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The synthesis, characterization and reactivity of the diferrocenylphosphenium ion [Fc2P]+ was extended to the heavier diferrocenylpnictogenium ions, [Fc2E]+ (E=As, Sb, Bi). The lighter diferrocenylnitrenium ion, [Fc2N]+, was detected by mass spectrometry, but could not be isolated. The molecular structures of [Fc2E]+ (E=P, As, Sb, Bi) reveal intramolecular coordination of the iron atoms, which counterbalance the electron deficiency of the pnictogens without affecting the strong Lewis acidities, which were determined according to the method of Gutmann and Beckett. The (electro−)chemical oxidation and reduction afforded the dications [Fc2E]2+ (E=P (unstable), As) and the neutral dipnictogens Fc2EEFc2 (E=P, As). [ABSTRACT FROM AUTHOR]

The newly prepared and fully characterized stibenium and bismuthenium ions [RindMesE]+ (E=Sb, Bi; Rind=dispiro[fluorene‐9,3′‐(1′,1′,7′,7′‐tetramethyl‐s‐hydrindacen‐4′‐yl)‐5′,9′′‐fluorene) were rigorously compared to the previously communicated phosphenium and arsenium ions (E=P, As) as well as the bis(m‐terphenyl) pnictogenium ions [(2,6‐Mes2C6H3)2E]+ (E=Sb, Bi). It is demonstrated that the choice of the aryl substituents dramatically effects the molecular structures (e. g. the primary E−C bond lengths) and the electronic structures (e. g. the energy of the LUMOs). [ABSTRACT FROM AUTHOR]

The paper reviews data reported on the synthesis, molecular and electronic structure of heterocyclic derivatives of low valent silicon, germanium, tin, and lead for the period from 2016 to 2021. The main pathways of chemical transformations of these compounds are considered. [ABSTRACT FROM AUTHOR]

The synthesis, characterization and reactivity of the diferrocenylphosphenium ion [Fc 2 P] + was extended to the heavier diferrocenylpnictogenium ions, [Fc 2 E] + (E=As, Sb, Bi). The lighter diferrocenylnitrenium ion, [Fc 2 N] + , was detected by mass spectrometry, but could not be isolated. The molecular structures of [Fc 2 E] + (E=P, As, Sb, Bi) reveal intramolecular coordination of the iron atoms, which counterbalance the electron deficiency of the pnictogens without affecting the strong Lewis acidities, which were determined according to the method of Gutmann and Beckett. The (electro-)chemical oxidation and reduction afforded the dications [Fc 2 E] 2+ (E=P (unstable), As) and the neutral dipnictogens Fc 2 EEFc 2 (E=P, As)., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

Carbenes and their analogues have constantly enthralled chemists with their intriguing reactivity of ambiphilic character stemming from their electronic structures. Phosphenium and arsenium ions are fiercely reactive cationic species, the stabilization of which has been so far achieved in the condensed phase by dispersing the positive charge through electromeric conjugation with at least one electron‐rich substituent (frequently amido groups). Although observed in the gas phase, the isolation of dicoordinate phosphenium and arsenium ions lacking such stabilizing ligands has eluded chemists for decades. Herein we show that by judicious choice of aromatic substituents, dicoordinate, donor‐free, Lewis‐superacidic phosphenium and arsenium ions can be kinetically stabilized. They feature singlet electronic ground states possessing a vacant p‐orbital and an electron lone pair with predominantly s‐character. [ABSTRACT FROM AUTHOR]

Three series of N-heterocyclic carbene analogues including Arduengo-type systems (HCNBut)2E (1; E = C, Si, Ge, Sn), their benzannulated derivatives C6H4(NCH2But)2E (2; E = C, Si, Ge, Sn, Pb), and amidophenolates C6H2But2(O)NButE (3; E = Ge, Sn, Pb) were studied by the electron density of delocalized bonds (EDDB) method. The results obtained confirmed the π-aromaticity of systems 1–3. The aromaticity series were obtained. The degree of aromaticity of heavy carbene analogues increases on going down Group 14 of the periodic system. [ABSTRACT FROM AUTHOR]

