A new imidazolinium ligand precursor [L2H]Cl (2) was prepared in 86 % yield. Compared with its imidazolium counterpart, [L1H]Cl (1), 2 is very sensitive to moisture and can undergo ring-opening reactions very readily. Palladium complexes with the ring-opened products from imidazolinium salts were isolated and characterized by X-ray crystallography. Theoretical studies confirmed that the imidazolinium salt has a higher propensity for the ring-opening reaction than the imidazolium counterpart. New mixed phosphine/carbene palladium complexes, Cis-[PdCl2(L)(PR3)] (L = L1 and L2; R = Ph. Cy). were successfully prepared. These complexes are highly robust as revealed by variable-temperature NMR spectroscopic studies and thermal gravimetric analysis. The structural and electronic properties of the new complexes on varying the carbene group (imidazol-2-ylidene group (unsaturated carbene) vs. imidazolin-2-ylidene (saturated carbene)) and the phosphine group (PPh3 vs. PCy 3) were studied in detail by X-ray crystallography, X-ray photoelectron spectroscopy, and theoretical calculations. The catalytic study reveals that Cis-[PdCl2(L2)-(PCy3)] is a competent PdII precatalyst for Suzuki coupling reactions, in which unreactive aryl chlorides can be applied as substrates.
All Science Journal Classification (ASJC) codes
- Organic Chemistry