(Perfluoro)alkylsilyl-Substituted 2-[Bis(4-aryl)phosphino]pyridines:  Synthesis and Comparison of Their Palladium Complexes in Methoxycarbonylation of Phenylacetylene in Regular Solvents and Supercritical CO2

• Published in: Organometallics 2005-10, Vol.24 (22), p.5299-5310
• Main Authors: de Pater, Jeroen. J. M, Maljaars, C. Elizabeth P, de Wolf, Elwin, Lutz, Martin, Spek, Anthony L, Deelman, Berth-Jan, Elsevier, Cornelis J, van Koten, Gerard
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om050479+

The synthesis and characterization of three new 2-[bis{4-(bromo)phenyl}phosphino]pyridine (8), 2-[bis{4-(trimethylsilyl)phenyl}phosphino]pyridine (9), and 2-[bis{4-((2-(perfluorohexyl)ethyl)dimethylsilyl)phenyl}phosphino]pyridine (10) ligands (L) is reported. The corresponding compounds trans-/cis-[PdCl2(L)2] 11−13, trans-[PdCl(Me)(L)2] 14−16, and maleic anhydride complexes [Pd(L)2(cyclo-(−CHCHC(O)OC(O)−)] 17 and 18 were synthesized and characterized. In the methoxycarbonylation of phenylacetylene in methanol catalysts derived from [Pd(OAc)2] as the palladium source with either 9 or 10 as ligand showed the same activity (TON = 4000, 50 min reaction time) and selectivity (about 98% for the branched product) as the catalyst obtained from [Pd(OAc)2] and 2-[diphenylphosphino]pyridine (2). Both 2 and 10 were also tested in this reaction using a 1:1 mixture of methanol and α,α‘,α‘ ‘-trifluorotoluene as solvent system:  fluorous 10 generated a more active catalyst (TON = 3400 for 10 vs 3000 for 2). In supercritical CO2 the use of 10 as ligand (with [Pd(OAc)2]) in this reaction gave a TON of 2000 (50 min reaction time) and a selectivity of >99% for the branched product. Nonfluorous [Pd(2)2(cyclo-(CHCHC(O)OC(O)−)] gave a particularly active catalyst for the methoxycarbonylation of phenylacetylene (TON of about 8000, 50 min reaction time, TOF50 of about 30 000 mol phenylacetylene per mol Pd per hour in methanol) with no loss in selectivity (98% selectivity toward the branched product).