In this work, a rare monomeric organolithium complex was reported, stabilised by a neutral tetradentate amine ligand. Its structure and decomposition/reactivity were studied.

Organosodium chemistry is underdeveloped compared with organolithium chemistry, and all the reported organosodium complexes exhibit similar, if not identical, reactivity patterns to their lithium counterparts. Herein, we report a rare organosodium monomeric complex, namely, [Na(CH 2 SiMe 3 )(Me 6 Tren)] (1-Na) (Me 6 Tren: tris[2-(dimethylamino)ethyl]amine) stabilized by a tetra-dentate neutral amine ligand Me 6 Tren. Employing organo-carbonyl substrates (ketones, aldehydes, amides, ester), we demonstrated that 1-Na features distinct reactivity patterns compared with its lithium counterpart, [Li(CH 2 SiMe 3 )(Me 6 Tren)] (1-Li). Based on this knowledge, we further developed a ligand-catalysis strategy to conduct ketone/aldehyde methylenations, using [NaCH 2 SiMe 3 ] ∞ as the CH 2 feedstock, replacing the widely used but hazardous/expensive C�O methylenation methods, such as Wittig, Tebbe, Julia/Julia-Kocienśki, Peterson, and so on.

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-H···Sn interaction.

This work comprehensively investigated the coordination chemistry of a hexa -dentate neutral amine ligand, namely, N,N′,N” - tris -(2- N -diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN), with group-1 metal cations (Li + , Na + , K + , Rb + , Cs + ). Versatile coordination modes were observed, from four-coordinate trigonal pyramidal to six-coordinate trigonal prismatic, depending on the metal ionic radii and metal’s substituent. For comparison, the coordination chemistry of a tetra -dentate tris -[2-(dimethylamino)ethyl]amine (Me 6 Tren) ligand was also studied. This work defines the available coordination modes of two multidentate amine ligands (DETAN and Me 6 Tren), guiding future applications of these ligands for pursuing highly reactive and elusive s-block and rare-earth metal complexes.

Platinum nanoparticles stabilized by imidazolium-based phosphine-decorated Polymer Immobilized Ionic Liquids (PPh 2 -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@PPh 2 -PEGPIILS) more active than its N-alkylated counterpart (PtNP@PPh 2 -N-decylPIILS). The maximum initial TOF of 169 moleH 2 .molcat À 1 .min À 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 (E a ) of 23.9 kJ mol À 1 for the hydrolysis of NaBH 4 catalyzed by PtNP@PPh 2 -PEGPIILS is significantly lower than that of 35.6 kJ mol À 1 for PtNP@PPh 2 -N-decylPIILS. Primary kinetic isotope effects k H /k D of 1.8 and 2.1 obtained with PtNP@PPh 2 -PEGPIILS and PtNP@PPh 2 -N-decylPIILS, respectively, for the hydrolysis with D 2 O support a mechanism involving rate determining oxidative addition or σ-bond metathesis of the OÀ H bond. Catalyst stability and reuse studies showed that PtNP@PPh 2 -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.

The reaction between 1,2-C6H4(CH2Cl)2 and 2 equiv of in situ generated [R2P(BH3)]Li in THF gives the corresponding o-phenylene-bridged bis(phosphine–boranes) 1,2-C6H4{CH2P(BH3)R2}2 (R = iPr (1a), Ph (2a), Cy (3a)). Treatment of 1a–3a with 2 equiv of nBuLi and 2 equiv of tmeda yields the corresponding phosphine–borane-stabilized carbanion (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 1a with 2 equiv of MeK, followed by 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 reaction with the solvent. Treatment of 1a and 3a with the less aggressive metalating agent PhCH2K gives the corresponding dipotassium salts, the latter of which was isolated as the adduct [1,2-C6H4{CHP(BH3)Cy2}2][K(pmdeta)]2 (3c). X-ray crystallography reveals that 1b–3b adopt similar structures in which the lithium ions are coordinated by the carbanion centers and the borane hydrogen atoms of the phosphine–borane-stabilized carbanions. The potassium ion in 1c is coordinated by the carbanion center and by B–H···K contacts with both borane groups, whereas the two potassium ions in 3c exhibit multihapto interactions with the aromatic ring of the PBC ligand, along with B–H···K contacts. The reaction between 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)). Treatment of 4a or 5a with 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 5b adopts a linear structure in the solid state, while 5c adopts an unusual polycyclic structure by virtue of bridging K···H–B–H···K contacts.

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.

Multidentate neutral amine ligands play vital roles in coordination chemistry and catalysis. In particular, these ligands are used to tune the reactivity of Group-1 metal reagents, such as organolithium reagents. Most, if not all, of these Group-1 metal reagent-mediated reactions occur in solution. However, the solution-state coordination behaviors of these ligands with Group-1 metal cations are poorly understood, compared to the plethora of solid-state structural studies based on single-crystal X-ray diffraction (SCXRD) studies. In this work, we comprehensively mapped out the coordination modes with Group-1 metal cations for three multidentate neutral amine ligands: tridentate 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 TACN), tetradentate tris[2-(dimethylamino)ethyl]amine (Me 6 Tren), and hexadentate N,N′,N″-tris-(2-N-diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN). The macrocycles in the Me 3 TACN and DETAN are identified as the rigid structural directing motif, with the sidearms of DETAN providing flexible “on-demand” coordination sites. In comparison, the Me 6 Tren ligand features more robust coordination, with the sidearms less likely to undergo the decoordinating–coordinating equilibrium. This work will provide a guidance for coordination chemists in applying these three ligands, in particular, the new DETAN ligand to design metal complexes which suit their purposes.