| The catalytic reactions of group 10 metals-catalyzed dehydrogenative double silylation with tris(silyl)methane [H-SiCl2CH(SiHCl2)(SiMeCl2)] are comparatively studied with the aid of density functional calculation at the B3LYP level of theory.Under the three catalysts, the reaction undergoes four processes, the first Si-H oxidative addition, elimination of H2, acetylene insertion into M-Si bond, and reductive elimination of the product. Our study reveals that the Ni(PMe3)2 catalyst shows different behaviors which compared with the other two catalysts Pd(PMe3)2 and Pt(PMe3)2 possessing similar catalytic behaviors. In the process of H2 elimination catalyzed by Pd(PMe3)2 and Pt(PMe3)2, the two-step process has been observed to be associated with the Si-H oxidative addition followed by H2 reductive elimination. However, a one-step process involving theσ-bond metathesis is revealed for the reaction catalyzed by Ni(PMe3)2. Following the formation of the disilacyclic group 10 metal complexes, acetylene insertion into the M-Si occurs. Two possible mechanisms can be proposed. One is the coordination of acetylene to the metal to give trigonal bipyramidal complexes, followed by the direct acetylene insertion into M-Si bond to produce the insertion products. The second one is the substitution of PMe3 by acetylene to afford four-coordinated acetylene complexes, followed by acetylene insertion and the re-coordination of PMe3 to produce the insertion produc. For the second one, there are two possible paths. One is through an associative mechanism involving the formation of the trigonal bipyramidal complexes. The other go through a dissociative mechanism with first loss of a PMe3 followed by acetylene coordination.The process of H2 elimination is predicted to be rate-determining in all the three catalytic reactions. Clearly, the so called lanthanide contract effect involved in Pt element is responsible for the similarity mentioned above. |
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