Pentacarbonyltungsten-coordinated selenobenzaldehyde, [(CO),W(Se=C(Ph)H)] (l), reacts with tBu-C=C-SMe
(2)
by insertion of the C=C into the Se=C bond to form in a highly regio-and stereoselective manner the a,P-unsaturated thioselonocarboxylic ester complex (Z )
3). The thioselonocarboxylic ester ligand is cleaved intact from the metal by treatment of 3 with [NEt,]Br. Three complexes are formed in the reaction of 1 with Me-C=C-SMe (5): the thioselonocarboxylic ester complex [(CO),W[ql-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(organy1thio)alkynes RS-C=C-SR (9) [R = Me (a), iPr (b), 2,6-C6H3Me2 (c)] yields mixtures of the (E) and (Z)(C=C) isomers of the a,P-unsaturated a-organ-ylthio thioselonocarboxylic ester complexes [(CO),W(ql-Se=C(SR)C(SR)=C(Ph)H)] (loa-c). In contrast, the reaction of 1 with tert-butoxyethyne, H-C=C-OtBu ( l l ) , affords a bis(pentacarbony1tungsten) 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)5W [ q -Se = C (0tBu)C (H) = C (Ph)H] ] which then further reacts as a heterodiene by highly regioselective [4 + 21 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 tram arrangement of C(=Se)SMe and Ph is the kinetically controlled reaction product [ (E)-6 and (Z)-lOa, respectively]
. The formation of ( E ) -6 and (Z)-lOa is followed by isomerization until an (E)/(Z) equilibrium is reached. Complexes 3 and 7 were characterized by X-ray structural analyses.