Article pubs.acs.org/Organometallics
Reactivity of Scorpionate-Anchored Yttrium Alkyl Primary Amido Complexes toward Carbodiimides. Insertion Selectivity of Y−NHAr and Y−CH2Ph Bonds Weiyin Yi, Shujian Huang, Jie Zhang,* Zhenxia Chen, and Xigeng Zhou* Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, People’s Republic of China, and State Key Laboratory of Organometallic Chemistry, Shanghai 200032, People’s Republic of China S Supporting Information *
ABSTRACT: The TpMe2-supported yttrium dialkyl TpMe2Y(CH2Ph)2(THF) (TpMe2 = tri(3,5-dimethylpyrazolyl)borate) reacted with 1 equiv of ArNH2 in THF at room temperature to afford the yttrium alkyl primary amido complexes TpMe2YNHAr(CH2Ph)(THF) (Ar = Ph (1), C6H3-iPr2-2,6 (2)) in 84% and 88% isolated yields, respectively. Complex 1 reacted with iPrNCNiPr in THF at room temperature to give a yttrium dianionic guanidinate complex, TpMe2Y[(iPrN)2CNPh](THF)2 (3, 74%). However, the reaction of 1 with ArNCNAr (Ar = C6H3-iPr2-2,6) in the same conditions produced a Y−C bond insertion product, TpMe2Y[(ArN)2CCH2Ph](NHPh) (4, 87%). Moreover, treatment of 2 with 1 equiv of iPrNCNiPr in THF at room temperature afforded two yttrium complex, TpMe2Y[(iPrN)CNAr](THF) (5) and TpMe2Y[(iPrN)2CCH2Ph](NHAr) (6), in 58% and 19% isolated yields, respectively. These results indicated that carbodiimide can selectively insert into the Y−CH2Ph and Y−NHAr σbonds of TpMe2-supported yttrium alkyl primary amido complexes TpMe2YNHAr(CH2Ph)(THF), and this selectivity depends on the steric hindrance of the substituent groups R of cabodiimides and the primary amido ligands. All these new complexes were characterized by elemental analysis and spectroscopic methods, and their solid-state structures except 1 were also confirmed by single-crystal X-ray diffraction analysis.
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INTRODUCTION There is fundamental interest in reactivity of organolanthanide complexes with unsaturated substrates, because this is the source for developing new catalytic reactions and catalysts.1,2 Many efforts have focused on a detailed understanding of insertions of such substrates into various Ln−L (L = ligand) bonds such as the Ln−H,3 Ln−C,4 Ln−N,5 Ln−S,6 or Ln−P bond7 of organolanthanide complexes over the last two decades. However, during these studies, the organolanthanide complexes usually have only one kind of active Ln−L bond and easily incorporate unsaturated substrates to give well-defined products,3−7 and little is known about the selective insertion of these substrates into the Ln−L bonds of organolanthanide complexes with two or more different active Ln−L bonds.8 Our recent partial research interests are in investigating the selective insertion of Ln−N and N−H bonds of organolanthanide primary amido complexes, and we found that the N−H addition occurred more easily than Ln−N insertion in some cases.9 Continuing our recent investigations of the reactivity of TpMe2-supported lanthanide derivatives10 and learning more about the selectivity of two different Ln−L bond insertions, herein we report the selective insertions of carbodiimides into the Y−NHAr and Y−C σ-bonds of scorpionate-anchored yttrium alkyl primary amido complexes with two active Y− CH2Ph and Y−NHAr σ-bonds, TpMe2YCH2Ph(NHAr)(THF), and we found that this insertion selectivity depends on the © 2013 American Chemical Society
steric hindrance of the substituent groups of carbodiimides and the primary amido ligands.
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RESULTS AND DISCUSSION Synthesis and Characterizations of TpMe2-Supported Yttrium Alkyl Primary Amido Complexes TpMe2YNHAr(CH2Ph)(THF). As shown in Scheme 1, the reactions of the scorpionate-anchored yttrium dialkyl complex Tp Me2 Y(CH2Ph)2(THF) with 1 equiv of aromatic amine (ArNH2) in THF at room temperature gave the yttrium alkyl primary amido complexes TpMe2YNHAr(CH2Ph)(THF) (Ar = Ph (1), C6H3-iPr2-2,6 (2)) in 84% and 88% isolated yields, respectively, indicating that only one N−H bond protolysis of ArNH2 Scheme 1
Received: July 16, 2013 Published: September 12, 2013 5409
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the Cp and ArNH ligands, the Y−C16 distance (2.436(6) Å) is slightly shorter than the corresponding value found in (TpMe2)CpYCH2Ph(THF) (Y−C6 2.528(3) Å),10c possibly due to the smaller steric hindrance around the central metal ion Y3+ in 2, and is comparable to the corresponding values founds in TpMe2Y(CH2Ph)2(THF) (Y1−C1 2.457(8) Å, Y1−C8 2.418(8) Å).10a The Y−N7 bond length (2.242(5) Å) is a standard yttrium−nitrogen σ-bond.5 The other bond parameters are in the normal ranges. Reactions of Complexes 1 and 2 with Carbodiimides. Complexes 1 and 2 have two different active Y−CH2Ph and Y− NHAr bonds and provide a nice chance to explore the insertion selectivity toward unsaturated substrates. So we have also investigated the reactions of 1 and 2 with carbodiimides. Treatment of 1 with 1 equiv of N,N′-diisopropylcarbodiimide (iPrNCNiPr) in THF at room temperature afforded a yttrium dianionic guanidinate complex, TpMe2Y[(iPrN)2C NPh](THF)2 (3), in 74% isolated yield, accompanied with elimination of one toluene molecule. However, an equimolar reaction of 1 and N,N′-di(2,6-diisopropylphenyl)carbodiimide (ArNCNAr) in the same conditions gave the Y−C σ-bond insertion product TpMe2Y[(ArN)2CCH2Ph](NHPh) (4) in 87% isolated yield, as shown in Scheme 2. The formation of 3
