Facile Preparation of a Scandium Terminal Imido Complex Supported

Sep 26, 2013 - Changchun 130022, People,s Republic of China. ‡. University of Chinese Academy of Sciences, Beijing 100039, People,s Republic of Chin...
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Facile Preparation of a Scandium Terminal Imido Complex Supported by a Phosphazene Ligand Weifeng Rong,†,‡ Jianhua Cheng,† Zehuai Mou,†,‡ Hongyan Xie,†,‡ and Dongmei Cui*,† †

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China ‡ University of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China S Supporting Information *

ABSTRACT: The scandium bis(alkyl) complex bearing the phosphazene ligand L1Sc(CH2SiMe3)2 (1) (L1 = N(PPh2 NPh)2) reacted with an equimolar amount of 2,6-diisopropylaniline to afford the corresponding mixed alkyl/anilido complex L1Sc[NHC6H3(iPr)2](CH2SiMe3) (2). Under mild conditions (20 °C, 4 h or 0 °C, 12 h), complex 2 could be swiftly transformed to the terminal imido complex L1Sc N[C6H3(iPr)2](DMAP)2 (4) in the presence of DMAP (DMAP = 4-N,N-dimethylaminopyridine). Correspondingly, treatment of the yttrium and lutetium bis(alkyl) complexes L2Ln(CH2SiMe3)2 (L2 = N[Ph2PNC6H3(iPr)2]2; Ln = Y (7), Lu (8)) with equimolar amounts of 2,6-diisopropylaniline gave the mixed alkyl/anilido complexes L2Ln[NHC6H3(iPr)2](CH2SiMe3) (Ln = Y (9), Lu (10)), which, however, underwent dealkylation of the Ln−CH2SiMe3 species at temperatures of 60 °C for 9 and 100 °C for 10 to afford bis(anilido) complexes L2Ln[NHC6H3(iPr)2]2 (Ln = Y (11), Lu (12)) as redistribution products. All these complexes have been characterized by 1H, 13 C{1H}, and 31P{1H} NMR spectroscopy and X-ray diffraction analyses, and clear structural insight into the behavior of an imido functionality on a lanthanide metal center was provided.

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INTRODUCTION The chemistry of metal−nitrogen multiple-bond complexes has witnessed a dramatic surge in research interest in the past decades due to the ability of the MN functionality to undergo a wide range of reactivity.1 Group 4 metal2- and actinide3-based imido complexes have been extensively investigated, in which the imido moiety NR acts as both a spectator ligand and a reactive species. In stark contrast, examples of the lanthanide imido complexes remain scarce, which may be ascribed partially to the mismatch in metal and ligand orbital energies, rendering the formal LnNR highly polarized.4 Thus, lanthanide imido complexes usually adopt the more stable bi- or multinuclear geometry possessing bridging NR2− moieties5 and, sometimes, are stabilized by trialkylaluminum6 or sodium/lithium7 instead of terminal imido species. In 2008, this dilemma was resolved by Mindiola and his coworkers, who demonstrated the generation of scandium terminal imido intermediates by an isotopic labeling study and proved further that scandium imido species can promote intermolecular C−H bond activations.8 The landmark scandium terminal imido complexes were isolated and structurally characterized by Chen et al. by introducing side-armed tridentate (NNN) or tetradentate (NNNN) β-diketiminato ligands,9 and they revealed also the predicted very rich and diverse reactivity of the highly polarized ScN functionality.10 More research findings, thereafter, on metal terminal imido complexes were indicative of the crucial role of the welldesigned ligands.11 Recently, we disclosed the first Cp-based © 2013 American Chemical Society

scandium terminal imido complex, albeit without X-ray diffraction characterization, which can induce the intramolecular C−H bond activation of the phenyl group.12 We have reported that the bis-arylated phosphazene ligated scandium dialkyl complex shows excellent catalytic performance towards the polymerization of conjugated dienes.13 Herein by use of this dialkyl precursor, the scandium terminal imido complex has been successfully isolated at 20 °C or 0 °C in addition we provide a tentative investigation of yttrium and lutetium imido chemistry.

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RESULTS AND DISCUSSION Compared to the LnC bond, the LnN bond exhibits intrinsically stronger interactions due to the higher electronegativity and lower polarizability of the nitrogen atom versus the carbon atom.4 Thus an electron-rich ancillary ligand may be helpful in synthesizing a lanthanide imido complex. In view of such character, the bis-phenylated phosphazene ligand stabilized scandium bis(alkyl) complex 1 was initially chosen as a potential precursor. The stoichiometric reaction of 1 with 2,6-diisopropylaniline (NH2C6H3-2,6-iPr2) in C6D6 at ambient temperature was monitored by NMR techniques. The two sets of resonances around δ 0.91 and 0.39 ppm from methylene and trimethylsilyl disappeared within 2 h, suggesting an amination of the scandium alkyl species. The 31P{1H} NMR spectrum Received: August 9, 2013 Published: September 26, 2013 5523

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Scheme 1. Synthesis of Complexes 2 and 3

