The Reduction of [Fe(CO)₂L₂X₂] (L = P(OMe)₃, P(O<i>i</i>Pr)₃, PEt₃; X = Br, I)—From Iron(<scp>II</scp>) to Iron(0) via Stable Iron(<scp>I</scp>) Intermediates

Abstract

Abstract The reduction of [Fe(CO) 2 ‐L 2 X 2 ] (L = P(OMe) 3 X = Br ( 1a ), I ( 1b ); L = P(O i Pr) 3 , X = Br ( 2a ), I ( 2b ); L = PEt 3 , X = Br ( 3a ), I ( 3b )) with Zn in dioxane ( 1a,b ‐ 2a,b ) or PhLi in ether ( 3a,b ) led to formation of the corresponding dicarbonyl(halo)bis(phosphorus donor)iron(I) complexes (L = P(OMe) 3 , X = Br ( 4a ), I ( 4b ); L = P(O i Pr) 3 , X = Br ( 5a ), I ( 5b ); L = PEt 3 , X = Br ( 6a ), I ( 6b )). Slightly contaminated 5a,b and pure 6a,b were isolated as stable crystalline blue or blue‐green complexes. Complexes 4a,b were obtained, with only minor impurities, by comproportionation of 1a,b and the dicarbonyl(halo)bis‐(trimethylphosphite)ferrate anions 7a,b and characterized in THF solution. The comproportionation products 5a,b ‐ 6a,b were obtained in high yields by reaction of 2a,b ‐ 3a,b with the dinitrogen complexes 13 ‐ 15 . Further reduction of 4a,b ‐ 6a,b or exhaustive reduction of 1a,b ‐ 3a,b with sodium amalgam or i BuLi in THF afforded the nonisolable dicarbonyl‐(halo)bis(phosphorus donor)ferrate(o) anions ( 7a,b ‐ 9a,b ). The latter were characterized by acidification with trifluoroacetic acid or acetic acid yielding stable dicarbonyl (halo) hydridobis (phosphorus donor)iron(II) complexes (L = P(OMe) 3 , X = Br ( 10a ), I ( 10b ); L = P(O i Pr) 3 , X = Br ( 11a ), I ( 11b );L = PEt 3 , X = Br ( 12a ), I ( 12b )). In the presence of N 2 , 8a was transformed into dinitrogen complex [Fe(CO) 2 {P(O i Pr) 3 } 2 N 2 ] ( 13 ). With 9a,b the reaction led to formation of [Fe‐(CO) 2 (PEt 3 ) 2 ) 2 N 2 ] ( 14 ) and [{Fe(CO) 2 ‐(PEt 3 ) 2 } 2 (μ‐N 2 )] ( 15 ). In solution at low temperature (−90 to 0°C), the dinitrogen complexes 14 and 15 are in equilibrium with each other. Complexes 13, 14 , and 15 were characterized by IR, 1 H, 13 C, 31 P, and 15 N NMR spectroscopy. The structures of 5a, 6b, 14 , and 15 were determined by X‐ray diffraction studies.