Cationic and neutral diphenyldiazomethanerhodium(I) complexes as catalytically active species in the C-C coupling reaction of olefins and diphenyldiazomethane

Cationic rhodium(I) complexes cis-[Rh(acetone)(2)(L)(L')](+) (2. L = L' = C 8H14; 3: L = C8H14; L' = PiPr(3); 4: L = L'=PiPr(3)), prepared from [{RhCl- (C8H14)(2)}(2)] and isolated as PF, salts, catalyze the C-C coupling reacti on of diphenyldiazomethane with ethene, propene, and styrene. In most cases , a mixture of isomeric olefins and cyclopropanes were obtained which are f ormally; built up by one equivalent of RCH=CH2 (R=H. Me, Ph) and one equiva lent of CPh2. The efficiency and selectivity of the catalyst depends signif icantly on the coordination sphere around the rhodium(I) center. Treatment of 4 with Ph2CN2 in the molar ratio of 1:1 and 1:2 gave the complexes trans -[Rh-(PiPr(3))(2)(acetone) (eta(1)-N2CPh2)]PF6 (8) and trans-[Rh(PiPr(3))(2 )(eta(1)-N2CPh2)(2)]PF6 (9), of which 8 was characterized by X-ray crystall ography. Since 8 and 9 not only react with ethene but also catalyze the rea ction of C2H4 and free Ph2CN2, they can be regarded as intermediates (possi bly resting states) in the C-C coupling process. The lability of 8 and 9 is illustrated by the reactions with pyridine and NaX (X=Cl, Br, I, N-3) whic h afford the mono(diphenyldiazomethane)rhodium(I) compounds trans-[Rh(PiPr( 3))(2)(py)(eta'-N2CPh2)]PF6 (10) and trans-[RhX(eta'-N2CPh2)(PiPr(3))(2)] ( 11-14), respectively. The catalytic activity of the neutral complexes 11-14 is somewhat less than that of the cationic species 8, 9 and decreases in t he order Cl > Br > I > N-3.