Dianion and Monoanion Ligation of 1,4-Diaza-1,3-butadiene to

Article pubs.acs.org/Organometallics

Dianion and Monoanion Ligation of 1,4-Diaza-1,3-butadiene to Barium, Strontium, and Calcium Tarun K. Panda,†,‡ Hiroshi Kaneko,† Olaf Michel,§ Kuntal Pal,† Hayato Tsurugi,† Karl W. Törnroos,§ Reiner Anwander,§, ∥ and Kazushi Mashima*,† †

Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan Department of Chemistry, Indian Institute of Technology Hyderabad, Ordnance Factory Estate, Yeddumailaram 502205, Andhra Pradesh, India § Department of Chemistry, University of Bergen, Allégaten 41, 5007 Bergen, Norway ∥ Institut für Anorganische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany ‡

S Supporting Information *

ABSTRACT: Two synthetic protocols, a salt metathesis reaction and a direct metalation, were developed for preparing 1,4diaza-1,3-butadiene complexes of barium, strontium, and calcium, in which 1,4-diaza-1,3-butadiene serves as a dianionic or monoanionic ligand. A salt metathesis reaction of BaI2 with the dipotassium salt of N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3butadiene (1; abbreviated (Dip)2DAD) afforded the iodide-bridged dinuclear complex [[K((Dip)2DAD)(THF)2][Ba(μI)(THF)2]]2 (2) bearing a dianionic ene-diamide ligand, while the reaction of MI2 (M = Sr, Ca) with the dipotassium salt of 1 gave the mononuclear complexes [M((Dip)2DAD)[THF]4] (4, M = Sr; 5, M = Ca). A direct metalation reaction of barium powder with (Dip)2DAD in the presence of iodine (10 mol%) afforded an iodide-bridged dinuclear complex, [Ba((Dip)2DAD)(μ-I)(THF)2]2 (3), in which (Dip)2DAD coordinates as a monoanionic ligand to the barium center, as was evident from the X-ray analysis and the EPR spectral data. The products from the direct metalation reaction of Sr and Ca powders with 1 in the presence of a catalytic amount of iodine (1 mol%) resulted in the formation of mononuclear complexes 4 and 5 bearing the dianionic ene-diamide DAD ligand.

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INTRODUCTION Homoleptic and heteroleptic alkaline-earth-metal complexes intrigue organometallic chemists because their structural and chemical behaviors reflect the oxophilic and electropositive nature of alkaline-earth metals in relation to those of early dtransition metals.1 Various nitrogen-based ancillary ligands, such as tris(pyrazolyl)borates,2 aminotroponiminates,3 βdiketiminates,4 and bis(imino)pyrroles,5 have been employed for the preparation of alkaline-earth-metal complexes, revealing that the catalytic activity and selectivity of the alkaline-earthmetal complexes can be controlled via the well-defined nitrogen-based ligand architecture. The 1,4-diaza-1,3-butadiene ligand (DAD) is an important class of bidentate ligands due to its tunable and flexible coordination modes (A−E), depending on the type and redox properties of the central metal, as shown in Chart 1.6 The DAD ligand is widely utilized not only for early transition metals,7,8 f-block metals,9 and late transition metals,10 but also for s-block and p-block main-group elements.11−13 Recently, extensive investigations of magnesium and calcium DAD complexes demonstrated that these N,N© 2012 American Chemical Society

