The synthesis of electron-poorm ono-, di-and tri-(imidazolium)-substituted Cp-ylides is presented and their electronic properties are discussed based on NMRs pectroscopy,X-ray structurea nalyses, electrochemical investigations and DFT calculations as well as by their reactivity toward [Ru(CH 3 CN) 3 Cp*](PF 6). With mono-and di(imidazolium)-substituted cyclopentadienides the respective monocationic and dicationic ruthenocences are formed (X-ray), whereas tri(imi-dazolium)c yclopentadienides are too electron-poor to form the ruthenocenes.C yclic voltammetric analysiso ft he ruthenocenes shows reversible oxidation at ap otentialt hat increasesw ith every additional electron-withdrawing imidazolium substituent at the Cp ligand by 0.53-0.55 Vi na ne lectrolyte based on aw eakly coordinating anion. Ar eversible oxidation can be observed for the free 1,3-disubstituted ligand as well.
The synthesis and the analytical features of group 6 carbonyl complexes of electron-poor mono(imidazolium)-and bis(imidazolium)-substituted Cp ylides are presented. With the neutral ylidic imidazolium Cp and the monocationic 1,3bis(imidazolium) Cp ligand all of the group 6 carbonyl complexes were prepared, while in the case of the 1,2-disubstituted Cp ylide only the chromium Cp complex was accessible. The donor properties of the ligands were elucidated experimentally by means of the CO stretching frequencies of their group 6 metal complexes and theoretically by DFT calculations. Every imidazolium substituent and the planar conjugated π system of the imidazolium moieties annelated to the Cp ring increase the average CO stretching frequencies by about 20 cm −1 . Overall, the donor properties of the C-ylidic Cp ligands are still stronger than those of the benzene ligand. Additionally, the protonation of the Cp ligands was investigated, and the basicity correlates qualitatively with the electron-donor character of the ylidic Cp ligands.
Scandium complexes bearing a C-ylidic, electron-deficient Cp ligand are presented by starting from [ScCl 3 (thf) 3 ]. As ylidic ligands do not require salt metathesis, the coordination of the Cp ligand is realized by mere substitution of the tetrahydrofuran ligands. In acetonitrile an equilibrium among the free ligand, the half-sandwich complex, and the cationic metallocene with its tetrachloridoscandate counterion is observed via NMR spectroscopy. This equilibrium is fully confirmed by 1 H and 45 Sc NMR EXSY experiments. In the absence of coordinating solvents, the selective formation of all compounds of the equilibrium has been achieved, and the structures have been confirmed by NMR spectroscopy and X-ray structure analysis. Especially 45 Sc NMR spectroscopy reveals signals with characteristic chemical shifts for the half-sandwich complex and the metallocene. With scandium triflate the corresponding scandocene is also accessible.
Electron‐poor cyclopentadienide ligands based on neutral, cationic and dicationic imidazolium Cp ylides were prepared. The donating properties of these colorful compounds were analyzed by their oxidation potentials as well as that of their respective ruthenocene complexes. Each substitution by an imidazolium moiety increases the oxidation potential of about 500 mV. In addition, fixing the imidazolium moieties in the Cp plane by annellation also induces a withdrawing effect. More information can be found in the Full Paper by D. Kunz et al. on page 16291.
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