A Reversible Phase Transition of 2D Coordination Layers by B–H∙∙∙Cu(II) Interactions in a Coordination Polymer

Materials that combine flexibility and open metal sites are crucial for myriad applications. In this article, we report a 2D coordination polymer (CP) assembled from CuII ions and a flexible meta-carborane-based linker [Cu2(L1)2(Solv)2]•xSolv (1-DMA, 1-DMF, and 1-MeOH; L1: 1,7-di(4-carboxyphenyl)-1,7-dicarba-closo-dodecaborane). 1-DMF undergoes an unusual example of reversible phase transition on solvent treatment (i.e., MeOH and CH2Cl2). Solvent exchange, followed by thermal activation provided a new porous phase that exhibits an estimated Brunauer-Emmett-Teller (BET) surface area of 301 m2 g−1 and is capable of a CO2 uptake of 41 cm3 g−1. The transformation is reversible and 1-DMF is reformed on addition of DMF to the porous phase. We provide evidence for the reversible process being the result of the formation/cleavage of weak but attractive B–H∙∙∙Cu interactions by a combination of single-crystal (SCXRD), powder (PXRD) X-ray diffraction, Raman spectroscopy, and DFT calculations.This research was funded by MEC grant CTQ2016-75150-R and the Generalitat de Catalunya (2017/SGR/1720) and the Spanish MINECO through the Severo Ochoa Centers of Excellence Program, under Grant SEV-2015-0496

Counteranion-Dependent Reaction Pathways in the Protonation of Cationic Ruthenium−Vinylidene Complexes

The tetraphenylborate salts of the cationic vinylidene complexes [Cp*Ru=C=CHR(iPr2PNHPy)]+ (R = p-C6H4CF3 (1a-BPh4), Ph (1b-BPh4), p-C6H4CH3 (1c- BPh4), p-C6H4Br (1d-BPh4), tBu (1e-BPh4), H (1f-BPh4)) have been protonated using an excess of HBF4·OEt2 in CD2Cl2, furnishing the dicationic carbyne complexes [Cp*Ru≡CCH2R(iPr2PNHPy)]2+ (R = p-C6H4CF3 (2a), Ph (2b), p-C6H4CH3 (2c), p-C6H4Br (2d), tBu (2e), H (2f)), which were characterized in solution at low temperature by NMR spectroscopy. The corresponding reaction of the chloride salts 1a-Cl, 1b-Cl, 1c-Cl, and 1d-Cl followed a different pathway, instead affording the novel alkene complexes [Cp*RuCl(κ1(N),η2(C,C)-C5H4N-NHPiPr2CH=CHR)][BF4] (3a−d). In these species, the entering proton is located at the α- carbon atom of the former vinylidene ligand, which also forms a P−C bond with the phosphorus atom of the iPr2PNHPy ligand. To shed light on the reaction mechanism, DFT calculations have been performed by considering several protonation sites. The computational results suggest metal protonation followed by insertion. The coordination of chloride to ruthenium leads to alkenyl species which can undergo a P−C coupling to yield the corresponding alkene complexes. The noncoordinating nature of [BPh4]− does not allow the stabilization of the unsaturated species coming from the insertion step, thus preventing this alternative pathway

Counteranion and Solvent Assistance in Ruthenium-Mediated Alkyne to Vinylidene Isomerizations

The complex [Cp*RuCl(iPr2PNHPy)] (1) reacts with 1-alkynes HC≡CR (R = COOMe, C6H4CF3) in dichloromethane furnishing the corresponding vinylidene complexes [Cp*Ru≡C≡CHR(iPr2PNHPy)]Cl (R = COOMe (2a- Cl), C6H4CF3 (2b-Cl)), whereas reaction of 1 with NaBPh4 in MeOH followed by addition of HC≡CR (R = COOMe, C6H4CF3) yields the metastable π-alkyne complexes [Cp*Ru(η2-HC≡CR)(iPr2PNHPy)][BPh4] (R = COOMe (3a-BPh4), C6H4CF3 (3b-BPh4)). The transformation of 3a-BPh4/3b-BPh4 into their respective vinylidene isomers in dichloromethane is very slow and requires hours to its completion. However, this process is accelerated by addition of LiCl in methanol solution. Reaction of 1 with HC≡CR (R = COOMe, C6H4CF3) in MeOH goes through the intermediacy of the π-alkyne complexes [Cp*Ru(η2-HC≡CR)(iPr2PNHPy)]Cl (R = COOMe (3a-Cl), C6H4CF3 (3b-Cl)), which rearrange to vinylidenes in minutes, i.e., much faster than their counterparts containing the [BPh4]− anion. The kinetics of these isomerizations has been studied in solution by NMR. With the help of DFT studies, these observations have been interpreted in terms of chloride- and methanolassisted hydrogen migrations. Calculations suggest participation of a hydrido−alkynyl intermediate in the process, in which the hydrogen atom can be transferred from the metal to the β-carbon by means of species with weak basic character acting as proton shuttles

