title: The chemistry of the fac-[Re(CO)2(NO)]2+ fragment in aqueous solution.
abstract: The anions [ReX3(CO)2(NO)]- (with X = Cl, 1; X = Br, 2) have been prepared with different counterions. Complex 1 was found to lose its chloride ligands in water within 24 h. The [Re(H2O)3(CO)2(NO)]2+ cation obtained after hydrolysis is a strong acid, which consequently undergoes a slow condensation reaction in water to form the very stable [Re(mu3-O)(CO)2(NO)]4 cluster 4 at pH > 2, that precipitates from the aqueous solution and is insoluble also in organic solvents. Fast deprotonation of [Re(H2O)3(CO)2(NO)]2+ did not lead to 4 but rather to the mononuclear species [Re(OH)(H2O)2(CO)2(NO)]+. Subsequent attack of OH- at a CO group resulted in the formation of a rhenacarboxylic acid and its carboxylate anion. For solutions of even higher pH, IR spectroscopy provided evidence for the formation of a Re(C(O)ON(O)) species. These processes were found to be reversible on lowering the pH. Starting from cluster 4 it was possible to obtain complexes of the types [ReX(CO)2(NO)L2] or [Re(CO)2(NO)L3](L2 = 2-picolinate, 2,2'-bipyridine, L-phenylalanate; L3 = tris(pyrazolyl)methane, 1,4,7-trithiacyclononane) in the presence of an acid in protic solvents, but only in low yields. In further synthetic studies, complexes 1 and 2 were found to be superior starting materials for substitution reactions to form [ReX(CO)2(NO)L2] or [Re(CO)2(NO)L3] complexes.
authors.affiliation: Anorganisch-chemisches Institut, Universität Zurich, Winterthurerstr. 190, CH-8057, Zurich, Switzerland.
authors.forename: Philipp
authors.initials: P
authors.lastname: Kurz
authors.forename: Dirk
authors.initials: D
authors.lastname: Rattat
authors.forename: Daniela
authors.initials: D
authors.lastname: Angst
authors.forename: Helmut
authors.initials: H
authors.lastname: Schmalle
authors.forename: Bernhard
authors.initials: B
authors.lastname: Spingler
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
authors.forename: Heinz
authors.initials: H
authors.lastname: Berke
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Beck
mesh_terms: D009942:Organometallic Compounds / Q000737:chemistry*; D011522:Protons; D012211:Rhenium / Q000737:chemistry*; D012996:Solutions
chemical_list: D009942:Organometallic Compounds; D011522:Protons; D012996:Solutions; D012211:Rhenium