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Deqiang Wang Dr. Wanjian Ding Dr. Guohua Hou Prof. Guofu Zi Prof. Dr. Marc D. Walter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(22):6767-6782
The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η5-1,2,4-(Me3C)3C5H2]2U=P-2,4,6-tBu3C6H2 ( 1 ) yields the stable uranium metallacyclopropene, [η5-1,2,4-(Me3C)3C5H2]2U[η2-C2Ph2] ( 2 ). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U-(η2-C=C) moiety increases significantly compared to the related ThIV compound [η5-1,2,4-(Me3C)3C5H2]2Th[η2-C2Ph2], which also results in more covalent bonds between the [η5-1,2,4-(Me3C)3C5H2]2U2+ and [η2-C2Ph2]2− fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low-valent uranium(II) metallocene [η5-1,2,4-(Me3C)3C5H2]2UII when reacted with Ph2E2 (E=S, Se), alkynes and a variety of hetero-unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five-membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones. 相似文献
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Mechanism and Selectivity of RuII‐ and RhIII‐Catalyzed Oxidative Spiroannulation of Naphthols and Phenols with Alkynes through a C−H Activation/Dearomatization Strategy
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Mei Zhang Prof. Dr. Genping Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9356-9365
The ruthenium‐ and rhodium‐catalyzed oxidative spiroannulation of naphthols and phenols with alkynes was investigated by means of density functional theory calculations. The results show that the reaction undergoes O?H deprotonation/C(sp2)?H bond cleavage through a concerted metalation–deprotonation mechanism/migratory insertion of the alkyne into the M?C bond to deliver the eight‐membered metallacycle. However, the dearomatization through the originally proposed enol–keto tautomerization/C?C reductive elimination was calculated to be kinetically inaccessible. Alternatively, an unusual metallacyclopropene, generated from the isomerization of the eight‐membered metallacycle through rotation of the C?C double bond, was identified as a key intermediate to account for the experimental results. The subsequent C?C coupling between the carbene carbon atom and the carbon atom of the 2‐naphthol/phenol ring was calculated to be relatively facile, leading to the formation of the unexpected dearomatized products. The calculations reproduce quite well the experimentally observed formal [5+2] cycloaddition in the rhodium‐catalyzed oxidative annulation of 2‐vinylphenols with alkynes. The calculations show that compared with the case of 2‐alkenylphenols, the presence of conjugation effects and less steric repulsion between the phenol ring and the vinyl moiety make the competing reductive oxyl migration become dominant, which enables the selectivity switch from the spiroannulation to the formal [5+2] cycloaddition. 相似文献
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