title: Rhenium oxo complexes of a chelating diyne ligand. Synthesis and study of the kinetics of protonation.
abstract: A series of oxo complexes, Re(O)X(diyne) (X = I, Me, Et), have been prepared from 2,7-nonadiyne and Re(O)I(3)(PPh(3))(2). Addition of B(C(6)F(5))(3) to Re(O)I(2,7-nonadiyne) (5) results in coordination of the oxo ligand to the boron. The protonation of Re(O)(X)(2-butyne)(2) and Re(O)(X)(2,7-nonadiyne)(2) with a variety of acids has been examined. With 5 and HBF(4)/Et(2)O, the ultimate product was [Re(CH(3)CN)(3)(I)(2,7-nonadiyne)](2+) (7). The conversion of 5 to 7 changes the conformation of the diyne ligand from a "chair" to a "boat" and shifts its propargylic protons considerably downfield in the (1)H NMR. The kinetics of the protonation of Re(O)I(2,7-nonadiyne) (5) by CF(3)SO(3)H in CH(3)CN have been monitored by visible spectroscopy, in a stopped-flow apparatus, and by low temperature (1)H NMR. Two second-order rate constants, presumably successive protonations, were observed in the stopped-flow, k(1) = 11.9 M(-)(1) s(-)(1) and k(2) = 3.8 M(-)(1) s(-)(1). Low temperature (1)H NMR spectroscopy indicated that the resulting solution contained a mixture of two doubly protonated intermediates X and Y, each of which slowly formed the product 7 via an acid-independent process.
authors.affiliation: Department of Chemistry, Columbia University, Havemeyer Hall, 3000 Broadway, New York, NY 10027, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Han
authors.forename: C J
authors.initials: CJ
authors.lastname: Harlan
authors.forename: P
authors.initials: P
authors.lastname: Stoessel
authors.forename: B J
authors.initials: BJ
authors.lastname: Frost
authors.forename: J R
authors.initials: JR
authors.lastname: Norton
authors.forename: S
authors.initials: S
authors.lastname: Miller
authors.forename: B
authors.initials: B
authors.lastname: Bridgewater
authors.forename: Q
authors.initials: Q
authors.lastname: Xu