SOME HYDRIDO-BRIDGED TRANSITION-METAL DIMERS AND THEIR UNSUPPORTED ANALOGS - SPECULATIONS ON PENTUPLE BONDING AND PENTUPLE BRIDGING

Bonding and rotational barriers in M2L6 and M2L8 dimers in several alternative geometries are described. These barriers in most cases are determined by electronic factors, although steric requirements may occasionally play a dominant role. The magnitudes of the barriers depend on the number of electrons in the system and the electronic nature of the ligands. The dimer levels are then used to construct molecular orbitals for hydrido-bridged species. The conformational preferences of H3M2L6and H4M2L8 are compared to experiment and the possible existence of H5M2L6 and H3M2L8 (within a Dih geometry) is probed. The possibility of pentuple bonding in the latter system is explored. Different pathways for interconnecting stable conformations of the hydrides have been studied. These include separate considerations of rotating the bridging hydrides vs. rotation of one terminal ML group in H3M2L6 and H4M2L8 complexes. A coupled pseudorotation-rotation itinerary for H4M2L8 is also examined. © 1979, American Chemical Society. All rights reserved.