Novel (arene)Ruthenium(II) Complexes with halogen-substituted Scorpionates: Synthesis and Structural, Electrochemical and Catalytic Studies

Since their discovery in 1966,1 poly(pyrazolyl)borates (Bpx and Tpx), often indicated as scorpionates, have been extensively employed as anionic -donor ligands in a wide variety of metal complexes,2 as the steric and electronic properties of these ligands are easily modified by changing either the number of pyrazole rings or by substituents thereon or at the boron/carbon center. In recent works, we investigated the interaction of η6-arene Ru(II) with (pyrazol-1-yl)borates3 and (pyrazol-1-yl)alkanes,4 their coordination chemistry and their catalytic behaviour. Here we report some recent results obtained with bis- and tris-pyrazolylborate ligands bearing Br and iPr substituents in the pyrazole rings (Fig. 1) and some η6- arene ruthenium fragments (arene = benzene, para-cymene or hexamethylbenzene), together with the spectroscopic and structural characterization of the organometallic complexes. The comparison of the electron-donor character of Bp- and Tp- ligands has been supported by electrochemical studies. Furthermore preliminary catalytic results on diastereoselective nitroaldol reaction of benzaldehyde and nitroethane (Henry Reaction) will be reported.