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Protonation of trans-[Mo(η-MeCCH)(PhPCH CHPPh)]: Mechanism of formation of trans-[MoX(CHCHMe)(PhPCHCHPPh )] (X = Cl or Br) or trans-[MoF(CCHMe)(PhPCHCH PPh)]

Journal of the Chemical Society, Dalton Transactions, ISSN: 1472-7773, Issue: 15, Page: 2479-2487
1995
  • 15
    Citations
  • 0
    Usage
  • 3
    Captures
  • 0
    Mentions
  • 0
    Social Media
Metric Options:   Counts1 Year3 Year

Metrics Details

  • Citations
    15
    • Citation Indexes
      15
  • Captures
    3

Article Description

The reaction between trans-[Mo(η-MeCCH)(PhPCH CHPPh)] and an excess of anhydrous HX (X = Cl or Br) in tetrahydrofuran gives trans-[MoX(CHCHMe)(PhPCHCHPPh )] and the evolution of 1 mol equivalent of MeCCH. Mechanistic studies indicated that initial protonation of trans-[Mo(η-MeCCH)(PhPCH CHPPh)] occurs at a propyne ligand to form the vinyl species, trans-[Mo(CHCHMe)(η-MeCCH)(PhPCHCH PPh)], and at low concentrations of acid rate-limiting dissociation of the other trans-propyne, followed by attack of halide ion at the molybdenum, produces trans-[MoX(CHCHMe)(PhPCHCHPPh )]. At high concentrations of acid further rapid protonation of the vinyl ligand occurs to give trans-[Mo(CHCHMe)(η-MeCCH)(PhPCH CHPPh)]. This second protonation further labilises the trans-propyne which is lost in the rate-limiting step and subsequent attack of halide gives trans-[MoX(CHCHMe)(PhPCHCH PPh)]. Dissociation of a proton gives the product, trans-[MoX(CHCHMe)(PhPCHCHPPh )]. The reaction between trans-[Mo(η-MeCCH)(PhPCH CHPPh)] and HBF·OEt gives a mixture of trans-[MoF(CHCHMe)(PhPCHCHPPh )] and the alkylidyne complex: trans-[MoF(CCHMe)(PhPCHCH PPh)]. The alkylidyne complex has been isolated pure by fractional crystallisation. The factors which discriminate between the formation of the vinyl and alkylidyne species are discussed.

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