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A systematic study on Lewis‐acid/base adducts of N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAACMe (1‐(2,6‐di‐iso‐propylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene) with antimony(III) chlorides of the general formula SbCl2R (R=Cl, Ph, Mes) is presented. The reaction of the NHCs Me2ImMe (1,3,4,5‐tetra‐methyl‐imidazolin‐2‐ylidene), iPr2ImMe (1,3‐di‐isopropyl‐4,5‐dimethyl‐imidazolin‐2‐ylidene), Mes2Im, Dipp2Im (R2Im=1,3‐di‐organyl‐imidazolin‐2‐ylidene; Mes=2,4,6‐trimethylphenyl, Dipp=2,6‐di‐isopropylphenyl) and cAACMe with antimony(III) compounds SbCl2R (R=Cl (1), Ph (2) and Mes (3)) yields the adducts NHC ⋅ SbCl2R (R=Cl (4), Ph (5) and Mes (6); NHC=Me2ImMe (a), iPr2ImMe (b), Dipp2Im (c) and Mes2Im (d)) and cAACMe ⋅ SbCl2R (R=Cl (4 e) and Ph (5 e)). Thermal treatment of (Dipp2Im) ⋅ SbCl2Ar (Ar=Ph (5 c) and Mes (6 c)) in benzene leads to isomerization to the backbone coordinated aNHC‐adduct aDipp2Im ⋅ SbCl2Ar (Ar=Mes (7) and Ph (8)) ("a" denotes "abnormal" coordination mode of the NHC) in high yields. One of the chloride substituents at antimony of 7 can be abstracted by GaCl3 or Ag[BF4] to obtain the imidazolium salts [aDipp2Im ⋅ SbClMes][BF4] (9) and [aDipp2Im ⋅ SbClMes][GaCl4] (10). [ABSTRACT FROM AUTHOR]

Aminotroponiminate (ATI) ligands are a versatile class of redox‐active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron‐withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro‐substituent in the backbone. It is demonstrated that the NO2 group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N‐binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first "naked" (i. e. without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N‐coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT‐)NMR spectroscopy, single‐crystal X‐ray diffraction analysis, and DFT calculations. [ABSTRACT FROM AUTHOR]

Boroles are attracting broad interest for their myriad and diverse applications, including in synthesis, small molecule activation and functional materials. Their properties and reactivity are closely linked to the cyclic conjugated diene system, which has been shown to participate in cycloaddition reactions, such as the Diels‐Alder reaction with alkynes. The reaction steps leading to boranorbornadienes, borepins and tricyclic boracyclohexenes from the thermal reaction of boroles with alkynes are seemingly well understood as judged from the literature. Herein, we question the long‐established mechanistic picture of pericyclic rearrangements by demonstrating that seven‐membered borepins (i. e. heptaphenylborepin and two derivatives substituted with a thienyl and chloride substituent on boron) exist in a dynamic equilibrium with the corresponding bicyclic boranorbornadienes, the direct Diels‐Alder products, but are not isolable products from the reactions. Heating gradually converts the isomeric mixtures into fluorescent tricyclic boracyclohexenes, the most stable isomers in the series. Results from mechanistic DFT calculations reveal that the tricyclic compounds derive from the boranorbornadienes and not the borepins, which were previously believed to be intermediates in purely pericyclic processes. [ABSTRACT FROM AUTHOR]

2,3-Bis(dimethylamino)-substituted B2N2C2 heterocycles underwent selective dimethylamino/hydride exchange with either one or two equivalents of BH3 ⋅SMe2 to give the corresponding cyclic monohydrido- or ( cis)1,2-dihydridodiboranes(4), respectively. Upon either heating or irradiation in solution, the latter underwent ring contraction to the corresponding five-membered BN2C2 heterocycles, whereas irradiation of the 1,2-dimethylaminoethene-supported 1,2-dihydridodiborane(4) in the presence of PEt3 gave an unprecedented unsymmetrical 1,1-dihydrodiborane(5) phosphine adduct. [ABSTRACT FROM AUTHOR]

