Interaction between dipotassium hexahalogeno-osmates K 2OsX 6 (X = Cl, Br) and olefins: metal hydride formation by allylic hydrogen atom abstraction and catalytic isomerization of olefins

Abstract

Dipotassium hexahalogeno-osmates, K 2OsX 6 (X = Cl, Br) dissolved in non-aqueous inert organic solvents (benzene, o-dichlorobenzene, bromo-benzene) by addition of dicyclohexyl-18-crown-6 ether (C 20H 36O 6) are catalytic precursors for the multiple double bond shift in olefins. Studies on the interaction between K 2OgX 6 and several olefins (1-heptene, 1-heptene-3d 2, 1-pentene, cis-stilbene, 3,3-dimethyl-l-butene) support an osmium hydride species, probably [OsHX 5] =, as the true catalyst, which affords the olefin isomerization through successive 1,2-addition-elimination steps to the CC double bond. Such an alleged osmium hydride species is formed by allylic hydrogen atom abstraction from the olefin with formation of the corresponding conjugate diolefin.