Hydrogenolysis and Protonation of Polymetallic Lutetium Methylidene

Jul 22, 2013 - ABSTRACT: We report the hydrogenolysis and protonation reactions of a tetrametallic lutetium tetramethylidene complex. [Cp′Lu(μ3-CH2...
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Hydrogenolysis and Protonation of Polymetallic Lutetium Methylidene and Methyl Complexes Tingting Li,†,‡ Masayoshi Nishiura,‡,§ Jianhua Cheng,‡ Wenxiong Zhang,‡,§ Yang Li,† and Zhaomin Hou*,†,‡,§ †

State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China ‡ Organometallic Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan § Advanced Catalysis Research Group, RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan S Supporting Information *

ABSTRACT: We report the hydrogenolysis and protonation reactions of a tetrametallic lutetium tetramethylidene complex [Cp′Lu(μ3-CH2)]4 (Cp′ = C5Me4SiMe3) (1) and a trimetallic lutetium hexamethyl complex [Cp′Lu(μ2-CH3)2]3 (2) with H2 and ammonium borate compounds. The hydrogenolysis of 1 with H2 afforded the corresponding tetrahydride tetramethyl complex [Cp′4Lu4(μ4-H)(μ3-H)(μ2-H)2(μ2-Me)4] (3) in 87% yield. In this transformation, each of the four [Lu-μ2-CH2] methylidene groups in 1 reacted with one molecule of H2 to give a mixed methyl/hydride “Lu(H)CH3” unit. The reaction of 1 with [PhMe2NH][B(C6F5)4] gave the cationic tetrametallic lutetium monomethyl trimethylidene complex [Cp′4Lu4(μ3-CH2)3(μ3-CH3)][B(C6F5)4] (4) in 85% yield, through protonation of one of the four methylidene units in 1 with the anilinium borate. In contrast, the reaction of the trimetallic hexamethyl complex 2 with H2 led to formation of a tetrametallic lutetium monohydride heptamethyl complex [Cp′4Lu4(μ4-H)(μ3-Me)(μ2-Me)6] (5) in 65% yield, while the protonation reaction of 2 with 3 equiv of [Et3NH][BPh4] gave a monometallic lutetium monomethyl contact-ion-pair complex [Cp′LuMe(η6-Ph)(η1-Ph)BPh2] (6) in 81% yield. Complexes 3−6 were fully characterized by 1H and 13 C NMR, single-crystal X-ray diffraction, and micro elemental analyses.

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INTRODUCTION Carbene and alkylidene complexes of d-block transition metals have been the subject of extensive studies in the past four decades, because of their crucial roles as catalysts and reagents in a wide range of synthetic applications.1,2 In contrast, studies on rare-earth or f-block metal carbene or alkylidene complexes have remained rather limited.3−9 The formation of a rare-earth alkylidene species such as Li[Lu(CH2SiMe3)2(CHSiMe3)] was first described in 1979,3 while the first X-ray structural characterization of a rare-earth carbene complex such as [Sm{C(Ph2P=NSiMe3)2}(NCy2)(THF)] was achieved in 2000.4 Since then, various structurally characterized rare-earth carbene and methylidene complexes, including polymetallic methylidenes, have been reported.5−7 However, the reactivity studies of the rare-earth carbene or alkylidene complexes were mainly limited to reactions with unsaturated substrates, focusing on nucleophilic addition to unsaturated CX bonds (X = O, N). The hydrogenolysis of rare-earth alkyl complexes with H2 is a well-known useful method for the synthesis of rare-earth hydride complexes.10 On the other hand, the protonation of rare-earth dialkyl complexes by an anilinium borate compound such as [PhNMe2H][B(C6F5)4] can afford the corresponding cationic monoalkyl complexes acting as highly active olefin polymerization catalysts.10h,11 In contrast, the investigation on © XXXX American Chemical Society