The reactivity of the diaminoacetylene Pip-C≡C-Pip (Pip=piperidyl=NC5H10) towards phenyldichloro- and triphenylborane is presented. In the case of the less Lewis acidic PhBCl2, the first example of a double Lewis adduct of a vicinal dicarbenoid is reported. For the more Lewis acidic triphenylborane, coordination to the bifunctional carbene leads to a mild B-C bond activation, resulting in a syn-1,2-carboboration. Ensuing cis/trans isomerization yields a novel ethylene-bridged frustrated Lewis pair (FLP). The compounds were characterized using multinuclear NMR spectroscopy, structural analysis, and mass spectrometry. Reactivity studies of both isomers with the N-heterocyclic carbene 1,3-dimethylimidazol-2-ylidene (IMe) aided in elucidating the proposed isomerization pathway. DFT calculations were carried out to elucidate the reaction mechanism. The rather low free energy of activation is consistent with the observation that the reaction proceeds smoothly at room temperature. [ABSTRACT FROM AUTHOR]

A heterocyclic manganese complex (4) derived from a carbonyl–borylene coupling reaction undergoes isomerisation, during which the former borylene moiety migrates to the cyclopentadienyl ligand and inserts into a C–H bond. This reaction and a computational study of its mechanism are discussed. [ABSTRACT FROM AUTHOR]

Building upon our ongoing studies on the highyield synthetic route to 2,3,4,5-tetracarba-1,6-nido hexaborane derivative 5, we continue to explore the chemistry of this system to isolate a range of perphenylated C4B2-type carborane isomers. As a result, the photolysis of 5 for an elongated period yielded 6, which exhibits an intense luminescence upon excitation with a UV lamp (λex=366 nm). In contrast, the conversion of 5 under thermal conditions (microwave heating) generated the isomer 7, which does not show any luminescence. The structural disparity among the three isomers 5-7 is the position of the butadiene moiety with respect to the C4B2-carborane cage as deduced from single-crystal X-ray diffraction analyses. In an attempt to generate the classical structural motif of 5, an equimolar amount of KOtBu was added to a THF solution of 5, which immediately provided the boratacyclopentadiene derivative 8 in good yield. The observed rearrangement reactions were further investigated by quantum chemical calculations to suggest a plausible reaction pathway. According to the DFT calculations, the energetically favored reaction mechanism most likely involves tricyclic transition states and classical intermediate structures. In addition, the fluorescence emission properties of 6 were investigated in solution as well as in the solid state. [ABSTRACT FROM AUTHOR]

The photophysical properties and lysozyme affinities of [ReX(CO) 3 (L– k2N1,N2)] (L = 4′-(4-phenyl morpholine)-2,2′:6′,2′'-terpyridine, X = Br– (1), N 3 – (2), and triazolate (3)) complexes were investigated. • The kinetically formed triazolate N(1) type favored the isomerization to N(2) form. • Negative solvatochromism was observed in the case of triazolate compound. • The promising antimicrobial activity of the ligand was diminished upon complex formation. • Probability of exchange of the bromo ligand with the coordinating solvents. [ReX(CO) 3 (L– k2N1,N2)] (L = 4′-(4-phenyl morpholine)-2,2′:6′,2′'-terpyridine, X = Br– (1), N 3 – (2), and triazolate (3)) complexes were synthesized, and characterized using different spectroscopic and analytical tools including single-crystal X-ray diffraction analysis of 2. The 1,3-dipolar cycloaddition reaction between 2 , and 4,4,4-trifluoro-2-butynoic acid ethyl ester afforded triazolate 3. Although, the crystal structure of 2 showed that the azide ligand is terminally coordinated to Re(CO) 3 + unit, the 19F and 1H NMR analyses of 3 provided conversant evidences that the kinetically formed N(1) triazolate bound isomer favoured the isomerization to N(2) form. The photophysical properties of 1–3 were investigated by recording the absorption spectra of the compounds in solvents of different polarities. Complexes 1 and 3 were screened for their potential antimicrobial activities. The protein binding affinity of 1 , and 3 towards hen white egg lysozyme revealed that the bromide complex exchanges Br– with that protein, while the triazolate analogue sticked around. [ABSTRACT FROM AUTHOR]