The phenyl-substituted bis(imino)pyridine iron bis(dinitrogen) complex ( iPrPhPDI)Fe(N 2) 2 ( iPrPhPDI = 2,6-(2,6- iPr 2-C 6H 3N=CPh) 2C 5H 3N) 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- iPr 2-C 6H 3N=CMe) 2C 5H 3N; L = CO, n = 2; L = N 2, n = 1, 2), established a more electrophilic iron center for the phenyl-substituted cases. Comparing the productivity of ( iPrPhPDI) Fe(N 2) 2 to ( iPrPDI)Fe(N 2) 2 in the catalytic hydrogenation and hydrosilation of 1-hexene demonstrated higher turnover frequencies for ( iPrPhPDI)Fe(N 2) 2. For more hindered substrates such as cyclohexene and (+)-(R)-limonene, the opposite trend was observed, where the methyl-substituted precursor, ( iPrPDI)Fe(N 2) 2, produced more rapid conversion. The difference in catalytic performance resulted from competitive, irreversible formation of η 6-aryl and -phenyl compounds with the phenyl-substituted complex. Addition of coordinating solvents such as cyclohexene or THF resulted in exclusive formation of the η 6- phenyl derivative. When alkoxide substituents are introduced in the bis(imino)pyridine ligand backbone, the formation of η 6-aryl compounds was exclusive, as alkali metal reduction of ( iPrROPDI) FeBr 2 ( iPrROPDI = 2,6-(2,6- iPr 2-C 6H 3N=C(OR)) 2C 5H 3N, R = Me, Et) yielded only the catalytically inactive η 6-aryl species.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry