Five-Coordinate Low-Spin {FeNO}7 PNP Pincer Complexes

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Five-Coordinate Low-Spin {FeNO}7 PNP Pincer Complexes Jan Pecak,† Berthold Stöger,‡ Matthias Mastalir,† Luis F. Veiros,§ Liliana P. Ferreira,∥,⊥ Marc Pignitter,# Wolfgang Linert,† and Karl Kirchner*,† †

Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria X-Ray Center, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria § Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais No. 1, 1049-001 Lisboa, Portugal ∥ Biosystems and Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal ⊥ Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal # Department of Physiological Chemistry, Faculty of Chemistry, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria

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‡

S Supporting Information *

ABSTRACT: The synthesis and characterization of air-stable cationic mono nitrosonium Fe(I) PNP pincer complexes of the type [Fe(PNP)(NO)Cl]+ are described. These complexes are obtained via direct nitroslyation of [Fe(PNP)Cl2] with nitric oxide at ambient pressure. On the basis of magnetic and EPR measurements as well as DFT calculations, these compounds were found to adopt a low-spin d7 configuration and feature a nearly linear bound NO ligand suggesting FeINO+ rather than FeIINO• character. X-ray structures of all nitrosonium Fe(I) PNP complexes are presented. Preliminary investigations reveal that [Fe(PNPNH-iPr)(NO)(Cl)]+ efficiently catalyzes the conversion of primary alcohols and aromatic and benzylic amines to yield mono N-alkylated amines in good isolated yields.

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replacing CO by the isoelectronic NO+ ligand. Analogous ruthenium complexes, recently prepared by Milstein et al.,2 were shown to catalyze the dehydrogenative coupling of hexanol to hexyl hexanoate and were able to act as a mono oxygen transfer reagent.3 The introduction of a nitrosyl ligand has several implications. First, a complex with an extra positive charge is generated, making these systems more electrophilic. Second, NO+ is known to undergo an intramolecular 2e reduction forming NO− which temporarily provides a vacant coordination site for substrate binding and activation and may constitute a powerful tool for catalysis. As yet, not only nitrosyl iron but also nitrosyl ruthenium pincer complexes are exceedingly rare.4,5 Here we report the reaction of [Fe(PNP)Cl2] with both NO+ and nitric oxide.

INTRODUCTION Pentacoordinate and coordinatively unsaturated Fe(II) PNP pincer complexes of the type [Fe(PNP)Cl2], where the pyridine ring and the phosphine moieties of the PNP ligand are connected via NH linkers, were found to exhibit a remarkably different solid−gas and solution−gas chemistry with CO.1 While in the solid state cis-[Fe(PNP)(CO)(Cl)2] is selectively formed, in solution the corresponding trans isomer is obtained (Scheme 1). These transformations are fully reversible, and heating of solid samples of [Fe(PNP)(CO)(Cl)2] under a vacuum leads to the complete regeneration of [Fe(PNP)Cl2]. Interestingly, complexes with NR (R = alkyl, aryl) linkers did not react with CO. In the present contribution, we are interested in preparing analogous complexes of the type [Fe(PNP)(NO)(Cl)2]+ by

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RESULTS AND DISCUSSION In an attempt to obtain cationic nitrosyl Fe(II) PNP pincer complexes of the type cis- and trans-[Fe(PNP)(NO)(Cl)2]+, which are known for Ru(II) PNP pincer systems,2,3 Fe(II) PNP complexes [Fe(PNP)Cl2] (1a−c) were treated with stoichiometric amounts of NO+ (in the form of NOBF4 or

Scheme 1. Reversible Addition of CO to [Fe(PNP)Cl2] in Solution and in the Solid State

Received: January 24, 2019

© XXXX American Chemical Society

A

DOI: 10.1021/acs.inorgchem.9b00235 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

from the temperature dependence of the inverse molar magnetic susceptibility, which is well described by a Curie law above 10 K (one unpaired electron) (Figure 1). This value

NOSbF6). Contrary to expectations, no octahedral complexes were formed, but instead, Fe(I) PNP pincer complexes of the type [Fe(PNP)(NO)Cl]+ (2a−c) together with free PNP ligand and unidentified paramagnetic, presumably Fe(III), species were formed. Apparently, a disproportionation process took place and, thus, the yield of the Fe(I) complexes as BF4− (2aBF4, 2bBF4) and SbF6− (2cSbF6) salts, respectively, was merely in the range of 20−28%. Gratifyingly, direct nitrosylation of complexes 1a−c with nitric oxide at ambient pressure afforded the cationic fivecoordinate Fe(I) complexes 2a−c in 87−89% isolated yield (in the form of 2aCl−2cCl) (Scheme 2). This reaction could be Scheme 2. Formation of Nitrosonium Fe(I) PNP Pincer Complexes 2aCl−2cCl

