Abstract
Herein we present a series of new α-iminopyridine-based iron-PNN pincer complexes [FeBr2LPNN] (1), [Fe(CO)2LPNN] (2), [Fe(CO)2LPNN](BF4) (3), [Fe(F)(CO)2LPNN](BF4) (4), and [Fe(H)(CO)2LPNN](BF4) (5) with formal oxidation states ranging from Fe(0) to Fe(II) (LPNN = 2-[(di-tert-butylphosphino)methyl]-6-[1-(2,4,6-mesitylimino)ethyl]pyridine). The complexes were characterized by a variety of methods including 1H, 13C, 15N, and 31P NMR, IR, Mössbauer, and X-ray photoelectron spectroscopy (XPS) as well as electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopy, SQUID magnetometry, and X-ray crystallography, focusing on the assignment of the metal oxidation states. Ligand structural features suggest that the α-iminopyridine ligand behaves as a redox non-innocent ligand in some of these complexes, particularly in [Fe(CO)2LPNN] (2), in which it appears to adopt the monoanionic form. In addition, the NMR spectroscopic features (13C, 15N) indicate the accumulation of charge density on parts of the ligand for 2. However, a combination of spectroscopic measurements that more directly probe the iron oxidation state (e.g., XPS), density functional theory (DFT) calculations, and electronic absorption studies combined with time-dependent DFT calculations support the description of the metal atom in 2 as Fe(0). We conclude from our studies that ligand structural features, while useful in many assignments of ligand redox non-innocence, may not always accurately reflect the ligand charge state and, hence, the metal oxidation state. For complex 2, the ligand structural changes are interpreted in terms of strong back-donation from the metal center to the ligand as opposed to electron transfer. (Chemical Equation Presented).
| Original language | English |
|---|---|
| Pages (from-to) | 4909-4926 |
| Number of pages | 18 |
| Journal | Inorganic Chemistry |
| Volume | 54 |
| Issue number | 10 |
| DOIs | |
| Publication status | Published - May 18 2015 |
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ASJC Scopus subject areas
- Inorganic Chemistry
- Physical and Theoretical Chemistry
Cite this
How Innocent are Potentially Redox Non-Innocent Ligands? Electronic Structure and Metal Oxidation States in Iron-PNN Complexes as a Representative Case Study. / Butschke, Burkhard; Fillman, Kathlyn L.; Bendikov, Tatyana; Shimon, Linda J W; Diskin-Posner, Yael; Leitus, Gregory; Gorelsky, Serge I.; Neidig, Michael L.; Milstein, David.
In: Inorganic Chemistry, Vol. 54, No. 10, 18.05.2015, p. 4909-4926.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - How Innocent are Potentially Redox Non-Innocent Ligands? Electronic Structure and Metal Oxidation States in Iron-PNN Complexes as a Representative Case Study
AU - Butschke, Burkhard
AU - Fillman, Kathlyn L.
AU - Bendikov, Tatyana
AU - Shimon, Linda J W
AU - Diskin-Posner, Yael
AU - Leitus, Gregory
AU - Gorelsky, Serge I.
AU - Neidig, Michael L.
AU - Milstein, David
PY - 2015/5/18
Y1 - 2015/5/18
N2 - Herein we present a series of new α-iminopyridine-based iron-PNN pincer complexes [FeBr2LPNN] (1), [Fe(CO)2LPNN] (2), [Fe(CO)2LPNN](BF4) (3), [Fe(F)(CO)2LPNN](BF4) (4), and [Fe(H)(CO)2LPNN](BF4) (5) with formal oxidation states ranging from Fe(0) to Fe(II) (LPNN = 2-[(di-tert-butylphosphino)methyl]-6-[1-(2,4,6-mesitylimino)ethyl]pyridine). The complexes were characterized by a variety of methods including 1H, 13C, 15N, and 31P NMR, IR, Mössbauer, and X-ray photoelectron spectroscopy (XPS) as well as electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopy, SQUID magnetometry, and X-ray crystallography, focusing on the assignment of the metal oxidation states. Ligand structural features suggest that the α-iminopyridine ligand behaves as a redox non-innocent ligand in some of these complexes, particularly in [Fe(CO)2LPNN] (2), in which it appears to adopt the monoanionic form. In addition, the NMR spectroscopic features (13C, 15N) indicate the accumulation of charge density on parts of the ligand for 2. However, a combination of spectroscopic measurements that more directly probe the iron oxidation state (e.g., XPS), density functional theory (DFT) calculations, and electronic absorption studies combined with time-dependent DFT calculations support the description of the metal atom in 2 as Fe(0). We conclude from our studies that ligand structural features, while useful in many assignments of ligand redox non-innocence, may not always accurately reflect the ligand charge state and, hence, the metal oxidation state. For complex 2, the ligand structural changes are interpreted in terms of strong back-donation from the metal center to the ligand as opposed to electron transfer. (Chemical Equation Presented).
AB - Herein we present a series of new α-iminopyridine-based iron-PNN pincer complexes [FeBr2LPNN] (1), [Fe(CO)2LPNN] (2), [Fe(CO)2LPNN](BF4) (3), [Fe(F)(CO)2LPNN](BF4) (4), and [Fe(H)(CO)2LPNN](BF4) (5) with formal oxidation states ranging from Fe(0) to Fe(II) (LPNN = 2-[(di-tert-butylphosphino)methyl]-6-[1-(2,4,6-mesitylimino)ethyl]pyridine). The complexes were characterized by a variety of methods including 1H, 13C, 15N, and 31P NMR, IR, Mössbauer, and X-ray photoelectron spectroscopy (XPS) as well as electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopy, SQUID magnetometry, and X-ray crystallography, focusing on the assignment of the metal oxidation states. Ligand structural features suggest that the α-iminopyridine ligand behaves as a redox non-innocent ligand in some of these complexes, particularly in [Fe(CO)2LPNN] (2), in which it appears to adopt the monoanionic form. In addition, the NMR spectroscopic features (13C, 15N) indicate the accumulation of charge density on parts of the ligand for 2. However, a combination of spectroscopic measurements that more directly probe the iron oxidation state (e.g., XPS), density functional theory (DFT) calculations, and electronic absorption studies combined with time-dependent DFT calculations support the description of the metal atom in 2 as Fe(0). We conclude from our studies that ligand structural features, while useful in many assignments of ligand redox non-innocence, may not always accurately reflect the ligand charge state and, hence, the metal oxidation state. For complex 2, the ligand structural changes are interpreted in terms of strong back-donation from the metal center to the ligand as opposed to electron transfer. (Chemical Equation Presented).
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U2 - 10.1021/acs.inorgchem.5b00509
DO - 10.1021/acs.inorgchem.5b00509
M3 - Article
VL - 54
SP - 4909
EP - 4926
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 10
ER -