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(BH4) (L = κ3-[{2,5-(tBu2PCH2)2C5H2}Ru(C5H5)]) yields the dinuclear cationic Pd(II) tetrahydroborate with the bridging BH4− ligand [(LPd)2(μ,η1,2:η1,2-BH4)]+. The bifurcate dihydrogen-bonded complexes are the active intermediates of the first proton transfer in the step-wise alcoholysis of LPd(BH4), yielding eventually [(LPd)2(μ,η1,2:η1,2-BH4)]+. According to the X-ray and DFT/M06 geometry analysis, the BH4− ligand in both palladium tetrahydroborates has a mixed coordination mode η1,2. The possibility of BH3-group abstraction from LPd(BH4) by an excess of organic base (THF, Py) with the formation of hydride LPdIIH is shown. This Pd(II) hydride is a very reactive compound able to rapidly capture CO2 (ca. 15 min) converting into the formate complex LPdII(η1-OC(O)H). The hydrolysis of LPdH with subsequent CO2 insertion yields a hydrocarbonate complex LPdII(η1-OC(O)OH). The hydrocarbonate complex forms hydrogen-bonded dimers in the crystal due to hydrogen bonds between the OC(O)OH fragments.