Thiono, Selenothiono, and Dithiocarboxylic Ester Complexes from Pentacarbonyl(thiobenzaldehyde)tungsten and π‐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, 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) 5 W{η 1 ‐SC(XR′)C(R)=C(Ph)H}] ( 3 ) (R = Me: XR′ = SMe ( a ), SeEt ( b ); R = H: XR′ = OEt ( c ), O t Bu ( d )). The analogous reaction of 1 with bis(alkylthio)ethynes affords mixtures of the ( E ) and ( Z )(C=C) isomers of [(CO) 5 W{η 1 ‐S=C(SR)C(SR)=C(Ph)H}] ( 6 ) [R = Me ( a ), t Bu ( 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 = t Bu isomerization is significantly faster than for R = Me. 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 analysis.