Bi and trinuclear complexes in palladium carboxylate-assisted C–H activation reactions

Abstract

The role of polynuclear species in C-H activations assisted by palladium carboxylates has not been clear so far. The summary of the key findings covering this issue shows its important role under certain conditions. However, much more effort is necessary for a deeper understanding of the whole issue.

Functionalized 1,3‐Diaminotruxillic Acids by Pd‐Mediated C–H Activation and [2+2]‐Photocycloaddition of 5(4H)‐Oxazolones

“…Trinuclear complexes of stoichiometry [(C ^ N)Pd(µ‐OAc) 2 Pd(µ‐OAc) 2 Pd(C ^ N)], such as those shown in Scheme , are sometimes found in orthopalladation processes involving C–H bond activation, but these are quite rare. Such complexes have a symmetry that is compatible with the number of signals found in both the 1 H and 19 F NMR spectra of 2h and we therefore propose a trinuclear complex such as that shown in Scheme for the third compound in the mixture 2h .…”

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…The variety of additives and reaction conditions encountered in this field is also reflected by the range of metals which are applied as catalysts. There is no such thing as a single dominant metal species, but Pd, 48 , 49 Rh, 50 , 51 and Ru 52 – 54 share together the top spot. Moreover, increasing examples using Ni, 55 – 58 Co, 55 , 59 – 64 Ir, 64 – 66 Cu, 67 – 69 Fe, 3 , 55 , 63 , 70 , 71 and Mn 72 – 74 are appearing in the literature.…”

C–H Functionalizations by Palladium Carboxylates: The Acid Effect

“…This leads to the formation of palladacycles mainly existing in monomeric or dimeric forms, although polynuclear species were observed, too. 4 In the third (multiple) step, the reaction of palladacycle with a reagent leads to the formation of the product. Finally, the palladium precatalyst is regenerated and enters into a new catalytic cycle.…”

“…Deeper insight into the typical reaction scheme (Scheme 2) suggests that added carboxylic acids are the key factor for reactivity control. These acids may influence reaction by at least five different ways: (1) form a precatalyst from palladium acetate; (2) affect the reactivity of palladium in the C-H activation step; (3) protonate substrate; (4) affect oxidation potentials of palladacycles and thus their reactivity in functionalization step; 9 (5) exchange anions in other common reagents; e.g., PhI(OAc) 2 or Cu(OAc) 2 .…”