Zobi Fabio, Blacque Olivier, Steyl Gideon, Spingler Bernhard, Alberto Roger
Institute of Inorganic Chemistry, University of Zürich, Switzerland.
Inorg Chem. 2009 Jun 1;48(11):4963-70. doi: 10.1021/ic9002803.
The chemistry of [(tacn)-N-CO-Re(III)(CO)(2)Br]X (X = Cl or Br), obtained in good yield from the reaction of fac-[(tacn)Re(I)(CO)(3)]Br (1, tacn = 1,4,7-triazacyclononane) with X(2) in water, is described. The [(tacn)-N-CO-Re(III)(CO)(2)Br]X complex (2 with X = Br(-); 2a with X = BrCl(2)(-)), which we have previously communicated, is characterized by an unusual three-membered ring acyl amide bond. Complex 2 is stable as a solid but is reactive in aqueous solution. Under basic conditions (1 M NaOH), reductive decarbonylation was observed, and the bis-carbonyl complex [(tacn)Re(I)(CO)(2)Br] (3) was obtained in quantitative yield. The Br(-) ligand in 3 could be replaced by CN(-), giving the neutral complex [(tacn)Re(I)(CO)(2)(CN)] (4). In acidic media (1 M HBr), complex 2 partially converted to the monocarbonyl mu-oxo bridged dinuclear complex {(tacn)Re(III)(CO)BrO}(2+) (5 as PF(6) salt). Under mild oxidative conditions the trioxo (tacn)Re(VII)O(3) (6) was formed almost quantitatively, and small amounts of the uncommon Re(VI) complex (tacn)Re(VI)O(2)Br (7) were identified. Mechanistic investigations at the density functional level of theory (DFT) showed that the elementary steps in the formation of 2 from 1 and 3 from 2 involved reactions of the complexes with hydroxide. The calculated pathway is strongly exothermic (ca. -137 kcal/mol), confirming the energetically and kinetically highly favored formation of 3. The X-ray structures of 2a and 3-5 are reported and discussed.
描述了由fac-[(tacn)Re(I)(CO)₃]Br（1，tacn = 1,4,7-三氮杂环壬烷）与X₂在水中反应以良好产率得到的[(tacn)-N-CO-Re(III)(CO)₂Br]X（X = Cl或Br）的化学性质。我们之前报道过的[(tacn)-N-CO-Re(III)(CO)₂Br]X配合物（X = Br⁻时为2；X = BrCl₂⁻时为2a），其特征是具有不寻常的三元环酰基酰胺键。配合物2作为固体是稳定的，但在水溶液中具有反应活性。在碱性条件（1 M NaOH）下，观察到还原脱羰基反应，以定量产率得到双羰基配合物[(tacn)Re(I)(CO)₂Br]（3）。3中的Br⁻配体可被CN⁻取代，得到中性配合物[(tacn)Re(I)(CO)₂(CN)]（4）。在酸性介质（1 M HBr）中，配合物2部分转化为单羰基μ-氧桥联双核配合物{[(tacn)Re(III)(CO)Br]₂O}²⁺（5为[PF₆]⁻盐）。在温和的氧化条件下，几乎定量地形成了三氧代(tacn)Re(VII)O₃（6），并鉴定出少量不常见的Re(VI)配合物(tacn)Re(VI)O₂Br（7）。在密度泛函理论（DFT）水平上的机理研究表明，从1形成2以及从2形成3的基本步骤涉及配合物与氢氧化物的反应。计算出的反应途径是强烈放热的（约 -137 kcal/mol），证实了3在能量和动力学上都非常有利的形成过程。报道并讨论了2a和3 - 5的X射线结构。
