Activation of hydrogen by cationic cyclopentadienyl complexes with sulfido ligands. 3. Cationic complexes derived from reactions with halo esters, halo ketones, and acyl halides

Article abstract of DOI:10.1021/om00154a024

The dinuclear molybdenum complex (CpMo(μ-S))₂S₂CH₂ (Gp = C₅H₅; 1) reacts with methyl bromoacetate and with 1-bromo-2-butanone to form cationic derivatives of the formula [(CpMo)₂(S₂CH₂)(μ-S)(μ-SR)]Br, where R = CH₂CO₂CH₃ (2) or CH₂C(O)CH₂CH₃ (6). These cations react with hydrogen at room temperature to form methyl acetate and 2-butanone, respectively. In the presence of base, the α-carbon atom of the thiolate ligand in each cation is deprotonated. This process is accompanied by carbon-sulfur bond formation to form the 1,1-dithiolate-bridged complexes of general formula (CpMo)₂(S₂CH₂)(S₂C(H)R′), where R′ = CO₂CH₃ (3) or C(O)CH₂CH₃ (7). Complexes 3 and 7 also react with hydrogen at room temperature to form 1 and methyl acetate or 2-butanone. The reaction of acyl halides, R″COX, where R″ = CH₃, Ph, or CH₂Ph, with 1 under an atmosphere of hydrogen results in the formation of the corresponding aldehyde. A second reaction pathway reductively cleaves the carbonyl bond in the acyl halide to form water and a new molybdenum complex, [(CpMo)₂(S₂CH₂)(S₂CR″)]X (9). Complex 9 (R″ = CH₃; X = Br) has been characterized by an X-ray diffraction study. Crystals form in space group P2₁/c with a = 13.983 (3) A?, b = 8.197 (1) A?, c = 15.971 (3) A?, β = 90.72 (2)°, V = 1830.6 A?³, and Z = 4. The cation contains a bridging dithioacetate ligand which shows an η²-bonding mode to one molybdenum ion and a η⁸ mode to the second metal ion. Factors that influence the facile hydrogenolysis of carbon-sulfur and carbon-oxygen bonds in these systems are discussed.