THE PHOTOCHEMICAL BEHAVIOR OF MATRIX-ISOLATED W(CO)(6) IN THE PRESENCE OF ALKYNES

The outcome of UV photolysis of W(CO)(6) molecules isolated in a solid CH4 or Ar matrix in the presence of an alkyne RC=CR' (R,R'=H,H; Me,H; or Me,Me) at ca. 20 K has been monitored by recording the IR and UV-v is absorption spectra of the deposit. The results indicate that irradi ation with light having wavelengths near 313 nm results in the formati on of the (eta(2)-alkyne)tungsten pentacarbonyl complex, [(eta(2)-RC=C R')W(CO)(5)], in addition to [X...W(CO)(5)](X=CH4 or Ar), and free CO. In the case of a terminal alkyne, e.g. HC=CH or MeC=CH, however, phot olysis under these conditions gives, in addition to the eta(2)-alkyne complex and in significantly greater yield, what appears to be the vin ylidene derivative [R(H)C=C=W(CO)(5)](R=H or Me). Prolonged irradiatio n with UV light (lambda=ca. 313 or 369 nm) causes the various pentacar bonyl complexes to lose CO with the formation of tetracarbonyl species ; prominent among the products issuing from the W(CO)(6)/C2H2 system a re [(eta(2)-HC=CH)(eta(1)-H2C=C)W(CO)(4)](in C2H2-rich matrices) and [ (eta(2)-HC=CH)W(CO)(4)] in which the alkyne is acting formally as a 4e ligand. The results are significant in relation to the likely interme diate stages in the photocatalytic polymerization of terminal alkynes induced by tungsten hexacarbonyl.