σ-Alkenyl endo-palladacycle formation via regiospecific functionalisation of an unreactive NHC-tethered C(sp²)–H bond

Abstract

A highly unusual cyclometallation reaction in which an aliphatic vinylic C(sp2)–H bond is activated to form a σ-vinyl palladacyclic–NHC complex is reported.

Computational Studies of Carboxylate-Assisted C–H Activation and Functionalization at Group 8–10 Transition Metal Centers

“…sequential C(sp 2 )-H activations of 1-(pyridin-2-yl)-3-allyl-1H-imidazoliums, 34, at [Pd(OAc)2] have been characterised by M06 calculations by Willans and Ariafard where optimisations were carried out in MeCN solvent 95. The pyridine moiety acts as a directing group for the initial imidazolium C-H activation to form [Pd(κ 2 -OAc)(MeCN)(κ-N,C-34')] + .…”

Synthesis of Indolo[2,3-c]quinolin-6(7H)-ones and Antimalarial Isoneocryptolepine. Computational Study on the Pd-Catalyzed Intramolecular C–H Arylation

“…The preference of the 5-coordinate transition state contradicts the hitherto putative outer-sphere CMD mechanism of C–H activation reactions in the presence of bidentate ligands . To the best of our knowledge, such a rare CMD transition state, having a distorted trigonal bipyramidal geometry around the palladium (see Animation S11 in the Supporting Information), has only been mentioned in one publication for imidazolium deprotonation, but it is unprecedented for Pd-catalyzed C–H arylation reactions.…”

“…The preference of the 5-coordinate transition state contradicts the hitherto putative outer-sphere CMD mechanism of C−H activation reactions in the presence of bidentate ligands. 36 To the best of our knowledge, such a rare CMD transition state, having a distorted trigonal bipyramidal geometry around the palladium (see Animation S11 in the Supporting Information), has only been mentioned in one publication for imidazolium deprotonation, 37 but it is unprecedented for Pd-catalyzed C−H arylation reactions. As opposed to the 5-coordinate transition states of the imidazolium C−H and the subsequent vinylic C(sp 2 )−H activations described in the literature, where the protonated base remains bound to the palladium, during the present CMD reaction, the bicarbonate decoordinates simultaneously from the metal center.…”

Solid-state structure, solution-state behaviour and catalytic activity of electronically divergent C,N-chelating palladium–N-heterocyclic carbene complexes

“…In our hands, it has been observed that modest electronic alterations of the pyridyl function are able to activate the Pd centre toward unique reactivity. 39 In light of this, it appears that the mild electronic donation from the 4-methyl substituent of the pyridyl ring is sufficient in activating the metal such that one imidazolium unit is lost to provide a vacant coordination site, which is subsequently occupied by a vicinal bromide anion.…”

“…In our hands, it has been observed that modest electronic alterations of the pyridyl function are able to activate the Pd centre toward unique reactivity. 39 In light of this, it appears that the mild electronic donation from the 4-methyl substituent of the pyridyl ring is sufficient in activating the metal such that one imidazolium unit is lost to provide a vacant coordination site, which is subsequently occupied by a vicinal bromide anion. Further supporting this notion, 4-methoxy substituted imidazolium bromide 1d was treated with 0.5 equivalents Pd(OAc) 2 to furnish only the neutral [Pd(NHC)Br 2 ] complex 4d, as evidenced by microanalytical data and X-ray crystallography ( Figure 2).…”