The versatile cycloaddition chemistry of the Si−Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni0 complex 1, [(TMSL)ClSi→Ni(NHC)2] (TMSL=N(SiMe3)Dipp; Dipp=2,6‐iPr2C6H4; NHC=C[(iPr)NC(Me)]2), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene–metal complexes. Thus, 1:1 reaction of 1 with aldehydes, imines, alkynes, and even alkenes proceed to yield [2+2] cycloaddition products, leading to a range of four‐membered metallasilacycles. This cycloaddition is in fact reversible for ethylene, whereas addition of an excess of this olefin leads to quantitative sp2‐CH bond activation, via a 1‐nickela‐4‐silacyclohexane intermediate. These results have been supported by DFT calculations giving insights into key mechanistic aspects. [ABSTRACT FROM AUTHOR]

A cationic phosphanyl substituted plumbylene has been generated by chloride abstraction from a neutral bisplumbylene embedded into a bicyclic [3]ferrocenophane scaffold. The primary cationic bisplumbylene [Fe(C5H4PtBuPb)2Cl]+AlCl4– has been characterized by multinuclear NMR spectroscopy, mass spectrometry, and elemental analysis. It undergoes rapid chloride exchange with its neutral counterpart in solution, and adduct formation between both components has been identified via single‐crystal X‐ray diffraction. The energy balance for chloride abstraction and adduct formation has been explored for a simplified model system using DFT calculations, which was also used to assess the charge distribution within these molecules. The highly electrophilic nature of a cationic bis(phosphanylplumbylene) requires donor free solvents for chloride abstraction. [ABSTRACT FROM AUTHOR]

The inverse trans influence (ITI) is investigated in uranyl, UO22+, and its isoelectronic imido (U(NH)22+) and carbene (U(CH2)22+) analogues at the density functional and complete active space self consistent field levels of theory. The quantum theory of atoms in molecules is employed to quantify, for the first time, the effect of the ITI on covalent bond character and its relationship to bond lengths and complex stability. [ABSTRACT FROM AUTHOR]

Abstract: With the aim of exploring the effect of steric constraints imposed on the metal–metal interaction of bis‐carbene analogues of thallium by the linking scaffold, seven dinuclear thallium diyls with a series of rigid, semirigid, and flexible bridging scaffolds were synthesized. The solid‐state molecular structures were determined for four of these compounds by single‐crystal XRD and compared with the results of DFT calculations, which were performed for all substances. These compounds serve as models to investigate the metal–metal distance in the absence of co‐coordinated molecules (additional ligands, solvent molecules). In addition, the effect of the metal(I) precursor, and more specifically the counterion, on the synthetic access to bis‐carbene analogues of indium and thallium was investigated. For indium, only InI yields the desired dinuclear indium diyl. With InBr no reaction was observed, and using InCl gave rise to a mononuclear indium(III) compound. For thallium, both TlI and TlBr allow access to the related bis‐carbene analogue, although the yield with the latter is significantly lower. In contrast, no reactions were observed with TlCl and TlBF4. [ABSTRACT FROM AUTHOR]

Abstract: Kinetically stabilized congeners of carbenes, R2C, possessing six valence electrons (four bonding electrons and two non‐bonding electrons) have been restricted to Group 14 elements, R2E (E=Si, Ge, Sn, Pb; R=alkyl or aryl) whereas isoelectronic Group 15 cations, divalent species of type [R2E]+ (E=P, As, Sb, Bi; R=alkyl or aryl), were unknown. Herein, we report the first two examples, namely the bismuthenium ion [(2,6‐Mes2C6H3)2Bi][BArF4] (1; Mes=2,4,6‐Me3C6H2, ArF=3,5‐(CF3)2C6H3) and the stibenium ion [(2,6‐Mes2C6H3)2Sb][B(C6F5)4] (2), which were obtained by using a combination of bulky meta‐terphenyl substituents and weakly coordinating anions. [ABSTRACT FROM AUTHOR]

The present article discusses a theoretical possibility of a novel class of sandwiched organometallic compounds based on the group 13 analogues of N-Heterocyclic carbene. The structure, stability and bonding pattern of the Fe(NHE) 2 complexes (where E = B, Al and Ga) have been studied using density functional theory. The bond dissociation energy and binding energy are comparable with ferrocene. In addition, the topological study of the electron density describes the partial covalent interaction of the ligands with the metal atom. The synthetic possibility of such complexes with bulky substituent at the nitrogen center are addressed as well. [ABSTRACT FROM AUTHOR]