the hydrogenolysis of a rare-earth carbene or alkylidene complex with H2 or protonation with an ammonium borate compound has not been reported as far as we are aware. A cationic rare-earth carbene or alkylidene complex has remained unknown to date, in contrast with plenty of cationic alkyl complexes.12 We recently reported the synthesis and structural characterization of the first cubane-type tetrametallic rare-earth methylidene complexes [Cp′Ln(μ3-CH2)]4 (Ln = Tm, Lu; Cp′ = C5Me4SiMe3)6 and their reactions with some unsaturated substrates such as benzophenone, CO, PhNCO, and a carbodiimide compound.6,7 In this paper, we report the hydrogenolysis of the tetrametallic lutetium methylidene complex [Cp′Lu(μ3-CH2)]4 (1, Cp′ = C5Me4SiMe3) with H2 and its protonation reaction with [PhNMe2H][B(C6F5)4], which afford the corresponding tetrametallic mixed tetrahydride and tetramethyl lutetium complex and a novel cationic trimethylidene methyl lutetium complex, respectively. For comparison, the similar hydrogenolysis and protonation reactions of a trimetallic hexamethyl lutetium complex [Cp′Lu(μ2-CH3)2]3 are also examined. Received: April 9, 2013

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RESULTS AND DISCUSSION Reaction of [Cp′Lu(μ3-CH2)]4 with H2. The hydrogenolysis of the tetramethylidene lutetium complex 1 with H2 (1 atm) in C6H6 at 70 °C took place smoothly, affording the corresponding mixed tetrahydride/tetramethyl complex [Cp′4Lu4(μ2-H)2(μ3-H)(μ4-H)(μ2-Me)4] (3) in 87% isolated yield in 4 h (Scheme 1). In this transformation, each of the four Scheme 1. Hydrogenolysis of a Cubane-Type Tetramethylidene Lutetium Complex with H2

[Lu-μ2-CH2] methylidene groups reacted with one molecule of H2 to give a mixed methyl/hydride “Lu(H)CH3” unit, and therefore, complex 3 can be viewed as a self-assembly of four “Cp′Lu(H)(CH3)” units. The reaction of 1 with D2 at 70 °C yielded the corresponding deuterated analogue [Cp′4Lu4(μD)4(μ-CH2D)4] (3-D) similarly. Complex 3 is soluble in common organic solvents such as THF, benzene, and hexane. Single crystals suitable for X-ray structural analysis were obtained by recrystallization from a hexane solution. The tetrametallic lutetium frame in 3 is close to a regular tetrahedron (Figure 1). One of the four hydride ligands is body-centered in a μ4-H fashion, one is face-capped in a μ3-H form, and two are edge-bridged in a μ2-H style, while all of the four methyl ligands are bonded to the lutetium atoms in a μ2-bonding mode. The overall structure of 3 is similar to those of the tetrametallic rare-earth octahydride complexes such as [Cp′4Ln4(μ4-H)(μ3-H)(μ-H)6(thf)] (Ln = Y, Lu)13 and [Cp′4Y4(μ4-H)(μ3-H)(μ-H)6],13b if the methyl groups in 3 are regarded as hydrides. The average bond length (2.478 Å) of the μ2-Me ligands in 3 is similar to that (2.491 Å) in [Cp′Lu(μ3Me)2]3 (2).6 Complex 3 represents a rare example of structurally characterized polymetallic rare-earth complexes bearing mixed hydride and methyl ligands.14 Complex 3 showed well-resolved 1H and 13C NMR spectra in C6D6 at room temperature. The hydride ligands showed three singlets at δ 6.31, 8.65, 8.96 ppm in a 1:2:1 integration ratio, which can be assigned to one μ4-hydride, two μ2-hydride, and one μ3-hydride ligands, respectively. These results indicate that the “Lu4(μ4-H)(μ3-H)(μ2-H)2(μ2-Me)4” core structure in 3 is rather rigid, and the three different types of hydride ligands could be distinguished from each other on the NMR time scale. This is in sharp contrast with those in the octahydride complexes such as Cp′4Lu4H8(thf),13 which showed one broad singlet at 9.46 ppm due to rapid site exchange in solution. Reaction of [Cp′Lu(μ3-CH2)]4 with [PhMe2NH][B(C6F5)4]. The reaction of 1 with 1 equiv of [PhMe2NH][B(C6 F 5) 4 ] in chlorobenzene gave the ion-pair complex [Cp′4Lu4(μ3-CH2)3(μ3-Me)][B(C6F5)4] (4) containing one CH3 group and three CH2 units, through addition of a proton (H+) to one of the four methylidene groups in 1 (Scheme 2). Complex 4 is insoluble in hexane and toluene, but soluble in chlorobenzene and THF. The 1H NMR spectrum in C6D5Cl

