Interaction of TiF 4 with the donor solvents SO 2, PhCN, and MeCN : Isolation and structural characterization of the first trimeric fluorine bridged donor–acceptor adduct {TiF 4(PhCN)} 3

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The trinuclear {TiF 4 (PhCN)} 3 complex is the first fully characterized example of a {TiF 4 L} n donor adduct and the first structurally characterized trimeric pseudo pentahalide MX 4 L (M = Ti, Zr, X = halogen, L = ligand). There has been speculations on the structures of TiF 4 polymeric complexes {TiF 4 L} n (L = molecular donor) for several decades, however no structurally characterized examples have been reported. In this work the complex {TiF 4 (PhCN)} 3 was isolated from a solution of TiF 4 in PhCN (donor number DN = 11.9 kcal mol −1 ) as well as from the mixtures PhCN/CH 2 Cl 2 and PhCN/toluene and characterized by X-ray, IR, NMR, EI-MS. The structure of the complex {TiF 4 (PhCN)} 3 can be regarded as formed by combining three face -TiF 3 (PhCN)( μ -F) units, containing octahedrally coordinated titanium centers surrounded by three terminal fluorine atoms on the face of the octahedron and the bridging fluorine atoms in cis -positions with respect to each other. The structure of {TiF 4 (PhCN)} 3 represents the first example of a trimeric pseudo pentahalide MX 4 L (M = Ti, Zr, X = halogen, D = ligand), a class of potentially interesting Lewis acids. The characterization of {TiF 4 (PhCN)} 3 by 19 F NMR revealed that in solution it dissociated to a mixture of [TiF 3 (PhCN) 3 ] + , TiF 4 (PhCN) 2 and oligomers including [Ti 4 F 18 ] 2− and {TiF 4 (PhCN)} n . The existence of oligomeric complexes containing face -{TiF 3 (PhCN) 3− n ( μ -F) n } ( n = 1–3) fragments was established by one- and two-dimensional variable temperature 19 F NMR. In contrast, TiF 4 has a low solubility in SO 2 , because the donor strength of SO 2 (DN = 6.5 ± 2.2 kcal mol −1 ) is too weak to fully convert polymeric TiF 4 into soluble TiF 4 –SO 2 donor–acceptor adducts. TiF 4 and MeCN (DN = 14.1 kcal mol −1 ) formed only the molecular complex TiF 4 (MeCN) 2 , characterized by preliminary X-ray structure, IR and EI-MS. Thus mononuclear donor–acceptor complexes TiF 4 L 2 can only be isolated from MeCN and stronger basic solvents.