Structural and catalytic properties of the [Ni(BIPHEP)X-2] complexes, BIPHEP=2,2-diphenylphosphino-1,1-biphenyl; X = Cl, Br
Abstrakt
The synthesis and catalytic properties in Kumada C-C coupling of the [Ni(BIPHEP)X-2] complexes, X = Cl (1), Br (2), are described. The crystal structures of the BIPHEP ligand and 2 are also presented and compared with previously reported crystal structures of atropisomeric bidentate phosphine ligands (P,P) and related [M (P,P)X-2] complexes (M = Ni, Pd, Pt).
BIPHEP crystallizes in the C2/c space group, with both enantiomers present in the unit cell. This is consistent with BIPHEP being a "tropos" ligand.
Complex 2 crystallizes in the P21/a space group. There are two symmetry-independent molecules in the asymmetric unit, namely 2a and 2b, in which the BIPHEP ligand adopts the S or the R configuration, respectively.
Complexes 2a and 2b exhibit a severely tetrahedrally-distorted square planar NiP2Br2 coordination sphere, with a PNiP bite angle of 93.3 degrees and 94.7 degrees, respectively. The observed catalytic behavior of complexes 1 and 2 in the Kumada coupling between p-tert-butyl-halogenobenzene and p-tolylmagnesium chloride is benchmarked against that of [Ni(dppp)Cl-2], dppp = 1,3-bis(diphenylphoshpino)propane.
However, all three complexes are catalytically inactive in the Suzuki-Miyaura coupling reaction.