Web Release Date: March 1,
Synthesis of Monodentate Ferrocenylphosphines and Their Application to the Palladium-Catalyzed Suzuki Reaction of Aryl Chlorides
and
Department of Chemistry, Cardiff University, P.O. Box 912, Cardiff, CF10 3TB, UK, and Department of Chemistry, Queen Mary, University of London, Mile End Road, London, E1 4NS, UK
Received October 10, 2002
Abstract:
Racemic and enantiopure (pS)-1-bromo-2-methylferrocene 6 were synthesized in 4 steps from 2-(4,4-dimethyloxazolinyl)ferrocene and (S)-2-(4-methylethyloxazolinyl)ferrocene, respectively (46 and 81%
overall yield). Bromolithium exchange and addition of ClPR2 gave the corresponding racemic or
enantiopure 2-methylferrocenyl phosphine ligands 2-MeFcPR2 11 (R = Ph), 12 (R = Cy), and 13 (R
= tBu) in 28-93% yield. Use of PCl3 gave the C3-symmetric phosphine (2-MeFc)3P 5 from (pS)-6
(72% yield) but racemic 6 did not lead to the formation of triferrocenyl phosphines. Combination of
5 and Pd2(dba)3 gave an active catalyst for the Suzuki reaction of aryl chlorides, for example,
4-chlorotoluene and phenylboronic acid reacted at only 60 
C in dioxane (86% yield). Other examples
are reported together with the use of 12 in this same protocol. From the X-ray crystal structure of
5 the cone angle was determined as 211. With this, and the electronic character of 11, 12, and
other phosphines (derived from 
CO of trans-[(R3P)2Rh(CO)Cl]), an analysis is made of the steric
and electronic influences on ligand activity in the Suzuki reaction.
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