Analytical Service. FAB mass spectra were obtained from the University of A Coruña Mass Spectrometric Service; data given refer to the most abundant molecular ion isotopomer. [QuinCH2ImHMe]Br. This imidazolium salt was prepared as described previously for [QuinCH2ImHBu]Br,20 but using 1methylimidazole instead of 1-butylimidazole: A solution of 1methylimidazole (200 mL, 2.5 mmol) and 8-bromomethylquinoline was stirred in acetonitrile (10 mL) at reflux temperature for 2.5 h. The volatiles were removed under reduced pressure, and the resulting residue was washed with diethyl ether (2 × 20 mL) to give the product as a white solid (663 mg, 97%). Anal. Calcd for C14H14BrN3 (304.17): C, 55.28; H, 4.64; N, 13.81. Found: C, 55.47; H, 4.76; N, 13.68. 1H NMR (CD2Cl2, 293 K, 300.1 MHz, ppm): δ 10.73 (s, br, 1H), 9.05 (dd, J = 1.7, 4.2 Hz, 1H), 8.37 (d, br, J = 7.0 Hz, 1H), 8.28 (dd, J = 1.7, 8.3 Hz, 1H), 7.96 (dd, J = 1.4, 8.3 Hz, 1H), 7.77 (d, J = 1.8 Hz, 1H), 7.66 (dd, J = 7.0, 8.3 Hz, 1H), 7.55 (dd, J = 4.2, 8.3 Hz, 1H), 7.16 (d, J = 1.8 Hz, 1H), 6.21 (s, 2 H), 4.01 (s, 3 H). 13C{1H} and DEPT NMR (CD2Cl2, 100.1 MHz, 293 K): δ 151.9 (CH), 147.3 (C), 139.1 (CH), 137.9 (CH), 133.1 (CH), 133.0 (C), 131.2 (CH), 129.8 (C), 127.9 (CH), 124.4 (CH), 123.8 (CH), 123.2(CH), 50.3 (CH2), 37.8 (CH3).
great basicity of NHCs, have been previously observed in reactions of other NHCs with [Ru4(μ-H)4(CO)12].16b A subsequent heating of this ionic species in toluene at reflux temperature led to the tretranuclear derivative [Ru4(μH)4(κCNHC-QuinCH2ImMe)(CO)11] (3), which was isolated as an orange solid (Scheme 3). The monosubstituted structure of compound 3 was established by its IR spectrum, whose νCO absorption pattern is similar to those of the known monosubstituted compounds [Ru4(μ-H)4(κC-NHC)(CO)11] (NHC = MeImMe, MeImPh, PhImPh, MesImMes)16a and was confirmed by its FAB mass spectrum, which contains the peaks expected for the corresponding molecular ion isotopomers. The fact that compound 3 is stable in refluxing toluene contrasts with the previous observation that [Ru 4 (μH)4(CO)12] reacts with various functionalized NHCs in refluxing toluene to give disubstituted derivatives of the type [Ru 4 (μ-H) 4 (κ 2 -L)(CO) 10 ] (L = Ph 2 PCH 2 CH 2 ImMe, Ph 2 PC 6 H 4 CH 2 ImMe, MepyCH 2 ImMe, HpyCH 2 ImMe, MeSCH2CH2ImMe),16b indicating that the particular structure 8118
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Table 2. Crystal, Measurement, and Refinement Data for Compound 2 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
C22H13N3O8Ru3 750.56 monoclinic P21/c 10.3260(2), 14.5123(2) 15.9712(2) 90, 97.268(1), 90 2374.12(3) 4 1448 2.100 15.743
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
0.08 × 0.05 × 0.02 123(2) 4.10−70.00 −12/8, −17/16, −19/14 8984 4450 3792 334/0 1.018 0.028 0.070 −0.696/0.683
