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

Abstract

The 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.

Metal triangles versus metal chains and terminal versus bridging hydrogen atoms in trinuclear osmium carbonyl hydride chemistry

“…However, no H 2 Os 3 (CO) n structures with m 3 -H ligands bridging all three osmium atoms of the Os 3 triangle are found, in contrast to our previous study of trinuclear rhenium carbonyl hydrides H 3 Re 3 (CO) n (n = 12, 11, 10, 9). 9 None of the low-energy H 2 Os 3 (CO) n (n = 11, 10) structures have bridging carbonyl groups.…”

“…8 This paper presents a theoretical study of these and related trinuclear osmium carbonyl hydrides using density functional methods similar to those used in a previous theoretical study of rhenium carbonyl hydrides. 9 In addition to the experimentally known H 2 Os 3 (CO) n (n = 12, 11, 10) systems, the more highly unsaturated H 2 Os 3 (CO) n (n = 9, 8) are included in this study.…”

“…Dissociation energies (kcal mol À1 ) for successive removal of carbonyls from H 2 Os 3 (CO) n (n =12,11,10,9) …”