2049-55-0Relevant articles and documents
Heterogeneous or homogeneous catalysis? Mechanistic studies of the rhodium-catalyzed dehydrocoupling of amine-borane and phosphine-borane adducts
Jaska, Cory A.,Manners, Ian
, p. 9776 - 9785 (2004)
In depth, comparative studies on the catalytic dehydrocoupling of the amine-borane adduct Me2NH-BH3 (to form [Me 2N-BH2]2) and the phosphine-borane adduct Ph2PH·BH3 (to form Ph2PH-BH 2-PPh2-BH3) with a variety of Rh (pre)catalysts such as [{Rh(1,5-cod)(μ-Cl)}2], Rh/Al2O3, Rhcolloid/[Oc4N]Cl, and [Rh(1,5-cOd)2]OTf have been performed in order to determine whether the dehydrocoupling proceeds by a homogeneous or heterogeneous mechanism. The results obtained suggest that the catalytic dehydrocoupling of Me2NH·BH3 is heterogeneous in nature involving Rh(0) colloids, while that of Ph 2PH·BH3 proceeds by a homogeneous mechanism even when starting with Rh(0) precursors such as Rh/Al2O3. The catalytic dehydrocoupling reactions are thought to proceed by different mechanisms due to a combination of factors such as (i) the greater reducing strength of amine-borane adducts, (ii) the increased ease of dissociation of phosphine-borane adducts, and (iii) phosphine ligation and/or poisoning of active catalytic sites on metal colloids.
Solubility-Driven Isolation of a Metastable Nonagold Cluster with Body-Centered Cubic Structure
Shen, Hui,Selenius, Elli,Ruan, Pengpeng,Li, Xihua,Yuan, Peng,Lopez-Estrada, Omar,Malola, Sami,Lin, Shuichao,Teo, Boon K.,H?kkinen, Hannu,Zheng, Nanfeng
, p. 8465 - 8470 (2020)
The conventional synthetic methodology for atomically precise gold nanoclusters by using reduction in solution offers only the thermodynamically most stable nanoclusters. Herein, a solubility-driven isolation strategy is reported to access a metastable gold cluster. The cluster, with the composition of [Au9(PPh3)8]+ (1), displays an unusual, nearly perfect body-centered cubic (bcc) structure. As revealed by ESI-MS and UV/Vis measurements, the cluster is metastable in solution and converts to the well-known [Au11(PPh3)8Cl2]+ (2) within just 90 min. DFT calculations revealed that although both 1 and 2 are eight-electron superatoms, there is a driving force to convert 1 to 2 as shown by the increased cohesion and larger HOMO–LUMO energy gap of 2. The isolation and crystallization of the metastable gold cluster were achieved in a biphasic reaction system in which reduction of gold precursors and crystallization of 1 took place concurrently. This synthetic protocol represents a successful strategy for investigations of other metastable species in metal nanocluster chemistry.
Coordination Chemistry of Borane in Solution: Application to a STING Agonist
Lemaire, Sébastien,Zhdanko, Alexander,van der Worp, Boris A.
, (2022/04/09)
Equilibrium constants were determined for ligand exchange reactions of borane complexes with various oxygen, sulfur, nitrogen, and phosphorus nucleophiles in solution, and a binding affinity scale was built spanning a range of 12 orders of magnitude. While the Keq are minimally dependent on the solvent, the rate of ligand exchange varies significantly. The fastest and slowest rates were observed in THF and CDCl3, respectively. Moreover, the ligand exchange rate differs in a very broad range depending on stability of the starting complex. Binding of BH3 was found to be much more sensitive to steric factors than protonation. Comparing nitrogen bases having equal steric properties, a linear correlation of BH3 binding affinity vs. Br?nsted acidity was found. This correlation can be used to quickly estimate the BH3 binding affinity of a substrate if pKa is known. Kinetic studies suggest the ligand exchange to occur as a bimolecular SN2 reaction unless other nucleophilic species were present in the reaction mixture.
Activation of sodium borohydride via carbonyl reduction for the synthesis of amine- And phosphine-boranes
Hamann, Henry J.,Lin, Randy,Veeraraghavan Ramachandran, P.
supporting information, p. 16770 - 16774 (2021/12/08)
A highly versatile synthesis of amine-boranes via carbonyl reduction by sodium borohydride is described. Unlike the prior bicarbonate-mediated protocol, which proceeds via a salt metathesis reaction, the carbon dioxide-mediated synthesis proceeds via reduction to a monoformatoborohydride intermediate. This has been verified by spectroscopic analysis, and by using aldehydes and ketones as the carbonyl source for the activation of sodium borohydride. This process has been used to produce borane complexes with 1°-, 2°-, and 3°-amines, including those with borane reactive functionalities, heteroarylamines, and a series of phosphines.
Synthesis of Allylboranes via Cu(I)-Catalyzed B-H Insertion of Vinyldiazoacetates into Phosphine-Borane Adducts
Drikermann, Denis,M??el, Robert S.,Al-Jammal, Walid K.,Vilotijevic, Ivan
supporting information, p. 1091 - 1095 (2020/02/15)
Cu(I) catalysts enable C-B bond formation via direct insertion of vinyldiazoacetates into B-H bonds of borane-phosphine Lewis adducts to form phosphine-protected allylboranes under mild conditions. The resulting allylborane-phosphine Lewis adducts can be used in the diastereoselective allylation of aldehydes directly without the need for removal of the phosphine. The allylation reaction proceeds with high diastereoselectivity and yields 5,6-disubstituted dihydropyranones after treatment with an appropriate acid.
