Detection of Ethylene with Defined Metal Complexes: Strategies and Recent Advances

Abstract

Despite its relative simplicity, ethylene is an interesting molecule with wide‐ranging impact in modern chemistry and biology. Stemming from ethylene's role as a critical plant hormone, there has been significant effort to develop selective and sensitive molecular sensors for ethylene. Late transition metal complexes have played an important role in detection strategies due to ethylene's lack of structural complexity and limited reactivity. Two main approaches to ethylene detection are identified: (1) coordination‐based sensors, wherein ethylene binds reversibly to a metal center, and (2) activity‐based sensors, wherein ethylene undergoes a reaction at a metal center, resulting in the formation and destruction of covalent bonds. Herein, we describe the advantages and disadvantages of various approaches, and the challenges remaining for sensor development.

A Transfer Hydrogenation Approach to Activity-Based Sensing of Formate in Living Cells

“…Activity-based sensing (ABS) methods achieve selectivity by judicious exploitation of the intrinsic reactivity of an analyte of interest for its detection, rather than traditional binding-based approaches that rely on lock-and-key molecular recognition. , This strategy is particularly attractive for detection of reactive small molecules in biological systems, such as reactive carbon species, − , as these species are often transient and can interconvert between competing biological analytes of similar shape and size. In this regard, we recognized that formate is a hydride donor (Δ G ° = 24.1 kcal/mol in H 2 O) .…”

“…Along these lines, current methods for formate analysis in biological samples include its derivatization through amide bond formation to formyl-2-nitrophenyl-hydrazide for detection by LC-MS, , enzyme-mediated colorimetric detection in postlysis specimens, , and NMR analysis, all of which enable formate quantification but only in simple biochemical mixtures and/or with extensive sample processing/destruction. We envisioned that activity-based sensing (ABS), which leverages the intrinsic chemical reactivity of an analyte for its selective and sensitive detection, , could present a complementary strategy for formate analysis that is compatible with live cells and can provide spatiotemporal information regarding one-carbon metabolic flux. − As part of a growing field to discover and decipher the chemical roles that dynamic one-carbon metabolites play at a cellular level, our laboratory and others have developed ABS methods for carbon monoxide, − formaldehyde, ,− and carbon dioxide, , as well as related carbon signaling molecules such as ethylene. − …”

Understanding Copper(I)–Ethylene Bonding Using Cu K-Edge X-ray Absorption Spectroscopy

“…The related [HB­(3,5-(CF 3 ) 2 Pz) 3 ]­Cu­(C 2 H 4 ), which features a highly fluorinated tris­(pyrazolyl)­borate, is a remarkably stable solid and quite resistant to O 2 and the loss of coordinated ethylene . These copper-ethylene complexes are effective carbene transfer (e.g., from ethyl diazoacetate to alkenes and alkynes to form cyclopropanes and cyclopropenes), and nitrene transfer (e.g., from PhI=NTs to yield aziridines) catalysts. , [HB­(3,5-(CF 3 ) 2 Pz) 3 ]­Cu­(C 2 H 4 ) has also been utilized in ethylene sensing applications, − while the bis­(pyrazolyl)­borate complex {[H 2 B­(3,5-(CF 3 ) 2 Pz) 2 ]­Cu} 3 is a very effective material for the selective separation of ethylene from ethane …”

Red-shifted activity-based sensors for ethylene via direct conjugation of fluorophore to metal–carbene

“…8 Molecular detection of ethylene has largely focused on roles in plant systems inspiring several elegant strategies due to the lack of main group reactivity under mild conditions. 9,10 To detect this simple alkene, transition metals have emerged as an obvious choice owing to the wealth of coordination chemistry and reactivity accessible under ambient conditions due to additional bonding interactions such as pi-back bonding. 11 Approaches reported for molecular ethylene detection can be broadly categorized as coordination-based sensors [12][13][14][15][16] or activitybased sensors (ABS) [17][18][19][20][21][22][23][24] with the latter emerging as an attractive approach for selective ethylene detection in complex environments.…”

“…11 Approaches reported for molecular ethylene detection can be broadly categorized as coordination-based sensors [12][13][14][15][16] or activitybased sensors (ABS) [17][18][19][20][21][22][23][24] with the latter emerging as an attractive approach for selective ethylene detection in complex environments. 9,25,26 In 2018, our group reported a fluorescent tagged Hoveyda-Grubbs-type complex that provided sensitive and selective detection of ethylene (Fig. 1(A)).…”