ARTICLE pubs.acs.org/Organometallics
Versatile Reactivities of ansa-Heteroborabenzene Divalent Ytterbium Amide toward Alkali-Metal Salts and the Generation of Heterometallic YtterbiumAlkali-Metal Boratabenzene Complexes Peng Cui, Yaofeng Chen,* Guangyu Li, and Wei Xia State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, People’s Republic of China
bS Supporting Information ABSTRACT:
Reactions of the ansa-heteroborabenzene divalent ytterbium amide [C5H5BCH2(CH3)2PfBC5H5]YbN(SiMe3)2 (1) with alkalimetal salts (KC5Me5, NaOiPr, NaOAr, LiNHAr, LiN(SiMe3)2, LiNEt2, and KCH2Ar) were studied. The reaction of 1 with KC5Me5 caused a ligand displacement of neutral borabenzene by KC5Me5 at the Yb ion to give a heterometallic YbK boratabenzene complex with a polymeric structure, while that with NaOiPr caused a ligand displacement of the anionic amido ligand at the Yb ion by an isopropoxyl ligand to give a heterometallic YbNa boratabenzene complex with a polymeric structure. When LiNEt2 or KCH2Ar was employed as the reagent, the [NEt2] or [CH2Ar] group underwent nucleophilic attack at the B atom on the neutral borabenzene to cause the disassociation of the PfB coordination bond and the generation of new boratabenzene ligands.
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ince the pioneering work of Herberich and Ashe on the synthesis of boratabenzene derivertives of [CpCoC5H5BPh]þ and Li[C5H5BC6H5],1,2 the fascinating area of boratabenzene chemistry has been opened up. Though they are analogous to the well-known Cp-type ligands, the heterocyclic boratabenzenes are generally weaker donors.3 The last three decades have witnessed a significant progress in boratabenzene chemistry, and numerous metal complexes bearing boratabenzenes, in particular the derivatives of group 4, 6, and 8 metals, have been reported.4 In contrast to those achievements in boratabenzene transitionmetal chemistry, the boratabenzene derivatives of lanthanide metals are very rare and their chemistry remains mostly unexplored.5 On the other hand, lanthanide metal complexes containing Cp-type ligands have exhibited rich and diversified coordinating properties and reactivities.6 Recently, we have prepared several divalent lanthanide boratabenzene complexes,7a,b ansa-heteroborabenzene divalent ytterbium complexes,7c,d as well as trivalent lanthanide metal boratabenzene amide and alkyl complexes.8 Herein we report the reactions of [C5H5BCH2(CH3)2PfBC5H5]YbN(SiMe3)2 (1)7c with various alkali-metal salts (KC5Me5, NaOiPr, NaOAr, LiNHAr, LiN(SiMe3)2, LiNEt2, and KCH2Ar), which show diversified reaction patterns, and give some notable new boratabenzene r 2011 American Chemical Society
metal complexes, including the first boratabenzene derivatives of heterometallic lanthanidealkali-metal.
’ RESULTS AND DISCUSSION Synthesis and Crystal Structure of 2. Mixing 1 with 1 equiv of KC5Me5 in benzene gave a dark blue reaction mixture, from which black needles of 2 precipitated in 3 days in 67% yield (Scheme 1). 2 was characterized by single-crystal X-ray diffraction analysis (Figure 1). It revealed that the reaction caused a ligand displacement of neutral borabenzene by KC5Me5 at the Yb ion to give a heterometallic YbK boratabenzene complex with polymeric structure (Figure S1, showing the polymeric structure of 2, is given in the Supporting Information). In the complex, Yb ion is coordinated by anionic boratabenzene, [C5Me5], and an amido group. The coordination mode of the K ion is very impressive, as it is coordinated by three different types of aromatic ligands: [C5Me5], anionic boratabenzene, and neutral borabenzene. To our knowledge, 2 represents the first example Received: January 17, 2011 Published: March 16, 2011 2012
dx.doi.org/10.1021/om200040z | Organometallics 2011, 30, 2012–2017
Organometallics Scheme 1
Figure 1. Extended molecular structure of 2 with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): YbB1 = 3.089(8), YbC1 = 2.985(7), YbC2 = 2.897(8), YbC3 = 2.851(7), YbC4 = 2.840(7), YbC5 = 2.929(8), YbC14 = 2.753(7), YbC15 = 2.725(8), YbC16 = 2.714(7), YbC17 = 2.735(7), YbC18 = 2.758(8), YbN1 = 2.335(6), P1C6 = 1.798(7), P1C7 = 1.765(9), P1C8 = 1.804(10), P1B2 = 1.921(11), KB1 = 3.458(11), KC1 = 3.734(10), KC2 = 3.641(9), KC3 = 3.330(9), KC4 = 3.100(7), KC5 = 3.156(8), KB2 = 3.286(10), KC9 = 3.199(10), KC10 = 3.182(13), KC11 = 3.226(19), KC12 = 3.299(17), KC13 = 3.330(11), KC14A = 3.312(8), KC15A = 3.174(8), KC16A = 2.994(7), KC17A = 3.036(8), KC18A = 3.221(8); Si1N1Yb1 = 118.1(3), Si2N1Yb1 = 112.7(3), Si1N1Si2 = 128.7(4).
