Thiono, Selenothiono, and Dithiocarboxylic Ester Complexes from Pentacarbonyl(thiobenzaldehyde)tungsten and π‐Donor Substituted Alkynes and Decomplexation of the Esters

Pentacarbonyltungsten-coordinated thiobenzaldehyde, [(CO)5W{S=C(Ph)H}] (1), reacts with 1-methylthio-1-propyne, 1-ethylseleno-1-propyne, and alkoxyethynes by insertion of the CC into the S=C bond to form in a highly regio-and stereoselective manner the α,β-unsaturated dithio, selenothiono, and thionocarboxylic ester complexes (E)(CC)-[(CO)5W{η1-SC(XR′)C(R)=C(Ph)H}] (3) (R = Me: XR′ = SMe (a), SeEt (b); R = H: XR′ = OEt (c), OtBu (d)). The analogous reaction of 1 with bis(alkylthio)ethynes affords mixtures of the (E) and (Z)(C=C) isomers of [(CO)5W{η1-S=C(SR)C(SR)=C(Ph)H}] (6) [R = Me (a), tBu (b)]. The Z isomers 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 = Me. The dithio and thiono ester ligands can be cleaved intact from the metal by treatment with [NEt4]Br as shown by the examples of 3a, 3c, and 6a. Complex 3c has been characterized by an X-ray structural analysis.