Coordination of palladium

PdF2 is that rare substance, a paramagnetic palladium compound, explicable in terms of (distorted) octahedral coordination of palladium with octahedra sharing corners [15], It exists in two forms, both having /zeff 2.0 /xB, rather below the spin only value for two unpaired electrons. Bond lengths are Pd-F 2.172 A (two) and 2.143 A (four) in the tetragonal form (rutile structure). 

Figure 3.67 Part of the hexameric [Pd(SPr )2]6 molecule showing square-planar coordination of palladium. (Reproduced with permission from Acta Crystallogr. Sect. B, 1968, 24, 1623.)...

The mechanism of the reaction in Figure 15.4 involves coordination of palladium to the alkene and nucleophilic attack of oxygen at the internal carbon atom to form the flve-membered ring. Palladium is bonded to the exocyclic carbon atom. (3-hydride elimination gives the exocyclic methylene,... 

A crystal structure determination for this compound showed that while the square planar coordination of palladium is retained, strain within the molecule is relieved by a folding of the ligand239 similar to that described above for salicylaldimine complexes. The fl position of these ligands may be substituted by electrophilic reagents before or after complexation.282... 

Palladation of an arene is a very facile reaction when, before the C-H activation step, coordination of palladium to a nearby ligand functionality in the molecule occurs. The first report of a stoichiometric intramolecular palladation is probably the reaction of diazobenzene and palladium chloride by Cope in 1967 [6a], Intramolecular palladation is a widespread reaction that has often been used as a starting point for synthesizing new molecules using insertion reactions in the arylpal-... 

Controlling the coordination of palladium intermediates with silver salts was the key to developing highly diastereo- and enantioselective Heck reactions.58 For example, the presence of silver phosphate in the key cyclization step during the synthesis of various alkaloids reversed the stereochemistry at the newly created spiro center (Scheme 10.33).59... 

The peripheral coordination of metals on MPc complexes results in aggregation and blueshifting of the spectra [50], Coordination of palladium to (2,3,9,10,16, 17,23,24-octakis-benzyl thiophthalocyaninato) magnesium(II) [MgPc(SBz)8] and (2,3,9,10,16,17,23,24-octakis-benzhydryl thiophthalocyaninato) magnesium(II),... 

Pd(acac)2 can be made from acetylacetone and tetra-chloropalladate salts or palladium acetate. It has a monomeric stmcture with a square-planar coordination of palladium to the four oxygens of two chelating acetylacetonates. 

In the present study the positional parameters are precisely determined (to better than 0.002 in x, y, z coordinates) except for the z coordinate of palladium. The reason for the lower precision of this parameter is not clear. It may be due in part to the small number of reflections in the pattern for which I is dominant, which arises from the short c axis and frequent extinction of Okl and hOl reflections. 

Backvall et al. reported that palladium-catalyzed 1,2-oxidation of the allenic tosylamides 231 with lithium bromide produced the 2-(l-bromoalkenyl)-iV-tosylpyrrolidines 232 in good yields (Scheme 75).148 This reaction proceeds through the coordination of palladium(II) to the allene moiety of 231, followed by nucleophilic attack of bromine atom, formation of the jr-allylpalladium intermediate 233, and the intramolecular nucleophilic attack of NHTs to the jr-allyl center carbon. 

The supported version of the catalyst was obtained via ROMP using the molybdenum-based Schrock catalyst. An inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis of the polymer revealed a palladium to bis (pyrimidine) ratio of 2 1. The authors speculated that this could be explained by coordination of palladium by alternate and repetitive bis (pyrimidine) units of the polymer chains. 

Coordination of palladium with the adjacent pyridine ring is likely to facilitate the acylation of 2-arylpyridines with ct-diketones. In the presence of t-butyl hydroperoxide (TBHP), cleavage of the diketones yields radicals that may allow the formation of intermediates such as (115), which yield the acylated products after reductive elimination. Interestingly the ortfto-aroylation of 2-aryl pyridines may also be achieved using the palladium-catalysed reaction with toluene in the presence of TBHP. Here the mechanism is likely to involve initial benzylation followed by oxidation at the benzylic position to give the acylated product. Acetanilides may also be acylated at the ort/jo-position using toluene and TBHP to yield products such as (116). Here a possible mechanism involves initial formation of a cyclopalladated intermediate followed by reaction with an acyl radical formed by oxidation of the toluene. ... 

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