Figure 1. ORTEP drawing of 3 with 30% thermal ellipsoids. Me groups on Cp′ ligands and the hydrogen atoms on methyl units have been omitted for clarity. Selected bond lengths (Å) and angles (deg) in 3: Lu1−H1, 2.12(9); Lu1−H2, 2.29(9); Lu1−H4, 2.09(9); Lu1− C1, 2.490(9); Lu1−C2, 2.470(9); Lu2−H1, 2.03(9); Lu2−H3, 2.12(9); Lu2−C1, 2.452(9); Lu2−C3, 2.491(8); Lu3−H1, 2.22(9); Lu3−H2, 2.16(9); Lu3−H3, 2.10(9); Lu3−C2, 2.499(9); Lu3−C4, 2.467(9); Lu4−H1, 2.09(9); Lu4−H2, 2.39(9); Lu4−H4, 1.95(9); Lu4−C3, 2.503(9); Lu4−C4, 2.451(8); Lu1−C1−Lu2, 90.2(3); Lu1− C2−Lu3, 84.6(3); Lu2−C3−Lu4, 91.1(3); Lu3−C4−Lu4, 86.5(3); Lu(1)···Lu(2), 3.5015(6); Lu(1)···Lu(3), 3.3458(7); Lu(1)···Lu(4), 3.3605(7); Lu(2)···Lu(3), 3.5063(7); Lu(2)···Lu(4), 3.5639(6); Lu(3)···Lu(4), 3.3687(6).

Scheme 2. Protonation of a Cubane-Type Tetramethylidene Lutetium Complex with [PhMe2NH][B(C6F5)4]

showed a sharp singlet at 0.52 ppm (3H) and 1.57 ppm (6H), respectively, for the methyl and the three methylidene units. Single crystals suitable for X-ray analysis were obtained by recrystallization from a mixed chlorobenzene/hexane solution at room temperature. It was revealed that the cationic part of 4 possesses a cubane-like core structure seemingly similar to that of the tetramethylidene complex 1 (Figure 2). The difference Fourier synthesis did not lead to location of all the hydrogen atoms bonding to the methylene and methyl groups in the core, but an examination of the bond distances suggests that C2 may be assigned to a methyl carbon because the average bond distance (2.44 Å) of Lu(1,3,4)-C2 is somewhat longer than those of Lu(1,2,3)-C1 (2.41 Å), Lu(1,2,4)-C3 (2.39 Å), and Lu(2,3,4)-C4 (2.41 Å). The average bond length of the Lu-(μ3CH2) methylidene bonds in 4 (2.41 Å) is slightly longer than that in 1 (2.37 Å). No direct bonding interaction between the cationic tetrametallic lutetium part and the borate anion was observed. To the best of our knowledge, complex 4 represents B

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An X-ray analysis revealed that the hydride ligand in 5 is located at the center of the Lu4 tetrahedron in a μ4-fashion, one methyl group caps a Lu3 plane in a μ3-form, and six methyl groups each bridge a Lu···Lu edge in a μ2-mode (Figure 3). The

Figure 2. ORTEP drawing the cationic part of 4 with 30% thermal ellipsoids. Me groups on Cp′ ligands have been omitted for clarity. Selected bond lengths (Å) and angles (deg) in 4: Lu1−C1, 2.397(9); Lu1−C2, 2.490(8); Lu1−C3, 2.367(8); Lu2−C1, 2.384(9); Lu2−C3, 2.398(8); Lu2−C4, 2.449(7); Lu3−C1, 2.458(8); Lu3−C2, 2.405(8); Lu3−C4, 2.395(8); Lu4−C2, 2.417(9); Lu4−C3, 2.412(7); Lu4−C4, 2.394(8); Lu1−C1−Lu2, 88.4(3); Lu2−C1−Lu3, 89.4(3); Lu1−C1− Lu3, 91.4(3); C1−Lu1−C2, 88.7(3); C1−Lu1−C3, 91.5(3); C2− Lu1−C3, 89.2(3); Lu(1)···Lu(2), 3.3331(13); Lu(1)···Lu(3), 3.4749(15); Lu(1)···Lu(4), 3.4376(16); Lu(2)···Lu(3), 3.406(1); Lu(2)···Lu(4), 3.458(1); Lu(3)···Lu(4), 3.3419(11).

