Pyridine 2- -, palladium complex

Nitrogen nucleophiles, in a similar manner to oxygen- and sulfur-based functionality, undergo transition metal-catalyzed cross-coupling with halopyridines. The use of palladium(O) catalysts is most effective in combination with chelating bis-(phosphine) ligands such as BINAP that prevent the formation of pyridine-palladium complexes that... 

Hydrosilylation of dienes accompanied by cyclization is emerging as a potential route to the synthesis of functionalized carbocycles. However, the utility of cycliza-tion/hydrosilylation has been Umited because of the absence of an asymmetric protocol. One example of asymmetric cycUzation/hydrosilylation has been reported very recently using a chiral pyridine-oxazoUne ligand instead of 1,10-phenanthroline of the cationic palladium complex (53) [60]. As shown in Scheme 3-21, the pyridine-oxazoUne Ugand is more effective than the bisoxazoUne ligand in this asymmetric cyclization/hydrosilylation of a 1,6-diene. 

Figure 6.16. Aerobic oxidation of 1-phenylethanol catalysed by palladium complexes of a fluorous pyridine...

A single report appears in the literature regarding the use of chirally modified palladium catalysts in reductive enyne cyclization.60 Upon exposure of 1,6-enyne 36a to the indicated palladium pyridine-oxazoline complex in the presence of EtjSiH, cyclization product 36b is formed in good yield, but with only modest levels of asymmetric induction (Scheme 26). 

Another palladium complex, namely, a six-membered cyclopalladate complex of 2-benzoyl pyridine, has also been used for the hydrogenation of polymers [77, 78]. Possible catalytic mechanisms for the hydrogenation of natural rubber [76] and NBR [77] catalyzed by these two complexes were proposed, but unfortunately the authors did not provide sufficient evidence to support their proposed mechanisms. 

The insertion of allenes in the palladium-carbon a bond of cyclopalladated pyridine derivative 295 (cf. 00CRV3067) affords stable, isolable (ry -allyl) palladium complexes (e.g., 296) (03JOM(687)313). The ideally located imine unit when depalladated reacts selectively with the allyl functionality to yield methylene morphanthridizinium salts 297a-c. 

Table 7 Asymmetric cyclization/hydrosilylation of dimethyl diallyl malonate catalyzed by palladium pyridine-oxazoline complexes...

The asymmetric Baeyer-Villiger oxidation using a palladium complex of 2-(phosphinophenyl)pyridine ligand provides a useful procedure for the synthesis... 

C2H,N, Pyridine, 3,5-dimethyl-palladium complex, 26 210 CbHsNO, Benzoyl isocyanide chromium com-C HbO, Ethanone, 1-phenyl-manganese complex, 26 156-158 CBH, 02, Methyl benzoate chromium complex, 26 32 C H i, o-Xylylene magnesium complex, 26 147 ChH P, Phosphine, dimethylphenyl-iron complex, 26 61 ruthenium complex, 26 273 ChH12, 1,5-Cyclooctadiene iridium complex, 26 122 ruthenium complexes, 26 69-72, 253-256 ChH OjPS, 2-Butenedioic acid, 2-(dimethylphosphinothioyl)-dimethyl ester, manganese complex, 26 163... 

NC12Hm, Pyridine, 2-(phenylmethyl)-palladium complex, 26 208-210 NCi2H,j, Naphthalenamine, /V.A -dimethyl-lithium complex, 26 154 NCi2Hv, Benzo[/i]quinoline ruthenium complex, 26 177 NCojCuO CuH, Ruthenium, (acetonitrile)-dodecacarbonyltricobaltcopper-, 26 359 NCo Oi RuC,2H2(1, Ruthenate(l-), dodeca-carbonyltricobalt-tetraethylammonium, 26 358 NCrFeOvP2C45Hji, Chromate(l-), hydri-dononacarbonyliron-(x-nitrido-bis( triphenylphosphorus)( 1 +), 26 338... 

Balch ei al. (306) have given a detailed report on novel A-frame-type methylene bridged palladium complexes of composition Pd2(dpm)2( p-CHR)X2 (X = I, Br, Cl R = H, CH3) and [Pd2(dpm)2(joi-CH2)L2]2+ (L = pyridine, methylisocyanide). It was demonstrated that the Pd—C (methylene) bond resists insertion of carbon monoxide, isocyanides, or sulfur dioxide. Protonation of Pd2(dpm)2(/x-CH2)I2 with fluoroboric acid yields the compound [Pd2(dpm)2(ju.-I)(CH3)I]BF4 in which the bridging methylene group of the precursor has been converted into a terminal methyl group, a process that has also been encountered in a previous example (52). 

Zn2+ correlate can be obtained, as pyridinium salt, by reaction of corrole with zinc acetate in pyridine [25] in a procedure similar to that reported for the preparation of nickel and palladium complexes of corrole [11]. The zinc derivative is not paramagnetic and its formulation has been made on the basis of its proton NMR spectrum. Attempts to isolate the neutral zinc complex have been unsuccessful. 

A similar borderline system, fran -bis[2-(2-chloroethyl)pyridine]palladium chloride (1), has been prepared and structurally characterized by X-ray spectroscopy and computational study.2 A study on the elimination reaction of (1) induced by quinuclidine in acetonitrile has been performed (Scheme 1). The results suggest that the initial product of elimination is a palladium complex of vinylpyridine and that displacement from this complex is partially rate determining in the formation of the uncoordinated product. Despite experimental efforts, it was not possible to distinguish between two possible mechanisms, E2 concerted or ElcB. 

Pd(II) catalysts have been widely used for aerobic oxidation of alcohols. The catalytic systems Pd(OAc)2-(CH3)2SO [14] and Pd(OAc)2-pyridine [15] oxidize allylic and benzylic alcohols to the corresponding aldehydes and ketones. Secondary aliphatic alcohols, with relatively high water solubility, have been oxidized to the corresponding ketones by air at high pressure, at 100 °C in water, by using a water-soluble bathophenanthroline disulfonate palladium complex [PhenS Pd(OAc)2] [5d]. The Pd catalyst has also been successfully used for aerobic oxidative kinetic resolution of secondary alcohols, using (-)-sparteine [16]. 

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