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'=C8H14; 3: L=C8H14; L'=PiPr3; 4: L=L'=PiPr3), prepared from RhCl(C8H14)2]2] and isolated as PF6 salts, catalyze the C-C coupling reaction of diphenyldiazomethane with ethene, propene, and styrene. In most cases, a mixture of isomeric olefins and cyclopropanes were obtained which are formally built up by one equivalent of RCH=CH2 (R = H, Me, Ph) and one equivalent of CPh2. The efficiency and selectivity of the catalyst depends significantly 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(PiPr3)2(acetone)(eta1-N2CPh2)]PF6 (8) and trans-Rh(PiPr3)2(eta1-N2CPh2)2]PF6 (9), of which 8 was characterized by X-ray crystallography. Since 8 and 9 not only react with ethene but also catalyze the reaction of C2H4 and free Ph2CN2, they can be regarded as intermediates (possibly 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, N3) which afford the mono(diphenyldiazomethane)rhodium(I) compounds trans-Rh(PiPr3)2(py)(eta1-N2CPh2)]PF6 (10) and trans-RhX(eta1-N2CPh2)(PiPr3)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 the order Cl > Br> I > N3.