Abstract
A new sterically bulky chelating bis-(alkoxide) ligand 3,3'-([1,1':4',1''-terphen-yl]-2,2''-di-yl)bis-(2,2,4,4-tetra-methyl-pentan-3-ol), (H2[OO]tBu), was prepared in a two-step process as the di-chloro-methane monosolvate, C36H50O2·CH2Cl2. The first step is a Suzuki-Miyaura coupling reaction between 2-bromo-phenyl-boronic acid and 1,4-di-iodo-benzene. The resulting 2,2''-di-bromo-1,1':4',1''-terphenyl was reacted with t BuLi and hexa-methyl-acetone to obtain the desired product. The crystal structure of H2[OO]tBu revealed an anti conformation of the [CPh2(OH)] fragments relative to the central phenyl. Furthermore, the hydroxyl groups point away from each other. Likely because of this anti-anti conformation, the attempts to synthesize first-row transition-metal complexes with H2[OO]tBu were not successful.
Highlights
A new sterically bulky chelating bis(alkoxide) ligand 3,30-([1,10:40,100-terphenyl]2,200-diyl)bis(2,2,4,4-tetramethylpentan-3-ol), (H2[OO]tBu), was prepared in a two-step process as the dichloromethane monosolvate, C36H50O2ÁCH2Cl2
The crystal structure of H2[OO]tBu revealed an anti conformation of the [CPh2(OH)] fragments relative to the central phenyl
We have previously reported bulky monodentate alkoxides that led to reactive chromium and iron nitrene-transfer catalysts, (Bellow et al, 2015; Wannipurage et al, 2021; Yousif et al, 2015, 2018) and a series of low-coordinate cobalt carbene complexes capable of carbene transfer to isocyanides (Bellow et al, 2016a; Grass et al, 2019a, 2020)
Summary
Bulky alkoxides are becoming increasingly used as ancillary ligands in group-transfer chemistry and catalysis (Brazeau & Doerrer, 2019; Chua & Duong, 2014; Hannigan et al, 2017; Jayasundara et al, 2018; Wannipurage et al, 2020). The resulting iron complex exhibited broader range of nitrene transfer reactivity, forming a variety of symmetric azoarenes The success of this strategy led us to design a new, even bulkier ligand (H2[OO]tBu). 1H NMR spectroscopy demonstrates the presence of two isomers at room temperature in an approximately 2:1 ratio, as manifested by two tert-butyl resonances (1.05 and 1.03 ppm) and two OH resonances (2.09 and 2.07 ppm) This observation suggests that, in contrast to H2[OO]Ph, various isomers of H2[OO]tBu do not readily interconvert at room temperature, possibly due to the more significant steric hindrance of the tert-butyl groups.
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