Aryl-Containing Pyridine-Imine and Azaallyl Chelates of Iron toward Strong Field Coordination Compounds

• Published in: Organometallics 2010-01, Vol.29 (2), p.364-377
• Main Authors: Volpe, Emily C, Wolczanski, Peter T, Lobkovsky, Emil B
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om900793c

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-(Me3P)4FeMe2 and imino-based ligand precursors afforded trans-{κ-C,N,N′-(XAr-2-yl)CH2NCH-2-py}(PMe3)2FeIICH3 (X = H, 1; p-OMe, 2; o-Cl, 3) and trans-{κ-C,N,N′-(p-tBu-Ar-2-yl)CHNCH2-2-py}(PMe3)2FeIICH3 (4) concomitant with 2 PMe3 and CH4 via ArH activation. Thermolysis of 4 + PMe3 gave CH4 and py CH activation to provide mer-{κ-C,N,C′-(p-tBu-Ar-2-yl)CHNCH2(2-py-3-yl)}(PMe3)3FeII (6). Derivatization of 6 with MeOTf produced [mer-{κ-C,N,C′-(p-tBu-Ar-2-yl)CHNCH2(2-py-NCH3-3-yl)}(PMe3)3FeII]OTf (7), which could be deprotonated to give the zwitterionic azaallyl mer-{κ-C,N,C′-(p-tBu-Ar-2-yl)CHNCH(2-py-NCH3-3-yl)}(PMe3)3FeII (8). Oxidation of 4 with AgOTf generated [trans-{κ-C,N,N′-(p-tBu-Ar-2-yl)CHNCH2-2-py}(PMe3)2FeIIICH3]OTf (9), and its deprotonation with KH produced azaallyl trans-{κ-C,N,N′-(p-tBu-Ar-2-yl)CHNCH-2-py}(PMe3)2FeIIICH3 (10). Exposure of cis-(Me3P)4FeMe2 to diarylimines gave double arene CH activation products {mer-κ-C,N,C′-(Ar-2-yl)CH2NCH(Ar-2-yl-X)}Fe(PMe3)3 (X = H, 11; 4-CF3, 12; 3-OMe, 13) with loss of 2 CH4 and PMe3. Treatment of the parent diarylimine complex (11) with AgOTf afforded [mer-κ-C,N,C′-{(Ar-2-yl)CH2NCH(Ar-2-yl-X)}FeIII(PMe3)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.