Carbon-Silicon and Carbon-Carbon Bond Formation by Elimination Reactions at Metal N-Heterocyclic Carbene Complexes

Two functional groups can be delivered at once to organo-rare earth complexes, (L)MR2 and (L)(2)MR (M = Sc, Y; L = ({1-C(NDipp-CH2CH2N)}CH2CMe2O), Dipp = 2,6-Pr-t(2)-C6H3; R = CH2SiMe3, CH2CMe3), via the addition of E-X across the metal carbene bond to form a zwitterionic imidazolinium metal complex, (L-E)MR2X, where L-E = {1-EC(NDippCH(2)CH(2)N)}CH2CMe2O, E is a p-block functional group such as SiR3, PR2, or SnR3, and X is a halide. The "ate" complex (L-Li)ScR3 is readily accessible and is best described as a Li carbene adduct, ({1-Li(THF)C(NDippCH(2)CH(2)N)}CH2CMe2O)Sc(CH2SiMe3)(3), since structural characterization shows the alkoxide ligand bridging the two metals and the carbene Li-bound with the shortest yet recorded Li C bond distance. This can be converted via lithium halide-eliminating salt metathesis reactions to alkylated or silylated imidazolinium derivatives, (L-E)ScR3 (E = SiMe3 or CPh3). All the E-functionalized imidazolinium complexes spontaneously eliminate functionalized hydrocarbyl compounds upon warming to room temperature or slightly above, forming new organic products ER, i.e., forming C-Si, C-P, and C-Sn bonds, and re-forming the inorganic metal carbene (L)MR(X) or (L)(2)MX complex, respectively. Warming the tris(alkyl) complexes (L-E)MR3 forms organic products arising from C C or C Si bond formation, which appears to proceed via the same elimination route. Treatment of (L)(2)Sc(CH2SiMe3) with iodopentafluorobenzene results in the "reverse sense" addition, which upon thermolysis forms the metal aryl complex (L)(2)Sc(C6F5) and releases the iodoalkane Me3SiCH2I, again facilitated by the reversible functionalization of the N-heterocyclic carbene group in these tethered systems.