Synthesis and structural characterization of the phosphido cluster [ir₄H(CO)₁₀(μ-PPh₂)] and its facile carbonyl substitution reactions with a series of phosphines and phosphites

The tetranuclear cluster [Ir₄H(CO)₁₀(μ-PPh₂)] 1 is formed from [Ir₄(CO)₁₁(PPh₂)] 2 by deprotonation, which yields [Ir₄(CO)₁₀(μ-PPh₂)]^- 3, followed by protonation of the anion. It has been fully characterized by an X-ray analysis, and exhibits a tetrahedral arrangement of metal atoms with the three basal edges bridged by a phosphido, a hydrido and a carbonyl ligand. Both 1 and 3 undergo facile carbonyl substitution reactions with phosphites and phosphines L [PPh₃, PPhMe₂, P(OPh)₃ or P(C₆H₄X-4)₃ (X = F, Cl, Me, 4-Ome or 2-OMe)] to give [Ir₄H(CO)₉L(μ-PPh₂)] 4a-4h and [Ir₄(CO)₉L(μ-PPh₂)]^- 5a-5h respectively, the latter being converted into the corresponding hydride derivatives by protonation. Further substitution of a CO in 4a-4h affords [Ir₄H(CO)₈L₂(μ-PPh₂)] 6a-6h. An X-Ray analysis of [Ir₄H(CO)₉(PPh₃)(μ-PPh₂)] 4a shows that carbonyl substitution has occurred at a basal Ir atom which is not bridged by the phosphido ligand.