Chart 1. Coordination Modes of 1,4-Diaza-1,3-butadiene Ligands to Transition Metals

chelating ligands can coordinate in a σ2-monoanion (mode B), σ2-enediamido (mode C), σ2,π-enediamido (mode D), or μσ2,π-enediamido (mode E) fashion,6,11d,g and that salt metaReceived: January 24, 2012 Published: March 20, 2012 3178

dx.doi.org/10.1021/om300054h | Organometallics 2012, 31, 3178−3184

Organometallics

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Scheme 1. Preparation of Barium Complexes with Dianionic and Monoanionic (Dip)2DAD Ligands

thesis reactions were used predominantly for their synthesis. However, the structures and coordination behaviors of DAD ligands on heavier alkaline earth metals, such as Sr and Ba, have been less explored.11a,13c Moreover, direct reactions of metallic magnesium or calcium have been applied to the preparation of Mg(DAD) and Ca(DAD) complexes,11d,13a and we thus attempted to extend this method to the synthesis of DAD complexes of heavier alkaline-earth metals. Herein, we report two synthetic methodologies to obtain (Dip)2DAD complexes of the heavier group 2 metals: a salt metathesis reaction of group 2 metal diiodides with 1 equiv of the dipotassium salt of the (Dip)2DAD ligand afforded mononuclear and dinuclear group 2 metal complexes with the dianionic (Dip)2DAD ligand, while a direct reduction of the (Dip)2DAD ligand with group 2 metal powders in the presence of iodine gave the iodidebridged dinuclear barium complex with the monoanionic (Dip)2DAD ligand, and strontium and calcium complexes, ((Dip)2DAD)M(THF)4 (M = Sr, Ca), having the dianionic (Dip)2DAD ligand.

Figure 1. Molecular structure of barium complex 2. All hydrogen atoms, carbon atoms of THF molecules, and the isopropyl group of the (Dip)2DAD ligand are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ba1−N1 = 2.716(5), Ba1−N2 = 2.652(5), Ba1−O1 = 2.797(5), Ba1−O2 = 2.765(5), Ba1−I1 = 3.5662(10), Ba1−I1* = 3.5786(11), K1−N1 = 2.935(6), K1−N2 = 2.863(2), K1− I1 = 3.5436(17), N1−C1 = 1.409(4), N2−C2 = 1.416(7), C1−C2 = 1.360(8); N1−Ba1−N2 = 68.23(15), N1−K1−N2 = 62.57(15), Ba1− I1−Ba1* = 101.872(15).

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RESULTS AND DISCUSSION Two dinuclear barium complexes bearing N,N′-bis(2,6diisopropylphenyl)-1,4-diaza-1,3-butadiene (1; (Dip)2DAD), [[K((Dip)2DAD)(THF)2][Ba(μ-I)(THF)2]]2 (2) and [Ba((Dip)2DAD)(μ-I)(THF)2]2 (3), were obtained depending on the selected reaction conditions (Scheme 1). Complex 2 was prepared by the reaction of barium diiodide with the dipotassium salt of 1 in THF in 67% yield and characterized by spectral data, combustion analysis, and a single-crystal X-ray analysis. The 1H NMR spectrum of 2 in THF-d8 displayed a broad singlet at δ 5.29 assignable to the olefinic protons of the ligand backbone, along with a septet signal at δ 3.81 and a broad resonance at δ 1.15 due to the isopropyl groups of the (Dip)2DAD ligand. In the 13C{1H} NMR spectrum of 2, a resonance at δ 114.4 can be assigned to the olefinic carbon of the (Dip)2DAD ligand. These results indicated that the (Dip)2DAD ligand coordinated in a dianionic mode to the barium metal. Figure 1 shows a dimeric structure of 2, in which two iodine atoms bridge two barium atoms and each (Dip)2DAD ligand coordinates in a dianionic ene-diamide canonical form to the barium atom, as evident from the long− short−long bonding sequence of the (Dip)2DAD ligand of 2