Figure 1. Inverse of the molar susceptibility for samples: 2aCl (squares) and 2bCl (circles). The lines are the result of linear fits of the modified Curie law to the data [squares, 2.2(1) μB (temperature independent paramagnetism (TIP) = 7.8(1) × 10−4 cm3/mol); circles, 2.2(1) μB (TIP = 9.9(1) × 10−4 cm3/mol)].

is higher than the one expected for the spin-only approximation and is explained by a spin orbit coupling contribution, being consistent with a low-spin square-pyramidal complex.6 Also, solution effective magnetic moments of complexes 2a−c in acetone (BF4−, SbF6− salts) or methanol (Cl− salts) of 1.9− 2.1 μB agree well with a low-spin d7 center. To further characterize 2aBF4, an X-band EPR spectrum was recorded in CH2Cl2 at 298 and 100 K. At both temperatures, this compound displays an isotropic multiplet at giso = 2.037 with a well-resolved hyperfine coupling to the nitrogen and phosphorus atoms (AN = 11.9 G and AP = 20.3 G) (Figure 2, at 100 K) and again is consistent with low-spin Fe(I) (S = 1/2). In fact, most reported low-spin {FeNO}7 systems exhibit EPR spectra with g values close to 2.0.7,8

viewed as a formal one-electron reduction of the metal center by the NO radical from Fe(II) to Fe(I), if NO is counted as NO+. In the course of this reaction, one chloride ligand is liberated. The chloride counterion can be readily exchanged upon treatment with Ag+ salts, as exemplarily shown for the preparation of 2aBF4 from 2aCl. Complexes 2a−2c are thermally robust purple solids, which are air-stable in the solid state for about 1 day but decompose in solution when exposed to air for a few hours. The same products were obtained when the reaction was carried out as a solid−gas reaction. Exposure of solid 1a−c (which are yellow complexes) to gaseous NO (1 bar) for 2 h yielded quantitatively the purple complexes 2aCl−2cCl on the basis of IR spectroscopy. Nitric oxide binding is irreversible and heating up to 120 °C under a vacuum of the solid compounds for several hours did not result in liberation of NO and the complexes remained unchanged. Characterization was accomplished by a combination of magnetic measurements in the solid state and solution (SQUID, Evans method), IR spectroscopy, electron paramagnetic resonance (EPR), DFT calculations, and elemental analysis. Due to the paramagnetic nature of these complexes the 1H NMR signals were very broadened and featureless, and thus not informative. In the IR spectrum, complexes 2aBF4, 2bBF4, and 2cSbF6 exhibit a strong absorption band assignable to the NO stretching frequencies at 1747, 1753, and 1736 cm−1, respectively (cf. the related complexes [Fe(PCPNEt-iPr)(CO)(NO)], [Fe(κ3P,CH,P-P(CH)PNEt-iPr)(CO)(NO)]+, and [Fe(PNPO-iPr)(CO)(NO)]+ exhibit the NO stretching frequencies at 1663, 1720, and 1732 cm−1, respectively).4b,c Concurrent IR spectra are obtained for 2aCl−2cCl (1748, 1751, and 1730 cm−1). As judged by SQUID, solution magnetic susceptibility measurements (acetone or methanol, Evans method), and electron paramagnetic resonance (EPR) studies, these compounds are low-spin complexes. The magnetic moments of μeff = 2.2 μB for complexes 2aCl and 2bCl were derived

Figure 2. X-Band EPR spectrum at a microwave frequency of 9.86 GHz at 100 K of 2aBF4 in CH2Cl2. The red curve shows the simulation with giso = 2.037, A(31P) = 20.3 G, and A(14N) = 11.9 G.

