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.

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.

Yes They Can: Small-molecule Activation with Stable Diaminocarbenes

2011 ◽  
Vol 64 (8) ◽  
pp. 1109 ◽  
Author(s):  
Ulrich Siemeling
Keyword(s):  
Transition Metal ◽  
Small Molecule ◽  
Main Group ◽  
Heterocyclic Carbenes ◽  
Group Element ◽  
Small Molecule Activation ◽  
Transition Metal Chemistry ◽  
Metal Chemistry ◽  
Main Group Element ◽  
Singlet Carbenes

Although small-molecule activation has long been the exclusive domain of transition metal chemistry, it has been increasingly realized that subvalent heavier main-group element compounds, too, are capable of activating H2, NH3, CO, etc. In a remarkable breakthrough, it was recently discovered that this is even possible with certain selected carbon(ii) compounds, viz. (alkyl)(amino)carbenes. However, N-heterocyclic carbenes and related diaminocarbenes, which represent the largest and most widely applied class of singlet carbenes, have been judged to be incapable of exhibiting similar reactivity. It now turns out that this is not quite true and that their reactivity needs to be reassessed.

Catalytic Fluorination of Boron Compounds at a Bismuth Redox Platform

2019 ◽  
Author(s):  
Oriol Planas ◽  
Feng Wang ◽  
Markus Leutzsch ◽  
Josep Cornella
Keyword(s):  
Transition Metal ◽  
Main Group ◽  
Group Element ◽  
Oxidation States ◽  
Boron Compounds ◽  
Main Text ◽  
Main Group Element ◽  
Rational Ligand Design ◽  
Supplementary Material

The ability of bismuth to maneuver between different oxidation states in a catalytic redox cycle, mimicking the canonical organometallic steps associated to a transition metal, is an elusive and unprecedented approach in the field of homogeneous catalysis. Herein we present a catalytic protocol based on bismuth, a benign and sustainable main-group element, capable of performing every organometallic step in the context of oxidative fluorination of boron compounds; a territory reserved to transition metals. A rational ligand design featuring hypervalent coordination together with a mechanistic understanding of the fundamental steps, permitted a catalytic fluorination protocol based on a Bi(III)/Bi(V) redox couple, which represents a unique example where a main-group element is capable of outperforming its transition metal counterparts.<br>A main text and supplementary material have been attached as pdf files containing all the methodology, techniques and characterization of the compounds reported.<br>

scholarly journals On the Coordination Role of Pyridyl-Nitrogen in the Structural Chemistry of Pyridyl-Substituted Dithiocarbamate Ligands

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 286
Author(s):  
Edward R.T. Tiekink
Keyword(s):  
Transition Metal ◽  
Main Group ◽  
Group Element ◽  
Systematic Research ◽  
Pyridyl Nitrogen ◽  
General Observation ◽  
Supramolecular Architectures ◽  
Main Group Element ◽  
Metal Dithiocarbamates

A search of the Cambridge Structural Database was conducted for pyridyl-substituted dithiocarbamate ligands. This entailed molecules containing both an NCS2− residue and pyridyl group(s), in order to study their complexation behavior in their transition metal and main group element crystals, i.e., d- and p-block elements. In all, 73 different structures were identified with 30 distinct dithiocarbamate ligands. As a general observation, the structures of the transition metal dithiocarbamates resembled those of their non-pyridyl derivatives, there being no role for the pyridyl-nitrogen atom in coordination. While the same is true for many main group element dithiocarbamates, a far greater role for coordination of the pyridyl-nitrogen atoms was evident, in particular, for the heavier elements. The participation of pyridyl-nitrogen in coordination often leads to the formation of dimeric aggregates but also one-dimensional chains and two-dimensional arrays. Capricious behaviour in closely related species that adopted very different architectures is noted. Sometimes different molecules comprising the asymmetric-unit of a crystal behave differently. The foregoing suggests this to be an area in early development and is a fertile avenue for systematic research for probing further crystallization outcomes and for the rational generation of supramolecular architectures.

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