Photochemical nitrogenation of alkanes and arenes by a strongly luminescent osmium(VI) nitrido complex

Jing Xiang,Shun-Cheung Cheng,Tai-Chu Lau,Xin-Xin Jin,Chi-Chiu Ko,Liangliang Wu,Minying Xue,Chi-Ming Che,Wai-Lun Man,Qian-Qian Su

doi:10.1038/s42004-019-0142-3

Abstract

The search for a highly active nitrido complex that can transfer its nitrogen atom to inert organic molecules remains a challenge to chemists. In this regard, the use of solar energy to generate a reactive nitrido species is an appealing strategy to solve this problem. Here we report the design of a strongly luminescent osmium(VI) nitrido compound, [OsVI(N)(NO2-L)(CN)3]− (NO2-OsN) with emission quantum yield (Φ) and life time (τ) of 3.0% and 0.48 μs, respectively in dichloromethane solution. Upon irradiation with visible light, this complex readily activates the aliphatic C-H bonds of various hydrocarbons, including alkanes. The excited state of NO2-OsN can undergo ring-nitrogenation of arenes, including benzene. Photophysical and computational studies suggest that the excited state of NO2-OsN arises from O^N ligand to Os ≡ N charge transfer transitions, and as a result it possesses [Os = N•] nitridyl character and is highly electrophilic.

Highlights

The search for a highly active nitrido complex that can transfer its nitrogen atom to inert organic molecules remains a challenge to chemists
In the infrared (IR) spectrum, the v(Os≡N) stretch is found at 1074 cm−1, which is shifted to 1046 cm−1 upon 15N labeling
Experimental results and density functional theory (DFT) calculations indicate that the emissive excited state of this complex exhibits LML′CT [π(N^O)→dπ*(Os≡N)] character, which is different from reported luminescent osmium nitrido complexes with predominant d–d transition character

Summary

Introduction

The search for a highly active nitrido complex that can transfer its nitrogen atom to inert organic molecules remains a challenge to chemists. Pioneering work by Meyer and Huynh[6] has shown that [OsVI(terpy)(N)Cl2]+ (terpy=2,2′:6′,2′′-terpyridine) and related complexes are highly electrophilic/oxidizing; they react with a variety of organic substrates resulting in the formation of novel osmium complexes in lower oxidation states These complexes do not undergo C–H bond activation, especially for substrates with unactivated C–H bonds, such as alkanes. A number of d2 nitrido complexes, such as those of ReV and OsVI, have long-lived emissive excited states[15,16,17,18,19,20,21]; the emissions of these complexes were shown to originate mainly from metalcentered ligand field 3[(dxy)1(dπ*)1] excited states Some of these complexes are strong one-electron oxidants in their excited states, nitrogen atom transfer reactions of these complexes, especially towards inert organic substrates, have not been demonstrated

Methods

Results

Conclusion