DFT calculations with the OPBE functional reveal that the low-spin {FeNO}7 complex with S = 1/2 adopts a distorted square-pyramidal geometry and is 7.8 kcal/mol more stable than the illusive corresponding Fe(I) complex in a high-spin configuration with S = 3/2. The frontier orbitals of complex 2a are typical of a low spin d7 species with a square-pyramidal geometry (Figure 3). The SOMO (singly occupied) is based on the metal z2 orbital with a strong component pointing to the empty sixth coordination position, and the LUMO is the B


Article

Inorganic Chemistry

2aBF 4 and 2cSbF 6 are provided in the Supporting Information). The five-coordinate geometry of these cationic complexes is best described as a distorted square-pyramid with NO in the apical position and the PNP and Cl ligands in the basal position (τ5 = 0.10−0.32).15 The Fe−N−O bond angles for 2aBF4, 2bBF4, and 2cSbF6 are 161.4(6), 177.0(1), and 161.6(9)°, respectively, and the Fe−N−O moiety can thus be considered as nearly linear. This is consistent with NO being essentially a NO+ cation. For comparison, also Meyer and coworkers described recently an example of an {FeNO}7 complex that features an almost-linear Fe−N−O unit (Fe−N−O 176.9°).8 Since Fe(II) PNP pincer complexes were shown to be catalytically active for acceptorless dehydrogenations of alcohols,16−18 we have begun to investigate the potential of the nitrosyl Fe(I) complexes as a catalyst for alkylations of aromatic and benzylic amines with primary alcohols as the first test reaction. Complex 2aCl (4 mol % based on alcohols) was reacted with various alcohols (1.2 equiv) and amines (1.0 equiv) in toluene (3 mL) at 90 °C with t-BuOK (1.3 equiv) as the additive. All reactions were performed in a closed vial. The results are summarized in Table 1. All organic products were

Figure 3. (left) Frontier orbitals (d-splitting) and (right) spin density of [Fe(PNPNH-iPr)(NO)Cl]+ (2a).

Fe−L σ* orbital involving the x2−y2 metal orbital, antibonding to all four coordinating atoms on the PNP plane. The other three metal d orbitals, xy, xz, and yz, are involved in filled molecular orbitals, HOMO−1, HOMO−3, and HOMO−4, respectively. Accordingly, the spin density of the molecule is located on the metal atom, as also shown in Figure 3. The same results were obtained with the functionals B3LYP and BP86 (see Figure S3, Supporting Information). Since the accurate description of the electronic structures of iron nitrosyl complexes by DFT calculations is challenging,9,10 additional calculations were carried out to prove the validity of the spin-unrestricted Kohn−Sham DFT approach. Unrestricted corresponding orbitals (UCOs)12 were calculated using the ORCA 4.0 program package.11 UCO analysis involves a unitary transformation of the canonical MOs to generate a set of α and β orbitals with maximum overlap. By this means, it can be shown that there is a perfect match between all α and β orbitals, leaving one singly occupied orbital (SOMO, zero overlap) unmatched. This indicates that magnetic coupling, as suggested in various {MNO}x systems, is rather unlikely.13,14 In addition to the magnetic and spectroscopic characterization, the solid-state structures of 2aBF4, 2bBF4, and 2cSbF6 were determined by single-crystal X-ray diffraction. A structural diagram of 2bBF4 is depicted in Figure 4 with selected bond distances and angles given in the caption (the structures of

Table 1. Coupling of Primary Alcohols and Amines Catalyzed by 2aCla,b

a

Reaction conditions: 1.2 mmol of alcohol, 1.0 mmol of amine, 1.2 mmol of KOtBu, 4.0 mol % catalyst, 3 mL of toluene. bIsolated yields.

characterized by 1H and 13C{1H} NMR spectroscopy and ESI MS and identified by comparison with authentic samples reported elsewhere.17 In general, isolated yields after purification by column chromatography are reported. In all cases, mono N-alkylated amines were isolated in good yields. Dialkylated amines were not formed. The present system exhibits comparable reactivity to related PNP pincer Fe catalysts17 and may proceed via a hydride species of the type [Fe(PNPNMe-iPr)(NO)H]+.

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Figure 4. Structural views of [Fe(PNPNMe-iPr)(NO)Cl]BF4·1/2THF (2bBF4·1/2THF) showing 50% displacement ellipsoids (H atoms, BF4− counterion, and solvent molecule omitted for clarity). Selected bond lengths (Å) and angles (deg): Fe1−N1 1.992(2), Fe1−Cl1 2.2613(6), Fe1−N4 1.676(2), Fe1−P1 2.2599(6), Fe1−P2 2.2481(6), P2−Fe1−P1 157.66(3), N4−Fe1−Cl1 109.41(6), N1− Fe1−Cl1 143.98(5), Fe1−N4−O1 177.0(1).