of a complex having an alkali-metalneutral borabenzene interaction. Inspection of the distance from the Yb ion to the boratabenzene ring [B1, C15] shows that the YbC distances are longer for C1 (2.985(7) Å), C5 (2.929(8) Å), and B1 (3.089(8) Å) vs C2 (2.897(8) Å), C3 (2.851(7) Å), and C4 (2.840(7) Å), indicating a slippage of the Yb ion away from the B atom and toward the C3 atom to give an intermediate η3η6 coordination mode, as observed in 17c and (C5H5BNPh2)2Yb(THF)2.7b However, the average YbC(boratabenzene) bond length of 2.90 Å is significantly longer than those in 1 (2.83 Å) and (C5H5BNPh2)2Yb(THF)2 (2.83 Å). The distances from the Yb ion to carbon atoms on [C5Me5] ring range from 2.714(7) to 2.758(8) Å, and the average distance (2.74 Å) is longer than those in (C5Me5)2Yb (2.66 and 2.67 Å)9 and (C5Me5)2Yb(THF) (2.65 and 2.67 Å).10 Such an elongation of
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the YbC(boratabenzene) and YbC(Cp*) distances in 2 can be attributed to the coordination of anionic boratabenzene and [C5Me5] with K ion on the other side. The distances from the K ion to the C4 and C5 atoms on the anionic boratabenzene are 3.100(7) and 3.156(8) Å, respectively, while those to B1, C1, C2, and C3 atoms are rather long: 3.458(11), 3.734(10), 3.641(9), and 3.330(9) Å, respectively. Thus, the anionic boratabenzene coordinates to the K ion in an η2 fashion. The distances from the K ion to the neutral borabenzene indicate an intermediate η3η6 coordination between the neutral borabenzene and the K ion (KC9 = 3.199(10) Å, KC10 = 3.182(13) Å, KC11 = 3.226(19) Å vs KB2 = 3.286(10) Å, KC12 = 3.299(17) Å, KC13 = 3.330(11) Å). The coordination mode between the [C5Me5] ring and the K ion can be described as an η2η5 intermediate fashion; the distances from the K ion to C16A and C17A atoms (2.994(7) and 3.036(8) Å) are shorter than those to C14A, C15A, and C18A atoms (3.312(8), 3.174(8), and 3.221(8) Å). The former are within the range of 2.963.06 Å reported for [(C5Me5)K(Py)2]¥.11 The average KC(Cp*) distance (3.147 Å) is comparable to those in [(μ-C5Me5)Sm(OAr)(μ-C5Me5)K(THF)2]¥ (Ar = 2,6-tBu2C6H3, 3.15(3) and 3.13(3) Å; Ar = 2,6-tBu2-4-MeC6H2, 3.142(7) and 3.157(8) Å).12 2 is nearly insoluble in benzene, toluene, and hexane but readily soluble in THF. Dissolution of the black 2 in THF-d8 immediately gave a dark red solution. In the 1H NMR spectrum of 2, six signals in the range of 5.967.16 ppm were observed for the anionic boratabenzene and neutral borabenzene; the signals for the CH2P(CH3)2 linkage appear at 1.85 and 1.65 ppm. [C5Me5] and N(SiMe3)2 display sharp singlets at 1.97 and 0.07 ppm, respectively. The 11B NMR and 31P NMR chemical shifts for 2 (11B NMR, 31.7 and 24.0 ppm; 31P NMR, 12.1 ppm) are very