Conclusion
The DFT calculations presented here indeed support the view that the activation of the H-E (E=Ge, Si, Sn) σ-bond proceeds by itd η2-coordination and next by oxidative addition to tungsten or molybdenum. First, structures of the six-coordinate σ-bond complexes [M(CO)3(η2-H-EEt3)(η4-nbd)] (M=W, Mo; E=Si, Ge, Sn) were optimized by DFT calculations. The oxidative addition of the σ-bonds of the η2-H-EEt3 ligand to the metal center of complex 1 leads to the formation of complex 1(W=Ge) into 2 leads to the formation of at least four complexes (2a-2d) in a moderately endoergic (∆G from 34 to 51 KJ/mol) processes. For comparison of the structure and the NMR chemical shift of the type 2a the formation of a new C-H bond (1.157-1.169 Å) is predicted between one of the four olefin carbons of the η2-H-E bond of complex 1. The unstable complex 2a can be the intermediate complex that plays the crucial role on the way of the hydride transfer from the H-E bond to the olefin bond of the norbornadiene ligand coordinated to tungsten or molybdenum. The calculated value of chemical shift for hydride in complexes of type 1 and 2 are in acceptable agreement with the available experimental photochemical reaction not only seven but also six-coordinate complexes of tungsten(II) can be formed and detected by NMR.