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 PCBut, in the presence of TlBF4, gave the η4-1,3-diphosphacyclobutadiene complex [Rh(triphos){η4-(PCBut)2}][BF4] 1a which formed the diadducts [Rh(triphos){η4∶η1∶η1-[W(CO)5]2(PCBut)2}][BF4] 2 or [Rh(triphos){η4∶η1∶η1-[PtCl2(PEt3)]2(PCBut)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-(PCBut)2}][BPh4] 1b, and the latter to the mono-η1-adduct [Rh(triphos){η4∶η1-[PtCl2(PEt3)](PCBut)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.