close to those for 1 (11B NMR, 33.7 and 25.8 ppm; 31 P NMR, 14.6 ppm), while the 171Yb NMR signal of 2 (480 ppm) is greatly upshifted compared to that of 1 (1175 ppm). Synthesis and Crystal Structure of 3. Mixing 1 with 1 equiv of NaOiPr in benzene gave a dark purple reaction mixture, from which black crystalline blocks of 3 precipitated in 3 days in 70% yield (Scheme 2). The solid-state structure of 3 was determined by crystallographic methods (Figure 2). 3 can be simply described as centrosymmetric dimers of ansa-heteroborabenzene divalent ytterbium alkoxide linked by centrosymmetric dimers of sodium amide. Therefore, a ligand displacement of the anionic amido ligand at Yb ion by isopropoxyl ligand occurs during the reaction, and the eliminated sodium amide does not “move away” from the Yb complex but acts as the linker to form a notable polymer (Figure S2, showing the polymeric structure of 3, is given in the Supporting Information). In 3, the Yb ion is pseudotetrahedrally coordinated by ansaheteroborabenzene and two isopropoxyl ligands. As observed in 2, the anionic boratabenzene ligand coordinates to the Yb ion in an intermediate η3η6 fashion; the distances from the Yb ion to the B1, C1, and C5 atoms (3.090(7), 3.016(5), and 3.051(7) Å) are significantly longer than those to the C2, C3, and C4 atoms (2.871(5), 2.806(6), and 2.857(6) Å). The average YbC(boratabenzene) bond length (2.92 Å) is close to that in 2 (2.90 Å) but significantly longer than those in 1 (2.83 Å) and (C5H5BNPh2)2Yb(THF)2 (2.83 Å) due to the Naboratabenzene interaction. The neutral borabenzene is η6 coordinated; the distances from the Yb ion to the B2 and C9C13 atoms range from 2.905(6) to 3.011(5) Å. The isopropoxyl ligand is coordinated to two Yb ions at YbO separations of 2.288(3) and 2.297(3) Å, 2013
dx.doi.org/10.1021/om200040z |Organometallics 2011, 30, 2012–2017
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Scheme 2
Figure 2. Extended molecular structure of 3 with thermal ellipsoids at the 30% probability level. Methyl substituents of isopropoxyl and amido ligands, hydrogen atoms, and the benzene molecule in the lattice are omitted for clarity. Selected bond distances (Å) and angles (deg): YbO1 = 2.288(3), YbO1A = 2.297(3), YbYbA = 3.554(6), YbB1 = 3.090(7), YbC1 = 3.016(5), YbC2 = 2.871(5), YbC3 = 2.806(6), YbC4 = 2.857(6), YbC5 = 3.051(7), YbB2 = 2.983(6), YbC9 = 3.011(5), YbC10 = 3.003(5), YbC11 = 2.951(5), YbC12 = 2.905(6), YbC13 = 2.918(6), P1C6 = 1.725(7), P1C7 = 1.807(7), P1C8 = 1.820(6), P1B2 = 1.921(7), NaB1A = 3.436(7), NaC1A = 3.317(8), NaC2A = 3.098(7), NaC3A = 2.949(7), NaC4A = 3.024(5), NaC5A = 3.240(6), NaN1 = 2.417(6), NaN1A = 2.469(5); O1YbO1A = 78.37(13), YbO1YbA = 101.63(13), NaN1NaA = 80.73(18), N1NaN1A = 99.27(18).