Abstract: Direct conversion of 1‐decene to petroleum range alkanes was obtained using hydro‐metathesis reaction. To understand this reaction we employed three different well‐defined single site catalysts precursors; [(≡Si‐O‐)W(CH3)5] 1, [(≡Si‐O‐)Mo(≡CtBu)(CH2tBu)2] 2 and [(≡Si‐O)Ta(=CHtBu)(CH2tBu)2] 3. We witnessed that in our conditions olefin metathesis/isomerization of 1‐decene occurs much faster followed by reduction of the newly formed olefins rather than reduction of the 1‐decene to decane, followed by metathesis of decane. We found that Mo‐based catalyst favors [2+2] cycloaddition of 1‐decene forming metallocarbene, followed by reduction of the newly formed olefins to alkanes. However, in the case of W and Ta‐based catalysts, a rapid isomerization (migration) of the double bond followed by olefin metathesis and reduction of the newly formed olefins were observed. We witnessed that silica supported W catalyst precursor 1 and Mo catalyst precursor 2 are better catalysts for hydro‐metathesis reaction with TONs of 818 and 808 than Ta‐based catalyst 3 (TON of 334). This comparison of the catalysts provides us a better understanding that, if a catalyst is efficient in olefin metathesis reaction it would be a better catalyst for hydro‐metathesis reaction. [ABSTRACT FROM AUTHOR]

Abstract: The immobilization of the molybdenum alkylidyne complex [(p‐OMe‐C6H4C≡)Mo(OCMe(CF3)2)3⋅DME] (DME=1,2‐dimethoxyethane) on silica using a silica‐supported N‐heterocyclic carbene (NHC), that is, 1,3‐di(isopropyl)imidazol‐2‐ylidene, is reported. Two different types of silica, that is, silica 60 and partially dehydroxylated silica 60 obtained via heating to 650 °C (SiO2‐650) were used. In both cases, excess silanol groups were end‐capped with trimethylsilyl chloride. Immobilization of both the NHC precursor and the metal alkylidyne was followed by 19F magic angle spinning (MAS) and 13C cross‐polarization magic angle spinning (CPMAS) NMR and inductively‐coupled optical emission spectroscopy (ICP–OES). The metal alkylidyne supported on both types of silica was active in alkyne metathesis and showed activity for a series of functional 2‐alkynes. Most importantly, the metal alkylidyne supported on SiO2‐650 displayed a substantially higher alkyne metathesis activity than the homogeneous analog or the one supported on regular silica, which is attributed to a site isolation effect and, as a result, reduced bimolecular decomposition. [ABSTRACT FROM AUTHOR]

Abstract: Two pyrene‐tagged N‐heterocyclic carbene (NHC) complexes of rhodium(I) were obtained and characterized. The two complexes were supported onto reduced graphene oxide (rGO), generating two new materials in which the molecular complexes are immobilized by π–π stacking interactions onto the surface of the solid. The catalytic activity of both complexes and solid hybrid materials were studied in the 1,4‐addition of phenylboronic acid to cyclohex‐2‐one, and in the hydrosilylation of terminal alkynes. The studies showed that for both reactions, the dimetallic complex displayed better catalytic performances than the monometallic one. This accounted for both the reactions performed in homogeneous conditions and for the reactions performed with the solid. In the case of the addition of phenylboronic acid to cyclohexanone, the solid containing the dimetallic catalyst could be effectively recycled up to five times, with negligible loss of activity, whereas the monometallic catalyst rapidly became inactive. In the hydrosilylation of terminal alkynes, the selectivity towards the β‐(Z)vinylsilane was improved if the immobilized dimetallic catalyst was used, although the catalyst started to lose activity after the second run. [ABSTRACT FROM AUTHOR]

Abstract: The development of efficient and stable catalyst systems with low‐cost, abundant, and non‐toxic materials is the primary demand for electrochemical water oxidation. A unique method is reported for the syntheses of metal hydroxide carbonate templated Prussian blue analogues (PBAs) on carbon cloth and their outstanding water oxidation activities in alkaline medium. The best water oxidation activity is obtained with cobalt hydroxide carbonate templated t‐CoII‐CoIII with an overpotential as low as 240 mV to reach a current density of 10 mA cm−2. It produces constant current over 50 h in chronoamperometric measurements. Moreover, the catalysts outperform the activities of the PBAs prepared without any template and even the noble metal catalyst RuO2. Spectroscopic and microscopic studies show that the PBAs are transformed into layered hydroxide–oxyhydroxide structures during electrochemical process and provide the active sites for the water oxidation. [ABSTRACT FROM AUTHOR]

