Synthesis, Structure, and Reactivity Study of Iron(II) Complexes with

Article pubs.acs.org/Organometallics

Synthesis, Structure, and Reactivity Study of Iron(II) Complexes with Bulky Bis(anilido)thioether Ligation Jie Xiao and Liang Deng* State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai, People’s Republic of China 200032 S Supporting Information *

ABSTRACT: The synthesis, molecular structure, and ligand substitution reactivity of iron(II) complexes bearing the bulky N,N′dimesityl-2,2′-diamidophenyl sulfide ligand have been studied. The ligand H2(mesNSN) (1) was synthesized by a Pd-mediated Buchwald−Hartwig amination method. An amine elimination reaction between 1 and [Fe(NTMS2)2]2 afforded the high-spin complex [(mesNSN)Fe(THF)] (2), displaying a distorted trigonal-monopyramidal geometry. Interaction of 2 with PMe3 and 2,5di-tert-butylimidazol-1-ylidene (IBut) gave the ligand substitution products [(mesNSN)Fe(PMe3)] (3) and [(mesNSN)Fe(IBut)] (4), respectively. Both 3 and 4 are high spin and display molecular geometry similar to that of 2. The reaction of 2 with 3 equiv of isocyanide gave the low-spin complexes [(mesNSN)Fe(CNR)3] (R = But (5), Ph-2,6-Me2 (6)). Recrystallization of 6 has led to the isolation of the carbon−sulfur bond cleavage product [(mesNS)Fe(CNPh-2,6-Me2)3] (7). Quite unexpectedly, the interaction of 2 with 3-hexyne and deuterated benzene could induce Fe−N(amido) bond cleavage, giving [(mesHNSN)2Fe(THF)] (8) and [(mesHNSN)2Fe] (9), respectively. The formation of 7−9 suggests the lability of the [(mesNSN)Fe] fragment, which could suffer from degradation in the presence of bulky strong field ligands.

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pyridine,10 and o-phenylenediamido11 constitute the few examples (Chart 1). The evident of this scarcity is quite

INTRODUCTION Bulky amido anions are useful ligands for the construction of iron complexes with unusual structural features, providing unparalleled opportunities to explore the versatile chemical and physical properties of the iron compounds.1 For example, the bis(trimethylsilyl)amido anion [N(TMS)2]−, as the simplest bulky amido ligand, could coordinate to an iron(II) center to furnish the low-coordinate iron(II) compound [Fe(N(TMS)2)2]2, which is a very useful precursor for the preparation of iron complexes.1,2 The more bulky anilido ligands [NHC6H3-2,6-Ar2]− (Ar = Mes, Dipp) are able to stabilize two-coordinated iron complexes [Fe(NHC6H3-2,6-Ar2)2] with large quenching of first-order orbital angular momentum.3 The trianionic ligands [N(o-C6H4NR)3]3−,4 [N(CH2CONAr)3]3‑,5 [tpaAr]3− (tpa = tris(pyrrolylmethyl)amine),6a−c and [tpeMes]3− (tpe = tris(pyrrolyl)ethane)6d,e could support trigonal-monopyramidal iron centers, offering unique platforms to study ironmediated small-molecule activation and carbon−hydrogen bond hydroxylation. Recently, a category of hexadentate amido ligands has been developed. Their application in iron chemistry has resulted in the successful preparation of tri- and hexanuclear iron complexes having unusual redox and magnetic properties.7 We note that the bulky amido ligands applied in iron chemistry are dominated by mono- and trianionic species, whereas dianionic ligands are rare; 1,8-bis(silylamido)naphthalene, 8 bis(enamido)pyridine, 9 2,6-bis(anilido)© 2011 American Chemical Society