(C−N = 1.409(8) and 1.416(7) Å and CC = 1.360(8) Å).7−9,11−13 Although the coordination of the (Dip)2DAD ligand is clearly confirmed as a dianionic bridging mode (mode E in Chart 1), there are two possible scenarios for 2: one is the contact of potassium iodide with the Ba−(Dip)2DAD unit, and the other is the interaction of the potassium cation with the [((Dip)2DAD)BaI}2 dianion, comparable to lanthanide DAD complexes showing an interaction of the Li cation with the Ln− Cl moiety.14 The mean Ba−N distance (Ba1−N1 = 2.716(5) Å and Ba1−N2 = 2.652(5) Å) is close to that of a Ba−N covalent bond.3b,4b,c,15 On the other hand, the K−N bond lengths (K1− N1 = 2.935(6) Å, K1−N2 = 2.863(2) Å) are longer than those observed for ((Dip)2DAD)K2(THF)5,9g and the Ba−I distances (Ba1−I1 = 3.5662(10) Å, Ba1−I1* = 3.5786(11) Å) for 2 are comparatively longer than those found for other Ba−I covalent bonds.16 These results suggested a strong contact of potassium iodide with the Ba−(Dip)2DAD unit. Complex 3 was obtained as a deep red powder in 15% yield (yield based on barium metal) by the direct metalation reaction of finely divided barium metal powder with 1 equiv of 1 in the 3179


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presence of iodine (10 mol%) in THF (Scheme 1). In sharp contrast to the diamagnetic complex 2, no resonance was observed in the 1H NMR spectrum of 3. Thus, complex 3 was characterized by its EPR spectrum, combustion analysis, and single-crystal X-ray analysis (vide infra). Figure 2 shows the

Figure 2. Molecular structure of barium complex 3. All hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ba1−N1 = 2.720(4), Ba1−N2 = 2.706(4), Ba1−O1 = 2.730(4), Ba1−O2 = 2.748(4), Ba1−I1 = 3.4069(5), Ba1−I1* = 3.4537(6); N1−Ba1−N2 = 62.29(13), N1− Ba1−O1 = 103.79(15), N1−Ba1−O2 = 154.58(13), N1−Ba1−I1 = 100.41(8), N1−Ba1−I1* = 101.84(9).

Figure 3. EPR spectrum of barium complex 3 in toluene at 298 K: (a) experimental; (b) simulated for 2 14N and 2 1H atoms with 5.5 G hyperfine coupling.

dinuclear iodo-bridged structure of 3, in which a monoanionic radical DAD ligand coordinates to each “BaI” unit (mode B in Chart 1). The coordination geometry around the barium atom is best described as a slightly distorted octahedron. One iodide and one nitrogen atom of the (Dip)2DAD ligand occupy the apical positions, and two oxygen atoms of the THF molecules, one nitrogen atom of the (Dip)2DAD ligand, and one iodide are located at the equatorial sites. The shortened C−N bond lengths (1.343(7) and 1.314(7) Å) and elongated C−C bond length (1.401(7) Å) of the (Dip)2DAD ligand of 3 in comparison with those in 2 are consistent with the monoanionic character of the (Dip)2DAD ligand.7−9,11−13 In addition, the Ba−N distances (Ba−N1 = 2.720(4) Å and Ba1− N2 = 2.706(4) Å) lie in the expected range of Ba−N bonds.3b,4b,c,15 As shown in Figure 3, the EPR spectrum of 3 in toluene displayed a seven-line hyperfine resonance (g = 2.003), while the spectrum was simulated by taking into account hyperfine coupling with virtually identical values (ca. 5.5 G) for two equivalent nitrogen atoms and two equivalent hydrogen atoms of the (Dip)2DAD ligand backbone.17 This g value is common for free radicals in organic compounds, indicating that an unpaired electron in 3 is predominantly localized at the (Dip)2DAD ligand. The monoanionic (Dip)2DAD ligand could be reduced to the dianionic form by the reaction of 3 with elemental potassium: treatment of complex 3 with 2 equiv of elemental potassium in THF gave the barium complex 2 in 87% yield via one-electron reduction of the monoanionic (Dip)2DAD ligand in complex 3. Remarkably, even when 0.5 equiv of iodine with respect to barium metal powder were used, the yield of 3 could not be significantly improved. Treatment of barium metal with 1 equiv of 1 in the presence of 0.5 equiv of iodine resulted in a 26% yield of 3. To gain additional insight into the formation process of 3, we conducted control experiments: (1) a mixture of (Dip)2DAD and BaI2 in THF did not afford adduct of BaI2((Dip)2DAD), (2) a mixture of (Dip)2DAD and barium

also showed no reaction, and (3) a mixture of stoichiometric amounts of Ba and BaI2 in the presence of 2 equiv of (Dip)2DAD gave complex 3 in 75% yield (Scheme 2). Scheme 2. Reactivity of (Dip)2DAD toward Barium Metal and Barium Diiodide

