STRUCTURE AND BONDING IN CR(CO)5H2 AND CR(CO)4(H2)2 COMPLEXES

The electronic structure of Cr(CO)5(H2) and Cr(CO)4(H2)2 complexes has been investigated using ab initio electronic wave functions and effective core potentials. In Cr(CO)5(H2) η2-H2 coordination is found to be energetically preferred, in agreement with experimental results. The formation of the dihydride form is an energy-demanding process; this explains why under D2 pressure no isotope exchange is observed. Cr(CO)4(H2)2 contains two coordinated hydrogen molecules; polyhydrogen forms are found to be highly unstable. A mechanism is proposed to explain the observed formation of Cr(CO)5(HD) during H2/D2 exchange in Cr(CO)4(H2)2; it implies the formation of a dihydrogen-dihydride complex. The calculations predict also the possible existence of a stable open H3 ligand in the hypothetical [Cr(CO)5(H3)]+ complex. © 1990, American Chemical Society. All rights reserved.