THIONO, SELENOTHIONO, AND DITHIOCARBOXYLIC ESTER COMPLEXES FROM PENTACARBONYL(THIOBENZALDEHYDE)TUNGSTEN AND PI-DONOR SUBSTITUTED ALKYNES AND DECOMPLEXATION OF THE ESTERS

Pentacarbonyltungsten-coordinated thiobenzaldehyde, [(CO)(5)W{S=C(Ph)H }] (1), reacts with 1-methylthio-1-propyne, 1-ethylseleno-1-propyne, a nd alkoxyethynes by insertion of the C=C into the S=C bond to form in a highly regio- and stereoselective manner the alpha,beta-unsaturated dithio, selenothiono, and thionocarboxylic ester complexes (E)(C=C)[(C O)(5)W{eta(1)-S=C(XR')C(R)=C(Ph)H}] (3) (R=Me: XR'=SMe (a), SeEt (b); R=H: XR'=Oft (c), OtBu (d)). The analogous reaction of 1 with bis(alky lthio)ethynes affords mixtures of the (E) and (Z)(C=C) isomers of [(CO )(5)W{eta(1)-S=C(SR)C(SR)=C(Ph)H)I (6) [R=Me (a), tBu (b)]. The Z isom ers are the initially formed products. Formation of (Z)-6 is followed by Z-->E isomerization until an equilibrium [E/Z=1 (6a), 1.5 (6b)] is obtained. For R=tBu isomerization is significantly faster than for R=M e. The dithio and thiono ester ligands can be cleaved intact from the metal by treatment with [NEt(4)]Br as shown by the examples of 3a, 3c, and 6a. Complex 3c has been characterized by an X-ray structural anal ysis.