An unusual germole-to-silole transformation is described. As key intermediates hetero-fulvenes are formed which rearrange to more stable bicyclic carbene analogues. The so-formed germylenes undergo a reductive elimination yielding elemental germanium and siloles. In contrast, the analogous silylenes are stable at ambient conditions and were identified by MS spectrometry and NMR spectroscopy supported by the results of quantum mechanical calculations. These bicyclic silylenes are stable derivatives of the global minimum of the C4Si2H6 potential energy surface. [ABSTRACT FROM AUTHOR]

Chemical reactions involving quantum mechanical tunneling (QMT) increasingly attract the attention of scientists. In contrast to the hydrogen-tunneling as frequently observed in chemistry and biology, tunneling solely by heavy atoms is rare. Herein, we report heavy-atom tunneling in trifluoroacetyl nitrene, CF3C(O)N. The carbonyl nitrene CF3C(O)N in the triplet ground state was generated in cryogenic matrices by laser (193 or 266 nm) photolysis of CF3C(O)N3 and characterized by IR and EPR spectroscopy. In contrast to the theoretically predicted activation barriers (>10 kcal mol−1), CF3C(O)N undergoes rapid rearrangement into CF3NCO with half-life times of less than 10 min and unprecedentedly large 14N/15N kinetic isotope effects (1.18-1.33) in solid Ar, Ne, and N2 matrices even at 2.8 K. The tunneling disappearance of CF3C(O)N becomes much slower in the chemically active toluene and in 2-methyltetrahydrofuran at 5 K. [ABSTRACT FROM AUTHOR]

Deprotonation of the diruthenium μ-methylidyne complex [(Cp*Ru)2(μ-NtBu)(μ-CH)][BF4] (Cp* = η5-C5Me5) with 2 equiv of KN(SiMe3)2 in the presence of CuCN, AgOTf, or AuCl(SMe2) afforded the trigonal planar bridging carbido complexes [(Cp*Ru)2(μ-NtBu)(μ3-C)M{N(SiMe3)2}] (M = Cu (4), Ag (5), and Au (6)). Complexes 4 and 6 were characterized crystallographically. The M-C bonding in these complexes showed considerable similarity with that in the N-heterocyclic carbene (NHC) derivatives (NHC)M{N(SiMe3)2} (M = Cu and Au), illustrating the analogy between the diruthenium carbido ligand [(Cp*Ru)2(μ-NtBu)(μ-C)] and NHCs. The reaction of 4 with 2,6-di-tert-butylphenol allowed derivatization via protonolytic exchange of the disilazide moiety, yielding the aryloxo complex [(Cp*Ru)2(μ-NtBu)(μ3-C)Cu(OAr)] (7; Ar = 2,6-tBu2C6H3), which was also structurally characterized. The electron donor ability and steric bulkiness of the diruthenium carbido ligand were studied by computational methods. [ABSTRACT FROM AUTHOR]

The reaction of vinylazides with alkenyldiazo compounds in the presence of [Cu(CH3CN)4][BF4] provided cyclopentene derivatives with retention of the azide functionality. This process likely involves a sequence comprising: 1) decomposition of the diazo component with generation of a copper alkenylcarbene species; 2) stepwise regioselective [3+2] cycloaddition; 3) allylic azide rearrangement. This method is compatible with a broad range of substrates. We also show that the azide-containing cycloadducts can be efficiently converted into the corresponding amine and triazole derivatives. [ABSTRACT FROM AUTHOR]

We describe the isolation and spectroscopic characterization of the heavier phosphorus-containing analogue of isocyanic acid (HPCO), and its isotopologue (DPCO). This fundamental small molecule, which has been postulated to exist in interstellar space, has thus far only been observed at low gas phase concentrations or in inert gas matrices. In this report we describe its synthesis, spectroscopic properties, and reactivity in solution. [ABSTRACT FROM AUTHOR]

o-Phenylenediamido Pb(ii) and Sn(ii) complexes react with mesityl azide in analogous C–H activation reactions. The Pb(ii) complex forms a Lewis pair with ONMe3. The Sn(ii) analogue reacts with AgOTf yielding a paramagnetic stannylene; such compounds have been previously observed in situ, but hitherto have not been isolated. [ABSTRACT FROM AUTHOR]