Scheme 2. Synthesis of Complex 4

revealed that the sharp singlet at δ 33.55 ppm attributed to complex 1 disappeared completely, while two singlets at δ 33.27 and 32.85 ppm (6:1) appeared, which were attributed to the targeted mixed alkyl/anilido complex 2 (major) and the bis(anilido) complex 3 (minor) (vide inf ra). Dropwise addition of an equimolar amount of 2,6-diisopropylaniline to a toluene solution of 1 at −30 °C and allowing the solution to warm to room temperature and then reacting for another 2 h afforded white solid complex 2, which gave only one sharp singlet, at δ 33.27 ppm, in the 31P{1H} NMR spectrum (yield: 75%). The methylene protons of the scandium alkyl moiety Sc−CH2SiMe3 showed a sharp singlet at δ 0.83 ppm, while the isopropyl groups of the scandium anilido species Sc−NHC6H3-2,6-iPr2 gave a doublet at δ 1.39 (3JHH = 6.4 Hz) and a multiple resonance centered at δ 3.68 ppm (the resonance from amino proton NH was not observed). The integral ratio of the alkyl and anilido ligands was 1:1. Treatment of complex 1 with 2 equivalents of 2,6-diisopropylaniline (NH2C6H3-2,6-iPr2) yielded the bis(anilido) scandium complex 3, which gave a single resonance at δ 32.85 ppm in the 1P{1H} NMR spectrum (Scheme 1). Given that a terminal imido complex can be generated via thermally induced alkane elimination,11b,14−17 the scandium anilido/alkyl complex 2 was first heated in C6D6 at 50 °C for 24 h, but the anticipated alkane elimination via proton abstraction did not happen, but gave complex 3 due to ligand redistribution. As reported previously, addition of an external Lewis base can promote this abstraction,9,11,12 and 4-N,Ndimethylaminopyridine (DMAP) was chosen as a feasible external donor to induce alkane elimination. Addition of DMAP to a toluene solution of 2 at room temperature caused a gradual color change from colorless to orange and dark red within half an hour, suggesting formation of a scandium

terminal imido species.9,12 The targeted scandium terminal imido complex 4 was easily isolated from a mixture of a toluene/n-hexane solution at −30 °C as dark red crystal in 68% yield (Scheme 2). This was in agreement with the 31P{1H} NMR spectrum, which confirmed that the signal assigned to complex 2 (δ = 33.27 ppm) became weakened and disappeared completely in 4 h when the reaction was performed at 20 °C (or at 0 °C for 12 h), while a sharp singlet at δ 28.85 ppm attributed to complex 4 became stronger and stronger. The upfield shift of complex 4 in the 31P{1H} NMR spectrum compared with its precursor 2 indicated the increase of the electron density around the metal center and P atoms, which might be attributed to the formation of a terminal imido species and incorporation of two electron-donating DMAP molecules (δ 2.07, 5.92, 8.66 ppm in the 1H NMR spectrum (C6D6)), as the other part of the complex is similar to that of complex 2. Complex 4 is sparingly soluble in toluene and benzene but soluble in THF without occurrence of intramolecular11c,12 or intermolecular8,11a,b C−H bond activation in this polar solvent. The molecular structure of complex 4 was resolved by X-ray diffraction analysis to crystallize in the monoclinic space group P2(1)/c containing two toluene molecules in the unit cell (4· 2C7H8), as depicted in Figure 1. Complex 4 is a six-coordinate monomer, where the Sc3+ ion is bound to the terminal imido ligand [NC6H3-2,6-iPr2]2− and the pincer-like phosphazene ligand in a κ3 fashion through three nitrogen atoms, different from other structurally characterized five-coordinate scandium terminal imido complexes.9 In addition, there are two DMAP molecules coordinating to the Sc3+ ion as neutral donors. The distances from the Sc3+ ion to nitrogen atoms of the ancillary ligand are 2.564(3), 2.380(3), and 2.282(3) Å, which are longer than those in its dialkyl precursor 1. The Sc−NDMAP bond lengths (2.379(3) and 2.326(3) Å) fall within the normal range 5524

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significant change in Sc−N bonding property.9 The bond angle of Sc−Nimido−C37 of 168.8(3)° is comparable to the reported values (167.90(17)°, 169.6(5)°),9 consistent with the metal− imido bond characteristics. Encouraged by the facile synthesis of the scandium terminal imido complex 4, we attempted to synthesize the yttrium and lutetium analogues.18,19a Reaction of the bis-phenylated phosphazene-stabilized yttrium and lutetium dialkyl complexes (L1Y(CH2SiMe3)2 (5); L1Lu(CH2SiMe3)2 (6)) with equimolar amounts of 2,6-diisopropylaniline at −30 °C led to a mixture of alkyl/anilido and bis(anilido) complexes. Attempts to isolate pure alkyl/anilido complexes failed. To avoid the disproportionation, the yttrium and lutetium dialkyl complexes bearing a more bulky ligand, L 2 Ln(CH 2 SiMe 3 ) 2 (L 2 = N(PPh2NC6H3(iPr)2)2; Ln = Y (7), Lu (8)), were employed to react with 2,6-diisopropylaniline, and the corresponding mixed alkyl/anilido yttrium complex 9 and lutetium complex 10 were isolated in high yields (Scheme 3). It was worth noting that no bis(anilido) complexes were generated during this process even under the presence of excess aniline at their respective temperature. Unlike their scandium analogue 2, the 1H NMR spectra of complexes 9 and 10 exhibited clearly the signal of the amino proton as a doublet at δ 4.86 ppm (2JYH = 1.2 Hz) for Y−NHAr and a singlet at δ 4.51 ppm for Lu−NHAr. X-ray diffraction study further confirmed complexes 9 and 10 were isostructural (Figure 2 and Figure S27). Taking complex 9 as an example, the central yttrium ion is five-coordinate, adopting a distorted tetragonal-pyramidal geometry with the four nitrogen atoms taking the equatorial positions and the metal alkyl carbon atom (C61) occupying the apex. The Y1−C61 bond is almost perpendicular to the plane formed by N1, N2, N3, and N4. The average distance between yttrium and nitrogen atoms of the phosphazene ligand (2.42 Å) is much longer than the Y−Nanilide bond length (2.23 Å) which is consistent with the previously reported Y−Nanilide bond lengths (2.19−2.26).19 Complexes 9 and 10 were heated (Scheme 3), and their behaviors were recorded by 31P{1H} NMR spectroscopy. The results revealed that complex 9 was transformed completely into the corresponding bis(anilido) complex 11 and free ligand

