Synthesis and characterization of the octahydrotriborate complexes Cp*V(B3H8)2 and Cp*Cr(B 3H8)2 and the unusual cobaltaborane cluster Cp*2Co2(B6H14)

Do Young Kim, Gregory S. Girolami

Research output: Contribution to journalArticlepeer-review

Abstract

The new compounds Cp*V(B3H8)2, Cp*Cr(B3H8)2, and Cp*2Co 2(B6H14) have been synthesized by treating the pentamethylcyclopentadienyl complexes [Cp*VCl2] 3,[Cp*CrCl2]2, and [Cp*CoCl] 2 with NaB3H8. X-ray crystallography shows that Cp*V(B3H8)2 and Cp*Cr(B 3H8)2 have the same ligand sets but different molecular structures: the vanadium compound contains two bidentate B 3H8 ligands (i.e., bound to the metal center via two vicinal hydrogen atoms), whereas the chromium compound has one bidentate B 3H8 ligand and one B3H8 ligand bound in an unprecedented fashion via two geminal hydrogen atoms. The "gem-bound" B3H8 group itself has an atypical structure consisting of a BH2-BH2-BH3 triangle with one additional hydrogen atom bridging the unique BH2-BH 2 edge. The B-B distances are nearly identical within experimental error at 1.790(5), 1.792(5), and 1.786(6) Å. The relationship between the electronic and molecular structures of the V and Cr compounds is briefly discussed. The structure of Cp*2Co2(B 6H14) can be viewed in two different ways: as a dicobalt complex in which two Cp*Co units are each bound to four adjacent boron atoms of an S-shaped B6H14 ligand, or as an eight-vertex hypho cluster compound. In the former case, the B6H14 ligand is best regarded as a dianionic bi-borallyl group H3B(μ-H) BH(μ-H)-BHBH(μ-H)BH(μ-H)BH3 in which one hydrogen at each end of the chain is involved in an agostic interaction. From a cluster point of view, the structure of Cp*2Co2(B6H 14) can be generated by removing three adjacent high-connectivity vertices from the eleven-vertex closo polyhedron. The Co-B distances vary from 2.008(5) to 2.183(4) Å, and the B-B distances within in the S-shaped chain range from 1.734(8) to 1.889(6) Å. Finally, a new synthesis of the known molybdenum compound Cp*2Mo2(B5H 9) is described; its structure as established by X-ray crystallography closely resembles that of the previously described (C 5H4Me) analogue.

Original languageEnglish (US)
Pages (from-to)10969-10977
Number of pages9
JournalJournal of the American Chemical Society
Volume128
Issue number33
DOIs
StatePublished - Aug 23 2006

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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