Synthesis and Characterization of DMAP-Stabilized Aryl(silylene) Complexes and (Arylsilyl)(DMAP) Complexes of Tungsten: Mechanistic Study on the Interconversion between These Complexes via 1,2-Aryl Migration

Photoreaction of a mixture of Cp*(CO)3WMe (Cp* = η5-C5Me5) and HSiR2Ar [R2Ar = Me2Ph, Me2(p-Tol), Me(p-Tol)2, and (p-Tol)3] in the presence of 4-(dimethylamino)pyridine (DMAP) gave DMAP-stabilized aryl(silylene) complexes Cp*(CO)2W(Ar)(SiR2·DMAP) [1a, R = Me, Ar = Ph; 1b, R = Me, Ar = p-Tol; 1c, R2 = Me(p-Tol), Ar = p-Tol; 1d, R = Ar = p-Tol] via 1,2-migration of the aryl group from a silyl ligand to a tungsten center. Thermal reactions of Cp*(CO)2W(DMAP)Me (2) with HSiR2Ar at room temperature also gave 1a−d, and in all cases the yields were higher than those in the photoreaction. Silylene complexes 1a−d easily isomerized to arylsilyl complexes Cp*(CO)2W(DMAP)(SiR2Ar) [3a, R = Me, Ar = Ph; 3b, R = Me, Ar = p-Tol; 3c, R2 = Me(p-Tol), Ar = p-Tol; 3d, R = Ar = p-Tol] at 40−55 °C. On the other hand, irradiation of arylsilyl complexes 3a−d reproduced silylene complexes 1a−d, implying that the 1,2-aryl-migration between tungsten and silicon is reversible. The molecular structures of 1c, 2, 3a, and 3d were determined by X-ray crystallography. A kinetic study on the 1,2-aryl-migration in the thermal isomerization from 1a−d to 3a−d suggests that the rate-determining step involves dissociation of DMAP from 1a−d.