Toward a more detailed understanding of oxidative-addition mechanisms: Combined experimental and quantum-chemical study of the insertion of titanium atoms into C-H, Si-H, and Sn-H bonds

The reactions between Ti atoms and CH4, SiH4, and SnH4 at a temperature of 12 K in Ar matrixes were studied experimentally by IR spectroscopy, taking in the effect of isotopic substitution, and by quantum-chemical calculations. The experiments show that the reactivity changes considerably from CH4 to SiH4 or SnH4. The reaction between Ti and CH4 proceeds inefficiently, and only after photolytic activation of the Ti atoms does insertion occur to give HTiCH3, which features only terminal Ti-H and C-H bonds. On the other hand, reactions with SiH4 and SnH4 occur upon deposition, leading to the products cis- and trans-HTi(mu-H)(2)SiH and HTi(mu-H)(3)E (E = Si, Sn). Selective photolysis can be used to increase the yields of these products. In agreement with the experimental results, quantum-chemical calculations predict the lowest energy form of a molecule with the overall formula TiEH4 to be HTiCH3 with only terminal H atoms for E = C but HTi(mu-H)(3)E with three bridging H atoms in the case of E = Si, Sn.