Gas‐phase functionalized carbon‐carbon coupling reactions catalyzed by Ni (II) complexes

Abstract

Gas‐phase C―C coupling reactions mediated by Ni (II) complexes were studied using a linear quadrupole ion trap mass spectrometer. Ternary nickel cationic carboxylate complexes, [(phen)Ni (OOCR1)]+ (where phen = 1,10‐phenanthroline), were formed by electrospray ionization. Upon collision‐induced dissociation (CID), they extrude CO2 forming the organometallic cation [(phen)Ni(R1)]+, which undergoes gas‐phase ion‐molecule reactions (IMR) with acetate esters CH3COOR2 to yield the acetate complex [(phen)Ni (OOCCH3)]+ and a C―C coupling product R1‐R2. These Ni(II)/phenanthroline‐mediated coupling reactions can be performed with a variety of carbon substituents R1 and R2 (sp3, sp2, or aromatic), some of them functionalized. Reaction rates do not seem to be strongly dependent on the nature of the substituents, as sp3‐sp3 or sp2‐sp2 coupling reactions proceed rapidly. Experimental results are supported by density functional theory calculations, which provide insights into the energetics associated with the C―C bond coupling step.

Modeling Metal-Catalyzed Polyethylene Depolymerization: [(Phen)Pd(X)]+ (X = H and CH3) Catalyze the Decomposition of Hexane into a Mixture of Alkenes via a Complex Reaction Network

“…This is explained by the additional stabilization of Pd-hexyl complex 3-Pd by Pd−H agostic interactions. We have reported similar interactions in the gas phase found in Ni-organic complexes 18 and in Pd and Ni complexes with alkyl chains with two carbons or longer. 9,10 These types of interactions have also been found in solution and in the solid phase for Ni, Pd, and Pt complexes.…”

Gas‐Phase Models for the Nickel‐ and Palladium‐Catalyzed Deoxygenation of Fatty Acids

“…Most of the previous gas‐phase decarboxylation reactions [Eq. (4)] were limited to simple coordinated anions such as formate, acetate, and benzoate [31,32] which undergo decarboxylation upon CID. Decarboxylation accompanied by dehydrogenation, as seen with the fatty acids above, can only be observed for carboxylic acids with α and β hydrogen atoms in the side chain.…”

“…The resulting conformer of 1‐Pd is then stabilized via agostic interactions between Pd and β‐H atom of the side chain. Such interactions are quite well known, [31,38] and their importance in subsequent fragmentation reactions will be addressed below. The next barrier, lower in energy than the critical one by 6.4 kJ/mol, corresponds to the extrusion of CO 2 via a four‐membered TS, leading to the formation of organopalladium species 2‐Pd .…”

Ion‐molecule reactions of mass‐selected ions

“…Another C–C coupling system published by Piacentino et al demonstrated the ability of Pesci decarboxylation products (O'Hair & Rijs, 2015) to react with a wide range of esters to form new C–C bonds as shown in Equations () and () below. (Piacentino et al, 2019) $$${[(\text{phen}){\rm{M}}({{\rm{O}}}_{2}\text{CR})]}^{+}\to {[(\text{phen}){\rm{M}}({\rm{R}})]}^{+}+{\text{CO}}_{2},$$$ $$${[(\text{phen}){\rm{M}}({\rm{R}})]}^{+}+{{\rm{R}}^{\prime} {\rm{O}}}_{2}\text{CR''}\to {[(\text{phen}){\rm{M}}({{\rm{O}}}_{2}\text{CR}^{\prime\prime} )]}^{+}+{\rm{R}} \mbox{-} {\rm{R}}^{\prime} ,$$$ $$$* catalytic\,if\,R\mbox{''}=R.$$$…”