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.