Synthesis, X-ray Crystal Structure, and Phosphine-Exchange Reactions of the Hafnium(III)-Hafnium(III) Dimer Hf2Cl6(PEt3)4

Matthew E. Riehl, Scott R. Wilson, Gregory S Girolami

Research output: Contribution to journalArticlepeer-review

Abstract

Reduction of HfCl4 with sodium-potassium alloy in the presence of PEt3 yields the dark green hafnium(III)-hafnium(III) dimer Hf2Cl6(PEt3)4. The X-ray crystal structure shows that molecules of Hf2Cl6(PEt3)4 consist of two octahedral hafnium centers that are connected by a hafnium-hafnium bond and two bridging chloride ligands. The two independent molecules in the unit cell have slightly different structures due to differences in the relative orientations of the ethyl groups of the PEt3 ligands. In both molecules, the PEt3 groups are trans to the bridging chloride ligands. Average distances and angles for the two independent molecules: Hf-Hf = 3.097 (1) and 3.118 (1) Å, Hf-P = 2.748 (2) and 2.761 (2) Å, Hf-Clt = 2.417 (2) and 2.415 (2) Å, Hf-Clb = 2.533 (2) and 2.538 (2) Å, Hf-Clb-Hf = 75.38 (5) and 75.78 (4)°, Clb-Hf-Clb = 104.62 (5) and 104.22 (5)°, Cl,-Hf-Clt = 165.75 (6) and 165.33 (6)°, and P-Hf-P = 92.67 (5) and 98.95 (6)°. The triethylphosphine complex undergoes exchange with trimethylphosphine to afford successively the complexes Hf2Cl6(PEt3)3(PMe3), Hf2Cl6(PEt3)2(PMe3)2, Hf2-Cl6(PEt3)(PMe3)3, and Hf2Cl6(PMe3)4; two of the three possible isomers of Hf2Cl6(PEt3)2(PMe3)2 are formed. The sequential replacement of PEt3 groups by PMe3 was followed by 31P{1H} NMR spectroscopy. Interestingly, the JPP coupling constants for phosphorus nuclei attached to different hafnium centers are <2 Hz, while the JPP coupling constants for adjacent phosphines are small at 3–4 Hz. Crystal data for Hf2Cl6(PEt3)4 at−75 °C: monoclinic, space group P21/c, with a = 10.256 (4) Å,b= 18.787 (8) Å, c = 20.275 (6) Å, β = 94.52 (3)°, V = 3894 (4) Å3, Z = 4, RF = 0.028, and RwF = 0.035 for 326 variables and 5081 data with I > 2.58σ(I).

Original languageEnglish (US)
Pages (from-to)218-222
Number of pages5
JournalInorganic Chemistry
Volume32
Issue number2
DOIs
StatePublished - Jan 1 1993

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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