Figure 1. X-ray structure of 4 with 35% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Sc(1)−N(1) 2.564(3); Sc(1)−N(2) 2.380(3); Sc(1)−N(3) 2.282(3); Sc(1)−N(4) 2.379(3); Sc(1)−N(5) 2.326(3); Sc(1)−N(6) 1.853(3); C(37)−N(6)−Sc(1) 168.8(3); N(6)−Sc(1)− N(1) 153.82(12).

for Sc−N single bonds.5,8−13 The scandium imido bond length Sc−Nimido (1.853(3) Å) is close to those observed in the Sc terminal imido complex supported by a tridentate or tetradentate nitrogen β-diketiminato ligand (1.881(5) and 1.8591(18) Å),9 but clearly shorter than those in the scandium μ2-bridged imido complex [({C5H4(CH2)2NMe2}Sc{μ2-NC(Ph)C6H10})2] (2.017(2), 2.056(2) Å)5f and the zwitterionic scandium imido complex [(PNP)Sc{N(Ar)Al(CH 3 ) 3 }] (1.9366(14) Å)8 and much shorter than those of scandium amido bond lengths Sc−Nanilide reported to date,8,9 revealing a Scheme 3. Synthesis of Complexes 9, 10, 11, and 12

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Figure 3. X-ray structure of 11 with thermal ellipsoids drawn at 35% probability. Hydrogen atoms are partly omitted for clarity. Selected bond distances (Å) and angles (deg): Y(1)−N(1) 2.445(3); Y(1)− N(2) 2.490(3); Y(1)−N(3) 2.420(3); Y(1)−N(4) 2.211(3); Y(1)− N(5) 2.206(3); N(4)−Y(1)−N(5) 111.84(12); N(4)−Y(1)−N(2) 121.90(10); N(5)−Y(1)−N(2) 126.22(10).

Figure 2. X-ray structure of 9 with 35% probability thermal ellipsoids. Hydrogen atoms are partly omitted for clarity. Selected bond distances (Å) and angles (deg): Y(1)−N(1) 2.342(5); Y(1)−N(2) 2.561(4); Y(1)−N(3) 2.375(4); Y(1)−N(4) 2.230(5); Y(1)−C(61) 2.366(6); C(61)−Y(1)−N(1) 127.0(2); C(61)−Y(1)−N(2) 103.94(12); C(61)−Y(1)−N(3) 106.69(19); C(61)−Y(1)−N(4) 103.3(2); N(4)−Y(1)−N(1) 90.91(19); N(4)−Y(1)−N(2) 149.75(19); N(4)−Y(1)−N(3) 121.74(18).

the products contained an imido complex or involved an imido intermediate was uncertain.

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CONCLUSIONS We have demonstrated here that a scandium terminal imido complex supported by a pincer-like bis-arylated phosphazene ligand can be swiftly synthesized from its alkyl/anilido precursor via intramolecular alkane abstraction under assistance from the strong Lewis base DMAP, which is stable to intra- or intermolecular C−H bond activation even in polar solvents. Xray structural characterization reveals that the Sc−Nimido bond length in this scandium terminal complex is very close to that of the two structurally well-defined scandium terminal imido complexes reported to date. In contrast, following a similar procedure, the yttrium (lutetium) alkyl/anilido analogue bearing a more bulky bis-arylated phosphazene ligand gives a mixture of intractable materials in the presence of DMAP at room temperature or higher, which undergoes a ligand redistribution during the thermolysis to yield a very stable bis(anilido) complex. The reactivity of the scandium terminal imido complex is under investigation.