Figure 3. ORTEP drawing of 5 with 30% thermal ellipsoids. Me groups on Cp′ ligands and the hydrogen atoms on methyl units have been omitted for clarity. Selected bond lengths (Å) and angles (deg) in 5: Lu1−H1, 2.109(10); Lu1−C1, 2.611(4); Lu1−C2, 2.447(4); Lu1−C3, 2.477(4); Lu1−C5, 2.554(4); Lu2−H1, 2.089(10); Lu2− C1, 2.595(4); Lu2−C2, 2.461(4); Lu2−C4, 2.469(4); Lu2−C7, 2.565(4); Lu3−H1, 2.177(10); Lu3−C5, 2.447(4); Lu3−C6, 2.436(4); Lu3−C7, 2.461(4); Lu4−H1, 2.212(10); Lu4−C1, 2.573(4); Lu4−C3, 2.468(5); Lu4−C4, 2.480(5); Lu4−C6, 2.531(4); Lu1−C1−Lu2, 80.12(12); Lu1−C1−Lu4, 80.87(12); Lu1−C2−Lu2, 86.12(13); Lu1−C3−Lu4, 85.69(14); Lu1−C5−Lu3, 93.55(14); Lu2−C1−Lu4, 80.66(12); Lu2−C4−Lu4, 85.05(14); Lu2−C7−Lu3, 92.81(14); Lu3−C6−Lu4, 93.54(14); Lu1···Lu2, 3.3509(8); Lu1···Lu3, 3.6450(3); Lu1···Lu4, 3.3623(3); Lu2···Lu3, 3.6406(3); Lu2···Lu4, 3.3448(3); Lu3···Lu4, 3.6200(3).

the first example of a structurally characterized cationic methylidene complex as well as the first example of a cubanetype complex with mixed (μ3-CH2)/(μ3-CH3) units. It is also the first example of a well-defined cationic polymetallic rareearth alkyl (or alkylidene) complex.15,16 Reaction of [Cp′Lu(μ3-Me)2]3 with H2. It is well-known that the hydrogenolysis of monometallic rare-earth dialkyl complexes with H2 can yield the corresponding polymetallic polyhydrides.10 However, the reaction of a polymetallic rareearth polymethyl complex with H2 has not been reported. To see possible difference in reactivity with H2 between the tetramethylidene complex 1 and a polymethyl complex, the reaction of the trimetallic Lu hexamethyl complex [Cp′Lu(μ3Me)2]3 (2) with H2 (1 atm) in C6H6 was then carried out, which afforded a tetrametallic monohydride heptamethyl complex [Cp′4Lu4(μ4-H)(μ3-Me)(μ2-Me)6] (5) in 65% isolated yield at 70 °C in 2 h (Scheme 3). In the course of this hydrogenolysis reaction, an arrangement of the metal core structure from trinuclear to tetranuclear took place. A prolonged reaction time (>4 h) led to formation of a mixture of unidentified hydride species.

overall bonding fashion in 5 is similar to those of the tetramethyl tetrahydride complex 3 and the octahydride complex [Cp′4Lu4(μ4-H)(μ3-H)(μ-H)6(thf)].13a,d The average bond length (2.593 Å) of the Lu-μ3-Me bonds in 5 is longer than that (2.483 Å) of the Lu-μ2-Me bonds. It is noteworthy the average Lu···Lu distance in the heptamethyl monohydride complex 5 (3.494 Å) is only slightly longer than that in the Lu(μ-Me)-free octahydride analogue [Cp′4Lu4(μ4-H)(μ3-H)(μH)6(thf)] (3.451 Å),13a,d despite the presence of seven Mebridges in 5 whose Lu-Me bond distances (2.436(4)−2.611(4) Å) are much longer than those (1.86(6)−2.30(6) Å) in the octahydride analogue. Obviously, the interstitial μ4-H atom plays an important role in formation of the tetrahedral metal skeleton. This may explain why the mixed hydride/methyl complex 5 adopts a tetrahedral core structure, in contrast to the hydride-free methyl analogue 2, which forms a trimetallic structure. Complex 5 is highly soluble in organic solvents such as hexane, toluene, and THF and showed well-resolved 1H and 13 C NMR spectra. The seven methyl groups in 5 showed a singlet at −0.20 ppm (21H) in the 1H NMR spectrum at room temperature in benzene-d6, suggesting that all of the methyl ligands are equivalent on the NMR time scale due to a rapid site exchange in solution. The hydride ligand showed a singlet at 6.47 ppm (1H). Reaction of [Cp′Lu(μ3-Me)2]3 with [Et3NH][BPh4]. When [PhMe2NH][B(C6F5)4] was used to react with the hexamethyl

