Phosphaalkyne cyclodimerization at a rhodium(I) centre. Syntheses of a cationic eta(4)-1,3-diphosphacyclobutadiene rhodium complex and of its platinum(II) or tungsten(0) adducts

Treatment of [RhCl(triphos)] [triphos = PPh(CH2CH2PPh2)(2)] in thf with P=B u-t, in the presence of TlBF4, gave the eta(4)-1,3-diphosphacyclobutadiene complex [Rh(triphos){eta(4)-(PCBut)(2)}][BF4] 1a which formed the diadducts [Rh(triphos){eta(4) : eta(1) : eta(1)-[W(CO)(5)](2)(PCBut)(2)}][BF4] 2 or [Rh(triphos){eta(4) : eta(1) : eta(1)-[PtCl2(PEt3)](2)(PCBut)(2)}][BF4] 3 o n reaction with [W(CO)(5)(thf)] or [Pt2Cl4(PEt3)(2)], respectively. These a dducts dissociated in solution, the former in the presence of Na[BPh4] to g ive [Rh(triphos){eta(4)-(PCBut)(2)}][BPh4] 1b, and the latter to the mono-e ta(1)-adduct [Rh(triphos){eta(4) : eta(1)-[PtCl2(PEt3)](PCBut)(2)}][BF4] 4. Reactions of [RhCl(triphos)] in thf with the 1-alkynes HC=CR (R = CO2Me or CO2Et) in the presence of Tl[BF4] afforded the corresponding benzene deriv ative complexes [Rh(triphos){eta(4)-(HCCR)(3)}][BF4] 5a or 5b.