An EPR and ENDOR investigation of a series of diazabutadiene-group 13 complexes

Paramagnetic diazabutadienegallium(II or III) complexes, [(Ar-DAB)(2)Ga] and [{(Ar-DAB(.))GaX}(2)] (X = Br or I; Ar-DAB = {N(Ar)C(H)}(2), Ar = 2,6-diisopropylphenyl), have been prepared by reactions of an anionic gallium N-heterocyclic carbene analogue, [K(tmeda)][:Ga(Ar-DAB)], with either "GaI" or [MoBr2(CO)(2)(PPh3)(2)]. A related In-III complex, [(Ar-DAB(.))InCl2(thf)], has also been prepared. These compounds were characterised by X-ray crystallography and EPR/ENDOR spectroscopy. ne EPR spectra of all metal(m) complexes incorporating the Ar-DAB ligand, [(Ar-DAB(.))MX2(thf)(n)] (M = Al, Ga or In; X = Cl or I; n = 0 or 1) and [(Ar-DAB)(2)Ga], confirmed that the unpaired spin density is primarily ligand centred, with weak hyperfine couplings to Al (a = 2.85 G), Ga (a = 17-25 G) or In (a = 26.1 G) nuclei. Changing the N substituents of the diazabutadiene ligand to tert-butyl groups in the gallium complex, [(tBu-DAB(.))GaI2] (tBu-DAB = {N(tBu)C(H)}(2)), changes the unpaired electron spin distribution producing H-1 and N-14 couplings of 1.4 G and 8.62 G, while the aryl-substituted complex, [(Ar-DAB(.))GaI2], produces couplings of about 5.0 G. These variations were also manifested in the gallium couplings, namely a(Ga) similar to 1.4 G for [(tBu-DAB(.))GaI2] and a(Ga) similar to 25 G for [(Ar-DAB(.))GaI2]. The EPR spectra of the gallium(II) and indium(II) diradical complexes, [{(Ar-DAB(.))GaBr}(2)], [{(Ar-DAB(.))GaI}(2)], [{(tBu-DAB(.))GaI}(2)] and [{(Ar-DAB(.))InCl}(2)], revealed doublet ground states, indicating that the Ga-Ga and In-In bonds prevent dipole-dipole coupling of the two unpaired electrons. The EPR spectrum of the previously reported complex, [(Ar-BIAN(.))GaI2] (Ar-BIAN = bis(2,6-diiso-propylphenylimino)acenaphthene) is also described. The hyperfine tensors for the imine protons, and the aryl and tert-butyl protons were obtained by ENDOR spectroscopy. In [(Ar-DAB(.))-GaI2], gallium hyperfine and quadrupolar couplings were detected for the first time.