occurred in this process. Complexes 1 and 2 are stable and cannot further turn into the corresponding yttrium terminal imido complex TpMe2YNAr(THF)11 by heating for 24 h at THF reflux temperature, except for a little TpMe2 ligand degradation Complexes 1 and 2 are air- and moisture-sensitive and readily soluble in THF and toluene but are slightly soluble in hexane and benzene. They are characterized by elemental analysis and 1H and 13C NMR spectroscopy, which are in good agreement with the proposed structures. In the 1H NMR spectrum of 1 (d8-THF, RT), the peak for 4H-TpMe2 is separated into two single peaks at 5.97 and 5.70 ppm as a molar ratio of 2:1, and the peaks for 3- and 5-Me-TpMe2 are also split into four single peaks at 2.50, 2.42, 2.24, and 1.83 ppm in a 1:2:2:1 ratio. There are three multiple peaks at 6.65−6.07 ppm, which are attributed to the phenyl ring proton of the benzyl and phenyl amino groups. Two characteristic single peaks at 4.75 and 2.31 ppm are assigned to the resonances of NHPh and CH2Ph groups. Moreover, two multiple peaks at 3.62 and 1.77 ppm are assigned to the resonances of the coordinated THF molecule. Similar peaks of the 1H NMR spectrum of 2 (in C6D6, RT) were observed with the additional resonances of two isopropyl groups at 3.14 ppm for CH(CH3)2 and 1.00 ppm for CH(CH3)2 with J = 6.4 Hz. The solid-state structure of 2 was further confirmed by single-crystal X-ray diffraction analysis. The molecular structure of 2, including selected bond lengths and angles, is compiled in Figure 1. The X-ray structural
Scheme 2
disclosed an interesting carbodiimide insertion selectivity between the Y−CH2Ph and Y−NHPh bond of 1. As it is known, the metal−carbon σ-bond is usually more reactive than the metal−nitrogen σ-bond in the two chemical bond coexisting systems,8a,13 and carbodiimide is prone to first insertion of the Y−CH2Ph bond of 1 during the reaction of 1 with iPrNCNiPr to give the Y−C bond insertion product Tp Me2 Y[( iPrN) 2 CCH2Ph](NHPh), similar to 4. So we speculated that the formation of 3 underwent a N−H bond addition process of the primary amido group to the CN double bond of carbodiimide due to the existence of an active N−H bond in the primary amido ligand and then underwent a guanidinate protolysis and toluene elimination process (Scheme 3, pathway a). Indeed, we also cannot exclude other possible progress of the reaction such as formation a yttrium
Figure 1. Molecular structure of TpMe2YCH2Ph(NHAr)(THF) (2) with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Y1−N7 2.242(5), Y1−O1 2.371(5), Y1−C16 2.436(6), Y1−N1 2.449(6), Y1−N3 2.395(5), Y1−N5 2.521(5), C16−Y1−O1 93.7(2), C16−Y1−N7 91.1(2), N7−Y1−O1 99.5(2).
Scheme 3. Two Possible Processes of the Formation of 2
analysis results show that 2 is a solvated monomer with the yttrium atom bonded to a κ3-TpMe2 ligand, a primary amido ligand, a η1-benzyl group, and one THF molecule to form a distorted facial-octahedral geometry. The bonding mode of the benzyl group to metal is similar to that observed in (TpMe2)CpYCH2Ph(THF) and TpMe2Y(CH2Ph)2(THF),10a,c but different from that observed in [(Me3Si)2NC(NCy)2]Ln(η3-CH2Ph) (Ln = Er, Y).12 Considering the steric difference of 5410
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double peaks, at 1.52 (J = 6.8 Hz) and 1.21 (J = 6.4 Hz) ppm, assignable to the resonances of four CH(CH3)2 groups in a 12:12 ratio. This might be attributed to the symmetric coordination mode of the dianionic guanidinate ligand (iPrN)2CNAr with the center metal (vide infra). In the 1H NMR spectrum of 4 (C6D6, RT), the peak for 4HTpMe2 is also separated into two single peaks at 5.72 and 5.36 ppm in a molar ratio of 1:2, and the peaks for 3- and 5-MeTpMe2 split into four single peaks at 2.39, 2.12, 2.08, and 1.79 ppm in a 3:3:6:6 ratio. The multiple peaks at 6.88−7.26 ppm are attributed to the resonances of the phenyl ring proton of C6H5 and C6H3. Two characteristic single peaks at 5.51 and 3.90 ppm are assigned to the resonances of NHPh and CH2Ph. Two multiple peaks at 3.66 and 3.46 ppm are assigned to the resonances of CH(CH3)2 in a 2:2 ratio, and four double peaks at 1.59, 1.50, 1.00, and 0.68 ppm are assigned to the resonances of CH(CH3)2 with J = 6.4 Hz in a 6:6:6:6 ratio. Similar peaks in the 1H NMR spectrum of 6 (in C6D6, RT) were observed with the resonances of two additional isopropyl groups and slight differences in the chemical shift between 6 and 4. The molecular structures and selected bond parameters of 3−6 are given in Figures 2−5, respectively. Figure 2 displays
