Non-Innocent Ligand Effects on Low-Oxidation-State Indium Complexes

Attempts to coordinate neutral ligands to low oxidation state indium centers are often hindered by disproportionation pathways that produce elemental indium and higher oxidation state species. In contrast, we find that reactions of the salt, InOTf (OTf=trifluoromethanesulfonate), with α‐diimine ligands yielded intensely colored compounds with no evidence of decomposition. X‐ray structural analysis of InOTf⋅MesDABMe (MesDABMe=N,N‐dimesityl‐2,3‐dimethyl‐diazabutadiene; 1) reveals a discrete molecular compound with a pyramidal coordination environment at the indium center, consistent with the presence of a stereochemically active lone pair of electrons on indium and a neutral diazabutadiene chelate ligand. The use of the less‐electron‐rich MesDABH ligand (MesDABH=N,N‐dimesityl‐diazabutadiene) engenders dramatically different reactivity and produces a metallopolymer (InOTf⋅MesDABH)∞ (2) linked via CC and InIn bonds. The difference in reactivity is rationalized by cyclic voltammetry and DFT studies that suggest more facile electron transfer from InI to the MesDABH and bis(aryl)acenaphthenequinonediimine (BIAN) ligands. Solution EPR spectroscopy indicates the presence of non‐interacting ligand‐based radicals in solution, whereas solid‐state EPR studies reflect the presence of a thermally accessible spin triplet consistent with reversible CC bond cleavage. Not so In‐nocent: Insights into the nature of substituent effects in “non‐innocent” α‐diimine ligands are obtained by using unusually stable indium(I) compounds as a probe (see scheme; Mes=mesityl, OTf=trifluoromethanesulfonate, Dipp=2,6‐diisopropylphenyl). The results are derived from investigations that include synthesis, X‐ray crystallography, cyclic voltammetry, EPR spectroscopy, and DFT calculations.