Chart 1. Representative Bulky Dianionic Amido Ligands in Iron Complexes

surprising, as dianionic amido ligands are readily available and their application in early-transition-metal chemistry has been widely studied. In view of this status quo, we decide to set the stage for a systematic study of iron chemistry under bulky dianionic amido ligation. With respect to this goal, we report herein the synthesis, structure, and reactivity study of iron(II) complexes bearing bulky dianionic bis(anilido)thioether ligation. Received: October 21, 2011 Published: December 15, 2011 428

dx.doi.org/10.1021/om201010a | Organometallics 2012, 31, 428−434

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and Hidai13 and applied as tridentate ligands in zirconium and ruthenium chemistry. Very recently, the parent ligand [NSN]2− was used as a surrogate for the cyclopentadienyl anion in tantalum chemistry.14 Four-Coordinated Complexes [(mesNSN)FeL] (L = THF, PMe3, IBut). Treatment of H2(mesNSN) (1) with 1 equiv of Fe(N(TMS)2)2 in THF, after workup, gave the yellow ferrous complex [(mesNSN)Fe(THF)] (2) in 68% yield (Scheme 2). Complex 2 is air- and moisture-sensitive and is soluble in lowpolarity organic solvents such as THF and Et2O. In d8-THF, its 1 H NMR spectrum shows nine broad peaks in the range −38 to +47 ppm, indicating unconstrained rotation of the mesityl and THF moieties. A solution magnetic moment measurement by the Evans method gave μeff = 4.4(2) μB. This value is in line with the spin-only value for a quintet ground state. The molecular structure of 2 in the solid state has been established by a single-crystal X-ray diffraction study. As shown in Figure 1, 2 displays pseudo-Cs symmetry, in which the iron center is four-coordinated with one tridentate ligand [MesNSN]2− and one THF molecule, forming a heavily distorted trigonal monopyramidal geometry. Selected structural parameters of 2 are compiled in Table 1. Important structural features for 2 include (1) coplanarity of the iron center with the N(1)−N(2)−O(1) plane, with the sum of the three angles around Fe(1) being 354.5(2)°, (2) out-of-vertical alignment of the S(1)−Fe(1) bond toward the N(1)−N(2)−O(1)−Fe(1) plane having an S(1)−Fe(1)−O(1) angle of 135.2(1)°, (3) a larger N(1)−Fe(1)−N(2) angle compared with those observed in the five- and six-coordinated Zr, Ru, and Ta complexes,12,13 and (4) an Fe(1)−S(1) separation (2.480(1) Å) longer than those observed in the high-spin ferrous complexes with tris(thioether) ligation.15 These structural features point to a weak Fe−S interaction, which is found quite commonly in the other [(mesNSN)Fe] fragments (vide infra).

RESULTS AND DISCUSSION Synthesis of the Ligand. The bulky ligand N,N′dimesityl-2,2′-diamidophenyl sulfide (H2(mesNSN), 1) was prepared by a palladium-catalyzed coupling reaction between 2,2′-diamidophenyl sulfide and an excess amount of mesityl bromide in 78% yield (Scheme 1). Compound 1 is a new Scheme 1. Preparation of the Ligand H2(mesNSN)

member of the bis(anilido)thioether ligand family. Similar ligands with less sterically demanding substituents, including H2(PrNSN),12 H2(BuNSN),12 H2(xyNSN),13 and H2(xyfNSN)13 (xy = 3,5-dimethylphenyl, xyf = 3,5-ditrifluoromethylphenyl) (Chart 2), have been independently developed by Schrock12 Chart 2. The Diamidophenyl Sulfide Ligand Family

Scheme 2. Preparation of the Iron(II) Complexes

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Figure 1. Molecular structures of [(mesNSN)Fe(THF)] (2, left), [(mesNSN)Fe(PMe3)] (3, middle), and [(mesNSN)Fe(IBut)] (4, right), showing 30% probability ellipsoids and partial atom-numbering schemes.

