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

Benjamin, Sophie L., Levason, William, Pugh, David, Reid, Gillian and Zhang, Wenjian (2012) Preparation and structures of coordination complexes of the very hard Lewis acids ZrF4 and HfF4. Dalton Transactions, 41 (40), 12548-12557. (doi:10.1039/c2dt31501g).

Abstract

[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(?-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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Contributors

Author: William Levason

Author: Gillian Reid

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