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

[MF4(dmso)(2)] (M = Zr or Hf) and [MF4(dmf)(2)], prepared by dissolving MF4 center dot 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 OPR3 (R = Me or Ph) or OAsPh3 (L) in anhydrous CH2Cl2 to form six-coordinate [MF4L2] which exist as a mixture of cis (predominant form) and trans isomers in CH2Cl2 solution but which crystallise as trans (OPPh3, OAsPh3) or cis (OPMe3) forms. Cis-[ZrF4(OAsPh3)(2)] crystals were obtained from MeCN. Cis-[MF4(pyNO)(2)] and eight-coordinate (distorted dodecahedral) [MF4(L-L)(2)] (L-L = 2,2'-bipy, or 1,10-phen), and [MF4(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-[ZrF4(OPPh3)(2)], cis- and trans-[ZrF4(OAsPh3)(2)], cis-[HfF4(OPMe3)(2)], [ZrF4(2,2'-bipy)(2)], cis-[HfF4(dmf)(2)], and geometric isomers (both pentagonal bipyramidal) of [(dmso)(2)F3M(mu-F)(2)MF3(dmso)(2)]. The failed attempts to make IDiPP adducts led to crystals of [IDiPPH](3)[M3F15] containing discrete anions based upon a triangle of M atoms with single F bridges. The results are compared with previous work on TiF4 adducts and with complexes of MCl4, and demonstrate that the MF4 are very hard Lewis acids, with a marked preference for O- over N-donors.