HL2 (HN[Ph2PNC6H3(iPr)2]2) when heated at 60 °C for 12 h by giving a new doublet resonance at δ 28.85 ppm (2JYP = 5.2 Hz) arising from 11 and a signal at δ 21.07 ppm assigned to the free phosphazene ligand (Scheme 3 and Figure S16), while thermolysis of complex 10, operated at 100 °C for 12 h, underwent the same pathway to give the bis(anilido) complex 12 (Scheme 3 and Figure S23). Complexes 11 and 12 may result from a ligand redistribution reaction and the thermal decomposition of the generated dialkyl species with release of the neutral phosphzaene ligand.17b,19a No evidence of a transient imido intermediate was observed in the process. An X-ray diffraction study of 11 revealed that the yttrium atom is bound by three nitrogen atoms of the phosphazene ligand and two nitrogen atoms of the anilido fragments (Figure 3). Notably, the measured dihedral angle of the fused fourmembered rings Y1N1P1N2 and Y1N3P2N2 is 173.27°, in contrast to the angle 135.51° in complex 9, suggesting that the overall NPNPNY skeleton takes a slightly distorted planar geometry due to tremendous steric hindrances of eight isopropyl substituents. Furthermore, addition of 2 equivalents of DMAP to 9 and 10 (in C6D6) gave more than one new product with the absence of complexes 9 and 10, which were evidenced by several new sets of resonances at δ 35.47 (t), 9.52 (t), and −7.53 (s) ppm for Y and 35.76 (d), 29.74 (s), 20.81 (s), 10.67 (d) ppm for Lu in the 31 P NMR spectra (Figures S18, S19, S24, and S25). The 1H NMR spectra gave a clear resonance at δ 4.88 ppm for Y (δ 4.59 ppm for Lu), very close to that at δ 4.86 ppm for Y−NH in 9 (δ 4.51 ppm for Lu−NH in 10), seemingly indicating that the linkage of Ln−NH existed in the final products, but whether

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EXPERIMENTAL SECTION

General Methods and Materials. All reactions were carried out under a dry and oxygen-free argon atmosphere by using Schlenk techniques or under a nitrogen atmosphere in an MBraun glovebox. All solvents were purified with an MBraun SPS system. Organometallic samples for NMR spectroscopic measurements were prepared in the glovebox by use of NMR tubes sealed by paraffin film. 1H and 13C{1H} NMR spectra were recorded on a Bruker AV400 (FT, 400 MHz for 1 H; 100 MHz for 13C) spectrometer. 31P{1H} NMR spectra were recorded on a Bruker AV400 (FT, 162 MHz) spectrometer. Elemental analyses were performed at the National Analytical Research Centre of Changchun Institute of Applied Chemistry (CIAC). 2,6-Diisopropylaniline was dried over CaH2 under stirring for 24 h and distilled under reduced pressure before use. 4-Dimethylaminopyridine was purchased from Aldrich and sublimed before use. All the dialkyl complexes were prepared according to literature procedures.13 5526

