Reactions of the cyclometallated triosmium cluster [os₃H₂(CO)₉{P(C₆H₄)Ph}] with brøsnsted acids and dihydrogen: Synthesis and X-ray crystal structure of [os₃H₂(CF₃CO₂)(CO) ₉(μ-PPh₂)]

The cyclometallated cluster [Os₃H₂(CO)₉{P(C₆H₄) Ph}] (1) reacts with Brøsnsted acids HX via a protonation then anion co-ordination sequence to give the addition products [Os₃H₂(X) (CO)₉-(PPh₂)] [X = Cl (2), Br (3), CF₃CO₂ (4), or MeCO₂ (6)]. An X-ray analysis of (4) shows that the triangular metal framework of (1) is retained, and the oxygen-bound CF₃CO₂ ligand occupies a terminal axial site on the Os atom which is not bridged by the μ-PPh₂ group. With HBF₄·Et₂O the cationic cluster [Os₃H₃(CO)₉{P(C₆H ₄)Ph}]⁺ (5) is obtained, and this reaction may be thought of as involving the isolation of an intermediate in the above reactions. With HBr, addition of excess of acid to (1) leads to metal bond cleavage and cluster fragmentation, providing a novel route to new dimeric phosphido-bridged complexes [Os₂H₃(CO)₆(PPh₂)] (7), [Os₂H₂(Br) (CO)₆(PPh₂)] (8), and [Os₂H(Br)₂(CO)₆(PPh₂)] (9). In contrast, reaction of (1) with H₂ leads to carbon-phosphorus bond cleavage to give the phosphinidene-capped cluster [Os₃H₂(CO)₉(μ₃-PPh)] (10).