terminal imido species C by the protolysis of the N−H bond with another Y−CH2C6H5 bond under the coordination interaction of the carbodiimide moiety,11 accompanied with toluene molecule elimination and undergoing a cycloaddition with one of the CN double bonds of the carbodiimide to form 3 (Scheme 3, pathway b). Moreover, the insertion selectivity between the Y−CH2Ph and Y−NHPh bonds of 1 depends on the steric hindrance of the substituent groups of carbodiimides R. To extend the scope of these reactions and explore more the steric hindrance of the primary amido ligand toward the influence of insertion selectivity, we also studied the reaction of 2 with iPrNCNiPr in the same conditions and found that the two products TpMe2Y[(iPrN)CNAr](THF) (5) and TpMe2Y[(iPrN)2CCH2Ph](NHAr) (6) were isolated in 58% and 19% yields, respectively (Scheme 4). This result revealed Scheme 4
that the two insertions of Y−CH2Ph and Y−NHAr bonds (or N−H bond addition) are competitive in the reactions. So we have performed 1H NMR monitoring experiments of the reaction of 1 with iPrNCNiPr or ArNCNAr (Ar = C6H3-iPr2-2,6) in D8-THF at room temperature and showed that the reaction of 1 with iPrNCNiPr produced 3 and TpMe2Y[(iPrN)2CCH2Ph](NHPh) in about 9:1 molar ratio; however, the reaction of 1 with ArNCNAr gave only 4, and no N−H bond addition product TpMe2Y[(ArN)C NAr](THF) was detected. These results indicated that the insertion of Y−NHAr bonds (or N−H bond addition) is more easily effected by the steric hindrances of carbodiimides and primary amido ligands than that of the Y−CH2Ph bond. Complexes 3−6 were also characterized by elemental analysis, 1H and 13C NMR spectroscopy, and single-crystal Xray analysis. The 1H NMR spectra of these compounds displayed a different number of signals, in agreement with their solid-state structures. For example, three single peaks in the 1H NMR spectrum of 3 (C6D6, RT) at 5.55, 2.26, and 2.08 ppm are assigned to the resonances of 4H-TpMe2 and 3- and 5-MeTpMe2 in a 3:9:9 ratio, and two group peaks at 4.82 (1H), 4.34 (1H), 2.51 (6H), 2.49 (3H), and 2.30 (3H) ppm are assigned to the resonances of two isopropyl groups with J = 6.4 Hz. The resonances of two coordinated THF molecules display two multiple peaks at 3.49 and 2.11 ppm in a 8:8 ratio. The multiple peaks in the range 7.01−7.24 ppm are assigned to the resonance of the phenyl group. However, the peak for 4HTpMe2 in the 1H NMR spectrum of 5 (C6D6, RT) is separated into two single peaks at 5.60 and 5.57 ppm in a molar ratio of 2:1, and the peaks for 3- and 5-Me-TpMe2 also split into four single peaks at 2.40, 2.38, 2.08, and 2.06 ppm in a 6:3:6:3 ratio. Two multiple peaks at 3.56 and 1.43 ppm in 5 are assigned to the resonances of the coordinated THF molecule in a 4:4 molar ratio, indicating that only one THF molecule is coordinated with the central metal ion Y3+ in 5. Moreover, although there are four isopropyl groups in 5, the number of peaks assignable to them is fewer than that observed in 3. There are only two
Figure 2. Molecular structure of TpMe2Y[(iPrN)2CNPh](THF)2 (3) with thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Y1−N1 2.297(3), Y1−N3 2.289(3), Y1−O1 2.510(3), Y1−O1 2.461(3), N1−C1 1.441(5), N2−C1 1.305(5), N3−C1 1.374(5), N1−C1−N2 127.4(4), N1−C1−N3 108.8(4), N2−C1−N3 123.4(4).
that complex 3 is a solvated monomer with the yttrium atom bonded to a κ3-TpMe2 ligand, a chelating guanidinate ligand, and two THF molecules to form a distorted one-capped octahedral geometry. The key structural data show that the dianionic guanidinate ligand [iPrNC(NiPr)Ph] is constructed and connected with the Y3+ ion in an asymmetric coordination mode, similar to that of the reported dianionic guanidinatesupported metal complexes such as [(iPrN)2CNMe2]2Ti[iPrNC(NiPr)NC6F5].14 This asymmetric coordination mode has also been confirmed by the 1H NMR spectra of 3 in solution. The distance of the central carbon and noncoordinated nitrogen (C1−N2 1.305(4) Å) is slight longer than the standard C(sp2)N(sp3) double bond length (1.28 Å).15 Consistent with this observation, the C1−N1 and C1−N3 5411
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Figure 5. Molecular structure of TpMe2Y[(iPrN)2CCH2Ph](NHAr) (6) with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Y1−N7 2.218(3), Y1−N8 2.338(3),Y1−N9 2.360(3), N8−C28 1.327(5), N9−C28 1.330(5), C28−C29 1.517(5), N8−C28−C29 122.1(4), N9−C28−C29 123.8(4), N8−C28−N9 114.1(4).