Scheme 3. Hydrogenolysis of a Trimetallic Hexamethyl Lutetium Complex with H2

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CONCLUSION The hydrogenation (hydrogenolysis and protonation) reactions of the tetrametallic lutetium tetramethylidene complex 1 and the trimetallic lutetium hexamethyl complex 2 with H2 and some ammonium borate compounds have been examined. In the hydrogenolysis of 1, each of the four methylidene groups reacted with one molecule of H2, affording the mixed tetrahydride and tetramethyl complex 3. In contrast, the reaction of the trimetallic lutetium hexamethyl complex 2 with H2 yielded the tetrametallic monohydride heptamethyl complex 5. The reaction of the methylidene complex 1 with [PhMe2NH][B(C6F5)4] afforded the cationic tetrametallic lutetium monomethyl trimethylidene complex 4, constituting the first example of a structurally characterized cationic rareearth methylidene complex. The reaction of the trimetallic hexamethyl complex 2 with [Et 3 NH][BPh 4 ] gave the monometallic monomethyl complex 6 having a contact-ionpair structure. The results described in this paper together with those reported previously6,7 have demonstrated that the cubane-type methylidene rare-earth complexes can show rich reaction chemistry and serve as unique precursors for the synthesis of a new family of well-defined polymetallic rare-earth complexes.

lutetium complex 2, an oily product difficult to identify was obtained. In contrast, the reaction of 1 equiv of [Et3NH][BPh4] with 2 at room temperature in benzene gave the half-sandwich lutetium monomethyl borate compound [Cp′LuMe(η6-Ph)(η1Ph)BPh2] (6) as the only isolable crystalline product. The use of 3 equiv of [Et3NH][BPh4] to react with 2 afforded 6 in 81% yield (Scheme 4). Scheme 4. Protonation of a Trimetallic Hexamethyl Lutetium Complex with [Et3NH][BPh4]

An X-ray diffraction study revealed that 6 is a contact ion pair. There are two independent molecules in the unit cell, and only one is shown in Figure 4. The lutetium atom is bonded to

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EXPERIMENTAL SECTION

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. The argon was purified by being passed through a Dryclean column (4 Å molecular sieves, Nikka Seiko Co.) and a Gasclean GC-XR column (Nikka Seiko Co.). The nitrogen in the glovebox was constantly circulated through a copper/ molecular sieves catalyst unit. The oxygen and moisture content in the glovebox atmosphere were monitered by an O2/H2O Combi-Analyzer (MBRAUN) to ensure both were below 1 ppm. Samples for NMR spectroscopic measurements were prepared in the glovebox by use of J. Young valve NMR tubes. 1H and 13C NMR spectra were recorded on a JEOL-AL400 spectrometer or a JNM-AL300 spectrometer. Elemental analyses were performed by a MICRO CORDER JM10. Anhydrous THF, hexane, benzene, and diethyl ether were purified by Mbraun SPS-800 Solvent Purification System and dried over fresh Na chips in the glovebox. Chlorbenzene was distilled from CaH2 under nitrogen and dried over 4 Å molecular sieves in the glovebox. LuCl3 and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate were purchased from Strem Chemicals Ltd. LiCH2SiMe3 (in hexane) was purchased from Wako Pure Chemical Industries. Ltd., and the hexane solvent was removed under vacuum to obtain LiCH2SiMe3 solid. AlMe3 was purchased from Tosoh Fine Chemical Co. Other commercially available reagents were purchased and used without purification. [(C5Me4SiMe3)4Lu4(μ4-H)(μ3-H)(μ2-H)2(μ2-Me)4] (3). A benzene solution (2 mL) of 1 (81 mg, 0.053 mmol) was settled in a 30 mL Schlenk tube with a Teflon stopcock. The tube was frozen in liquid nitrogen, pumped, and backfilled with H2 (1 atm). The mixture was allowed to warm to room temperature and heated at 70 °C for 4 h. After removal of the solvent by slow evaporation, the resulting white residue was dissolved in hexane. Recrystallization from hexane at −30 °C gave 3 as colorless crystals, which were collected on a filter, washed with hexane, and dried under vacuum (71 mg, 0.046 mmol, 87% isolated yield). 1H NMR (400 MHz, C6D6, RT): δ −0.35 (s, 12H; μ2Me), 0.45 (s, 36H; C5Me4SiMe3), 2.07 (s, 24H; C5Me4SiMe3), 2.30 (s, 24H; C5Me4SiMe3), 6.31 (bs, 1H; Lu-H), 8.65 (bs, 2H; Lu-H), 8.96 ppm (s, 1H; Lu-H). 13C NMR (100 MHz, C6D6, RT): δ 2.7 (s, C5Me4SiMe3), 12.2 (s, C5Me4SiMe3), 15.1 (s, C5Me4SiMe3), 24.9 (μ2Me), 114.6 (s, C5Me4SiMe3), 123.4 (s, C5Me4SiMe3), 126.6 ppm (s, C5Me4SiMe3). Anal. Calcd for C52H100Si4Lu4: C, 40.62; H, 6.55. Found: C, 40.96; H, 6.41. 1H NMR monitoring of the reaction of 1 with D2 at 70 °C showed the formation of [(C5Me4SiMe3)4Lu4(μ-

