Rhodium Complexes of 2,6-Bis(dialkylphosphinomethyl)pyridines: Improved C–H Activation, Expanded Reaction Scope, and Catalytic Direct Arylation

Abstract

The reactivity of (PNP)Rh(Ph) (PNP = 2,6bis(dialkylphosphinomethyl)pyridine) toward a variety of electrophiles (Ar−I, ArCH 2 Cl, O 2 , I 2 , B 2 pin 2 , and ArSO 3 H) was explored, and several new modes of oxidative reactivity were observed. Substituting t Bu 2 P for i Pr 2 P provided 100-fold rate enhancement toward C−H bond activation and addressed the previously reported challenge of N 2 inhibition. Studying the stoichiometric reactivity of (PNP)Rh complexes toward C−H cleavage and oxidative functionalization led to (PNP)Rhcatalyzed cross-coupling of aryl iodides with sp 2 and sp 3 C−H bonds.

Nucleopincers? Rhodium Complexes of Pyrimidine‐centered PNP Pincer Ligands Derived from Nitrogenous Nucleobases Uracil and Thymine

“…The trans ‐disposition of the two inequivalent phosphines was apparent from the strong 2 J P‐P coupling of 410 Hz for both complexes. The 1 J Rh‐P coupling constants in 2H‐RhCl and 2Me‐RhCl were 150 and 156 Hz, consistent with compounds 3‐RhCl , 4‐RhCl , and other analogous neutral pyridine‐based PNP complexes of Rh reported in the literature ( J Rh–P =145–154 Hz) [7,8,19–22] …”

“…The 1 J Rh-P coupling constants in 2H-RhCl and 2Me-RhCl were 150 and 156 Hz, consistent with compounds 3-RhCl, 4-RhCl, and other analogous neutral pyridine-based PNP complexes of Rh reported in the literature (J Rh-P = 145-154 Hz). [7,8,[19][20][21][22] The solid-state structures of 2H-RhCl and 2Me-RhCl were determined by X-ray diffractometry on the appropriate single crystals. The two structures show no significant metric differences.…”

Use of Ligand Steric Properties to Control the Thermodynamics and Kinetics of Oxidative Addition and Reductive Elimination with Pincer-Ligated Rh Complexes

“…Thus, in contrast to the t Bu variant 1b , 2b is stable against MeX (X = Cl, I) reductive elimination. ( iPr PNP)­RhI ( 2c ) was then synthesized independently by mixing 2a and NaI in acetone . Charging MeCl to a THF- d 8 solution of complex 2c gives three isomers of 2b according to NMR spectra.…”

“…A reported procedure was used . In a glass vial, an acetone (0.6 mL) solution of NaI (45.5 mg, 304 μmol) was added to an acetone (0.5 mL) solution of ( iPr PNP)­RhCl (72.7 mg, 152 μmol).…”

Transition‐Metal‐Free Glucose‐Derived Carbonaceous Catalyst Catalyzes Direct C‐H Arylation of Unactivated Arenes with Aryl Halides

“… Abstract Transition metal free coupling reactions have gained lot of importance recently. The traditional method for the synthesis of biaryl's uses organometallic reagents for the arylation reactions . There are certain drawbacks associated with such traditional methods.…”