Uranium(Ⅲ)-Mediated C-C-Coupling of Terminal Alkynes: Formation of Dinuclear Uranium(Ⅳ) Vinyl Complexes

摘要

The previously reported uranium(Ⅲ) complex [((~(Ad)ArO)_3N)- U~Ⅲ(DME)] (1; Ad = adamantane, DME = 1,2-dimethoxyethane) reacts with the terminal bis-alkynes 1,7-octadiyne or 1,6-heptadiyne in C-C-coupling reactions to form the uranium(IV) vinyl complexes [{(((~(Ad)ArO)_3N)U~Ⅳ}_2(μ-η~2:η~1-1,2-(CH)_2- cyclohexane)] (2) and [{(((~(Ad)ArO)_3N)U~Ⅳ}_2(μ-η~2:η~2-1,2-(CH)_2-cyclopentane)] (3). With the monoalkynes 1-hexyne or 4-~tbutyl-phenylacetylene, the complexes [{((~(Ad)ArO)_3N)U~Ⅳ}_2(μ-η~2(C1):η~1(C4)-2-~nBu-1,3-octadiene)] (4) and [{((~(Ad)ArO)_3N)U~Ⅳ}_2(μ-η~2(C4):η~1(C1)-1,3-di-(p-~tBu-phenyl)butadiene))] (5), are formed. These are the first four examples of uranium vinyl complexes that are reported and crystallographically characterized. In addition, detailed DFT calculations are presented to establish a possible mechanism for their formation and explain the differences found for the coordination of the hydrocarbon fragments. In contrast to a previously proposed monometallic pathway for catalytic hydroamination of alkynes and alkyne dimerization involving a uranium vinyl intermediate at uranium(Ⅲ) complexes, the calculations clearly support a bimetallic mechanism, since its transition states are energetically the most favored.