Figure 4. ORTEP drawing of 6 with 30% thermal ellipsoids. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg) in 6: Lu1−C1, 2.291(5); Lu1−C14, 2.815(5); Lu1−C15, 2.860(5); Lu1−C16, 2.868(5); Lu1−C17, 2.808(5); Lu1−C18, 2.742(4); Lu1−C19, 2.786(4); Lu1−C20, 2.730(5); C1−Lu1−C20, 97.23(18); C19−B1−C21, 100.3(3).

one Cp′ ligand, one terminal methyl group, and two phenyl groups of [BPh4]. The bonding mode of the interaction between the Lu atom and the borate unit in 6 is similar to that previously observed in the samarium(II) complex [(C5Me5)Sm(thf)(η6-Ph)(η1-Ph)BPh2],17 in which one Ph group is bonded to the metal center in an η6 fashion and the other in an η1 form. The bond length of the Lu1-η1-Ph(C20) bond (2.730(5) Å) is shorter than those of the Lu-η6-Ph bonds Lu1C(14−19) (2.742(4)−2.868(5) Å). The Lu-Me bond (2.291(5) Å) in 6 is slightly shorter than that (2.331(4) Å) in the thf-coordinated analogue [(C5Me4SiMe3)LuMe(thf)3][BPh4], which was prepared previously by the reaction of [(C5Me4SiMe3)Lu{(μ-Me)2(AlMe2)}2] with [Et3NH][BPh4] in THF.18 D

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Table 1. Crystal and Data Collection Parameters of Complexes 3−6 empirical formula formula weight temperature [K] wavelength [Å] crystal system, space group a [Å] b [Å] c [Å] α [deg] β [deg] γ [deg] volume [Å3] Z, calcd density [g cm−1] absorption coeff [mm−1] F (000) crystal size [mm] θ range for data collection [deg] max and min transmission data/restraints/parameters goodness-of-fit on F2 final R indices [I > 2σ(I)] R indices (all data)

3

4

5

[6·0.25C6H6]2

C52H100Lu4Si4 1537.56 173(2) 0.71073 monoclinic, C2/c 23.104(4) 12.656(2) 40.687(8) 90 93.394(2) 90 11876(4) 8, 1.720 6.703 6016 0.50 × 0.48 × 0.45 1.77 to 25.00 0.1524 and 0.1345 10420/12/591 1.207 R1 = 0.0395; wR2 = 0.0823 R1 = 0.0436; wR2 = 0.0838

C76H93BF20Lu4Si4 2209.55 173(2) 0.71073 monoclinic, P21/n 15.345(8) 27.761(14) 19.677(10) 90 93.665(9) 90 8365(7) 4, 1.747 4.820 4260 0.35 × 0.28 × 0.25 1.47 to 25.00 0.3787 and 0.2832 14663/34/875 1.038 R1 = 0.0536; wR2 = 0.1418 R1 = 0.0621; wR2 = 0.1492

