Cobalt-promoted B–H and C–H activation in the three-component reactions of 16-electron cobalt carboranedithiolate, alkyne and bronsted acids

Abstract

The three-component reactions of Cp#Co(S2C2B10H10) (Cp# = Cp, 1a; MeCp, 1b; Me4Cp, 1c; Me5Cp, 1d), methyl propiolate (2) and Bronsted acid organic ligands (L1–L8) are reported. Only can 1a and 1b lead to selective B-functionalization at carborane with cyclopentadienyl or methyl-cyclopentadienyl as a functional group at ambient temperature in good yields. Four types of products containing a coupled B–C bond are obtained dependent on the type of the used Bronsted acids (L1–L8). If stronger coordinating ligands L1–L3 are chosen compounds 3a(L1–L3) and 3b(L1–L3) are isolated where L1–L3 loses one proton to provide 3 electrons to metal and alkyne is reduced to olefin. If L4 and L5 are used, products 4a or 4b are generated where the Bronsted acid is not observed but the alkyne is reduced to sp3 and forms a five-membered ring with Co center. Allenes (L6 and L7) lead to 5a(L6) and 5a(L7) where an allyl unit is coordinated to metal. In case of CpH (L8), compounds 6a and 6b are produced which contains an in-situ generated unusual carborane-functionalized dithiolate ligand from 4 + 2 cycloaddition of alkyne and the added cyclopentadiene. All products were fully characterized by spectroscopic techniques and elemental analysis. All products were fully characterized and some typical solid-state structures were further determined by X-ray crystallographic analysis. The co-promoted mechanisms by metal and Bronsted acids to lead both B–H and C–H activation are proposed on the basis of deuterium labeling as well as NMR, MS, GC monitoring experiments.