Unsymmetrisch substituierte alkin- und dialkinkomplexe von wolfram(IV) und molybdän(IV). Die kristallstruktur von [W 2Cl 8(PhCCCCSiMe 3)(pyridin) 2

Abstract

The unsymmetrically substituted alkyne ClCCSiMe 3 and the dialkynes PhCCCCSiMe 3 and PhCCSiMe 2CCPh react with tungsten hexachloride in CCl 4, in the presence of C 2Cl 4 as a reducing agent, and with molybdenum pentachloride in CCl 4, respectively, to form the alkyne complexes [MoCl 4-(ClCCiMe 3)] 2 ( 1), [WCl 4(ClCCSiMe 3)] 2 ( 2), [WCl 4(PhCCCCSiMe 3)] 2 ( 3), [W 2Cl 8(PhCCCCSiMe 3)] x ( 4), [W 2Cl 8(PhCCSiMe 2CCPh)] x ( 5), [Mo 2Cl 8-(PhCCSiMe 2CCPh)] x ( 6). In all cases the alkyne ligand is side-on coordinated to the metal (η 2), the bonding features correspond to the cyclopropene type. The coordination number of the metal is 7; the complexes 1–3 are dimerised via MCl 2M bridges and the bifunctional complexes 4–6 are polymerised via analogous bridges. In 3, the tungsten atom is coordinatd to the alkyne group adjacent to the phenyl substituent. In the molybdenum compounds the alkyne ligand is cleaved with Lewis bases such as pyridine or diethyl ether forming solvate complexes of molybdenum(IV), whereas in the corresponding tungsten complexes only the chloro bridges are cleaved. The pyridine adducts [W 2Cl 8(PhCCCCSiMe 3)(pyridine) 2] ( 7) and [W 2Cl 8(PhCCSiMe 2CCPh)(pyridine) 2] ( 8) are described in further detail. All complexes are characterized by elemental analyses, mass and IR spectra, the tungsten compounds (as ether adducts) also by their 13C NMR spectra. 7 was obtained in single crystals and has been subjected to a X-ray diffraction study. It crystallises in the monoclinic space group P2 1/ c with four formula units per unit cell (4154 independent, observed reflexions, R = 0.096) and with the lattice constants a 880.0(6), b 2866.0(20), c 1501.2(10) pm; β 94.4(3)°. EAch tungsten atom is surrounded by four chlorine atoms in equatorial positions, both alkyne groups are bonded side-on (η 2) to the tungsten atoms, whereas the N atoms of the pyridine molecules are located trans to the alkyne groups. The CC bond lengths of the alkyne groups are 125 pm (adjacent to the phenyl substituent) and 140 pm (adjacent to the SiMe 3 group), respectively. A strong trans-effect of the two alkyne groups is observed, resulting in shifting the tungsten atoms out of the Cl 4 planes by about 33 pm. The dihedral angle of 94.9°, enclosed by the two WC 2 planes, is remarkable.