title: Characterization of steric and electronic properties of NiN2S2 complexes as S-donor metallodithiolate ligands.
abstract: The physical properties and structures of a series of six complexes of the type (NiN(2)S(2))W(CO)(4) have been used to establish electronic and steric parameters for square planar NiN(2)S(2) complexes as bidentate, S-donor ligands. According to the nu(CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of the tungsten carbonyl adducts, there is little difference in donor abilities of the five neutral NiN(2)S(2) metallodithiolate ligands in the series. The dianionic Ni(ema)(2)(-) (ema = N,N'-ethylenebis(2-mercaptoacetamide)) complex transfers more electron density onto the W(CO)(4) moiety. A ranking of donor abilities and a comparison with classical bidentate ligands is as follows: Ni(ema)(=) > {[NiN(2)S(2)](0)} > bipy approximately phen > Ph(2)PCH(2)CH(2)PPh(2) > Ph(2)PCH(2)PPh(2). Electrochemical data from cyclic voltammetry find that the reduction event in the (NiN(2)S(2))W(CO)(4) derivatives is shifted to more positive potentials by ca. 0.5 V compared to the ca. -2 V Ni(II/I) redox event in the free NiN(2)S(2) ligand, consistent with the electron drain from the nickel-dithiolate ligands by the W(CO)(4) acceptor. Differences in Ni(II/I) DeltaE(1/2) values appear to have a ligand dependence which is related to a structural feature of the hinge angle imposed by the (mu-SR)(2) bridges. Thus the angle formed by the intersection of NiN(2)S(2)/WS(2)C(2) planes has been established by X-ray diffraction analyses as a unique orientational feature of the nickel-dithiolate ligands in contrast to classical diphosphine or diimine ligands and ranges in value from 136 to 107 degrees . Variable-temperature (13)C NMR studies show that the spatial orientations of the ligands remained fixed with respect to the W(CO)(4) moiety to temperatures of 100 degrees C.
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Marilyn V
authors.initials: MV
authors.lastname: Rampersad
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Jeffery
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Golden
authors.forename: Jonghyuk
authors.initials: J
authors.lastname: Lee
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Reibenspies
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Darensbourg
authors.forename: Marcetta Y
authors.initials: MY
authors.lastname: Darensbourg
mesh_terms: D001665:Binding Sites; D004583:Electrons; D008024:Ligands; D008956:Models, Chemical; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D013455:Sulfur; D009532:Nickel; D009584:Nitrogen