Heterometallic Potassium Rare-Earth-Metal Allyl and Hydrido

Dec 10, 2012 - The macrocyclic diamino diamine (1,7-Me2TACD)H2 (1,7-Me2TACD = 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, 1,7-Me2[12]aneN4), ...
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Heterometallic Potassium Rare-Earth-Metal Allyl and Hydrido Complexes Stabilized by a Dianionic (NNNN)-Type Macrocyclic Ancillary Ligand Peng Cui, Thomas P. Spaniol, and Jun Okuda* Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen, Germany S Supporting Information *

ABSTRACT: The macrocyclic diamino diamine (1,7-Me2TACD)H2 (1,7-Me2TACD = 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, 1,7-Me2[12]aneN4), reacted under propylene elimination with [Ln(η3-C3H5)3(diox)] (Ln = Y, La) to give the mono(allyl) complexes [(1,7-Me2TACD)Ln(η3-C3H5)]2 (Ln = Y (1a), La (1b)). A single-crystal X-ray diffraction study shows 1b to be a centrosymmetric dimer with lanthanum atoms bridged by one of the two amido nitrogen atoms. Complexes 1a,b were treated with 2 equiv of the potassium allyl KC3H5 to give the corresponding heterometallic allyl complexes [(1,7Me2TACD)Ln(η3-C3H5)2K(THF)]n (Ln = Y (2a), La (2b)). A single-crystal X-ray diffraction study revealed that 2a,b are polymeric in the solid state with allyl ligands bridging the metal centers in addition to the presence of μ2-amido functions of the 1,7-Me2TACD ligand. Hydrogenolysis of the yttrium compound 2a with 1 bar of H2 led to the formation of the heterometallic Y4K2 hydrido complex [(1,7-Me2TACD)2Y2H3K(THF)2]2 (3a), which can also be synthesized from a 1:1 mixture of 1a and KC3H5 with 1 bar of H2. A single-crystal X-ray diffraction study of 3a revealed a dimer of heterotrinuclear Y2K trihydride aggregate. Treatment of 2b with 1 bar of H2 afforded the heptanuclear La3K4 heptahydrido complex [(1,7Me2TACD)3La3H7K4(THF)7] (3b).

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INTRODUCTION In contrast to the numerous homometallic rare-earth-metal hydrido complexes, heterometallic hydrido complexes containing Ln−H−M bonds (M = s- or d-block metal) remain mostly unexplored.1,2 This may be due to the shortage of rational synthetic methods and intrinsic difficulties associated with assembling such heterometallic Ln−H−M aggregates. Since the first synthesis of a heterometallic Y/Zr polyhydrido complex by the reaction of 1/2 equiv of [(η5-C5H4Me)2ZrH2]2 with [(η5C5H4Me)2YH(THF)]2,3 only a few examples of heterometallic rare-earth-metal/d-block transition-metal hydrido complexes have been prepared, either by alkane/hydrogen elimination4 or by σ-bond/salt metathesis.5 The latter reactions are primarily based on the higher Brønsted acidity of d-block transition-metal hydrides. Recent studies have shown that reversible addition and release of H2 can be realized in heterometallic Y/W and Y/ Mo polyhydrido complexes.4e Heterometallic rare-earth-metal/ s-block metal hydrido complexes are even more sparse.6 The high polarity of both Ln−H and M−H bonds (M = s-block metal) makes these complexes highly reactive. The syntheses of such compounds are usually not straightforward, resulting © 2012 American Chemical Society

either in low yields or in the formation of unexpected products,6b,c hampering further reactivity studies. More recently, molecular main-group-metal hydrido complexes have shown some new reactivity patterns toward small molecules and have drawn attention as potential hydrogen storage materials.7 We became interested in exploring effective synthetic methods for the heterometallic hydrido complexes containing reactive Ln−H−M (M = s-block metal) aggregates. Such complexes are thought to serve as suitable precursors for other heterometallic hydrido complexes. Recent studies have shown that the (NNNN)-type macrocyclic ancillary ligand Me3TACD (Me3TACD = 1,4,7trimethyl-1,4,7,10-tetraazacyclododecane, Me3[12]aneN4), can stabilize reactive rare-earth-metal dihydrido fragments even for the largest rare-earth metal, lanthanum.2d,8 Modification of this ligand leads to the dianionic 1,7-Me2TACD ligand (1,7Me2TACD = 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, Special Issue: Recent Advances in Organo-f-Element Chemistry Received: October 21, 2012 Published: December 10, 2012 1176

dx.doi.org/10.1021/om300986w | Organometallics 2013, 32, 1176−1182

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Scheme 1. Synthesis of Allyl Complexes

1,7-Me2[12]aneN4) with Cs symmetry (disregarding ring conformations2d), which was initially thought to be a surrogate for the bis(cyclopentadienyl) scaffold. In the course of our work on Me3TACD complexes, we became aware that the amido function can form intermolecular bridges.7e,8d Therefore, it was thought that the sterically more open diamido ligand 1,7Me2TACD may be capable of assembling heterometallic Ln− H−M (M = s-block metal) aggregates. We report here on the synthesis and structure of heterometallic potassium rare-earthmetal allyl and hydrido complexes supported by this new type of diamido diamine ligand.