respectively, which fall in the range of 2.272.32 Å observed for YbO bonds in other reported divalent ytterbium complexes containing bridged alkoxyl ligands.13 The YbYbA separation is 3.554(6) Å; therefore, there is no bonding interaction between the two metal centers. The distances from the Na ion to the C2A, C3A, and C4A atoms on the anionic boratabenzene are 3.098(7), 2.949(7), and 3.024(5) Å, respectively, while those to B1A, C1A, and C5A atoms are longer (>3.15 Å), indicating an η3 coordination fashion between Na ion and the anionic boratabenzene. The amido group bridges two Na ions, and NaN bond lengths (2.417(6) and 2.469(5) Å) are close to those reported in [(C5HR4)2Ln(μ-Cl)(Na)μ-N(SiMe3)2]2 (Ln = La, 2.407 and 2.423 Å; Ln = Pr, 2.403 and 2.438 Å; Ln = Nd, 2.404 and 2.414 Å).14 Similar to the case for 2, 3 is nearly insoluble in benzene, toluene, and hexane but readily soluble in THF. Dissolution of the black 3 in THF-d8 immediately gave a dark red solution; however, the 1H NMR spectrum indicates rapid decomposition of 3 with the release of HN(SiMe3)2. The reactions of 1 with sodium phenoxides were
also studied. When the bulky sodium phenoxide NaO(4-Me2,6-tBu2)C6H2 was used as the reagent, no reaction occurred even at elevated temperature; on the other hand, the reaction of 1 with the less bulky sodium phenoxide NaO(4-tBu)C6H4 gave some unidentified mixtures. Synthesis and Crystal Structure of 4a. The reactions of 1 with alkali-metal amides were then studied. When KN(SiMe3)2 or LiNHC6H3-2,6-iPr2 was used as the reagent, only some unidentified mixtures were formed. However, 1 cleanly reacted with 2 equiv of LiNEt2 to give the two products 4a,b (Scheme 3). 4a,b were successfully separated on the basis of their different solubilities in hexane; 4a is soluble in hexane, while 4b is insoluble in hexane. 4a was characterized by single-crystal X-ray diffraction analysis, which reveals that 4a exists as a tetramer of the diethylaminoboratabenzene lithiumbis(trimethylsilyl)amido lithium adduct [Li(C5H5BNEt2)LiN(SiMe3)2]4 (Figure 3). 4a shows a centrosymmetric square; four nitrogen atoms of the bis(trimethylsilyl)amido ligands occupy the corners with the four LiboratabenzeneLi units making up the sides. The N2 3 3 3 N4 and N2 3 3 3 N4A distances are 7.58 and 7.69 Å, respectively, while the N4A 3 3 3 N2 3 3 3 N4 and N2 3 3 3 N4 3 3 3 N2 angles are 91.8 and 88.2, respectively. All diethylamino substituents of the anionic boratabenzenes point toward the outside to form a hole in the middle of this tetramer with a C3 3 3 3 C3A distance of 5.18 Å and a C18 3 3 3 C18A distance of 6.03 Å. The anionic boratabenzene is coordinated by two Li ions on both sides, and the LiboratabenzeneLi unit shows a distorted-pentagonal-bipyramidal geometry. The distance from the Li ion to the boratabenzene ring indicates a slippage of the Li ion away from the B atom and toward the C3 atom to give an intermediate η3η5 coordination mode. The average LiC(boratabenzene) distance of 2.35 Å is shorter than that of 2.42 Å in [(C5H5BH)2Li][Li(THF)4].15 The Li ions are also bridged by the bis(trimethylsilyl)amido ligands; the LiN distances (1.946(7)1.958(6) Å) are shorter than those in [(Me3Si)2NLi(OEt2)]2 (2.055(5) Å)16 and [(Me3Si)2NLi(THF)]2 (2.025(9) Å).17 4a is soluble in toluene, benzene, and hexane. The 1H NMR spectrum of 4a in C6D6 shows resonances for the boratabenzene ring (7.47, 6.12, and 6.00 ppm), NEt2 (3.16 and 1.18 ppm), and N(SiMe3)2 (0.08 ppm). The 11 B NMR spectrum shows a broad signal at 30.1 ppm. 4b is nearly insoluble in toluene, benzene, and hexane but readily soluble in THF. Dissolution of the dark brown 4b in THF-d8 gave a dark red solution. The 11B NMR spectrum shows one singlet at 31.4 ppm, which is close to that for B of anionic boratabenzene in 1 (33.7 ppm) and different from that for B of neutral borabenzene in 1 (25.8 ppm). The 171Yb NMR spectrum of 4b shows one singlet at 452 ppm. The 31P NMR signal of 4b is 2014
