Synthesis and characterisation of a range of Fe, Co, Ru and Rh triphos complexes and investigations into the catalytic hydrogenation of levulinic acid

The coordination chemistry of the N-triphos ligand (NP3Ph, 1b) has been investigated with a range of Fe, Co and Rh precursors and found to form either tridentate or bidentate complexes. Reaction of NP3Ph with [Rh(COD)(CH3CN)(2)]BF4 resulted in the formation of the tridentate complex [Rh(COD)(kappa(3)-NP3Ph)]BF4 (3) in the solid state, however, in solution a bidentate complex predominates in more polar solvents. Reaction of NP3Ph with Fe carbonyl precursors revealed the formation of the bidentate complexes [Fe(CO)(3)(kappa(1), kappa(2)-NP3Ph)Fe(CO)(4)] (4) and [Fe(CO)(3)(kappa(2)-NP3Ph)] (5), while reaction with FeBr2 resulted in the paramagnetic bidentate complex [Fe(Br)(2)(kappa(2)-NP3Ph)] (6). Reaction of NP3Ph with CoCl2 gave a dimeric Co species [(kappa(2)-NP3Ph)CoCl(kappa(1), kappa(2)-NP3Ph)CoCl3] (7), while Zn powder reduction of NP3Ph Co halides resulted in the formation of the tridentate complexes of the type: [Co(X)(kappa(3)-NP3Ph)]. The related triphos Ru complex, [Ru(CO3)(CO)(kappa(3)-NP3Ph)] (2), has also been isolated and characterised. Preliminary catalytic hydrogenation of levulinic acid (LA) was conducted with 2 and 3. The Ru complex was found to be catalytically active, giving high conversions of LA to form gamma-vvvalerolactone (GVL) and 1,4-pentanediol (1,4-PDO), while 3 was found to be catalytically inactive. In situ catalytic testing with lb and Fe(BF4)(2)center dot 6H(2)O resulted in low conversions of LA while a combination of lb and Co(BF4)(2)center dot 6H(2)O gave high conversions to GVL. (C) 2020 Elsevier B.V. All rights reserved.