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 )2 PPh) Academic Article uri icon

abstract

  • © 2017 American Chemical Society. Reactions of Fe(CO)3(n4-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 (2a-c, 28-70%), which are treated with Grubbs' catalyst (15 mol %; refluxing CH2Cl2). NMR analyses of the crude interligand metathesis products trans-Fe(CO)3(PhP((CH2)mCH=CH(CH2)m)2PPh) (3a-c, 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-Fe(CO)3(PhP((CH2)n)2PPh) (4a-c, 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. Variableerature 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; δG≲273 K ≤ 12.8 kcal/mol), but that in 4a is not (RT to 105 °C; δG≲378 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-Fe(CO)3(P((CH2)n)3P).

author list (cited authors)

  • Steigleder, E., Shima, T., Lang, G. M., Ehnbom, A., Hampel, F., & Gladysz, J. A.

publication date

  • January 1, 2017 11:11 AM