Novel Urea Derivatives as Two-Step Redox Systems

Weiß, Robert; Reichel, Silvia

doi:10.1002/1099-0682(200009)2000:9<1935::aid-ejic1935>3.0.co;2-u

Cited by 43 publications

(10 citation statements)

References 4 publications

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“…They pointed out the unusual high s-character of that carbene σ-orbital by a 1 J CH coupling constant of 232.6 Hz, which corresponds to a hybridization of only sp 1.15 . Although they had prepared the respective selenourea, the 77 Se NMR chemical shift was not reported [39,47–48]. We showed that the tert -butyl substituted dipyridocarbene dipiy tBu exhibits an unusual high thermal stability and proofed the alternating bond lengths in the conjugated π-system of this carbene (similar to heptafulvalene) as well as the very low N–C–N angle by X-ray structure analysis [41].…”

Section: Introductionmentioning

confidence: 93%

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Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

Nonnenmacher¹,

Buck²,

Kunz³

2016

Beilstein J. Org. Chem.

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SummaryRh(CO)2Cl(NHC) complexes of dipyrido-annelated N-heterocyclic carbenes were prepared. From the C–H coupling constant of the respective imidazolium salts and the N–C–N angle of the N-heterocyclic carbene (NHC), a weaker σ-donor character than that of typical unsaturated NHCs is expected. However, the IR stretching frequencies of their Rh(CO)2Cl complexes suggest an electron-donor character even stronger than that of saturated NHCs. We ascribe this to the extremely weak π-acceptor character of the dipyrido-annelated NHCs caused by the conjugated 14 πe− system that thus allows for an enhanced Rh–CO backbonding. This extremely low π-acceptor ability is also corroborated by the 77Se NMR chemical shift of −55.8 ppm for the respective selenourea, the lowest value ever measured for imidazole derived selenoureas. DFT-calculations of the free carbene confirm the low σ-donor character by the fact that the σ-orbital of the carbene is the HOMO−1 that lies 0.58 eV below the HOMO which is located at the π-system. Natural population analysis reveals the lowest occupation of the pπ-orbital for the saturated carbene carbon atom and the highest for the pyrido-annelated carbene. Going from the free carbene to the Rh(CO)2Cl(NHC) complexes, the increase in occupancy of the complete π-system of the carbene ligand upon coordination is lowest for the pyrido-annelated carbene and highest for the saturated carbene.

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Section: Introductionmentioning

confidence: 93%

“…1) [39,47]. They pointed out the unusual high s-character of that carbene σ-orbital by a 1 J CH coupling constant of 232.6 Hz, which corresponds to a hybridization of only sp 1.15 .…”

Section: Introductionmentioning

confidence: 99%

Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

Nonnenmacher¹,

Buck²,

Kunz³

2016

Beilstein J. Org. Chem.

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“…Free or in situ generated NHCs react with elemental sulfur, − selenium, − ,− ,, and tellurium − ,, similarly to other main group compounds with unshared electron pairs (e.g., phosphines or heavier carbene analogues) to give the corresponding chalcogenoureas 1054 – 1056 in high yields (Scheme ). Reactivity of other NHCs (e.g., CAACs, 1,2,4-triazolin-5-ylidenes, , and bis(imidazolidin-2-ylidenes) , ) toward elemental chalcogens is similar.…”

Section: Nhc Complexes Of Main Group Elementsmentioning

confidence: 99%

“…918,919 Analogously, reactions of NHC−AgCl complexes with elemental sulfur led to the formation of thiones. 920 Oxidation of [SIMes-H]I with PhI(OAc) 2 in the presence of succinimide 921 Free or in situ generated NHCs react with elemental sulfur, 926−932 selenium, [54][55][56][927][928][929]933,934 and tellurium [927][928][929]935,936 similarly to other main group compounds with unshared electron pairs (e.g., phosphines or heavier carbene analogues) to give the corresponding chalcogenoureas 1054−1056 in high yields (Scheme 240). Reactivity of other NHCs (e.g., CAACs, 927 1,2,4-triazolin-5-ylidenes, 937,938 and bis(imidazolidin-2-ylidenes) 939,940 ) toward elemental chalcogens is similar.…”

Section: Nhc Complexes Of Group 16 Elementsmentioning

confidence: 99%

NHCs in Main Group Chemistry

et al. 2018

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Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

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“…Weiss et al was the first person to develop and introduce the Bipyridocarbene (L18 and L19) which is a highly electron-rich NHC (Figure 8) [20,21]. This is evident from the strong high-field shift of its carbene signal (196 ppm) in the 13 C NMR spectrum [22].…”

Section: -Membered Nhcmentioning

confidence: 99%

Recent Development of Carbenes: Synthesis, Structure, Photophysical Properties and Applications

Manna¹,

Verma²,

Panja³

et al. 2022

Carbene

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Carbenes are highly reactive intermediates in organic synthesis. These divalent carbon species are generally transient in nature and cannot be isolated. However, they can form stabile metal complexes. Later on, the development of N-heterocyclic carbene (NHC) and other stable carbene led to the application of these carbon (II) donor ligands in the synthesis of complex natural products, transition metal catalysis, organo-catalysis and several other synthetic methodologies. Here in this short review, we will discuss the brief history of the development of carbenes, synthesis of stable carbenes (NHC in particular), and their applications in natural products synthesis transition metal chemistry/organometallics. In addition to synthesis and application, the chapter will consist of a detailed structural analysis of carbenes and exciting photophysics of this class of compounds. Special emphasis will be given to electronic structure. The role of carbene in the development of luminescent NHC transition metal complexes, the tuning of emission properties as well as their active role as photocatalysts in the reduction of CO2 will also be discussed.

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Novel Urea Derivatives as Two-Step Redox Systems

Cited by 43 publications

References 4 publications

Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

NHCs in Main Group Chemistry

Recent Development of Carbenes: Synthesis, Structure, Photophysical Properties and Applications

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