Side-on bonded dinitrogen and dioxygen complexes of rhodium(I). Synthesis and crystal structures of trans-chloro(dinitrogen)-, chloro-(dioxygen)-, and chloro(ethylene)-bis(tri-isopropylphosphine)rhodium(I)

Abstract

The complexes [RhCl(N2)(PPri3)2] (1), [RhCl(O2)(PPri3)2] (2), [RhCl(C2H4)(PPri3)2] (3), and [RhCl(CO)-(PPri3)2] (4) have been prepared. The crystal structures of (1)-(3) have been determined by a three-dimensional X-ray study from diffractometer data (Mo-Kα radiation). Crystals of the three complexes are monoclinic, space group P21/c, with the following unit-cell dimensions: (1), a = 8.156(1), b = 8.935(2), c = 16.695(5) Å, β = 93.5(1)°, Z = 2; (2), a = 8.184(3), b = 9.001(4), c = 16.401(7) Å, β = 93.1(1)°, Z = 2; (3), a 16.316(3), b = 9.164(2), c = 16.544(3) Å, β = 93.8(1)°, Z = 4. The structures have been solved by Patterson and Fourier methods and refined by full-matrix least squares to R 0.048 (1), 0.039 (2), and 0.022 (3) for 1 603, 1 327, and 4 586 independent observations respectively. The three complexes show similar molecular structures: the rhodium atom displays square-planar co-ordination with the two phosphines in trans positions and the N2, O2, and C2H4 ligands bonded side-on to the metal atom. The molecules of (1) and (2) lie on crystallographic centres of symmetry with a consequent disordered disposition of the chlorine atoms and N2 or O2 ligands. Short N-N [0.83(2) Å] and O-O [1.03(1) Å], and long Rh-N [2.51(1) Å] and Rh-O [2.28(1), 2.28(1) Å] bond distances are observed, which are scarcely significant because of the disorder. Infrared spectra are in accord, with weak Rh-N2 and Rh-O2 interactions, on the basis of the relatively high values of the N-N and O-O stretching frequencies. The 1H n.m.r. spectrum of C2H4 in (3) shows that the ethylene co-ordination is similar to that of other square-planar rhodium complexes. The C-C [1.319(4) Å] and Rh-C [2.116(2), 2.128(2) Å] distances are also close to those observed in other square-planar complexes. The three complexes represent the first case of a homogeneous series containing the three ligands N2, O2, and C2H4 and the first example of four-co-ordinate complexes containing 'side-on' dinitrogen and dioxygen.