3 years ago

Partially Shielded Fe(CO)3 Rotors: Syntheses, Structures, and Dynamic Properties of Complexes with Doubly trans Spanning Diphosphines, trans-Fe(CO)3(PhP((CH2)n)2PPh)

Partially Shielded Fe(CO)3 Rotors: Syntheses, Structures, and Dynamic Properties of Complexes with Doubly trans Spanning Diphosphines, trans-Fe(CO)3(PhP((CH2)n)2PPh)
Georgette M. Lang, Esther Steigleder, Frank Hampel, John A. Gladysz, Takanori Shima, Andreas Ehnbom
Reactions of Fe(CO)34-benzylideneacetone) and PhP((CH2)mCH═CH2)2 (m = a, 4; b, 5; c, 6) give trans-Fe(CO)3(PhP((CH2)mCH═CH2)2)2 (2ac, 28–70%), which are treated with Grubbs’ catalyst (15 mol %; refluxing CH2Cl2). NMR analyses of the crude interligand metathesis products trans-tiebar above startFe(CO)3(PhP((CH2)mCH═CH(CH2)m)2tiebar above endPPh) (3ac, 30–31%) suggest Z/E C═C mixtures and/or byproducts from intraligand metathesis or oligomers. Subsequent hydrogenations (5 bar/cat. Rh(Cl)(PPh3)3 or PtO2) afford trans-tiebar above startFe(CO)3(PhP((CH2)n)2tiebar above endPPh) (4ac, 69–77%; n = 2m + 2, synperiplanar phenyl groups), which density functional theory calculations show to be more stable than isomers derived from other metathesis modes. Crystallizations give (E,E)-3a and 4b, the X-ray structures of which are determined and analyzed. Variable-temperature 13C{1H} NMR experiments show that rotation of the Fe(CO)3 moiety in 4b is rapid on the NMR time scale (RT to 0 °C; ΔG273 K ≤ 12.8 kcal/mol), but that in 4a is not (RT to 105 °C; ΔG378 K ≥ 17.9 kcal/mol). These data indicate rotational barriers lower than those in analogues in which three methylene chains connect the phosphorus atoms, trans-tiebar above startFe(CO)3(P((CH2)n)3tiebar above endP).

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00330

DOI: 10.1021/acs.organomet.7b00330

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