Synthesis and reduction chemistry of mixed-Lewis-base-stabilised chloroborylenes.


Institut für Anorganische Chemie , The Institute for Sustainable Chemistry & Catalysis with Boron , Julius-Maximilians-Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . Email: [Email]


The one-electron reduction of (CAACMe)BCl3 (CAACMe = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) yields the dichloroboryl radical [(CAACMe)BCl2]˙. Furthermore, the twofold reduction of (CAACMe)BCl3 in the presence of a range of Lewis bases (L = CAACMe, N-heterocyclic carbene, phosphine) yields a series of doubly base-supported (CAACMe)LBCl chloroborylenes, all of which were structurally characterised. NMR and UV-vis spectroscopic and electrochemical data for (CAACMe)LBCl show that the boron centre becomes more electron-rich and the HOMO-LUMO gap widens as L becomes less π-accepting. A [(CAACMe)BCl2]- boryl anion coordination polymer was isolated as a potential intermediate in these reductions. In most cases the reduction of the chloroborylenes resulted in the formation of the corresponding hydroborylenes or derivatives thereof, as well as ligand C-H activation products.

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