Recent advances in annellated NHCs and their metal complexes

Electronic Asymmetry of an Annelated Pyridyl–Mesoionic Carbene Scaffold: Application in Pd(II)-Catalyzed Wacker-Type Oxidation of Olefins

“…One class of ligands which are particularly suitable to endure harsh conditions in oxidation chemistry is mesoionic carbenes (MICs) . Moreover, annelated carbenes exhibit unique stereoelectronic properties which can result in improved catalytic activity and selectivity of their metal complexes . An annelated pyridyl–MIC (aPmic) ligand (Scheme e) was reported from our group for Ru­(II)-catalyzed selective CC bond scission of olefins to aldehydes using NaIO 4 as an oxidant at room temperature .…”

“…15 Moreover, annelated carbenes exhibit unique stereoelectronic properties which can result in improved catalytic activity and selectivity of their metal complexes. 16 An annelated pyridyl−MIC (aPmic) ligand (Scheme 1e) was reported from our group for Ru(II)-catalyzed selective CC bond scission of olefins to aldehydes using NaIO 4 as an oxidant at room temperature. 17 We now unravel the electronic asymmetric nature of aPmic in Pd-catalyzed Wacker-type oxidations.…”

Influence of the Flexibility of Nickel PCP‐Pincer Complexes on C−H and P−C Bond Activation and Ethylene Reactivity: A Combined Experimental and Theoretical Investigation

“…[48][49][50][51][52][53][54][55][56] Consequently, it is not surprising that the chemistry of nickel complexes with NHC-containing pincer-type ligands is developing very fast, as documented in recent articles and reviews. [4,35,53,57] The stereoelectronic properties of NHCs can be modulated by the nature of the N-substituents (or wingtip substituents) and of the heterocycle itself by including or not electronic unsaturation, annelation, [22] or by varying its ring size, typically from five to six. In contrast to five-membered ring NHCs, which attract the most attention, expanded ring NHCs are endowed with higher basicity, [58][59][60][61] display larger NÀ C NHC À N angles, [59,62,63] and represent promising platforms for transition metal reactivity and catalysis.…”

Experimental and Theoretical Study of NiII‐ and PdII‐Promoted Double Geminal C(sp3)−H Bond Activation Providing Facile Access to NHC Pincer Complexes: Isolated Intermediates and Mechanism

“…[2][3][4][5]7,8,13,15,16,19,[41][42][43][44][45][46][47][48][49] The steric properties of NHCs can typically be modified by the choice of the N-substituents (or wingtip substituents) or the size of the heterocycle, whereas electronic properties are influenced by the nature and number of endocyclic heteroatoms, the site of attachment of the metal on the ring, the electronic saturation or unsaturation of the heterocycle, and a possible annellation resulting from fusing an additional ring on the basic framework. [50] Most synthetic methods leading to NHC complexes or to NHC-containing pincer complexes involve i) deprotonation of azolium salts to give a free or a coordinated NHC ligand (when a metal-bound ligand acts as an internal base), [7,8,41,[51][52][53] ii) transmetallation from silver, copper or mercury reagents, [7,8,23,[54][55][56][57] both approaches occur without modification of the metal oxidation state, [3,7,8,23,41] or iii) oxidative addition of an azolium C sp 2 (2)À H bond across a zerovalent metal precursor, which was introduced about 20 years ago. [58][59][60][61]…”