Cyclopropenation and Related Reactions of Ruthenium Vinylidene Complexes

Abstract

Facile deprotonation of a number of cationic ruthenium vinylidene complexes, followed by cyclopropenation, is accomplished in acetone. The deprotonation of [Ru] C (Ph)CH 2 R +, ([Ru] = (η 5 -C 5 H 5 )(PPh 3 ) 2 Ru) by n -Bu 4 NOH induces a novel cyclization reaction and yields the neutral cyclopropenyl complexes [Ru]−C C(Ph)CHR ( 3b, R = CN; 3c, R = Ph; 3d, R = CH CH 2; 3e, R = CH CMe 2 ). Complex [Ru]−C C(C 6 H 9 )CHCN + ( 3k ) is similarly prepared. Protonation of 3b − 3e regenerates the corresponding vinylidene complexes. Deprotonation of [Ru] C C(Ph)CH 2 COOMe + ( 2h ) by n -Bu 4 NOH induces a different type of cyclization and yields the neutral furan complex [Ru]−C C(Ph)CH C(O)OMe ( 4h ). The cyclopropenyl complex containing a methoxy substituent cannot be prepared from [Ru] C C(Ph)CH 2 OCH 3 + ( 2i ), but F - of n -Bu 4 NF attacks the C α of 2i to produce the unstable vinyl complex [Ru]C(F) C(Ph)CH 2 OCH 3 ( 5 ). Complex [Ru]−C C(Ph)C(CN)OCH 3 ( 9b ) was indirectly prepared from the addition of TCNQ to 3b, giving [Ru] C C(Ph)CH(CN)TCNQ ( 6b ) followed by methanolysis. Unlike 3, complex 9b is not converted to vinylidene complex, instead, removal of the methoxy substituent by acid gives the cationic cyclopropenylium complex [Ru]−C C(Ph)C(CN) + ( 10b ). Complex [Ru]−C C(Ph)C(COOMe) + ( 10h ) is similarly prepared from 4h via a TCNQ complex 6h followed by a methoxy-substituted complex 9h . In the presence of allyl iodide, opening of the three-membered ring of 3b, followed by a subsequent oxidative coupling reaction, gives a dimeric dicationic product {[Ru] C C(Ph)−CHCN} 2 2+ ( 11 ). Proton abstraction of 11 by n -Bu 4 NF gives the biscyclopropenyl complex {[Ru]−C C(Ph)CCN} 2 ( 12 ). Molecular structures of complexes 3b, 3f, 4h, 6b, 9b, and 11 have been confirmed by X-ray diffraction analysis.