Abstract
Nickel complexes in sulfur-rich environments have been prepared to determine those factors which stabilize organonickel species and permit access to low valent nickel. Nickel tetrathiolate complexes were initially used as precursors to disubstituted L2Ni(SAr)2 species (L = nitrogen or phosphorus donor ligands). Addition of carbon monoxide to both the tetrathiolates and phosphine-disubstituted products led to reductive elimination at nickel, thus oxidation of the thiolate ligands to disulfide, and nickel carbonyl products. Sulfur-site alkylation or trans-Ni(Ph2PCH2CH2S)2 led to cationic thioether products, [Ni(Ph2PCH2CH2SR)2][^2+]. Higher order multidentate ligands were prepared using ICH2CH2OH and ICH2CH2OCH2CH2I as alkylating agents. Better routes to the desired complexes utilized the P2S2O or PSOH preformed ligands. The Ni[^II] complex of the pentadentate ligand [Ph2PCH2CH2SCH2CH2]2O was prepared as its BF4- salt and characterized by x-ray crystallography. The molecular structure finds a square planar P2S2Ni complex with the O-donor inclined toward Ni but beyond bonding distance (Ni ... 0 = 2.84 A ). Spectroscopic results suggested a four-coordinate complex in the PSOH complex as well. While the thiolate Ni(Ph2PCH2CH2S)2 showed no accessible low-valent nickel by cyclic voltammetry, the S-alkylated complexes displayed two reduction waves ascribed to Ni[^II/I] and Ni[^1/0]. Spectroscopic results determined the P2S2 ligand of the Ni^0 species to be bound only through phosphorus. The Ni^0 species provided synthetic entry into organonickel chemistry. The addition of appropriate alkyl halides led to formation of Ni-CH3 and Ni-CH2C6H5 species. Acetyl products resulting either from addition of RC(O)X to Ni^0 or by CO insertion into the nickel alkyls were identified at low temperature. Upon warming, decarbonylation products and nickel carbonyls were formed. The Ni^II complex was reactive toward the π-accepting cyanide and underwent a structural rearrangement to produce a square pyramidal five-coordinate Ni-CN species whose structure was determined by x-ray crystallography. The reaction of Ni(Ph2PCH2CH2S)2 with (NBD)Mo(CO)4 resulted in isolation of a cis-NiP2S2Mo bimetallic compound which was characterized by x-ray crystallography. The severe NiS2/MoS2 dihedral angle of 103.4° places a carbonyl near the nickel center; low temperature spectroscopy indicated a similar solution structure.
Chojnacki, Stephen Shane (1993). Ligand effects on the organometallic chemistry of nickel. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1475409.