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-K_α 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.