AN UNUSUAL SELECTIVE REDUCTION OF AN OXIME INTO AN IMINE GROUP IN HALOGENOMETHYLRHODOXIMES

[Rh(dmgH)(2)(PPh3)](-) ([Rh](-), 1) {[Rh] = [Rh(dmgH)(2)(PPh3)]; (dmgH )(2) = dimethylglyoxime}, obtained by reduction of [Rh]-Cl with NaBH4 in methanolic KOH, reacts with dihalogenomethanes CH2X2 (X = Br, Cl) t o give besides the known complexes [Rh]-CH2X (X = Br, 2a; X = Cl, 2b) the complexes [Rh(CH2X) {ON=C(Me)-C(Me)=NH}(dmgH)(PPh3)] (X = Br, 3a; X = Cl, 3b) where one oxime unit is reduced to an imine. Due to the st rong alkaline medium (methanolic KOH) 3a was found to react partially, yielding [Rh(CH2OMe) {ON=C(Me)-C(Me)=NH} (dmgH)(PPh3)] (3c). All thre e complexes were characterized by H-1-, C-13-, P-31-NMR spectroscopy. 3a crystallizes in the triclinic space group P (1) over bar with two m olecules in the asymmetric unit. These molecules are linked via two N- H ... O hydrogen bridges forming a dimer. The rhodium atoms display a distorted octahedral coordination with the dmgH/ON=C(Me)-C(Me)=NH liga nds in the equatorial plane and PPh3 and the CH2Br ligands in the axia l positions. (C) 1998 Elsevier Science S.A. All rights reserved.