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Synthesis of the Complex L1Sc[NHC6H3(iPr)2](CH2SiMe3) (2). Under a nitrogen atmosphere, 2,6-diisopropylaniline (0.0676 g, 0.38 mmol) in 5 mL of toluene was added dropwise to a toluene solution (10 mL) of complex 1 (0.3 g, 0.38 mmol) over 30 min at −30 °C. The reaction mixture was stirred for 2 h, and then the volatiles were removed under vacuum to give pale yellow, microcrystalline solids. The solids were washed with a small amount of hexane to remove impurities and dried in vacuo to give a white powder of 2 (0.236 g, 75%). 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 0.39 (s, 9H, CH2SiMe3), 0.83 (s, 2H, CH2SiMe3), 1.39 (d, 3JHH = 6.4 Hz, 12H, CH(CH3)2), 3.68 (sept, 3JHH = 6.4 Hz, 2H, CH(CH3)2), 6.64−6.71 (m, 6H, Ar H), 6.85−6.88 (m, 6H, Ar H), 6.91−7.00 (m, 7H, Ar H), 7.25−7.30 (m, 6H, Ar H), 7.38−7.43 (dd, 4H, Ar H), 7.69−7.74 (dd, 4H, Ar H). 13C{1H} NMR (100 MHz, C6D6, 128.06 ppm, 25 °C): δ 4.12 (s, 3C, CH2SiMe3), 24.20 (s, 4C, CH(CH3)2), 30.26 (s, 2C, CH(CH3)2), 116.75 (s, 2C, N-Ph ispo-C), 121.32 (s, Ar CH), 122.71 (s, Ar CH), 122.78 (s, Ar CH), 122.84 (s, Ar CH), 123.12 (s, Ar CH), 128.44−128.68 (m, Ar CH), 129.27 (s, Ar CH), 129.35 (d, JCP = 5.4 Hz, 1C, Ar ispo-C), 130.46 (d, JCP = 5.3 Hz, 1C, Ar ispo-C), 130.61 (d, JCP = 3.0 Hz, 1C, Ar ispo-C), 131.78 (d, JCP = 3.3 Hz, 1C, Ar ispo-C), 132.20−132.42 (m, Ar CH), 134.29 (s, Ar CH), 146.85 (s, 2C, (iPr)2Ph, ispo-C), 151.21 (s, 1C, NH-Ar, ispo-C). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 33.27 ppm. Anal. Calcd (%) for C52H59N4P2SiSc: C, 71.31; H, 6.74; N, 6.40. Found: C, 71.02; H, 6.55; N, 6.23. Synthesis of the Complex L1Sc[NHC6H3(iPr)2]2 (3). Under a nitrogen atmosphere, 2,6-diisopropylaniline (0.1356 g, 0.77 mmol) in 5 mL of toluene was added to 1 (0.3 g, 0.38 mmol) in 10 mL of toluene in one portion at room temperature. The reaction mixture was stirred for 6 h, and evaporation of the solvent left 3 as pale crystalline solids (0.216 g, 59%), which were washed with a small amount of hexane to remove impurities and dried in vacuo. 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 1.27 (d, 3JHH = 6.4 Hz, 24H, CH(CH3)2), 3.54 (sept, 3JHH = 6.4 Hz, 4H, CH(CH3)2), 6.56−6.62 (m, 4H, Ar H), 6.76−6.97 (m, 16H, Ar H), 7.23−7.30 (m, 8H, Ar H), 7.59−7.64 (m, 8H,Ar H). 13C{1H} NMR (100 MHz, C6D6, 128.06 ppm, 25 °C): δ 23.98 (s, 8C, CH(CH3)2), 30.07 (s, 4C, CH(CH3)2), 117.01 (s, Ar ispo-C), 121.15 (s, Ar CH), 122.45−122.59 (m, Ar CH), 123.12 (s, Ar CH), 128.65 (s, Ar CH), 128.71 (s, Ar CH), 129.19 (s, Ar CH), 129.69 (d, JCP = 1.7 Hz, 2C, Ar ispo-C), 130.82 (d, JCP = 1.4 Hz, 2C, Ar ispoC), 132.28−132.56 (m, Ar CH), 134.57 (s, Ar CH), 146.71 (s, Ar CH), 151.25 (s, 2C, NH-Ar, ispo-C). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 32.85 ppm. Anal. Calcd (%) for C60H66N5P2Sc: C, 74.77; H, 6.85; N, 7.26. Found: C, 74.42; H, 6.91; N, 7.34. Synthesis of the Complex L1ScN[C6H3(iPr)2](DMAP)2 (4). Under a nitrogen atmosphere, 4-dimethylaminopyridine (0.0708 g, 0.58 mmol) in 5 mL of toluene was added dropwise to 2 (0.2538 g, 0.29 mmol) in 10 mL of toluene at 20 °C. The reaction mixture was stirred for 4 h, then the red solution was carefully concentrated to 5 mL, and one drop of hexane was added. Upon standing at −30 °C for 24 h the product crystallized out of solution as dark red crystals (0.237 g, 68%). 1H NMR (400 MHz, C6D5Cl, 7.14, 6.99, and 6.96 ppm, 25 °C): δ 1.36 (d, 3JHH = 6.8 Hz, 12H, CH(CH3)2), 2.32 (s, 12H, N(CH3)2), 4.88 (sept, 3JHH = 6.8 Hz, 2H, CH(CH3)2), 5.88 (d, 3JHH = 6.0 Hz, 4H, Me2NC5H4N), 6.54−6.61 (m, 3H, Ar H), 6.85 (t, 4H, Ar H), 6.94−7.17 (m, PhCH3 + C6D5Cl + Ar H), 7.59−7.65 (m, 13H, Ar H), 8.49 (d, 3JHH = 5.6 Hz, 4H, Me2NC5H4N). 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 1.53 (d, 3JHH = 6.8 Hz, 12H, CH(CH3)2), 2.07 (s, 12H, N(CH3)2), 4.92 (sept, 3JHH = 6.8 Hz, 2H, CH(CH3)2), 5.92 (d, 3JHH = 5.2 Hz, 4H, Me2NC5H4N), 6.67 (t, 3JHH = 7.2 Hz, 2H, Ar H), 6.78−7.13 (m, PhCH3 + Ar H), 7.43 (d, 3JHH = 7.6 Hz, 2H, Ar H), 7.52 (d, 3JHH = 8.0 Hz, 4H, Ar H), 7.71 (br s, 9H, Ar H), 8.66 (d, 3 JHH = 5.2 Hz, 4H, Me2NC5H4N). 13C{1H} NMR (100 MHz, C6D5Cl, 134.19, 129.26, 128.25, 125.96 ppm, 25 °C): δ 25.09 (s, 4C, CH(CH 3 ) 2 ), 27.52 (s, 2C, CH(CH 3 ) 2 ), 38.21 (s, 4C, (CH3)2NC5H4N), 106.16 (s, 4C, (CH3)2NC5H4N), 109.24 (s, ArC), 119.16 (s, Ar-C), 121.88 (s, Ar-C), 123.93 (t, Ar-C), 125.53 (s, ArCH), 128.14 (s, Ar-C), 128.21 (s, Ar-C), 128.62 (s, Ar-C), 131.30 (s, Ar-C), 132.37 (t, Ar-C), 137.73 (s, Ar-C), 139.30 (s, Ar-C), 149.03 (s, Ar-C), 149.96 (s, 4C, (CH 3 ) 2 NC 5 H 4 N), 154.19 (s, 2C, (CH3)2NC5H4N), 156.74 (s, ScN-C). 31P{1H} NMR (162 MHz,

