Mechanistic Insights of a Concerted Metalation–Deprotonation Reaction with [Cp*RhCl₂]₂

Abstract

The effect of the carboxylate used in a concerted metalation−deprotonation reaction is probed and shows a direct correlation of pK a to observed rate up to a pK a of 4.3, where the rate drops off at higher pK a . The rate of the C−H activation of 2-(4-methoxyphenyl)pyridine with [Cp*RhCl 2 ] 2 and carboxylate follows first-order kinetics in the active metal species, Cp*RhCl(κ 2 -OAc), and zero-order kinetics in substrate when in a 1:1 ratio. There is a first-order dependence on substrate observed when excess substrate is present. The evaluation of the mechanism using kinetic studies allowed for a mechanistic proposal in which a second Ph′Py coordinates prior to the rate-determining C−H activation.

Synthesis of [5,6]‐Bicyclic Heterocycles with a Ring‐Junction Nitrogen Atom: Rhodium(III)‐Catalyzed C−H Functionalization of Alkenyl Azoles

“…MeOH as solvent. THF = tetrahydrofuran.metalation/deprotonation of alkenyl triazole to form the rhodacycle A (Scheme 1a) [13]. Migratory insertion of 3hexyne gives the intermediate B,a nd reductive elimination yields 3m.O xidation of rhodium(I) then regenerates the rhodium(III) catalyst.…”

Rh(iii)-catalyzed diastereoselective C–H bond addition/cyclization cascade of enone tethered aldehydes

“…The first step of this process proceeds via concerted metalation/deprotonation of 1 to generate rhodacycle 4 , which has previously been proposed as an intermediate in other Rh-catalyzed C–H functionalization reactions. 3 , 13 Coordination of the enone π-bond provides 5 , which undergoes conjugate addition to give rhodium enolate 6 . The rhodium enolate 6 can then undergo an intramolecular aldol reaction with the tethered aldehyde to form rhodium alkoxide 7 .…”

C−O Activation by a Rhodium Bis(N‐Heterocyclic Carbene) Catalyst: Aryl Carbamates as Arylating Reagents in Directed C−H Arylation

“…Ap ossible mechanism is shown in Scheme 6. Although Rh I (L6) 2 species A can activate both C À Ha nd C À Ob onds, the initial C À Ha ctivation only leads to non-productive H/D exchange via intermediate B.T he catalytic cycle that gives arylated product 3 begins with oxidative addition of the CÀO bond in carbamate 2 to form arylrhodium(III) intermediate C.T he subsequent ortho CÀHa ctivation by rhodium(III) species C,p resumably through ac oncerted metalation/ deprotonation pathway, [15] gives diarylrhodium D,w hich finally gives arylated product 3 with concurrent regeneration of A.…”