Palladium complexes spectra

A series of papers have reported35 palladium complexes of the type [Pd(B(pz)4)(A—B)], where A —B is a chelate with a carbon atom and a nitrogen or sulfur atom attached to the metal, (33). All four pz rings are equivalent in the H NMR spectrum and the tumbling mechanism is proposed. 

Thus, the historical development of the chemistry of metallocorrolates until 1980 includes complexes with Cu2+, Ni2+, Pd2+, Fe3+, Co3+, Rh+, Mo5+ and Cr5+. The palladium complex has been isolated as its pyridinium salt since the neutral species was too unstable to be isolated or spectroscopically characterized [19]. The nickel complex was non-aromatic, with one of the potentially tautomeric hydrogens displaced from nitrogen to carbon in such a way as to interrupt the chromophore. In contrast the electronic spectrum of the paramagnetic copper complex is similar to those of the fully conjugated lV(21)-methyl derivatives [11],... 

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. 

The resulting spectrum displays crosspeaks correlating carbon chemical shifts in f2 and proton shifts in f] which are further spread by homonuclear proton couplings in fi. Fig. 6.32 displays a part of the carbon-proton shift correlation spectrum of the palladium complex 6.11. Despite the extensive crowding in the aromatic region, the carbon shifts are sufficiently dispersed to resolve all correlations (note some resonances are broadened by restricted dynamic processes within the molecule and some are split by coupling to phosphorus). 

Figure 8.43. Selected ID gradient NOESY spectra of the palladium complex 8.20 recorded with a mixing time of 800 ms in each case, (a) Parent ID spectrum, (b) He selected (not shown) and (c) N-Me selected (not shown).

However, the H NMR spectrum of this compound, and that of a similar palladium complex, shows temperature dependence, which is considered to reflect site inversion about the selenium atom, rather than ring inversion (i.e. (20) (2l) and (22) (23) (Scheme 12) <76JCS(D)1227>. 

The coupling constant between trans phosphorus atoms is very large (>500 c./sec.) in platinum and palladium complexes, so and Pb give an AB spectrum. The remaining assignment can be given in terms of an AMX rather than the accurate ABX analysis. The resonances from the phosphonate P are sufficiently narrow for the doublet structure from to be resolved. The second phosphonate... 

Zirconocene-aryne complexes can also be transmetallated, opening the way to a broad spectrum of synthetic operations such as oxidation, halogenation and cross-coupling (Scheme 5). For example, transmetallation of zirconocene-aryne complex 26 with the palladium complex generated from Pd(0) and m-bromo(trifluoromethyl)benzene regioselectively affords palladium(ll) complex 27, which after reductive elimination can be iodinated to 28 [22]. Alternatively, treatment of 26 with B(OEt)3 results in the formation of 29, and its iodination and oxidation leads to 30 [23]. 

NMR spectrum with proton decoupling of an allyl palladium complex. 

These concerns were supported by the first test reactirais in which we tried to couple benzoic acid with 4-bromoanisole in the presence of palladium complexes. We encountered great difficulties with generating the palladium benzoate from palladium bromide complexes in the absence of silver salts. Phosphine-stabilized palladium benzoates, especially aiylpalladium(ll) benzoates similar to i, did not extrude CO2 even at high temperatures. Only a small spectrum of palladium arenecarboxylates and phenylacetates was identified that lost CO2 upon heating. This is in agreement with a study of the protodecarboxylation activity of palladium published subsequently by Kozlowski [28]. 

The palladium complex with 2,2-dimethyl-4,5-bis (diphenylphosphinomethyl)-l,3-dioxolan 94 and platinum reagent with l,2-bis[(diphenylphosphinomethyl)benzene] 95 are effective for alkenes, aUenes, and alkynes. The substrate displaces the ethylene hgand, and the P NMR spectrum is monitored for enantiomeric discrimination. " ... 

Complexes of the divalent metals [M(ttcn)2]2+ undergo electrochemical oxidation to paramagnetic [M(ttcn)2]3+. Red [Pd(ttcn)2]3+ has a tetragonally distorted octahedral structure (d7, Jahn-Teller distortion) with Pd—S 2.356-2.369 A (equatorial) and 2.545 A (axial) in keeping with the ESR spectrum (gj = 2.049, gy = 2.009) which also displays 105Pd hfs. Similarly, electrochemical oxidation of the palladium(II) tacn complex (at a rather lower... 

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