Edge‐Bridging and Face‐Bridging Hydrogen Atoms in Trinuclear Rhenium Carbonyl Hydrides

Abstract

AbstractThe structures of the trinuclear rhenium carbonyl hydrides H3Re3(CO)n (n = 12, 11, 10, 9) have been investigated by density functional theory (DFT). The only structure found for H3Re3(CO)12 is the experimentally known structure with each approximately 3.3 Å edge of a singly bonded Re3 triangle bridged by a hydrogen atom and all terminal carbonyl groups. The two lowest energy H3Re3(CO)11 structures lie within 0.5 kcal/mol in energy and are derived from this H3Re3(CO)12 structure by loss of a carbonyl group with retention of the central Re3(μ‐H)3 core. A higher energy H3Re3(CO)11 structure, closely related to the experimental structure for the isoelectronic dianion H3Re3(CO)102–, is also found in which one of the Re=Re edges of double bond length (2.79 Å) is bridged by two hydrogen atoms. Loss of a carbonyl group from this H3Re3(CO)11 structure with concurrent conversion of one of the edge‐bridging hydrogen atoms to a face‐bridging hydrogen atom gives the lowest energy H3Re3(CO)10 structure. Further loss of a carbonyl group from this (μ3‐H)(μ‐H)2Re3(CO)10 structure with concurrent conversion of a second edge‐bridging hydrogen atom to a face‐bridging hydrogen atom leads to the lowest energy H3Re3(CO)9 structure. This (μ3‐H)2(μ‐H)Re3(CO)9 structure with a central Re3(μ3‐H)2 trigonal bipyramid appears to be a very favorable structure since it not only is the lowest energy H3Re3(CO)9 structure but lies more than 22 kcal/mol below the next lowest energy H3Re3(CO)9 structure.