Carbene complexes. Part VII. Chloromethyleneammonium chlorides. Electron-rich carbenoids, as precursors to secondary carbene metal complexes; crystal and molecular structure of trichloro(dimethylaminomethylene)bis(triethylphosphine)rhodium(III)

Abstract

The reaction of dialkyl(chloromethylene)ammonium chlorides (R2NCHCl)+Cl–, (R = Me, Et, Pri, or Bun), with RhI substrates [RhCl(PPh3)3], [RhCl(CO)PPh3]2, or [RhCl(CO)2]2 affords RhIII secondary carbene complexes, [L′RhCl3CHNR2]n[L′= CO, n= 2; L′=(PPh3)CO, n= 1; L′=(PEt3)2 or (PPh3)2, n= 1], via a three-fragment oxidative-addition reaction. The secondary carbene RhIII complexes are characterised by a high degree of CN double-bonding, greater than in tertiary carbene complexes or carboxylic acid dialkylamides. The Ccarb–H1H n.m.r. resonance is at low field (τca. –1), ν(Ccarb–H) at ca. 3050 cm–1, and ν(Ccarb[graphic omitted]N) at ca. 1600 cm–1; coupling of Ccarb–H resonances are identified: 2J(103Rh–1H), 3J(31P–1H), and cis- and trans-4J(C1H3N–1H). A single-crystal X-ray analysis of [RhCl3(PEt3)2CHNMe2] has been carried out to R= 0·050; the complex has an approximately octahedral Rh environment with mutually trans-phosphine ligands. Bond distances (A) are Rh–Ccarb= 1·961(11), Ccarb–N = 1·289(14), Ccarb–H = 1·14(4), Rh–P = 2·368(3) and 2·372(3), Rh–Cl (mutually trans)= 2·357(4) and 2·364(3), Rh–Cl (trans-carbene)= 2·445(4). The high trans-influence of the secondary carbene ligand is discussed in terms of X-ray, i.r., and n.m.r. data, and it appears to have the highest trans-influence of a neutral ligand of RhIII.