Metal-proton interactions in benzylamine complexes of palladium(II): The effect of methyl substitution at nitrogen and the role of the interaction during cyclopalladation. X-ray crystal structure of tetrabenzylaminepalladium(II) acetate chloride

Abstract

Reaction of Pd(OzCMe)2 with PhCH2NHz leads to either Pd(NH2CH2Ph)2(02CMe)2 or [Pd(NH2CH2Ph)4] [02CMe],. The X-ray crystal structure of [Pd(NHZCH2Ph),] [Cl] [02CMe] shows pairs of [Pd (NH2CH2Ph),12 + ions held together by hydrogen bonds from the NH proton to chlorine and oxygen atoms of the anions, and the absence of interactions between phenyl ring ortho protons and the metal. PhCH2NHMe reacts with Pd(02CMe)2 giving Pd(NHMeCH2Ph)2(OZCMe) and PhCHzNMe2 gives the cyclometallate [Pd(NMe2CH2Ph-C,N)(p-OzCMe)]2. 'H n.m.r. spectra indicate that the complexes Pd(NMezCH2Ph)(L)(02CMe)z (L = PhNH2, o-MeC6H4NHz) prepared from [Pd(L)(02CMe)(p-02CMe)12, contain an interaction of the benzylamine ortho aromatic protons with the metal whereas Pd(NHMeCHzPh)(L)(02CMe)z (L = o-MeC,H4NH2) does not. 'H n.m.r. analysis of PdC142-and PhCH2NMe2 in (2Hl)methanol at 400 MHz indicates a 1 : 1 reaction stoichiometry and metal-proton interactions in intermediates containing above-plane and in-plane geometry of the aromatic ring, before metallation takes place. A 400-MHz spectral analysis of Pd(02CMe), and PhCH2NMe2 in CDC1, suggests similarly orientated species arise in the reaction giving [Pd(NMezCHzPh-C,N)(p-OzCMe)]2.See for example Thompson,

Computational study of the cyclopalladation mechanism of azobenzene with PdCl2 in N,N-dimethylformamide

“…On the other hand, the mechanistic schemes considered by Thummel and Jahng [31] were bound to a fixed square coordination around Pd and, consequentially, any ligand exchange, including cyclopalladation reaction, was initiated by the approach to the axial position. In a combined IR and 1 H NMR study of cyclopalladation of 3,4-dihydronaphthalene-1-one oximes with tetrachloropalladate [33], Nielson proposed a mechanism which begins with a dimeric adduct (related to 3a,b-R) and proceeds by symmetric dissociation to an unstable intermediate that could be related to the unsaturated complex 4-R. A similar proposal was advanced in a study of cyclopalladation of N,N-dimethylbenzylamine with tetrachloropalladate [34]. The reaction with Pd acetate was examined in the same study, but the spectra were too complex to identify the appropriate chemical species.…”

“…as that produced by dissociation of one ligand molecule from the bis(ligand) adduct. It is relatively unstable because Pd is k 2 -coordinated by one acetate ion, which is unlikely to be the most stable form [34], at least not in strongly coordinating solvents such as acetonitrile. The authors considered three possible pathways for proton transfer e to the pendant and coordinating oxygen atoms from acetate and to the Pd atom in an oxidative addition mechanism.…”

Chasing the CMD/AMLA Mechanism C–H···Pd Interactions in the Cyclopalladation Reaction of N,N-Dimethylbenzylamine with Pd(OAc)2

“…However, various studies have shown that the initial ligand coordination to Pd­(OAc) 2 forms dimeric complexes, so that anagostic complexes identified in 1 H NMR studies by a downfield shift of the ortho C–H bond hydrogens in comparison to the free ligand are likely to be of this form. In our very early 1 H NMR studies on the reaction at 400 MHz using a 1:1 ratio of the reactants, we were only able to find the remanent of such a complex as it appeared to have a short lifetime . By the time the reactants were mixed and the spectrum could be obtained, a poorly resolved and low-intensity resonance shifted downfield by 0.96 ppm in comparison to the free ligand was deemed to be the anagostic complex.…”

“…In our very early 1 H NMR studies on the reaction at 400 MHz using a 1:1 ratio of the reactants, we were only able to find the remanent of such a complex as it appeared to have a short lifetime. 12 By the time the reactants were mixed and the spectrum could be obtained, a poorly resolved and lowintensity resonance shifted downfield by 0.96 ppm in comparison to the free ligand was deemed to be the anagostic complex. In comparison, the reaction of N,N-dimethylbenzylamine with Li 2 PdCl 4 in CD 3 OD showed that the anagostic intermediate identified by a similar downfield shift had a much longer lifetime, 12 and this was similarly found for our more recent study of the reaction of 1-tetralone oxime with Li 2 PdCl 4 [Scheme 1 (b)].…”

A noncovalent interaction insight onto the concerted metallation deprotonation mechanism

“…In this study, we address the CMD/AMLA mechanism of cyclopalladation of N,N-dimethylbenzylamine 28 from the point of view of non-covalent interactions, by resorting not only to a standard GGA DFT-D3(BJ) method 29 to compute the associated stationary geometries, to the quantum theory of atoms in molecule 25 (QTAIM)-based methods such as the Interacting…”