Palladate chloride complexes

The results on Pd complexes as catalyst for the 1 1 codimerization are very limited at this time (85-87). Schneider (85, 86) found that palladous chloride in conjunction with dibutylaluminum chloride catalyzes the formation of exclusively trans-1,4-hexadiene as the 1 1 codimerization product of ethylene and butadiene. A vyn-7r-crotylpalladium complex was postulated as the key intermediate. The criterion for selectivity toward... 

My last comment concerns the reaction of palladium olefin complexes with carbon monoxide discovered by Tsuji. I agree that this is most likely to proceed by an insertion rather than an ionic mechanism. Chloride attack on coordinated olefin is rare however. Chloride ion is an inhibitor, for example in the palladous chloride catalyzed hydration of ethylene (0). I, therefore, wondered whether carbon monoxide was affecting the ease with which chloride attacks olefin. One can postulate that carbon monoxide participates in this insertion either as a gas phase reactant or by first forming a carbonyl olefin complex. Such complexes of the noble metals were unknown, but examining the reaction between carbon monoxide and the halogen bridged olefin complexes of platinum revealed that they are formed very readily... 

Dichlor-palladous Acid, H2PdCl2(OH)2.—On adding a silver salt to a solution of palladous chloride a precipitate is obtained, not of silver chloride, but of a complex compound of composition PdCl2.2AgOH or [PdCl2(OH)2]Ag2. It seems possible, therefore, that palladous chloride can, in aqueous solution, act like an acid, yielding the ions ... 

Palladium chlorophthalocyanine is formed when phthalonitrile is heated with palladous chloride. Like other nuclear halogen-substituted phthalocyanines, it will not sublime (11, 278). The unsubstituted derivative may be prepared by the dehydrogenation of tetracyclohexenotetrazaporphin with palladium black (113), or by the action of palladous chloride on lithium phthalocyanine in absolute alcohol (11). It is also possible to prepare the complex by dissolving palladium black in boiling phthalonitrile, a really remarkable reaction. 

Palladous chloride is soluble in hydrochloric acid, forming the ion [PdClJ2- and will also react with many ligands, L, such as amines, benzo-nitrile and phosphines to give complexes of the types L2PdCl2 and [LPdCl2]2 PtCl2 is similar. 

Palladous chloride sodium dichromate a,y -Ethyleneketones and a-diketones from ethylene derivatives via palladous chloride jr-allyl complexes... 

Several examples of the cyclization of indole derivatives with alkenic side chains in the 3-position have been reported.6 In these examples, palladium chloride in combination with silver tetrafluoroborate is the cyclizing agent. The palladium tetrafluoroborate, presumably formed, should be a very reactive palladating species and probably is the reason why these reactions proceed at room temperature, although the mechanism is not yet completely clear. These reactions were worked up reductively (by addition of sodium borohydride) in order to reduce the expected alkenic product or any relatively stable organopalladium complexes that may have been formed (equation 4).6... 

C. Marie and R. Marquis, and I. Bellucei and D. Venditori. W. Manchot and A. Waldmiiller obtained with palladium salts the complexes palladous dinitrosyl-chloride, PdCl2.2NO, and palladous dinitrosylsulphate, PdS04.2N0. They are unstable salts giving off nitric oxide in the presence of water. Nitric oxide with palladous nitrate yields Pd(N02)2. Hence, nitric oxide is known to form complexes with the salts of Cu, Mn, Fe, Co, Ni, and Pd. 

Addition of cupric chloride (CuCl2) influences the ratio of the Markovnikov-like to the anti-Markovnikov-like product.21 Palladation of 2-methyl-2-butene without CuCl2 preferentially removed Ha to give 348 (71% 348 + 29% 347). Addition of CuCl2, however, led to removal of Hb to give 74% of 347 and 26% of 348. 1 The general order for removal of allylic protons appears to be CH3 > CH2 CH.21/ Conformational effects can alter this order or reactivity, however. The syn-complex usually predominates, as in the reaction of 4-methyl-3-heptene to give 345. Both ( )- and (Z)-isomers of the alkene led to the syn-isomer 345, without a trace of the anti-isomer (349). 

A 2.134-g. (0.0202-mol) quantity of palladium metal is dissolved in aqua regia (3 ml. of 15 N HNOj + 12 ml. of 12 N HCl) which has been allowed to stand for about 30 minutes. If powdered palladium is used, no heat is required to effect solution for other forms of palladium metal, some heating is usually required. The solution is evaporated on a steam bath to a brown-black syrup, which is then covered with 5 ml. of 12 N hydrochloric acid and evaporated to moist salts. This treatment with hydrochloric acid is repeated twice more to remove nitric acid and to destroy nitrosyl complexes. The resulting tetrachloro-palladic(II) acid is dissolved, with stirring and heating, in a minimum volume of water (approximately 100 ml.), and 4.0 g. (0.068 mol) of sodium chloride is added. The dark brown solution is concentrated to one-half its volume on a hot plate and is then evaporated to dryness on a steam bath. This evaporation removes excess hydrochloric acid, which if allowed to remain leads to contamination of the tetra-amminepalladium(II) tetrachloropalladate(II) with the isomeric hydrochloric acid also prevents loss of product owing to... 

There are two structurally characterized examples in which an arylpalladium(ll) coordinates to silver(l) in a type 11 fashion (Scheme 10). First, Kickham and Loeb [40] reported that an attempt to abstract the chloride ligand in a palladated thiacyclo-phane with two equivalents of silver(l) triflate unexpectedly resulted in the formation of a bimetallic complex in which the silver(l) ion is encapsulated by three oxygen atoms and an interaction with the Pd-C bond. Then, Braunstein et al. [41] synthesized a remarkable one-dimensional coordination polymer by reacting the phosphanyl immolate palladium complex depicted in Scheme 10 (bottom) with silver(l) triflate. 

Another study used a novel approach involving a nonchelating diolefin, which forms a stable 77-allyl complex upon hydroxypalladation. As shown in Scheme 9 the stereochemistry of the consistent complex was only with anti addition. Some of the objections applied to previous studies apply here. The solvent is not pure water and the system is chloride starved. However, an even more important objection applies in this example. Thus, as will be discussed in Sect. C, cyclohexene-type structures undergo anti hydroxy-palladation even under the usual Wacker conditions. Thus, the cyclohexadiene is not a valid model for the acyclic olefins of interest. 

Procedure. One drop of a saturated mercuric cyanide solution, followed by a drop of the test solution, and a further drop of mercuric cyanide solution, are placed on filter paper. The palladium is precipitated as palladous cyanide in the middle of the fleck, whereas the gold and platinum complex cyanides diffuse outwards, and can be completely washed away with several drops of water. Stannous chloride is then placed on the middle of the fleck. A dark orange to yellow-gold color appears if palladium is present. 

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