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 ₄ ) (L = κ ³ -[{2,5-( ^t Bu ₂ PCH ₂ ) ₂ C ₅ H ₂ }Ru(C ₅ H ₅ )]) yields the dinuclear cationic Pd(ii) tetrahydroborate with the bridging BH ₄ ^- ligand [(LPd) ₂ (μ,η ^1,2 :η ^1,2 -BH ₄ )] ⁺ . The bifurcate dihydrogen-bonded complexes are the active intermediates of the first proton transfer in the step-wise alcoholysis of LPd(BH ₄ ), yielding eventually [(LPd) ₂ (μ,η ^1,2 :η ^1,2 -BH ₄ )] ⁺ . According to the X-ray and DFT/M06 geometry analysis, the BH ₄ ^- ligand in both palladium tetrahydroborates has a mixed coordination mode η ^1,2 . The possibility of BH ₃ -group abstraction from LPd(BH ₄ ) by an excess of organic base (THF, Py) with the formation of hydride LPd ^II H is shown. This Pd(ii) hydride is a very reactive compound able to rapidly capture CO ₂ (ca. 15 min) converting into the formate complex LPd ^II (η ¹ -OC(O)H). The hydrolysis of LPdH with subsequent CO ₂ insertion yields a hydrocarbonate complex LPd ^II (η ¹ -OC(O)OH). The hydrocarbonate complex forms hydrogen-bonded dimers in the crystal due to hydrogen bonds between the OC(O)OH fragments.