Ab Initio Study of the Coordination Modes of Tetrahydroborato Ligands: Structure of the Ti(BH<inf>4</inf>)<inf>3</inf> Complex

The structure of the d1-Ti(BH4)3 complex is studied by means of ab initio UHF calculations including correlation energy at the MP2 level. Twenty structures which differ by the coordination mode of the BH4-ligands are optimized through an analytical gradient method, using the double-ζ basis set I. In agreement with the experimental data, the C3h (η3, η3, η3) structure is found to be the most stable, a result which is confirmed by calculations with the extended basis set II. The geometry of the absolute minimum and the energy ordering of the other structures are rationalized through electron counting around the metal atom. Average bond lengths are given for each coordination mode, and a mechanism for exchange between bridging and terminal hydrogen atoms is proposed, with an activation energy of only 5.1 kcal/mol (basis set II). © 1993, American Chemical Society. All rights reserved.