monomer with the yttrium atom bonded to a κ3-TpMe2 ligand, a chelating amidinate group, and an aryl amido moiety to form a distorted octahedron geometry. The newly formed amidinate group forms essentially a planar four-membered ring with the yttrium atom, and the bond angles around C16 are consistent with sp2 hybridization. The equivalent C16−N7 and C16−N8 distances (1.345(6) and 1.340(6) Å) of the amidinate group are intermediate values between the C−N single- and double-bond distances, indicating that the π-electrons of the CN double bond in the present structure are partially delocalized.16 Consistent with this observation, the Y−N7 and Y−N8 distances, 2.398(5) and 2.385(5) Å, are approximately equivalent and are intermediate between the values observed for a Y−N single or donor bond. The Y−N9 distance (2.223(5) Å) is also a standard Y−N σ-bond.5 A single-crystal X-ray diffraction study for 5 (Figure 4) revealed its structural similarity to 3. Unlike 3, the dianionic guanidinate moiety [(iPrN)2CNAr] in 5 coordinates the yttrium center through two nitrogen atoms bonded to the isopropyl groups with Y−N bond lengths of 2.230(3) and 2.219(3) Å, respectively, while the nitrogen atom bonded to the aryl group is not coordinated to the yttrium center. The C16− N9 distance is 1.305(4) Å and is comparable to the corresponding value found in 3 (C1−N2 1.292(4) Å). The nonequivalence of the two C−N bonds for the guanidinate ligand is pronounced (C1−N1 1.441(5) Å; C1−N3 1.374(5) Å). It is also noteworthy that the dianionic guanidinate ligand bonding mode in 5 is different from that of [( i PrN) 2 CNMe 2 ]2 Ti[ iPrNC(N i Pr)NC 6 F 5 ]14 and 3, in which the guanidinate ligands are bonded to the metal center in a asymmetric coordination mode. Moreover, the yttrium metal also bound one coordinated THF molecule in 5. The structural discrimination between 5 and 3 might be attributed to the difference of the steric hindrance of the aryl and phenyl groups. Figure 5 shows that the total molecular structure of 6 is similar to that of 4, except for the difference of the substituents of the amidinate and amido groups. The newly formed amidinate ligand [(iPrN)2CCH2Ph] also coordinates with the yttrium metal in a η2-bonding mode. The corresponding bond distances (C28−N8 1.327(5) Å, C28−N9 1.330(5) Å, Y−N8 2.338(3) Å, Y−N9 2.360(3) Å) are slightly shorter than those
Figure 3. Molecular structure of TpMe2Y[(ArN)2CCH2Ph](NHPh) (4) with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Y1−N7 2.398(4), Y1−N8 2.385(4), Y1−N9 2.223(5), N7− C16 1.345(6), N8−C16 1.340(6), C17−C16 1.532(7), N7−C16− C17 120.9(5), N7−C16−N8 115.9(4), N8−C16−C17 123.1(5).
Figure 4. Molecular structure of TpMe2Y[(iPrN)CNAr](THF) (5) with thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Y1−N7 2.230(3), Y1−N8 2.219(3), Y1−O1 2.362(3), N7−C16 1.404(5), N8−C16 1.369(5), N9−C16 1.292(4), N7−C16−N8 108.8(3), N7−C16−N9 130.3(4), N8−C16−N9 120.9(3).
distances are 1.441(5) and 1.374(5) Å, respectively, in the range of the C(sp2)−N single bond.5 Moreover, the yttrium metal also bound two coordinated THF molecules, and its coordination number is seven. Complex 4 (Figure 3) crystallizes in the monoclinic space group P2(1)/c, and its overall structure is a solvent-free 5412
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colorless crystals of 2. Yield: 0.319 g (88%). Anal. Calcd for C38H55N7BOY (725.60): C, 62.90; H, 7.64; N, 13.51. Found: C, 63.09; H, 7.72; N, 13.26. 1H NMR (400 MHz, C6D6): δ 6.68−7.22 (m, 8H, C6H5 and C6H3), 5.55 (s, 3H, 4H-TpMe2), 5.00 (s, 1H, NH), 3.54 (m, 4H, O(CH2CH2)2), 3.14 (m, 2H, CH(CH3)2), 2.18−2.30 (three overlapped peaks, 20, CH3-TpMe2 and CH2Ph), 1.46 (m, 4H, O(CH2CH2)2), 1.00 (d, 12H, CH(CH3)2, J = 6.4 Hz). 13C NMR (100 MHz, C6D6): 155.84 (s, 3-C-Pz), 152.16 (s, 3-C-Pz), 150.72 (s, 3-CPz), 145.45 (s, 5-C-Pz), 135.09 (s, 5-C-Pz), 128.72 (s, C6H5 or C6H3), 123.74 (s, C6H5 or C6H3), 122.61 (s, C6H5 or C6H3), 116.70 (s, C6H5 or C6H3), 116.03 (s, C6H5 or C6H3), 106.22 (s, 4-C-Pz), 67.94 (s, THF), 51.99 (d, Y-CH2C6H5, JY−C = 9 Hz), 28.16 (s, CHMe2), 25.85 (s, THF), 24.28 (s, CHMe2), 14.38 (s, 3-Me-Pz), 12.96 (s, 5-Me-Pz). Synthesis of TpMe2Y[(iPrN)2CNPh](THF)2 (3). In the glovebox, to a 15 mL THF solution of 1 (0.321 g, 0.50 mmol) was slowly added i PrNCNiPr (0.063 g, 0.50 mmol). After stirring overnight at room temperature, the solution was concentrated to dryness under reduced pressure. After washing by n-hexane (2 × 10 mL), 10 mL of toluene was added to the residue, and then the solution was concentrated to ca. 5 mL by reduced pressure. Colorless crystals of 3 were obtained at −35 °C for several days. Yield: 0.276 g (74%). Anal. Calcd for C36H57BN9O2Y (747.63): C, 57.84; H, 7.69; N, 16.86. Found: C, 57.62; H, 7.64; N, 16.98. 