T. Szymanskabuzar et al., MATRIX-ISOLATION STUDIES OF ALKYNE COMPLEXES IN THE PHOTOCHEMICAL-REACTIONS OF MO(CO)(6) WITH ALKYNES, Journal of organometallic chemistry, 495(1-2), 1995, pp. 149-161
Photolysis of a low-temperature matrix X (X = Ar or CH4) doped with mo
lybdenum hexacarbonyl and an alkyne RC=CR' (HC=CH, MeC=CH, or MeC=CMe)
leads to the formation of the corresponding alkyne complex of molybde
num pentacarbonyl, [(eta(2)-RC=CR')Mo(CO)(5)], in addition to [X... Mo
(CO)(5)] and CO; the products have been detected and characterised by
their IR and UV-vis absorption spectra. The species [(eta(2)-RC=CR')Mo
(CO)(5)], unlike [X...Mo(CO)(5)], is stable with respect to irradiatio
n in the green region of the visible spectrum, and a scheme has been d
evised for the photochemical interconversion of the three species [Mo(
CO)(6)], [(eta(2)-RC=CR')Mo(CO)(5)] and [X...Mo(CO)(5)] in a mixed mat
rix composed of RC=CR' and X molecules. An eta(2)-alkyne complex of th
e type [(RC=CH)Mo(CO)(5)] (R=H or Me) undergoes rearrangement to give
what is believed to be a vinylidene complex [R(H)C=C=Mo(CO)(5)]. Conti
nued irradiation at lambda = 313 nm causes the various pentacarbonyl c
omplexes to lose CO with the formation of tetracarbonyl species. More
significantly, irradiation at lambda = 369 nm also results in photoeje
ction of CO; this favours the formation of a product believed, on the
evidence of its IR spectrum and of experiments with C2D2 and (CCH2)-C-
12-C-13, to be [(eta(2)-RCCR')Mo(Co-4] (R,R' = H,H or Me,Me) in which
the alkyne is acting formally as a 4e ligand. The IR spectra serve not
ice of further changes on prolonged photolysis under these conditions.
The results are discussed in relation to intermediates in the catalyt
ic polymerization of 1-alkynes.