Regioselective addition of mixed-chalcogenide iron carbonyl clusters Fe<SUB>2</SUB>(CO)<SUB>6</SUB>(&#956;-EE') (E &#8800; E', E, E' = S, Se, Te) to a carbon-carbon triple bond activated by a metal carbene fragment. Structural characterization of new trimetallic adducts Fe<SUB>2</SUB>(CO)<SUB>6</SUB>{&#956;-SC(Ph)=C(Te)[(OEt)C=Cr(CO)<SUB>5</SUB>]}, Fe<SUB>2</SUB>(CO)<SUB>6</SUB>- {&#956;-SC(Ph)=C(Se)[(OEt)C=W(CO)<SUB>5</SUB>]}, and Fe<SUB>2</SUB>(CO)<SUB>6</SUB>{&#956;-SeC(Ph)=C(Te)[(OEt)C=W(CO)<SUB>5</SUB>]}

From the room-temperature reaction of the transition-metal alkynyl Fischer carbene complexes (CO)5M=C(OEt)(C&#8801;CPh) (M = Cr, W) with the mixed-chalcogenide compounds Fe2(CO)6(&#956;-EE') (E &#8800; E', E, E' = S, Se, Te), the following new trimetallic adducts were obtained: Fe2(CO)6{&#956;-EC(Ph)=C(E')[(OEt)C=M(CO)5]} 1-6 (1, 85%, E = S, E' = Se, M = Cr; 2, 82%, E = S, E' = Se, M = W; 3, 84%, E = S, E' = Te, M = Cr; 4, 80%, E = S, E' = Te, M = W; 5, 83%, E = Se, E' = Te, M = Cr; 6, 81%, E = Se, E' = Te, M = W). In addition, trace amounts of the corresponding alkenyl Fischer carbene complexes (CO)5M=C(OEt){(CH=C(OMe)Ph} 7-8 (7, M = Cr; 8, M = W) were also formed in each case. Compounds 1-6 were characterized by IR and 1H, 13C, 77Se, and 125Te NMR spectroscopy. Crystallographic analyses of the compounds 2, 3, and 6 were carried out. The structures of 2, 3, and 6 can be described as Fe2EE' (E, E' = S, Se, Te) tetrahedral butterfly cores containing the alkynyl Fischer carbene as a bridge between the two wingtip chalcogens with three terminally bonded carbonyl groups on each Fe atom