312920-38-0Relevant academic research and scientific papers
Octaethyldiphosphaferrocene: An efficient ligand in the palladium-catalyzed suzuki cross-coupling reaction
Sava, Xavier
, p. 4899 - 4903 (2000)
Syntheses of octaethyldiphosphaferrocene 4 and tetraethylphosphaferrocene 5 are presented. Tetraethylzirconacyclopentadiene 1 reacts with PCl3 in dichloromethane to yield the 1-chlorotetraethylphosphole 2, which upon reduction by lithium in excess, yields the teraethylphospholide anion 3. Anion 3 was subsequently converted into 4 or 5 by treatment with FeCl2 or with [Fe(η6-C9H12)(η5-C5H5)][PF6] respectively. The structure of diphosphaferrocene 4 was determined. Two conformations are present in the cell: a C2 conformation (α = 51.1°) in which the P atom of each ring is located above the α-carbon atom of the other ring, and a C2h conformation (α = 180°) in which P atoms point in opposite directions. Reaction of ligand 4 with [Pd(dba)2] yields the bis(octaethyldiphosphaferrocene)palladium(0) complex 6. An X-ray crystallographic study reveals that the overall geometry around palladium is nearly tetrahedral and that both ligands, whose geometry is not significantly perturbed, adopt a bridging mode involving a side-on coordination of the lone pairs. Complex 6 behaves as an efficient catalyst for the coupling reaction between phenylboronic acid and 4-bromoacetophenone in refluxing toluene. A conversion of 98% was obtained with 1×10-4% of catalyst (TON = 9.80×105). The catalytic activity of 6 in coupling reactions between phenylboronic acid and 3-bromothiophene, 2-bromoanisole, and bromobenzene was also investigated.
