Synthesis and characterization of new titanium(II) carbonyls of stoichiometry TiX2(CO)2(dmpe)2: an NMR study

Michael D. Spencer, Gregory S. Girolami

Research output: Contribution to journalArticle

Abstract

The titanium(II) coordination complexes trans-TiX2(dmpe)2 (X Cl, Br) react with carbon monoxide at low temperatures to afford thermally unstable eight-coordinate titanium(II) dicarbonyl complexes of stoichiometry TiX2(CO)2 (dmpe)2. The stoichiometries have been established from NMR studies; if 13CO is employed, the NMR spectra correpond to the X and AB parts of AA′BB′XX′ spin systems in the 13C{H} and 31P{1H} NMR spectra, respectively. Treatment of the mixed halide complex TiClBr(dmpe)2 with CO gives the corresponding dicarbonyl complex TiClBr(CO)2(dmpe)2, which exhibits an ABCD spin system in its 31P{H}-NMR spectrum. The phosphorus-phosphorus, phosphorus-carbon, and carbon-carbon coupling constants for TiCl2(CO)2(dmpe)2, TiBr2(CO)2(dmpe)2, and TiBrCl(CO)2(dmpe)2 suggest that these complexes adopt bi-capped octahedral structures, with the halide ligands in the capping sites and the carbonyl ligands mutually cis. When cold (-78°C) solutions of TiC exposed to carbon monoxide for short periods, an intermediate is detectable that slowly converts to TiCl2(CO)2(dmpe)2. The intermediate contains one bidentate and one unidentate dmpe ligand as judged from its 31P{1H} NMR spectrum. There are two equal- intensity 13C NMR resonances for the bound carbonyl groups at δ 453.6 and 456.7; these chemical shifts are quite unusual and are among the largest measured for any 13C nucleus. Taken together, the data suggest that this intermediate is a 16-electron seven-coordinate complex of stoichiometry TiCl2 (CO)2(dmpe)(n1-dmpe).

Original languageEnglish (US)
Pages (from-to)99-106
Number of pages8
JournalJournal of Organometallic Chemistry
Volume483
Issue number1-2
DOIs
StatePublished - Dec 13 1994

Keywords

  • Carbon-13
  • Carbonyl
  • Group 4
  • NMR
  • Phosphine complexes
  • Titanium

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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