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RESULTS AND DISCUSSION Potassium Rare-Earth-Metal Allyl Complexes. The ligand precursor (1,7-Me2TACD)H2 was prepared according to the literature procedure.2d,9 Pure (1,7-Me2TACD)H2 was isolated as colorless crystals after purification by distillation in vacuo. Propylene elimination from [Ln(η3-C3H5)3(diox)] (Ln = Y, La; diox =1,4-dioxane) with 1 equiv of (1,7-Me2TACD)H2 in THF at room temperature smoothly afforded the mono(allyl) complexes [(1,7-Me2TACD)Ln(η3-C3H5)]2 (Ln = Y (1a), La (1b)) in good yield (Scheme 1). Whereas the yttrium complex 1a is only sparingly soluble in THF, the lanthanum homologue 1b is moderately soluble in THF. Both complexes are insoluble in aliphatic and aromatic hydrocarbons. 1a was characterized only by elemental analysis, while the lanthanum complex 1b could be fully characterized by elemental analysis and NMR spectroscopy as well as by a single-crystal X-ray diffraction study. Single crystals of the lanthanum complex 1b were obtained from THF/pentane solution at −35 °C. As shown in Figure 1, the structure consists of a centrosymmetric dimer with a La2N2 core containing amido nitrogen atoms of the 1,7-Me2TACD ligand. The short La−N bond distance of 2.388(4) Å for La1− N3 is explained by the sp2 character of this amido atom (sum of the bond angles of 358° at N3). As expected, the amido donors of the La2N2 core show significantly longer bond distances of 2.573(3) Å (La1−N1) and 2.618(3) Å (La1−N1′). The La−N bond distances involving both neutral amine atoms N2 (2.709(4) Å) and N4 (2.691(4) Å) are longer. The dianionic 1,7-Me2TACD ligand formally acts as a 10-electron donor but adopts a Cs-symmetric conformation, indicating an L2+2X2 type ligand function. This conformation is distinct from that observed in rare-earth-metal alkyl, allyl, or hydrido complexes containing the monoanionic Me3TACD ligand.2d,8 The average La−Callyl bond length of 2.84 Å is comparable to the value of 2.87 Å in [(Me3TACD)La(η3-C3H5)2]8a and of 2.80 Å in [La(η3-C3H5)3(TMEDA)].10 The La···La distance of 4.0924(5) Å excludes any bonding interaction between the lanthanum centers. In the solid state, 1b does not contain any coordinated solvent molecules, even though the reaction was performed in

Figure 1. Molecular structure of 1b with displacement parameters at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): La1−C1 = 2.834(5), La1−C2 = 2.843(5), La1−C3 = 2.828(5), La1−N1 = 2.573(3), La1− N2 = 2.709(4), La1−N3 = 2.388(4), La1−N4 = 2.691(4), La1−N1′ = 2.618(3), La1···La1′ = 4.0924(5); La1−N1−La1′ = 104.04(12), N1− La1−N1′ = 75.96(12), N1−La1−N3 = 97.66(12), N2−La1−N4 = 111.56(12).

THF. Coordination of additional donor molecules may be prevented due to the 16-electron configuration of the lanthanum center. The structure is reminiscent of that for a calcium allyl compound with the Me 3 TACD ligand, [(Me3TACD)Ca(η3-C3H5)]2.7e Treating the homometallic allyl complexes 1a,b with 2 equiv of KC3H5 in THF cleanly afforded the corresponding heterometallic potassium rare-earth-metal allyl complexes [(1,7-Me2TACD)Ln(η3-C3H5)2K(THF)]n in high yield (Ln = Y (2a), La (2b)) (Scheme 1). 2a,b are both soluble in THF but insoluble in aliphatic and aromatic hydrocarbons. They were characterized by elemental analysis and NMR spectroscopy. Single crystals of 2a,b were obtained from THF/pentane solution at −35 °C. An X-ray diffraction study on the crystal of the lanthanum complex 2b revealed a polymer of composition [(1,7-Me2TACD)La(η3-C3H5)2K(THF)]n. Because of the low quality of the crystal data set, probably due to the nonresolved disorder of additional solvent molecules in the crystal packing, the structure will not be discussed further.11 A single-crystal Xray diffraction study was also performed for the yttrium complex 2a. The arrangement within the solid state is shown in Figure 2. The metal atoms Y1 and K1 are bridged by allyl ligands and by one of the two amido nitrogen atoms of the 1,7-Me2TACD ligand, leading to a polymeric structure. The yttrium centers, bonded by four nitrogen atoms of the 1,7-Me2TACD ligand and the terminal carbon atoms of two allyl ligands, adopt a square-antiprismatic coordination geometry. The Y−N(amine) bond lengths range from 2.537(3) to 2.555 (3) Å, which are 1177

