Density functional and MP2 studies of germylene insertion into C-H, Si-H, N-H, P-H, O-H, S-H, F-H, and Cl-H bonds

The potential energy surfaces for the insertion reactions of germylene into XHn molecules have been characterized in detail using ab initio molecular orbital theory and density functional theory. The model system Ge(CH3)(2) XHn (X = C, N, O, F, Si, P, S, and Cl; n = 1-4) has been chosen for the pr esent study. All the interactions involve the initial formation of a donor- acceptor complex, followed by a high-energy transition state, and then an i nsertion product. The agreement between MP2 and B3LYP results indicates tha t the latter provides an adequate theoretical level for further investigati ons of molecular geometries, electronic structures, and kinetic features of the germylene reactions. The following conclusions emerge from this work: (i) the X-H insertion reactions of germylene occur in a concerted manner vi a a three-membered-ring transition state, and that the stereochemistry at t he heteroatom X center is preserved; (ii) the stabilization energies of the germylene-XHn complexes increase in the order NH3 > H2O > PH3 > H2S simila r to HF > HCl much greater than SiH4 similar to CH4; (iii) the order of rea ctivity for X-H bonds toward germylene insertion is Cl > F > S > O > P > N much greater than Si > C. In other words, the greater the atomic number of heteroatom (X) in a given row, the easier the insertion reaction of XHn hyd rides and the larger the exothermicity. Moreover, the present study demonst rates that both electronic and steric effects play a major role in the cour se of insertion reactions of germylene into X-H bonds. This work also indic ates that the chemical behavior of germylene should be more similar to that of silylene than to that of carbene species.