Search

Atropisomeric N-chloroamides were efficiently accessed by electrophilic halogenation of ortho-substituted secondary anilides. The stereodynamics of atropisomerism in these novel scaffolds was interrogated by detailed experimental and computational studies, revealing that racemization is correlated with amide isomerization. The stereoelectronic nature of the amide was shown to significantly influence racemization rates, with potentially important implications for other C-N atropisomeric scaffolds. [ABSTRACT FROM AUTHOR]

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO2 to formate; the initial TOF of 500 h−1 is markedly higher than either unmodified catalyst or its benzylamine and N,N-dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst. [ABSTRACT FROM AUTHOR]

Aromatic amides can be used to construct light‐harvesting materials with valuable optical properties. The amide bond is formed using well‐known coupling agents in near quantitative yield, as illustrated here through the synthesis of two boron dipyrromethene derivatives bearing an amide linkage. The primary concern with acyl amides is rotation around the C−N bond, leading to cis and trans isomers. Using NMR spectroscopy, quantum chemical calculations and critical comparison to simpler benzamides, the stereochemistry of the target compounds has been addressed. The N‐cyclohexyl derivative gave diffraction quality crystals that established a trans geometry for the amide bond. Quantum chemical calculations support the trans geometry as being the lowest‐energy structure in solution but indicate that inversion of the aryl ring is an important structural feature. Indeed, rotation around the C(sp2)−C(aryl) bond has a strong influence on the solution‐phase NMR spectra. The amide connection has minimal effect on the photophysical properties. [ABSTRACT FROM AUTHOR]

Ditetrelenes R2E=ER2 (E=Si, Ge, Sn, Pb) substituted by multiple N/P/O/S‐donor groups are extremely rare due to their propensity to disaggregate into their tetrylene monomers R2E. We report the synthesis of the first fully phosphanyl‐substituted digermene {(Mes)2P}2Ge=Ge{P(Mes)2}2 (3, Mes=2,4,6‐Me3C6H2), which adopts a highly unusual structure in the solid state, that is both strongly trans‐bent and highly twisted. Variable‐temperature 31P{1H} NMR spectroscopy suggests that 3 persists in solution, but is subject to a dynamic equilibrium between two conformations, which have different geometries about the Ge=Ge bond (twisted/non‐twisted) due to a difference in the nature of their π‐stacking interactions. Compound 3 undergoes unprecedented, spontaneous decomposition in solution to give a unique GeI cluster {(Mes)2P}4Ge4⋅5 CyMe (7). [ABSTRACT FROM AUTHOR]

Monomeric organolithium (LiR) complexes could provide enhanced Li–C bond reactivity and suggest mechanisms for a plethora of LiR-mediated reactions. They are highly sought-after but remain a synthetic challenge for organometallic chemists. In this work, we report the synthesis and characterisation of a monomeric (trimethylsilyl)methyl lithium complex, namely [Li(CH2SiMe3)(κ3-N,N′,N′′-Me6Tren)] (1), where Me6Tren is a tetradentate neutral amine ligand. The structure of 1 was comprehensively examined by single-crystal X-ray diffraction, variable temperature NMR spectroscopy and electron absorption spectroscopy. Complex 1 decomposes via ligand C–H and C–N activations to produce a Li amide complex 2. Preliminary reactivity studies of 1 reveal C＝O insertion and C–H activation reaction patterns. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles stabilized by imidazolium‐based phosphine‐decorated Polymer Immobilized Ionic Liquids (PPh2‐PIIL) catalyze the hydrolytic evolution of hydrogen from sodium borohydride with remarkable efficiency, under mild conditions. The composition of the polymer influences efficiency with the catalyst based on a polyethylene glycol modified imidazolium monomer (PtNP@PPh2‐PEGPIILS) more active than its N‐alkylated counterpart (PtNP@PPh2‐N‐decylPIILS). The maximum initial TOF of 169 moleH2.molcat−1.min−1 obtained at 30 °C with a catalyst loading of 0.08 mol% is among the highest to be reported for the aqueous phase hydrolysis of sodium borohydride catalyzed by a PtNP‐based system. Kinetic studies revealed that the apparent activation energy (Ea) of 23.9 kJ mol−1 for the hydrolysis of NaBH4 catalyzed by PtNP@PPh2‐PEGPIILS is significantly lower than that of 35.6 kJ mol−1 for PtNP@PPh2‐N‐decylPIILS. Primary kinetic isotope effects kH/kD of 1.8 and 2.1 obtained with PtNP@PPh2‐PEGPIILS and PtNP@PPh2‐N‐decylPIILS, respectively, for the hydrolysis with D2O support a mechanism involving rate determining oxidative addition or σ‐bond metathesis of the O−H bond. Catalyst stability and reuse studies showed that PtNP@PPh2‐PEGPIILS retained 70 % of its activity across five runs; the gradual drop in conversion appears to be due to poisoning of the catalyst by the accumulated metaborate product as well as the increased viscosity of the reaction mixture. [ABSTRACT FROM AUTHOR]

