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Stable group 8 metal porphyrin mono- and bis(dialkylcarbene) complexes. Synthesis, characterization, and catalytic activity

Abstract

Alkyl-substituted carbene (CHR or CR2, R = alkyl) complexes have been extensively studied for alkylcarbene (CHR) ligands coordinated with high-valent early transition metal ions (a.k.a. Schrock carbenes or alkylidenes), yet dialkylcarbene (CR2) complexes remain less developed with bis(dialkylcarbene) species being little (if any) explored. Herein, several group 8 metal porphyrin dialkylcarbene complexes, including Fe- and Ru-mono(dialkylcarbene) complexes [M(Por)(Ad)] (1a,b, M = Fe, Por = porphyrinato dianion, Ad = 2-adamantylidene; 2a,b, M = Ru) and Os-bis(dialkylcarbene) complexes [Os(Por)(Ad)2] (3a-c), are synthesized and crystallographically characterized. Detailed investigations into their electronic structures reveal that these complexes are formally low-valent M(II)-carbene in nature. These complexes display remarkable thermal stability and chemical inertness, which are rationalized by a synergistic effect of strong metal-carbene covalency, hyperconjugation effect, and a rigid diamondoid carbene skeleton. Various spectroscopic techniques and DFT calculations suggest that dialkylcarbene Ad ligand is unique to other common carbene ligands as it acts as both a potent σ-donor and π-acceptor; its unique electronic and structural features, together with the steric effect of porphyrin macrocycle, render its Fe porphyrin complex 1a an active and robust catalyst for intermolecular diarylcarbene transfer reactions including cyclopropanation (up to 90% yield) and X–H (X = S, N, O, C) insertion (up to 99% yield) reactions.

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Article information


Submitted
28 Oct 2019
Accepted
30 Dec 2019
First published
31 Dec 2019

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020, Accepted Manuscript
Article type
Edge Article

Stable group 8 metal porphyrin mono- and bis(dialkylcarbene) complexes. Synthesis, characterization, and catalytic activity

H. Wang, Q. Wan, K. Low, C. Zhou, J. Huang, J. Zhang and C. Che, Chem. Sci., 2020, Accepted Manuscript , DOI: 10.1039/C9SC05432D

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