Computational characterization of the role of the base in the Suzuki-Miyaura cross-coupling reaction

The role of the base in the transmetalation step of the Suzuki-Miyaura cross-coupling reaction is analyzed computationally by means of DFT calculations with the Becke3LYP functional. The model system studied consists of Pd(CH=CH(2))(PH(3))(2)Br as the starting catalyst complex, CH(2)=CHB(OH)(2) as the organoboronic acid, and OH(-) as the base. The two main mechanistic proposals, consisting of the base attacking first either the palladium complex or the organoboronic acid, are evaluated through geometry optimization of the corresponding intermediates and transition states. Supplementary calculations are carried out on the uncatalyzed reaction and on a process where the starting complex is Pd(CH=CH(2))(PH(3))(2)(OH). These calculations, considered together with available experimental data, strongly suggest that the main mechanism of transmetalation in the catalytic cycle starts with the reaction of the base and the organoboronic acid.127259298930

Computational study of the transmetalation process in the Suzuki-Miyaura cross-coupling of aryls

The transmetalation step of the Suzuki-Miyaura cross-coupling between aryl groups is analyzed by means of DFT calculations with the Becke3LYP functional. The halide considered is Ph-Br, and the organoboronic acid is Ph-B(OH)(2). The model catalyst is Pd(PH(3))(2), and the base, OH(-). The transmetalation is considered to start from the Pd(Ph)(PH(3))(2)Br complex, the product of the oxidative addition. The results are compared with those of a previous study on the analogous reaction with vinyl groups, and it is shown that the reaction mechanism is very similar. (c) 2006 Elsevier B.V. All rights reserved.69121SI4459446

Mechanism of formation of silver N-heterocyclic carbenes using silver oxide: A theoretical study

The reasons for the efficiency of the silver oxide route in the synthesis of Ag(I) N-heterocyclic carbene complexes have been investigated by means of DFT calculations. A general reaction system that incorporates two N,N-dimethyl imidazolium cations, two iodides as the counterions, Ag2O, and dichloromethane solvent was considered. Exploration of several pathways for the formation of the two silver−NHC cations gives a clear picture for the reaction mechanism. The favored route involves a barrierless and very exergonic deprotonation of the first imidazolium followed by a low barrier and also exergonic metalation, affording the first silver−NHC. The second imidazolium assists these two steps stabilizing intermediates and the transition state by the formation of a strong Cimidazolium−H···OAg hydrogen bond. The formed [R2NHC]−AgI then diffuses in the solution, while silver hydroxide deprotonates the second imidazolium salt in a slightly endergonic process. After metalation, the second silver−NHC is obtained. The overall reaction is thermodynamically driven, the conversion of two imidazolium salts to two silver carbenes entailing a system stabilization of more than 70 kcal mol-1. As the acid−base reaction between the imidazolium salt and the silver base plays a key role in the process, pKa calculations were performed to compare the basicity of the N-heterocyclic carbene with those of the silver bases Ag2O, AgOH, and AgOAc. From the pKa values obtained, the advantage of silver oxide in the generation of silver carbenes is attributed to its stronger basicity

A reversible phase transition of 2D coordination layers by B-H···Cu(II) interactions in a coordination polymer

Materials that combine flexibility and open metal sites are crucial for myriad applications. In this article, we report a 2D coordination polymer (CP) assembled from CuII ions and a flexible meta-carborane-based linker [Cu(L1)(Solv)]•xSolv (1-DMA, 1-DMF, and 1-MeOH; L1: 1,7-di(4-carboxyphenyl)-1,7-dicarba-closo-dodecaborane). 1-DMF undergoes an unusual example of reversible phase transition on solvent treatment (i.e., MeOH and CHCl). Solvent exchange, followed by thermal activation provided a new porous phase that exhibits an estimated Brunauer-Emmett-Teller (BET) surface area of 301 m g and is capable of a CO uptake of 41 cm g. The transformation is reversible and 1-DMF is reformed on addition of DMF to the porous phase. We provide evidence for the reversible process being the result of the formation/cleavage of weak but attractive B-H···Cu interactions by a combination of single-crystal (SCXRD), powder (PXRD) X-ray diffraction, Raman spectroscopy, and DFT calculations