title: Syntheses and structural systematics of trialkylphosphine complexes of open titanocenes, zirconocenes and hafnocenes.
abstract: The synthesis and characterization of the open hafnocene, Hf(2,4-C7H11)2(PMe3)(C7H11 = dimethylpentadienyl), is reported. Additionally, a much improved synthetic procedure has been developed for Hf(2,4-C7H11)2(PEt3). Structural data have been obtained for these complexes, and for Ti(2,4-C7H11)2(PEt3) and Zr(2,4-C7H11)2(PMe3), thereby allowing for detailed comparisons between all M(2,4-C7H11)2(PX3) species (M = Ti, Zr, Hf; X = Me, Et). The presence of the coordinated phosphines led in all cases to the adoption of the expected syn-eclipsed geometries, with the phosphines positioned by the open dienyl edges. These phosphine ligands lead to substantial alterations of the bonding patterns in these species, relative to ligand-free complexes. Most notably, the shortest M-C distances involve the central dienyl carbon atoms. Additionally, the data reveal high degrees of steric crowding within these complexes, especially for the weakly bound Ti(2,4-C7H11)2(PEt3), and also demonstrate that significant deformations which have taken place within the dienyl ligands were substantially determined by the relative sizes of the metal centers.
authors.affiliation: Department of Chemistry, University of Utah, 315 S. 1400 E., Salt Lake City, Utah 84112-0850, USA.
authors.forename: Benjamin G
authors.initials: BG
authors.lastname: Harvey
authors.forename: Rehan
authors.initials: R
authors.lastname: Basta
authors.forename: Atta M
authors.initials: AM
authors.lastname: Arif
authors.forename: Richard D
authors.initials: RD
authors.lastname: Ernst