Accordingly, we propose that barium metal is first oxidized with iodine to generate BaI2, which is then partially reduced by barium metal, as a slow but crucial step, to give the transient species “BaI”, which is immediately oxidized by (Dip)2DAD to afford the Ba2+ complex 3. A similar methodology by a mixture of metal, metal halide, and DAD ligand, giving the corresponding DAD complexes, was reported for yttrium complexes by our group9g and for aluminum complexes by Jones et al.18 In contrast to the complexation of the (Dip)2DAD ligand to barium, (Dip)2DAD complexes of strontium and calcium [M((Dip)2DAD)(THF)4] (4, M = Sr; 5, M = Ca), in which (Dip)2DAD coordinates in a dianionic fashion to the metal (mode C in Chart 1), were prepared by both a salt metathesis reaction and a direct metalation reaction, as shown in Scheme 3. Treatment of MI2 (M = Sr, Ca) with 1 equiv of the dipotassium salt of 1 in THF gave the corresponding monomeric complexes 4 and 5 in 75% and 70% yields, respectively. Yang et al. recently reported that reaction of CaCl2 3180


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Scheme 3. Preparation of Strontium and Calcium Complexes with a Dianionic (Dip)2DAD Ligand

with 1 equiv of the dipotassium salt of N,N′-bis(2,6diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene afforded a polymeric potassium ion-contacted calcium complex of N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3butadiene.11g In addition, polymeric complexes of N,N′bis(2,6-diethylphenyl)-1,4-diaza-2,3-dimethyl-1,3-butadiene were also reported for sodium and zinc derivatives.11c,d Reactions of (Dip)2DAD with equimolar amounts of finely divided strontium and calcium metal powder activated by iodine (1 mol %) in THF respectively afforded 4 (75% yield) and 5 (50% yield) as red powders. The two complexes 4 and 5 were characterized by spectral data, combustion analysis, and single-crystal X-ray diffraction studies. In the 1H NMR spectrum of 4 in C6D6, a broad singlet at δ 5.47 was assigned to the olefinic protons of the ligand backbone, suggesting that (Dip)2DAD coordination corresponds to a dianionic enediamido ligand (mode C in Chart 1). In addition, no resonance was observed in the ESR spectrum of 4, evidencing noncontamination with any Sr complex bearing a monoanionic (Dip)2DAD ligand. The molecular structures of 4 (Figure 4) and 5 (Figure 5) revealed that the monomeric complexes adopt a distorted-octahedral geometry and feature a dianionic (Dip)2DAD ligand, as confirmed by a long−short−long bonding sequence, two longer N−C bonds (1.41 Å for 4; 1.40 Å for 5), and a shorter C−C bond (1.340(7) Å for 4; 1.356(4) Å for 5) in comparison to those of the neutral (Dip)2DAD ligand.7−9,11−13 The mean M−N distances (Sr−N = 2.46 Å for 4 and Ca−N = 2.35 Å for 5) lie in the range of M− N covalent bonds.2−6 Such different results between the barium complex 3 and strontium and calcium complexes 4 and 5 might be due to the different activities of the metal surfaces generated by the addition of iodine to the corresponding metal powders. It can be assumed that the reaction of strontium or calcium metal powder with iodine give very active Sr or Ca surfaces, which are oxidized by the (Dip)2DAD ligand without generation of the corresponding MI2. When 0.5 equiv of iodine were added in the direct metalation method employing Sr and Ca metal powders, similar to the preparation of europium and neodymium complexes having one iodide ligand per one metal center,9g paramagnetic complexes were obtained as deep red solids, respectively (see the Supporting Information). The room-temperature EPR spectra of the complexes in toluene displayed a seven-line hyperfine resonance (g = 2.0030 for the Sr complex and g = 2.0032 for the Ca complex) due to the (Dip)2DAD ligandlocalized radical.17 All attempts to isolate crystals of either Sr or Ca complexes were unsuccessful, but it can be speculated about that such Sr and Ca complexes have presumably monomeric or

