New Diphosphine Ligands Containing Ethyleneglycol and Amino Alcohol Spacers for the Rhodium-Catalyzed Carbonylation of Methanol

摘要

The new diphosphine ligands PhPCHC(O)X(CH)OC(O)CHPPh (: X=NH; : X=NPh; : X=O) and PhPCHC(O)O(CH)O(CH)OC(O)CHPPh () as well as the monophosphine ligand PhPCHC(O)X(CH)OH () have been prepared from 2-diphenylphosphinobenzoic acid and the corresponding amino alcohols or diols. Coordination of the diphosphine ligands to rhodium, iridium, and platinum resulted in the formation of the square-planar complexes [(PP)Rh(CO)Cl] (: PP=; : PP=; : PP=), [(PP)Rh(CO)Cl] (: PP=), [(P-P)Ir(cod)Cl] (: PP=; : PP=; : PP=), [(PP)Ir(CO)Cl] (: PP=; : PP=; : PP=), and [(PP)PtI] (: PP=). In all complexes, the diphosphine ligands are trans coordinated to the metal center, thanks to the large spacer groups, which allow the two phosphorus atoms to occupy opposite positions in the square-planar coordination geometry. The trans coordination is demonstrated unambiguously by the single-crystal X-ray structure analysis of complex . In the case of the diphosphine ligand , the spacer group is so large that dinuclear complexes with ligand in bridging positions are formed, maintaining the trans coordination of the P atoms on each metal center, as shown by the crystal structure analysis of . The monophosphine ligand reacts with [{Ir(cod)Cl}] (cod=cyclooctadiene) to give the simple derivative [()Ir(cod)Cl] () which is converted into the carbonyl complex [()Ir(CO)Cl] () with carbon monoxide. The crystal structure analysis of also reveals a square-planar coordination geometry in which the phosphine ligand occupies a position cis with respect to the chloro ligand. The diphosphine ligands , , , and have been tested as cocatalysts in combination with the catalyst precursors [{Rh(CO)Cl}] and [{Ir(cod)Cl}] or [HIrCl] for the carbonylation of methanol at 170 °C and 22 bar CO. The best results (TON 800 after 15 min) are obtained for the combination /[{Rh(CO)Cl}]. After the catalytic reaction, complex is identified in the reaction mixture and can be isolated; it is active for further runs without loss of catalytic activity.