NMR studies of the structure, isomerism and photochemical reactions of trans-[W(CO)(4)(eta(2)-alkene)(2)] complexes

UV broad-band photolysis of W(CO)(6) in the presence of propene and 1-butan e has been used to synthesise the bis-alkene complexes trans-[W(CO)(4)(eta( 2)-CH2=CHCH3)(2)] 1 and trans-[W(CO)(4)(eta(2)-CH2=CHCH2CH3)(2)] 2. The H-1 - and C-13-NMR spectra are discussed in detail in relation to the structure and isomerism of these alkene compounds. On the evidence of the spectra me asured at different temperatures. the barrier to alkene rotation is ca. 46 and 48 kJ mol(-1) in 1 and 2, respectively. The NMR method has been used fo r the identification and characterisation of the unstable alkene = propene or 1-butene complexes [W(CO)(5)(eta(2)-alkene)] and cis-[W(CO)(4)(eta(2)-al kene)(2)] and of hydride derivatives formed in photochemical reactions of t rans-[W(CO)(4)(eta(2)-alkene)(2)] occurring in solution at ca. 200 K. (C) 1 999 Elsevier Science S.A. All rights reserved.