Enhanced Reactivity of 2-Rhodaoxetanes through a Labile Acetonitrile Ligand

Abstract

New cationic, square-planar, ethene complexes [(Rbpa)RhI(C2H4)]+ [2 a]+–[2 c]+ (Rbpa= N-alkyl-N,N-di(2-pyridylmethyl)amine; [2 a]+: alkyl=R=Me; [2 b]+: R= Bu; [2 c]+: R= Bz) have been selectively oxygenated in acetonitrile by aqueous hydrogen peroxide to 2-rhoda(III)oxetanes with a labile acetonitrile ligand, [(Rbpa)RhIII(κ2-C,O-CH2CH2O−)(MeCN)]+, [3 a]+–[3 c]+. The rate of elimination of acetaldehyde from [(Rbpa)RhIII(κ2-C,O-CH2CH2O−)(MeCN)]+ increases in the order R=Me<R=Bu<R=Bz. Elimination of acetaldehyde from [(Bzbpa)RhIII(κ2-C,O-CH2CH2O)(MeCN)]+ [3 c]+, in the presence of ethene results in regeneration of ethene complex [(Bzbpa)RhI(C2H4)]+ [2 c]+, and closes a catalytic cycle. In the presence of Z,Z-1,5-cyclooctadiene (cod) the corresponding cod complex [(Bzbpa)RhI(cod)]+ [6c]+ is formed. Further oxidation of [3 c]+ by H2O2 results in the transient formylmethyl-hydroxy complex [(Bzbpa)RhIII(OH){κ1-C-CH2C(O)H}]+ [5 c]+.