The ketimide ligand, R2C=N-, has been employed, by the Hayton group and others, for the preparation of a wide series both f and d block complexes. In particular, there exists by now a series of homoleptic d block complexes of general formula M(N=CR2)4, where M = Ti, V, Nb, Ta, Cr, Mo, W, Mn, Fe, and Co; R = tert-butyl (most commonly) or phenyl and other aliphatic or aryl groups. It is relatively rare to have such an extensive series, across a period and across groups, of homoleptic complexes. Such a series allows the ketimide ligand to be characterized in terms of its σ-donor and π-donor and π-acceptor abilities. Particularly informative for this purpose and for overall understanding of these M(N=CR2)4 complexes is the application of electron paramagnetic resonance (EPR) spectroscopy to those that are paramagnetic. This is the case for M = V, Nb, and Ta (nd1, S = 1/2) and for M = Mn (nd3) which also has spin doublet (S = 1/2) ground state, and is thus a rare example of a low-spin d3 electronic configuration - especially for only four-coordination. We will describe how electronic absorption and EPR spectroscopies, in combination with ligand-field theory and computational methods (DFT) provide a complete picture of the electronic structure of the Group 5 (see figure of HOMO for V(IV) complex) and Mn ketimide complexes. In addition, Mössbauer studies of the diamagnetic Fe(IV) (3d4) complex including computational analysis will be described. These studies show the unique ability of the ketimide ligand as a strong σ-donor, a moderate π-donor, and, most importantly, a strong π-acceptor.

Synthetic, spectroscopic, and computational studies of tetraketimide complexes with an emphasis on Group 5

251st National Meeting (2016)

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