Phosphaalkyne cyclodimerization at a rhodium(I) centre. Syntheses of a cationic η4-1,3-diphosphacyclobutadiene rhodium complex and of its platinum(II) or tungsten(0) adducts

Abstract

Treatment of [RhCl(triphos)] [triphos = PPh(CH₂CH₂PPh₂)₂] in thf with PCBu^t, in the presence of TlBF₄, gave the η⁴-1,3-diphosphacyclobutadiene complex [Rh(triphos){η⁴-(PCBu^t)₂}][BF₄] 1a which formed the diadducts [Rh(triphos){η⁴∶η¹∶η¹-[W(CO)₅]₂(PCBu^t)₂}][BF₄] 2 or [Rh(triphos){η⁴∶η¹∶η¹-[PtCl₂(PEt₃)]₂(PCBu^t)₂}][BF₄] 3 on reaction with [W(CO)₅(thf)] or [Pt₂Cl₄(PEt₃)₂], respectively. These adducts dissociated in solution, the former in the presence of Na[BPh₄] to give [Rh(triphos){η⁴-(PCBu^t)₂}][BPh₄] 1b, and the latter to the mono-η¹-adduct [Rh(triphos){η⁴∶η¹-[PtCl₂(PEt₃)](PCBu^t)₂}][BF₄] 4. Reactions of [RhCl(triphos)] in thf with the 1-alkynes HCCR (R = CO₂Me or CO₂Et) in the presence of Tl[BF₄] afforded the corresponding benzene derivative complexes [Rh(triphos){η⁴-(HCCR)₃}][BF₄] 5a or 5b.