title: Structural and spectroscopic demonstration of agostic C-C interactions in electron-deficient metallacyclobutanes and related cage complexes: possible implications for olefin polymerizations and metatheses.
abstract: The reaction of the half-open titanocene, Ti(C5H5)(c-C8H11)(PMe3) (c-C8H11 = cyclooctadienyl), with two equivalents of PhC2SiMe3 leads to their incorporation and coupling to the dienyl fragment. One alkyne inserts into a C-H bond of the central CH2 group of the c-C8H11 ligand's edge-bridge, while the second undergoes a 5+2 coupling with the dienyl fragment, yielding coordinated sigma-allyl and olefin fragments, as demonstrated by X-ray diffraction. Together with the C5H5 and PMe3 coordinations, this leads to a 14-electron count. While the very electron-deficient titanium center passes up potential pi coordination of the allyl fragment, it instead engages in interactions with one or two C-C bonds, and perhaps a C-H bond, as revealed from the structural and spectroscopic data. Similar interactions have been found in electron-deficient metallacyclobutane complexes of titanium and zirconium, but not in the 18-electron molybdenum and tungsten analogues. These and other observations may have implications relating to metatheses and polymerizations of olefins.
authors.affiliation: Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850, USA.
authors.forename: Benjamin G
authors.initials: BG
authors.lastname: Harvey
authors.forename: Charles L
authors.initials: CL
authors.lastname: Mayne
authors.forename: Atta M
authors.initials: AM
authors.lastname: Arif
authors.forename: Robert
authors.initials: R
authors.lastname: Tomaszewski
authors.forename: Richard D
authors.initials: RD
authors.lastname: Ernst