1H NMR (C6D6, 400 MHz): δ 7.01−7.24 (m, 5H, C6H5), 5.55 (s, 3H, 4H-TpMe2), 4.82 (m, 1H, CH(CH3)2), 4.34 (m, 1H, CH(CH3)2), 3.49 (s, 8H, O(CH2CH2)2), 2.26 (s, 9H, CH3 of TpMe2), 2.11 (s, 8H, O(CH2CH2)2), 2.08 (s, 9H, CH3 of TpMe2), 1.51 (d, 6H, CH(CH3)2, J = 6.4 Hz),1.49 (d, 3H, CH(CH3)2, J = 6.4 Hz), 1.30 (d, 3H, CH(CH3)2, J = 6.4 Hz). 13C NMR (100 MHz, C6D6): δ 182.44 (s, NCN) 154.39 (s, 3-C-Pz), 150.43 (s, 3-C-Pz), 145.93 (s, 5-C-Pz), 137.83 (s, 5-C-Pz), 129.34 (s, C6H5), 128.58 (s, C6H5), 125.71 (s, C6H5), 106.00 (s, 4-C-Pz), 70.57 (s, THF), 46.45, 27.15 (s, CHMe2), 26.00 (s, THF), 23.06 (s, CHMe2), 21.46 (s, CHMe2), 13.92 (s, 3-Me-Pz), 12.94 (s, 3-Me-Pz). Synthesis of TpMe2Y[(ArN)2CCH2Ph](NHPh) (4). In the glovebox, to a 15 mL THF solution of 1 (0.321 g, 0.50 mmol) was slowly added ArNCNAr (0.181 g, 0.50 mmol). After stirring overnight at room temperature, the solution was concentrated to dryness under reduced pressure. After washeing by n-hexane (2 × 10 mL), 10 mL of toluene was added to the residue, and then diffusion of n-hexane to the concentrated toluene solution gave colorless crystals of 4. Yield: 0.405 g (87%). Anal. Calcd for C53H69BN9Y (931.89): C, 68.31; H, 7.46; N, 13.53. Found: C, 68.47; H, 7.55; N, 13.34. 1H NMR (C6D6, 400 MHz): δ 6.88−7.26 (m, 16H, C6H5 or C6H3), 5.72 (s, 1H, 4H-TpMe2), 5.51 (s, 1H, NH), 5.36 (s, 2H, 4H-TpMe2), 3.90 (s, 2H, CH2Ph), 3.66 (m, 2H, CH(CH3)2), 3.46 (m, 2H, CH(CH3)2), 2.39 (s, 3H, CH3 of TpMe2), 2.12 (s, 3H, CH3 of TpMe2), 2.08 (s, 6H, CH3 of TpMe2), 1.79 (s, 6H, CH3 of TpMe2), 1.59 (d, 6H, CH(CH3)2, J = 6 Hz), 1.55 (d, 6H, CH(CH3)2, J = 6 Hz), 1.00 (d, 6H, CH(CH3)2, J = 6.4 Hz), 0.68 (d, 6H, CH(CH3)2, J = 6.4 Hz). 13C NMR (100 MHz, C6D6): δ 178.40 (s, NCN), 150.92 (s, 3-C-Pz), 145.47 (s, 3-C-Pz), 143.70 (s, 3C-Pz), 142.94 (s, 5-C-Pz), 142.21 (s, 5-C-Pz), 135.77 (s, 5-C-Pz), 130.28 (s, C6H5 or C6H3), 128.71 (s, C6H5 or C6H3), 126.58 (s, C6H5 or C6H3), 125.55 (s, C6H5 or C6H3), 124.92 (s, C6H5 or C6H3), 124.06 (s, C6H5 or C6H3), 123.79 (s, C6H5 or C6H3), 116.19 (s, C6H5 or C 6 H 3 ), 106.16 (s, 4-C-Pz), 105.68 (s, 4-C-Pz), 36.32 (s, (ArN)2CCH2Ph), 29.56 (s, CHMe2), 29.38 (s, CHMe2), 27.81 (s, CHMe2), 26.98 (s, CHMe2), 25.34 (s, CHMe2), 24.66 (s, CHMe2), 23.65 (s, CHMe2), 23.42 (s, CHMe2), 16.45 (s, 3-Me-Pz), 13.59 (s, 3Me-Pz), 13.01 (s, 5-Me-Pz), 12.98 (s, 5-Me-Pz). Synthesis of TpMe2Y[(iPrN)CNAr](THF) (5) and TpMe2Y[(iPrN)2CCH2Ph](NHAr) (6). In the glovebox, to a 15 mL THF solution of 2 (0.507 g, 0.70 mmol) was slowly added iPrNCNiPr (0.088 g, 0.70 mmol). After stirring overnight at room temperature, the solution was concentrated to dryness under reduced pressure. After washing by n-hexane (2 × 10 mL), 10 mL of toluene was added to the residue, and then the solution was concentrated to ca. 5 mL by reduced pressure. Colorless crystals of 5 were obtained at −35 °C for several days. Yield: 0.308 g (58%). Anal. Calcd for C38H61N9BOY (759.68): C, 60.08; H, 8.09; N, 16.59. Found: C, 60.30; H, 8.11; N, 16.30. 1H NMR (400 MHz, C6D6): δ 7.04−7.30 (m, 3H, C6H5), 5.60
observed in complex 4 (C16−N7 1.345(6) Å, C16−N8 1.340(6) Å, Y−N7 2.398(5) Å, Y−N8 2.385(5) Å). This might be attributed to the stronger steric hindrance of the substituents of the amidinate ligand in the latter. Consistent with this observation, the Y−N7 distance (2.218(3) Å) is also slightly shorter than that of 4 (Y−N9 2.223(5) Å), though the steric hindrance of the Ar group is larger than that of the phenyl group.
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CONCLUSION In summary, the selectivity of carbodiimide insertion of Y−C and Y−N σ-bonds of TpMe2-supported yttrium alkyl primary amido complexes was investigated for the first time and revealed that this selectivity depends on the steric hindrance of the substituent groups of carbodiimides and the primary amido unit. The newly formed dianionic guanidinate ligands bonded with the yttrium ion in the symmetric and asymmetric coordination modes.