The synthesis of a bicyclic germylene from the reaction of a germole dianion with hafnocene dichloride is reported. This germylene is stabilized by a homoconjugative interaction of the dicoordinated germanium atom with a remote C=C double bond. First reactivity studies revealed its nucleophilic character and resulted in the synthesis of bimetallic hafnium/iron and hafnium/tungsten complexes with a germylene group linker. [ABSTRACT FROM AUTHOR]

N-Heterocyclic carbenes (NHC's) are known to serve as efficient substrates for the stabilization of various transient species possessing low-valent Group 14 elements and for the generation of double E=C bonds. Herein, we report that the thermal tri- and tetramerizations of pyridoannulated silylene 1 lead to the formation of remarkably stable silenes 2 and 3 featuring zwitterionic distribution of electron density. Co-oligomerization of 1 and its germanium analogue gives a related tetrameric product 4 containing low-valent germanium atom stabilized by binding with the partial carbene-character C atom. Bonding situations in 2- 4 are best described as silene or germene with the significant zwitterionic distribution of electron density. The singlet diradical electronic state of 2 is 10 kcal mol−1 higher than the ground state configuration. [ABSTRACT FROM AUTHOR]

The reactivity of tin(II) catecholate complex CatSn ( 1) (where Cat = 3,6-di- tert-butylcatecholate dianion) and two o-amidophenolate complexes DippAPSn ( 2) and PhAPSn ( 3) [where DippAP = 4,6-di- tert-butyl- N-(2,6-diisopropylphenyl)amidophenolate; PhAP = 4,6-di- tert-butyl- N-(phenyl)amidophenolate dianions] towards different reagents is reported. Products of the insertion of 1 and 2 into the S-S bond of tetramethylthiuram disulfide were obtained and characterised by X-ray diffraction analyses. The low temperature oxidation of complexes 1 and 2 with 2-ethoxy-3,6-di- tert-butylphenoxy radical enabled us to detect formation of paramagnetic tin(II) derivatives containing the radical-anion form of the redox-active ligand. The reaction of tin derivative 3 with Ni(CO)4 leads to substitution of one of the CO groups in the latter with the formation of a new bimetallic product. [ABSTRACT FROM AUTHOR]

Ready for the open waters? Recent developments have fundamentally changed our knowledge of vinyl cation reactivity. The myth that they are too reactive for a predictable reaction design has been debunked, and the applicability of their most distinguished feature, namely their carbene‐like reactivity, has taken a major leap forwards. Vinyl cations have thus matured into distinct reactive intermediates with a bright future ahead. [ABSTRACT FROM AUTHOR]

Density functional theory calculations (B3LYP and B2PLYP-D2) have been utilized to design and characterize novel homoatomic lithium(0) organometallic complexes of the NHC → Li–Li ← NHC type (NHC = N-heterocyclic carbenes). The computed Li–Li bond length and energy are consistent with those experimentally observed for Li 2 (g). These and other structural and energetic data suggest that such organolithium compounds should be viable targets for synthesis. These compounds would represent a new class of molecular “allotropes” and could have novel reactivities. [ABSTRACT FROM AUTHOR]

Five Ru(ii)–N-heterocyclic carbenes (NHC) (1–5) were synthesized by reacting the appropriately substituted imidazolium chlorides with Ag2O, forming the NHC-silver chloride in situ followed by transmetalation with dimeric p-cymene ruthenium(ii) dichloride. All the complexes were characterized by NMR and ESI-MS, and complex 1 was also characterized by single-crystal X-ray diffraction. The IC50 values of these five complexes were determined by the MTT-based assay on four human cancer cell lines, SKOV-3 (ovarian), PC-3 (prostate), MDA-MB-231 (breast) and EC109 (esophagus). The cytotoxicities of these complexes changed from a moderate effect to a fine one, corresponding to the increasing lipophilicity order of the complex of 2 ＜ 1 ＜ 3 ＜ 4 ＜ 5 (0.91, 0.88, 1.36, 1.85 and 2.62 for 1–5 respectively). Complex 5 showed the most cytotoxicity with the IC50 values 10.3 ± 0.3 μM for SKOV-3, 2.9 ± 0.1 μM for PC-3, 8.2 ± 0.6 μM for MDA-MB-231, 6.4 ± 0.2 μM for EC109 cell lines. Due to the superior cytotoxicity of complex 5 against the PC-3 cell lines, further biological evaluations were carried out to elucidate its action mechanism. The morphologic changes and cell cycle analysis showed that complex 5 can inhibit PC-3 cell lines by inducing cell cycle arrest at the G2/M phase. The DNA binding experiments further demonstrate that complex 5 has a better binding ability for DNA (Kb = 2.2 × 106 M−1) than complexes 1–4 (3.8 × 105, 7.0 × 105, 5.7 × 105, and 1.9 × 105 respectively). [ABSTRACT FROM AUTHOR]

