Synthesis, structural properties and reactivity of ruthenocene-based pincer Pd(ii) tetrahydroborate.

Two novel ruthenocene-based pincer palladium tetrahydroborates were characterized by XRD, NMR and FTIR. The alcoholysis of Pd(ii) tetrahydroborate LPd(BH) (L = κ-[{2,5-(BuPCH)CH}Ru(CH)]) yields the dinuclear cationic Pd(ii) tetrahydroborate with the bridging BH ligand [(LPd)(μ,η:η-BH)]. The bifurcate dihydrogen-bonded complexes are the active intermediates of the first proton transfer in the step-wise alcoholysis of LPd(BH), yielding eventually [(LPd)(μ,η:η-BH)]. According to the X-ray and DFT/M06 geometry analysis, the BH ligand in both palladium tetrahydroborates has a mixed coordination mode η. The possibility of BH-group abstraction from LPd(BH) by an excess of organic base (THF, Py) with the formation of hydride LPdH is shown. This Pd(ii) hydride is a very reactive compound able to rapidly capture CO (ca. 15 min) converting into the formate complex LPd(η-OC(O)H). The hydrolysis of LPdH with subsequent CO insertion yields a hydrocarbonate complex LPd(η-OC(O)OH). The hydrocarbonate complex forms hydrogen-bonded dimers in the crystal due to hydrogen bonds between the OC(O)OH fragments.