24981-80-4

On the basis of fundamental studies on oxidative addition of carboxylic anhydrides to zerovalent palladium complexes to yield acyl(carboxylato)bis(tertiary phosphine)palladium(II) complexes and their reactions with organoboronic acids to yield ketones, a novel catalytic process has been developed. This converts carboxylic anhydrides and organoboron compounds into ketones catalyzed by palladium complexes under mild conditions. The process provides a general, versatile, synthetic method to produce various symmetrical and unsymmetrical ketones with aromatic, aliphatic, and heterocyclic groups. The catalytic cycle is proposed to comprise (a) oxidative addition of a carboxylic anhydride to produce an acyl(carboxylato)palladium intermediate, (b) transmetallation with an organoboron compound to give an acyl(organo)palladium intermediate, and (c) its reductive elimination to yield a ketone. Not only homogeneous catalyst systems but also heterogeneous systems were found to give ketones under mild conditions.

A novel redox reaction involving fluoride and phosphine complexes of palladium(II) is reported. The scope of this reaction has been investigated using the ligands PPh3, Ph2P(CH2)nPPh2 (n = 1-4), Ph2PCH2C(CH3)2CH2PPh 2, Ph2PCH3, and P(CH2CH2CN)3; several solvents including DMSO, pyridine, acetonitrile, and THF; and either n-Bu4NF·3H2O or KF/18-crown-6 as the fluoride source. The reduction products are palladium(0) phosphine complexes for which this reaction offers a convenient synthetic route. 31P and 19F NMR spectra permitted identification of the initial oxidation products as difluorophosphoranes (R3PF2), which subsequently hydrolyzed, forming phosphine oxides if a hydrated fluoride source is used. Results implicating a fluoride-induced redox reaction in the thermal decomposition of [(Ph3P)3PdCl]BF4 to yield [Pd3Cl(PPh2)2(PPh3) 3]BF4 are also presented. Preliminary results indicate that platinum complexes also undergo this reaction, but nickel complexes yield NiF2. The X-ray parameters for Pd(dppp)2 (dppp = 1,3-bis(diphenyphosphino)propane) are: monoclinic, space group C2/c (No. 15), a = 18.396 (2) A?, b = 13.290 (1) A?, c = 20.186 (2) A?, β = 109.383 (5)°, and Z = 4.

The palladium(II) complexes Pd(NO2)2L2 (L = PPh3, PMePh2, PMe2Ph, PEt3) react with CO to form Pd4(CO)5L4. These reaction products have been characterized by IR and 31P, 1H, and 13C NMR spectroscopy. Pd4(CO)5(PPh3)4 crystallized in the monoclinic space group C2/c with Z = 4, a = 24.957 (5) ?, b = 16.138 (3) ?, c = 17.758 (3) ?, and β = 103.47 (2)°. The palladium atoms are at the corners of a distorted tetrahedron in which five of the six edges are bridged by the carbonyl ligands. The unbridged edge has a Pd-Pd distance of 3.209 (1) ?, indicating the absence of a metal-metal bond. The average bonding Pd-Pd distances are 2.753 (1) and 2.758 (13) ?. The average Pd-P distance is 2.318 (2) ?, and the average Pd-C-Pd angle is 82.0°. Pd(NO2)2(PEt2Ph)2 and PdCl(NO2)(PEt2Ph)2 react with CO to form the novel Pd(I) dimer Pd2(CO)Cl2(PEt2Ph)3, which was also structurally characterized by X-ray crystallography. The compound crystallized in the monoclinic space group P21/a with Z = 4, a = 20.041 (3) ?, b = 11.353 (3) ?, c = 19.920 (5) ?, and β = 129.16 (1)°. The molecule is dimeric with a Pd-Pd bond and is the first example of a semibridging carbonyl ligand in palladium complexes. Pd2 has roughly square-planar geometry with two phosphines, one chloride, and Pd1 comprising its coordination sphere. One phosphine, one chloride, Pd2, and the carbonyl ligand comprise the coordination sphere of Pd1. The semibridging carbonyl produces severe distortion in the coordination geometry of both Pd1 and Pd2. Some important distances and angles include Pd1-Pd2 = 2.6521 (3) ?, Pd1-C = 1.874 (3) ?, Pd2-C = 2.110 (3) ?, and Pd1-C-Pd2 = 83.3 (1)°.

A variety of mono- and diorganopalladium complexes, trans-PdR(X)L2 (R = Me, Et, and Ph; X = Cl, Br, I, and aryloxo; L = teritary phosphine ligand) and cis-PdMe2L2, react with carbon monoxide and secondary amines under mild conditions to give α-keto amides as double-carbonylation products. A series of acylpalladium complexes, trans-Pd(COR)X(PMePh2)2 (R = Ph, X = Cl, Br, and I; R = Me, X = Cl), the presumed reaction intermediates, were prepared, and their reactions with carbon monoxide and amines were investigated. The reaction of benzoylpalladium having bromo and iodo ligands with CO and amines proceeds more smoothly in a solvent of higher polarity than in nonpolar solvents, whereas the reaction with benzoyl(chloro)palladium complex takes place more readily in nonpolar solvents. On the basis of the effect of the solvent polarity on the reactions, two types of reaction pathways have been proposed: one involves an ionic acyl(carbonyl)palladium intermediate [PhCOPd(CO)L2]+X- attacked by amine to give acyl-carbamoyl species, from which α-keto amide is reductively eliminated, while the other mechanism proceeds through a neutral acyl-carbonyl intermediate [Pd(COR)(CO)XL]. Evidence to support the former mechanism has been obtained from the experiments using trans-[Pd(COPh)(CO)(PMePh2)2]ClO4, which is prepared by the treatment of trans-Pd(COPh)Cl(PMePh2)2 with AgClO4 and CO.

Some cyclopentadienyl complexes of palladium and platinum, when treated with tertiary phosphines, are shown to promote and undergo H-D exchange reactions with a range of deuterated solvents. Two or more routes are involved in the exchange process, one of which depends on base catalysis via zerovalent metal complexes generated during the course of the reactions.

[Pd(η3-allyl)(η5-C5Me 5)] complexes react with tertiary phosphines and phosphites in a stepwise manner to give initially (η1-allyl)palladium complexes of the type [PdL(η1-allyl)(η5-C5Me5)]. Reaction with a second ligand molecule leads to transfer of a hydrogen atom from a ring-methyl group to the allyl group to give the (tetramethylfulvene)palladium(0) complex [PdL2(η2-CH2=C5Me4)]. The coordination of the fulvene molecule to the metal through the exo-methylene group has been established by an X-ray crystal structure determination of the trimethylphosphine adduct (space group P21/a, a = 12.139 (2) A?, b = 13.468 (2) A?, c = 12.294 (1) A?, β = 105.874 (8)°, Z = 4).