ORGANOMETALLIC CHEMISTRY OF SULFUR PHOSPHORUS DONOR LIGAND COMPLEXES OF NICKEL(II) AND NICKEL(0)
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The X-ray crystal structures and electrochemical properties as well as chemical reactivity of 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) , b = 15.766(3) , c = 17.177(3) , V = 2492.6(8) 3, Z = 4, and final R = 0.050 (Rw = 0.050) for 2212 unique reflections. Complex 5 crystallized in the monoclinic space group P21/c, with a = 10.267(2) , b = 13.102(2) , c = 13.263(2) , = 93.750(10), V = 1780.3(5) 3, Z = 2, and final R = 0.076 (Rw = 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- lengthening of both the NiS and NiP 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 NiII/I and NiI/0, whereas the thiolate 4 shows only a sulfur-based irreversible oxidation and no reduction. Complexes 5 and 6 can be chemically reduced to Ni species, 5R and 6R, with Na/Hg amalgam. The 1H NMR spectra of the reduced complexes indicate loss of one thioether donor for 5R and both for 6R. Protonation of the reduced species produced a NiH and reaction with both CH3I or CH3C(O)C1 gave rise to NiCH3 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 Ni1H or NiICH3, or for NiIIIH or NiIIICH3 species. The NiC (O)CH3 compounds rapidly and reversibly decarbonylate in solution (at temperatures >30 C). A contrast of the abilities of structurally analogous PSR vs NSR ligands to stabilize subvalent nickel and organonickel functionalities is made. 1993, American Chemical Society. All rights reserved.