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EXPERIMENTAL SECTION
General Methods. All reactions were carried out under a dry and inert atmosphere either using standard Schlenk techniques or under a nitrogen atmosphere in an MBraun glovebox. The nitrogen in the glovebox was constantly circulated through a copper/molecular sieves catalyst unit. The oxygen and moisture concentrations in the glovebox atmosphere were monitored by an O2/H2O Combi-Analyzer (MBraun) to ensure both were always below 1 ppm. The solutions such as tetrahydrofuran, toluene, and n-hexane were refluxed and distilled over sodium benzophenone ketyl under nitrogen immediately prior to use. Benzene-d6 and tetrahydrofuran-d8 were heated to reflux over Na/K alloy and vacuum-transferred. TpMe2Y(CH2Ph)2(THF) was synthesized by the literature method.10a N,N′-Diisopropylcarbodiimide, N,N′-di(2,6-diisopropylphenyl)carbodiimide (ArNCNAr, Ar = C6H3-iPr2-2,6), and 2,6-diisopropylphenyl amine (ArNH2) were purchased from TCI Chemical (Shanghai) Company and used as received without further purification. Phenyl amine was distilled prior to use. Elemental analysis for C, H, and N was carried out on a Rapid CHN-O analyzer. 1H and 13C NMR data were obtained on a Brüker DMX-400 NMR spectrometer (FT, 400 MHz for 1H NMR; 100 MHz for 13C NMR). Synthesis of TpMe2YCH2Ph(NHPh)(THF) (1). In the glovebox, to a 15 mL THF solution of TpMe2Y(CH2Ph)2(THF) (0.961 g, 1.50 mmol) was slowly added PhNH2 (0.140 g, 1.50 mmol). After stirring overnight at room temperature, the solution was concentrated to dryness under reduced pressure. After washing by n-hexane (2 × 10 mL), 10 mL of toluene was added to the residue, and then diffusion of n-hexane to the concentrated toluene solution gave colorless microcrystals of 1. Yield: 0.812 g (84%). Anal. Calcd for C32H43BN7OY (641.46): C, 59.92; H, 6.76; N, 15.29. Found: C, 59.65; H, 6.65; N, 15.47. 1H NMR (400 MHz, d8-THF): δ 6.65 (m, 4H, C6H5), 6.26 (m, 4H, C6H5), 6.07 (m, 2H, C6H5), 5.97 (s, 1H, 4HTpMe2), 5.70 (s, 2H, 4H-TpMe2), 4.75 (b, 1H, NH), 3.62 (m, 4H, O(CH2CH2)2), 2.50 (s, 3H, CH3-TpMe2), 2.42 (s, 6H, CH3-TpMe2), 2.31 (s, 2H, CH2Ph), 2.24 (s, 6H, CH3-TpMe2), 1.83 (s, 3H, CH3TpMe2), 1.77 (m, 4H, O(CH2CH2)2). 13C NMR (100 MHz, d8-THF): 151.45 (s, 3-C-Pz), 151.00 (s, 3-C-Pz), 150.48 (s, 5-C-Pz), 149.66 (s, 5-C-Pz), 128.88 (s, C6H5), 128.75 (s, C6H5), 128.48 (s, C6H5), 121.69 (s, C6H5), 116.64 (s, C6H5), 116.40 (s, C6H5), 107.24 (s, 4-C-Pz), 105.94 (s, 4-C-Pz), 32.33 (s, Y-CH2C6H5), 14.22 (s, 3-Me-Pz), 13.27 (s, 3-Me-Pz), 12.89 (s, 5-Me-Pz), 12.43 (s, 5-Me-Pz). Synthesis of TpMe2YCH2Ph(NHAr)(THF) (2, Ar = C6H3-iPr2-2,6). In the glovebox, to a 15 mL THF solution of TpMe2Y(CH2Ph)2(THF) (0.320 g, 0.50 mmol) was slowly added ArNH2 (0.089 g, 0.50 mmol). After stirring overnight at room temperature, the solution was concentrated to dryness under reduced pressure. After washing by nhexane (2 × 10 mL), 10 mL of toluene was added to the residue, and then diffusion of n-hexane to the concentrated toluene solution gave 5413
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Organometallics
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(s, 2H, 4H-TpMe2), 5.57 (s, 1H, 4H-TpMe2), 4.43 (m, 2H, CH(CH3)2), 3.82 (m, 2H, CH(CH3)2), 3.56 (m, 4H, O(CH2CH2)2), 2.40 (s, 6H, CH3-TpMe2), 2.38 (s, 3H, CH3-TpMe2), 2.08 (s, 6H, CH3-TpMe2), 2.06 (s, 3H, CH3-TpMe2), 1.52 (d, 12H, CH(CH3)2, J = 6.8 Hz), 1.43 (m, 4H, O(CH2CH2)2). 1.21 (d, 12H, CH(CH3)2, J = 6.4 Hz). 13C NMR (100 MHz, THF-d8): δ 179.08 (s, NCN), 151.16 (s, 3-C-Pz), 147.70 (s, 3-C-Pz), 138.53 (s, 5-C-Pz), 129.53 (s, C6H3), 123.94 (s, C6H3), 122.17 (s, C6H3), 106.95 (s, 4-C-Pz), 68.85 (s, THF), 28.08 (s, CHMe2), 27.00 (s, THF), 24.26 (s, CHMe2), 24.15 (s, CHMe2), 15.27 (s, 3-Me-Pz), 13.83 (s, 5-Me-Pz). Further crystallization by diffusion of n-hexane into the above mother liquor yielded colorless crystals of 6. Yield: 0.104 g (19%). Anal. Calcd for C41H61BN9Y (779.71): C, 63.16; H, 7.89; N, 16.17. Found: C, 62.90; H, 7.81; N, 16.34. 