Crystal structure of trans-[W(CO)(4)(eta(2)-C2H4)(2)] and IR and H-1 NMR studies of the reactions of this and related ethene carbonyl complexes of tungsten(0), [W(CO)(n)(eta(2)-C2H4)(6-n)] (n=3-5)

摘要

The structure of trans-[W(CO)(4) (eta(2)-C2H4)(2)] 1 has been determined by X-ray crystallography at 293 K [orthorhombic, space group Aba2, a = 12.458(3), b = 6.370(2), c = 12.557(3) Angstrom Z = 4, R = 0.022] to confirm that the C=C bonds of the two ethene ligands are mutually staggered while eclipsing the central W(CO), unit. Reversible isomerisation of trans- to cis-[W(CO)(4)(eta(2)-C2H4)(2)] 2 under the action of selective irradiation has been shown to occur in solid argon matrices at 14-16 K. H-1 NMR measurements have also been applied to the identification of not only 1 and 2 but also the labile 18e complexes [W(CO)(5)(eta(2)-C2H4)] 3, mer-[W(CO)(3)(eta(2)-C2H4)(3)] 4, and fac-[W(CO)(3)(eta(2)-C2H4)(3)] 5 formed by broad-band UV-visible photolysis of ethene-saturated hydrocarbon solutions of 1 or CW(CO),I in the temperature range 200-293 K. In these circumstances the mixed ethene carbonyl complexes 2-5 decay thermally with dissociation of an ethene ligand and substitution by CO in reactions which have been monitored by reference to the relevant 1H NMR signals. Pseudo-first-order decay constants in the range 0.6-12 x 10(-4) s(-1) have thus been estimated with temperature-dependences implying activation energies, E-a, that decrease in the order 3 > 2 > 4 > 5. [References: 41]