Final Report Summary - FUNCBONDS (Chasing a Fundamental Challenge in Catalysis: A Combined Cleavage of Carbon-Carbon Bonds and Carbon Dioxide for Preparing Functionalized Molecules) FUNCBONDS was designed as a project to face fundamental challenges in the area of inert bond-activation, with a particular emphasis on tuning and controlling the ability to promote carbon dioxide fixation (CO2) into organic matter. At present, CO2 fixation is primarily based on C-O bond-forming reactions or reduction events en route to formic acid, methanol or carbon monoxide. In contrast, the ability to use CO2 in catalytic carbon-carbon bond-forming reactions still remains a largely void scenario, and is essentially confined to the use of highly reactive, and stoichiometric organometallic reagents, thus reinforcing a change in strategy. This ERC project aimed at filling this gap, representing a formidable opportunity to use CO2 as a C1 source en route to carboxylic acids, motifs of utmost relevance in pharmaceuticals. Specifically, we have designed new nickel catalysts that are capable of promoting carbon dioxide fixation with exceptionally ease and exquisite chemoselectivity (for example: J. Am. Chem. Soc. 2013, 135, 1221; J. Am. Chem. Soc. 2014, 136, 11212; J. Am. Chem. Soc. 2014, 136, 17702; J. Am. Chem. Soc. 2015, 137, 8924; J. Am. Chem. Soc. 2015, 137, 6476; J. Am. Chem. Soc. 2016, 138, 7504). As no air-sensitive or highly reactive, stoichiometric organometallic reagents were necessary, these reports changed the prevailing perception that the thermodynamic stability and kinetic inertness of carbon dioxide requires the use of harsh conditions or highly reactive entities. These studies set the basis for expanding the scope to heterocumelenes other than carbon dioxide, resulting in innovative methods for obtaining industrially-relevant amide derivatives (J. Am. Chem. Soc. 2014, 136, 7253; Angew. Chem. Int. Ed. 2016, 55, 11207; J. Am. Chem. Soc. 2016, 138, 15531). As part of the objectives in FUNBONDS, we have discovered new strategies for catalytic carbon-carbon bond-activation, leading to functionalized molecules from simple precursors. Specifically, we have discovered palladium catalysts that can promote ring-opening reactions of strained compounds (for example: Org. Lett. 2012, 14, 1266; Chem. Commun. 2013, 49, 4286), nickel catalysts that can trigger cycloaddition processes (Angew. Chem. Int. Ed. 2015, 54, 9537) and iron catalysts that promote site-selective carbon-carbon cleavage of unstrained bonds (J. Am. Chem. Soc. 2013, 135, 12576). In depth mechanistic studies allowed for isolating putative reaction intermediates, and the study of their reactivity unravel unconventional pathways by which nickel catalysts promote inert bond-activations (J. Am. Chem. Soc. 2013, 135, 1997). Recent unpublished mechanistic data in collaboration with theoretical chemists have allowed to establish new rationales in other related scenarios. These studies set the stage for innovative activation of related strong sigma bonds by nickel catalysts, for example via carbon-oxygen or carbon-fluorine bonds (J. Am. Chem. Soc. 2014, 136, 1062; J. Am. Chem. Soc. 2014, 136, 2236; J. Am. Chem. Soc. 2014, 136, 7253; J. Am. Chem. Soc. 2015, 137, 12470; J. Am. Chem. Soc. 2015, 137, 6754; Angew. Chem. Int. Ed. 2015, 54, 4075; J. Am. Chem. Soc 2017, DOI: 10.1021/jacs.6b10998). Overall, FUNCBONDS have defined new paradigms in the area of metal-catalyzed reactions, designing new protocols for CO2 fixation, carbon-carbon bond-activation and related activation processes. In particular, we have changed the common perception that CO2 fixation for carbon-carbon bond-formation necessarily requires highly reactive, air-sensitive organometallic reagents, resulting in innovative, simple, and highly chemoselective carboxylation protocols en route to pharmaceutically-relevant carboxylic acids. Such strategy has allowed to establish nickel catalysts as privileged vehicles for CO2 fixation and other inert bond-activation protocols. This is illustrated by the wide number of transformations we discovered by which nickel catalysts can catalyze a variety of processes via carbon-carbon bond-activation and related events. According to the impact and visibility of the transformations gathered by FUNCBONDS, we believe that we have provided new knowledge in synthetic design that will likely set the basis for unravelling the potential of inert bond-activation protocols.
