LATE TRANSITION-METAL MU-OXO AND MU-IMIDO COMPLEXES .10. RHODIUM ARYLIMIDO ARYLAMIDO RING REACTIONS - ELECTROPHILIC ADDITIONS

Tautomeric mixtures of the arylimido/arylamido complexes Rh2(mu-N(4-R-C6H4)(CO)2(mu-dPPM)2/Rh2(mu-NH(4-R-C6H4))(CO)2(mu-dppm-H)(mu-dppm) (1/2) (dppm = bis(diphenylphosphino)methane, dppm-H = bis(diphenylphosphino)methanide) react with carbon-based electrophiles, R'X, to give the arylimido ring addition products [Rh2(mu-N(4,4-R,R'-C6H4))(CO)2(mu-dppm)2]+X- (3 (R, R'= Me, Me; H, Me; Me, CH2Ph; Me, CH2Cl; F, CH2Ph) (X = Cl, I, OTf)). Crystals of 3 (R, R' = Me, Me; X = Cl).CH2Cl2 from CH2Cl2/ether are monoclinic (C2/c) with a = 37.20 (1) angstrom, b = 12.827 (3) angstrom, c = 26.497 (6) angstrom, beta = 97.35 (2)-degrees, V = 12538 angstrom3, d(calc) = 1.38 g.cm-3, and Z = 8. The structure reveals an A-frame cationic complex with a quinoid-like group bridging the Rh atoms via the nitrogen atom. Weaker electrophiles with the less nucleophilic 1/2 (R = H) allow other reactions to predominate, giving products resulting from loss of the imido/amido group. Attack of the electrophile at the nitrogen atom of imido tautomer 1 or at the dppm-H ligand of amido tautomer 2 is prevented by the sterically demanding dppm ligand directing the attack to the ring. An interesting ring-to-nitrogen rearrangement of 3 (R, R' = H, Me) is catalyzed by 1/2 via deprotonation to Rh2(mu-N(4-Me-C6H4))(CO)2(mu-dPPM)2 followed by protonation to the cationic amido complex [Rh2(mu-NH(4-Me-C6H4))(CO)2(mu-dppm)2]+X-. This rearrangement occurs in the synthesis of 3 (R, R' = H, Me; X = OTf) if a deficiency of MeOTf is used, and high yields of 3 are only obtained with 1 equiv or more of MeOTf. A similar rearrangement occurs with MeI, but the intermediate Rh2(mu-N(4-Me-C6H4))(CO)2(mu-dppm)2 is trapped by Mel to give its ring addition product 3 (R, R' = Me, Me; X = 1).