C6D5Cl, 25 °C): δ 29.10 ppm. 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 28.85 ppm. Anal. Calcd (%) for C62H67N8P2Sc·2C7H8: C, 75.10; H, 6.88; N, 9.22. Found: C, 75.47; H, 6.93; N, 9.14. Synthesis of the Complex L2Y[NHC6H3(iPr)2](CH2SiMe3) (9). By a procedure similar to that described for the preparation of 2, treatment of 2,6-diisopropylaniline (0.055 g, 0.31 mmol) with L2Y(CH2SiMe3)2 (7) (0.30 g, 0.30 mmol) at room temperature for 5 h gave white solids of 9. Recrystallization from toluene and hexane at room temperature gave colorless crystalline solids (0.225 g, 69%). Single crystals suitable for X-ray analysis were obtained from benzene and cyclohexane at room temperature overnight. 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 0.27 (d, 2JYH = 3.2 Hz, 2H, CH2SiMe3), 0.46 (s, 9H, CH2SiMe3), 0.54−0.84 (br, 12H, PN−ArCH(CH3)2), 1.12 (d, 3JHH = 6.4 Hz, 12H, NH−ArCH(CH3)2), 1.30−1.50 (br, 12H, PN−ArCH(CH3)2), 2.30 (sept, 3JHH = 6.4 Hz, 2H, NH− ArCH(CH3)2), 3.75 (br, 4H, PN−ArCH(CH3)2), 4.87 (d, 2JYH = 1.2 Hz, 1H, Y−NH), 6.45−6.48 (m, 4H, Ar H), 6.65 (t, 2H, Ar H), 6.77 (t, 1H, Ar H), 6.96−7.07 (m, 8H, Ar H), 7.12−7.14 (m, 6H, Ar H), 7.19−7.22 (m, 4H, Ar H), 7.72−7.77 (m, 4H, Ar H). 13C{1H} NMR (100 MHz, C6D6, 128.06 ppm, 25 °C): δ 5.01 (s, 3C, CH2SiMe3), 24.42 (s, 4C, NH−ArCH(CH3)2), 24.61−28.53 (br, 8C, PN−ArCH(CH3)2), 29.30 (br, 4C, PN−ArCH(CH3)2), 30.29 (s, 2C, NH−ArCH(CH3)2), 37.12 (d, JYC = 46.4 Hz, 1C, CH2SiMe3), 115.30 (s, Ar CH), 122.86 (s, Ar CH), 124.91 (s, Ar CH), 125.20 (s, Ar CH), 125.70 (s, Ar ispo-C), 127.51−127.63 (m, Ar CH), 129.34 (s, Ar CH), 131.23 (s, Ar CH), 131.61 (s, Ar CH), 132.12−132.64 (m, Ar CH), 133.31 (s, Ar CH), 133.93 (d, JCP = 3.6 Hz, 2C, Ar ispo-C), 135.13 (d, JCP = 3.4 Hz, 2C, Ar ispo-C), 140.08 (s, Ar ispo-C), 151.76 (d, JCY = 4.1 Hz, 1C, Y-NH-Ar, ispo-C). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 26.57 ppm (d, 2JYP = 5.7 Hz). Anal. Calcd (%) for C64H83N4P2SiY: C, 70.70; H, 7.69; N, 5.15. Found: C, 70.93; H, 7.61; N, 5.09. Synthesis of L2Lu(NHAr)(CH2SiMe3) (10). To a toluene solution (20 mL) of L2Lu(CH2SiMe3)2 (8) (0.326 g, 0.3 mmol) was added dropwise 1 equiv of 2,6-diisopropylaniline (0.054 g, 0.3 mmol in 2 mL of toluene) at room temperature. The mixture was stirred for 12 h at 60 °C and then concentrated to about 2 mL. Standing at room temperature for 2 days afforded colorless crystals, which were washed with a small amount of hexane and dried in vacuo to give white solids of 10 (0.165 g, 47%). 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 0.12 (s, 2H, CH2SiMe3), 0.50 (s, 9H, CH2SiMe3), 0.55−0.82 (br d, 12H, PN−ArCH(CH3)2), 1.08 (d, 3JHH = 6.4 Hz, 12H, NH− ArCH(CH3)2), 1.28−1.58 (br d, 12H, PN−ArCH(CH3)2), 2.34 (sept, 3JHH = 6.4 Hz, 2H, NH−ArCH(CH3)2), 3.55−4.05 (br d, 4H, PN−ArCH(CH3)2), 4.51 (s, 1H, Lu−NH), 6.45−6.48 (m, 4H, Ar H), 6.65 (t, 2H, Ar H), 6.75 (t, 1H, Ar H), 6.96−7.07 (m, 8H, Ar H), 7.12−7.14 (m, 6H, Ar H), 7.19−7.21 (m, 4H, Ar H), 7.72−7.77 (m, 4H, Ar H). 13C{1H} NMR (100 MHz, C6D6, 128.06 ppm, 25 °C): δ 5.26 (s, 3C, CH2SiMe3), 23.66−25.54 (br, 8C, PN−ArCH(CH3)2), 24.81 (s, 4C, NH−ArCH(CH3)2), 29.09 (br, 4C, PN−ArCH(CH3)2), 29.96 (s, 2C, NH−ArCH(CH3)2), 40.77 (s, 1C, CH2SiMe3), 115.48 (s, Ar CH), 122.91 (s, Ar CH), 125.13 (s, Ar CH), 127.55 (m, Ar CH), 128.63 (s, Ar ispo-C), 131.28 (s, Ar CH), 131.63 (s, Ar CH), 132.23 (s, Ar CH), 132.52 (s, Ar CH), 133.79 (d, JCP = 2.8 Hz, 2C, Ar ispo-C), 134.11 (s, Ar CH), 135.00 (d, JCP = 2.8 Hz, 2C, Ar ispo-C), 139.99 (s, Ar ispo-C), 145.00 (s, Ar ispo-C), 145.96 (s, Ar ispo-C), 152.56 (s, 1C, Lu-NH-Ar, ispo-C). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 27.59 ppm (s). Anal. Calcd (%) for C64H83N4P2SiLu: C, 65.51; H, 7.13; N, 4.77. Found: C, 65.83; H, 7.02; N, 4.70. Synthesis of the Complex L2Y[NHC6H3(iPr)2]2 (11). A toluene solution of 9 (0.217 g, 0.2 mmol) was heated at 60 °C for 12 h, concentrated to remove half of the solvent, and recrystallized in toluene and benzene at room temperature. Colorless crystals of complex 11 grew on the walls of a round-bottomed flask and were carefully collected and dried under vacuum (0.0599 g, 26%). 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 0.24 (br s, 12H, PN− ArCH(CH3)2), 1.23 (br s, 24H, NH−ArCH(CH3)2), 1.34 (d, 3JHH = 6.4 Hz, 12H, PN−ArCH(CH 3 ) 2 ), 3.29 (br, 4H, NH− ArCH(CH3)2), 3.74 (br, 4H, PN−ArCH(CH3)2), 5.72 (d, 2JYH = 2.4 Hz, 2H, Y−NH), 6.78 (t, 3JHH = 7.2 Hz, 2H, Ar H), 6.89−7.13 (m, 5527

