ORGANOMETALLIC CHEMISTRY OF SULFUR PHOSPHORUS DONOR LIGAND COMPLEXES OF NICKEL(II) AND NICKEL(0)

The X-ray crystal structures and electrochemical properties as well as chemical reactivity o the thioether complexes [Ni(Ph2PCH2CH2SEt)2][BF4]2 (5) and [Ni(Ph2PCH2CH2SCH2CH2CH2SCH2CH2PPh2)][BF4]2 (6), [Ni(PSSP)]2+, are compared with the thiolate Ni(Ph2PCH2CH2S)2 (4). Complex 4 crystallized in the orthorhombic space group Pbca (No. 61) with a 9.204(2) angstrom, b = 15.766(3) angstrom, c = 17.177(3) angstrom, V = 2492.6(8) angstrom3 Z = 4, and fin R = 0.050 (R, = 0.050) for 2212 unique reflections. Complex 5 crystallized in the monoclinic space group P2(1)/c, with a = 10.267(2) angstrom, b = 13.102(2) angstrom, c = 13.263(2) angstrom, beta = 93.750(10)-degrees, V = 1780.3(5) angstrom3, Z = 2, and final R = 0.076 (R(w) = 0.072) for 1777 unique reflections. The square-planar structures of 4 and 5 have sulfur donors in a trans arrangement and show a 0.04-angstrom lengthening of both the Ni-S and Ni-P bonds on going from the thiolate to the thioether complex. Within the CH3CN solvent window, the cyclic voltammograms of 5 and 6 show two reversible redox events assigned to Ni(II/I) and Ni(I/0), whereas the thiolate 4 shows only a sulfur-based irreversible oxidation and no reduction. Complexes 5 and 6 can be chemically reduced to Ni0 species, 5R and 6R, with Na/Hg amalgam. The H-1 NMR spectra of the reduced complexes indicate loss of one thioether donor for 5R and both for 6 . Protonation of the reduced species produced a Ni-H and reaction with both CH3I or CH3C(=O)Cl gave rise to Ni-CH3 and NiC(O)CH3 functionalities, respectively. The tetradentate derivatives [HNi(PSSP)]+ and [CH3Ni(PSSP)]+ are more stable than their bidentate analogues and show loss of reversible redox activity; i.e., the cyclic voltammograms find no evidence for stable Ni(I)-H or Ni(I)-CH3, or for Ni(III)-H or Ni(III)-CH3 species. The NiC(O)CH3 compounds rapidly and reversibly decarbonylate in solution (at temperatures >-30-degrees-C). A contrast of the abilities of structurally analogous P-SR vs N-SR ligands to stabilize subvalent nickel and organonickel functionalities is made.