dx.doi.org/10.1021/om200040z |Organometallics 2011, 30, 2012–2017
Organometallics
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Scheme 3
Figure 3. Molecular structure of 4a with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Li1N2 = 1.958(6), Li1B1 = 2.469(7), Li1C1 = 2.401(7), Li1C2 = 2.342(7), Li1C3 = 2.316(7), Li1C4 = 2.339(7), Li1C5 = 2.392(7), Li2N2 = 1.957(7), Li2B2 = 2.491(8), Li2C16 = 2.400(8), Li2C17 = 2.317(7), Li2C18 = 2.290(7), Li2C19 = 2.315(7), Li2C20 = 2.387(7), Li3N4 = 1.946(7), Li3B2 = 2.481(8), Li3C16 = 2.375(7), Li3C17 = 2.310(8), Li3C18 = 2.311(8), Li3C19 = 2.327(8), Li3C20 = 2.402(7), Li4N4 = 1.954(6), Li4B1(A) = 2.486(7), Li4C1(A) = 2.394(7), Li4C2(A) = 2.336(7), Li4C3(A) = 2.347(7), Li4C4(A) = 2.346(7), Li4C5(A) = 2.393(7); Li1N2Li2 = 102.0(3), Li3N4Li4 = 99.3(3).
a singlet and appears at much higher field than those in 1 and 2 (51.4 ppm vs 14.6 and 12.1 ppm), indicating the P atom is not coordinated to the B atom, unlike the case for 1 and 2. The 1 H NMR spectrum of 4b in THF-d8 is very complex, and more than two sets of signals for the boratabenzene were observed. This is possibly due to the complexity of the aggregation structure of the complex in THF. Attempts to obtain single crystals of 4b for X-ray diffraction analysis were hampered by the poor solubility of the complex in toluene, benzene, and hexane, and the recrystallization of 4b in the presence of THF or pyridine always gave an oily product. The formation of 4a,b shows that the reaction pattern of 1 with LiNEt2 is very different from those with KC5Me5 and NaOiPr. During the reaction, a nucleophilic attack of the anionic diethylamido group at the B atom of the neutral borabenzene occurred, which caused the disassociation of the PfB coordination bond and the generation of the new boratabenzene ligand [C5H5BNEt2]. Then a series of ligand redistributions led to the final products 4a,b.
The reactions of 1 with potassium benzyls (KCH2C6H5, KCH2C6H3-3,5-Me2, and KCH2C6H4-o-(N(CH3)2) were also investigated, which were monitored by NMR spectroscopy in C6D6. The 31P NMR spectra reveal the upfield shift of the signals from 14.6 ppm in 1 to about 50 ppm in the products. We propose that the reactions proceed through a nucleophilic attack of the anionic benzyl group at the B atom on the neutral borabenzene and the disassociation of the PfB coordination bond, as observed in the reaction of 1 with LiNEt2. These reactions gave the crude products as oils; attempts to obtain crystalline products from these oily crude products by recrystallization failed. In summary, on the basis of its unique structural features, the ansa-heteroborabenzene divalent ytterbium amide [C5H5 BCH2(CH3)2PfBC5H5]YbN(SiMe3)2 (1) shows versatile reactivities toward various alkali-metal salts. The displacement of neutral borabenzene or anionic amido ligand at the Yb ion or the disassociation of the PfB coordination bond occurs, depending on the nature of the alkali-metal salt. The reactions of 1 with KC5Me5 and NaOiPr caused a ligand displacement of neutral borabenzene or anionic amido ligand at the Yb ion, respectively, which is possibly associated with the steric and electron donor number demands of the Yb ion. On the other hand, the strong BN bond formation tendency caused a nucleophilic attack of the [NEt2] group at the B atom of the neutral borabenzene in the reaction with LiNEt2. The “soft” ligands [CH2Ar] reasonably attack at the B atom of the neutral borabenzene instead of the Yb ion. These reactions have given the first boratabenzene derivatives of heterometallic lanthanidealkali-metal, which have notable structural features. In these heterometallic complexes, the anionic boratabenzene is coordinated by lanthanide and alkali-metal ions on both sides, while the neutral borabenzene only coordinates to one metal ion: lanthanide or alkali-metal ion. The structural characterization also reveals the first example of an alkali-metal ionneutral borabenzene interaction.
