Selectivity of Allenylidene versus Butadienyl Protonation in an Osmium−Bisphosphine System

The complex [OsH(CCCPh2)(CH3CN)2(PiPr3)2]BF4 (1) reacts with 2-methyl-1-buten-3-yne to give [Os{(E)-CHCHC(CH3)CH2}(CCCPh2)(CH3CN)2(PiPr3)2]BF4 (2). Treatment of 2 with HBF4leads to the alkenylcarbene−allenylidene derivative [Os{CHCHC(CH3)2}(CCCPh2)(CH3CN)2(PiPr3)2][BF4]2 (3). In contrast to its reaction with HBF4, the reactions of 2 with acetic acid, acetylacetone, and acetone oxime afford the butadienyl−alkenylcarbyne species [Os{(E)-CHCHC(CH3)CH2}(κ2-O2CCH3)(CCHCPh2)(PiPr3)2]BF4 (4), [Os{(E)-CHCHC(CH3)CH2}(κ2O,O′-acac)(CCHCPh2)(PiPr3)2]BF4 (5), and [Os{(E)-CHCHC(CH3)CH2}{κ2N,O-[ONC(CH3)2]}(CCHCPh2)(PiPr3)2]BF4 (6), respectively. The X-ray structures of 4 and 6 are also reported.