Palladium-catalyzed, base-free olefin arylation is possible. Thus, reaction of chlorobenzene with styrene and zinc to yield cis-stilbene is catalyzed by Pd-(dippp)2 (2) (or by Pd(OAc)2 + 2dippp; dippp = 1,3-bis(diisopropylphosphino)propane). Other aryl chlorides are also reactive, whereas aryl bromides undergo substantial reduction and coupling. The reaction was discovered as a result of the observation that cis-(dippp)-Pd(Ph)Cl, formed upon oxidative addition of PhCl to 2, reacts with excess styrene (in the presence or absence of base) to generate H2 and yield (dippp)Pd(styrene) and (dippp)PdCl2(5). The latter complex is formed as a result of the instability of the putative cis-(dippp)Pd(H)Cl. 5 can be reduced to Pd(dippp)2 with zinc in the presence of dippp. Pd(dippb)2 (1) (dippb = 1,4-bis(diisopropylphosphino)butane), which yields a trans-oxidative-addition product with PhCl, is inactive in the base-free catalysis, and monophosphines are not effective. This novel reaction is complementary to the normal vinylation of aryl chlorides catalyzed by Pd(dippb)2 under basic conditions, which leads to trans products.
|Number of pages||2|
|Publication status||Published - 1993|
ASJC Scopus subject areas
- Inorganic Chemistry
- Organic Chemistry