Figure 4. Molecular structure of strontium complex 4. All hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Sr−N1 = 2.475(4), Sr−N2 = 2.458(5), Sr−O1 = 2.582(4), Sr−O2 = 2.448(16), Sr−O3 = 2.592(4), Sr−O4 = 2.613(4), N1−C1 = 1.410(6), N2−C2 = 1.405(8), C1−C2 = 1.340(7); N1−Sr−N2 = 74.36(15). N1−Sr−O1 = 164.73(15), N1− Sr−O2 = 105.9(3), N1−Sr−O3 = 90.08(13), N1−Sr−O4 = 118.85(13).

Figure 5. Molecular structure of calcium complex 5. All hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ca−N1 = 2.361(2), Ca−N2 = 2.335(2), Ca−O1 = 2.399(2), Ca−O2 = 2.499(2), Ca−O3 = 2.434(2), Ca−O4 = 2.399(2), N1−C1 = 1.396(3), N2−C2 = 1.401(3), C1−C2 = 1.356(4); N1−Ca−N2 = 78.50(8), N1−Ca−O1 = 96.60(8), N1−Ca− O2 = 173.69(8), N1−Ca−O3 = 92.69(7), N1−Ca−O4 = 103.68(8).

dimeric structures with one monoanionic (Dip)2DAD and one iodide ligand.

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SUMMARY We demonstrated two protocols, the salt metathesis reaction and direct metalation, to be applicable for synthesis of heavier group 2 complexes of (Dip)2DAD. Notably, the redox-active DAD ligand coordinated to barium, strontium, and calcium in a dianionic mode or monoanionic mode, depending on the 3181


