Transition metal polyhydride complexes.: 9.: The effect of ligand - and -bonding on the H-Ta-H bond angle in six-coordinate tantalum(V) dihydride complexes
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abstract
In the known structures of the pseudo-octahedral complexes [Ta(OR)2L(H)2L]+, with L = PR3 and L= Cl-, OR-, the "trans" hydrides are bent away from the sterically less demanding ligand (L) toward the bulkier phosphine group (L). Here, ab initio calculations on a series of analogous model complexes (R = H; L, L = OH-, F-, Cl-, Br-, CO, CN-, CS, BF, N2, CH3-, NH3, PH3, CH3CN, NH2-, and H-) are used to examine the effect of the - and -bonding of the ligands L and L on the direction of H-Ta-H bending. While the trend in the trans influence, which dominates the Ta-L bond length of the ligand trans to L, originates primarily from -bonding, the direction of the distortion of the "trans" hydrides originates primarily from the relative -acceptor ability of the ligand L to that of the ligand L. Generally, as the ligands are varied, the hydrides will bend toward the stronger -acceptor (L vs L). With certain ligand pairs the possibility of two isomers exists, one with hydrides bent toward L and another with hydrides bent toward L.