’ EXPERIMENTAL SECTION General Procedures. All operations were carried out under an atmosphere of argon using Schlenk techniques or in a nitrogen-filled glovebox. THF was distilled from Nabenzophenone ketyl and degassed by freezethawvacuum prior to use. Toluene, hexane, C6D6, and THF-d8 were dried over Na/K alloy, followed by vacuum transfer, and stored in the glovebox. 1 was prepared as we previously reported.7c KC5Me5 was synthesized according to the literature procedure.11 1H, 13 C, and 31P NMR spectra were recorded on a Varian 400 MHz spectrometer at 400, 100, and 160 MHz, respectively. 11B and 171Yb NMR spectra were recorded on a Bruker DXP 400 MHz spectrometer at 128 and 70 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, to external BF3 3 OEt2 and H3PO4 for boron and phosphorus chemical shifts, and to 0.171 M 2015
dx.doi.org/10.1021/om200040z |Organometallics 2011, 30, 2012–2017
Organometallics [Yb(C5Me5)2(THF)2] in THF (δ(171Yb) 0 ppm for Ξ(171Yb) = 17.499 306 MHz) for ytterbium chemical shifts. Elemental analysis was performed by the Analytical Laboratory of the Shanghai Institute of Organic Chemistry. Synthesis of 2. 1 (40 mg, 0.071 mmol) and KC5Me5 (12.5 mg, 0.071 mmol) were mixed in 1.5 mL of benzene. The dark blue reaction mixture stood at room temperature for 3 days, and black needles of 2 precipitated from the solution, which were isolated, washed with benzene and hexane, and dried under vacuum (35 mg, 67% yield). 1H NMR (400 MHz, THFd8, 25 C): δ (ppm) 7.16 (m, 2H, PBCHCHCH), 6.98 (t, 3JHH = 8.2 Hz, 2H; PBCHCHCH), 6.76 (t, 3JHH = 8.8 Hz, 2H; CBCHCHCH), 6.41 (t, 3JHH = 6.4 Hz, 1H; CBCHCHCH), 6.26 (d, 3JHH = 9.6 Hz, 2H; CBCHCHCH), 5.96 (t, 3JHH = 7.0 Hz, 1H; PBCHCHCH), 1.97 (s, 15H; C5Me5), 1.85 (d, 2JPH = 16.0 Hz, 2H; PCH2), 1.65 (d, 2JPH = 11.6 Hz, 6H; P(CH3)2), 0.07 (s, 18H; N(Si(CH3)3)2). 13C NMR (100 MHz, THF-d8, 25 C): δ (ppm) 133.5, 133.1 (d, 2JPC = 15.9 Hz), 128.3 (br s), 117.7, 112.1, 111.1, 111.0 (borabenzene-C and C5Me5), 17.4 (br d, 1JPC = 23.0 Hz, PCH2), 11.8 (d, 1JPC = 41.0 Hz, P(CH3)2), 11.5 (C5Me5), 5.5 (N(Si(CH3)3)2). 31P NMR (160 MHz, THF-d8, 25 C): δ (ppm) 12.1 (br d, 1JBP = 126.4 Hz). 11B NMR (128 MHz, THF-d8, 25 C): δ (ppm) 31.7 (br s, CB), 24.0 (br s, PB). 171Yb NMR (70 MHz, THF-d8, 25 C): δ (ppm) 480 (br s). Anal. Calcd for C29H51B2KNPSi2Yb: C, 47.41; H, 7.00; N, 1.91. Found: C, 46.44; H, 6.78; N, 1.70. Synthesis of 3. 1 (50 mg, 0.089 mmol) and NaOiPr (7.3 mg, 0.089 mmol) were mixed in 2.5 mL of benzene. The dark purple reaction mixture stood at room temperature for 3 days, and black crystals of 3 precipitated from the solution, which were isolated, washed with benzene and hexane, and dried under vacuum (40 mg, 70% yield). The complex is nearly insoluble in toluene and benzene and decomposes in THF with release of HN(SiMe3)2. Anal. Calcd for C22H43B2NNaOPSi2Yb: C, 41.13; H, 6.75; N, 2.18. Found: C, 41.62; H, 6.81; N, 2.09. Synthesis