Palladium(II) complexes with o-aryl substituted 1,1′-bis(phosphino)ferrocenes [Fe(η5-C5H4PR2)2Pd(NCMe)n](OTf)2 (R = o-MeOC6H4, o-MeC6H4, o-PriC6H4, C6F5): Synthesis, structure and catalytic properties in methoxycarbonylation of ethylene

The cationic palladium(II) complexes with 1,1′-bis(phosphino)ferrocenes [Fe(η5-C5H4PR2)2Pd(NCMe)n](OTf)2 (n = 0–2) (OTf = CF3SO3; 5, R = o-MeOC6H4, n = 0; 6, R = o-MeC6H4, n = 1; 7, R = o-PriC6H4, n = 1; 8, R = C6F5, n = 1) have been prepared by treatment of the corresponding dichlorides [Fe(η5-C5H4PR2)2PdCl2] (1–4) with silver triflate in the presence of acetonitrile. The structures of 5 and 7 have been determined crystallographically. The oxygen of one of the methoxy groups in 5 has been found to coordinate the palladium resulting in decrease of the bite angle P–Pd–P to 94.74(5)°. In contrast, the bulky ortho-isopropylphenyl groups at the phosphorus atoms in 7 increase the P–Pd–P angle to 99.98(6)° and cause also a significant distortion of the square-planar coordination around the palladium atom. A preliminary study on methoxycarbonylation of ethylene catalyzed by 5–8 has been carried out and revealed great effect of the ortho-aryl substituent on both catalyst’s activity and selectivity. The anisyl complex 5 was moderately active for production of alternating polyketone, while the o-tolyl derivative 6 gave selectively methyl propanoate. The cationic palladium(II) complexes with highly sterically congested isopropylphenyl ligand and strongly electron withdrawing pentafluorophenyl substituted phosphine, 7 and 8, respectively, under the reaction conditions undergo facile reduction to Pd0/PdI species and are therefore inactive in the process.