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)(2)Re=C(Tol)(C=CPh ) (1a) led to formation of the dihydrophospholium complex Cp(CO)(2)Re[C=C(P h)PPh2CH2CH(Tol)] (4). When the reaction was monitored by low temperature N MR spectroscopy, initial phosphine addition to the carbene carbon atom of 1 a to give sigma -propargyl complex Cp(CO)2(-)ReC(PPh2CH3)(Tol)C drop CPh (5 ) was observed at -78 degreesC. Upon warming to -20 degreesC, 5 rearranged to the a-allenyl complex Cp(Co)(2)Re(Tol)C=C=C(Ph) (PPh2CH3) (6) via phosph ine 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 pro duces the cationic allene complex Cp(CO)(2)Re[eta (2)-2,3-(Tol)DC=C=C(Ph)(P Ph2CH3)]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)(2)Re[C-C(Ph)pph(2)CHCH(2)C(Tol)](8). (C) 2001 Elsevier Science B.V. All rights reserved.