Benzamidinatorhodium complexes. X-Ray structures of [Rh{CPh(NPh)2}(cod)] and [Rh2{µ-CPh(NPh)2}2(tfbb)2]

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Abstract
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].

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