Medium and high oxidation state metal/non-metal fluoride and oxide–fluoride complexes with neutral donor ligands

Abstract

While most high and medium oxidation state (O.S. ≥ 3) metal and non-metal fluorides and oxide fluorides are strong Lewis acids, exploration of their coordination chemistry with neutral ligands has been limited and mostly non-systematic. This is despite the very different properties conferred on the acceptor centre by the small electronegative fluoride ligands compared to the heavier halides. This article sets out these key differences, discusses possible synthetic routes, the key characterisation techniques, and appropriate bonding models. Current knowledge of the coordination chemistry of d, f and p-block fluorides and oxide fluorides with neutral ligands (with donor atoms drawn from Groups 15 and 16 and including N-heterocyclic carbenes) is then presented and discussed, and the differences in properties compared to complexes containing the heavier halides are illustrated. The emphasis is on work published post 1990, but earlier work is also included as essential background and where no more recent information exists. Attention is drawn to unexplored areas meriting investigation and to possible applications of these complexes.

Coordination chemistry of the main group elements with phosphine, arsine and stibine ligands

“…As discussed for aluminium (Section 6.2), other factors sometimes complicate interpretation of Lewis acidity based upon bond length data, but it seems clear in the case of gallium(III) that, apart from a few anomalies, the data indicate an order with halide Cl > Br > I [131,170,171]. Analogous to the aluminium system, GaF 3 is an inert polymer and no soft donor complexes are known [130]. For neutral phosphines and arsines, the gallium(III) overwhelmingly favours distorted tetrahedral four-coordination, and six-coordination is achieved only in some chelating diphosphine adducts.…”

“…Whilst tetrahedral four coordination is still the norm, five-or six-coordination is found in some aluminium complexes. Very few complexes (none with soft donors) are known for AlF 3 , which unlike the molecular BF 3 is an inert fluorine-bridged polymer [130]. Monodentate ER 3 adducts of AlR 3 (R = alkyl) have been thoroughly investigated, but detailed studies of complexes of AlX 3 are surprisingly rare and complexes with bi-and polydentates have received very limited study.…”

“…The complexes are usually prepared by reaction of InX 3 (X = Cl, Br, I) (there are no examples with X = F [130]) with the phosphine + redrawn from Ref. [182].…”

Synthesis and structure of [CeF4(Me2SO)2]—A rare neutral ligand complex of a lanthanide tetrafluoride

“…Although their study was neglected for many years, recent work has revealed an extensive coordination chemistry of early transition metal fluorides, including TiF 4 , ZrF 4 , HfF 4 , NbF 5 , TaF 5 and WF 6 [1]. In marked contrast, the coordination chemistry of lanthanide fluorides is limited to a range of fluorometallate anions, and a few, usually poorly characterised hydrates [1,2].…”

Structural chemistry of fluoride and oxofluoride complexes of titanium(IV)

“…Many fluoride complexes of this type are described in the literature [6]. The chemistry and structure of p-, d-, and f-block metal fluoride and oxofluoride complexes with neutral donor ligands, including TiF 4 complexes with O-and N-donor ligands, were systematized by Benjamin et al [10].…”