Aerobic Palladium(II)-Catalyzed Dehydrogenative Heck Reaction in the Synthesis of Pyrenyl Fluorophores. A Photophysical Study of β-Pyrenyl Acrylates in Solution and in the Solid State

Abstract

An aerobic dehydrogenative Heck reaction of pyrene (1a) and 2,7-di-tert-butylpyrene (1b) with ethyl acrylate is reported. The reaction is catalyzed by a Pd(OAc)2/4,5-diazafluoren-9-one (DAF) system and takes place in acetic or pivalic acid as solvents at 110-130 °C. The reaction of 1a afforded a 6:1 mixture of C-1- and C-4-alkenylated pyrenes (2a and 3a, respectively) in 71% yield. In the case of 1b, only a C-4-substituted product (3b) was formed in 46% yield. Compounds 2a and 3a,b exhibited fluorescence in solution and in the solid state. In chloroform and THF solution the fluorescence maxima were in the range of 440-465 nm, and quantum yields decreased in the order 2a > 3a> 3b. In the solid state, 3a,b showed blue-green fluorescence (ΦF = 0.26 and 0.14, respectively), whereas 2a emitted yellow-green fluorescence) (ΦF = 0.35). Besides blue-emitting monomers, the presence of green-emitting aggregated species (preformed dimers) in the crystals of 3a,b and red-emitting dynamic excimers in the crystals of 2a has been demonstrated. Single-crystal X-ray diffraction analyses of 2a and 3b confirmed π-stacking of pyrenyl moieties in the crystals of the former and the absence of stacking in the crystals of the latter compound.

Synthesis, regioselective aerobic Pd(ii)-catalyzed C–H bond alkenylation and the photophysical properties of pyrenylphenylpyrazoles

“…We performed alkenylation of 2a with n-butyl acrylate under conditions we had described earlier for alkenylation of ferrocene and pyrene. [30][31][32] The reaction was conducted in boiling acetic acid under oxygen (1 atm) in the presence of a catalytic amount (5 mol%) of Pd(OAc) 2 and 4,5-diazafluoren-9-one (DAF, 10 mol%) (Scheme 2).…”

Mechanofluorochromism of pyrenyl acrylates with different substitutional position and steric hindrance

“…Our groups have explored the synthetic diversity of pyrene derivatives and demonstrated the fluorescence properties both in solution and in the solid state. [9][10][11][12] The solid-state fluorescence of pyrene derivatives is getting more common recently, and several examples of MFC with planar/branch structural features have been reported. [13][14][15][16][17][18] Therefore, it is of great interest to establish a new library of organic MFC materials by investigating their dynamic photophysical properties in solid state.…”

“…As a series of our reported pyrene derivatives, we here focused on C-1-and C-4-alkenylated pyrenes with and without tert-butyl groups for their solid-state blue/green fluorescence properties up to 0.35 quantum yields. [11] Since these fluorescent molecules bear a planar unit with chain-like side groups, the emission color change is expected to be accompanied by intermolecular arrangement changes. In addition, systematic MFC study on the J o u r n a l P r e -p r o o f compounds w/ and w/o specific chemical groups and positional isomers would provide a clue to correlate the steric structures and MFC properties.…”

“…The target molecules were prepared following the reported synthetic methods. [11] As-synthesized powder samples are defined as pristine condition. To study the spectroscopy of the ground form, a quartz plate was directly scratched with a pestle immediately after grinding of the powder (Figure 1).…”

Operando Spectroscopic and Kinetic Characterization of Aerobic Allylic C–H Acetoxylation Catalyzed by Pd(OAc)2/4,5-Diazafluoren-9-one

“…31,58 The implications of these observations were not extended to catalytic conditions, however, and the present study provides a comprehensive analysis of the catalytic mechanism, including kinetic studies and operando X-ray absorption spectroscopy (XAS) and NMR spectroscopic analysis of the catalytic reaction, which reveal changes in the identity of the turnover limiting step and evolution of the catalyst species during the reaction. The results provide valuable insights into Pdcatalyzed allylic oxidation reactions and the ability of DAF to support aerobic catalytic turnover, [59][60][61][62][63][64][65][66][67][68][69] and this study establishes an important foundation for future empirical and mechanistic efforts directed toward the identification of more efficient and synthetically useful allylic C-H oxidation catalyst systems.…”