24692-24-8Relevant academic research and scientific papers
Orthogonal Nanoparticle Catalysis with Organogermanes
Fricke, Christoph,Sherborne, Grant J.,Funes-Ardoiz, Ignacio,Senol, Erdem,Guven, Sinem,Schoenebeck, Franziska
supporting information, p. 17788 - 17795 (2019/11/13)
Although nanoparticles are widely used as catalysts, little is known about their potential ability to trigger privileged transformations as compared to homogeneous molecular or bulk heterogeneous catalysts. We herein demonstrate (and rationalize) that nanoparticles display orthogonal reactivity to molecular catalysts in the cross-coupling of aryl halides with aryl germanes. While the aryl germanes are unreactive in LnPd0/LnPdII catalysis and allow selective functionalization of established coupling partners in their presence, they display superior reactivity under Pd nanoparticle conditions, outcompeting established coupling partners (such as ArBPin and ArBMIDA) and allowing air-tolerant, base-free, and orthogonal access to valuable and challenging biaryl motifs. As opposed to the notoriously unstable polyfluoroaryl- and 2-pyridylboronic acids, the corresponding germanes are highly stable and readily coupled. Our mechanistic and computational studies provide unambiguous support of nanoparticle catalysis and suggest that owing to the electron richness of aryl germanes, they preferentially react by electrophilic aromatic substitution, and in turn are preferentially activated by the more electrophilic nanoparticles.
Kinetic and mechanistic studies of the transformation of the catalyst, tris(pentafluorophenyl)borane, in the presence of silyl and germyl hydrides
Rubinsztajn, Slawomir,Chojnowski, Julian,Cypryk, Marek,Mizerska, Urszula,Fortuniak, Witold,Bak-Sypien, Irena I.
, p. 90 - 99 (2019/10/09)
Tris(pentafluorophenyl)borane catalyzed Si-H bond activation opens the door to numerous transition-metal-free reduction processes and is widely used in organic and polymer chemistry. However, chemical stability of B(C6F5)3 in the presence of silyl hydrides is limited, which can strongly affect its catalytic activity. Transformations of B(C6F5)3 in the presence of phenyldimethylsilane, triethylsilane and triethylgermane were studied by 19F NMR and UV spectroscopy, GC/MS and quantum-mechanical calculations. The observed exchange of pentafluorophenyl group attached to boron to hydrogen results in the formation of bis(pentafluorophenyl)borane, which has a strongly reduced ability to activate the Si-H bond. The substitution kinetics were studied by following the disappearance of absorption of the B(C6F5)3 charge transfer peak in the UV spectrum. Complementary quantum mechanical calculations allowed us to propose a mechanism of the ligand exchange reaction, which involves electrophilic substitution of the pentafluorophenyl group through a four-center transition state.
