title: Unprecedented boron-functionalized carborane derivatives by facile and selective cobalt-induced B-H activation.
abstract: The 16-electron complex CpCoS2C2B10H10 (1) is found to react with the alkynes HC≡CC(O)R [R = methyl (Me), phenyl (Ph), styryl (St), ferrocenyl (Fc)] at ambient temperature to give two types of 17-electron cobalt complexes 2a-d and 3a-d containing unique B(3)/B(6)-norbornyl carborane moieties. A formation mechanism via a tandem sequence of metal-induced B-H activation, B-Cp formation, Cp delivery and Diels-Alder addition is proposed on the basis of DFT calculations. The reactivity of these paramagnetic 17-electron complexes has been studied: Exposed to a combination of air, moisture and silica, complexes 2a-d undergo alkyl C-S cleavage to give 16-electron complexes 4a-c containing a boron-norbornadienyl moiety, and simultaneous carboranyl C-S cleavage to afford cobalt-free carborane derivatives 5a-d containing a boron-norbornyl unit. Both 2a-d and 3a-d allow further alkyne insertion into the Co-S bond to generate cobalt-free boron-norbornyl carborane derivatives (Z/E)-7a-d and (Z/E)-8a-d, both containing a vinyl sulfido group. Addition of AlCl3 not only promotes the conversion of 2a-d, but also leads predominantly to (E)-9a-d as retro-Diels-Alder products. Upon heating, the isomerization from E to Z-configuration of the vinyl group and reorganization of the norbornyl moiety of (Z/E)-7a-d occur to lead to (Z)-9a-d as well as the unexpected [1,2]-H shifted products (Z)-10b,c. Thus, the 17-electron complexes 2a-d and 3a-d serve as intermediates for synthesis of variety of boron-functionalized carborane derivatives. In this study, efficient routes have been developed through cobalt-mediated B-H activation to prepare boron-functionalized carborane derivatives that are unavailable by conventional routes.
authors.affiliation: State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu 210093, China.
authors.forename: Zhaojin
authors.initials: Z
authors.lastname: Wang
authors.forename: Hongde
authors.initials: H
authors.lastname: Ye
authors.forename: Yuguang
authors.initials: Y
authors.lastname: Li
authors.forename: Yizhi
authors.initials: Y
authors.lastname: Li
authors.forename: Hong
authors.initials: H
authors.lastname: Yan
mesh_terms: D000480:Alkynes / Q000737:chemistry; D001895:Boron / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D058116:Lewis Acids / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory
chemical_list: D000480:Alkynes; D058116:Lewis Acids; D003035:Cobalt; D002244:Carbon; D006859:Hydrogen; D001895:Boron