Taking TiF4 complexes to extremes - the first examples with phosphine co-ligands

Abstract

The first soft donor adducts of TiF₄, [TiF₄(diphosphine)] (diphosphine = o-C₆H₄(PMe₂)₂, R₂P(CH₂)₂PR₂, R = Me or Et) have been prepared from [TiF₄(MeCN)₂] and the diphosphines in rigorously anhydrous CH₂Cl₂, as extremely moisture sensitive yellow solids, and characterised by multinuclear NMR (¹H, ³¹P, ¹⁹F), IR and UV/vis spectroscopy. The crystal structure of [TiF₄{Et₂P(CH₂)₂PEt₂}] has been determined and shows a distorted six-coordinate geometry with disparate Ti–F_transF and Ti–F_transP distances and long Ti–P bonds. Weaker soft donor ligands including Ph₃P, Ph₂P(CH₂)₂PPh₂, o-C₆H₄(PPh₂)₂, Ph₂As(CH₂)₂AsPh₂, o-C₆H₄(AsMe₂)₂ and ⁱPrS(CH₂)₂SⁱPr do not form stable complexes with TiF₄, although surprisingly, fluorotitanate(IV) salts of the previously unknown doubly protonated ligand cations [LH₂][Ti₄F₁₈] (L = o-C₆H₄(PPh₂)₂, o-C₆H₄(AsMe₂)₂ and ⁱPrS(CH₂)₂SⁱPr) are formed in some cases as minor by-products. The structure of [o-C₆H₄(PPh₂H)₂][Ti₄F₁₈] shows the first authenticated example of a diprotonated o-phenylene-diphosphine. The synthesis and full spectroscopic characterisation are reported for a range of TiF₄ adducts with hard N– or O-donor ligands for comparison purposes, along with crystal structures of [TiF₄(thf)₂], [TiF₄(Ph₃EO)₂]·2CH₂Cl₂ (E = P or As), and [TiF₄(bipy)].