Base Hydrolysis of Coordinated Thiophene in (C5R5)Rh(C4Me4S)2+: Nucleophilic Attack at Divalent Sulfur and the Reversible Cleavage of C-S Bonds

Anton E. Skaugset, Thomas B. Rauchfuss, Scott R. Wilson

Research output: Contribution to journalArticlepeer-review

Abstract

This report describes studies on the base hydrolysis of [(C5Me5)Rh(C4Me4S)]2+ (1) which gives an acyl thiolate (C5Me5)Rh(η4-SC3Me3C(O)Me) (2) concomitant with cleavage of one C-S bond (C4Me4S = 2,3,4,5-tetramethylthiophene). The C-S cleavage event involves deprotonation of [(C5Me5)Rh(C4Me4S-2-OH)]+ (3). This cation was prepared by protonation of 2 using HOTf or NH4PF6. The conversion of 2 to 3 is proposed to involve protonation of the carbonyl oxygen followed by intramolecular alkylation of the thiolate ligand. This alkylation was modeled by the addition of MeOTf to 2 to give [(C5Me5)Rh(MeSC3Me3C(O)Me)]OTf (4). Single-crystal X-ray diffraction studies show that both 3 and 4 can be described as η4-thioether allyl complexes of RhIII. Earlier steps in the base hydrolysis reaction were uncovered following the discovery that addition of excess OH to the tetramethylcyclopentadienyl complex [(C5Me4H)Rh(C4Me4S)]2+ gave the S-oxide (C5Me4H)Rh(C4Me4S-1-O), not the acyl thiolate. This S-oxide species reacts with NH4PF6 to give [(C5Me4H)Rh(C4Me4S-2-OH)]OTf, an analog of 3, which in turn deprotonates to give the acyl thiolate (C5Me4H)Rh(SC3Me3C(O)Me), an analog of 2. This conversion establishes that the S-oxide is a kinetic product, less stable thermodynamically than the acyl thiolate isomer. Thus the S-oxide (C5Me5)Rh(η4-C4Me4S-1-O) reacts with NH4PF6 to give 2 and high [OH] favors the conversion of 1 to (C5Me5)Rh(η4-C4Me4S-1-O).

Original languageEnglish (US)
Pages (from-to)8521-8526
Number of pages6
JournalJournal of the American Chemical Society
Volume114
Issue number22
DOIs
StatePublished - Oct 1 1992

ASJC Scopus subject areas

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

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