Unusual structural and spectroscopic features of some PNP-pincer complexes of iron

Elizabeth M. Pelczar; Thomas J. Emge; Karsten Krogh-Jespersen; Alan S Goldman

doi:10.1021/om800425p

Unusual structural and spectroscopic features of some PNP-pincer complexes of iron

Elizabeth M. Pelczar, Thomas J. Emge, Karsten Krogh-Jespersen, Alan S Goldman

Rutgers University

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49 Citations (Scopus)

Abstract

We report a structural, spectroscopic, and computational study of two ^tBuPNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) complexes of iron, (^tBuPNP)FeCl₂ (1) and (^tBuPNP)Fe(CO) ₂ (3). Complex 1, (^tBuPNP)FeCl₂, also independently synthesized by Milstein, has unusually long iron-ligand bond distances. DFT calculations show that these are clearly attributable to its high-spin electronic structure, and in particular to occupancy of the strongly antibonding dx²-y² orbital. The crystal structure of 3 reveals two unusual aspects. (1) The geometry around the iron atom in 3 is much closer to square pyramidal (SQP; apical CO) than to trigonal bipyramidal (TBP), although five-coordinate Fe(O) complexes are generally expected to be TBP; moreover, Chirik et al. have reported that (^iPrPNP)Fe(CO)₂ has essentially a perfect TBP structure (^iPrPNP = 2,6-bis(di-isopropyl-phosphinomethyl)pyridine). (2) The apical carbonyl ligand in 3 deviates significantly from linearity (Fe-C-O = 171.9°). Additionally, complex 3 is intensely blue in color, which is unusual for an Fe(O) complex and also significantly different from the red color of Chirik's ( ^iPrTNP)Fe(CO)₂ species. Results from DFT calculations reproduce and explain these structural and spectroscopic aspects as well as the contrast between 3 and its ^iPrPNP analogue.

Original language	English
Pages (from-to)	5759-5767
Number of pages	9
Journal	Organometallics
Volume	27
Issue number	22
DOIs	https://doi.org/10.1021/om800425p
Publication status	Published - Nov 24 2008

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ASJC Scopus subject areas

Organic Chemistry
Physical and Theoretical Chemistry
Inorganic Chemistry

Cite this

Pelczar, E. M., Emge, T. J., Krogh-Jespersen, K., & Goldman, A. S. (2008). Unusual structural and spectroscopic features of some PNP-pincer complexes of iron. Organometallics, 27(22), 5759-5767. https://doi.org/10.1021/om800425p

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title = "Unusual structural and spectroscopic features of some PNP-pincer complexes of iron",

abstract = "We report a structural, spectroscopic, and computational study of two tBuPNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) complexes of iron, (tBuPNP)FeCl2 (1) and (tBuPNP)Fe(CO) 2 (3). Complex 1, (tBuPNP)FeCl2, also independently synthesized by Milstein, has unusually long iron-ligand bond distances. DFT calculations show that these are clearly attributable to its high-spin electronic structure, and in particular to occupancy of the strongly antibonding dx2-y2 orbital. The crystal structure of 3 reveals two unusual aspects. (1) The geometry around the iron atom in 3 is much closer to square pyramidal (SQP; apical CO) than to trigonal bipyramidal (TBP), although five-coordinate Fe(O) complexes are generally expected to be TBP; moreover, Chirik et al. have reported that (iPrPNP)Fe(CO)2 has essentially a perfect TBP structure (iPrPNP = 2,6-bis(di-isopropyl-phosphinomethyl)pyridine). (2) The apical carbonyl ligand in 3 deviates significantly from linearity (Fe-C-O = 171.9°). Additionally, complex 3 is intensely blue in color, which is unusual for an Fe(O) complex and also significantly different from the red color of Chirik's ( iPrTNP)Fe(CO)2 species. Results from DFT calculations reproduce and explain these structural and spectroscopic aspects as well as the contrast between 3 and its iPrPNP analogue.",

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T1 - Unusual structural and spectroscopic features of some PNP-pincer complexes of iron

AU - Pelczar, Elizabeth M.

AU - Emge, Thomas J.

AU - Krogh-Jespersen, Karsten

AU - Goldman, Alan S

PY - 2008/11/24

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N2 - We report a structural, spectroscopic, and computational study of two tBuPNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) complexes of iron, (tBuPNP)FeCl2 (1) and (tBuPNP)Fe(CO) 2 (3). Complex 1, (tBuPNP)FeCl2, also independently synthesized by Milstein, has unusually long iron-ligand bond distances. DFT calculations show that these are clearly attributable to its high-spin electronic structure, and in particular to occupancy of the strongly antibonding dx2-y2 orbital. The crystal structure of 3 reveals two unusual aspects. (1) The geometry around the iron atom in 3 is much closer to square pyramidal (SQP; apical CO) than to trigonal bipyramidal (TBP), although five-coordinate Fe(O) complexes are generally expected to be TBP; moreover, Chirik et al. have reported that (iPrPNP)Fe(CO)2 has essentially a perfect TBP structure (iPrPNP = 2,6-bis(di-isopropyl-phosphinomethyl)pyridine). (2) The apical carbonyl ligand in 3 deviates significantly from linearity (Fe-C-O = 171.9°). Additionally, complex 3 is intensely blue in color, which is unusual for an Fe(O) complex and also significantly different from the red color of Chirik's ( iPrTNP)Fe(CO)2 species. Results from DFT calculations reproduce and explain these structural and spectroscopic aspects as well as the contrast between 3 and its iPrPNP analogue.

AB - We report a structural, spectroscopic, and computational study of two tBuPNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) complexes of iron, (tBuPNP)FeCl2 (1) and (tBuPNP)Fe(CO) 2 (3). Complex 1, (tBuPNP)FeCl2, also independently synthesized by Milstein, has unusually long iron-ligand bond distances. DFT calculations show that these are clearly attributable to its high-spin electronic structure, and in particular to occupancy of the strongly antibonding dx2-y2 orbital. The crystal structure of 3 reveals two unusual aspects. (1) The geometry around the iron atom in 3 is much closer to square pyramidal (SQP; apical CO) than to trigonal bipyramidal (TBP), although five-coordinate Fe(O) complexes are generally expected to be TBP; moreover, Chirik et al. have reported that (iPrPNP)Fe(CO)2 has essentially a perfect TBP structure (iPrPNP = 2,6-bis(di-isopropyl-phosphinomethyl)pyridine). (2) The apical carbonyl ligand in 3 deviates significantly from linearity (Fe-C-O = 171.9°). Additionally, complex 3 is intensely blue in color, which is unusual for an Fe(O) complex and also significantly different from the red color of Chirik's ( iPrTNP)Fe(CO)2 species. Results from DFT calculations reproduce and explain these structural and spectroscopic aspects as well as the contrast between 3 and its iPrPNP analogue.

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10.1021/om800425p