of 4a,b. 1 (90 mg, 0.161 mmol) and LiNEt2 (25.4 mg, 0.321 mmol) were mixed in 5 mL of toluene. The dark brown-red reaction mixture was stirred at room temperature for 2 days. The solvent was removed under vacuum, and the dark brown-red residue was extracted with 3 5 mL of hexane. The hexane was removed under vacuum, and recrystallization of the residue with hexane gave 4a as pale white needles (30 mg, 58% yield). The dark brown solid residue after hexane extraction was identified as 4b (46 mg, 73%). 4a: 1H NMR (400 MHz, C6D6, 25 C) δ (ppm) 7.47 (dd, 3JHH = 6.8 Hz, 3JHH = 6.4 Hz, 2H; BCHCHCH), 6.12 (d, 3JHH = 10.4 Hz, 2H; BCHCHCH), 6.00 (t, 3 JHH = 6.8 Hz, 1H; BCHCHCH), 3.16 (q, 3JHH = 7.2 Hz, 4H; CH2CH3), 1.18 (t, 3JHH = 7.2 Hz, 6H; CH2CH3), 0.08 (s, 18H, SiMe3); 13C NMR (100 MHz, C6D6, 25 C) δ (ppm) 135.2, 113.7, 97.3 (boratabenzene-C), 43.0, 15.6, 5.9; 11B NMR (128 MHz, C6D6, 25 C): δ (ppm) 30.1 (br s). Anal. Calcd for C30H66B2Li4N4Si4: C, 55.90; H, 10.32; N, 8.69. Found: C, 56.05; H, 10.66; N, 8.60. 4b: 31P NMR (160 MHz, THF-d8, 25 C) δ (ppm) 51.4 (br s); 11B NMR (128 MHz, THF-d8, 25 C) δ (ppm) 31.4 (br s); 171Yb NMR (70 MHz, THF-d8, 25 C) δ (ppm) 452 (br s). The 1H NMR spectrum of 4b in THF-d8 is too complex to give useful information. Anal. Calcd for C12H23BNPYb: C, 36.38; H, 5.85; N, 3.54. Found: C, 36.25; H, 5.82; N, 3.85. X-ray Crystallography. Suitable single crystals of 2 and 3 were sealed in thin-walled glass capillaries; data collections were performed at 20(2) C on a Bruker SMART diffractometer with graphite-monochromated Mo KR radiation (λ = 0.710 73 Å). For 4a, a suitable single crystal was mounted under nitrogen on a glass fiber, and data collection was performed at 133(2) C on a Bruker APEX2 diffractometer with graphite-monochromated Mo KR radiation (λ = 0.710 73 Å). The SMART program package was used to determine the unit cell parameters. The absorption correction was applied using SADABS. The structures were solved by direct methods and refined on F2 by full-matrix least-squares techniques with anisotropic thermal parameters for nonhydrogen atoms. Hydrogen atoms were placed at calculated positions
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and were included in the structure calculation without further refinement of the parameters. All calculations were carried out using the SHELXL-97 program. The software used is listed in the references.18 Crystallographic data and refinement details for 2, 3, and 4a are given in Table S1 in the Supporting Information.
’ ASSOCIATED CONTENT
bS
Supporting Information. CIF files giving X-ray crystallographic data for 2, 3, and 4a, a table giving crystallographic data and refinement details for 2, 3, and 4a, and Figures S1 and S2, showing the polymeric structures of 2 and 3. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. Fax: (þ86)21-64166128.
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