Reaction of rhenium alkynyl carbene complexes with tertiary phosphines produces dihydrophospholium rhenium complexes by a formal CH insertion process

Addition of PPh2CH3 to the alkynyl carbene complex Cp(CO)2ReC(Tol)(CCPh) (1a) led to formation of the dihydrophospholium complex Cp(CO)2Re[CC(Ph)PPh2CH2CH(Tol)] (4). When the reaction was monitored by low temperature NMR spectroscopy, initial phosphine addition to the carbene carbon atom of 1a to give σ-propargyl complex Cp(CO)2ReC(PPh2CH3)(Tol)CCPh (5) was observed at −78°C. Upon warming to −20°C, 5 rearranged to the σ-allenyl complex Cp(CO)2Re(Tol)CCC(Ph)(PPh2CH3) (6) via phosphine dissociation and readdition. Upon further warming to room temperature, 6 rearranged to 4. A protonation-deprotonation mechanism for the conversion of 6 to 4 is supported by the observation that reaction of 6 with DOTf produces the cationic allene complex Cp(CO)2Re[η2-2,3-(Tol)DCCC(Ph)(PPh2CH3)]OTf (11-d), which is converted to 4-d upon treatment with KO-t-Bu. The reaction of 1a with Ph2PCHCH2 led to the formation of the cyclopropane Cp(CO)2Re[CC(Ph)PPh2CHCH2C(Tol)] (8).