We report the discovery that 1,3-bis(aryl)imidazolidin-2-ylidenes, one of the most widely studied classes of N-heterocyclic carbenes (NHCs), undergo quantitative conversion to zwitterionic 'NHC-CDI' amidinates upon heating to ≈100 °C in solution. The mechanism of this novel NHC decomposition process is studied in detail. These studies enabled the rational synthesis of a new class of bench stable amidinates from a panel of NHCs and carbodiimides. We expect these constructs to find utility in a variety of applications. [ABSTRACT FROM AUTHOR]

Design of stable heavier carbene analogues M(II) (M = Ge, Sn, Pb) with structural motifs different from the traditional di-coordinate analogues is extremely of interest and challengeable. In this paper, we computationally designed a novel class of tri-coordinate cyclic heavier analogues of carbenes covering a number of substituents, i.e., RM(μ-R)2AlR2(M = Ge, Sn, Pb)1, in which two sets of inter-molecular donor–acceptor interactions were formed between the di-coordinate carbene MR2and the AlR3moiety. The M-centre was found to undergo both the nucleophilic and insertion reactions, indicative of the ‘carbene’ character. We also designedc-1starting from the known di-coordinate cyclic MR2and AlR3under 16 kinds of substituents [NR′2, OR′, PR′2, SR′(R′ = H, Me,iPr, Ph)];c-1also has favourable thermodynamic stability. After the only known cyclic tri-coordinate M(II) [M2,R4] inter-molecularly formed between two di-coordinate MR2, the presently designed new tri-coordinate cyclic heavier carbene analogues should expand the higher coordinate M(II) family and await future laboratory synthesis. [ABSTRACT FROM AUTHOR]

The synthesis of two novel titanium carbene complexes from the bis(thiophosphinoyl)methanediide geminal dianion 1 (SCS2-) is described. Dianion 1 reacts cleanly with 0.5 equivalents of [TiCl4(thf)2] to afford the bis-carbene complex [(SCS)2Ti] (2) in 86% yield. The mono-carbene complex [(SCS)TiCl2(thf)] (3) can also be obtained by using an excess of [TiCl4(thf)2]. The structures of 2 and 3 are confirmed by Xray crystallography. A strong nucleophilic reactivity towards various electrophiles (ketones and aldehydes) is observed. The reaction of 3 with N,N'-dicyclohexylcarbodiimide (DCC) and phenyl isocyanate leads to the formation of two novel diphosphinoketenimines 8a and 8b. The bis-titanium guanidinate complex 9 is trapped as the by-product of the reaction with DCC. The X-ray crystal structures of 8a and 9 are presented. The mechanism of the reaction between complex 3 and DCC is rationalized by DFT studies. [ABSTRACT FROM AUTHOR]