C55H106Lu4Si4 1579.64 173(2) 0.71073 monoclinic, C2/c 23.0700(13) 12.8629(7) 41.788(2) 90 92.6550(10) 90 12387.2(12) 8, 1.694 6.428 6208 0.15 × 0.10 × 0.10 1.77 to 26.05 0.5657 and 0.4456 12154/3/571 0.944 R1 = 0.0261; wR2 = 0.0427 R1 = 0.0363; wR2 = 0.0447

C77H91B2Lu2Si2 1444.24 173(2) 0.71073 triclinic, P-1 13.754(12) 15.228(13) 18.018(15) 108.885(14) 106.214(14) 97.900(16) 3319(5) 2, 1.445 3.035 1466 0.34 × 0.28 × 0.23 1.53 to 25.00 0.5419 and 0.4251 11471/2/748 1.048 R1 = 0.0316; wR2 = 0.0768 R1 = 0.0406; wR2 = 0.0809

D)4(μ-CH2D)4] (3-D). 1H NMR (400 MHz, C6D6, RT): δ −0.38 (s, 8H; μ2-CH2D), 0.45 (s, 36H; C5Me 4SiMe3), 2.07 (s, 24H; C5Me4SiMe3), 2.30 (s, 24H; C5Me4SiMe3). [(C5Me4SiMe3)4Lu4(μ3-CH2)3(μ3-CH3)][B(C6F5)4] (4). A chlorobenzene solution (2 mL) of [PhMe2NH][B(C6F5)4] (38 mg, 0.048 mmol) was added to a chlorobenzene solution (5 mL) of 1 (73 mg, 0.048 mmol) at room temperature. After 30 min, the solution was filtrated and condensed under reduced pressure. Addition of a small amount of hexane to the solution gave 4 as yellow crystals, which were collected on a filter, washed with hexane, and dried under vacuum (91 mg, 0.041 mmol, 85% isolated yield). 1H NMR (400 MHz, C6D5Cl, RT): δ 0.32 (s, 9H; C5Me4SiMe3), 0.33 (s, 27H; C5Me4SiMe3), 0.52 (s, 3H; CH3), 1.57 (s, 6H; CH2), 1.99 (s, 18H; C5Me4SiMe3), 2.00 (s, 6H; C5Me4SiMe3), 2.18 (s, 6H; C5Me4SiMe3), 2.20 ppm (s, 18H; C5Me4SiMe3). 13C NMR (100 MHz, C6D5Cl, RT): δ 2.2 (s, C5Me4SiMe3), 11.6 (s, C5Me4SiMe3), 13.9 (s, C5Me4SiMe3), 27.8 (s, CH3), 117.9 (s, CH2), 121.7 (s, C5Me4SiMe3), 124.5 (br m, C6F5), 130.5 (s, C5Me4SiMe3), 132.0 (s, C5Me4SiMe3), 136.5 (d, JC−F = 245.3 Hz, C6F5), 138.4 (dt, J1 C−F = 246.3 Hz, J2 C−F = 12.1 Hz, C6F5), 148.6 ppm (d, JC−F = 243.3 Hz, C6F5). Anal. Calcd for C76H93BF20Lu4Si4: C, 41.31; H 4.24. Found: C, 41.53; H, 4.21. [(C5Me4SiMe3)4Lu4(μ4-H)(μ2-Me)7] (5). A benzene solution (1 mL) of 2 (55 mg, 0.046 mmol) was settled in a J. Young valve NMR tube with a Teflon stopcock. The tube was frozen in liquid nitrogen, pumped, and backfilled with H2 (1 atm). The mixture was allowed to warm to room temperature and heated at 70 °C for 2 h. The solvent was removed under reduced pressure to give a white powder. Recrystallization from hexane solution at −30 °C gave 5 as colorless crystals, which were collected on a filter, washed with hexane, dried under vacuum (35 mg, 0.022 mmol, 65% isolated yield). 1H NMR (400 MHz, C6D6, RT): δ −0.20 (s, 21H; Lu-Me), 0.44 (s, 36H; C 5 Me 4 SiMe 3 ), 1.92 (s, 24H; C 5 Me 4 SiMe 3 ), 2.23 (s, 24H; C5Me4SiMe3), 6.47 ppm (s, 1H; Lu-H). 13C NMR (100 MHz, C6D6, RT): δ 3.0 (s, C5Me4SiMe3), 12.5 (s, C5Me4SiMe3), 15.7 (s, C5Me4SiMe3), 27.0 (Lu-Me), 112.9 (s, C5Me4SiMe3), 122.3 (s, C5Me4SiMe3), 126.1 ppm (s, C5Me4SiMe3). Anal. Calcd for C55H106Si4Lu4: C, 41.82; H, 6.76. Found: C, 41.99; H, 6.73. [Cp′LuMe(η6-Ph)(η1-Ph)BPh2] (6). A benzene solution (2 mL) of [Et3NH][BPh4] (198 mg, 0.471 mmol) was added to a benzene solution (5 mL) of 2 (187 mg, 0.157 mmol) at room temperature. After 5 h, the solution was filtrated and condensed under reduced

