Synthesis of Parent Acetylide and Dicarbide Complexes of Thorium and Uranium and an Examination of Their Electronic Structures.

The reaction of [AnCl(NR)] (An = U or Th; R = SiMe) with NaCCH and tetramethylethylenediamine (TMEDA) results in the formation of [An(C≡CH)(NR)] (, An = U; , An = Th), which can be isolated in good yields after workup. Similarly, the reaction of 3 equiv of NaCCH and TMEDA with [AnCl(NR)] results in the formation of [Na(TMEDA)][An(C≡CH)(NR)] (, An = U; , An = Th), which can be isolated in fair yields after workup. The reaction of with 2 equiv of KC and 1 equiv of 2.2.2-cryptand in tetrahydrofuran results in formation of the uranium(III) acetylide complex [K(2.2.2-cryptand)][U(C≡CH)(NR)] (). Thermolysis of or results in formation of the bimetallic dicarbide complexes [{An(NR)}(μ,η:η-C)] (, An = U; , An = Th), whereas the reaction of with [Th{(R)(SiMeH)}(NR)] results in the formation of [U(NR)(μ,η:η-C)Th(NR)] (). The C NMR chemical shifts of the α-acetylide carbon atoms in , , and exhibit a characteristic spin-orbit-induced downfield shift, due to participation of the 5f orbitals in the Th-C bonds. Magnetism measurements demonstrate that displays weak ferromagnetic coupling between the uranium(IV) centers ( = 1.78 cm).