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

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Abstract Addition of PPh 2 CH 3 to the alkynyl carbene complex Cp(CO) 2 ReC(Tol)(CCPh) ( 1a ) led to formation of the dihydrophospholium complex Cp(CO) 2 Re[CC(Ph)PPh 2 CH 2 CH(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) 2 ReC(PPh 2 CH 3 )(Tol)CCPh ( 5 ) was observed at −78°C. Upon warming to −20°C, 5 rearranged to the σ-allenyl complex Cp(CO) 2 Re(Tol)CCC(Ph)(PPh 2 CH 3 ) ( 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) 2 Re[η 2 -2,3-(Tol)DCCC(Ph)(PPh 2 CH 3 )]OTf ( 11 - d ), which is converted to 4 - d upon treatment with KO- t -Bu. The reaction of 1a with Ph 2 PCHCH 2 led to the formation of the cyclopropane Cp(CO) 2 Re[CC(Ph)PPh 2 CHCH 2 C(Tol)] ( 8 ).