Coordination of tetradentate X2N2 (X = P, S, O) ligands to iron(II) metal center and catalytic application in the transfer hydrogenation of ketones.
A series of mixed tetradentate ligands associating two iminophosphorane moieties with two phosphino, thiophosphino, or phosphine oxide groups (labelled 2, 3, and 4 respectively) have been prepared from the corresponding aminophosphonium derivatives. Their coordination to the iron dichloride metal fragment was achieved using the [FeCl(2)(THF)(1.5)] precursor leading to [(P(2)N(2))FeCl(2)] (5), [(S(2)N(2))FeCl(2)] (6), and [(O(2)N(2))FeCl(2)] (7). These complexes were shown to be paramagnetic. Moreover, those ligands can act as bi, tri or tetradentate, as evidenced by X-ray structure analysis of the complexes, depending on the nature of the pendant PY coordinating ligand (Y = lone pair, S, O). Indeed, while only one phosphorus atom is coordinated to iron in 5 (PNN coordination), no thiophosphine moiety is connected to Fe in 6 (NN coordination), whereas both phosphine oxide arms are linked to the metal in 7 (ONNO) coordination. For ligand 2, coordination reactions were also performed with a non-chlorinated iron precursor (either [Fe(CH(3)CN)(6)](BF(4))(2) or [Fe(H(2)O)(6)](BF(4))(2)) leading to complexes 8 and 9 depending on the reaction conditions. The different iron(II) complexes 5-9 were tested in catalytic transfer hydrogenation of acetophenone, and were found to be efficient for reactions carried out at 82 degrees C.
Laboratoire Hétéroéléments et Coordination, Ecole Polytechnique, CNRS, Route de Saclay, 91128, Palaiseau, France.
Antoine
A
Buchard
Hadrien
H
Heuclin
Audrey
A
Auffrant
Xavier F
XF
Le Goff
Pascal
P
Le Floch