REACTIONS OF ELECTRON-RICH ARYLPALLADIUM COMPLEXES WITH OLEFINS - ORIGIN OF THE CHELATE EFFECT IN VINYLATION CATALYSIS

Citation
M. Portnoy et al., REACTIONS OF ELECTRON-RICH ARYLPALLADIUM COMPLEXES WITH OLEFINS - ORIGIN OF THE CHELATE EFFECT IN VINYLATION CATALYSIS, Organometallics, 13(9), 1994, pp. 3465-3479
Citations number
50
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry Inorganic & Nuclear","Chemistry Inorganic & Nuclear
Journal title
ISSN journal
0276-7333
Volume
13
Issue
9
Year of publication
1994
Pages
3465 - 3479
Database
ISI
SICI code
0276-7333(1994)13:9<3465:ROEACW>2.0.ZU;2-9
Abstract
Reaction of (dippp)Pd(Ph)Cl(1) with norbornene or styrene yields (dipp p)PdCl2 (8) and (dippp)Pd(eta(2)-olefin). Kinetic follow-up reveals fa st formation of (dippp)Pd(phenylnorbornyl)Cl (10), followed by its slo w decomposition, with k(insertion) = 0.50 x 10(-3) L mol(-1) s(-1) and k(decomposition) = 0.90 X 10(-4) S-1. Phenylnorbornane and (with styr ene) stilbenes are also formed. Faster reaction is observed with (dppp )Pd(Ph)Br (2) and faster still with (dippe)Pd(Cl (4) to yield, in the latter case, the stable (dippe)Pd(phenylnorbornyl)Cl (18). The rates o f these reactions are strongly solvent dependent (DMF >> dioxane), are strongly retarded by added Cl-, and are unaffected by added phosphine , indicating that halide dissociation, followed by olefin coordination and rate-determining olefin insertion, are involved. In contrast, rea ction of trans-(P(i)Pr(2)(n)Bu)(2)Pd(Ph)X (X = Cl, 5; X = Br, 6) with norbornene (or styrene) involves phosphine dissociation and leads to f ormation of (P(i)Pr(2)(n)Bu)(2)Pd(H)X. In the case of norbornene, beta -carbon elimination of the unobserved intermediate phenylnorbornyl com plexes followed by beta-H elimination yields 1-methylene-2-phenylcyclo hexenes. Complexes of the ligand dippb are unique in that both eta(1) and eta(2) coordination modes are easily accessible. While reaction pr oducts are similar to those obtained with dippp and dippe complexes, d ependence of the reaction rate on reaction variables is intermediate b etween those observed for complexes of chelating and monodentate phosp hines. The implications of these findings on catalysis are outlined.