When is addition of X-Y to M not oxidative?


Charles W. Hamilton, chamilton@lanl.gov1, David E. Morris2, Michael W. Blair3, Neil J. Henson, neil.henson@lanl.gov4, Richard L. Martin2, Jeffrey L. Cross, jlcross@lanl.gov5, Andrew D. Sutton, adsutton@lanl.gov5, Kimberly C. Jantunen, jantunen@lanl.gov6, Brian L. Scott7, and R. Tom Baker, bakertom@lanl.gov5. (1) Inorganic, Isotope and Actinide Chemistry Group, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, (2) Los Alamos National Laboratory, Los Alamos, NM 87545, (3) Earth & Environmental Science (EES) Division, Los Alamos National Laboratory, J495, Los Alamos, NM 87545, (4) Physics and Chemistry of Materials, Los Alamos National Laboratory, P. O. Box 1663, Los Alamos, NM 87545, (5) Chemistry Division, Los Alamos National Laboratory, MS J514, Los Alamos, NM 87545, (6) Chemistry and Theoretical Divisions, Los Alamos National Laboratory, MS J514, Los Alamos, NM 87545, (7) Materials, Physics and Applications Division, Los Alamos National Laboratory, MS J514, Los Alamos, NM 87545
Addition of a single bond to a metal center normally increases its formal oxidation state (oxidative addition) such as addition of PPh2H to divalent Cp*MoCl(N2)(PMe3)2 to give tetravalent Cp*MoHCl(PPh2)(PMe3). Reaction of zerovalent Ni(1,5-cyclooctadiene)2 with the di(arylamino)chlorophosphine, PCl(NmesCH2CH2Nmes) (PClN2), affords dimeric [NiCl(μ-PN2)]2, 1, with trigonal Ni centers (mes = mesityl, -1,3,5-Me3C6H2). At first glance this reaction appears to involve oxidation of the nickel center as the cationic diaminophosphenium fragment (PN2)+ is converted to a bridging diaminophosphido ligand (PN2)-. Determination of the molecular and electronic structure of this unusual dimer by X-ray diffraction and DFT calculations, however, reveals an unsymmetrical structure composed of strongly interacting zerovalent 14 e- [NiCl(PN2)2]+ and 12 e- [NiCl]- ions. Accordingly, mononuclear phosphine addition complexes NiCl(PN2)Ln (n = 1, L = PCy3; n = 2, L = PMe3) and [Ni(PN2)(PMe3)3]Cl derived from 1 all exhibit geometries consistent with d10 metal centers. The electronic structure of 1 indicates that the LUMO resides largely on the PN2 bridges and a reversible reduction is observed at -1.77 V (vs. Cp2Fe0/+) in the cyclic voltammogram. Bulk reduction with Na(benzophenone) in THF yields a stable dinuclear radical anion with large hyperfine couplings to the inequivalent bridge 31P nuclei observed in the isotropic EPR spectrum.

General Inorganic Chemistry
9:00 AM-1:00 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 219, Oral

Division of Inorganic Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008