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Ar H), 7.28 (br, Ar H). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 28.85 ppm (d, 2JYP = 5.2 Hz). Anal. Calcd (%) for C72H90N5P2Y: C, 73.51; H, 7.71; N, 5.95. Found: C, 73.23; H, 7.85; N, 6.03. Synthesis of the Complex L2Lu[NHC6H3(iPr)2]2 (12). A toluene solution of 10 (0.235 g, 0.2 mmol) was heated at 100 °C for 12 h, concentrated to remove half of the solvent, and recrystallized at room temperature. A white crystalline solid of complex 12 grew on the walls of a round-bottomed flask and were carefully collected and dried under vacuum (0.0858 g, 34%). 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 0.23 + 1.23 + 1.35 (br s, 24H, PN−ArCH(CH3)2), 0.99 (d, 3 JHH = 6.8 Hz, 12H, NH−ArCH(CH3)2), 1.14 (d, 3JHH = 6.8 Hz, 12H, NH−ArCH(CH 3 ) 2 ), 2.64 (sept, 3J HH = 6.8 Hz, 2H, NH− ArCH(CH3)2), 3.19 + 3.37 + 3.80 (br, 4H, PN−ArCH(CH3)2), 3.89 (sept, 3JHH = 6.8 Hz, 2H, NH−ArCH(CH3)2), 5.41 (s, 2H, Lu− NH), 6.77 (t, 3JHH = 7.2 Hz, 2H, Ar H), 6.88−7.13 (m, Ar H), 7.74 (m, Ar H). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ 29.69 ppm (s). Anal. Calcd (%) for C72H90N5P2Lu: C, 68.50; H, 7.19; N, 5.55. Found: C, 68.93; H, 7.01; N, 5.69. X-ray Crystallographic Studies. Crystals for X-ray analysis were obtained as described in the preparations. The crystals were manipulated in a glovebox. Data collections were performed at −88.5 °C on a Bruker SMART APEX diffractometer with a CCD area detector, using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The determination of crystal class and unit cell parameters was carried out by the SMART program package. The raw frame data were processed using SAINT and SADABS to yield the reflection data file. The structures were solved by using the SHELXTL program. Refinement was performed on F2 anisotropically for all non-hydrogen atoms by the full-matrix least-squares method. All non-hydrogen atoms and H atoms in the NH groups of anilido fragments were found from Fourier syntheses of electron density and were refined anisotropically and isotropically for hydrogens. All other hydrogen atoms were placed in calculated positions and were refined in the riding model. CCDC952899 (4), 952900 (9), 952901 (10), and 952898 (11) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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AUTHOR INFORMATION

