Ab initio study of the coordination modes of tetrahydroborato ligands: what is the actual structure of the tris(tetrahydroborato)bis(trimethylphosphine) titanium complex

The structure of the d 1 complex Ti(BH 4 ) 3 (PH 3 ) 2 is studied by means of ab initio UHF calculations including correlation energy at the MP2 level. This complex is used as a model for the Ti(BH 4 ) 3 (PMe 3 ) 2 complex characterized by Girolami et al. Sixteen structures which differ by the borohydride coordination modes are optimized through an analytical gradient method. The energetical ordering of these structures is analyzed through an electron count. We find that the optimal structure corresponds to a η 2 ,η 2 ,η 3 coordination mode, a result in disagreement with the experimental data, which have been interpreted in terms of η 1 ,η 1 ,η 2 coordination