Intramolecular CN Bond Activation and Ring-Expansion Reactions of N-Heterocyclic Carbenes

2014 ◽  
Vol 21 (4) ◽  
pp. 1434-1438 ◽  
Author(s):  
Patrick Hemberger ◽  
Andras Bodi ◽  
Johannes H. J. Berthel ◽  
Udo Radius
Keyword(s):  
Bond Activation ◽  
Ring Expansion ◽  
Heterocyclic Carbenes

Theoretical Investigation of Main-Group Element Hydride Insertion into Phosphorus-Heterocyclic Carbenes (PHCs)

2020 ◽  
Vol 73 (8) ◽  
pp. 787
Author(s):  
Khalidah H. M. Al Furaiji ◽  
Andrew Molino ◽  
Jason L. Dutton ◽  
David J. D. Wilson
Keyword(s):  
Computational Study ◽  
Ring Expansion ◽  
Heterocyclic Ring ◽  
Main Group ◽  
Heterocyclic Carbenes ◽  
Group Element ◽  
Steric Effects ◽  
Main Group Element ◽  
Theoretical Investigations ◽  
Electronic And Steric Effects

Initial reports of ring expansion reactions (RER) of N-heterocyclic carbenes (NHCs) with main-group element hydrides have led to several synthetic and theoretical investigations, which include reports of insertion by Be, B, Al, Si, and Zn hydrides. The RERs generally lead to insertion of the heteroatom into the endocyclic C–N bond with formation of an expanded heterocyclic ring. Following the recent isolation of a P-heterocyclic carbene (PHC), here we report results from a computational study (RI-SCS-MP2/def2-TZVP//M06–2X/def2-TZVP) of RERs with a series of PHCs for the ring-insertion of silicon (SiH4, SiH2Ph2) and boron (BH3, BH2NMe2) hydrides. In order to explore the roles of both electronic and steric effects on PHCs and their reactivity, a series of P-substituent PHCR (R=H, Me, Ph, and bulky Ar groups) were investigated. Bulky R groups serve to maximise ring planarity and the σ-donating capability of the PHC. For RER, the PHC analogues exhibit facile initial hydride transfer from the main-group hydrides to the carbene carbon, with barriers that are substantially lower than with NHCs. However, the full ring insertion mechanisms for PHCs are, in general, kinetically unfavourable due to a large barrier associated with the ring-expansion step. While bulky P-substituents maximise heterocycle planarity towards that of NHCs, the RER reactivity with bulky PHCs does not reflect that of an NHC.

25 years of N-heterocyclic carbenes: activation of both main-group element–element bonds and NHCs themselves

2016 ◽  
Vol 45 (14) ◽  
pp. 5880-5895 ◽  
Author(s):  
Sabrina Würtemberger-Pietsch ◽  
Udo Radius ◽  
Todd B. Marder
Keyword(s):  
Ring Expansion ◽  
Main Group ◽  
Heterocyclic Carbenes ◽  
Group Element ◽  
Main Group Element ◽  
The 1960S

Expanding the belt! NHC ring expansion reactions and E–E activation from the 1960s till the present are summarized.

Protonation of 2H-Azaphosphirene Complexes: PN Bond Activation and Ring-Expansion Reactions

2009 ◽  
Vol 15 (11) ◽  
pp. 2602-2616 ◽  
Author(s):  
Holger Helten ◽  
Marianne Engeser ◽  
Dietrich Gudat ◽  
Reinhold Schilling ◽  
Gregor Schnakenburg ◽  
...  
Keyword(s):  
Bond Activation ◽  
Ring Expansion

Novel Intramolecular CAryl–S Bond Activation by an Electron Rich, Ring-Expanded-NHC-Rh centre: A Combined Experimental and DFT Study

2011 ◽  
Vol 64 (8) ◽  
pp. 1141 ◽  
Author(s):  
Abeer Binobaid ◽  
Kingsley J. Cavell ◽  
Mikhail S. Nechaev ◽  
Benson M. Kariuki
Keyword(s):  
Bond Activation ◽  
Reaction Pathway ◽  
Heterocyclic Carbenes ◽  
Dft Study ◽  
Dft Studies ◽  
X Ray ◽  
Carbene Complex ◽  
Donor Capacity ◽  
Insight Into ◽  
Sulfur Bond

The reaction of (o-MeSPh)-N-functionalized tetrahydropyrimidinium salts with KN(SiMe3)2 and [Rh(COD)Cl]2 in THF leads to the formation of a novel dimeric RhIII bis-carbene complex. The reaction involves the unexpected cleavage/oxidative addition of the aryl-sulfur bond to give dimeric metallated RhIII with bridging MeS< moieties. This unusual reaction is probably a consequence of the sterically imposing structure and strong donor capacity of ring-expanded N-heterocyclic carbenes (RE-NHCs). An X-ray structure of the [(Ph,DIPP-NHC)Rh(Cl)(SMe)2] product complex has been obtained, and DFT studies were undertaken to gain an insight into the reaction pathway.

Room Temperature Ring Expansion of N-Heterocyclic Carbenes and BB Bond Cleavage of Diboron(4) Compounds

2015 ◽  
Vol 21 (25) ◽  
pp. 9018-9021 ◽  
Author(s):  
Sabrina Pietsch ◽  
Ursula Paul ◽  
Ian A. Cade ◽  
Michael J. Ingleson ◽  
Udo Radius ◽  
...  
Keyword(s):  
Room Temperature ◽  
Bond Cleavage ◽  
Ring Expansion ◽  
Heterocyclic Carbenes

Activation of C–F, Si–F, and S–F Bonds by N-Heterocyclic Carbenes and Their Isoelectronic Analogues

Synlett ◽  
2020 ◽  
Vol 31 (14) ◽  
pp. 1349-1360 ◽  
Author(s):  
Eunsung Lee ◽  
Ewa Pietrasiak
Keyword(s):  
Nucleophilic Substitution ◽  
Organic Synthesis ◽  
Bond Activation ◽  
Bond Cleavage ◽  
Oxidative Addition ◽  
Main Group ◽  
Heterocyclic Carbenes ◽  
Full Potential ◽  
Short Summary ◽  
Special Case

Reactions involving C–F, Si–F, and S–F bond cleavage with N-heterocyclic carbenes and isoelectronic species are reviewed. Most examples involve activation of aromatic C–F bond via an SNAr pathway and nucleophilic substitution of fluorine in electron-deficient olefins. The mechanism of the C–F bond activation depends on the reaction partners and the reaction can proceed via addition–elimination, oxidative addition (concerted or stepwise) or metathesis. The adducts formed upon substitution find applications in organic synthesis, as ligands and as stable radical precursors, but in most cases, their full potential remains unexplored.1 Introduction1.1 The C–F Bond1.2 C–F Bond Activation: A Short Summary1.3 C–F Bond Activation: A Special Case of SNAr1.4 N-Heterocyclic Carbenes (NHCs)1.5 The Purpose of this Article2 C–F bond Activation in Acyl Fluorides3 Activation of Vinylic C–F Bonds4 Activation of Aromatic C–F Bonds5 X–F Bond Activation (X = S or Si)6 C–F Bond Activation by Main Group Compounds Isoelectronic with NHCs7 Conclusions and Outlook

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