CONCLUSION In sum, we have prepared and characterized a series of novel air-stable cationic nitrosonium Fe(I) PNP pincer complexes of the type [Fe(PNP)(NO)Cl]+. These compounds were obtained via direct nitrosylation of the Fe(II) complexes C


Article

Inorganic Chemistry

[Fe(PNPNH-iPr)(NO)Cl]BF4 (2aBF4). Method A. To a solution of NOBF4 (25 mg, 0.21 mmol) in dichloromethane (5 mL) at −30 °C, [Fe(PNP-iPr)Cl2] (1a) (100 mg, 0.21 mmol) was added. The purple reaction mixture was stirred for 30 min and filtrated over a pad of Celite, and all volatiles were removed under a vacuum. The obtained solid was washed with pentane twice (5 mL) and dried in a vacuum. The analytically pure product was isolated via crystallization from THF/pentane. Yield: 33 mg (28%). Method B. To a solution of 2aCl (100 mg, 0.20 mmol) in dichloromethane (7 mL), AgBF4 (39 mg, 0.20 mmol) was added. The mixture was stirred for 1 h and then filtrated over Celite, and the solvent was removed under reduced pressure. The obtained solid was washed with n-pentane (5 mL) and dried under a vacuum. Yield: 90 mg (82%). Anal. Calcd for C17H33BClF4FeN4OP2 (549.52): C, 37.16; H, 6.05; N, 10.20. Found: C, 37.29; H, 6.11; N, 10.10. IR (ATR, cm−1): 1747 (νNO). μeff = 2.0 μB (acetone, Evans method). HR-MS (ESI+, CH2Cl2): m/z calcd for C17H33ClFeN4OP2 [M+] 462.1167, found 462.1154. [Fe(PNPNMe-iPr)(NO)Cl]BF4 (2bBF4). This complex was prepared analogously to 2aBF4 with 1b(100 mg, 0.20 mmol) and NOBF4 (24 mg, 0.20 mmol) as starting materials. The analytically pure product was isolated via crystallization from THF/pentane. Yield: 28 mg (24%). Anal. Calcd for C19H37BClF4FeN4OP2 (577.58): C, 39.51; H, 6.46; N, 9.70. Found: C, 39.68; H, 6.54; N, 9.80. IR (ATR, cm−1): 1753 (νNO). μeff = 2.0 μB (acetone, Evan method). HR-MS (ESI+, CH2Cl2): m/z calcd for C19H37ClFeN4OP2 [M+] 490.1480, found 490.1471. [Fe(PNPNH-tBu)(NO)Cl]SbF6 (2cSbF6). This complex was prepared analogously to 2aBF4 with 1c (80 mg, 0.15 mmol) and NOSbF6 (41 mg, 0.15 mmol) as starting materials. The analytically pure product was isolated via crystallization from THF/n-pentane. Yield: 19 mg (20%). Anal. Calcd for C21H41ClF6FeN4OP2Sb (754.58): C, 33.43; H, 5.48; N, 7.43. Found: C, 33.54; H, 5.41; N, 7.50. IR (ATR, cm−1): 1736 (νNO). μeff = 2.1 μB (acetone, Evans method). HR-MS (ESI+, CH2Cl2): m/z calcd for C21H41ClFeN4OP2 [M+] 518.1793, found 518.1778. [Fe(PNPNH-iPr)(NO)Cl]Cl (2aCl). Nitric oxide was bubbled into a solution of 1a (250 mg, 0.53 mmol) in MeOH (10 mL) for ca. 0.5 min and the mixture stirred for 1 h, whereupon the reaction mixture turned from yellow to purple. After removal of all volatiles under reduced pressure, the remaining solid was washed with n-pentane (6 mL) and dried under a vacuum at 60 °C. Yield: 230 mg (87%). Anal. Calcd for C17H33Cl2FeN4OP2 (498.17): C, 40.98; H, 6.68; N, 11.25. Found: C, 41.32; H, 6.62; N, 10.98. IR (ATR, cm−1): 1748 (νNO). μeff = 1.9 μB (CH3OH, Evans method). μeff = 2.2(1) μB (SQUID). [Fe(PNPNMe-iPr)(NO)Cl]Cl (2bCl). This complex was prepared analogously to 2a·Cl with 1b (250 mg, 0.50 mmol) as the starting material. Yield: 236 mg (89%). Anal. Calcd for C19H37Cl2FeN4OP2 (526.22). C, 43.36; H, 7.09; N, 10.65. Found: C, 43.71; H, 7.32; N, 10.37. IR (ATR, cm−1): 1751 (νNO). μeff = 2.1 μB (CH3OH, Evans method). μeff = 2.2(1) μB (SQUID). [Fe(PNPNH-tBu)(NO)Cl]Cl (2cCl). This complex was prepared analogously to 2a·Cl with 1c (100 mg, 0.19 mmol) as the starting material. Yield: 88 mg (83%). Anal. Calcd for C21H41Cl2FeN4OP2(554.27). C, 45.51; H, 7.45; N, 10.11. Found: C, 45.83; H, 7.73; N, 9.97. IR (ATR, cm−1): 1730 (νNO). μeff = 2.0 μB (CH3OH, Evans method). Crystal Structure Determination. X-ray diffraction data of 2aBF4, 2bBF4·1/2THF, and 2cSbF6 (CCDC 1866264−1866266) were collected at 100 K (2aBF4, 2bBF4·1/2THF) and 200 K (2cSbF6; fragmentation at lower temperatures attributed to a presumable phase transition) in a dry stream of nitrogen on a Bruker Kappa APEX II diffractometer system using graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å) and fine sliced φ- and ω-scans. All 2cSbF6 crystals were systematically twinned and featured poor diffraction quality. Two domains were identified using the RLATT module. Data were reduced to intensity values with SAINT, and an absorption correction was applied with the multiscan approach implemented in SADABS or TWINABS.23 The structures were solved by the dual-space approach implemented in SHELXT24 and refined against F2 with SHELXL.25 2cSbF6 models were refined against

