Palladium Complexes with Metallocene-Bridged Bidentate Diphosphine Ligands:  Synthesis, Structure, and Catalytic Activity in Amination and Cross-Coupling Reactions

Abstract

The syntheses and characterization of series of new metallocene-bridged diphosphines and the structures of complexes of some of them with Pd(II) are reported. These complexes were examined as the catalysts in amination reactions of halogenoarenes and in the Suzuki reaction. The complexes based on ruthenocene (2) and osmocene (3) showed lower activities then the palladium complex with dppf in amination reactions and the same activities in the Suzuki reaction. New palladium complexes with the bidentate bulky and electron-rich ligands Fe(η 5-C5H4P(o-Pr i C6H4)2)2 (6) and Fe(η 5-C5H4P(o-MeOC6H4)2)2 (5) showed a very high catalytic activity in amination and Suzuki coupling of aryl bromides. A complex with ligand 6 was used in the amination of 4-bromotoluene by primary and secondary amines and showed excellent activity.

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 complexes 5-8 were prepared by treatment of the dichloride complexes 1-4 [5], with silver triflate in the presence of acetonitrile (Scheme 1).…”

“…The phosphorus atoms are equivalent in [Fe(g 5 -C 5 H 4 -P{o-C 6 H 4 OMe} 2 ) 2 Pd(OTf)](OTf) (5) and [Fe(g 5 -C 5 H 4 P-{C 6 F 5 } 2 ) 2 Pd(NCMe)(OTf)](OTf) (8) and exhibit singlets at d 51.1, 17.2, respectively, in the 31 P{ 1 H} NMR spectra, which is consistent with complex cations being in fast exchange with solvent and triflate. The a-and b-cyclopentadienyl protons in the complexes with relatively small ortho-anisyl (5) and pentafluorophenyl (8) aryl substituents appear as non-resolved multiplets at d 4.74, 5.04 for 5 and at d 4.81, 5.35 for 8.…”

Fluoroarylphosphines as ligands

“…In only a very few examples, such as [(h 6 -C 6 H 6 )Cr(h 6 -C 6 F 5 )PPh 2 ] [7,8] and [Fe{h 5 -C 5 H 4 P(C 6 F 5 ) 2 } 2 ] [98], are substituents bound to a metal whilst phosphorus is not. The two most obvious effects of fluorination are the lowering of phosphine basicity and the increase in bulk, although other factors, such as ligand flexibility and the bite angle for bidentate ligands, are also important.…”

“…It was found that ligands bearing electron-withdrawing aryl substituents showed poor activity [98]. For the amination of 4-bromotoluene (Scheme 25) in dioxane at 100 8C, Fe(h 5 -C 5 H 4 PPh 2 ) 2 gave 63% conversion in 20 min, whereas Fe{h 5 -C 5 H 4 P(C 6 F 5 ) 2 } 2 gave only 13% conversion.…”

“…Fe{h 5 -C 5 H 4 P(C 6 F 5 ) 2 } 2 was assessed as a ligand for palladium(II) catalysts for the Suzuki coupling of 4-bromotoluene and 4-methoxyphenylboronic acid in dioxane at 100 8C [98]. Under the conditions of the study the catalyst derived from Fe{h 5 -C 5 H 4 P(C 6 F 5 ) 2 } 2 gave a yield of the product 4-methyl-4 0 -methoxybiphenyl of 52% after 10 min, which was similar to that given by [Fe(h 5 -C 5 H 4 PPh 2 ) 2 ] (60%), but lower than the quantitative yields obtained with [Fe{h 5 -C 5 H 4 P(C 6 H 4 Pr i -2) 2 } 2 ] and [Fe{h 5 -C 5 H 4 P(C 6 H 4 OMe-2) 2 } 2 ].…”