STABILIZATION OF RHODIUM(I)-ALKYL AND IRIDIUM(I)-ALKYL BONDS BY INTRAMOLECULAR COORDINATION OF AN IMINOPHOSPHORANE - X-RAY CRYSTAL-STRUCTURE OF [RH(CH2PPH2=N-C6H4-CH3-4)(COD)]

Lithium(iminophosphoranyl)methanide Li[CH2PPh2 = N-C6H4-CH3-4] (2a) reacts with the rhodium and iridium complexes [ML2Cl]2 (M = Rh, L2 = COD, L = CO: M = Ir, L2 = COD) to yield the complexes [M(CH2PPh2 = N-C6H4-CH3-4)L2] (3a, M = Rh, L2 = COD; 3c, M = Rh, L = CO; 3e, M = Ir, L2 = COD), in which the (iminophosphoranyl)methanide ligand is coordinated as a sigma-N,sigma-C chelate, forming a new four-membered metallacycle. The molecular structure of 3a has been determined by X-ray crystallographic analysis. Compound 3a crystallizes in space group P2(1)/n with a = 31.877 (3) angstrom, b = 12.932 (2) angstrom, c = 13.579 (2) angstrom, and beta = 99.14 (1)-degrees, and the structure was refined to R = 0.041 (R(W) = 0.043) by using 10 500 independently measured reflections. The square-planar coordination around rhodium (I) involves the two olefinic bonds of COD and the N and C atoms of the sigma-N,sigma-C chelated (iminophosphoranyl)methanide ligand (Rh-N = 2.132 (3) angstrom and Rh-C1 = 2.128 (3) angstrom). In the rhodium and iridium (iminophosphoranyl)methanide complexes the M-C(sp3) bond is effectively stabilized by intramolecular coordination of an iminophosphorane group, as illustrated by their thermal stability and the inertness of 3a,c toward small molecules such as CO and CO2, as well as activated olefins and acetylenes. Reactions of the rhodium complexes 3a,c with 1 equivalent of HCl gives either the sigma-N-coordinated iminophosphorane complex [Rh(4-CH3-C6H4-N = P(CH3)Ph2)L2Cl] (5) or the N-protonated species [Rh(CH2PPh2NH-C6H4-CH3-4)L2]Cl (6) depending on the ligand L and the applied conditions. The reaction proceeds most probably via an intermediate Rh(III) oxidative-addition product (a metal hydride was observed by IR spectroscopy) that further reacts via hydrogen migration reactions to yield 5 or 6, i.e. with a net protonation of the C atom or the N atom, respectively, in 3.