Diverse Roles of Hydrogen in Rhenium Carbonyl Chemistry: Hydrides, Dihydrogen Complexes, and a Formyl Derivative

Abstract

Rhenium carbonyl hydride chemistry dates back to the 1959 synthesis of HRe(CO)₅ by Hieber and Braun. The binuclear H₂Re₂(CO)₈ was subsequently synthesized as a stable compound with a central Re₂(μ-H)₂ unit analogous to the B₂(μ-H)₂ unit in diborane. The complete series of HRe(CO)(n) (n = 5, 4, 3) and H₂Re₂(CO)(n) (n = 9, 8, 7, 6) derivatives have now been investigated by density functional theory. In contrast to the corresponding manganese derivatives, all of the triplet rhenium structures are found to lie at relatively high energies compared with the corresponding singlet structures consistent with the higher ligand field splitting of rhenium relative to manganese. The lowest energy HRe(CO)₅ structure is the expected octahedral structure. Low-energy structures for HRe(CO)(n) (n = 4, 3) are singlet structures derived from the octahedral HRe(CO)₅ structure by removal of one or two carbonyl groups. For H₂Re₂(CO)₉ a structure HRe₂(CO)₉(μ-H), with one terminal and one bridging hydrogen atom, lies within 3 kcal/mol of the structure Re₂(CO)₉(η²-H₂), similar to that of Re₂(CO)₁₀. For H₂Re₂(CO)(n) (n = 8, 7, 6) the only low-energy structures are doubly bridged singlet Re₂(μ-H)₂(CO)(n) structures. Higher energy dihydrogen complex structures are also found.

Studies of the Structures and Bonding of Gold-Bridged Dirhenium Carbonyl Cluster Complexes

“…Jeiowska-Trzebiatowska et al analyzed the electronic structure of 2 by using Fenske–Hall (FH) and extended Hückel (EH) methods . King reported MPW1PW91 and BP86 geometry-optimized DFT calculations for 2 . To investigate the nature of the Re–Re bonding in 1 , we have performed geometry-optimized PBEsol DFT molecular orbital calculations.…”

“…28 King reported MPW1PW91 and BP86 geometryoptimized DFT calculations for 2. 29 To investigate the nature of the Re−Re bonding in 1, we have performed geometry-optimized PBEsol DFT molecular orbital calculations. For the purposes of comparison, we have also performed similar DFT calculations upon 2; see below.…”

Mechanistic Study of a Re-Catalyzed Monoalkylation of Phenols

“…Complex 15 is the second most abundant of these complexes and features one type of mequinol ligand whose NMR signals are minimally perturbed compared to nonligated mequinol ( 1 ). We propose the mequinol is oxygen bound to the Re instead of C-bound which would strongly perturb the 1 H and 13 C chemical shifts and coupling constants associated with mequinol. , In contrast, the most abundant complex ( 14 ) features two types of chemically inequivalent mequinol ligands with a 2:1 ligand stoichiometry, implying a total of at least three mequinol ligands on the complex. The major set of mequinol ligand signals in complex 14 are quite similar to that found in complex 15 , suggesting similar oxygen-bound coordination, while the minor set of mequinol ligand signals of 14 differ significantly as evidenced by the dramatic upfield shift in the 13 C signals signal for C2 and C3 of the arene ring (see Scheme for the atom numbering definition), namely ca.…”

“…This fractional order dependency is consistent with the catalyst resting state having to deaggregate prior to the turnover-limiting transition state. Several likely scenarios exist, particularly since dinuclear (Re 2 L n ) and tetranuclear (Re 4 L n ) rhenium carbonyl complexes have been reported. , The resting state catalyst could be dinuclear (ReL n ) 2 implying that the turnover-limiting step would feature a mononuclear form (ReL n ). In an alternate scenario, the catalyst resting state could be tetranuclear (ReL n ) 4 implying that the turnover-limiting step would feature a dinuclear form (ReL n ) 2 .…”

“…Next we shifted our attention toward understanding how mequinol interacts with Re 2 (CO) 10 . Independent reaction of either methanol or phenol with Re 2 (CO) 10 in the presence of trimethylamine- N -oxide, an oxidant used to remove CO ligands from metal carbonyls, provides bridged oxide (CO) n Re–(μ 2 -OR)­(μ 2 -H)–Re­(CO) n or their related dehydrogenated forms (CO) n Re–(μ 2 -OR) m –Re­(CO) n ( m = 2 or 3, R = Ph, Me, H) . Tetrameric Re clusters as well as linear oligomers have been characterized in the literature by both NMR spectroscopy and X-ray crystallography .…”