pressure. The residue was washed with hexane and dissolved in benzene. Slow evaporation of the solution afforded 6 as colorless blocks solvated with benzene (275 mg, 0.381 mmol, 81% isolated yield). 1H NMR (400 MHz, C6D6, RT): δ −1.08 (s, 3H; Lu-Me), 0.17 (s, 9H; C5Me4SiMe3), 1.52 (s, 6H; C5Me4SiMe3), 1.92 (s, 6H; C5Me4SiMe3), 6.88 (br, 4H; BPh4), 7.26 (t, J = 7.1 Hz, 8H; BPh4), 7.53 ppm (d, J = 6.8 Hz, 8H; BPh4). 13C NMR (100 MHz, C6D6, RT): δ 2.2 (s, C5Me4SiMe3), 11.3 (s, C5Me4SiMe3), 14.9 (s, C5Me4SiMe3), 28.9 (s, Lu-Me), 116.8 (s, C5Me4SiMe3), 124.3 (s, BPh4), 125.0 (s, C5Me4SiMe3), 128.4 (s, BPh4), 128.5 (s, C5Me4SiMe3), 130.3 (br s, BPh4), 135.4 ppm (s, BPh4). Anal. Calcd for C77H91B2Lu2Si2 ([6·0.25 C6H6]2): C, 64.03; H, 6.35. Found: C, 64.48; H, 6.44. X-ray Crystallographic Studies. The crystals were sealed in a thin-walled glass capillary under a microscope in the glovebox. Data collections were performed at −100 °C on a Bruker SMART APEX diffractometer with a CCD area detector using graphite-monochromated Mo Kα radiation (λ = 0.71069 Å). The determination of crystal class and unit cell parameters was carried out by the SMART program package.19 The raw-frame data were processed using SAINT20 and SADABS21 to yield the reflection data file. The structures were solved by using SHELXTL program.22 Refinements were performed on F2 anisotropically for all the non-hydrogen atoms by the full-matrix leastsquares method. The analytical scattering factors for neutral atoms were used throughout the analysis. The hydride ligands and the hydrogen atoms of the bridging methyl groups in 3 and 5 were located by difference Fourier synthesis, and their coordinates were refined. The hydrogen atoms of the bridging methylidene and methyl groups in 4 could not be located. Other hydrogen atoms were placed at the calculated positions and were included in the structure calculation without further refinement of the parameters. The C−H bond distances of the bridging methyl groups in 3 and some C−H bonds of the bridging methyl groups in 5 are fixed to 1.0 Å. The disordered cyclopentadienyl ligand on Lu2 in 4 was separated into two parts (C17−C28, Si2 and C17′−C28′, Si2′) and were treated with 59% and 41% occupancy, respectively. The same anisotropic displacement parameters were used for the disordered carbon atoms. The carbon (C78−C83) and fluorine (F16−F20) atoms of one of the four pentafluorophenyl groups in 4 were refined with the same anisotropic displacement parameters, respectively. In the case of 6, there are two independent molecules of the lutetium complexes and a half molecule of the benzene solvate in the unit cell, and two C−C bonds of the E

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benzene molecule were fixed to 1.41 Å. The residual electron densities were of no chemical significance. Crystal data and processing parameters are summarized in Table 1. CCDC-907756 (3), 907754 (4), 907757 (5), and 907755 (6) 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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ASSOCIATED CONTENT

S Supporting Information *

This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address §

Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research (B) (No. 24350030 to M.N.), a Grant-in-Aid for Scientific Research (S) (No. 21225004 to Z.H.) from JSPS. T.L. is grateful to China Scholarship Council and the RIKEN International Program Associate (IPA) for financial support. We thank Dr. Wylie O for help in carrying out the deuteration reaction of 1.

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