The Noyori‐Ikariya (arene)Ru(II)/TsDPEN precatalyst has been anchored to amorphous silica and DAVISIL through the η6‐coordinated arene ligand via a straightforward synthesis and the derived systems, (arene)Ru(II)/TsDPEN@silica and (arene)Ru(II)/TsDPEN@DAVISIL, form highly efficient catalysts for the asymmetric transfer hydrogenation of a range of electron‐rich and electron‐poor aromatic ketones, giving good conversion and excellent ee's under mild reaction conditions. Moreover, catalyst generated in situ immediately prior to addition of substrate and hydrogen donor, by reaction of silica‐supported [(arene)RuCl2]2 with (S,S)‐TsDPEN, was as efficient as that generated from its preformed counterpart [(arene)Ru{(S,S)‐TsDPEN}Cl]@silica. Gratifyingly, the initial TOFs (up to 1085 h−1) and ee's (96–97 %) obtained with these catalysts either rivalled or outperformed those previously reported for catalysts supported by either silica or polymer immobilized through one of the nitrogen atoms of TsDPEN. While the high ee's were also maintained during recycle studies, the conversion dropped steadily over the first three runs due to gradual leaching of the ruthenium. [ABSTRACT FROM AUTHOR]

Thereaction between 1,2-C6H4(CH2Cl)2and 2 equiv of in situ generated [R2P(BH3)]Li in THF givesthe corresponding o-phenylene-bridged bis(phosphine–boranes)1,2-C6H4{CH2P(BH3)R2}2(R = iPr (1a),Ph (2a), Cy (3a)). Treatment of 1a–3awith 2 equiv of nBuLi and2 equiv of tmeda yields the corresponding phosphine–borane-stabilizedcarbanion (PBC) complexes [1,2-C6H4{CHP(BH3)R2}2][Li(tmeda)]2·nL (R = iPr, n= 0 (1b); R = Ph, nL = THF (2b);R = Cy, nL = 2PhCH3(3b)).In contrast, treatment of 1awith 2 equiv of MeK, followedby 2 equiv of pmdeta, yields the monodeprotonation product [1,2-C6H4{CHP(BH3)iPr2}{CH2P(BH3)iPr2}][K(pmdeta)] (1c), due to a competing side reactionwith the solvent. Treatment of 1aand 3awith the less aggressive metalating agent PhCH2K givesthe corresponding dipotassium salts, the latter of which was isolatedas the adduct [1,2-C6H4{CHP(BH3)Cy2}2][K(pmdeta)]2(3c). X-raycrystallography reveals that 1b–3badopt similar structures in which the lithium ions are coordinatedby the carbanion centers and the borane hydrogen atoms of the phosphine–borane-stabilizedcarbanions. The potassium ion in 1cis coordinated bythe carbanion center and by B–H···K contactswith both borane groups, whereas the two potassium ions in 3cexhibit multihapto interactions with the aromatic ring of the PBCligand, along with B–H···K contacts. The reactionbetween ClSiMe2CH2CH2SiMe2Cl and 2 equiv of in situ generated [R2P(BH3)CH2]Li gives the bis(phosphine–boranes) [CH2SiMe2CH2P(BH3)R2]2(R = Me (4a), Ph (5a)). Treatmentof 4aor 5awith 2 equiv of nBuLi in THF readily yields the 1,6-dicarbanion complexes [CH2SiMe2CHP(BH3)R2]2[Li(THF)2]2(R = Me (4b), Ph (5b)). A similar reaction of 5a, 2 equiv of PhCH2K, and 2 equiv of pmdeta in THF gives the potassium complex[CH2SiMe2CHP(BH3)Ph2]2[K(pmdeta)]2(5c). Complex 5badopts a linear structure in the solid state, while 5cadopts an unusual polycyclic structure by virtue of bridging K···H–B–H···Kcontacts. [ABSTRACT FROM AUTHOR]

