PCP Pincer Complexes of Titanium in the +3 and +4 Oxidation States.

Ti(IV) and Ti(III) complexes using the tBuPCP ligand have been synthesized (tBuPCP = C6H3-2,6-(CH2PtBu2)2). The [tBuPCP]Li synthon can be reacted with TiCl4(THF)2 to form (tBuPCP)TiCl3 (1) in limited yields due to significant reduction of the titanium synthon. The Ti(III) complex (tBuPCP)TiCl2 (2) has been further characterized. This can have half an equivalent of halide abstracted to form [{(tBuPCP)TiCl}2{µ-Cl}][B(C6F5)4] (3) and can also be methylated, forming (tBuPCP)TiMe2 (4). All the Ti(III) complexes have been characterized using EPR and X-ray crystallography, giving insight into their electronic structures, which are further supported by DFT calculations.

Sigma/pi Bonding Preferences of Solvated Alkali-Metal Cations to Ditopic Arylmethyl Anions.

Arylmethyl anions allow alkali-metals to bind in a σ-fashion to the lateral carbanionic centre or a π-fashion to the aryl ring or in between these extremities, with the trend towards π bonding increasing on descending group 1. Here we review known alkali metal structures of diphenylmethane, fluorene, 2-benzylpyridine and 4-benzylpyridine. Next, we synthesise Li, Na, K monomers of these diarylmethyls using polydentate donors PMDETA or Me6 TREN to remove competing oligomerizing interactions, studying the effect that two aromatic rings has on negative charge (de)localisation via NMR, X-ray crystallographic and DFT studies. Diphenylmethyl and fluorenyl anions maintain C(H)-M interactions regardless of alkali-metal, although the adjacent arene carbons engage in interactions with larger alkali-metals. Introducing a nitrogen atom into the ring (at the 2- or 4-position) encourages relocalisation of negative charge away from the deprotonated carbon and onto nitrogen. Phenyl(2-pyridyl)methyl moves from an enamide formation at one extremity (lithium) to an aza-allyl formation at the other extremity (potassium), while C- or N-coordination modes become energetically viable for Na and K phenyl(4-pyridyl)methyl complexes.

Reversible Dissociation of a Dialumene*.

Dialumenes are neutral AlI compounds with Al=Al multiple bonds. We report the isolation of an amidophosphine-supported dialumene. Our X-ray crystallographic, spectroscopic, and computational DFT analyses reveal a long and extreme trans-bent Al=Al bond with a low dissociation energy and bond order. In solution, the dialumene can dissociate into monomeric AlI species. Reactivity studies reveal two modes of reaction: as dialumene or as aluminyl monomers.