940 [M]+. IR (CH2Cl2, cm−1): νCO 2083 (w), 2050 (vs), 2025 (vs), 2000 (m), 1982 (w). 1H NMR (CD2Cl2, 293 K, 300.1 MHz, ppm): δ 8.95 (dd, J = 4.2, 1.7 Hz, 1H), 8.22 (dd, J = 8.3, 1.7 Hz, 1H), 7.85 (m, 1H), 7.56−7.46 (m, 2H), 7.14 (m, 1H), 7.06 (d, J = 2.0 Hz, 1H), 6.92 (d, J = 2.0 Hz, 1H), 6.09 (s, 2H), 3.91 (s, 3H), −17.83 (s, 4H). 13 C{1H} and DEPT NMR (CD2Cl2, 100.1 MHz, 293 K): δ 189.7 (C), 167.7 (s, C), 150.7 (s, CH), 146.2 (s, C), 136.5 (s, CH), 134.6 (s, C), 128.8 (s, CH), 128.6 (s, C), 127.7 (s, CH), 126.5 (s, CH), 123.8 (s, CH), 123.0 (s, CH), 122.3 (s, CH), 53.6 (s, CH2), 41.2 (s, CH3). X-ray Diffraction Analysis. A crystal of 2 was analyzed by X-ray diffraction methods. A selection of crystal, measurement, and refinement data is given in the Table 2. Diffraction data were collected on an Oxford Diffraction Xcalibur Onyx Nova single-crystal diffractometer, using Cu Kα radiation. Empirical absorption correction was applied using the SCALE3 ABSPACK algorithm as implemented in the program CrysAlisPro RED.23 The structure was solved using the program SIR-97.24 Isotropic and full matrix anisotropic least-squares refinements were carried out using SHELXL.25 All non-H atoms were refined anisotropically. The positions of the hydride ligands were calculated with XHYDEX.26 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.27 The WINGX program system28 was used throughout the structure determinations. CCDC deposition number: 890315. Computational Details. Density functional theory (DFT) calculations were carried out using the Becke’s three-parameter hybrid exchange-correlation functional29 and the B3LYP nonlocal gradient correction.30 The LanL2DZ basis set, with relativistic effective core potentials, was used for the Ru atoms.31 The basis set used for the remaining atoms was the 6-31G, with addition of (d,p)-polarization.32 No simplified model compounds were used for the calculations. All stationary points of the mechanistic study were confirmed as energy minima (reactants, products, and intermediates; all positive eigenvalues) or transition states (one imaginary eigenvalue) by analytical calculation of frequencies. IRC calculations were used to verify that the transition states found were correct saddle points connecting the proposed minima. All energies given in this article are potential energies calculated in the gas phase. All calculations were carried out without symmetry constraints utilizing the Gaussian 03 package.33
[Ru3(κCNHC-QuinCH2ImMe)(CO)11] (1). A toluene solution of K[N(SiMe3)2] (616 μL, 0.5 M, 0.308 mmol) was added to a suspension of [QuinCH2ImHMe]Br (93 mg, 0.308 mmol) in THF (30 mL). After stirring for 20 min, finely powdered [Ru3(CO)12] (197 mg, 0.308 mmol) was added. The color changed from orange to red. The mixture was stirred for 30 min. 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 (2:3) eluted compound 1, which was isolated as a red solid upon solvent removal (162 mg, 63%). Anal. Calcd for C25H13N3O11Ru3 (834.60): C, 35.98; H, 1.57; N, 5.04. Found: C, 36.03; H, 1.58; N, 5.01. (+)-FAB MS: m/z 836 [M]+. IR (THF, cm−1): νCO 2090 (w), 2037 (s), 2018 (vs), 2004 (vs), 1975 (w), 1925 (w). 1H NMR (CD2Cl2, 293 K, 300.1 MHz, ppm): δ 8.95 (dd, J = 4.2, 1.8 Hz, 1H), 8.22 (dd, J = 8.3, 1.8 Hz, 1H), 7.85 (m, 1H), 7.60−7.43 (m, 2H), 7.18 (m, 1H), 7.06 (d, J = 2.0 Hz, 1H), 6.86 (d, J = 2.0 Hz, 1H), 6.03 (s, 2H), 3.86 (s, 3H). 