title: Quantifying the Electron Donor and Acceptor Abilities of the Ketimide Ligands in M(N═C(t)Bu2)4 (M = V, Nb, Ta).
abstract: Addition of 4 equiv of Li(N═C(t)Bu2) to VCl3 in THF, followed by addition of 0.5 equiv of I2, generates the homoleptic V(IV) ketimide complex, V(N═C(t)Bu2)4 (1), in 42% yield. Similarly, reaction of 4 equiv of Li(N═C(t)Bu2) with NbCl4(THF)2 in THF affords the homoleptic Nb(IV) ketimide complex, Nb(N═C(t)Bu2)4 (2), in 55% yield. Seeking to extend the series to the tantalum congener, a new Ta(IV) starting material, TaCl4(TMEDA) (3), was prepared via reduction of TaCl5 with Et3SiH, followed by addition of TMEDA. Reaction of 3 with 4 equiv of Li(N═C(t)Bu2) in THF results in the isolation of a Ta(V) ketimide complex, Ta(Cl)(N═C(t)Bu2)4 (5), which can be isolated in 32% yield. Reaction of 5 with Tl(OTf) yields Ta(OTf)(N═C(t)Bu2)4 (6) in 44% yield. Subsequent reduction of 6 with Cp*2Co in toluene generates the homoleptic Ta(IV) congener Ta(N═C(t)Bu2)4 (7), although the yields are poor. All three homoleptic group 5 ketimide complexes exhibit squashed tetrahedral geometries in the solid state, as determined by X-ray crystallography. This geometry leads to a d(x(2)-y(2))(1) ((2)B1 in D(2d)) ground state, as supported by DFT calculations. EPR spectroscopic analysis of 1 and 2, performed at X- and Q-band frequencies (∼9 and 35 GHz, respectively), further supports the (2)B1 ground-state assignment, whereas comparison of 1, 2, and 7 with related group 5 tetra(aryl), tetra(amido), and tetra(alkoxo) complexes shows a higher M-L covalency in the ketimide-metal interaction. In addition, a ligand field analysis of 1 and 2 demonstrates that the ketimide ligand is both a strong π-donor and strong π-acceptor, an unusual combination found in very few organometallic ligands.
authors.affiliation: Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Damon
authors.affiliation: Department of Biological, Chemical and Physical Sciences, Roosevelt University , 430 South Michigan Avenue, Chicago, Illinois 60605-1394, United States.
authors.forename: Cameron J
authors.initials: CJ
authors.lastname: Liss
authors.affiliation: Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Lewis
authors.affiliation: Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors.forename: Simona
authors.initials: S
authors.lastname: Morochnik
authors.affiliation: Department of Biological, Chemical and Physical Sciences, Roosevelt University , 430 South Michigan Avenue, Chicago, Illinois 60605-1394, United States.
authors.forename: David E
authors.initials: DE
authors.lastname: Szpunar
authors.affiliation: Department of Biological, Chemical and Physical Sciences, Roosevelt University , 430 South Michigan Avenue, Chicago, Illinois 60605-1394, United States.
authors.forename: Joshua
authors.initials: J
authors.lastname: Telser
authors.affiliation: Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States.
authors.forename: Trevor W
authors.initials: TW
authors.lastname: Hayton
mesh_terms: D018360:Crystallography, X-Ray; D004583:Electrons; D007094:Imides / Q000737:chemistry*; D008024:Ligands; D019216:Metals, Heavy / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D007094:Imides; D008024:Ligands; D019216:Metals, Heavy; D009942:Organometallic Compounds