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N2−La1−N4 = 111.56(12)°). The average Y−Callyl bond length of 2.77 Å is significantly longer than that of 2.69 Å in [(Me3TACD)Y(η3-C3H5)2],8a possibly as a consequence of potassium coordination on the opposite side of the allyl ligand. The distorted-tetrahedral coordination geometry at potassium is formed by two η3-bonded allyl ligands, one amido nitrogen atom, and one THF molecule (THF is omitted in Figure 2). Although the coordination of the potassium by cyclopentadienyl-type anions or arenes is known to generate a coordination polymer,12 the formation of a π complex by allyl ligands is rare.13 In “ate” type lanthanide allyl complexes with lithium, the smaller lithium prefers binding to ether ligands to form discrete ion pairs.14 The K−Callyl bond distances indicate that one allyl ligand is nearly symmetrically η3 bonded to the potassium ion (K1−C4 = 3.283(4) Å, K1−C5 = 2.970(3) Å, K1−C6 = 3.270(3) Å), while the other is η3 bonded in an unsymmetrical fashion (K1−C1′ = 3.179(4) Å, K1−C2′ = 3.021(4) Å, K1−C3′ = 3.287(4) Å). In both allyl ligands the methine carbon atoms are closer to the potassium than the terminal carbon atoms. The average K−Callyl bond lengths of 3.16 and 3.17 Å are close to that of 3.22 Å in [Sm{η3C3H3(SiMe3)2}3{μ-K(THF)2}]213b but are longer than that of 3.06 Å in [K(dme){η3-1,3-(SiMe3)2C3H3}]∞,15 due to the interaction of the allyl group with the yttrium atom. Potassium Rare-Earth-Metal Hydrido Complexes. The heterometallic allyl complexes 2a and 2b are suitable precursors for the heterometallic hydrido complexes (Scheme 2). The reaction of 2a with 1 bar of H2 was initially performed in THF, forming only small amounts of pale yellow crystals. Once crystallized, it is only sparingly soluble in THF. The 1H NMR spectrum of this compound in THF-d8 showed two distinct sets of hydride signals at δ 5.91 (t, 1JYH = 21.6 Hz) and 4.89 ppm (dd, 1JYH = 16.4 and 20.8 Hz), two singlets at δ 2.75 and 2.62 ppm for the methyl groups, and several sets of signals in the range of 3.5−2.0 ppm for the CH2 resonances of the 1,7Me2TACD ligand backbone. The structure of 3a was determined by a single-crystal X-ray diffraction study. Figure 3 shows the molecule with a crystallographic inversion center based on a [Y(μ3-H)2Y(μ2H)2Y(μ3-H)2Y] core. Each yttrium atom is coordinated by four nitrogen atoms of the 1,7-Me2TACD ligand, leading to a coordination number of 8 for both internal metal atoms Y2 and Y2′ with square-antiprismatic geometry. The terminal Y1 and Y1′ atoms within this aggregate are seven-coordinate by additional coordination to an amido nitrogen atom of a neighboring 1,7-Me2TACD ligand. The geometry at Y1 and Y1′ can be best described as capped trigonal prismatic. Each potassium within the K(thf)2 fragments connects to two amido nitrogen atoms and two μ3-bonded hydrides. All six metal atoms are located nearly in a plane (largest deviation of 0.1881(5) Å from the mean plane formed by four yttrium and two potassium atoms). The μ2 and μ3 bonding modes of the hydride ligands observed in the crystal structure are consistent with those observed in solution. In the 1H NMR spectrum of 3a, the triplet at δ 5.91 ppm (1JYH = 21.6 Hz) can be assigned to signals due to the μ2 hydrides, by comparing the coupling constants 1JYH with those of other reported dimeric yttrium hydride complexes.1c The doublet of doublets at δ 4.89 ppm results from the μ3 hydrides in an unsymmetrical surrounding within the Y2K aggregate and the unsymmetrical coordination mode of the two 1,7-Me2TACD ligands (see below). VT-NMR studies showed no significant change of the hydride signals in the temperature range of −50 to +55 °C. Broadening of the

Figure 2. (a) Detail of the crystal structure of 2a with displacement parameters at the 50% probability level. Hydrogen atoms and THF molecules coordinated to the potassium are omitted for clarity. (b) Representation of the polymeric chain structure of 2a along the crystallographic b axis. Selected bond lengths (Å) and angles (deg): Y1−C1 = 2.782(4), Y1−C2 = 2.721(3), Y1−C3 = 2.803(4), Y1−C4 = 2.858(3), Y1−C5 = 2.726(3),Y1−C6 = 2.757(3), Y1−N1 = 2.333(2), Y1−N2 = 2.537(3), Y1−N3 = 2.247(3), Y1−N4 = 2.555(3), K1−C1′ = 3.179(4), K1−C2′ = 3.021(4), K1−C3′ = 3.287(4), K1−C4 = 3.283(4), K1−C5 = 2.970(3), K1−C6 = 3.270(3), K1−N1′ = 2.770(2); N1−Y1−N3 = 92.12(9), N2−Y1−N4 = 127.26(10).

close to those of 2.567(2) to 2.632(2) Å observed in [(Me3TACD)Y(η3-C3H5)2].8a Trigonal-planar geometry at the nonbridging amido N3 atom (sum of the bond angles of 357° at N3) is associated with a short Y1−N3 distance of 2.247(3) Å. The 1,7-Me2TACD ligand backbone in 2a is strongly puckered toward two amido nitrogen atoms (N1−Y1−N3 = 92.12(9)°, N2−Y1−N4 = 127.26(10)°), which is less pronounced in complex 1b (N1−La1−N3 = 97.66(12)°, 1178