The reaction between the phosphine-borane-stabilised dicarbanion complex [1,2-C6H4{CHP(BH3)Cy2}2][Li(THF)n]2 and Cp2Sn gives the unusual stannyl-stannylene [[1,2-C6H4{CHP(BH3)Cy2}2]Sn]2·1½PhMe, in which one dicarbanion ligand chelates a tin centre, while the other bridges a tin-tin bond. The stannylene centre is stabilised by an agostic-type B-HSn interaction. [ABSTRACT FROM AUTHOR]

• Ultrafine RuNPs are stabilised by amino-modified polymer immobilized ionic liquid. • High activity for hydrolytic evolution of hydrogen from NaBH 4. • Kinetic studies confirm the hydrolysis is first order in catalyst and hydride. • Kinetic isotope studies with H 2 O/D 2 O and NaBH 4 /NaBD 4 support the proposed mechanism. • High activity retained over five reuses with only a minor reduction in conversion. Ruthenium nanoparticles stabilised by polymer immobilized ionic liquids catalyse the hydrolytic release of hydrogen from sodium borohydride. The composition of the polymer influences performance and ruthenium nanoparticles stabilised by an amine-decorated imidazolium-based polymer immobilised ionic liquid (RuNP@NH 2 -PIILS) was the most efficient with a maximum initial turnover frequency (TOF) of 177 mole H2.mol Ru −1.min−1, obtained at 30°C with a catalyst loading of 0.08 mol%; markedly higher than that of 69 mol H2.mol Ru −1.min−1 obtained with 5 wt% Ru/C and one of the highest to be reported for a RuNP catalyst. The apparent activation energy (Ea) of 38.9 kJ mol−1 for the hydrolysis of NaBH 4 catalysed by RuNP@NH 2 -PIILS is lower than that for the other polymer immobilized ionic liquid stabilised RuNPs, which is consistent with its efficacy. Comparison of the initial rates of hydrolysis in H 2 O and D 2 O catalysed by RuNP@NH 2 -PIILS gave a primary kinetic isotope effect (k H / k D) of 2.3 which supports a mechanism involving rate limiting oxidative addition of one of the O-H bonds in a strongly hydrogen-bonded surface-coordinated [BH 3 H−]—-H 2 O ensemble. The involvement of a surface-coordinated borohydride is further supported by an inverse kinetic isotope effect of 0.65 obtained from a comparison of the initial rates for the hydrolysis of NaBH 4 and NaBD 4 under the conditions of catalysis i.e., at a high hydride/catalyst mole ratio. Interestingly though, when the comparison of the initial rates of hydrolysis of NaBH 4 and NaBD 4 was conducted in dilute solution with a hydride/catalyst mole ratio of 1 a kinetic isotope effect (k H / k D) of 2.72 was obtained; this would be more consistent with concerted activation of both an O-H and B-H bond in the rate limiting step, possibly via a concerted oxidative addition-hydride transfer in the surface-coordinated hydrogen-bonded ensemble. Catalyst stability and reuse studies showed that RuNP@NH 2 -PIILS retained 71% of its activity over five runs; the gradual drop in the initial TOF with run number appears to be due to passivation of the catalyst by the sodium borate by-product as well as an increase in viscosity of the reaction mixture rather than leaching of the catalyst. [Display omitted] [ABSTRACT FROM AUTHOR]

Group 1 metal molecular chemistry is dominated by a +1 oxidation state, while a 0 oxidation state is widespread in the metals. A more exotic, yet still available, oxidation state of group 1 metal is -1, i.e., alkalide. Reported as early as the 1970s, the alkalides appear in every modern inorganic chemistry textbook as an iconic chemical curiosity, yet their reactivity remains unexplored. This is due to their synthetic hurdles. In this work, we report the first facile synthesis of the archetypical alkalide complex, [Na + (2,2,2-cryptand)Na - ], which allows us to unveil a versatile reactivity profile of this once exotic species.

