Catalytic Carbon–Carbon σ-Bond Hydrogenation with Water Catalyzed by Rhodium Porphyrins

Abstract

The catalytic carbon-carbon σ-bond activation and hydrogenation of [2.2]paracyclophane with water in a neutral reaction medium is demonstrated. The hydrogen from water is transferred to the hydrocarbon to furnish hydrogen enrichment in good yields.

Direct activation of relatively unstrained carbon–carbon bonds in homogeneous systems

“…47 Similar chemistry was developed by the group previously in the context of C–C activation using stoichiometric rhodium phorphyrin complexes. 48,49 In this transformation, PCP is catalytically converted to 4,4′-dimethyl-bibenzyl 113 under two possible conditions (eqn (29)).…”

“Broken-hearted” carbon bowl via electron shuttle reaction: energetics and electron coupling

“…37 The literature precedent for C-C bond scission primarily relies on the assistance of transition metal catalysts, high hydrogen pressure, elevated temperatures, or a combination of all three parameters. [38][39][40][41][42][43][44] Therefore, unexpected C-C bond cleavage (discovered from photophysical studies of alignment of electron donor (corannulene) and acceptor (7,7,8,TCNQ) in the solid state) reported herein led us to probe mechanistic pathways to determine the feasibility for p-bowl planarization and factors that could affect such a transformation including strain energy (E s ) and released energy (E 0 , Scheme 1, see more details in the ESI †). The electron coupling and charge transfer (CT) rates between "open" corannulene (or parent corannulene) and TCNQ were evaluated by applying Marcus theory.…”

Carbon–Carbon Bond Activation by Group 9 Metal Complexes

“…PCP was catalytically hydrogenated with H 2 O to give 79 % yield of 4,4,′‐dimethylbibenzyl 54 catalyzed by 10 mol‐% of Rh III (ttp)H (Table , entry 2). [41a] The catalytic transfer hydrogenation protocol is applicable with to Ir III (ttp)H catalyst as well (Table , entry 3). [41b] The stoichiometric reaction of Rh II (tmp) 48 with PCP resulted in the exclusive cleavage of the benzylic C–C bond to yield the di‐rhodium benzylic product 56 in 85 % yield (Scheme ).…”

“…[41a] The catalytic transfer hydrogenation protocol is applicable with to Ir III (ttp)H catalyst as well (Table , entry 3). [41b] The stoichiometric reaction of Rh II (tmp) 48 with PCP resulted in the exclusive cleavage of the benzylic C–C bond to yield the di‐rhodium benzylic product 56 in 85 % yield (Scheme ). Kinetic studies showed that the CCA reaction is second order on Rh II (tmp) and first order on PCP.…”

“…Interestingly, the cobalt porphyrin catalyzed transfer hydrogenation of PCP required DMF solvent as the better hydrogen atom donor in order to afford good yield of 54 (Table , entry 1). [41c] The proposed di‐cobalt benzylic intermediate cannot be observed due to the fast homolysis of weak Co–C bond (BDE = 23.7 kcal/mol in (PPh 3 )Co III (oep)CH 2 Ph) at 200 o C. This led to the rapid recombination of benzylic radicals to yield a mixture of oligomers 55 in benzene (Scheme ). The benzylic radical intermediate is unable to abstract a hydrogen atom from H 2 O (BDE = 118.8 kcal/mol), and instead undergoes hydrogen atom transfer with DMF to form the benzylic C–H bond (BDE = 89.7 kcal/mol).…”