Table 1. Selected Bond Lengths (Å) and Angles (deg) of Compounds 2−4 and 6 from X-ray Diffraction Studies

a

complex

geomc

α

β

γa

Fe−N(1)

Fe−N(2)

Fe−S

Fe−Xb

2 3 4 6

TMP TMP TMP octahedral

135.2(1) 124.7(1) 120.8(1)

136.4(2) 131.9(2) 122.3(1) 92.63(7)

354.5(2) 357.3(2) 358.4(1)

1.951(4) 1.960(4) 1.995(2) 2.033(2)

1.946(4) 1.967(4) 2.016(2) 2.113(2)

2.480(1) 2.489(1) 2.523(1) 2.262(1)

2.036(3) 2.431(1) 2.155(2)

γ = ∠N1−Fe−N2 + ∠N1−Fe−X + ∠N2−Fe−X. bX = O in 2, P in 3, and C in 4. cTMP = trigonal monopyramidal.

isocyanide-coordinated complexes are diamagnetic, and their H NMR spectra display resonances in the range 0−8 ppm. For 5, the 2:3 integral ratio of the methyl protons on the mesityl moieties (1.95, 2.26, and 2.29 ppm) to those of the tert-butyl groups (0.88 and 0.97 ppm) clearly demonstrates the presence of three ButNC ligands. Due to overlapping, the 1H NMR spectrum of 6 is less informative in revealing its formulation, but an X-ray single-crystal diffraction study has unequivocally established its structure. As shown in Figure 2, 6 adopts a

Complex 2 can readily undergo ligand substitution reactions, as the interaction of 2 with 1 equiv of trimethylphosphine or 2,5-di-tert-butylimidazol-1-ylidene (IBut)16 could result in replacement of THF by the corresponding ligand, giving [(mesNSN)Fe(PMe3)] (3) or [(mesNSN)Fe(IBut)] (4) in high yield (Scheme 2). Complexes 3 and 4 have been characterized by 1H NMR, elemental analyses, and X-ray diffraction studies. The 1H NMR spectra in C6D6 show eight broad peaks in the range −56 to +59 ppm for 3 and 11 peaks in the range −87 to +53 ppm for 4, revealing free and restricted rotation of the mesityl groups in 3 and 4, respectively. Consistent with the case for 2, both 3 and 4 have magnetic moments around 4.5 μB, indicative of their high-spin electronic configuration. X-ray diffraction studies revealed that 3 and 4 have a distorted-trigonal-monopyramidal geometry similar to that of 2 (Figure 1). For comparison, their selected bond distances and angles within the trigonal monopyramid are compiled in Table 1. A close examination of these data shows that the S−Fe−X (X = O, P, C) (α) and N(1)−Fe−N(2) (β) angles decrease in the order 2 > 3 > 4, while their Fe−N and Fe−S distances increase the other way around. These trends could be ascribed to the increasing bulkiness of the ancillary ligand from THF to PMe3 and to IBut. Reaction of [(mesNSN)Fe(THF)] with Isocyanides. The reactivity of 2 with isocyanides differs from the aforementioned ligand substitution reactions. Interaction of 2 with 3 equiv of ButNC and 2,6-Me2-PhNC in THF afforded [(mesNSN)Fe(CNBut)3] (5) and [(mesNSN)Fe(CNPh-2,6-Me2)3] (6), respectively, as red crystalline solids (Scheme 2). Complexes 5 and 6 have been characterized by 1H and 13C NMR and infrared spectroscopy, as well as elemental analyses. Both of the

1

Figure 2. Molecular structure of [(mesNSN)Fe(CNPh-2,6-Me2)3] (6), showing 30% probability ellipsoids and a partial atom-numbering scheme.

distorted-octahedral structure with the [mesNSN]2− ligand binding to the iron center in a facial fashion. Its Fe−N(amido) bond distances (2.033(2) and 2.113(2) Å) are slightly longer than those of 2−4, but the Fe−S bond (2.262(1) Å) is 430


