Synthesis and Chemistry of Zwitterionic Tantala-3-boratacyclopentenes: Olefin-like Reactivity of a Borataalkene Ligand

Citations Over TimeTop 14% of 2002 papers

Abstract

The compounds, where Cp' = C(5)H(5), a series, and C(5)H(4)Me, b series, are generated via treatment of with HB(C(6)F(5))(2). When allowed to undergo irreversible methane loss in the presence of an excess of the sterically modest alkynes 2-butyne or phenylacetylene, the putative intermediates 1a and 1b are trapped as the tantala-3-boratacyclopentene compounds 2 and 3, respectively. In these complexes, the alkyne and borataalkene ligands have reductively coupled at the d(2) tantalum center. For the unsymmetrical alkyne, a kinetic product resulting from coupling in the opposite regiochemical sense is observed; the thermodynamic products 3-t incorporate the phenyl group in the alpha position of the tantalaboratacyclic ring. Two of these compounds (2b and 3b-t) were characterized crystallographically. For bulkier alkynes (diphenylacetylene, 1-phenyl-1-propyne, and 3-hexyne), intermediates with similar spectroscopic properties to the tantala-3-boratacyclopentenes were observed, but the ultimate products were the vinylalkylidene compounds 5-(R,R'). Compound 5-(Ph,Me) was characterized crystallographically, and it was found that the vinylalkylidene binds to the metal in an eta(1)-bonding mode, with the tantalum center receiving further ligation through a hydridoborate moiety. Mechanistic studies suggest that these products arise via retrocyclization of the tantala-3-boratacyclopentenes formed kinetically. These studies represent the first studies concerning the reactivity of a borataalkene ligand at a transition metal center and show that it can behave in an "olefin-like" manner, despite having a more flexible array of bonding modes available to it than an olefin.

Related Papers

• → Reactions of a Trinuclear Ruthenium Complex Derived from 3-(2-Pyridyl)indene with Diphenylacetylene and Phenylacetylene: Insertion of Alkynes into the Ru−C bond(2011)20 cited
• → The cis-insertion of diphenylacetylene into an exo-polyhedral boron–hydrogen bond of a molybdenacarbaborane cage(1995)9 cited
• → New catalyst systems for polymerization of substituted acetylenes: W(NO) 2 (O 2 CR) 2 -MCl 4 (M=Ti, Sn)(1999)7 cited
• → Oxidative transformations of phenylacetylene in a Ph3MF2 (M=Bi, Sb)−CuCl system(1997)2 cited
• → ChemInform Abstract: Organic Heterocyclothiazenes. Part 2. Reaction of Tetrasulfur Tetranitride with Phenylacetylene and Diphenylacetylene.(1987)