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

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