1H NMR (400 MHz, C6D6): δ 6.89−7.42 (m, 8H, C6H5 or C6H3), 5.62 (s, 1H, 4H-TpMe2), 5.54 (s, 2H, 4H-TpMe2), 5.30 (s, 1H, NH), 3.79 (m, 3H, CH2Ph and CH(CH 3)2 ), 3.61−3.64 (m, 2H, CH(CH 3) 2), 2.96 (m, 1H, CH(CH3)2), 2.37 (s, 6H, CH3 of TpMe2), 2.23 (s, 3H, CH3 of TpMe2), 2.16 (s, 6H, CH3 of TpMe2), 2.10 (s, 3H, CH3 of TpMe2), 1.52 (br, 6H, CH(CH3)2), 1.20 (d, 6H, CH(CH3)2, J = 6 Hz), 0.91 (d, 6H, CH(CH3)2, J = 6 Hz), 0.72 (br, 6H, CH(CH3)2). 13C NMR (100 MHz, C6D6): δ 175.05 (s, NCN), 152.76 (s, 3-C-Pz), 150.56 (s, 3-CPz), 149.47 (s, 3-C-Pz), 145.68 (s, 5-C-Pz), 145.04 (s, 5-C-Pz), 137.57 (s, 5-C-Pz), 129.09 (s, C6H5 or C6H3), 128.80 (s, C6H5 or C6H3), 126.77 (s, C6H5 or C6H3), 115.42 (s, C6H5 or C6H3), 106.27 (s, 4-CPz), 48.10 (s, (iPrN)2CCH2Ph), 26.37 (s, CHMe2), 24.92 (s, CHMe2), 14.70 (s, 3-Me-Pz), 13.08 (s, 5-Me-Pz). NMR Tube Reaction of Complex 1 with iPrNCNiPr. In the glovebox, a J. Young valve NMR tube was charged with 1 (27 mg, 0.040 mmol), D8-THF (0.80 mL), and iPrNCNiPr (0.040 mmol). The reaction was immediately monitored by 1H NMR spectroscopy. A ca. 9:1 molar ratio of 3 and Tp Me2 Y[(iPrN)2CCH2Ph](NHPh) was observed after two days. NMR Tube Reaction of Complex 1 with ArNCNAr. In the glovebox, a J. Young valve NMR tube was charged with 1 (27 mg, 0.040 mmol), D8-THF (0.80 mL), and ArNCNAr (0.040 mmol). The reaction was immediately monitored by 1H NMR spectroscopy. Quantitative formation of 4 was observed after two days. X-ray Data Collection, Structure Determination, and Refinement. Suitable single crystals of complexes 2−6 were sealed under N2 gas in Lindemann glass capillaries for X-ray structural analysis. Diffraction data were collected on a Bruker SMART Apex CCD diffractometer using graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation. During the intensity data collection, no significant decay was observed. The intensities were corrected for Lorentz−polarization effects and empirical absorption with the SADABS program.17 The structures were solved by the direct method using the SHELXL-97 program.18 All non-hydrogen atoms were found from the difference Fourier syntheses. The H atoms were included in calculated positions with isotropic thermal parameters related to those of the supporting carbon atoms, but were not included in the refinement. All calculations were performed using the Bruker Smart program.
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ACKNOWLEDGMENTS We thank the NNSF, NSF of Shanghai, 973 Program (2012CB821600), and Shanghai Leading Academic Discipline Project (B108) for financial support.
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REFERENCES
(1) Reviews: (a) Zhou, X.; Zhu, M. J. Organomet. Chem. 2002, 647, 28. (b) Molander, G. A.; Romero, J. A. C. Chem. Rev. 2002, 102, 2161. (c) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673. (d) Weiss, C. J.; Marks, T. J. Dalton Trans. 2010, 6576. (2) (a) Roux, E. L.; Liang, Y.; Storz, M. P.; Anwander, R. J. Am. Chem. Soc. 2010, 132, 16368. (b) Seo, S.; Yu, X.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 263. (c) Weiss, C. J.; Wobser, S. D.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 2062. (d) Zhang, W.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2008, 47, 9700. (e) Yu, X.; Seo, S.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 7244. (f) Zhang, W.; Nishiura, M.; Hou, Z. J. Am. Chem. Soc. 2005, 127, 16788. (3) (a) Cheng, J.; Wang, H.; Nishiura, M.; Hou, Z. Chem. Sci. 2012, 3, 2230. (b) Venugopal, A.; Fegler, W.; Spaniol, T. P.; Maron, L.; Okuda, J. J. Am. Chem. Soc. 2011, 133, 17574. (c) Zhang, J.; Yi, W.; Zhang, Z.; Chen, Z.; Zhou, X. Organometallics 2011, 30, 4320. (d) Cheng, J.; Ferguson, M. J.; Takats, J. J. Am. Chem. Soc. 2010, 132, 2. (e) Takenaka, Y.; Shima, T.