Bridging phosphorus ligand substituted dirhenium octacarbonyl compounds. Preparation and reactions with water and methanol

Article abstract of DOI:10.1021/om00081a014

The bridging ligand substituted dirhenium octacarbonyl compounds, 1,2-eq,eq-Re₂(CO)₈(L-L), L-L = bis(dimethylphosphino)methane (dmpm), bis(diphenylphosphino)methane (dppm), bis(dimethylphosphino)ethane (dmpe), and bis(diphenylphosphino)ethane, (dppe), have been synthesized in high yield from L-L and (μ-H)(μ-CH=CHC₄H₉)Re₂(CO)₈. Re₂(CO)₈(dppe) and Re₂(CO)₈(dmpe) undergo rapid intramolecular exchange involving a twist about the Re-Re axis. The relative photochemical reaction rates of Re₂(CO)₈(L-L) with water or methanol are in the order dppe > dmpe > dppm > dmpm. The major products are (μ-H)(μ-OR)Re₂(CO)₆(L-L) and (μ-OR)₂Re₂(CO)₆(L-L) (R = H or CH₃). However, these products could be isolated from the reaction mixtures only for the dmpm and dppm compounds. The structure of (μ-H)(μ-OH)Re₂(CO)₆(dppm) was determined by conventional crystallographic techniques by using Mo Kα X-rays. The crystals belong to the triclinic space group P1 with a = 10.904 (2) A?, b = 11.099 (2) A?, c = 14.646 (2) A?, α = 84.69 (1)°, β = 83.18 (1)°, γ = 60.69 (1)°, and Z = 2. R_F = 0.031 for 5547 reflections having 2θ < 70° and I > 6σ(I). The molecular structure consists of two Re(CO)₃ units bridged by hydrido, hydroxo, and dppm ligands. The Re-Re distance is 3.030 (1) A?, the Re-H distances of the H-bridge are 1.84 (8) and 2.00 (8) A?, and the Re-O distances are 2.177 (5) and 2.160 (5) A?. Formation of (μ-H)(μ-OR)Re₂(CO)₆(L-L) and other products in the reactions is thought to proceed via two pathways, one involving metal-metal bond rupture and the other involving CO dissociation. The stability of (μ-H)(μ-OH)Re₂-(CO)₆(dppm) or (μ-H)(μ-OH)Re₂(CO)₆(dmpm) is ascribable to the presence of the relatively rigid bridging phosphine ligand that maintains the metal atoms in close proximity. Reactions of (μ-H)(μ-OR)Re₂(CO)₆(L-L) and (μ-OR)₂Re₂(CO)₆(L-L) with dry HCl leads to formation of (μ-H)(μ-Cl)Re₂(CO)₆(L-L) and (μ-Cl)₂Re₂(CO)₆(L-L), respectively.