Abstract : Monometallic complexes of the tetrakis(pyrazolyl)borate ligand ML(2)B(pz)(4)} M = Rh Ir L(2) = eta-
more
Abstract : Monometallic complexes of the tetrakis(pyrazolyl)borate ligand ML(2)B(pz)(4)} M = Rh Ir L(2) = eta-cod eta-nbd (CO)(2) (CO)(PPh(3))} have two free pyrazolyl rings which can be coordinated to a second ML(2) unit to give the dimeric compounds L(2)Mmu-B(pz)(4)}ML(2)(+) and to a metal halide to give heterobimetallic species L(2)Mmu-B(pz)(4)}MCl(2). (1)H NMR spectroscopy shows that (eta-cod)Rhmu-B(pz)(4)}Rh(eta-cod)(+) 1(+) (eta-nbd)Rhmu-B(pz)(4)}Rh(eta-nbd)(+) 2(+) (eta-cod)Irmu-B(pz)(4)}Ir(eta-cod)(+) 3(+) and (CO)(2)Rhmu-B(pz)(4)}Rh(CO)(2)(+) 4(+) are fluxional at room temperature. Cooling a solution of (eta-cod)Rhmu-B(pz)(4)}Rh(eta-cod)(+) 1(+) to -90 degrees C slows the fluxional process which involves inversion of the two B-(N-N)(2)-M six-membered rings. Attempts to synthesise the asymmetric complexes (eta-cod)Rhmu-B(pz)(4)}Rh(eta-nbd)(+) 7(+) (eta-cod)Rhmu-B(pz)(4)}Ir(eta-cod)(+) 8(+) and (eta-cod)Rhmu-B(pz)(4)}Rh(CO)(2)(+) 9(+) produced a mixture of L(2)Mmu-B(pz)(4)}ML(2)(+) L(2)Mmu-B(pz)(4)}ML(2)(+) and the desired species. The heterobimetallic complexes L(2)Rhmu-B(pz)(4)}MCl(2) (M = Co L(2) = eta-cod 10 M = Co L(2) = eta-nbd 11 M = Co L = CO 12 M = Co L(2) = (CO)(PPh(3)) 13 M = Zn L(2) = eta-cod 14 M = Zn L(2) = eta-nbd 15 M = Pd L(2) = eta-cod 16) possess square planar Rh(I) linked to square planar Pd(II) or tetrahedral Zn(II) and Co(II) centres. The paramagnetic Co(II) complexes give (1)H NMR spectra with signals shifted over a range of 75 ppm. The UV-Vis spectra of 10-13 show four bands one MLCT at Rh and three d-d transitions arising from the splitting of the (4)T(1)(P) excited state due to approximate C(2v) symmetry at Co.
less