The structure of the high-spin complex d2-V(BH4)3(PH3)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 complex V(BH4)3(PMe3)2 recently characterized by Girolami and co-workers, in which the three tetrahydroborato ligands are coordinated in an η2 fashion. Thirteen structures which differ in the coordination mode of the BH4- ligands (η1, η2, or η3) are optimized by an analytical gradient method. In agreement with experimental data, the (η2, η2, η2) structure, where all bridging hydrogens are lying in the plane of the boron atoms, is found to be the most stable. This result, together with the energy ordering of the other structures, is rationalized both through usual electron counting and through molecular orbital analysis. Average bond lengths are given for each coordination mode, and the mechanisms for exchange between bridging and terminal hydrogens in the BH4- group are briefly discussed. © 1991, American Chemical Society. All rights reserved.
|Publication status||Published - 1 Nov 1991|