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Scheme 2. Synthesis of Heterometallic Hydrido Complexes

genolysis. The formation of the previously reported potassium−samarium polyhydrido complex [(η5-C5Me5)Sm(μH)2]6[(μ-H)K(THF)2]3 is based on an unexpected redox process.6c Although initially the yield of 3a is relatively low (ca. 20%), direct hydrogenolysis of a 1:1 mixture of 1a and KC3H5 afforded the product in improved yields of up to 58%. Three different types of amido donors were found in 3a: N1 and N7 bridge the yttrium and potassium atoms, N5 bridges two yttrium atoms, and N3 only coordinates to Y1. As expected, the terminal amido atom N3 is sp2 hybridized with a short Y1−N3 bond distance of 2.291(5) Å. The other three amido donors showed longer bond distances of Y1−N1 = 2.341(5) Å, Y1−N5 = 2.397(4) Å, Y2−N5 = 2.406(4) Å, and Y2−N7 = 2.315(4) Å. The Y−N(amine) bond distances range from 2.589(4) to 2.594(4) Å for Y1 and from 2.568(4) to 2.570(4) Å for Y2, which are slightly longer than those of 2.537(3)−2.555(3) Å in 2a. The Y1···Y2 distance of 3.4682(7) Å is shorter than that in [(Me3TACD)Y(μ-H)2]3 (3.516(1) Å),2d while the internal Y2···Y2′ distance of 3.7293(9) Å is longer than those in [{(Me 3 Si) 2 NC(NCy) 2 } 2 Y(μ-H)] 2 (3.6522(5) Å) 16 and [{(Me 3 Si) 2 NC(N i Pr) 2 } 2 Y(μ-H)] 2 (3.6825(5) Å).17 The potassium atom possesses a distortedoctahedral coordination geometry, with two trans-arranged amido nitrogen atoms (N1−K1−N7′ = 154.88(13)°) in the axial positions, while there are two cis-arranged μ3 hydrides and two oxygen atoms of the THF in the equatorial plane. The interaction between the potassium atom and the amido nitrogen atoms (K1−N1 = 2.857(5) Å, K1−N7′ = 2.869(4) Å) is slightly weaker than that in 2a (2.770(2) Å), which is probably caused by their trans influence. The K−H bond lengths of 2.94(5) and 2.62(4) Å are comparable to those in [(η 5 -C 5 Me 5 )Sm(μ-H) 2 ] 6 [(μ-H)K(THF) 2 ] 3 (2.89(7) and 2.58(4) Å).6c The hydrogenolysis of the potassium−lanthanum allyl complex 2b under 1 bar of H2 was monitored in THF-d8, indicating complete consumption of 2b within 3 h. Furthermore, in addition to the signals for the free propylene, three new singlets at δ 10.16, 8.11, and 6.85 ppm were observed, suggesting the formation of new hydride species. From a reaction on a larger scale, colorless blocks of complex

Figure 3. Molecular structure of 3a with displacement parameters at the 50% probability level. Hydrogen atoms (except for the bridging atoms) are omitted for clarity. Selected bond lengths (Å) and angles (deg): Y1−N1 = 2.341(5), Y1−N2 = 2.589(4), Y1−N3 = 2.291(5), Y1−N4 = 2.594(4), Y1−N5 = 2.397(4), Y2−N5 = 2.406(4), Y2−N6 = 2.568(4), Y2−N7 = 2.315(4), Y2−N8 = 2.570(4), Y1−H1 = 2.21(5), Y1−H3 = 2.19(5), Y2−H1 = 2.34(5), Y2−H2 = 2.19(4), Y2− H3 = 2.31(5), Y2−H2′ = 2.31(5), K1−N1 = 2.857(5), K1−N7′ = 2.869(4), K1−O1 = 2.875(5), K1−O2 = 2.827(4), K1−H1 = 2.94(5), K1−H3 = 2.62(4), Y1···Y2 = 3.4682(7), Y2···Y2′ = 3.7293(9), Y1−K1 = 3.7023(13), Y2−K1 = 3.8794(12), Y2′-K1 = 4.2303(13); N1−Y1− N3 = 103.93(18), N2−Y1−N4 = 117.97(13), N3−Y1−N5 = 97.41(17), N5−Y2−N7 = 92.52(14), N6−Y2−N8 = 124.52(12), Y1−N5−Y2 = 92.45(13), Y1−N1−K1 = 90.28(14), Y2−N7−K1′ = 108.93(15), N1−K1−N7′ = 154.88(13).

signal was observed below −70 °C. These results indicate that the hydride exchange within the μ2 and μ3 sites cannot be excluded, but exchange between these sites is difficult. Similar fluxional behavior was reported for the Y−Mo and Y−W polyhydrido complexes.4e Exposure of the THF-d8 solution of 3a to 1 bar of D2 resulted in a slow H−D exchange at room temperature. Complete conversion was achieved within 3 days. To the best of our knowledge, 3a represents a rare example of a heterometallic potassium−yttrium polyhydrido complex synthesized from its heterometallic allyl precursor 2a by hydro1179

