5-COORDINATE TUNGSTEN(VI) PHENYLIMIDO ALKYLIDENE COMPLEXES AND ISOLATED PRECURSORS, CONTAINING A CHELATING ARYLAMINE LIGAND - MOLECULAR-STRUCTURE OF W(C6H4CH2NME2-2)(=CHSIME3)(CH2SIME3)(=NPH)

With monoanionic 2-[(dimethylamino)methyl]phenyl, an aryl ligand in wh ich a potentially chelating tertiary amine group is present, five-coor dinate tungsten(VI) phenylimido alkylidene complexes and their alkyltu ngsten(VI) precursor complexes have been isolated. For example, use of this potentially intramolecular coordinating ligand makes it possible to synthesize the tungsten(VI) alkylidene complex W(C6H4CH2NMe2-2)(=C HSiMe3)(CH2SiMe3)(=NPh) (5) via a simple one-step reaction from an eas ily accessible trialkyltungsten phenylimido precursor. Introduction of pi-electron donor substituents, such as tert-butoxide and 3,5-dimethy lphenoxide ligands, allows isolation and characterization of the respe ctive alkylidene precursor complexes; e.g. W(C6H4CH2NMe2-2)(CH2SiMe3)2 (=NPh)(OCMe3) (7). Complex 7 is unstable at elevated temperatures and decomposes via intramolecular H(alpha)-abstraction reactions. Reaction of 5 with tert-butyl alcohol affords a 1,2-addition of the alcohol at the alkylidene function and subsequent formation of 7; the same react ion with triphenylsilanol results in the instantaneous formation of th e new alkylidene complex W(C6H4CH2NMe2-2)(=CHSiMe3)(=NPh)(OSiPh3) (6), in which the alkyl group is replaced by the silanol group. The analyt ically pure alkylidene complexes 5 and 6 are inert toward linear olefi ns but react with aldehydes and ketones in a Wittig-type reaction. The olefin products of the reaction with the aldehydes are obtained as a cis/trans mixture in which the trans isomer is predominant. With cycli c olefins very fast ring opening metathesis polymerization (ROMP) reac tions take place; cyclic olefins in which two double bonds are present , such as norbornadiene and dicyclopentadiene, produce cross-linked po lymers, whereas reaction with norbornene leads to selective formation of cis-polycyclopentenamers. The five-coordinate structure of 5 that r esults from intramolecular W-N coordination has been proven in the sol id-state (X-ray diffraction) and in solution (NMR) spectroscopy). Crys tals of 5 are monoclinic, space group P2(1)/a with unit-cell dimension s a = 17.950(3) angstrom, b = 16.633(4) angstrom, c = 19.472(4) angstr om, beta = 115.48(2)degrees, final R = 0.0661, and R(w) = 0.0653.