α-Substituted Benzylic Complexes of Palladium(II) as Precursors of Palladium Hydrides

Abstract

The adoption of a pseudoallylic (η 3) form makes palladium benzylic derivatives a class of stabilized palladium alkyls that can undergo β-H elimination reactions in a more controlled way. α-(Pentafluorophenylmethyl)benzyl palladium complexes have been studied and they decompose by β-H elimination to give palladium hydrides that, depending on the auxiliary ligands can: a) transmetalate to another palladium atom and, by reductive elimination, give hydrogenated products; this process is favored for a combination of bridging ligands (i.e halogens) and low coordinating ligands. b) Be used as a hydride source and get trapped by a diene to give palladium allylic derivatives. The presence of carbon monoxide does not induce a β-H elimination reactions and only CO insertion into the Pdbenzyl bond to give acyl derivatives is observed.

[2,2′-Bipyridin]-6(1H)-one, a Truly Cooperating Ligand in the Palladium-Mediated C–H Activation Step: Experimental Evidence in the Direct C-3 Arylation of Pyridine

“…This indicates that the ligand is capable of assisting the C–H cleavage. The acid generated in the reaction is responsible for the formation of the reduction product ArH, either directly or through the generation of a Pd–H moiety by protonation of Pd(0) and subsequent H transmetalation in a dimer . In the presence of Cs 2 CO 3 , the amount of ArH is reduced, and Ar-py was observed in 82% yield.…”

Highly efficient vinylic addition polymerization of 5-vinyl-2-norbornene using benzylic palladium complexes as precatalysts

“…We have been working for some time with η 3 -benzylic palladium complexes and studying their structure and reactivity. 22,23 We rationalized that in the context of the vinylic addition (VA) polymerization of norbornenes these complexes might be ideal precursors since the η 3 -benzyl moiety can easily interconvert into the σ-benzyl form, leaving a coordination site available and facilitating the subsequent initiation by coordination and insertion of NB. Because of the easy transformation into the σ-benzyl, driven by the recovery of the aromaticity of the ring, these complexes might be superior precatalysts than the more commonly used η 3 -allyl palladium complexes (Scheme 2).…”

Polymerization of norbornene and alkenyl-norbornenes catalyzed by palladium-benzyl or nickel-aryl complexes: Effects in polymer structure and application as catalyst support

“…The data for the decomposition are collected in Table 1.3. 44 The times for complete decomposition are given and they show large differences in stability. The cationic derivatives are more stable than their neutral counterparts.…”

“…The pentacoordinated complexes 6d and 6e decompose fast even at low temperature (entries 5 and 6, Table 1.3). Both are fluxional and the dynamic behavior of complex 6d indicates a fast 44 Martín-Ruiz, B; Pérez-Ortega, I; Albéniz, A. C. Organometallics 2018, 37, 1665-1670 ligand exchange above 253 K (Scheme 1. 16 and Figure 1.16).…”

“…The study of the behavior of the palladium benzylic complexes as precursors of Pd-H and the trap of these species in the presence of olefins was studied before in Chapter 1 (section 1.2.3.2). 44 The initiation step for the vinylic addition polymerization of norbornene and their derivatives with the benzylic complex 4e is a particular case of the interaction of this complex with olefins and can follow two different pathways summarized in Scheme 2.11. In Path a), the polymerization starts by insertion of the endocyclic double bond into the Pd-H bond of the intermediate [PdHLn] + generated by -hydrogen elimination.…”