DESIGNING NEW CATALYTIC C-C AND C-N BOND FORMATIONS PROMOTED BY ORGANOACTINIDES

Organoactinides of the type Cp-2AnMe(2) (Cp* = C5Me5; An = Th; U) are active catalytic precursors for the oligomerization of terminal alkyn es HC=CR (R = alkyl, aryl, SiMe3). The regioselectivity and the extent of oligomerization depend strongly on the alkyne substituent R, where as the catalytic reactivity is similar for both organoactinides. React ion with tert-butylacetylene yields regioselectively the E-2,4-disubst ituted 1-buten-3-yne dimer whereas trimethylsilylacetylene is regiosel ective trimerized to the ,E-1,4,6-tris(trimethylsilyl)-1,3-hexadiene-5 -yne, with small amounts (3-5%) of the corresponding E-2,4-disubstitut ed 1-buten-3-yne dimer. Oligomerization with less bulky alkyl and aryl substituted alkynes produces a mixture of higher oligomers with no re gioselectivity. Using the (Cp2ThMe2)-Th- catalyst, we have recently d eveloped a strategic method to control the extent and in some cases th e regioselectivity of the catalyzed oligomerization of nonbulky termin al alkynes to dimers and/or trimers. The metallocene catalytic precurs ors ensure the selective synthesis of small oligomers by the addition of specific amines. Catalytic ''tailoring'' to dimer and trimers can b e achieved by using small or bulky amines, respectively. Kinetic and m echanistic data for the controlling experiments argue that the turnove r-limiting step involves the acetylide actinide complex formation with the rapid insertion of the alkyne and protonolysis by the amine. The analog (Cp2UMe2)-U- in the presence of primary amines induce the sele ctive C-N bond formation, producing enamines which are tautomerized to the corresponding imines. (C) 1998 Elsevier Science S.A.