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techniques. THF, pentane, and THF-d8 were dried over LiAlH4, followed by vacuum transfer. The ligand precursor (1,7-Me2TACD)H2 was synthesized according to the literature procedure9,2d and further purified by distillation at 80 °C in vacuo. [Ln(η3-C3H5)3(diox)] (Ln = Y, La; diox = 1,4-dioxane) were prepared as previously reported.19 1H and 13C{1H} NMR spectra were recorded at 25 °C on a Bruker DRX 400 spectrometer at 400 and 100 MHz, respectively. All chemical shifts were reported in δ units with references to the residual solvent resonance of the deuterated solvents for proton and carbon chemical shifts. Elemental analyses were performed by the microanalytical laboratory of this department. [(1,7-Me2TACD)Y(η3-C3H5)]2 (1a). (1,7-Me2TACD)H2 (134 mg, 0.666 mmol) in 1.5 mL of THF was slowly added to [Y(η3C3H5)3(diox)] (200 mg, 0.666 mmol) in 1.5 mL of THF at room temperature. A yellow solid precipitated from the brown solution. After the mixture was stirred for 10 min, the solution was decanted and the solid was washed with cold THF and pentane and dried under vacuum to give a yellow solid; yield 138 mg (63%). NMR spectra were not recorded due to poor solubility of the compound in THF or in any other common solvents. Anal. Calcd for C26H54N8Y2 (656.57 g/mol): C, 47.56; H, 8.29; N, 17.07. Found: C, 48.34; H, 8.69; N, 16.37. [(1,7-Me2TACD)La(η3-C3H5)]2 (1b). (1,7-Me2TACD)H2 (114 mg, 0.571 mmol) in 1.5 mL of THF was slowly added to [La(η3C3H5)3(diox)] (200 mg, 0.571 mmol) in 1.5 mL of THF at room temperature. A pale yellow crystalline solid precipitated from the yellow solution. After the mixture was stirred for 10 min, the solution was decanted and the solid was washed with cold THF and pentane and dried under vacuum to give yellow microcrystals; yield 145 mg (67%). 1H NMR (THF-d8): δ (ppm) 6.00 (quint, 3JHH = 12.0 Hz, 2H, CH2CHCH2), 3.45 (dd, 2JHH = 11.6 Hz, 3JHH = 5.2 Hz, 2H, CH2), 3.42 (dd, 2JHH = 11.6 Hz, 3JHH = 5.2 Hz, 2H, CH2), 3.28 (dd, 2JHH = 10.8 Hz, 3JHH = 1.6 Hz, 2H, CH2), 3.26 (dd, 2JHH = 12.4 Hz, 3JHH = 1.6 Hz, 2H, CH2), 3.25 (dd, 2JHH = 11.2 Hz, 3JHH = 2.0 Hz, 2H, CH2), 3.21 (dd, 2JHH = 10.4 Hz, 3JHH = 2.4 Hz, 2H, CH2), 3.12 (dd, 2JHH = 10.0 Hz, 3JHH = 2.4 Hz, 2H, CH2), 3.09 (dd, 2JHH = 10.4 Hz, 3JHH = 2.8 Hz, 2H, CH2), 2.94 (dd, 2JHH = 11.4 Hz, 3JHH = 5.2 Hz, 2H, CH2), 2.91 (dd, 2JHH = 12.0 Hz, 3JHH = 4.8 Hz, 2H, CH2), 2.70 (br s, 8H, CH2CHCH2), 2.63 (s, 12H, CH3), 2.62−2.56 (m, 8H, CH2), 2.08 (dd, 3 JHH = 3.6 Hz, 2.4 Hz, 2H, CH2), 2.05 (dd, 3JHH = 3.6 Hz, 2.4 Hz, 2H, CH2); 13C{1H} NMR (THF-d8): δ (ppm) 149.47 (CH2CHCH2), 72.54 (CH2CHCH2), 61.51 (CH2), 57.85 (CH2), 55.63 (CH2), 54.78 (CH2), 45.07 (CH3). Anal. Calcd for C26H54La2N8 (756.57 g/mol): C, 41.28; H, 7.19; N, 14.81. Found: C, 41.23; H, 6.95; N, 14.88. [(1,7-Me2TACD)Y(η3-C3H5)2K(THF)]n (2a). Potassium allyl (15.4 mg, 0.192 mmol) in 2 mL of THF was slowly added at room temperature to an orange slurry of 1a (60 mg, 0.091 mmol) in 3 mL of THF. The clear orange solution that formed was stirred for 10 min. After the solvent was removed under vacuum, the solid was washed with pentane and dried under vacuum to give orange microcrystals; yield 77 mg (88%). 1H NMR (THF-d8): δ (ppm) 6.22 (quint, 3JHH = 12.2 Hz, 2H, CH2CHCH2), 3.61 (m, 4H, α-THF), 3.15 (t, 3JHH = 4.6 Hz, 2H, CH2), 3.13 (t, 3JHH = 4.6 Hz, 2H, CH2), 2.96 (dd, 2JHH = 9.2 Hz, 3JHH = 4.2 Hz, 2H, CH2), 2.94 (dd, 2JHH = 8.8 Hz, 3JHH = 4.0 Hz, 2H, CH2), 2.80 (dd, 2JHH = 9.0 Hz, 3JHH = 4.6 Hz, 2H, CH2), 2.78 (dd, 2 JHH = 9.0 Hz, 3JHH = 4.6 Hz, 2H, CH2), 2.69 (t, 3JHH = 4.4 Hz, 2H, CH2), 2.66 (3JHH = 4.4 Hz, 2H, CH2), 2.48 (br s, 8H, CH2CHCH2), 2.47 (s, 6H, CH3), 1.78 (m, 4H, β-THF). 13C{1H} NMR (THF-d8): δ (ppm) 147.25 (CH2CHCH2), 68.05 (α-THF), 61.73 (CH2), 61.05 (br s, CH2CHCH2), 56.58 (CH2), 49.28 (CH3), 26.21 (β-THF). Anal. Calcd for C20H40KN4OY (480.56 g/mol): C, 49.99; H, 8.39; N, 11.66. Found: C, 49.85; H, 8.63; N, 11.98. [(1,7-Me2TACD)La(η3-C3H5)2K(THF)]n (2b). Potassium allyl (33.4 mg, 0.416 mmol) in 2 mL of THF was slowly added at room temperature to a slurry of 1b (150 mg, 0.198 mmol) in 2 mL of THF. A clear yellow solution was initially formed, from which colorless crystals precipitated. After the mixture was stirred for 10 min, the solution was decanted and the precipitate was washed with cold THF and pentane and dried under vacuum to give colorless crystals; yield 173 mg (83%). 1H NMR (THF-d8): δ (ppm) 5.97 (m, 2H, CH2CHCH2), 3.61 (m, 4H, α-THF), 3.19 (t, 3JHH = 4.4 Hz, 2H,