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2009, 48, 7888. (4) (a) Zhang, W.; Wang, Z.; Nishiura, M.; Xi, Z.; Hou, Z. J. Am. Chem. Soc. 2011, 133, 5712. (b) Hong, J.; Zhang, L.; Yu, X.; Li, M.; Zhang, Z.; Zheng, P.; Nishiura, M.; Hou, Z.; Zhou, X. Chem.Eur. J. 2011, 17, 2130. (c) Zhang, Z.; Zhang, L.; Li, Y.; Hong, L.; Chen, Z.; Zhou, X. Inorg. Chem. 2010, 49, 5715. (d) Evans, W. J.; Walensky, J. R.; Ziller, J. W. Inorg. Chem. 2010, 49, 1743. (e) Casely, I. J.; Suh, Y. S.; Ziller, J. W.; Evans, W. J. Organometallics 2010, 29, 5209. (f) Litlabo, R.; Zimmermann, M.; Saliu, K.; Takats, J.; Tö rnroos, K. W.; Anwander, R. Angew. Chem., Int. Ed. 2008, 47, 9560. (g) Evans, W. J.; Forrestal, K. J.; Ziller, J. W. J. Am. Chem. Soc. 1998, 120, 9273. (5) (a) Zhu, X.; Fan, J.; Wu, Y.; Wang, S.; Zhang, L.; Yang, G.; Wei, Y.; Yin, C.; Zhu, H.; Wu, S.; Zhang, H. Organometallics 2009, 28, 3882. (b) Zhang, J.; Han, Y.; Han, F.; Chen, Z.; Weng, L.; Zhou, X. Inorg. Chem. 2008, 47, 5552. (c) Ma, L.; Zhang, J.; Cai, R.; Chen, Z.; Zhou, X. Dalton Trans. 2007, 2718. (d) Liu, R.; Zhang, C.; Zhu, Z.; Luo, J.; Zhou, X.; Weng, L. Chem.Eur. J. 2006, 12, 6940. (e) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 959. (f) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2003, 22, 5385. (6) (a) Evans, W. J.; Miller, K. A.; Ziller, J. W. Inorg. Chem. 2006, 45, 424. (b) Zhang, C. M.; Liu, R. T.; Zhou, X.; Chen, Z.; Weng, L.; Lin, Y. Organometallics 2004, 23, 3246. (7) (a) Yi, W.; Zhang, J.; Hong, L.; Chen, Z.; Zhou, X. Organometallics 2011, 30, 5809. (b) Zhang, W.; Nishiura, M.; Mashiko, T.; Hou, Z. Chem.Eur. J. 2008, 14, 2167. (c) Douglass, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 2001, 123, 10221. (d) Douglass, M. R.; Marks, T. J. J. Am. Chem. Soc. 2000, 122, 1824. (8) (a) Schmiege, B. M.; Fieser, M. E.; Ziller, J. W.; Evans, W. J. Organometallics 2012, 31, 5591. (b) Han, F.; Zhang, J.; Yi, W.; Zhang, Z.; Yu, J.; Weng, L.; Zhou, X. Inorg. Chem. 2010, 49, 2793. (c) Zhang, J.; Ma, L.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2005, 24, 738. (9) (a) Zhang, J.; Zhou, X. Dalton Trans. 2011, 40, 9637. (b) Yi, W.; Zhang, J.; Chen, Z.; Zhou, X. Organometallics 2012, 31, 7213. (c) Han, Y.; Zhang, J.; Han, F.; Zhang, Z.; Weng, L.; Zhou, X. Organometallics 2009, 28, 3916. (10) (a) Yi, W.; Zhang, J.; Zhang, F.; Zhang, Y.; Chen, Z.; Zhou, X. Chem.Eur. J. 2013, DOI: 10.1002/chem.201300610. (b) Yi, W.; Zhang, J.; Chen, Z.; Zhou, X. Inorg. Chem. 2012, 51, 10631. (c) Yi, W.; Zhang, J.; Li, M.; Chen, Z.; Zhou, X. Inorg. Chem. 2011, 50, 11813. (d) Han, F.; Zhang, J.; Han, Y.; Zhang, Z.; Chen, Z.; Weng, L.; Zhou, X. Inorg. Chem. 2009, 48, 1774. (11) Examples of rare-earth metal terminated imido complexes: (a) Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J. C.; Mindiola, D. J. Angew. Chem., Int. Ed. 2008, 47, 8502. (b) Lu, E.; Li, Y.; Chen, Y. Chem. Commun. 2010, 46, 4469. (c) Chu, J.; Lu, E.; Liu, Z.; Chen, Y.;
ASSOCIATED CONTENT
S Supporting Information *
Tables of atomic coordinates and thermal parameters, all bond distances and angles, and experimental data for all structurally characterized complexes. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. Notes
The authors declare no competing financial interest. 5414
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Leng, X.; Song, H. Angew. Chem., Int. Ed. 2011, 50, 7677. (d) Wicker, B. F.; Fan, H.; Hickey, A. K.; Crestani, M. G.; Scott, J.; Pink, M.; Mindiola, D. J. J. Am. Chem. Soc. 2012, 134, 20081. (12) Zhang, Z.; Zhang, L.; Li, Y.; Hong, L.; Chen, Z.; Zhou, X. Inorg. Chem. 2010, 49, 5715. (13) Siladke, N. A.; Ziller, J. W.; Evans, W. J. J. Am. Chem. Soc. 2011, 133, 3507. (14) Ong, T. G.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2003, 125, 8100. (15) Mullins, S. M.; Duncan, A. P.; Bergman, R. G.; Arnold, J. Inorg. Chem. 2001, 40, 6952. (16) (a) Zhang, J.; Ruan, R.; Shao, Z.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2002, 21, 1420. (b) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G. J. Chem. Soc., Perkin Trans. 1987, S1. (17) Sheldrick, G. M. SADABS, A Program for Empirical Absorption Correction; University of Göttingen: Germany, 1998. (18) Sheldrick, G. M. SHELXL-97, Program for the Refinement of the Crystal Structure; University of Göttingen: Germany, 1997.
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