[Fe(PNP)Cl2] both in solution and in the solid state using gaseous nitric oxide (1 bar). These reactions are accompanied by color changes and spin-state changes. The starting materials are d6 high-spin (S = 2) species, while the products adopt a low-spin d7 configuration (S = 1/2), as established by magnetic measurements in solution (Evans method) and in the solid state (SQUID), EPR measurements, as well as DFT calculations. All Fe(I) complexes exhibit a distorted squarepyramidal geometry and feature a nearly linearly bound NO ligand in the apical position. X-ray structures of all nitrosonium Fe(I) PNP complexes are presented. All experimental data together with DFT calculations are in agreement with the formal oxidation states in complexes 2a−c having a strong FeINO+ rather than FeIINO• character. The latter is typically suggested for many non-heme and heme low spin systems.19 It has to be noted that the PNP pincer ligands used in this study do not engage in redox processes with the iron center unlike related bis(imino)pyridine-based pincer ligands. Preliminary investigations reveal that [Fe(PNPNH-iPr)(NO)(Cl)]+ efficiently and selectively catalyzed the conversion of primary alcohols and aromatic and benzylic amines to yield mono Nalkylated amines in good isolated yields.

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EXPERIMENTAL SECTION

General Information. All manipulations were performed under an inert atmosphere of argon by using Schlenk techniques or in an MBraun inert-gas glovebox. The solvents were purified according to standard procedures.20 The deuterated solvents were purchased from Aldrich and dried over 4 Å molecular sieves. Nitric oxide (NO 2.5) was purchased from MESSER GmbH (Gumpoldskirchen, Austria). Complexes [Fe(PNPNH-iPr)Cl2] (1a),1a21 [Fe(PNPNMe-iPr)Cl2] (1b),1c and [Fe(PNPNH-tBu)Cl2] (1c)1a were prepared according to the literature. 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded on Bruker AVANCE-250, AVANCE-400, and AVANCE600 spectrometers. 1H and 13C{1H} NMR spectra were referenced internally to residual protio-solvent and solvent resonances, respectively, and are reported relative to tetramethylsilane (δ = 0 ppm). 31P{1H} NMR spectra were referenced externally to H3PO4 (85%) (δ = 0 ppm). Room-temperature solution (acetone or CH3OH) magnetic moments were determined by 1H NMR spectroscopy using the method of Evans.22 CW-EPR spectroscopic analyses were performed on an X-band Bruker Elexsys-II E500 EPR spectrometer (Bruker Biospin GmbH, Rheinstetten, Germany) in solution (100 μM in CH2Cl2) at room temperature. A high sensitivity cavity (SHQE1119) was used for measurements setting the microwave frequency to 9.86 GHz, the modulation frequency to 100 kHz, the center field to 6000 G, the sweep width to 12000 G, the sweep time to 30.0 s, the modulation amplitude to 6 G, the microwave power to 15.9 mW, the conversion time to 7.33 ms, and the resolution to 4096 points. The spectrum of dichloromethane was subtracted from the sample spectra, which were analyzed using the Bruker Xepr software. High resolution-accurate mass data mass spectra were recorded on a hybrid Maxis Qq-aoTOF mass spectrometer (Bruker Daltonics, Bremen, Germany) fitted with an ESI source. Measured accurate mass data of the [M]+ ions for confirming calculated elemental compositions were typically within ±5 ppm accuracy. The mass calibration was done with a commercial mixture of perfluorinated trialkyl-triazines (ES Tuning Mix, Agilent Technologies, Santa Clara, CA, USA). Magnetization measurements as a function of temperature were performed on powder samples using a SQUID magnetometer (Quantum Design MPMS). The curves were obtained at 0.1 T for temperatures ranging from 5 to 300 K. The susceptibility values were corrected for diamagnetism of the constituent atoms using Pascal constants. D


