Monophosphine-o-Carborane Sulfide as a Noninnocent Ligand for C,S, S,S′, and B,S,S′ Coordination Modes of Half-Sandwich Iridium and Rhodium Complexes

Half-sandwich iridium and rhodium complexes with three different coordination modes were successfully synthesized by using the monophosphine-o-carborane sulfide 1-SPPh2-1,2-closo-C2B10H11 (1) as the ligand. Treatments of the dimeric metal complexes [Cp*M(μ-Cl)Cl]2 (M = Ir, Rh; Cp* = η5-C5Me5) with the lithium salt of monophosphine-o-carborane sulfide generate the C,S-coordinated complexes [Cp*IrCl(CabC,S)] (2) and [Cp*RhCl(CabC,S)] (3) (CabC,S = (1-SPPh2-1,2-closo- C2B10H10)−), respectively. Compound 1 can be modified to give the corresponding thiol 1-SH-2-SPPh2-1,2-closo-C2B10H10 (4). The unexpected B,S,S′ coordination mode product [Cp*Ir(CabB,S,S′)] (5) (CabB,S,S′ = (η1-S′)(η1-SPPh2)(η1-1,2-closo-C2B10H9)) through B–H activation was obtained by the reaction of [Cp*Ir(μ-Cl)Cl]2 with the lithium salt of 4. However, [Cp*Rh(μ-Cl)Cl]2 gave the product [Cp*RhCl(CabS,S′)] (6) (CabS,S′ = (1-S′-2-SPPh2-1,2-closo- C2B10H10)−) with the S,S′ mode under the same conditions. When it was heated in CH3OH, complex 6 gradually transformed from a closo-carborane complex to the zwitterionic nido-carborane complex [Cp*Rh(7-S′-8-(SPPh2)-7,8-C2B9H10)] (7). They represent the first examples of half-sandwich complexes incorporating a monophosphine-o-carborane sulfide ligand. In addition, the iridium complex 2 exhibits catalytic activity up to 1.40 × 106 g of PNB (mol of Ir)−1 h–1 for the polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. All complexes were fully characterized by elemental analysis and IR and NMR spectroscopy. The structures of 1, 2, and 5–7 were further confirmed by single-crystal X-ray diffraction.