Mitsuhiro Emoto

Reductive elimination of η3-allyl(aryl)palladium complexes promoted by allyl halides

Abstract Comparison between the reactivity patterns of the reactions of η 3 -allyl(aryl)palladium complexes with allyl chlorides and those with styrene, allylbenzene, methyl iodide and benzyl chloride suggested the dual role of allyl chloride in enhancing the reductive elimination of these complexes, namely coordination to Pd through the CC bond and removal of the electron density via oxidative addition. The product distribution pattern in the reductive elimination of Pd(η 3 -CH 2 CHCH 2 )(Ar)(EPh 3 ) ( 1 ) (E = P, As; Ar = C 6 H 3 Cl 2 -2,5) accelerated by CH 2 CMeCH 2 Cl (reaction A) and that of Pd(η 3 -CH 2 CMeCH 2 (Ar)(EPh 3 ) ( 2 ) accelerated by CH 2 CHCH 2 Cl (reaction B) has been determined. For the reaction of the AsPh 3 complexes both A and B carried out in toluene dichloromethane afforded, at the early stages, only the coupling product (allylbenzene derivative) associated with the allyl unit of the original complex itself. At the later stages the product derived from the substrate chloride increased owing to facile ligand exchange (allyl-methallyl and/or aryl-Cl) between 1 and 2 and the η 3 -allyl(chloro)palladium complex which is another product of the reductive elimination. Consistent with the oxidative addition of the allyl chlorides, the reaction of the PPh 3 complexes in dichloromethane and 1,2-di-chloroethane gave a greater quantity of the product derived from the substrate chloride than that from the complex even at the early stages.

Electronic effect of η5-cyclopentadienyl and η3-allyl ligands on the nature of the metal—olefin bond: Reversal of the relative olefin affinity of palladium(II) and platinum(II) ions

Abstract The barrier to olefin rotation in [Pt(η 3 -CH 2 CMeCH 2 )(olefin)(PPh 3 )]PF 6 ( 3 ) (olefin = CH 2 CH 2 , E -MeCHCHMe) has been found to be extremely low compared to those in the other known, 4-coordinate olefin complexes of Pt II . This can be ascribed to the smaller steric congestion around the olefin in 3 . The corresponding barrier in [Pt(η 5 -C 5 H 5 )(CH 2 CH 2 )(PPh 3 ]ClO 4 ( 2 ), possessing likewise small steric congestion, was substantially higher than that in 3 (olefin = CH 2 CH 2 ). The 13 C and 31 P NMR measurements have revealed much larger J (Pt-C(olefin)) in 2 than that in 3 (olefin = CH 2 CH 2 ), while J (Pt-P) are comparable in these two. Stability constant data suggested that Pd II ion in the Pd(η 5 -C 5 H 5 )(PPh 3 ) + moiety is a better π-donor to olefins than Pt II ion in the Pt(η 3 -CH 2 CMeCH 2 )(PPh 3 ) + moiety, a reversal of the normal trend in the relative olefin affinity of these metal ions. The above spectral and stability features have been related to the electronic effect of the Cp ligand in enhancing the π back-bond interaction in one particular orientation of the CC bond.

Unprecedented higher stability of E-than Z-olefin complexes of platinum(II). Molecular structures of the η3-methally(triphenylphosphine)(Z-and E-but-2-ene)-platinum(II) cation

The CC bond of Z-but-2-ene in one of the title complexes lies almost in the co-ordination plane, while that of the corresponding E-but-2-ene complex, which unprecedentedly is more stable in solution than the former, forms and angle of 67° with the plane.

Acceleration of the reductive elimination step in Pd-catalysed allylic alkylation by allylic substrates

Allylic electrophiles used in Pd-catalysed allysic alkylation greatly accelerate reductive elimination of η3-allyl(organo)palladium(II) complexes, via a PdIV intermediate, to give the coupling products and η3-allylpalladium(II) salts.

Relative stabilities of trans-dichloro(olefin)(pyridine)platinum(II) complexes. Re-examination of hammett equation for para-substituted styrene complexes

Relative solution stabilities of several olefin (L) complexes, trans-[PtCl2(py)L](1)(py = pyridine) have been measured by means of 1H n.m.r. spectroscopy by observing two separate methyl proton singlets of free CH2CHC6H4Me-o and (1; L = CH2 CHC6H4Me-o). Data for (1; L = CH2CHC6H4Y-p, Y = NMe2, OMe, Me, H, Cl, or NO2) show the higher stability for the more electron-donating olefin complex, with the Hammett ρ+ value being –0.82. This is consistent with previous 13C n.m.r. and structural trends which suggest olefin-to-Pt σ donation to be much more important than π backbonding in determining the stability of (1).