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Inorganic Chemistry HKLF5 data with overlap information. Non-hydrogen atoms were refined anisotropically. The H atoms connected to C atoms were placed in calculated positions and thereafter refined as riding on the parent atoms. The amine H’s were located from difference Fourier maps and restrained to a N−H distance of 0.87 Å. 2aBF4 and 2cSbF6 were modeled as positionally disordered with respect to the Fe atom and the NO and Cl ligands. Molecular graphics were generated with the program MERCURY.26 Computational Details. Calculations were performed using the Gaussian 09 software package27 and the OPBE functional without symmetry constraints. This functional combines Handy’s OPTX modification of Becke’s exchange functional28 with the gradient corrected correlation functional of Perdew, Burke, and Ernzerhof,29 and it was shown to be accurate in the calculation of spin state energy splitting for first transition row species.30 The geometry optimizations were accomplished without symmetry constraints using a standard 631G** basis set31 for all atoms except for iron for which it was used a SDD basis set.32 The orbitals and spin density plots were represented using Molekel.33 The drawings in Figure 3 correspond to α-spin orbitals.

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Bichler, B.; Mastalir, M.; Stöger, B.; Mereiter, K.; Weil, M.; Veiros, L. F.; Mösch-Zanetti, N. C.; Kirchner, K. FeII2P,N. Eur. J. Inorg. Chem. 2015, 2015, 5053−5065. (2) Fogler, E.; Iron, M. A.; Zhang, J.; Ben-David, Y.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J. W.; Milstein, D. Ru(0) and Ru(II) Nitrosyl Pincer Complexes: Structure, Reactivity, and Catalytic Activity. Inorg. Chem. 2013, 52, 11469−11479. (3) Fogler, E.; Efremenko, I.; Gargir, M.; Leitus, G.; Diskin-Posner, Y.; Ben-David, Y.; Martin, J. M. L.; Milstein, D. New Ruthenium Nitrosyl Pincer Complexes Bearing an O2 Ligand. Mono-Oxygen Transfer. Inorg. Chem. 2015, 54, 2253−2263. (4) For recent examples of nitrosyl iron pincer complexes, see: (a) Suzuki, T.; Matsumoto, J.; Kajita, Y.; Inomata, T.; Ozawa, T.; Masuda, H. Nitrosyl and carbene iron complexes bearing a k3. Dalton Trans. 2015, 44, 1017−1022. (b) Tondreau, A. M.; Boncella, J. M. The synthesis of PNP-supported low-spin nitro manganese(I) carbonyl complexes. Polyhedron 2016, 116, 96−104. (c) Himmelbauer, D.; Mastalir, M.; Stöger, B.; Pignitter, M.; Somoza, V.; Veiros, L. F.; Kirchner, K. Iron PCP Pincer Complexes in Three Oxidation States: Reversible Ligand Protonation to Afford an Fe(0) Complex with an Agostic C-H Arene Bond. Inorg. Chem. 2018, 57, 7925−7931. (d) Cheung, P. M.; Burns, K. T.; Kwon, Y. M.; Deshaye, M. Y.; Aguayo, K. J.; Oswald, V. F.; Seda, T.; Zakharov, L. N.; Kowalczyk, T.; JGilbertson, J. D. Hemilabile Proton Relays and Redox Activity Lead to {FeNO}x2− Reduction. J. Am. Chem. Soc. 2018, 140, 17040− 17050. (5) (a) Nagao, H.; Enomoto, K.; Wakabayashi, Y.; Komiya, G.; Hirano, T.; Oi, T. Synthesis of Nitrosylruthenium Complexes Containing 2,2’:6’,2’’-Terpyridine by Reactions of Alkoxo Complexes with Acids. Inorg. Chem. 