Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• electronic interactions noteworthy: part a) represents an NHC-to-metal σ → d donation, part b) shows back bonding from the metal to NHC d → π* donation, and part c) depicts the NHC-to-metal π → d donation. Review In the present review, it is intended to provide an overview of the literature spanning the last

On the cause of low thermal stability of ethyl halodiazoacetates

• Magnus Mortén,
• Martin Hennum and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2016, 12, 1590–1597, doi:10.3762/bjoc.12.155

• energy to the products than to the reactants. The barrier heights are thus dominated by the energy of the free carbene relative to its diazo precursor. All the studied halodiazoacetates have lower barriers towards N2 extrusion compared to EDA because π-donation of a free-electron pair from the halogen to

• only 8 kcal/mol for EDA (Figure 3). The π-donation ability from the halo substituents to provide carbene stabilization follows the order F > Cl > Br and presumably I as the least stabilizing carbene substituent [20]. The thermal stabilities of ethyl halodiazoacetates and their α-substituent effects are

• alkyl diazocompounds despite the presence of an α-electron-withdrawing-ester group (Figure 7). The primary reason for the low stability of halodiazoacetates is the relatively high stability of their corresponding carbenes due to π-donation from the halogens into the carbenes’ vacant p-orbitals. Ethyl

Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules

• Diego M. Andrada,
• Nicole Holzmann,
• Thomas Hamadi and
• Gernot Frenking

Beilstein J. Org. Chem. 2015, 11, 2727–2736, doi:10.3762/bjoc.11.294

• -Nancy, France 10.3762/bjoc.11.294 Abstract Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X→p(π) π-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO

• weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation. Keywords: bonding analysis; N-heterocyclic carbenes; π-donation; Introduction Since the isolation and unambiguous characterization of imidazol-2-ylidene by Arduengo in 1991 [1], the chemistry of stable singlet carbenes

• evaluate the intrinsic electronic π-donation strength. In this context, we quantitatively estimate the differences in the electronic structure of 15 archetypical carbenes (Scheme 1). Here compounds 1–4, 6, and 7 are typical NHCs while 5 is an acylic diamidocarbene. Compounds 8–10 are so-called abnormal or

Computational study of productive and non-productive cycles in fluoroalkene metathesis

• Markéta Rybáčková,
• Jan Hošek,
• Ondřej Šimůnek,
• Viola Kolaříková and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2015, 11, 2150–2157, doi:10.3762/bjoc.11.232

• the non-productive cycle (Figure 3). The difference in the stability of the corresponding complexes a2j and s2j can be explained partially by the π-donation of difluoromethylene carbene in analogy to [37], but also by the electron donation of the π-bond of the 1,1-difluoroethene (2) molecule with a

α-Bromodiazoacetamides – a new class of diazo compounds for catalyst-free, ambient temperature intramolecular C–H insertion reactions

• Åsmund Kaupang and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2013, 9, 1407–1413, doi:10.3762/bjoc.9.157

• stabilising effect of π-donation from a substituent on the carbene carbon into the vacant carbene 2p-orbital. This effect is predicted by theory, as well as observed experimentally [28][30][71][72][73]. The degree of stabilisation exerted by a bromine substituent has been quantified in the scale of carbenic

• selectivity conferred by π-donation from a halogen substituent on the carbene carbon (see above) [28][30][71][81][82][83][84]. Future perspectives A pronounced goal in the previously published syntheses of the piperidine-derived bicyclic β-lactams, analogues of 5b, was to develop a model system for the

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• site, and (2) there must be sufficient Mδ+═Eδ− or Mδ−═Eδ+ character (typically associated with incomplete E→M or M→E π donation) to induce reactivity with polar or polarizable substrates. The first requirement is fairly straightforward: if a transition metal is coordinatively saturated, it will be

• , ligand-to-metal π donation is not strong enough to fully attenuate either the π basicity of the ligand or the acidity of the metal (Figure 1a). This bonding scenario is frequently encountered, for example, with the classic Group 4 imido complexes of Bergman and Wolzcanski, or the Group 5 alkylidenes of

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• ligand on the structure of gold-substituted 3,3-dimethyl allyl cations of type D. Increasing trans σ-donation from the ligand and strongly π-acidic ligands such as phosphites (decreasing back π-donation from gold to C1) led to a longer C1–Au bond and hence a more carbocation-like character for the

• organogold species. By contrast, those ligands that increase gold-to-C1 back π-donation or decrease C1-to-gold σ-donation will induce a shorter C1–Au bond and a carbene-like reactivity (Scheme 4) [17]. These studies highlighted the tremendous influence of the substitution pattern and the ancillary ligand on