Mountford, P. Chem. Sci. 2012, 3, 819. (c) Tran, B. L.; Washington, M. P.; Henckel, D. A.; Gao, X.; Park, H.; Pink, M.; Mindiola, D. J. Chem. Commun. 2012, 48, 1529. (d) Basuli, F.; Kilgore, U. J.; Brown, D.; Huffman, J. C.; Mindiola, D. J. Organometallics 2004, 23, 6166. (3) (a) Ephritikhine, M. Organometallics 2013, 32, 2464. (b) Matson, E. M.; Forrest, W. P.; Fanwick, P. E.; Bart, S. C. Organometallics 2013, 32, 1484. (c) King, D. M.; Tuna, F.; McInnes, E. J. L.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Science 2012, 337, 717. (d) Ren, W.; Zi, G.; Fang, D.; Walter, M. D. J. Am. Chem. Soc. 2011, 133, 13183. (e) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Science 2005, 309, 1835. (f) Arney, D. S. J.; Schnabel, R. C.; Scott, B. L.; Burns, C. J. J. Am. Chem. Soc. 1996, 118, 6780. (g) Arney, D. S. J.; Burns, C. J. J. Am. Chem. Soc. 1995, 117, 9448. (h) Duttera, M. R.; Day, V. W.; Marks, T. J. J. Am. Chem. Soc. 1984, 106, 2907. (4) (a) Giesbrecht, G. R.; Gordon, J. C. Dalton Trans. 2004, 2387. (b) Clark, D. L.; Gordon, J. C.; Hay, P. J.; Poli, R. Organometallics 2005, 24, 5747. (c) Summerscales, O. T.; Gordon, J. C. RSC Adv. 2013, 3, 6682. (5) (a) Schädle, D.; Schädle, C.; Törnroos, K. W.; Anwander, R. Organometallics 2012, 31, 5101. (b) Pan, C.; Chen, W.; Song, S.; Zhang, H.; Li, X. Inorg. Chem. 2009, 48, 6344. (c) Berthet, J.; Thuéry, P.; Ephritikhine, M. Eur. J. Inorg. Chem. 2008, 5455. (d) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 959. (e) Avent, A. G.; Hitchcock, P. B.; Khvostov, A. V.; Lappert, M. F.; Protchenko, A. V. Dalton Trans. 2004, 2272. (f) Beetstra, D. J.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics 2003, 22, 4372. (g) Wang, S.; Yang, Q.; Mak, T. C. W.; Xie, Z. Organometallics 1999, 18, 5511. (h) Xie, Z.; Wang, S.; Yang, Q.; Mak, T. C. W. Organometallics 1999, 18, 1578. (i) Trifonov, A. A.; Bochkarev, M. N.; Schumann, H.; Loebel, J. Angew. Chem., Int. Ed. Engl. 1991, 30, 1149. (6) Gordon, J. C.; Giesbrecht, G. R.; Clark, D. L.; Hay, P. J.; Keogh, D. W.; Poli, R.; Scott, B. L.; Watkin, J. G. Organometallics 2002, 21, 4726. (7) Chan, H.; Li, H.; Xie, Z. Chem. Commun. 2002, 652. (8) Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J. C.; Mindiola, D. J. Angew. Chem., Int. Ed. 2008, 47, 8502. (9) (a) Lu, E.; Li, Y.; Chen, Y. Chem. Commun. 2010, 46, 4469. (b) Lu, E.; Chu, J.; Borzov, M. V.; Chen, Y.; Li, G. Chem. Commun. 2011, 47, 743. (10) (a) Chu, J.; Lu, E.; Liu, Z.; Chen, Y.; Leng, X.; Song, H. Angew. Chem., Int. Ed. 2011, 50, 7677. (b) Lu, E.; Zhou, Q.; Li, Y.; Chu, J.; Chen, Y.; Leng, X.; Sun, J. Chem. Commun. 2012, 48, 3403. (c) Chu, J.; Kefalidis, C. E.; Maron, L.; Leng, X.; Chen, Y. J. Am. Chem. Soc. 2013, 135, 8165. (d) Chu, J.; Lu, E.; Chen, Y.; Leng, X. Organometallics 2013, 32, 1137. (11) (a) 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. (b) Wicker, B. F.; Scott, J.; Fout, A. R.; Pink, M.; Mindiola, D. J. Organometallics 2011, 30, 2453. (c) Chu, T.; Piers, W. E.; Dutton, J. L.; Parvez, M. Organometallics 2013, 32, 1159. (12) Jian, Z.; Rong, W.; Mou, Z.; Pan, Y.; Xie, H.; Cui, D. Chem. Commun. 2012, 48, 7516. (13) Rong, W.; Liu, D.; Zuo, H.; Pan, Y.; Jian, Z.; Li, S.; Cui, D. Organometallics 2013, 32, 1166. (14) Conroy, K. D.; Hayes, P. G.; Piers, W. E.; Parvez, M. Organometallics 2007, 26, 4464. (15) (a) Johnson, K. R. D.; Hayes, P. G. Organometallics 2011, 30, 58. (b) Johnson, K. R. D.; Hayes, P. G. Chem. Soc. Rev. 2013, 42, 1947. (16) (a) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 8729. (b) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J. Am. Chem. Soc. 1988, 110, 8731. (c) Walsh, P. J.; Carney, M. J.; Bergman, R. G. J. Am. Chem. Soc. 1991, 113, 6343. (17) (a) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. Organometallics 2003, 22, 4705. (b) Knight, L. K.; Piers, W. E.; Fleurat-Lessard, P.; Parvez, M.; McDonald, R. Organometallics 2004, 23, 2087. (18) (a) Trambitas, A. G.; Yang, J.; Melcher, D.; Daniliuc, C. G.; Jones, P. G.; Xie, Z.; Tamm, M. Organometallics 2011, 30, 1122.

S Supporting Information *

Figures, a table, and CIF files giving 1H, 31P{1H}, and 13C{1H} NMR spectra of complexes and the crystallographic data and structure refinement details. This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Author

*E-mail: [email protected]. Fax: +86 431 85262774. Tel: +86 431 85262773. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partially supported by the National Natural Science Foundation of China for project nos. 20934006, 51073148, and 51021003 and the Ministry of Science and Technology of China for project no. 2011DRF50650.

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