The coordination chemistry of a diphosphine pincer ligand incorporating an N -heterocyclic phosphenium cation (PPP + ) and its halophosphine precursors [PP(X)P] has been explored using copper(I) reagents. In contrast to the P–X bond cleavage observed when other low valent transition metals are used, simple coordination compounds [PP(X)P]CuY (X = Y = Cl ( 1 ); X = Cl, Y = I ( 2 ); X = Y = I ( 3 )) are formed when halophosphine precursors are treated with CuY starting materials. Exposure of the N -heterocyclic iodophosphine complex 3 to THF results in ring-opening insertion to form the alkoxyphosphine complex [PP(O-CH 2 CH 2 CH 2 CH 2 -I)P]CuI ( 4 ). Since this reaction does not occur with the chlorophosphine compounds 1 and 2 , it is proposed that iodide dissociation exposes the electrophilic metal-bound phosphenium cation to allow THF coordination and subsequent ring-opening. The electrophilicity of the N -heterocyclic phosphenium is also apparent when the halide-free ligand precursor [PPP][BPh 4 ] is employed: CuCl reacts with [PPP][BPh 4 ] to form [PP(Ph)P]CuCl ( 5 ), the product of phenyl group abstraction from [BPh 4 ] − . A similar arylphosphine product [PP(Mes)P]CuCl ( 6 , Mes = 2,4,6-trimethylphenyl) is obtained via transmetallation between [PP(Cl)P] and mesitylcopper(I). The isolation of complexes 4 – 6 provide indirect evidence for the formation of an electrophilic copper–phosphenium intermediate {[PPP]CuCl} + . [ABSTRACT FROM AUTHOR]

Homogeneous catalysts for C-H functionalization typically require precious metals such as Pd, Ru, Rh, or Ir because of their facility in mediating two-electron redox mechanisms. Base metals such as Cu or Fe instead tend to undergo one-electron redox processes. By coupling together two base metal sites in a heterobimetallic catalyst design, base metal catalysts for photochemical C-H borylation were discovered. The optimal catalyst, (IPr)Cu- FeCp(CO)2, represents the first homogeneous catalyst for C-H borylation that contains no precious metals. Using metal-metal cooperativity in this way allows for base metal catalysts to replace precious metal catalysts while maintaining advantageous regioselectivity patterns. The proposed mechanism for heterobimetallic C-H borylation features bimetallic versions of classic organometallic reaction steps, serves as a guide for future catalyst designs, and opens the possibility for other precious metal transformations to be approached using metal-metal cooperativity as a design strategy. [ABSTRACT FROM AUTHOR]

The first examples of Lewis base catalyzed enantioselective boryl conjugate additions (BCAs) that generate products containing boron-substituted quaternary carbon stereogenic centers are disclosed. Reactions are performed in the presence of 1.0-5.0 mol % of a readily accessible chiral accessible N-heterocyclic carbene (NHC) and commercially available bis(pinacolato)diboron; cyclic or linear α,β-unsaturated ketones can be used and rigorous exclusion of air or moisture is not necessary. The desired products are obtained in 63-95 % yield and 91:9 to >99:1 enantiomeric ratio (e.r.). The special utility of the NHC-catalyzed approach is demonstrated in the context of an enantioselective synthesis of natural product antifungal (−)-crassinervic acid. [ABSTRACT FROM AUTHOR]

Abstract: The Al-Nacnac compound is isolobal to the imidazol-2-ylidene (NHC) and forms donor complexes with phosphines and NHCs. These structural types were studied by density functional calculations. They reveal a strong biradical character, since donor addition to the Al-Nacnac reduces the singlet stability of the free carbene-analogue. This facilitates further biradical reactions, such as a subsequent hydrogen shift to the final corresponding tetravalent aluminium product. The latter is determined by maximum singlet stability, i.e. a large singlet-triplet energy separation. Relevance to the analogues Wittig ylids is drawn; these are constituted formally by addition of a phosphine to a carbene, and are well-known as stable synthons in organic chemistry. [Copyright &y& Elsevier]

The observation that (iPr3Si)(tBu3Si)Si: (1) yields an intramolecular C–H bond insertion product at room temperature, together with earlier computational predictions that triplet 1 is slightly more stable (or isoenergetic) than singlet 1 and additional considerations, led previous investigators to conclude that 1 is the first silylene to exhibit triplet electronic state reactivity. In this paper we test, using DFT and ab initio methods, whether the occurrence of intramolecular C–H bond insertion indeed indicates the presence of a triplet-state silylene. DFT calculations at the B3LYP/6-31+G(d,p)//B3LYP/6-31+G(d,p) level show that singlet (iPr3Si)(tBuMe2Si)Si: (9), a close model of singlet 1, inserts intramolecularly into a C–H bond of the tBu group with a barrier of 22.7 kcal/mol (22.2 kcal/mol at SCS-MP2/cc-PVTZ). However, for triplet9 the barrier of this insertion reaction is significantly higher, 34.6 kcal/mol (41.9 kcal/mol at SCS-MP2/cc-PVTZ). This implies that at room temperature the intramolecular insertion reaction of the singlet is 109–1012 faster than that of the triplet. We conclude, in contrast to previous conclusions, that the observed intramolecular C–H bond insertion reactions of 1 as well as of (tBu3Si)2Si: (2) occur from the singlet state. Furthermore, the occurrence of an intramolecular C–H bond insertion cannot serve as evidence for the presence of a triplet silylene, either in cases where the singlet and triplet states are nearly isoenergetic (e.g., 1 and 9) or even for silylenes where the triplet state is the ground state (e.g., 2), because the corresponding singlet silylenes insert intramolecularly much faster. The search for a genuine reaction of a triplet silylene has to continue. [ABSTRACT FROM AUTHOR]