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reminiscent of those in the ferric complex [(C6F5NS)2Fe]−.18 The observation of the N-mesityl-o-amidobenzenethiolato ligand suggests a carbon−sulfur bond cleavage step in the conversion of 6 to 7. Despite the fact that the reaction mechanism is unclear, steric congestion between the bulky mesityl and 2,6-dimethylphenyl groups as revealed by long Fe− N(amido) separations in 6 (Table 1) might contribute to the instability of 6. Reactions of [(mesNSN)Fe(THF)] with 3-Hexyne and C6D6. In addition to the aforementioned monodentate ligands, we also examined the reactivity of 2 toward H2, Et3SiH, PhCHCH2, and EtCCEt; no reaction was observed when treating a THF solution of 2 with H2, Et3SiH, or PhCHCH2, but a noticeable color change from yellow to brown took place when treating the solution of 2 with 3 equiv of EtCCEt (Scheme 2). Recrystallization of the brown solution afforded the yellow solid [(mesHNSN)2Fe(THF)] (8) in 46% yield. Complex 8 is paramagnetic, as indicated by broad resonances in its 1H NMR spectrum. An X-ray diffraction study showed that this bis(amido)iron complex has pseudo-C2 symmetry, in which the iron center has a trigonal-bipyramidal geometry with long Fe−S (2.558(1), 2.582(4) Å), Fe−N(amido) (1.991(2), 1.993(3) Å), and Fe−O(THF) (2.136(2) Å) separations (Figure 4). Two appending amine side arms are dangling out of the coordination sphere and have N−H···π interactions with their neighboring mesityl rings (H···arene center distances 2.708 and 2.640 Å).19 The isolation of 8 rather than the alkyne-coordinated complex (mesNSN)Fe(η2-EtCCEt) is quite unexpected. We believe its formation might result from an alkyne-induced degradation process, presumably via the intermediate ( mes NSN)Fe(η 2 -EtCCEt), ( mes NSN)Fe(η 4 -C 4 Et 4 ), or ( mesNSN)Fe(η6-C6Et6), rather than protonation by the presence of a fortuitous proton. On the basis of this assumption, the reaction of 2 with benzene was attempted. Dissolution of 2 in C6D6 gave a red-brown solution which shows a distinct 1H NMR spectrum in comparison to that of 2 in d8-THF. Recrystallization of the solution by vapor diffusion yielded a small amount of yellow crystals, whose structure has been characterized by XRD as [(mesHNSN)2Fe] (9). As depicted in Figure 4, 9 displays Ci symmetry. Its ferrous ion

significantly shorter. The three isocyanide ligands are tightly bonded to the iron center with average Fe−C(isocyanide) distances around 1.801(1) Å, which are in line with those in other low-spin iron(II) isocyanide compounds, such as [Fe(CNBut)4(CN)2]17a and [Fe(CNPh-2,6-Me2)4Cl2].17b Although 5 and 6 are isostructural, they exhibit distinct stability in solution. Under an N2 atmosphere, the red solution of 5 in THF could be stored for weeks without a noticeable color change. However, a color change from red to greenishbrown was observed when performing recrystallization of 6 in THF, from which a small amount of green crystals of [(mesNS)Fe(CNPh-2,6-Me2)3] (7) has been isolated. The very low yield of 7 makes its full characterization difficult, but its structure has been confirmed by an X-ray diffraction study. As shown in Figure 3, 7 has a trigonal-bipyramidal geometry in

Figure 3. Molecular structure of [(mesNS)Fe(CNPh-2,6-Me2)3] (7), showing 30% probability ellipsoids and a partial atom-numbering scheme. Selected distances (Å) and angles (deg): Fe(1)−S(1) = 2.220(1), Fe(1)−N(1) = 1.884(2), Fe(1)−C(16) = 1.817(2), Fe(1)− C(25) = 1.793(3), Fe(1)−C(34) = 1.843(3); C(25)−Fe(1)−C(16) = 94.8(1), N(1)−Fe(1)−C(16) = 141.1(1), N(1)−Fe(1)−C(25) = 123.6(1), N(1)−Fe(1)−S(1) = 85.47(6).

which the iron center is coordinated with one N-mesityl-oamidobenzenethiolato ligand and three isocyanide molecules. The Fe−S and Fe−N bond distances in 7 are found to be

