One-electron oxidation of paramagnetic chromium(II) alkyl complexes with alkyl halides: Synthesis and structure of five-coordinate chromium(III) complexes

Michael D. Fryzuk, Daniel B. Leznoff, Steven J. Rettig, Victor G. Young

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33 Scopus citations

Abstract

The reaction of square-planar, high-spin CrR[N(SiMe2CH2PPh2)2] (R = Me, CH2SiMe3) with alkyl halides (MeI, CF3CH2I, MeBr, PhCH2Cl) generates one-electron oxidation products Cr(R)X[N(SiMe2CH2PPh2)2], unusual examples of five-coordinate chromium(III) complexes. Cr(Me)Br[N(SiMe2CH2PPh2)2] and Cr(CH2SiMe3)Cl[N-(SiMe2CH2PPh 2)2] have been structurally characterized. Alkylation of the latter complex with LiCH2SiMe3 gave a five-coordinate Cr(III) dialkyl complex Cr(CH2SiMe3)2[N(SiMe2CH 2PPh2)2], which was structurally characterized as well. Attempts to isolate sterically unencumbered Cr(III) dialkyl (e.g., dimethyl) complexes resulted in decomposition. Addition of an excess of PhCH2Cl to {[(Ph2PCH2SiMe2)2N]Cr} 2(μ-Cl)2 resulted in halide-transfer to form CrCl2(THF)[N(SiMe2CH2PPh2) 2] in low yield. Reaction of the low-spin CrCp[N(SiMe2CH2PPh2)2] complex with PhCH2Cl, however, gave both Cr(Cp)(CH2Ph)[N(SiMe2CH2PPh2) 2] and Cr(Cp)Cl[N(SiMe2CH2PPh2)2]. The five-coordinate Cr(III) alkyl halide complexes do not polymerize ethylene at 60°C and 1 atm; the dialkyl complex Cr(CH2SiMe3)2[N(SiMe2CH 2PPh2)2] does catalyze polyethylene formation but is quickly deactivated. A discussion comparing the structural distortions observed in these five-coordinate high-spin d3 Cr(III) complexes with those observed in the analogous low-spin d6 Ir(III) complexes is presented.

Original languageEnglish (US)
Pages (from-to)147-154
Number of pages8
JournalJournal of the Chemical Society - Dalton Transactions
Issue number2
DOIs
StatePublished - Jan 21 1999

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