Complexes of divalent tin 7- 12 with diethylenetriamines 1- 3 and related ligands 4- 6 were prepared from Lappert's stannylene, Sn[N(SiMe3)2]2, and the corresponding ligands. Reactivity of the stannylenes in insertion, oxidation and [1+4] cycloaddition reactions were studied. Composition and structures of the products were confirmed by elemental analyses and multinuclear (1H, 13C, 19F, and 119Sn) NMR spectroscopy. Crystal structures of the diethylenetriamines 1, 2, stannylenes 7, 8 and the product of the reaction of stannylene 8 with an azide, which contains an eight-membered (SnNPO)2 ring, were determined by X-ray diffraction study. [ABSTRACT FROM AUTHOR]

This review summarises some recent results on synthesis, structures, and reactivity of the heavier analogues of carbenes, alkenes, and dienes. With the isolation of the first diplumbenes, the series R2E&z.dbnd6;ER2, E=C&z.sbnd;Pb, has been completed. These double bond systems show enormous variations in the E&z.dbnd6;E bond lengths, E=Si&z.sbnd;Pb, and the trans-bent angles. Furthermore, new families of multiple-bonded species have been discovered, such as a spiropentasiladiene, molecules with conjugated Si&z.dbnd6;Si, Ge&z.dbnd6;Ge, and Ge&z.dbnd6;C double bonds, and a diplumbylene RPbPbR. However, no stable compounds featuring homonuclear triple bonding between heavier Group 14 elements are known. Theoretical insights on the nature of such triple bonds as well as first attempts to achieve this target are discussed. [Copyright &y& Elsevier]

Introduction: The clinical development of radioimmunotherapy with astatine-211 is limited by the lack of a stable radiolabeling method for antibody fragments. An astatinated N-heterocyclic carbene (NHC) Rhodium complex was assessed for the improvement of radiolabeling methodologies with astatine. Methods: Wet harvested astatine-211 in diisopropyl ether was used. Astatine was first reduced with cysteine then was reacted with a chlorinated Rh-NHC precursor to allow the formation of the astatinated analogue. Reaction conditions have been optimized. Astatine and iodine reactivity were also compared. Serum stability of the astatinated complex has been evaluated. Results: Quantitative formation of astatide was observed when cysteine amounts higher than 46.2 nmol/μl of astatine solution were added. Nucleophilic substitution kinetics showed that high radiolabeling yields were obtained within 15 min at 60°C (88%) or within 5 min at 100°C (95%). Chromatographic characteristics of this new astatinated compound have been correlated with the cold iodinated analog ones. The radioiodinated complex was also synthesized from the same precursor (5 min. at 100°C, up to 85%) using [125I]NaI as a radiotracer. In vitro stability of the astatinated complex was controlled after 15 h incubation in human serum at 4°C and 37°C. No degradation was observed, indicating the good chemical and enzymatic stability. Conclusion: The astatinated complex was obtained in good yield and exhibited good chemical and enzymatic stability. These preliminary results demonstrate the interest of this new radiolabeling methodology, and further functionalizations should open new possibilities in astatine chemistry. Advances in knowledge and implications for patient care: Although there are many steps and pitfalls before clinical use for a new prosthetic group from the family of NHC complexes, this work may open a new path for astatine-211 targeting. [ABSTRACT FROM AUTHOR]

Catalytically active cationic complexes generated in situ from newly synthesized gold(I) complexes containing triazolylidene ligands in combination with AgBF4 are used as effective catalysts in the reaction of isocyanides and aldehydes to form oxazolines. [ABSTRACT FROM AUTHOR]