3b were obtained in 51% yield by crystallization from a concentrated THF solution at −35 °C. As observed in the in situ NMR studies, the 1H NMR spectrum of isolated 3b in THF-d8 shows three singlets in a 1:3:3 ratio for the hydrides, four sets of multiplets, and two sets of singlets for the 1,7Me2TACD ligand backbone. A single-crystal X-ray diffraction study reveals 3b to be a C3-symmetric heptanuclear La3K4 complex consisting of three [(1,7-Me2TACD)La] units. The three lanthanum atoms form a triangle; each side of this triangle is bridged by a K(thf)2 fragment with the potassium atoms in the La3 plane. An additional K(thf) fragment is capping at the top of this plane, leading to a La3K pyramid. Due to the highly disordered THF molecules within the crystal packing and disorder within the THF ligands, the structure of 3b could not be fully refined and the hydride ligands could not be reliably located.18 However, elemental analysis as well as 1H and 13 C{1H} NMR spectra are consistent with the formulation of [(1,7-Me2TACD)3La3H7K4(THF)7]. On the basis of its 1H NMR spectrum and by comparison with the structure of 3a, we assign the singlet at δ 10.16 ppm to a μ3-hydride capping the Ln3 face or a μ4-hydride in the center of the La3K pyramid, while those at δ 8.11 and 6.85 ppm are assigned to μ2-hydrides bridging the lanthanum−potassium edges and lanthanum− lanthanum edges, respectively. An H−D exchange experiment performed in THF-d8 under 1 bar of D2 showed that all seven hydrides were exchanged with D2 at room temperature over a period of 4 days. The different aggregation states of 3a,b can be explained by the larger radius size of lanthanum in comparison to that of yttrium. Direct hydrogenolysis of a mixture of KC3H5 and 1b in a 2.7:1 molar ratio also gave 3b in good yield.

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CONCLUSION Starting from the mono(allyl) complexes [(1,7-Me2TACD)Ln(η3-C3H5)]2 (Ln = Y (1a) La (1b)) that contain the dianionic (NNNN)-type macrocyclic ligand 1,7-Me2TACD, the heterometallic potassium rare-earth-metal allyl complexes [(1,7Me2TACD)Ln(η3-C3H5)2K(THF)]n (Ln = Y (2a), La (2b)) were obtained in what can be regarded a Lewis acid−base reaction to give an “ate” complex. The potassium yttrium allyl complex 2a underwent hydrogenolysis to give [(1,7Me2TACD)2Y2H3K(THF)2]2 (3a), which can be considered as a dimer of the heterotrinuclear Y2K trihydrido complex. The latter unit can be thought of consisting of formally neutral [(1,7-Me 2 TACD)YH] and the “ate” complex [(1,7Me2TACD)YH2][K(THF)2]. The potassium lanthanum allyl complex 2b gave the heptanuclear La3K4 heptahydrido complex [(1,7-Me2TACD)3La3H7K4(THF)7] (3b), which probably features a [KLa3H7]3+ core. The formation of 3a,b can be seen as a selective “self-assembly” of the in situ generated [(1,7Me2TACD)LnH] and “KH” units. These hydrido complexes are stabilized by the 1,7-Me2TACD ligand through the bridging of the metal centers by the strongly basic amido nitrogen atoms. The ability of the 1,7-Me2TACD ligand, similarly to the Me3TACD ligand, to function as a bridging ligand7e,8d therefore helps to stabilize heterometallic hydrido complexes. We have now established a rational synthetic pathway to these heterometallic hydrido complexes and are in the process of studying their reactivity as well as preparing related systems containing other main-group and transition metals.

