Abstract:Complete 1H and 13C NMR assignments of several aryl‐substituted π‐allyl–Pd(II) complexes were achieved using modern gradient‐based 1D and 2D experiments. In addition, unambiguous 31P assignments were readily made using an improved gradient‐enhanced 1H–31P HMBC experiment from which the regiochemistry of cationic complexes containing asymmetric bidentate ligands could also be elucidated. The effect of the nature of the substituent on allylic proton and carbon chemical shifts is briefly evaluated. Finally, a par… Show more
“…2.2:1, 1.5:1, 1.5:1, and 1.3:1 for 4 , 5 , 7 , and 8 , respectively. Their 13 C NMR spectra reveal that the terminal allyl carbon signals within each pair of isomers have similar chemical shifts (see Figure and Tables and S1), although those for the 2-methallyl species 4 and 5 are, as expected from the literature, , somewhat different from those for the 1,3-diphenylallyl analogues 7 and 8 (see Table S2). 3 Section of the one-bond 13 C, 1 H correlation NMR spectrum for 4 , revealing the cross-peaks for the two terminal allyl carbons of the two isomers.…”
Several mono-phosphoramidite and bis-phosphoramidite 2-methallyl and 1,3-diphenylallyl allyl complexes of Pd(II) have been prepared. The solid-state structure for one of these has been determined. The mono-phosphoramidite chloro-allyl complexes of Pd(II) exist in two isomeric forms in solution. 1 H, 1 H NMR exchange spectroscopy reveals that the dinuclear species [Pd(µ-Cl)(η 3 -CH 2 C(Me)CH 2 )] 2 is involved in the interconversion between the two isomers. There is evidence to suggest that phosphoramidite dissociation is not responsible for this exchange. The cationic η 3 -2-methallyl bis-phosphoramidite Pd complexes reveal nonequiValent 31 P resonances, as a consequence of slow allyl dynamics and in agreement with the preliminary X-ray structure.
“…2.2:1, 1.5:1, 1.5:1, and 1.3:1 for 4 , 5 , 7 , and 8 , respectively. Their 13 C NMR spectra reveal that the terminal allyl carbon signals within each pair of isomers have similar chemical shifts (see Figure and Tables and S1), although those for the 2-methallyl species 4 and 5 are, as expected from the literature, , somewhat different from those for the 1,3-diphenylallyl analogues 7 and 8 (see Table S2). 3 Section of the one-bond 13 C, 1 H correlation NMR spectrum for 4 , revealing the cross-peaks for the two terminal allyl carbons of the two isomers.…”
Several mono-phosphoramidite and bis-phosphoramidite 2-methallyl and 1,3-diphenylallyl allyl complexes of Pd(II) have been prepared. The solid-state structure for one of these has been determined. The mono-phosphoramidite chloro-allyl complexes of Pd(II) exist in two isomeric forms in solution. 1 H, 1 H NMR exchange spectroscopy reveals that the dinuclear species [Pd(µ-Cl)(η 3 -CH 2 C(Me)CH 2 )] 2 is involved in the interconversion between the two isomers. There is evidence to suggest that phosphoramidite dissociation is not responsible for this exchange. The cationic η 3 -2-methallyl bis-phosphoramidite Pd complexes reveal nonequiValent 31 P resonances, as a consequence of slow allyl dynamics and in agreement with the preliminary X-ray structure.
“…The carbon pseudo- trans to the P-donor, at 79.0 ppm, is found at much higher frequency than that located pseudo- trans to chloride, 61.3 ppm. For a related PPh 3 complex, reported by Akermark,16a the two terminal allyl carbon resonances are found at 78.0 and 61.6 ppm, respectively; that is, there is little difference between these two.…”
Section: Resultsmentioning
confidence: 86%
“…Moreover, the relative changes in the adjacent carbons C-4 and C-5 are modest, so that there is no reason to believe that these atoms are involved in further bonding. The three allyl 13 C positions are rather normal with those pseudo- trans to phosphorus found at higher frequency relative to those that are pseudo- trans to the new bond . Interestingly, the allyl carbon pseudo- trans to the P-donor shifts markedly to higher frequency on going from the chloro complex to the cationic complex.…”
C NMR studies have shown that in both Pd(II)-and Pt(II)-allyl (modified-MOP) (MOP ) (S)-2-diarylphosphino-1,1′-binaphthyl) complexes the substituent on the MOP auxiliary can affect how the naphthyl backbone interacts with a metal center. With the MeO-MOP analogue, the metal binds the carbon in a weak η 1 -fashion, whereas with H-MOP it prefers an η 2 -binding mode. For the Pt complexes, the 1 J( 195 Pt, 13 C) values proved to be diagnostic tools. Both modes of bonding afford relatively weak bonds to the metal. Modifying the MOP ligand structure from a PPh 2 to a P(3,5-di-tert-butylphenyl) 2 analogue can markedly affect the bond distances within the coordination sphere, as indicated by the X-ray structural data for PdCl(η 3 -C 3 H 5 )(modified-MOP). 2-D NMR exchange spectroscopy can be used to recognize and distinguish between the two most common types of η 3 -η 1 -η 3 isomerization process, i.e., rotation around the allyl C-C bond versus rotation around the allyl M-C bond. For the complex PdCl(η 3 -C 3 H 5 )(H-MOP), the fastest isomerization process involves rotation around the allyl C-C bond.Supporting Information Available: Text giving experimental details and a full listing of crystallographic data for 13, including tables of positional and isotropic equivalent displacement parameters, anisotropic displacement parameters, calculated positions of the hydrogen atoms, bond distances, and bond angles. ORTEP figure showing the full numbering schemes. X-ray data are also available as a CIF file. This material is available free of charge via the Internet at http://pubs.acs.org. OM049039T
“…These values are coincident with those reported for the tetrafluoroborate of 12. [33] At the end of the reaction the signals of 2a reappeared as a consequence of the slow transfer of palladium back to macrocycle 1a.…”
Section: Allylation Of Diphenylamine With Cinnamyl Carbonatementioning
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