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24H, 3JHH = 6.6 Hz, CH(CH3)2), 1.37 (br, 16H, β-CH2 of THF), 3.48 (br, 16H, α-CH2 of THF), 3.88 (sep, 4H, 3JHH = 6,6 Hz, CH(CH3)2), 5.55 (s, 2H, CHCH), 7.02 (t, 2H, 3JHH = 7.4 Hz, p-Ar) 7.21 (d, 4H, 3JHH = 7.4 Hz, m-Ar). 13C NMR (100 MHz, C6D6, 30 °C): δ 25.3 (CH(CH3)2), 25.6 (β-CH2 of THF), 28.7 (CH(CH3)2), 69.0 (α-CH2 of THF), 112.7 (CH CH), 122.7 (Ar), 123.4 (Ar), 143.4 (ortho-Ar), 152.8 (ipso-Ar). Anal. Calcd for C83H131N4O8Sr2: C, 66.99; H, 8.87; N, 3.76. Found: C, 66.43; H, 8.51; N, 3.58. [Ca((Dip)2DAD)(THF)4] (5) was prepared according to the same procedure as for complex 4 and obtained as a deep red powder in 70% yield, mp 124−129 °C dec. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.31 (br, 16H, β-CH2 of THF), 1.32 (d, 24H, 3JHH = 6.6 Hz, CH(CH3)2), 3.38 (br, 16H, α-CH2 of THF), 3.83 (sep, 4H, 3JHH = 6,6 Hz, CH(CH3)2), 5.67 (s, 2H, CH2), 7.13 (d, 2H, 3JHH = 7.5 Hz, p-Ar), 7.13 (t, 4H, 3JHH = 7.5 Hz, m-Ar). 13C NMR (100 MHz, C6D6, 30 °C): δ 25.4 (CH(CH3)2), 25.5 (β-CH2 of THF), 28.7 (CH(CH3)2), 68.4 (α-CH2 of THF), 121.7 (CHCH), 121.9 (Ar), 124.1 (Ar), 144.1 (ortho-Ar), 152.9 (ipso-Ar). Anal. Calcd for C42H68N2O4Ca, C, 71.56; H, 9.48; N, 4.02. Found: C, 70.93; H, 9.02; N, 3.98. Direct Metalation Method. In a Schlenk tube were placed finely divided strontium metal powder (39.0 mg, 0.445 mmol) and 1 (168 mg, 0.445 mmol, 1.0 equiv), and THF (2 mL) was added at room temperature. After addition of iodine (1.10 mg, 4.5 × 10−3 mmol, 1 mol % to Sr metal) the reaction mixture was stirred for 12 h at room temperature. After the insoluble powders were removed by filtration, all volatiles were evaporated to give 4 as a deep red powder (250 mg, 0.332 mmol, 75% yield). According to the same procedure for preparing strontium complex 4, calcium complex 5 was obtained in 50% yield. X-ray Crystallographic Studies. Single crystals of 3−5 were obtained from the corresponding saturated solution of THF at −35 °C. Each suitable crystal was mounted on a CryoLoop (Hampton Research Corp.) with a layer of light mineral oil and placed in a nitrogen stream at 120 or 173 K. Crystal data and structure refinement parameters are summarized in Table S1 in the Supporting Information. The structures of all these complexes were solved by direct methods (SIR2004)20 and refined on F2 by full-matrix least-squares methods, using SHELXL-97.21 Non-hydrogen atoms of 2−5 were anisotropically refined. H atoms were included in the refinement on calculated positions riding on their carrier atoms. The function minimized was ∑w(Fo2 − Fc2)2 (w = 1/[σ2(Fo2) + (aP)2 + bP]), where P = (Max(Fo2,0) + 2Fc2)/3 with σ2(Fo2) from counting statistics. The functions R1 and wR2 are (∑||Fo| − |Fc||)/∑|Fo| and [∑w(Fo2 − Fc2)2/∑(wFo4)]1/2, respectively. The ORTEP-3 program22 was used to draw each molecule.

reaction conditions, as evidenced by NMR or EPR measurements as well as X-ray structure analysis. Application of these two synthesis protocols for the preparation of heavier group 2 metal complexes with various redox-active ligands is an ongoing topic in our laboratory.

