Benzamidinatorhodium complexes. X-Ray structures of [rh{CPh(NPh)2}(cod)] and [rh2{μ-CPh(NPh)2}2(tfbb)2]

Resumen

Complexes [{MCl(diolefin)}2] (M = Rh or Ir) react with N,N′-diphenylbenzamidinate to yield binuclear [Rh2{μ-CPh(NPh)2}2(diolefin)2] [diolefin = norbornadiene (nbd) or tetrafluorobarrelene (tfbb)] or mononuclear [M{CPh(NPh)2}(cod)] (cod = cycle-octa-1,5-diene) complexes. The rhodium complexes react with carbon monoxide to give [Rh2{μ-CPh(NPh)2}2(CO)4]. The latter complex undergoes a two-centre oxidative addition with iodine yielding the rhodium(II) complex [Rh2{μ-CPh(NPh)2}2I2(CO) 4]. An A-frame compound of formula [Rh2{μ-CPh(NPh)2}(μ-dppm)2(CO)] ClO4 (dppm = Ph2PCH2PPh2) has been isolated. Some related mononuclear complexes containing a unidentate benzamidine ligand have also been prepared. The crystal structures of the complexes [Rh{CPh(NPh)2}(cod)] (1) and [Rh2{μ-CPh(NPh)2}2(tfbb)2] (4) have been determined by X-ray diffraction methods. Complex (1) crystallizes in the monoclinic space group P21/n, with a = 10.315(2), b = 19.507(3), c = 11.429(3) Å, β = 103.62(1)°, and Z = 4. Crystals of compound (4) are monoclinic, space group P21/c, with Z = 4 and a unit cell of dimensions a = 21.692(2), b = 12.512(2), c = 19.969(2) Å, and β = 107.90(1)°. Both structures were solved by Patterson and Fourier methods and refined by full-matrix least squares to R 0.040 and 0.047, respectively. The structure of (1) is mononuclear with the N,N′-diphenylbenzamidinate acting as a chelating ligand, through the nitrogen atoms. In contrast, complex (4) is binuclear with the benzamidinate ligand bridging two rhodium atoms [Rh ⋯ Rh 2.982(3) Å].