13C{1H} and DEPT NMR (CD2Cl2, 100.1 MHz, 293 K): δ 205.1 (CO), 170.9 (C), 150.6 (CH), 146.3 (C), 136.6 (CH), 134.9 (C), 128.7 (CH), 128.6 (C), 128.3 (CH), 126.6 (CH), 124.5 (CH), 123.1 (CH), 122.1 (CH), 53.0 (CH2), 40.1 (CH3). [Ru3(μ-H)2(μ3-κ3N,C,CNHC-QuinCImMe)(CO)8] (2). A THF solution (20 mL) of compound 1 (80 mg, 0.096 mmol) was stirred at reflux temperature for 2.5 h. The color changed from red to yellow. The solvent was removed under reduced pressure, and the solid residue was washed with hexane (2 × 5 mL) to give compound 2 as a yellow solid (60 mg, 85%). Anal. Calcd for C22H13N3O8Ru3 (750.6): C, 35.21; H, 1.75; N, 5.60. Found: C, 35.30; H, 1.82; N, 5.56. (+)-FAB MS: m/z 752 [M]+. IR (THF, cm−1): νCO 2066 (s), 2021 (vs), 2010 (s), 1993 (s), 1977 (w), 1956 (m). 1H NMR (CD2Cl2, 293 K, 300.1 MHz, ppm): δ 9.07 (dd, J = 5.0, 1.5 Hz, 1H), 8.24 (dd, J = 8.3, 1.5 Hz, 1H), 8.00 (dd, J = 7.7, 1.2 Hz, 1H), 7.71 (d, J = 1.9 Hz, 1H), 7.58 (t, J = 7.7 Hz, 1H), 7.45 (dd, J = 7.7, 1.2 Hz, 1H), 7.35 (dd, J = 8.3, 5.0 Hz, 1H), 6.73 (d, J = 1.9 Hz, 1H), 3.71 (s, 3H), −11.03 (d, J = 1.5 Hz, 1H), −21.33 (d, J = 1.5 Hz, 1H). 13C{1H} and DEPT NMR (CD2Cl2, 100.1 MHz, 293 K): δ 200.3 (CO), 175.9 (C), 154.3 (CH), 150.6 (C), 137.9 (CH), 131.1 (C), 130.0 (C), 128.3 (CH), 126.7 (C), 123.7 (CH), 122.5 (CH), 121.5 (CH), 119.5 (CH), 118.1 (CH), 38.3 (CH3). Synthesis of [Ru4(μ-H)4(κCNHC-QuinCH2ImMe)(CO)11] (3). A toluene solution of K[N(SiMe3)2] (300 μL, 0.5 M, 0.150 mmol) was added to a suspension of [QuinCH2ImHMe]Br (35 mg, 0.115 mmol) in THF (30 mL). After stirring for 10 min, solid [Ru4(μ-H)4(CO)12] (86 mg, 0.116 mmol) was added. The IR spectrum of the resulting solution indicated the quantitative presence of the [Ru 4(μH)3(CO)12]− anion. The solvent was removed under reduced pressure, and toluene (30 mL) was added. The resulting mixture was heated to reflux for 1 h. The solvent was removed under reduced pressure, and the crude reaction mixture was subjected to a TLC separation on silica gel. Dichloromethane eluted two bands. The major band contained compound 3, which was isolated as an orange solid (62 mg, 57%). Anal. Calcd for C25H17N3O11Ru4 (939.70): C, 31.95; H, 1.82; N, 4.47. Found: C, 32.04; H, 1.91; N, 4.36. (+)-FAB MS: m/z
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ASSOCIATED CONTENT
S Supporting Information *
A table showing the evolution of selected interatomic distances along the reaction coordinate for the DFT-calculated mechanism of the reaction 1 → 2 + 3CO, tables of atomic coordinates for all DFT-optimized structures, and crystallographic data in CIF format for compound 2. This material is available free of charge via the Internet at http://pubs.acs.org. 8119
dx.doi.org/10.1021/om300651d | Organometallics 2012, 31, 8114−8120
Organometallics
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Article
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work has been supported by the Spanish MICINNFEDER grants CTQ2010-14933, MAT2010-15094, and CSD2006-00015.
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