Diphosphiranium (P2C) or Diphosphetanium (P2C2) Cyclic Cations: Different Fates for the Electrophile-Initiated Cyclodimerization of a Phosphaalkene

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• 作者：Joshua I. Bates ; Derek P. Gates
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：December 20, 2006
• 年：2006
• 卷：128
• 期：50
• 页码：15998 - 15999
• 全文大小：58K
• 年卷期：v.128,no.50(December 20, 2006)
• ISSN：1520-5126

文摘

The synthesis and crystallographic characterization of two new classes of cationic three- and four-membered organophosphorus heterocycles are reported. Treating phosphaalkene ^tBuP=CH^tBu (1) with triflic acid (2:1) afforded an unprecedented asymmetric diphosphiranium triflate [^tBuP-CH(^tBu)-P(^tBu)(CH₂^tBu)]OTf (2). Surprisingly, the analogous reaction of ^tBuP=CH^tBu with methyl triflate (2:1) afforded a 1,3-diphosphetanium salt [^tBu(Me)P-CH(^tBu)-P(^tBu)-CH(^tBu)]OTf (3a). Structural characterization of these novel P₂C and P₂C₂ rings confirmed their identity, and the metrical parameters were consistent with the strain expected for these ring systems. In preliminary mechanistic investigations by NMR spectroscopy, phosphenium species [^tBuPCH₂^tBu]OTf (4) was detected in the stoichiometric reaction of 1 with HOTf while methylenephosphonium [Me(^tBu)P=CH^tBu]OTf (5) was observed when 1 was treated with MeOTf. The opposite reactivity observed when the P=C bond is treated with MeOTf compared that with HOTf is surprising and, to our knowledge, has not been observed previously in phosphaalkene chemistry. In addition to their fundamental interest, we are interested in these species as ring-closed forms of the propagating species in the cationic polymerization of P=C bonds.