Formation of hexaosmium raft clusters from [Os6(CO)16(MeCN)2]: synthesis, structural characterisation and reactivities of [Os6(CO)16(µ3-η2-C5H4NS)2] and [Os6(CO)17(µ-H)(µ4-η2-C5H4NS)]

Abstract

Reaction of [Os₆(CO)₁₆(MeCN)₂] with 1 equivalent of 2-Aldrithol in CH₂Cl₂ under ambient conditions afforded two new raft clusters [Os₆(CO)₁₆(µ₃-η²-C₅H₄NS)₂] 1 and [Os₆(CO)₁₇(µ-H)(µ₄-η²-C₅H₄NS)] 2 in moderate and fair yields, respectively. Cyclic voltammograms of compound 1 exhibited two metal-based, one-electron reduction couples at E_1/2 = –0.36 and –0.20 V together with an irreversible ligand-based anodic wave at ca. E_pa = +0.31 V vs. Ag–AgNO₃. Protonation of 1 with CF₃CO₂H produced an unstable species [Os₆(CO)₁₆(µ₃-η²-C₅H₅NSH)(µ₃-η²-C₅H₅NS)][CO₂CF₃] 3, which upon standing in CH₂Cl₂ quickly decomposed. All compounds have been fully characterised by spectroscopic methods, while the molecular structures of 1 and 2 were established by crystallographic techniques. Both 1 and 2 contain ‘ladder’-type and edge-fused raft cluster cores, with the sulfur atom in 2 being drawn intimately into the cluster envelope. These clusters serve as good models for substrates adsorbed onto metal surfaces.