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[MF4(dmso)2] (M = Zr or Hf) and [MF4(dmf)2], prepared by dissolving MF4·nH2O 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(Me4-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)2F3M(μ-F)2MF3(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.
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