SYNTHESIS AND COMPARATIVE-STUDY OF IRON TRIAD M(CO)4(ETA-2-ALKYNE) COMPLEXES (M = FE, RU, OS ALKYNE = BIS(TRIMETHYLSILYL)ACETYLENE)

Photolysis (λ ≥370 nm) of Os3(CO)12(lc) with a high intensity irradiation source (500 W) in the presence of bis(trimethylsilyl)acetylene gave, in moderate yield, the first simple mononuclear carbonyl-alkyne complex of osmium, Os(CO)4(η2-Me3SiC2SiMe3) (2c). The X-ray molecular structure of 2c (orthorhombic, P212121, a = 13.391 (3) A, b = 13.871 (3) A, c = 9.879 (3) A, Z = 4; R = 0.030, Rw= 0.037 for 2073 reflections with I > 3σ(I)) verified the expected trigonal-bipyramidal disposition of the ligands but with distinct bending of the axial carbonyl groups toward the equatorial alkyne moiety. Involvement from the second full π ± moof the alkyne in the bonding is presented as a plausible reason for the distortion. The analogous Ru compound was obtained from in situ prepared Ru(CO)5 and completed the series of iron triad complexes M(CO)4(η2-Me3SiC2SiMe3) (M = Fe, Ru, Os). Comparisons of the stability sequence and spectroscopic properties of the complexes, including AG* for carbonyl group scrambling from variable-temperature13C NMR studies, indicate that both a and π components are of import in determining the strength of the M-(η2-alkyne) interaction. © 1987, American Chemical Society. All rights reserved.