Alkylation of Rhodium Porphyrin Complexes with Primary Alcohols under Basic Conditions

Abstract

Primary alcohols were successfully utilized as the alkylating reagents to conveniently access rhodium porphyrin alkyl complexes in up to 91% yields under basic conditions. Mechanistic investigations suggest two possible pathways for the C–O bond cleavage: (1) nucleophilic substitution with rhodium­(I) porphyrin anion and (2) a borrowing hydrogen pathway via rhodium­(III) porphyrin hydride.

Base-Promoted C–O Bond Cleavage of Primary Alcohols by Iridium(III) Porphyrin Chloride

“…Previously, we reported that Rh­(ttp)­Cl could cleave the C–OH bond of benzyl alcohols and aliphatic alcohols in benzonitrile solvent under basic conditions at 120 °C to form Rh­(ttp)­Bn and Rh­(ttp)-alkyls, respectively . Considering the analogous reactivity of Ir­(por) complexes to Rh­(por) complexes in bond activation, we anticipated that the C–O bonds of various alcohols could be cleaved with Ir­(ttp)­(CO)Cl ( 1a ) under the above conditions.…”

“…Alternatively, Ir­(ttp)­OCH 2 Ph can be generated by the reaction between PhCH 2 OH ( 2a ) and Ir­(ttp)­OH from the ligand substitution of Ir­(ttp)­(CO)Cl ( 1a ) and KOH. Ir­(ttp)­OCH 2 Ph then undergoes β-H elimination with KOH to yield the Ir­(ttp) − anion and benzaldehyde. , Ir­(ttp) − can also be protonated to Ir­(ttp)H ( 1b ) by H 2 O (the p K a of Ir­(ttp)H is 15). , Subsequently, the nucleophilic Ir­(ttp) − anion attacks the carbonyl carbon in benzaldehyde to give the α-hydroxyalkyl complex Ir­(ttp)­CH­(OH)­Ph upon protonation with H 2 O. , Finally, Ir­(ttp)­CH­(OH)­Ph can be reduced by Ir­(ttp)H ( 1b ) to the desired C–O cleavage product Ir­(ttp)­CH 2 Ph ( 3a ) and Ir­(ttp)­OH, probably via σ-bond metathesis . Then, Ir­(ttp)­OH is either reused to react with PhCH 2 OH ( 2a ) or converted directly to the Ir­(ttp) − anion according to the pathway in Scheme .…”

“…In benzonitrile solvent for aliphatic alcohols, the (PhCN)Ir(ttp) − anion is formed by the solvent ligation of the Ir(ttp) − anion and serves as a nucleophile, because the (PhCN)Ir(ttp) − anion is more nucleophilic than the Ir(ttp) − anion. 10,16 ■ CONCLUSION In short, the alkylation of Ir(por)s was successfully achieved with benzyl and alkyl alcohols as the alkylating reagents. This C−O bond cleavage reaction could proceed smoothly in benzene or benzonitrile solvent under basic conditions and gave up to a 92% yield of Ir(ttp) complexes.…”

“…9,17 Finally, Ir(ttp)CH(OH)Ph can be reduced by Ir(ttp)H (1b) to the desired C−O cleavage product Ir(ttp)CH 2 Ph (3a) and Ir(ttp)OH, probably via σ-bond metathesis. 10 Then, Ir(ttp)-OH is either reused to react with PhCH 2 OH (2a) or converted directly to the Ir(ttp) − anion according to the pathway in Scheme 2. In benzonitrile solvent for aliphatic alcohols, the (PhCN)Ir(ttp) − anion is formed by the solvent ligation of the Ir(ttp) − anion and serves as a nucleophile, because the (PhCN)Ir(ttp) − anion is more nucleophilic than the Ir(ttp) − anion.…”

A binuclear Cu(ii) complex as an efficient photocatalyst for N-alkylation of aromatic amines

“…20,21 The Banerjee group added the nickel complex in this series in 2017. 22 Direct N-alkylation of amines with primary alcohols through the hydrogen auto-transfer reaction has been explored with rhodium-, [23][24][25] iridium-, [26][27][28][29] ruthenium-, [30][31][32][33] and osmium 34 -containing catalysts. Due to the ecological and economic benefits, it is desirable to use cheap metal-based catalysts in organic synthesis.…”