Giant Residual Dipolar super(13)C- super(1)H Couplings in High-Spin Organoiron Complexes: Elucidation of Their Structures in Solution by super(13)CNMR Spectroscopy

• Published in: Chemistry : a European journal Vol. 19; no. 5; pp. 1599 - 1606
• Main Authors: Kruck, Matthias, Wadepohl, Hubert, Enders, Markus, Gade, Lutz H
• Format: Journal Article
• Language: English
• Published: 01.01.2013
• Subjects: Alignment; Coordination compounds; Couplings; Deviation; Mathematical analysis; Spectra; Tensors
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201203450

High-spin Fe super(II)-alkyl complexes with bis(pyridylimino)isoindolato ligands were synthesized and their paramagnetic super(1)H and super(13)CNMR spectra were analyzed comprehensively. The experimental super(13)C- super(1)H coupling values are temperature (T super(-1))- as well as magnetic-field (B super(2))-dependent and deviate considerably from typical scalar super(1)J sub(CH) couplings constants. This deviation is attributed to residual dipolar couplings (RDCs), which arise from partial alignment of the complexes in the presence of a strong magnetic field. The analysis of the experimental RDCs allows an unambiguous assignment of all super(13)CNMR resonances and, additionally, a structural refinement of the conformation of the complexes in solution. Moreover the RDCs can be used for the analysis of the alignment tensor and hence the tensor of the anisotropy of the magnetic susceptibility. Aligning the dipoles: Giant residual dipolar couplings (RDCs) of up to 30Hz have been observed in paramagnetic NMR spectra of high-spin Fe super(II)-alkyl complexes. Analysis of the measured RDCs allowed the structural refinement of these relatively small molecules in solution and hence adds a valuable analytical tool for the identification of paramagnetic complexes in solution (see figure).