Direct Arylation of Heterocycles: The Performances of Ferrocene‐Based Polyphosphane Ligands in Palladium‐Catalyzed CH Bond Activation

Abstract

The palladium‐catalyzed direct arylation of alkylated‐ furan, thiophene, and thiazole and benzoxazole heterocycles with electronically and sterically deactivated bromoarenes was selectively and efficiently promoted by ferrocenyl polyphosphanes. In this CH bond activation reaction of heteroaromatics, the performances of polydentate di‐, tri‐, and tetraphosphane ligands were compared, showing that the triphosphane 1,1′,2‐tris(diphenylphosphino)‐4‐tert‐butylferrocene 3 was the most effective for the coupling. The introduction of more electron‐donating (iPr) or electron‐withdrawing (furyl) groups on the phosphorus atoms did not improve the ligand performances. The coordination behavior of 3 towards palladium(II) and other group 10 metals, NiII and PtII, was studied and the corresponding 1,2‐P chelating phosphorus complexes were isolated in high yields and fully characterized by multinuclear 1H, 13C, 31P NMR (3⋅PdCl2, 3⋅PtCl2) and X‐ray structures (3⋅NiBr2). It was found that the triphosphane ligand 3 was able to accommodate bidentate chelating cis coordination to group 10 metals, and additionally a much rarely described bis monodentate trans configuration. The combination of these two modes of coordination in a multimetallic species was clearly evidenced for the first time for a ferrocenyl polyphosphane. This versatility in bonding is a clear difference of coordination potential of this catalytically more efficient triphosphane compared to analogous ferrocenyl di‐ or tetraphosphanes.

Hexaphosphine: A Multifaceted Ligand for Transition Metal Coordination

“…The X-ray structure of 2 is centrosymmetric, and the C2h molecular symmetry of polyphosphane ligand 1 is conserved in the complex ( Figure 2 Such a bis-facial coordination of Hexaphosphine was also observed in rhodium complex 3. [36] [RhCl(CO) 2 ] 2 with 1, red crystals precipitate in less than 24 h at 20°C.…”

Eco‐Friendly Solvents for Palladium‐Catalyzed Desulfitative CH Bond Arylation of Heteroarenes

“…2-n-Butyl-5-naphthalen-1-ylfuran (10) [31] 2-n-Butylfuran (0.124 g, 1mmol) and 1-naphthalenesulfonyl chloride (0.340 g, 1.5 mmol) were used, and the residue was purified by flash chromatography on silica gel (heptane/ethyl acetate, 90:10) to affordt he desired compound 10 in 55 %( 0.138 g) yield. 2-(4-Cyanophenyl)-3,6-dimethyl-4,5,6,7-tetrahydrobenzofuran (11) [5b]…”

Direct Arylation of Heteroaromatic Compounds with Congested, Functionalised Aryl Bromides at Low Palladium/Triphosphane Catalyst Loading

“…[19] We discovered superior efficiency of ferrocenyl triphosphane ligands relative to related mono-, di-and tetraphosphanes. We then focused our efforts to provide an efficient palladium-catalysed methodology for the challenging intermolecular arylation of functionalised aryl chlorides by using systems that incorporated modified ferrocenyl triphosphanes (Scheme 1).…”

“…[15b, 19,21] The most striking feature of L5 compared to the other ligands depicted in Scheme 2 is the net eclipsed position of P2 and P3, possibly due to the lower steric hindrance of the isopropyl groups. Therefore, upon chelation of palladium with P1 and P2, the influence of P3 on the area of palladium reactivity should be significant enough to promote cross-coupling of congested aryl bromides.…”