Thioselonocarboxylic Ester, Selenetane, and Dihydrodiselenine Complexes Prepared from Pentacarbonyl(selenobenzaldehyde)tungsten with π‐Donor‐Substituted Alkynes

Pentacarbonyltungsten‐coordinated selenobenzaldehyde, [(CO) 5 W{Se=C(Ph)H}] ( 1 ), reacts with t Bu‐CC‐SMe ( 2 ) by insertion of the CC into the Se=C bond to form in a highly regio‐ and stereoselective manner the α,β‐unsaturated thioselonocarboxylic ester complex (Z)(C=C)‐[(CO) 5 W{ 1 ‐Se=C(SMe)C( t Bu)=C(Ph)H}] ( 3 ). The thioselonocarboxylic ester ligand is cleaved intact from the metal by treatment of 3 with [NEt 4 ]Br. Three complexes are formed in the reaction of 1 with Me‐CC‐SMe ( 5 ): the thioselonocarboxylic ester complex [(CO) 5 W{ 1 ‐Se=C(SMe)C(Me)=C(Ph)H}] ( 6 ) as a mixture of the ( E ) and (Z)(C=C) isomers, a selenetane complex ( 7 ) and a dihydrodiselenine complex ( 8 ). The product distribution depends on the ratio 1:5 and on the solvent. The reaction of 1 with the bis(organylthio)alkynes RS‐CC‐SR ( 9 ) [R = Me ( a ), i Pr ( b ), 2,6‐C 6 H 3 Me 2 ( c )] yields mixtures of the ( E ) and (Z)(C=C) isomers of the α,β‐unsaturated α‐organylthio thioselonocarboxylic ester complexes [(CO) 5 W{ 1 ‐Se=C(SR)C(SR)=C(Ph)H)] ( 10a‐c ). In contrast, the reaction of 1 with tert ‐butoxyethyne, H‐CC‐O t Bu ( 11 ), affords a bis(pentacarbonyltungsten) 5,6‐dihydro‐1,2‐diselenine complex ( 12 ). Compound 12 is probably formed by consecutive reaction of 1 with 11 to give the selonocarboxylic ester complex [(CO) 5 W{ 1 ‐Se=C(O t Bu)C(H)=C(Ph)H}] which then further reacts as a heterodiene by highly regioselective [4 + 2] cycloaddition with the Se=C bond of a second molecule of 1 to give 12 . In the reaction of 1 with 5 and 9a the isomer with a trans arrangement of C(=Se)SMe and Ph is the kinetically controlled reaction product [( E )‐ 6 and (Z)‐ 10a , respectively]. The formation of ( E )‐ 6 and (Z)‐ 10a is followed by isomerization until an ( E )/(Z) equilibrium is reached. Complexes 3 and 7 were characterized by X‐ray structural analyses.