Preparation and structures of coordination complexes of the very hard Lewis acids ZrF4 and HfF4.

[MF(4)(dmso)(2)] (M = Zr or Hf) and [MF(4)(dmf)(2)], prepared by dissolving MF(4)·nH(2)O in the appropriate solvent, have been used as synthons for a range of complexes of these otherwise intractable tetrafluorides. These reagents react with OPR(3) (R = Me or Ph) or OAsPh(3) (L) in anhydrous CH(2)Cl(2) to form six-coordinate [MF(4)L(2)] which exist as a mixture of cis (predominant form) and trans isomers in CH(2)Cl(2) solution but which crystallise as trans (OPPh(3), OAsPh(3)) or cis (OPMe(3)) forms. Cis-[ZrF(4)(OAsPh(3))(2)] crystals were obtained from MeCN. Cis-[MF(4)(pyNO)(2)] and eight-coordinate (distorted dodecahedral) [MF(4)(L-L)(2)] (L-L = 2,2'-bipy, or 1,10-phen), and [MF(4)(Me(4)-cyclam)] were also obtained. Attempts to prepare complexes with the N-heterocyclic carbene, 1,3-(2,6-di-isopropylphenyl)imidazol-2-ylidene (IDiPP) or alkyl diphosphines were unsuccessful. Crystal structures are reported for trans-[ZrF(4)(OPPh(3))(2)], cis- and trans-[ZrF(4)(OAsPh(3))(2)], cis-[HfF(4)(OPMe(3))(2)], [ZrF(4)(2,2'-bipy)(2)], cis-[HfF(4)(dmf)(2)], and geometric isomers (both pentagonal bipyramidal) of [(dmso)(2)F(3)M(μ-F)(2)MF(3)(dmso)(2)]. The failed attempts to make IDiPP adducts led to crystals of [IDiPPH](3)[M(3)F(15)] containing discrete anions based upon a triangle of M atoms with single F bridges. The results are compared with previous work on TiF(4) adducts and with complexes of MCl(4), and demonstrate that the MF(4) are very hard Lewis acids, with a marked preference for O- over N-donors.