Figure 4. Molecular structures of [(mesHNSN)2Fe(THF)] (8, left) and [(mesHNSN)2Fe] (9, right), showing 30% probability ellipsoids and partial atom-numbering schemes. Selected distances (Å) and angles (deg): for 8, Fe(1)−S(1) = 2.558(1), Fe(1)−S(1) = 2.526(3), Fe(1)−N(1) = 1.991(2), Fe(1)−N(3) = 1.993(3), Fe(1)−O(1) = 2.136(2), N(1)−Fe(1)−N(3) = 131.3(1), S(1)−Fe(1)−S(2) = 168.6(1), N(1)−Fe(1)−O(1) = 114.6(1), N(3)−Fe(1)−O(1) = 114.1(1); for 9: Fe(1)−S(1) = 2.480(1), Fe(1)−N(1) = 1.969(2), N(1)−Fe(1)−S(1) = 82.88(5), N(1)−Fe(1)− S(1A) = 97.12(5). 431


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APEX CCD-based diffractometer equipped with an Oxford lowtemperature apparatus. Data were collected with scans of 0.3 s/frame for 30 s. Cell parameters were retrieved with SMART software and refined using SAINT software on all reflections. Data integration was performed with SAINT, which corrects for Lorentz−polarization and decay. Absorption corrections were applied using SADABS.21 Space groups were assigned unambiguously by analysis of symmetry and systematic absences determined by XPREP. All structures were solved and refined using SHELXTL.22 Metal and first-coordination-sphere atoms were located from direct-methods E maps; other non-hydrogen atoms were found in alternating difference Fourier synthesis and leastsquares refinement cycles and during final cycles were refined anisotropically. Hydrogen atoms were placed in calculated positions employing a riding model. Final crystal parameters and agreement factors are reported in Table S1. Preparation of N,N′-Dimesityl-2,2′-diamidophenyl Sulfide (H2(mesNSN), 1). A 250 mL round-bottomed flask equipped with a nitrogen inlet was charged with bis(2-aminophenyl) sulfide (1.30 g, 6.00 mmol), tris(dibenzylideneacetone)dipalladium (0.266 g, 0.29 mmol), rac-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (0.463 g, 0.74 mmol), sodium tert-butoxide (1.70 g, 17.7 mmol), toluene (80 mL), and mesityl bromide (10.5 mL, 69.6 mmol). The reaction mixture was refluxed at 110 °C under a nitrogen atmosphere for 48 h. After it was cooled to room temperature, the mixture was quenched with saturated NH4Cl aqueous solution and extracted with methylene chloride. The extracts were combined, dried with anhydrous MgSO 4, and concentrated to dryness under reduced pressure to afford a brown oil. This crude product was purified via flash column chromatography (SiO2, 200−300 mesh, CH2Cl2/n-hexanes, 1/4, as eluent) to give a pale pink solid (2.12 g, 78% yield). 1H NMR (300 MHz, CDCl3): δ 1.90 (s, 12H, o-CH3), 2.24 (s, 6H, p-CH3), 5.92 (s, 2H, NH), 6.08 (d, J = 8.1 Hz, 2H, C6H4), 6.61 (t, J = 7.5 Hz, 2H, C6H4), 6.84 (s, 4H, Me3C6H2), 6.98 (t, J = 7.5 Hz, 2H, C6H4), 7.38 (d, J = 7.8 Hz, 2H, C6H4). 13C NMR (75 MHz, CDCl3): δ 17.7, 20.8, 111.7, 116.0, 117.8, 129.0, 129.4, 133.9, 134.8, 135.7, 136.1, 146.5. MALDI MS: calcd for C30H32N2SNa+, m/z 475.2178; found, 475.2186. Preparation of [(mesNSN)Fe(THF)] (2). To a solution of N,N′dimesityl-2,2′-diamidophenyl sulfide (1; 45.2 mg, 0.10 mmol) in THF (15 mL) was added [Fe(NTMS2)2]2 (38 mg, 0.05 mmol) at room temperature. The yellow solution was stirred overnight at room temperature and then filtered. After removal of the solvent, the solid residue was dissolved in diethyl ether (6 mL) and n-hexane (1 mL) was added. Slow evaporation of Et2O afforded the product as a yellow crystalline solid (39.3 mg, 68%). The 1H NMR spectrum of this paramagnetic complex displayed nine characteristic peaks in the range −150 to +150 ppm in d8-THF. 1H NMR (400 MHz, d8-THF): δ −38.35 (s, 4H, OC4H8), −5.43 (s, 4H, OC4H8), 2.45 (s, 2H, C6H4), 21.78 (s, 2H, C6H4), 24.82 (s, 6H, p-CH3), 28.53 (s, 2H, C6H4), 32.54 (s, 12H, o-CH3), 37.43 (s, 2H, C6H4), 46.92 (s, 4H, Me3C6H2). Magnetic susceptibility (C6D6): μeff = 4.4(2) μB. Anal. Calcd for C34H38FeN2OS: C, 70.58; H, 6.62; N, 4.84. Found: C, 69.90; H, 7.01; N, 5.03. Preparation of [(mesNSN)Fe(PMe3)] (3). To a yellow solution of 2 (0.115 g, 0.20 mmol) in diethyl ether (15 mL) was added PMe3 (0.80 mL, 0.30 M in n-hexane, 0.24 mmol). After the mixture was stirred overnight at room temperature, the color of the solution changed to red. After filtration, the filtrate was concentrated to about 5 mL and n-hexane (1 mL) was added. Slow evaporation of Et2O afforded the product as a red crystalline solid (60.6 mg, 52%). The 1H NMR spectrum of this paramagnetic complex displayed eight characteristic peaks in the range −100 to +100 ppm. 1H NMR (400 MHz, C6D6): δ −56.01, −4.92, 38.46, 38.83, 40.28, 47.05, 57.32, 58.28. Magnetic susceptibility (C6D6): μeff = 4.5(1) μB. Anal. Calcd for C33H39FeN2PS: C, 68.04; H, 6.75; N, 4.81. Found: C, 67.38; H, 6.95; N, 4.72. Preparation of [(mesNSN)Fe(IBut)] (4). In a long test tube, a solution of 2,5-di-tert-butylimidazol-1-ylidene (IBut; 18.0 mg, 0.10 mmol) in n-hexane (4 mL) was carefully layered on a solution of 2 (57.8 mg, 0.10 mmol) in diethyl ether (5 mL). Slow diffusion over 4 days afforded the product as a yellow crystalline solid (30.9 mg, 45%).

