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

Abstract

Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium C sp2 À H bond with [Ni(cod) 2 ] affording a carbanionic ligand in [NiCl(PC sp3 H P)] (8) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PC NHC P)]PF 6 (9) upon halide abstraction; 3) ethylene insertion into the NiÀ H bond of the latter and ethyl migration to the NÀ CÀ N carbon atom of the heterocycle in [Ni(PC Et P)]PF 6 (10); and 4) an unprecedented CÀ P bond activation transforming the PÀ C NHC À P pincer ligand of 8 in a CÀ C NHC À P pincer and a terminal phosphanido ligand in [Ni(PPh 2 )(CC NHC P)] (15). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.

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

“…In both cases, the chloride ligand contributes to the stabilization of the complex. It is noteworthy that the preference for alkyl versus NHC coordination has been rarely encountered in structurally characterized examples (Zr, [93] Mn, [94] Ni, [95,96] Pd, [62,97,98] and Ir [76] ).…”

Mechanistic insights into C(sp2)-H activation in 1-Phenyl-4-vinyl-1H-1,2,3-triazole derivatives: a theoretical study with palladium acetate catalyst

“…In addition, several studies have pointed to the use of auxiliary ligands that have allowed the selective activation of C-H bonds in complex molecules. [18][19] In this context, the mechanism for activation of C-H bonds can occur by a variety of pathways, such as concerted metalation deprotonation (CMD), Aromatic Electrophilic Substitution (SeAr), Internal Electrophilic Substitution (IES) and Base-Assisted IES (BIES) and Ambiphilic Metal-Ligand Assistance (AMLA), [20][21][22][23][24][25] thus broadening the scope and potential of this eld of research on C-H activation mechanisms. [26] Computational methods are a valuable tool for exploring the inherent complexity of the carboxylateassisted C-H bond activation process.…”

New Pyridine Dicarbene Pincer Ligands with Ring Expanded NHCs and their Nickel and Chromium Complexes

“… [1a,c,i,j] In a limited number of studies, mesoionic triazol‐based wingtips (type II in Figure 1) have been employed; [7] in contrast, wingtips based on the RE‐NHCs (type III in Figure 1) are unknown [8] . Interestingly, the picture regarding the nature of the NHC as bridgehead functionality shows more abundant usage of RE‐6 NHCs, that have led to remarkable structural and reactivity differences compared to analogous 5‐membered moieties (in particular, with donor atoms OC NHC O of aryloxide, [9] NC NHC N of pyridine or imine, [10] PC NHC P [11] of dialkyl‐ or diaryl‐phosphane). Herein, we report the synthesis of pyridine dicarbene pincer (pro)‐ligands featuring RE‐6 NHC wingtips (type III , E=N) and their usage in accessing Ni and Cr complexes of catalytic relevance.…”