Arene Coordination in Bis(imino)pyridine Iron Complexes: Identification of Catalyst Deactivation Pathways in Iron-Catalyzed Hydrogenation and Hydrosilation

Abstract

The phenyl-substituted bis(imino)pyridine iron bis(dinitrogen) complex (iPrPhPDI)Fe(N2)2 (iPrPhPDI = 2,6-(2,6-iPr2-C6H3NCPh)2C5H3N) was prepared by sodium amalgam reduction of the corresponding ferrous dichloride precursor under 4 atm of dinitrogen. Comparison of the infrared stretching frequencies of the bis(dinitrogen), mono(dinitrogen), and related dicarbonyl derivatives to those of the corresponding bis(imino)pyridine iron compounds bearing the methyl-substituted ligand, (iPrPDI)Fe(L)n (iPrPDI = 2,6-(2,6-iPr2-C6H3NCMe)2C5H3N; L = CO, n = 2; L = N2, n = 1, 2), established a more electrophilic iron center for the phenyl-substituted cases. Comparing the productivity of (iPrPhPDI)Fe(N2)2 to (iPrPDI)Fe(N2)2 in the catalytic hydrogenation and hydrosilation of 1-hexene demonstrated higher turnover frequencies for (iPrPhPDI)Fe(N2)2. For more hindered substrates such as cyclohexene and (+)-(R)-limonene, the opposite trend was observed, where the methyl-substituted precursor, (iPrPDI)Fe(N2)2, produced more rapi...