Abstract
The complexes [CpFe{Ph2P(CH2)(n)PPh2}NCMe]-PF6, [CpFe(PPh2Me)(2)NCMe]PF6, and [CpFe{Ph2P(CH2)(n)PPh2}-PPh2(OR)PF6, R = Me, Et, and iPr, with chelate ring sizes between 4 and 7 were synthesized and characterized by spectroscopy and Xray analysis. In these complexes, the monodentate ligands acetonitrile and PPh2(OR) tend to dissociate. The kinetics of the ligand exchanges MeCN/P(OMe)(3) and ...
Abstract
The complexes [CpFe{Ph2P(CH2)(n)PPh2}NCMe]-PF6, [CpFe(PPh2Me)(2)NCMe]PF6, and [CpFe{Ph2P(CH2)(n)PPh2}-PPh2(OR)PF6, R = Me, Et, and iPr, with chelate ring sizes between 4 and 7 were synthesized and characterized by spectroscopy and Xray analysis. In these complexes, the monodentate ligands acetonitrile and PPh2(OR) tend to dissociate. The kinetics of the ligand exchanges MeCN/P(OMe)(3) and PPh2(OR)/P(OMe)(3) was measured. In the acetonitrile series, the first-order reaction of the five-membered chelate complex [CpFe(dppe)NCMe]PF6 had a half-life of 549 min in CDCl3 at 293 K. The other chelate complexes [CpFe(P-P)NCMe]PF6 and the nonchelate analogue [CpFe(PPh2Me)(2)NCMe]PF6 reacted faster by factors of 20-50. The PPh2(OR) series revealed a dramatic difference between the complexes [CpFe(P-P)PPh2(OR)]PF6 with five- and six-membered chelate rings. The PPh2(OR)/P(OMe)(3) exchange in the dppp complex (six-membered chelate ring) was 500 times faster than in the dppe complex (five-membered chelate ring). This is due to the increase of the P-Fe-P angle in the dppp chelate ring, which diminishes the binding pocket of the PPh2(OR) ligand. In the nonchelate complex [CpFe(PPh2Me)(2)NCMe]PF6, a novel and unexpected bimolecular PPh2Me/PPh2(OMe) substitution was observed.
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