Ligand Sphere Conversions in Terminal Carbide Complexes

Metathesis
is introduced as a preparative route to terminal carbide
complexes. The chloride ligands of the terminal carbide complex [RuC­(Cl)2(PCy3)2] (RuC) can be exchanged,
paving the way for a systematic variation of the ligand sphere. A
series of substituted complexes, including the first example of a
cationic terminal carbide complex, [RuC­(Cl)­(CH3CN)­(PCy3)2]+, is described and characterized
by NMR, MS, X-ray crystallography, and computational studies. The
experimentally observed irregular variation of the carbide 13C chemical shift is shown to be accurately reproduced by DFT, which
also demonstrates that details of the coordination geometry affect
the carbide chemical shift equally as much as variations in the nature
of the auxiliary ligands. Furthermore, the kinetics of formation of
the sqaure pyramidal dicyano complex, trans-[RuC­(CN)2(PCy3)2], from RuC has
been examined and the reaction found to be quite sluggish and of first
order in both RuC and cyanide with a rate constant of k = 0.0104(6) M–1 s–1. Further reaction with cyanide
leads to loss of the carbide ligand and formation of trans-[Ru­(CN)4(PCy3)2]2–, which was isolated and structurally characterized as its PPh4+ salt.