Hydrodefluorination of pentafluoropyridine at rhodium using dihydrogen: detection of unusual rhodium hydrido complexes

Abstract

The pentafluoropyridyl complex [Rh(4-C5NF4)(PEt3)3] (3) reacts with H2 to give initially the dihydrido complex cis-mer-[Rh(H)2(4-C5NF4)(PEt3)3] (6). Within a few hours 2,3,5,6-tetrafluoropyridine as well as two rhodium(III) complexes mer-[Rh(H)3(PEt3)3] (mer-) and fac-[Rh(H)3(PEt3)3] (fac-) are formed. A catalytic C-F activation process for the formation of 2,3,5,6-tetrafluoropyridine starting from pentafluoropyridine and dihydrogen using 3 as a catalyst has been developed. Reaction of [RhH(PEt3)3] (1) with hydrogen affords fac-[Rh(H)3(PEt3)3] (fac-7) and mer-[Rh(H)3(PEt3)3] (mer-7) in a ratio of 1 : 7.25 at 193 K. The latter complex represents the first mononuclear rhodium compound bearing trans-hydrides.

Conversion of Carbon–Fluorine Bonds α to Transition Metal Centers to Carbon–Hydrogen, Carbon–Carbon, and Carbon–Heteroatom Bonds

“…With both positive and negative properties in mind, our group and others [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] have approached the selective activation of C-F bonds using transition metal complexes. A different positive role for compounds containing C-F bonds has now evolved in bioorganic chemistry, [24][25][26] leading to significant recent interest in generating new methodology for synthesis of carbon stereocenters bearing a fluorine or fluoroalkyl group.…”

Stepwise Oxygenation of Pinacolborane by a Rhodiumperoxo Complex: Detection of an Intermediate Metal Borate and Perborate

“…The rhodium-phosphorus coupling constant of 92 Hz for the signal at d = 30.4 ppm in the 31 P NMR spectrum reveals the presence of a rhodium(III) complex. [13,16] …”

“…Furthermore, there is no band corresponding to a peroxo unit upon 18 O substitution. [16] A band at 632 cm À1 (612 cm À1 for 3 a) may possibly be assigned to a RhO vibration.…”

Activation and Formation of Aromatic C–F Bonds

“…39) [84]. The use of H 2 in the presence of TEA and Cs 2 CO 3 with (34) yielded the hydrodefluorinated product over a period of days.…”