Abstract
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 [MoBr~2~(CO)~2~(PPh~3~)~2~]. A related In^III^ complex, [(Ar‐DAB^.^)InCl~2~(thf)], has also been prepared. These compounds were characterised by X‐ray crystallography and EPR/ENDOR spectroscopy. The EPR spectra of all metal(III) complexes incorporating the Ar‐DAB ligand, [(Ar‐DAB^.^)MX~2~(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, [(__t__Bu‐DAB^.^)GaI~2~] (__t__Bu‐DAB={N(__t__Bu)C(H)}~2~), changes the unpaired electron spin distribution producing ^1^H and ^14^N couplings of 1.4 G and 8.62 G, while the aryl‐substituted complex, [(Ar‐DAB^.^)GaI~2~], produces couplings of about 5.0 G. These variations were also manifested in the gallium couplings, namely a~Ga~ ∼1.4 G for [(__t__Bu‐DAB^.^)GaI~2~] and a~Ga~ ∼25 G for [(Ar‐DAB^.^)GaI~2~]. The EPR spectra of the gallium(II) and indium(II) diradical complexes, [{(Ar‐DAB^.^)GaBr}~2~], [{(Ar‐DAB^.^)GaI}~2~], [{(__t__Bu‐DAB^.^)GaI}~2~] and [{(Ar‐DAB^.^)InCl}~2~], revealed doublet ground states, indicating that the GaGa and InIn bonds prevent dipole–dipole coupling of the two unpaired electrons. The EPR spectrum of the previously reported complex, [(Ar‐BIAN^.^)GaI~2~] (Ar‐BIAN=bis(2,6‐diisopropylphenylimino)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^.^)GaI~2~], gallium hyperfine and quadrupolar couplings were detected for the first time.