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EXPERIMENTAL SECTION

General Considerations. All operations were performed under an inert atmosphere of argon using standard Schlenk-line or glovebox 1180

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CH2), 3.16 (t, 3JHH = 4.4 Hz, 2H, CH2), 3.02 (dd, 2JHH = 8.4 Hz, 3JHH = 4.4 Hz, 2H, CH2), 2.99 (dd, 2JHH = 8.0 Hz, 3JHH = 4.0 Hz, 2H, CH2), 2.80−2.70 (m, 8H, CH2), 2.54 (s, 6H, CH3), 2.53 (br s, 4H, CH2CHCH2), 2.50 (br s, 4H, CH2CHCH2), 1.77 (m, 4H, β-THF). 13 C{1H} NMR (THF-d8): δ (ppm) 146.41 (CH2CHCH2), 68.04 (αTHF), 65.24 (br s, CH2CHCH2), 61.06 (CH2), 56.87 (CH2), 47.86 (CH3), 26.20 (β-THF). Anal. Calcd for C20H40KLaN4O (530.56 g/ mol): C, 45.28; H, 7.60; N, 10.56. Found: C, 44.72; H, 7.89; N, 10.75. [(1,7-Me2TACD)2Y2H3K(THF)2]2 (3a). A mixture of 1a (60 mg, 0.091 mmol) and potassium allyl (7.4 mg, 0.092 mmol) in 2 mL of THF was degassed and treated with 1 bar of H2. A clear dark orange solution was formed within the first few hours and was then allowed to stand at room temperature for 2 days, during which time large pale yellow crystals precipitated from the solution. The solution was decanted, and the crystals were washed with cold THF and pentane and dried under vacuum to give yellow crystals; yield 40 mg (58%). 1H NMR (THF-d8): δ (ppm) 5.91 (t, 1JYH = 21.6 Hz, 2H, YH), 4.89 (dd, 1 JYH = 20.8, 16.4 Hz, 4H, YKH), 3.62 (m, 16H, α-THF), 3.29 (dd, 2 JHH = 11.2 Hz, 3JHH = 5.6 Hz, 2H, CH2), 3.27 (dd, 2JHH = 11.6 Hz, 3 JHH = 5.6 Hz, 2H, CH2), 3.16 (m, 4H, CH2), 2.99 (dd, 2JHH = 12.1 Hz, 3JHH = 4.4 Hz, 1H, CH2), 2.96 (dd, 2JHH = 12.1 Hz, 3JHH = 4.4 Hz, 1H, CH2), 2.93 (dd, 2JHH = 12.1 Hz, 3JHH = 4.4 Hz, 1H, CH2), 2.89 (dd, 2JHH = 12.1 Hz, 3JHH = 4.4 Hz, 1H, CH2), 2.84−2.71 (m, 12H, CH2), 2.75 (s, 12H, CH3), 2.71−2.56 (m, 32H, CH2), 2.62 (s, 12H, CH3), 2.39 (br d, 2JHH = 10.0 Hz, 4H, CH2), 2.26 (m, 4H, CH2), 1.77 (m, 16H, β-THF). The 13C{1H} NMR spectrum was not recorded due to poor solubility of the compound in THF or in any other common solvents. Anal. Calcd for C56H126K2N16O4Y4 (1521.52 g/mol): C, 44.21; H, 8.35; N, 14.73. Found: C, 43.96; H, 8.67; N, 15.16. [(1,7-Me2TACD)3La3H7K4(THF)7] (3b). A suspension of 2b (169 mg, 0.319 mmol) in 5 mL of THF was degassed and treated with 1 bar of H2. A clear yellow solution gradually formed, which was allowed to stand at room temperature for 2 days. The solvent volume was reduced to about 2 mL under vacuum, and after filtration the clear yellow solution was stored at −35 °C to give colorless crystals; yield 91 mg (51% based on La). 1H NMR (THF-d8): δ (ppm) 10.16 (s, 1H, LaHK), 8.11 (s, 3H, LaHK), 6.85 (s, 3H, LaHK), 3.62 (m, 28H, αTHF), 3.33−3.30 (m, 6H, CH2), 3.10−2.99 (m, 12H, CH2), 2.93− 2.88 (m, 6H, CH2), 2.80 (s, 9H, CH3), 2.72−2.59 (m, 24H, CH2), 2.62 (s, 9H, CH3), 1.78 (m, 28H, β-THF). 13C{1H} NMR (THF-d8): δ (ppm) 68.04 (α-THF), 61.94 (CH2), 60.27 (CH2), 57.60 (CH2), 48.23 (CH3), 47.51 (CH3), 26.20 (β-THF). Anal. Calcd for C58H129K4La3N12O7 (1679.83 g/mol): C, 41.47; H, 7.74; N, 10.01. Found: C, 41.64; H, 7.54; N, 10.04. X-ray Crystallography. Data were collected on a Bruker CCD area-detector diffractometer with Mo Kα radiation (monolayer optics, λ = 0.71073 Å) using ω scans.20a The SMART program package was used for the data collection and unit cell determination, processing of the raw frame data was performed using SAINT, and absorption corrections were applied with SADABS.20b The structures were solved by direct methods and refined against F2 using all reflections with SHELXL-97, as implemented in the WinGX program system.20c−e Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were placed in calculated positions. Crystallographic data and refinement details for 1b, 2a, and 3a are given in Table 1. The crystal structure of 3a suffers from disorder in the region of the exocyclic O and N donors. A comparatively simple disorder model with split positions for the atoms C5, C6, C7, C8, and C10 has been refined. The metal-bonded hydrido ligands were identified in a difference Fourier synthesis as local maxima of 0.8 e/Å3. After convergence of this model, all relevant residual electron density maxima are either located very close (1.1 Å) to the lanthanide cations or are associated with the disordered donor ligands in the periphery, making the assignment of the metal-bonded hydrogen atoms very reliable.

