Coordination of bis(azol-1-yl)methane-based bisphosphines towards RuII, RhI, PdII and PtII: synthesis, structural and catalytic studies

Abstract

The coordination chemistry of bisphosphine ligands assembled on the five-membered heterocyclic platform of bis(azol-1-yl)methane viz.: bis(2-diphenylphosphinoimidazol-1-yl)methane (1), bis(5-diphenylphosphinopyrazol-1-yl)methane (2) and bis(5-diphenylphosphino-1,2,4-triazol-1-yl)methane (3) with Ru^II, Rh^I, Pd^II and Pt^II is described. The bisphosphines 1–3 react with elemental selenium to give the corresponding bis-selenoyl derivatives 4–6. The reactions of 1–3 with transition metal derivatives produce complexes with different coordination modes. Bisphosphine 1 showed a preference for the κ²-P,P mode of coordination, whereas bisphosphines 2 and 3, besides the κ²-P,P mode also showed a head-to-tail κ²-P,N coordination mode resulting in the formation of binuclear complexes [Rh₂(COD)₂{(CH₂(1,2-C₃H₂N₂PPh₂)₂)-κ²P,N}][BF₄]₂ (14), [Rh₂(COD)₂{(CH₂(1,2,4-C₂HN₃PPh₂)₂)-κ²P,N}][BF₄]₂ (15), [Pd₂(η³-C₃H₅)₂{(CH₂(1,2-C₃H₂N₂PPh₂)₂)-κ²P,N}][BF₄]₂ (21) and [Pd₂(η³-C₃H₅)₂{(CH₂(1,2,4-C₂HN₃PPh₂)₂)-κ²P,N}][BF₄]₂ (22). Several of these complexes have also been structurally characterized. The in situ generated Rh^I complex of bisphosphine 1 showed moderate to good selectivity in the hydroformylation of various styrene derivatives.