Redox and Lewis Acid Reactivity of Unsaturated Os^II

Abstract

Abstract A synthesis of [(PNP)OsI] {PNP = ( t Bu 2 PCH 2 SiMe 2 ) 2 N} permits evaluation of its reactivity, both Lewis acidity and reducing power (i.e., ability to be oxidized). It binds two molecules of PhCN, into trans sites, but only one of ethylene, and, upon binding of one N 2 , there is heterolytic splitting of one t Bu C–H bond to put the proton on amide N and the carbon on Os, leaving divalent metal in [{PN(H)P*}Os(N 2 )( I )]. Two moles of H 2 add, forming [{PN(H)P}OsH(H 2 )I], via H–H bond heterolysis. Thermolysis of [(PNP)OsI] gives the product of adding a t Bu methyl C–H bond across the Os/N bond, and also net dehydrogenation of this intermediate, forming a carbene complex; the released H 2 forms [(PNP)OsH 2 I], and the chemistry of [(PNP)Os] hydridohalides is described. Reaction with O 2 occurs with no detectable intermediate, to completely split the O=O bond, and form trans ‐[(PNP)Os(O) 2 I], a product of four electron redox change. Attempted two electron oxidation by oxygen atom transfer with pyridine N ‐oxide or Me 3 NO or N 2 O surprisingly effect transposition of N from its silyl substituents onto the metal, and replace N by O, forming a nitride complex of a bis(silyl ether, phosphane) chelate whose oxygen fails to bind to Os. The product is thus four‐coordinate, tetrahedral [(POP)Os(N)I], with an Os/N triple bond.