Synthetic, Structural, and Spectroscopic Characterization of a Novel Family of High-Spin Iron(II) [(β-Diketiminate)(phosphanylphosphido)] Complexes

Rafał Grubba; Kinga Kaniewska; Łukasz Ponikiewski; Beata Cristóvão; Wiesława Ferenc; Alina Dragulescu-Andrasi; J Krzystek; Sebastian A Stoian; Jerzy Pikies

doi:10.1021/acs.inorgchem.7b01374

Synthetic, Structural, and Spectroscopic Characterization of a Novel Family of High-Spin Iron(II) [(β-Diketiminate)(phosphanylphosphido)] Complexes

Inorg Chem. 2017 Sep 18;56(18):11030-11042. doi: 10.1021/acs.inorgchem.7b01374. Epub 2017 Aug 25.

Authors

Affiliations

¹ Department of Inorganic Chemistry, Chemical Faculty, Gdańsk University of Technology , G. Narutowicza St. 11/12, Gdańsk PL-80-233, Poland.
² Department of General and Coordination Chemistry, Faculty of Chemistry, Maria Curie-Skłodowska University , Maria Curie-Skłodowska Sq. 2, Lublin PL-20-031, Poland.
³ Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States.
⁴ National High Magnetic Field Laboratory, Florida State University , Tallahassee, Florida 32310, United States.
⁵ Department of Chemistry, University of Idaho , Moscow, Idaho 83844, United States.

PMID: 28841309
DOI: 10.1021/acs.inorgchem.7b01374

Abstract

This work describes a series of iron(II) phosphanylphosphido complexes. These compounds were obtained by reacting lithiated diphosphanes R₂PP(SiMe₃)Li (R = t-Bu, i-Pr) with an iron(II) β-diketiminate complex, [LFe(μ₂-Cl)₂Li(DME)₂] (1), where DME = 1,2-dimethoxyethane and L = Dippnacnac (β-diketiminate). While the reaction of 1 with t-Bu₂PP(SiMe₃)Li yields [LFe(η¹-Me₃SiPP-t-Bu₂)] (2), that of 1 with equimolar amounts of i-Pr₂PP(SiMe₃)Li, in DME, leads to [LFe(η²-i-Pr₂PPSiMe₃)] (3). In contrast, the reaction of 1 with (i-Pr₂N)₂PP(SiMe₃)Li provides not an iron-containing complex but 1-[(diisopropylamino)phosphine]-2,4-bis(diisopropylamino)-3-(trimethylsilyl)tetraphosphetane (4). The structures of 2-4 were determined using diffractometry. Thus, 2 exhibits a three-coordinate iron site and 3 a four-coordinate iron site. The increase in the coordination number is induced by the change from an anticlinal to a synclinal conformation of the phoshpanylphosphido ligands. The electronic structures of 2 and 3 were assessed through a combined field-dependent ⁵⁷Fe Mössbauer and high-frequency and -field electron paramagnetic resonance spectroscopic investigation in conjunction with analysis of their magnetic susceptibility and magnetization data. These studies revealed two high-spin iron(II) sites with S = 2 ground states that have different properties. While 2 exhibits a zero-field splitting described by a positive D parameter (D = +17.4 cm^-1; E/D = 0.11) for 3, this parameter is negative [D = -25(5) cm^-1; E/D = 0.15(5)]. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations provide insights into the origin of these differences and allow us to rationalize the fine and hyperfine structure parameters of 2 and 3. Thus, for 2, the spin-orbit coupling mixes a z²-type ground state with two low-lying {xz/yz} orbital states. These interactions lead to an easy plane of magnetization, which is essentially parallel to the plane defined by the N-Fe-N atoms. For 3, we find a yz-type ground state that is strongly mixed with a low-lying z²-type orbital state. In this case, the spin-orbit interaction leads to a partial unquenching of the orbital momentum along the x axis, that is, to an easy axis of magnetization oriented roughly along the Fe-P bond of the phosphido moiety.