title: Formation and reactivity of [(tacn)-N-CO-Re(III)Br(CO)(2)](+) in water: a theoretical and experimental study.
abstract: 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)Br](2)O}(2+) (5 as [PF(6)](-) salt). Under mild oxidative conditions the trioxo [(tacn)Re(VII)O(3)](ReO(4)(-)) (6) was formed almost quantitatively, and small amounts of the uncommon Re(VI) complex [(tacn)Re(VI)O(2)Br](ReO(4)(-)) (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.
authors.affiliation: Institute of Inorganic Chemistry, University of Zürich, Switzerland. fzobi@aci.uzh.ch
authors.forename: Fabio
authors.initials: F
authors.lastname: Zobi
authors.forename: Olivier
authors.initials: O
authors.lastname: Blacque
authors.forename: Gideon
authors.initials: G
authors.lastname: Steyl
authors.forename: Bernhard
authors.initials: B
authors.lastname: Spingler
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
mesh_terms: D003198:Computer Simulation; D018360:Crystallography, X-Ray; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D014867:Water