Palladium derivatives

The TV-protected pyrrole (212) can be palladated, but not lithiated, in the 3-position to give the stable complex (213) this is readily converted into the 3-methoxycarbonylpyrrole (214) (82JOM(234)l23). The use of palladium derivatives thus further increases the range of transformations made possible through the intermediacy of metallo groups. 

Gold palladium binuclear complexes [141] can be synthesized by reaction of [Au (C6F5)(tht)] with the palladium derivative trans-[pdRR (dppm)2] where R = R = QF5 R = R = CgCls R = C Fs, R = Cl. It was however not possible to distinguish the two structures for these complexes shown in Figure 3.20 ... 

The high-pressure carbonylation of dimeric palladium derivatives 183 (R = Me or cyclopropyl) in ethanol or methanol/ chloroform leads in moderate yields to fused isoindoles 184 as mixtures with their alkoxy derivatives 185, easily separated by flash chromatography (Equation (25) a991JOM371)). 

Tetrammino-palladous Salts, [PdNH3)4]R2.—These are formed by exposing anhydrous palladium salts to the action of ammonia, or by treating an aqueous solution of the palladous salt, or the corresponding diammino-palladium derivative, with excess of ammonia. The solution formed is unstable and readily loses ammonia on evaporation, passing into the more stable series mentioned above. If, however, evaporation takes place in an atmosphere of ammonia the salts may be separated. In the dry state they slowly lose ammonia in air, more rapidly on heating or in vacuo. This series of compounds are almost colourless and are soluble in water. Acids transform them easily into the diammino-compounds. 

JOM(234)l23). The use of palladium derivatives thus further increases the range of transformations made possible through the intermediacy of metallo groups. 

The vinylogous elimination to give alkenylcyclopropanes may also be effected via rt-allyl palladium complexes34,35. The palladium(0)-catalyzed substitution of allylic esters with stabilized carbon nucleophiles via 7i-allyl palladium derivatives stereospecifically proceeds with net retention (double inversion) of configuration. Thus, the chirality of an allylic substrate is transferred to resultant alkenylcyclopropanes in the intramolecular S J/ reaction via 7i-allyl palladiums (equation 21)36,3. ... 

Finally, we should mention that, in the light of these results, which established the first contact points between the chemistry of the carbonyl derivatives of nickel and platinum, some analogous palladium derivatives could be expected. Until now, however, all attempts to prepare them have failed giving only palladium metal under a variety of conditions 95). 

Up to the end of 1972, more than 350 compounds containing silicon-transition-metal bonds had been synthesized, but their distribution among the d-block elements is by no means uniform. It can be inferred that the stability of such complexes decreases from right to left in a transition series and with increasing oxidation state of the transition metal. Nevertheless, it is remarkable that no silyl derivatives of the vanadium group have been prepared and that there are few nickel or palladium derivatives, as can be seen in the complete list of compounds given in Section 6. 

Emphasis on the employment of transition metal catalysts to achieve useful synthetic transformations is illustrated by three procedures in this volume. The reaction of allylic alcohols with aryl halides in the presence of a palladium derived catalyst can be used to prepare various /3-arylaldehydes. This is illustrated by the preparation of 2-METHYL-... 

Figure 6.5 Nitrile-functionalised pyridinium ionic liquid and palladium derivatives...

It was also possible to obtain the mono zinc or palladium derivatives using equimolecular amounts of the metal salt (Scheme 76) <1995CC1077>. 

Before looking at the silver complexes, it is worth considering the palladium and platinmn complexes. These complexes (Kg. 35A) were readily made but proved rather finistrating. The platinum materials were nonmesomorphic, and while some of the longer-chain palladium derivatives showed Sc phases, this was at rather elevated temperatures (45). However, Maitlis smd co-workers showed that if the chloride ligands were replaced by long-chain alkanoates (Fig. 35B), transition temperatures were reduced and a nematic phase was observed (46). These results later proved to be more important than was realized at the time, as discussed later. 

The only electrochemical study available on palladium derivatives reports that Pd(acac)2 in acetonitrile undergoes an irreversible two-electron reduction to palladium metal Ep = -0.97 V, vs. SCE)23 . 

Palladium Derivative.—h. palladium derivative has been isolated which is almost black, and is prepared in the usual manner., ... 

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