Wang Hai-Xu, Wan Qingyun, Low Kam-Hung, Zhou Cong-Ying, Huang Jie-Sheng, Zhang Jun-Long, Che Chi-Ming
State Key Laboratory of Synthetic Chemistry , Department of Chemistry , The University of Hong Kong , Pokfulam Road , Hong Kong SAR , China . Email:
College of Chemistry and Materials Science , Jinan University , Guangzhou , China.
Chem Sci. 2019 Dec 31;11(8):2243-2259. doi: 10.1039/c9sc05432d. eCollection 2020 Feb 28.
Alkyl-substituted carbene (CHR or CR, 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 (CR) complexes remain less developed with bis(dialkylcarbene) species being little (if at all) explored. Herein, several group 8 metal porphyrin dialkylcarbene complexes, including Fe- and Ru-mono(dialkylcarbene) complexes [M(Por)(Ad)] (, M = Fe, Por = porphyrinato dianion, Ad = 2-adamantylidene; , M = Ru) and Os-bis(dialkylcarbene) complexes [Os(Por)(Ad)] (), 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, and a rigid diamondoid carbene skeleton. Various spectroscopic techniques and DFT calculations suggest that the dialkylcarbene Ad ligand is unique compared 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 the porphyrin macrocycle, make its Fe porphyrin complex 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.
烷基取代的卡宾（CHR或CR，R = 烷基）配合物已被广泛研究，用于与高价早期过渡金属离子配位的烷基卡宾（CHR）配体（也称为施罗克卡宾或亚烷基），然而二烷基卡宾（CR）配合物的研究仍较少，双（二烷基卡宾）物种几乎未被探索（如果有探索的话）。在此，合成了几种第8族金属卟啉二烷基卡宾配合物，包括铁和钌的单（二烷基卡宾）配合物[M(Por)(Ad)]（，M = Fe，Por = 卟啉二价阴离子，Ad = 2-金刚烷亚基；，M = Ru）和锇的双（二烷基卡宾）配合物[Os(Por)(Ad)]（），并通过晶体学对其进行了表征。对它们电子结构的详细研究表明，这些配合物本质上是形式上的低价M(ii)-卡宾。这些配合物表现出显著的热稳定性和化学惰性，这可通过强金属-卡宾共价性、超共轭和刚性类金刚石卡宾骨架的协同效应来解释。各种光谱技术和密度泛函理论计算表明，与其他常见卡宾配体相比，二烷基卡宾Ad配体是独特的，因为它既作为强σ供体又作为π受体；其独特的电子和结构特征，连同卟啉大环的空间效应，使其铁卟啉配合物成为分子间二芳基卡宾转移反应（包括环丙烷化反应（产率高达90%）和X-H（X = S、N、O、C）插入反应（产率高达99%））的活性且稳健的催化剂。
