Selective extraction of N2 from air by diarylimine iron complexes

Treatment of cis-(Me3P)4FeMe2 with ortho-substituted diarylimines afforded 2 equiv of MeH, PMe3, and {mer-κC,N,C'-(Ar-2-yl)CH2N═CH(Ar'-2-yl)}Fe(PMe3)3 (Ar = 3,4,6-(F)3-C6H, Ar' = 3,5-(CF3)2-C6H2, 1a; Ar = 3,4,6-(F)3-C6H, Ar' = 3,4,5-(F)3-C6H, 1b; Ar = 4,5,6-(F)3-C6H, Ar' = 3,5-(CF3)2-C6H2, 1c; Ar = C6H4, Ar' = 3-(OMe)-C6H3, 1d; Ar = 4,5,6-(F)3-C6H, Ar' = 3,6-Me2-C6H3, 1e; Ar = C6H4, Ar' = 3,6-Me2-C6H2, 1f). Exposure of 1a-f to O2 caused rapid degradation, but substitution of the unique PMe3 with N2 occurred when 1a-f were exposed to air or N2 (1 atm), yielding {mer-κC,N,C'-(Ar-2-yl)CH2N═CH(Ar'-2-yl)}Fe(PMe3)2L (L = N2, 2a-f); CO, CNMe, and N2CPh2 derivatives (L = CO, 3a-d,f; L = CNMe, 8b; L = N2CPh2, 9b) were prepared. Dihydrogen or NH3 binding to {mer-κC,N,C'-(3,4,6-(F)3-C6H-2-yl)CH2N═CH-(3,4,5-(F)3-C6H-2-yl)}Fe(PMe3)2 (1b', S = 1 (calc)) to provide 5b (L = H2) or 6b (L = NH3) was found comparable to that of N2, while PMe3 (1b) and pyridine (L = py, 7b) adducts were unfavorable. Protolytic conditions were modeled using HCCR as weak acids, and trans-{κC,N-(3,4,5-(F)3-C6H2)CH2N═CH(3,4,6-(F)3-C6H-2-yl)}Fe(PMe3)3(CCR) (R = Me, 4b-Me; R = Ph, 4b-Ph) were generated from 1b. Exposure of 1b to N2O or N3SO2tol generated 2b and Me3PO or Me3P═N(SO2)tol, respectively. Calculations revealed 2b to be thermodynamically and kinetically favored over the calculated Fe(III) superoxide complex, (3)[FeO2], relative to 1b' + N2 + O2. The correlation of 1b' + (3)O2 to (3)[FeO2] is likely to have a relatively high intersystem crossing point (ICP) relative to 1b' + N2 to 2b, thereby explaining the dinitrogen selectivity.