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EXPERIMENTAL SECTION

General Conditions. All manipulations for air- and moisturesensitive complexes were carried out under argon using standard Schlenk techniques or an argon-filled glovebox. Potassium metal and MI2 (M = Ba, Sr, Ca) were purchased from Aldrich and used as received. N,N′-Bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (1; abbreviated (Dip)2DAD, Dip = 2,6-diisopropylphenyl)19 and its dipotassium complex9g were prepared according to literature procedures. Tetrahydrofuran, pentane, toluene, benzene-d6, and THF-d8 were dried over CaH2, degassed by trap-to-trap distillation, and stored in an argon-filled glovebox. 1H NMR (300 MHz, 400 MHz) and 13C NMR (75 MHz, 100 MHz) spectra were measured on Varian Unity INOVA-300 and Bruker AvanceIII-400 spectrometers. EPR measurements were recorded at 298 K on a Bruker EMX-10/12 spectrometer in toluene. Elemental analyses were recorded with a Perkin-Elmer 2400 instrument at the Faculty of Engineering Science, Osaka University, or with an Elementar Vario MICRO instrument at the Department of Chemistry, Tübingen University. Melting points were measured in sealed tubes and were not corrected. Synthesis of [[K((Dip)2DAD)(THF)2][Ba(μ-I)(THF)2]]2 (2). To a suspension of BaI2 (391 mg, 1.00 mmol) in THF (5 mL) was added a solution of a freshly prepared dipotassium complex of (Dip)2DAD (376 mg, 1.00 mmol, 1.0 equiv) in THF (10 mL) at room temperature via a syringe. The disappearance of the white suspension of BaI2 in THF indicated the initiation of the complexation reaction. After the reaction mixture was stirred for 12 h, the reaction solution was concentrated and stored at −35 °C to give 2 as red crystals (490 mg, 0.674 mmol, 67% yield), mp 115−118 °C dec. Direct crystallization of complex 2 from the reaction solution was necessary; otherwise, a single product was not isolated from the reaction mixture, and the mother liquor of the crystallization contained unidentified products (see the Supporting Information). 1H NMR (300 MHz, THF-d8, 35 °C): δ 1.15 (d, 24H, 3JHH = 8.0 Hz, CH(CH3)2), 1.29 (br, 8H, β-CH2 of THF), 3.53 (br, 8H, α-CH2 of THF), 3.81 (sep, 4H, 3JHH = 8.0 Hz, CH(CH3)2), 5.29 (s, 2H, CHCH), 6.23−6.27 (m, 2H, p-Ar), 6.70− 6.72 (m, 4H, m-Ar). 13C NMR (75 MHz, THF-d8, 35 °C): δ 26.5 (CH(CH3)2), 28.9 (CH(CH3)2), 114.4 (CHCH), 121.5 (Ar), 123.6 (Ar), 139.7 (ortho-Ar), 141.3 (ipso-Ar). Anal. Calcd for C84H136Ba2I2K2N4O8: C, 52.10; H, 7.08; N, 2.89. Found: C, 51.83; H, 6.99; N, 2.68. Synthesis of [Ba(μ-I)((Dip)2DAD)(THF)2]2 (3). To a mixture of finely divided barium metal powder (150 mg, 0.986 mmol) and 1 (371 mg, 0.986 mmol, 1.0 equiv) in THF (5 mL) at room temperature was added iodine (25.3 mg, 0.100 mmol, 0.10 equiv). The reaction mixture was stirred for 13 h at room temperature to give a deep red suspension. After insoluble materials were removed by filtration, all volatiles were evaporated to give 3 as a deep red powder (204 mg, 0.148 mmol, 15% yield), mp 143−147 °C dec. EPR (toluene): g = 2.0031 (Aiso = 5.5 G). Anal. Calcd for C68H104I2N4O4Ba2: C, 52.02; H, 6.68; N, 3.57. Found: C, 51.45; H, 7.01; N, 3.67. Synthesis of [M((Dip)2DAD)(THF)4] (4, M = Sr; 5, M = Ca). Salt Metathesis Method. A solution of a freshly prepared dipotassium complex of (Dip)2DAD (376 mg, 1.00 mmol) in THF (10 mL) was added to a suspension of SrI2 (341 mg, 1.00 mmol, 1.0 equiv) in THF (5 mL) at room temperature via a syringe. The white suspension of SrI2 in THF gradually was consumed. The reaction mixture was stirred for 12 h at room temperature, and then the solvent was evaporated under reduced pressure. The remaining residue was extracted with toluene (15 mL). After the solvent was evaporated, the resulting solid was washed with pentane (10 mL) to give 4 as a deep red powder (564 mg, 0.750 mmol, 75% yield), mp 121− 125 °C dec. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.34 (d,

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ASSOCIATED CONTENT

S Supporting Information *

Figures, tables, text, and CIF files giving 1H NMR data for complex 2, reaction details for the preparation of Sr and Ca complexes with a monoanionic (Dip)2DAD ligand, and crystallographic data for 2−5. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 81-6-68506245. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS H.K. and O.M. thank the Global COE Program, “Global Education and Research Center for Bio-Environmental Chemistry”, of Osaka University for supporting their internship. This work was supported by the Core Research for Evolutional 3182


Organometallics

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Organometallics

Article

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