sits on the inversion center and is bonding with two monoanionic bidentate amido thioether ligands [mesHNSN]− having Fe−N(amido) and Fe−S bond distances of 1.969(2) and 2.480(1) Å, respectively. Similar to the case for 8, two appending amine side arms were also observed in the molecular structure of 9. These results, in addition to the isolation of 7, suggest the instability of the [(mesNSN)Fe] fragment when interacting with sterically demanding strong field ligands.

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CONCLUSION In this report, we have studied the synthesis, structure, and ligand substitution reactivity of the iron(II) complex [(mesNSN)Fe(THF)] (2) having bulky dianionic bis(anilido)thioether ligation. Complex 2 has a high-spin electronic configuration and adopts a distorted-trigonal-monopyramidal geometry. Depending on both the steric and electronic properties of the ancillary ligands, the four-coordinated iron(II) complex displays versatile reactivity when treated with different ancillary ligands. The reaction of 2 with PMe3 and IBut resulted in replacement of the THF ligand, giving [(mesNSN)Fe(PMe3)] (3) and [(mesNSN)Fe(IBut)] (4), respectively, both of which are high spin and have a distorted-trigonal-monopyramidal geometry. When 2 was reacted with isocyanides, which are sterically less demanding and strong field ligands, the low-spin octahedral complexes [( mes NSN)Fe(CNBu t ) 3 ] (5) and [(mesNSN)Fe(CNPh-2,6-Me2)3] (6) were obtained. All these iron(II) complexes have a [(fac-mesNSN)Fe] motif. In addition to ligand substitution/coordination, “noninnocent” reactivity within the [(mesNSN)Fe] fragment has been found in these iron(II) complexes. The observation of conversions of [( mes NSN)Fe(CNPh-2,6-Me 2 ) 3 ] (6) to [(mesNS)Fe(CNPh-2,6-Me2)3] (7) and of [(mesNSN)Fe(THF)] (2) to [( m e s HNSN) 2 Fe(THF)] (8) and [(mesHNSN)2Fe] (9) revealed the instability of the [(mesNSN)Fe] fragment, which could suffer from degradation in the presence of bulky strong field ligands. With this understanding, we are now modifying the bis(anilido) ligand, aiming to enforce its bonding with the iron center.