Table 1. Crystallographic and Refinement Data for 1b, 2a, and 3a 1b formula fw cryst size/mm cryst syst space group T, K a, Å b, Å c, Å β, deg U, Å3 Z Dcalcd, Mg/m3 F(000) θ range, deg no. of rflns collected no. of indep rflns (Rint) no. of rflns obsd (I > 2σ(I)) no. of data/ restraints/ params R1, wR2 (I > 2σ(I)) R1, wR2 (all data) goodness of fit on F2 Δρmax, Δρmin, e Å−3

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C26H54La2N8 756.59 0.23 × 0.14 × 0.07 tetragonal P42/n 100(2) 17.8105(18) 17.8105(18) 9.7851(10)

2a

3a

3104.0(7) 4 1.619 1520 1.14−30.78 45999

C20H40KN4OY 480.57 0.27 × 0.15 × 0.12 monoclinic C2/c 100(2) 31.638(3) 9.9754(11) 18.728(2) 125.754(2) 4796.6(9) 8 1.331 2032 2.18−26.44 28259

C56H126K2N16O4Y4 1521.57 0.26 × 0.21 × 0.18 monoclinic P21/c 100(2) 15.997(2) 12.200(2) 18.525(4) 98.590(3) 3574.8(11) 2 1.414 1600 2.01−26.57 41485

4713 (0.0917)

4929 (0.0924)

7375 (0.1128)

3830

3484

5060

4713/0 /166

4929/30/291

7375/18/470

0.0355, 0.1021

0.0409, 0.0834

0.0589, 0.1403

0.0480, 0.1089

0.0721, 0.0949

0.0930, 0.1586

1.010

0.996

1.022

0.708, −0.820

0.418, −0.354

3.319, −0.455

ASSOCIATED CONTENT

S Supporting Information *

Figures giving 1H and 13C{1H} NMR spectra of complexes 1a,b−3a,b and CIF files giving crystallographic data for compounds 1b, 2a, and 3a. 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: +49 241 8092644. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the Deutsche Forschungsgemeinschaft for financial support and to the Alexander von Humboldt Foundation for a postdoctoral fellowship to P.C.

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REFERENCES

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2003, 22, 3028−3030. (c) Woodman, T. J.; Schormann, M.; Hughes, D. L.; Bochmann, M. Organometallics 2004, 23, 2972− 2979. (d) For potassium tris(allyl)strontiate, see: Jochmann, P.; Davin, J. P.; Maslek, S.; Spaniol, T. P.; Sarazin, Y.; Carpentier, J.-F.; Okuda, J. Dalton Trans. 2012, 41, 9176−9181. (14) (a) Huang, Z. E.; Chen, M. Q.; Qiu, W. J.; Wu, W. L. Inorg. Chim. Acta 1987, 139, 203−207. (b) Taube, R.; Windisch, R.; Görlitz, F.; Schumann, H. J. Organomet. Chem. 1993, 445, 85−91. (c) Taube, R.; Maiwald, S.; Sieler, J. J. Organomet. Chem. 1996, 513, 37−47. (15) Simpson, C. K.; White, R. E.; Carlson, C. N.; Wrobleski, D. A.; Kuehl, C. J.; Croce, T. A.; Steele, I. M.; Scott, B. L.; Young, V. G., Jr.; Hanusa, T. P.; Sattelberger, A. P.; John, K. D. Organometallics 2005, 24, 3685−3691. (16) Lyubov, D. M.; Bubnov, A. M.; Fukin, G. K.; Dolgushin, F. M.; Antipin, M. Y.; Pelcé, O.; Schappacher, M.; Guillaume, S. M.; Trifonov, A. A. Eur. J. Inorg. Chem. 2008, 2090−2098. (17) Trifonov, A. A.; Skvortsov, G. G.; Lyubov, D. M.; Skorodumova, N. A.; Fukin, G. K.; Baranov, E. V.; Glushakova, V. N. Chem. Eur. J. 2006, 12, 5320−5327. (18) A colorless plate of 3b of dimensions 0.14 × 0.30 × 0.32 mm was obtained from THF at −35 °C. The unit cell dimensions were determined as a = b = 16.4323(7) Å, c = 27.4313(10) Å, α = β = 90°, γ = 120°, V = 6414.7(5) Å3, and tentative space group R3. The crystal structure could be solved by direct methods and clearly shows the connectivity as described in the text. However, the THF ligands at the metal center are disordered. The crystal lattice contains further THF molecules in strongly disordered positions. The poor quality of the crystallographic data precludes further discussion of the results. (19) Robert, D.; Abinet, E.; Spaniol, T. P.; Okuda, J. Chem. Eur. J. 2009, 15, 11937−11947. (20) (a) SAINT-Plus; Bruker AXS, Madison, WI, 1999. (b) SADABS; Bruker AXS: Madison, WI, 2004. (c) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr. 1993, 26, 343−350. (d) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112−122. (e) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838.

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dx.doi.org/10.1021/om300986w | Organometallics 2013, 32, 1176−1182