A series of aryl-and pyridyl-imine iron complexes have been prepared to explore the generation of strong fields provided by aryl chelates and the potential support of an azaallyl functionality. cis-(Me 3 P) 4 FeMe 2 and imino-based ligand precursors afforded trans-{κ-C,N,N 0 -(XAr-2-yl)-CH 2 NdCH-2-py}(PMe 3 ) 2 Fe II CH 3 (X = H, 1; p-OMe, 2; o-Cl, 3) and trans-{κ-C,N,N 0 -(p-t Bu-Ar-2-yl)-CHdNCH 2 -2-py}(PMe 3 ) 2 Fe II CH 3 (4) concomitant with 2 PMe 3 and CH 4 via ArH activation. Thermolysis of 4 þ PMe 3 gave CH 4 and py CH activation to provide mer 7), which could be deprotonated to give the zwitterionic azaallyl mer-{κ-C,N,C 0 -(p-t Bu-Ar-2-yl)CHNCH(2-py-NCH 3 -3-yl)}-(PMe 3 ) 3 Fe II (8). Oxidation of 4 with AgOTf generated [trans-{κ-C,N,N 0 -(p-t Bu-Ar-2-yl)CHdNCH 2 -2-py}(PMe 3 ) 2 Fe III CH 3 ]OTf (9), and its deprotonation with KH produced azaallyl trans-{κ-C,N, N 0 -(p-t Bu-Ar-2-yl)CHNCH-2-py}(PMe 3 ) 2 Fe III CH 3 (10). Exposure of cis-(Me 3 P) 4 FeMe 2 to diarylimines gave double arene CH activation products {mer-κ-C,N,C 0 -(Ar-2-yl)CH 2 NdCH(Ar-2-yl-X)}-Fe(PMe 3 ) 3 (X = H, 11; 4-CF 3 , 12; 3-OMe, 13) with loss of 2 CH 4 and PMe 3 . Treatment of the parent diarylimine complex (11) with AgOTf afforded [mer-κ-C,N,C 0 -{(Ar-2-yl)CH 2 NdCH(Ar-2-yl-X)}Fe III -(PMe 3 ) 3 ]OTf ( 14), but attempts to deprotonate it to form an azaallyl failed. Structures of 7, 8, and 14 are detailed. Discussions regarding the feasibility of aryl chelates and utilization of the azaallyl functionality to support high oxidation states are provided, in addition to an interpretation of the UV-vis spectra of the azaallyls.

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Aryl-oxazoline synthons have been explored for the preparation of strong-field first-row transition metal chelate species. With 4,4-dimethyl-2-phenyloxazoline (HPhOx), no CH bond activations afforded complexation, and aside from Zn(κ-C,N-4,4-Me 2 -2-(o-C 6 H 4 )oxazoline) 2 (Zn(PhOx) 2 ), aryl-coupling reactions were noted with 4,4-dimethyl-2-(2-lithiophenyl)oxazoline (LiPhOx) and MX 2 ; [κ-N,N-{4,4-Me 2 -(2-o-C 6 H 4 )-2-oxazoline} 2 ]CoCl 2 (1-Co) was structurally characterized. Metalations with 4,4-dimethyl-2-benzyloxazoline (PhCH 2 Ox) were prone to deprotonation, as exemplified by (Me 2 62 ), and iron, i.e., {κ-C,N-{(o-C 6 H 4 )CMe 2 (COCH 2 CMe 2 N)}Fe(py)Cl ( 7) products. Bis-aryloxazoline metal complexes proved difficult to prepare, with {κ-C,N-(o-C 6 H 4 )-CMe 2 (COCH 2 CMe 2 N)} 2 M (M=Ni, 9) the only clear example, although NMR evidence exists for M=Fe (8). ‡ Dedicated to Dietmar Seyferth on the occasion of his retirement as Editor, for his distinguished service, and for 35þ years of friendship to an old student.

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.