The Reversible and Stereoselective N- to C-bonded Rearrangement of Tris(2-pyridylmethyl)-1,4,7-triazacyclononanecobalt(III)
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- 作者：W. Gregory Jackson ; Josephine A. McKeon ; David C. R. Hockless ; and Anthony C. Willis
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：May 15, 2006
- 年：2006
- 卷：45
- 期：10
- 页码：4119 - 4135
- 全文大小：422K
- 年卷期：v.45,no.10(May 15, 2006)
- ISSN：1520-510X
文摘
The hexaaminecobalt(III) complex [Co(tmptacn)]3+ (tmptacn = 1,4,7-tris(2'-pyridylmethyl)-1,4,7-triazacyclononane)undergoes a novel base-catalyzed N- to C-bonded rearrangement in which a tacn nitrogen is displaced by the
rs/alpha.gif" BORDER=0>-carbon which deprotonates and binds to the metal ion as a carbanion. The X-ray structure establishes theconfiguration for the regio- and stereoselectively (100%) formed product. The reaction involves both ring expansionsand ring contraction. The carbanion is part of a strained four-membered ring. The kinetics are reported for the N-to C-rearrangement, shown to be retentive for the optically resolved (+)-[Co(tmptacn)]3+ reactant, and also thekinetics for a competitive and somewhat faster base-catalyzed racemization reaction of this complex. The reactionis completely but very slowly reversed in acid, also with retention, and in D2O/D+ there is 1:1 D-incorporation intothe two sets of inequivalent tacn carbons. Extensive 1D and 2D NMR studies establish mechanistic details, andalternative mechanisms are proposed for the forward and reverse reactions. In neutral solution, there is a competitiveoxidation reaction for the reverse C- to N-bonded process, involving the regio- and stereoselective (100%) incorporationof an rs/alpha.gif" BORDER=0>-OH substituent into the tacn ring.
rs/alpha.gif" BORDER=0>-carbon which deprotonates and binds to the metal ion as a carbanion. The X-ray structure establishes theconfiguration for the regio- and stereoselectively (100%) formed product. The reaction involves both ring expansionsand ring contraction. The carbanion is part of a strained four-membered ring. The kinetics are reported for the N-to C-rearrangement, shown to be retentive for the optically resolved (+)-[Co(tmptacn)]3+ reactant, and also thekinetics for a competitive and somewhat faster base-catalyzed racemization reaction of this complex. The reactionis completely but very slowly reversed in acid, also with retention, and in D2O/D+ there is 1:1 D-incorporation intothe two sets of inequivalent tacn carbons. Extensive 1D and 2D NMR studies establish mechanistic details, andalternative mechanisms are proposed for the forward and reverse reactions. In neutral solution, there is a competitiveoxidation reaction for the reverse C- to N-bonded process, involving the regio- and stereoselective (100%) incorporationof an rs/alpha.gif" BORDER=0>-OH substituent into the tacn ring.