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⋅(Mes) DAB(Me) ((Mes) DAB(Me) =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 (Mes) DAB(H) ligand ((Mes) DAB(H) =N,N-dimesityl-diazabutadiene) engenders dramatically different reactivity and produces a metallopolymer (InOTf⋅(Mes) DAB(H) )∞ (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 In(I) to the (Mes) DAB(H) 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.

New dihexadecyldithiophosphate SAMs on gold provide insight into the unusual dependence of adsorbate chelation on substrate morphology in SAMs of dialkyldithiophosphinic acids.

We report the formation and characterization of new self-assembled monolayers (SAMs) formed from dihexadecyldithiophosphate (C16)2DDP and compare their properties with those of SAMs formed from the structurally similar adsorbate dihexadecyldithiophosphinic acid (C16)2DTPA. The new (C16)2DDP SAMs were characterized using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, contact angle measurements, and electrochemical impedance spectroscopy. The data indicate that (C16)2DDP forms SAMs on gold films formed by e-beam evaporation in which all adsorbates chelate to gold, in contrast to (C16)2DTPA SAMs, in which 40% of the adsorbates are monodentate. The alkyl chains of the (C16)2DDP SAM are also less densely packed and ordered than those of the (C16)2DTPA SAM. To understand these differences, we present density functional theory calculations that show that there are only minimal differences between the geometric and electronic structures of the two adsorbates and that the energetic difference between monodentate and bidentate binding of a gold(I) ion are surprisingly small for both adsorbates. This study leads to the conclusion that differences in intermolecular interactions within the SAM are the driving force for the difference in chelation between the two adsorbates.