Palladium nanoparticles stabilised by aniline modified polymer immobilised ionic liquid is a remarkably active catalyst for the hydrogenation of CO 2 to formate; the initial TOF of 500 h -1 is markedly higher than either unmodified catalyst or its benzylamine and N , N -dimethylaniline modified counterparts and is among the highest to be reported for a PdNP-based catalyst.

Aromatic amides can be used to construct light-harvesting materials with valuable optical properties. The amide bond is formed using well-known coupling agents in near quantitative yield, as illustrated here through the synthesis of two boron dipyrromethene derivatives bearing an amide linkage. The primary concern with acyl amides is rotation around the C-N bond, leading to cis and trans isomers. Using NMR spectroscopy, quantum chemical calculations and critical comparison to simpler benzamides, the stereochemistry of the target compounds has been addressed. The N-cyclohexyl derivative gave diffraction quality crystals that established a trans geometry for the amide bond. Quantum chemical calculations support the trans geometry as being the lowest-energy structure in solution but indicate that inversion of the aryl ring is an important structural feature. Indeed, rotation around the C(sp 2 )-C(aryl) bond has a strong influence on the solution-phase NMR spectra. The amide connection has minimal effect on the photophysical properties., (© 2023 Wiley-VCH GmbH.)

Ditetrelenes R 2 E=ER 2 (E=Si, Ge, Sn, Pb) substituted by multiple N/P/O/S-donor groups are extremely rare due to their propensity to disaggregate into their tetrylene monomers R 2 E. We report the synthesis of the first fully phosphanyl-substituted digermene {(Mes) 2 P} 2 Ge=Ge{P(Mes) 2 } 2 (3, Mes=2,4,6-Me 3 C 6 H 2 ), which adopts a highly unusual structure in the solid state, that is both strongly trans-bent and highly twisted. Variable-temperature 31 P{ 1 H} NMR spectroscopy suggests that 3 persists in solution, but is subject to a dynamic equilibrium between two conformations, which have different geometries about the Ge=Ge bond (twisted/non-twisted) due to a difference in the nature of their π-stacking interactions. Compound 3 undergoes unprecedented, spontaneous decomposition in solution to give a unique Ge I cluster {(Mes) 2 P} 4 Ge 4 ⋅5 CyMe (7)., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Monomeric organolithium (LiR) complexes could provide enhanced Li-C bond reactivity and suggest mechanisms for a plethora of LiR-mediated reactions. They are highly sought-after but remain a synthetic challenge for organometallic chemists. In this work, we report the synthesis and characterisation of a monomeric (trimethylsilyl)methyl lithium complex, namely [Li(CH 2 SiMe 3 )(κ 3 - N , N ', N ''-Me 6 Tren)] (1), where Me 6 Tren is a tetradentate neutral amine ligand. The structure of 1 was comprehensively examined by single-crystal X-ray diffraction, variable temperature NMR spectroscopy and electron absorption spectroscopy. Complex 1 decomposes via ligand C-H and C-N activations to produce a Li amide complex 2. Preliminary reactivity studies of 1 reveal CO insertion and C-H activation reaction patterns.

A small series of boranil complexes has been studied by fluorescence spectroscopy. Weakly fluorescent in most organic solvents at room temperature, the target compounds display bright emission in the crystalline phase. X-ray diffraction patterns obtained for single crystals indicate a distorted tetrahedral geometry around the O-B-N center with the boron atom being displaced from the plane of the heterobicyclic ring. Consideration of the various bond lengths in comparison with those of reference compounds indicates that the ancillary phenyl ring, bearing different para-substituents, does not make a prominent contribution to the molecular dipole moment in the solid state. Absorption and fluorescence spectra recorded for the crystals remain remarkably similar to those for liquid solutions and display large Stokes shifts. Proximity broadening is observed in one case. The nitrophenyl derivative exhibits additional absorption and emission bands unique to the solid state and could be indicative of an intermolecular charge-transfer transition. The optical properties are discussed in terms of the crystal packing diagrams.