NHC Complexes of Osmium Clusters: A Structural and Reactivity Study

Abstract

A carbene transfer agent, 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene-silver(I)chloride ([IMes]-AgCl), was treated with various osmium clusters. Reaction of ([IMes]AgCl) with [Os 3 (µ-H) 2 (CO) 10 ] gave [Os 3 (µ-H)(µ-Cl)(CO) 9 (IMes)] (1), an osmium N-heterocyclic carbene complex. The reaction of ([IMes]AgCl) with the cluster [Os 3 (CO) 10 (CH 3 CN) 2 ] yielded two products, [Os 3 (µ-Cl)(CO) 10 (µ-Ag(IMes)] (2) and [(IMes-H)][Os 3 (µ-Cl)(CO) 10 ](µ 4 -Ag)[Os 3 (µ-Cl)(CO) 10 ] (3). Compound (2) is a heterobimetallic carbene complex resulting from the complete incorporation of ([IMes]AgCl). Transmetalation using [(IMes)AgCl] and the cluster [Os 4 (µ-H) 4 (CO) 12 ] in the presence of trimethylamine-N-oxide resulted in the formation of [Os 4 (µ-H) 4 (CO) 11 (n • IMes)] (4), where (n denotes normal carbene bonding, i.e., through C 2 ). [Os 4 (µ-H) 4 (CO) 10 (IMes) 2 ] (5) was formed using the activated cluster [Os 4 (µ-H) 4 (CO) 10 (CH 3 CN) 2 ] and [(IMes)AgCl]. Compound (5) was found to be sensitive to silica gel column chromatography in the presence of dichloromethane decomposing to [Os 4 (µ-H) 3 (µ-Cl)(CO) 11 (IMes)] ( 6), which possessed a butterfly metal skeleton. The ruthenium analogue of ( 4), [Ru 4 (µ-H) 4 (CO) 11 (IMes)] ( 7), was prepared and identified spectroscopically but was found to be thermally unstable. Thermolysis of (4) in benzene yielded four products. The abnormal carbene complex [Os 4 (µ-H) 4 (CO) 11 (a • IMes)] (10) (a denotes abnormal carbene bonding through C 3 or C 4 ), an isomer of (4), and {Os 4 (µ-H 11), an unusual complex resulting from the activation of benzene and activation of three C-H bonds on IMes, were isolated in modest yields. Two higher-nuclearity clusters, {Os 5 (µ 5 -C)(CO) 14 [η-C-η-NC 2 H 2 (Mes)]} ( 8) and [Os 6 (µ-H) 4 (µ 5 -C)(CO) 15 (IMes)] ( 9), both of which contain carbide ligands, were also isolated. {Os 4 (µ-H)(CO) 10 [(η-C)N(Mes)C 2 H 2 NC 6 H 2 (CH 3 ) 2 (η 2 -C)(η-C)CHC(CH 3 )-C 2 H 2 (η 2 -C)]} (12), an analogue of (10), resulted from the thermolysis of (4) in toluene indicates that the reaction is potentially general and exhibits some regioselectivity. Crystal structure determinations were completed on all 11 osmium cluster complexes.

The N-heterocyclic carbene chemistry of transition-metal carbonyl clusters

“…31 In all these [M 3 (NHC)(CO) 11 ] (M = Ru, Os) cluster compounds, the very strong basicity of NHCs increases the electron density of the metal atoms to which they are attached and this enhances the tendency of these metals to get involved in oxidative addition processes. 32 It is now well established that NHC-silver(I) complexes, which can be easily made by treating the corresponding imidazolium halide with silver(I) oxide, 33 are able to transfer their NHC ligands to another transition metals, 33 12 ] with [AgCl(Mes 2 Im)] in the presence of Me 3 NO (as decarbonylating reagent), 36 but it was assigned an incorrect structure. A combination of these two factors (unsaturated and electron-rich metals) with the fact that some ligand bonds and cluster metal atoms can be very close to each other rationalize the synthesis of compounds 17-26, in which decarbonylation (and, occasionally, cluster condensation as in 23 and 24) is accompanied by processes that involve the (multiple) activation of ligand bonds.…”

Synthesis and structural characterisation of the palladium N-heterocyclic carbene cluster complexes [Pd3(μ-CO)3(NHC)3] and [Pd3(μ-SO2)3(NHC)3]

“…The resulting suspension was then heated at 70°C for 16 h. The red solution was cannula filtered and the filtrate reduced to dryness to leave a mixture of red and white solids. The red product was extracted in MeOH (2 mL), filtered, reduced to dryness and the red solid of [Pd 3 (l-CO) 3 ,5.51;N,6.38. Found: C,57.63;H,5.61;N,6.45%.…”

“…The red product was extracted in MeOH (2 mL), filtered, reduced to dryness and the red solid of [Pd 3 (l-CO) 3 ,5.51;N,6.38. Found: C,57.63;H,5.61;N,6.45%. Repeated attempts to determine the CHN content gave a consistently low % carbon.…”

“…Palladium dichloride (300 mg, 1.69 mmol), [I i Pr 2 H]Cl (637 mg, 3.38 mmol) and caesium carbonate (4.9 g, 15.21 mmol) were suspended in dioxane (10 mL) and heated at 80°C for 16 6.69;N,11.63. Found: C,44.52;H,6.54;N,11.58%.…”

Reactivity of [Ru4(μ-H)4(CO)12] with bidentate ligands containing at least one N-heterocyclic carbene moiety

“…The hitherto reported reactions of NHCs with transition-metal carbonyl clusters and the transformations underwent by the NHC-containing species initially formed in those reactions have shown that the polynuclear character of these metallic compounds or, more precisely, the close proximity of one or more metal atoms to that which is or can be attached to the NHC ligand, is responsible for reactivity patterns (multiple CeH, CeC and CeN bond activation processes [3e6]) that have no parallel in the NHC chemistry of mononuclear complexes. Most of this chemistry has been performed using triruthenium complexes as metal precursors, the hitherto reported works dealing with reactions of NHCs with tetraruthenium complexes being very scarce and they involve only monodentate NHCs [7,8].…”