MarjoW

Nature, Published online: 21 October 2021; doi:10.1038/d41586-021-02887-8

Urgent reform is needed: Photocatalytic reforming of biomass is highly desired, yet progress in this direction has been limited. The key to achieving these goals is to develop efficient photocatalysts. Carbon nitride has attracted much attention for this purpose. This Review concerns the design and preparation of functional carbon nitride and its photocatalytic properties for the reforming of biomass.

Abstract

Photoreforming of biomass into hydrogen, biofuels, and chemicals is highly desired, yet this field of research is still in its infancy. Developing an efficient, novel, and environmentally friendly photocatalyst is key to achieving these goals. To date, the nonmetallic and eco-friendly material carbon nitride has found many uses in reactions such as water splitting, CO₂ reduction, N₂ fixation, and biorefinery, owing to its outstanding photocatalytic activity. However, a narrow light absorption range and fast charge recombination are often encountered in the pristine carbon nitride photocatalytic system, which resulted in unsatisfying photocatalytic activity. To improve the photocatalytic performance of pure carbon nitride in biomass reforming, modification is needed. In this Review, the design and preparation of functional carbon nitride, as well as its photocatalytic properties for the synthesis of hydrogen, biofuels, and chemicals through biomass reforming, are discussed alongside potential avenues for its future development.

The direct functionalization of C−H bonds is among the most important transformations in organic synthesis, but its efficiency depends on its selectivity that can be controlled by the innate reactivity of the substrate or a directing group. We review and discuss in a comprehensive manner C−H functionalization processes based on the transient directing group strategy. For more information, see the Review by Gwilherm Evano et al. on page 13899.

Synlett
DOI: 10.1055/a-1608-5633

Organic photoredox catalysts with a long excited-state lifetime have emerged as promising alternatives to transition-metal-complex photocatalysts. This paper explains the effectiveness of using long-lifetime photoredox catalysts for organic transformations, focusing on the structures and photophysics that enable long excited-state lifetimes. The electrochemical potentials of the reported organic, long-lifetime photocatalysts are compiled and compared with those of the representative Ir(III)- and Ru(II)-based catalysts. This paper closes by providing recent demonstrations of the synthetic utility of the organic catalysts.1 Introduction2 Molecular Structure and Photophysics3 Photoredox Catalysis Performance4 Catalysis Mediated by Long-Lifetime Organic Photocatalysts4.1 Photoredox Catalytic Generation of a Radical Species and its Addition to Alkenes4.2 Photoredox Catalytic Generation of a Radical Species and its Addition to Arenes4.3 Photoredox Catalytic Generation of a Radical Species and its Addition to Imines4.4 Photoredox Catalytic Generation of a Radical Species and its Addition to Substrates Having C≡X Bonds (X=C, N)4.5 Photoredox Catalytic Generation of a Radical Species and its Bond Formation with Transition Metals4.6 Miscellaneous Reactions of Radical Species Generated by Photoredox Catalysis5 Conclusions
[...]

Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

A combination of AlCl₃ and tetramethylsilane was studied for the bridgehead methylation of adamantane derivatives. The influence of rearrangements was illustrated with various examples and the synthetic utility was demonstrated by scaling-up of the reaction. Mechanistic studies suggest the formation of a reaction methylation complex formed from tetramethylsilane and AlCl₃.

Abstract

A methylation protocol of adamantane derivatives was investigated and optimized using AlCl₃ and tetramethylsilane as the methylation agent. Substrates underwent exhaustive methylation of all available bridgehead positions with yields ranging from 62 to 86 %, and up to six methyl groups introduced in one step. Scaling-up of the reaction was demonstrated by performing the >40 gram-scale synthesis of 1,3,5,7-tetramethyladamantane with 62 % yield. For several substrates, rearrangements were observed, as well as cleavage of functional groups or C_sp ³−C_sp ² bonds or even cyclohexyl-adamantyl bonds. Based on mechanistic studies, it is suggested that a reactive methylation complex is formed from tetramethylsilane and AlCl₃. X-ray diffraction structures of hexamethylated bis-adamantyls reveal elongation or widening of sp³ carbon bonds between adamantyl moieties to 1.585(3) Å and 125.26(9)° due to repulsive H⋅⋅⋅H contacts.