Synthesis and Characterization of κ2C,N-N-Silyliminoacyl Tungsten Complexes Cp*(CO)2W{κ2C,N-C(R)═NSiR′3} [R = Me, Et, i-Pr, t-Bu; R′3 = (p-Tol)2Me, (p-Tol)3, Et3; Cp* = η5-C5Me5]: Thermally Induced Carbon−Carbon Bond Cleavage of Their Iminoacyl Ligands

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DMAP-stabilized ( p -tolyl)(silylene) complexes Cp*(CO) 2 W( p -Tol){═Si( p -Tol)R′·DMAP} [ 1a, R′ = Me; 1b, R′ = p -Tol; DMAP = 4-(dimethylamino)pyridine] reacted with excess nitrile RCN (R = Me, Et, i -Pr, t -Bu) in toluene to give κ 2 C,N - N -silyliminoacyl tungsten complexes Cp*(CO) 2 W{κ 2 C,N -C(R)═NSi( p -Tol) 2 R′} ( 2a, R = Me, R′ = Me; 2b, R = Et, R′ = Me; 2c, R = i -Pr, R′ = Me; 2d, R = t -Bu, R′ = Me; 3a, R = Me, R′ = p -Tol; 3b, R = Et, R′ = p -Tol; 3c, R = i -Pr, R′ = p -Tol; 3d, R = t -Bu, R′ = p -Tol). This reaction proceeds through 1,2-migration of a p -tolyl group from a tungsten center to a silylene ligand. Complexes 3a and 3b and similar complexes Cp*(CO) 2 W{κ 2 C,N -C(R)═NSiEt 3 } ( 4a, R = Me; 4b, R = Et) were also synthesized by reactions of methyl(nitrile) complexes Cp*(CO) 2 W(NCR)Me ( A, R = Me; B, R = Et) with hydrosilanes HSiR′ 3 (R′ = p -Tol, Et). A kinetic study on the dynamic process of 2c involving inversion of the chiral tungsten center reveals that the inversion can occur via dissociation of the iminoacyl nitrogen atom coordinating to the tungsten center. Thermal reaction of a toluene solution of N -silyliminoacyl complexes 3a and 3b at 120 °C in a sealed tube gave a cis / trans mixture of alkyl(silylisocyanide) complexes cis / trans -Cp*(CO) 2 W(R){CNSi( p -Tol) 3 } ( 5a, R = Me; 5b, R = Et) through cleavage of the C−C bond between the iminoacyl carbon and the alkyl substituent R in 3a or 3b . The molecular structures of 3b and cis -5b were determined by X-ray crystallography.