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EXPERIMENTAL SECTION

General Procedures. All experiments were performed under an atmosphere of dry dinitrogen with the rigid exclusion of air and moisture using standard Schlenk or cannula techniques or in a glovebox. All organic solvents were freshly distilled from sodium benzophenone ketyl immediately prior to use. [Fe(NTMS2)2]22 and 2,5-di-tert-butylimidazol-1-ylidene (IBut)16 were prepared according to literature methods. All chemicals were purchased from either Strem or J&K Chemical Co. and used as received unless otherwise noted. 1H and 13C NMR spectra were recorded on a Varian Mercury 300 or 400 MHz spectrometer. All chemical shifts were reported in δ units with reference to the residual protons of the deuterated solvents for proton chemical shifts and the 13C of deuterated solvents for carbon chemical shifts. MALDI/DHB mass spectra were recorded with an IonSpec 4.7 T FTMS spectrometer. GC/MS was performed on a Shimadzu GCMS-QP2010 Plus spectrometer. Elemental analysis was performed by the Analytical Laboratory of the Shanghai Institute of Organic Chemistry (CAS). Magnetic moments were measured at 23 °C by the method originally described by Evans with stock and experimental solutions containing a known amount of a (CH3)3SiOSi(CH3)3 standard.20 Infrared spectra were obtained from KBr pellets prepared in the glovebox on a Perkin-Elmer 1600 Fourier transform spectrometer. X-ray Structure Determinations. The structures of the seven compounds in Table S1 (Supporting Information) were determined. Crystals were coated with Paratone-N oil and mounted on a Bruker 432