2007, 46, 1431−1439. (b) Walstrom, A.; Pink, M.; Fan, H.; Tomaszewski, J.; Caulton, K. G. Radical (NO) and Nonradical (N2O) Reagents Convert a Ruthenium(IV) Nitride to the Same Nitrosyl Complex. Inorg. Chem. 2007, 46, 7704−7706. (6) (a) Carlin, R. L. Magnetochemistry; Springer-Verlag: Heidelberg, Germany, 1986. (b) Orchard, A. F. Magnetochemistry; Oxford University Press: 2003. (7) For recent examples of Fe(I) pincer complexes, see: (a) Tondreau, A. M.; Milsmann, C.; Lobkovsky, E.; Chirik, P. J. Oxidation and Reduction of Bis(imino)pyridine Iron Dicarbonyl Complexes. Inorg. Chem. 2011, 50, 9888−9895. (b) Thompson, C. V.; Arman, H. D.; Tonzetich, Z. J. A Pyrrole-Based Pincer Ligand Permits Access to Three Oxidation States of Iron in Organometallic Complexes. Organometallics 2017, 36, 1795−1802. (c) Thompson, C. V.; Davis, I.; DeGayner, J. A.; Arman, H. D.; Tonzetich, Z. J. Iron Pincer Complexes Incorporating Bipyridine: A Strategy for Stabilization of Reactive Species. Organometallics 2017, 36, 4928−4935. (d) Ehrlich, N.; Kreye, M.; Baabe, D.; Schweyen, P.; Freytag, M.; Jones, P. G.; Walter, M. D. Synthesis and Electronic Ground-State Properties of Pyrrolyl-Based Iron Pincer Complexes: Revisited. Inorg. Chem. 2017, 56, 8415−8422. (e) Kuriyama, S.; Arashiba, K.; Nakajima, K.; Matsuo, Y.; Tanaka, H.; Ishii, K.; Yoshizawa, K.; Nishibayashi, Y. Catalytic transformation of dinitrogen into ammonia and hydrazine by iron-dinitrogen complexes bearing pincer ligand. Nat. Commun. 2016, 7, 12181. (8) Kupper, C.; Schober, A.; Demeshko, S.; Bergner, M.; Meyer, F. An Exclusively Organometallic {FeNO}7. Inorg. Chem. 2015, 54, 3096−3098. (9) Boguslawski, K.; Jacob, C. R.; Reiher, M. Can DFT Accurately Predict Spin Densities? Analysis of Discrepancies in Iron Nitrosyl Complexes. J. Chem. Theory Comput. 2011, 7, 2740−2752. (10) Conradie, J.; Ghosh, A. DFT Calculations on the SpinCrossover Complex Fe(salen)(NO): A Quest for the Best Functional. J. Phys. Chem. B 2007, 111, 12621−12624. (11) Neese, F. The Orca Program System. WIREs Comput. Mol. Sci. 2012, 2, 73−78. (12) Neese, F. Definition of corresponding orbitals and the diradical character in broken symmetry DFT calculations on spin coupled systems. J. Phys. Chem. Solids 2004, 65, 781−785.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00235. 1 H and 13C{1H} NMR and ESI MS spectra of all organic products (PDF) Optimized Cartesian coordinates for DFT-calculated structures of 2a with S = 1/2 and S = 3/2 (XYZ) Accession Codes

CCDC 1866264−1866266 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: (+43) 1 58801 163611. Fax: (+43) 1 58801 16399. ORCID

Luis F. Veiros: 0000-0001-5841-3519 Marc Pignitter: 0000-0002-5793-8572 Karl Kirchner: 0000-0003-0872-6159 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by the Austrian Science Fund (FWF) is gratefully acknowledged (Project No. P29584-N28). L.F.V. acknowledges Fundaçaõ para a Ciência e Tecnologia, UID/ QUI/00100/2013.

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REFERENCES

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Article

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