Organometallics The 1H NMR spectrum of this paramagnetic complex displayed 11 characteristic peaks in the range −100 to +100 ppm. 1H NMR (400 MHz, C6D6): δ −86.41, −36.43, −17.88, −15.40, −6.65, 24.15, 26.91, 32.45, 37.15, 38.22, 53.24. Magnetic susceptibility (C6D6): μeff = 4.6(2) μB. Anal. Calcd for C41H50FeN4S: C, 71.70; H, 7.34; N, 8.16. Found: C, 71.36; H, 7.34; N, 7.71. Preparation of [(mesNSN)Fe(CNBut)3] (5). To a solution of 2 (57.8 mg, 0.10 mmol) in THF (10 mL) was added ButNC (1.0 mL, 0.30 M in n-hexane, 0.30 mmol). The reaction mixture was stirred overnight at room temperature, providing a red solution. After filtration and removal of the solvent, the red residue was dissolved in diethyl ether (6 mL) and n-hexane (1 mL) was added. Slow evaporation of Et2O afforded the product as a red crystalline solid (49.1 mg, 65%). 1H NMR (400 MHz, C6D6): δ 0.88 (18H, C(CH3)3NC), 0.96 (9H, C(CH3)3NC), 1.95 (6H, p-CH3), 2.26− 2.29 (12H, o-CH3), 6.22−6.28 (4H, Me3C6H2), 6.82−6.89 (6H, C6H4), 7.71−7.73 (2H, C6H4). 13C NMR (100 MHz, C6D6): δ 19.81, 20.85, 22.00, 29.71, 30.27, 56.07, 56.28, 109.2, 115.5, 123.5, 128.9, 129.2, 129.5, 130.2, 132.4, 135.5, 138.7, 152.8, 161.8, 162.4, 165.0. IR (KBr, cm−1): νCN 2170 (s), 2132 (s). Anal. Calcd for C45H57FeN5S: C, 71.50; H, 7.60; N, 9.27. Found: C, 71.43; H, 7.74; N, 9.02. Preparation of [(mesNSN)Fe(CNPh-2,6-Me2)3] (6). Method 1. In a long test tube, a solution of 2,6-dimethylphenyl isocyanide (CNPh-2,6-Me2) (39.3 mg, 0.30 mmol) in n-hexane (4 mL) was layered on a solution of 2 (57.8 mg, 0.10 mmol) in diethyl ether (5 mL). Slow diffusion over 2 days afforded the product as a red crystalline solid (36 mg, 40%). 1H NMR (400 MHz, C6D6): δ 1.97 (3H, Me 3 C 6 H 2 ), 2.07−2.11 (18H, Me 2 C 6 H3 NC), 2.16 (6H, Me3C6H2), 2.23 (6H, Me3C6H2), 2.30 (3H, Me3C6H2), 6.31−6.39 (3H, Me2C6H3NC), 6.60−6.62 (4H, C6H4), 6.68−6.70 (3H, Me2C6H3NC), 6.75−6.79 (4H, C6H4), 6.88−6.93 (2H, Me3C6H2), 6.99 (1H, Me2C6H3NC), 7.38−7.39 (1H, Me2C6H3NC), 7.55−7.57 (1H, Me2C6H3NC), 7.78−7.80 (2H, Me3C6H2). Due to the low solubility of 6 in C6D6 and d8-THF, a satisfactory 13C NMR spectrum was not obtained. IR (KBr, cm−1): νCN 2139 (s), 2092 (s). Anal. Calcd for C57H57FeN5S: C, 76.07; H, 6.38; N, 7.78. Found: C, 75.25; H, 6.22; N, 7.90. Method 2. To a solution of 2 (57.8 mg, 0.10 mmol) in THF (10 mL) was added was added 2,6-dimethylphenyl isocyanide (39.3 mg, 0.30 mmol) at room temperature. The reaction mixture was stirred overnight and then filtered. The filtrate was concentrated to ca. 4 mL. Slow evaporation of THF afforded the product as a red crystalline solid (19 mg, 21%). The composition of this material was identical with that of the product from method A. Anal. Calcd for C57H57FeN5S: C, 76.07; H, 6.38; N, 7.78. Found: C, 75.41; H, 6.98; N, 6.95. A very small quantity of platelike green crystals was separated from the bulk product and shown to be [(mesNS)Fe(CNPh-2,6-Me2)3] (7) by an X-ray structure determination. Preparation of [(mesHNSN)2Fe(THF)] (8). To a solution of 2 (57.8 mg, 0.10 mmol) in diethyl ether (10 mL) was added 3-hexyne (24.6 mg, 0.30 mmol, dried with CaH2) at room temperature. The reaction mixture was stirred overnight, providing a brown solution. After filtration, the filtrate was concentrated to about 5 mL and nhexane (1 mL) was added. Slow evaporation of Et2O afforded the product as a yellow crystalline solid (24 mg, 46%). 1H NMR (400 MHz, C6D6): δ 1.36−1.39 (4H, OC4H8), 1.89−2.08 (36H, Me3C6H2), 3.52−3.57 (4H, OC4H8), 6.04−6.22 (6H, Me3C6H2), 6.50−6.83 (16H, C6H2), 7.47−7.49 (2H, Me3C6H2). Magnetic susceptibility (C6D6): μeff = 4.8(2) μB. Anal. Calcd for C64H70FeN4OS2: C, 74.54; H, 6.84; N, 5.43. Found: C, 74.21; H, 6.94; N, 5.38. Isolation of [(mesHNSN)2Fe] (9). Dissolution of 2 (11.5 mg, 0.02 mmol) in C6D6 (0.5 mL) gave a red-brown solution. Slow vapor diffusion of n-hexane into the solution afforded a small amount of yellow crystals, whose structure has been established as [(mesHNSN)2Fe] (9) by a single-crystal X-ray diffraction study.

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ASSOCIATED CONTENT

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AUTHOR INFORMATION

Article

* Supporting Information A table and CIF files giving X-ray crystallographic data. This material is available free of charge via the Internet at http:// pubs.acs.org. S

Corresponding Author *[email protected].

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ACKNOWLEDGMENTS This research was financially supported by the National Basic Research Program of China (973 Program, No. 2011CB808705) and the National Natural Science Foundation of China (Nos. 21002114 and 20872168).

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REFERENCES

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