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Feb 20, 2011 - (4) Here, we report a new series of tetra-, penta-, and hexanuclear yttrium polyhydride complexes derived from the hydrogenolysis of th...
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Tetra-, Penta-, and Hexanuclear Yttrium Hydride Clusters from Half-Sandwich Bis(aminobenzyl) Complexes Containing Various Cyclopentadienyl Ligands Takanori Shima, Masayoshi Nishiura, and Zhaomin Hou* Organometallic Chemistry Laboratory and Advanced Catalyst Research Team, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

bS Supporting Information ABSTRACT: The novel series of half-sandwich tetrahydrofuran (THF)-free yttrium bis(aminobenzyl) complexes [(C5Me4R)Y(CH2C6H4NMe2-o)2] (R = SiMe3 (1a), Me (1b), Et (1c), H (1d)) was prepared by treatment of [Y(CH2C6H4NMe2-o)3] with C5Me4RH, and their reactions with H2 and with PhSiH3 in aromatic solvents or in THF were examined. The reaction of 1a with H2 in benzene gave the pentanuclear yttrium decahydride complex [{Cp0 Y(μ-H)2}5] (Cp0 = η5-C5Me4SiMe3) (3), which could not be obtained by the reaction of the corresponding THF-coordinated dialkyl complex [Cp0 Y(CH2SiMe3)2(THF)] with H2. The reaction of 1b with H2 in toluene gave the partially hydrogenated tetranuclear mixed aminobenzyl/hydride complex [(Cp*Y)2(CH2C6H4NMe2-o)(μ-H)3]2 (4; Cp* = η5-C5Me5), and no further hydrogenation reaction occurred, whereas the corresponding reaction of 1b with H2 in THF gave the pentanuclear yttrium polyhydride complex [{Cp*Y(μ-H)2}5(THF)2] (5). Hydrogenolysis of the sterically less demanding C5Me4H-ligated complex 1d with H2 in THF gave the tetranuclear octahydride complex [{CpHY(μ-H)2}4(THF)4] (6; CpH = η5-C5Me4H), which has one coordinating THF ligand on each metal atom. The hexanuclear yttrium dodecahydride complex {[Cp*Y(μ-H)2]6} (7) was obtained by treatment of 1b with PhSiH3 in benzene. The structures of 1a,b,d, 3, 4, [{(C5Me4Et)Y(μ-H)2}5(THF)2] (50 ), 6, and 7 were determined by X-ray single-crystal diffraction studies.

’ INTRODUCTION The chemistry of rare-earth-metal monohydride complexes bearing two anionic ancillary ligands per metal such as Cp2LnH has been intensively studied over the past three decades, partly because of their promise of high activity in various stoichiometric and catalytic processes.1 Recently, rare-earth-metal polyhydride complexes consisting of the dihydride species LLnH2 with one ancillary ligand per metal have received intense interest,2-4 because of their fascinating structure and reactivity, which are remarkably different from those of their monohydride relatives L2LnH. However, the number and the type of this new class of rare-earth-metal dihydride or polyhydride complexes are still very limited. In particular, although various cyclopentadienyl (Cp) ligands have been predominantly used in many rare-earth complexes, the Cp ligands used for the stabilization of rare-earth dihydrides or polyhydrides reported so far in the literature are almost limited to the sterically demanding C5Me4SiMe3 group. Although the hydrogenolysis of the C5Me4SiMe3-coordinated rare-earth bis(trimethylsilylmethyl) complexes [Cp0 Ln(CH2SiMe3)2(THF)] (Cp0 = η5-C5Me4SiMe3) with H2 could easily afford the corresponding tetranuclear octahydrides with a general formula of [Cp0 Ln(μ-H)2]4(THF)n (n = 0-2),2a,b,3a-3q previous attempts to hydrogenate the sterically less demanding r 2011 American Chemical Society

C5Me5-ligated dialkyl complexes [Cp*Lu(CH2CMe3)2(THF)] and [Cp*Lu(CH2CMe3){CH(SiMe3)2}(THF)] (Cp* = η5C5Me5) did not give a structurally characterizable hydride species.5 The Cp*-ligated samarium dihydride species Cp*SmH2 was previously isolated serendipitously together with KH(THF)2 in the Sm(III)/K heteropolymetallic polyhydride form [{Cp*Sm(μ-H)2}6{KH(THF)2}3] by the reaction (σ-bond metathesis and subsequent oxidation) of the Sm(II) alkyl complex [Cp*SmCH(SiMe3)2{Cp*K(THF)2}]n with an excess amount of PhSiH3.3r More recently, several non-Cp-ligated tri-, tetra-, and hexanuclear polyhydride complexes consisting of the dihydride species {(L)LnH2} have been reported by tuning the size of the supporting ligands.4 Here, we report a new series of tetra-, penta-, and hexanuclear yttrium polyhydride complexes derived from the hydrogenolysis of the half-sandwich yttrium bis(aminobenzyl) complexes bearing various cyclopentadienyl ligands [(C5Me4R)Y(CH2C6H4NMe2-o)2] (R = SiMe3 (1a), Me (1b), Et (1c), H (1d)).

Received: December 28, 2010 Published: February 20, 2011 2513

dx.doi.org/10.1021/om1012055 | Organometallics 2011, 30, 2513–2524

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’ RESULTS AND DISCUSSION Synthesis of the Mono(cyclopentadienyl)-Ligated Bis(aminobenzyl) Complexes [(C5Me4R)Y(CH2C6H4NMe2-o)2] (R = SiMe3, Me, Et, H). The alkane elimination reaction between

the yttrium tris(aminobenzyl) complex [Y(CH2C6H4NMe2-o)3]6,7c and 1 equiv of Cp0 H in THF at 70 °C for 12 h gave the corresponding THF-free mono-Cp0 -ligated yttrium bis(aminobenzyl) complex [Cp0 Y(CH2C6H4NMe2-o)2] (1a) in 65% isolated yield (Scheme 1).7 The analogous complexes [(C5Me4R)Y(CH2C6H4 NMe2-o)2] (R = Me (1b), Et (1c), H (1d)) were similarly obtained by the treatment of [Y(CH2C6H4NMe2-o)3] with 1 equiv of the corresponding C5Me4RH (Scheme 1). Complexes 1a-d are thermally stable and showed no decomposition even at 100 °C. The new complexes were fully characterized by means of 1H and 13C NMR spectroscopy, elemental analysis, and X-ray crystallography (for 1a,b,d). Complexes 1a,b,d have similar structures. The molecular structure of 1b, with selected bond lengths and angles, is shown in Figure 1 (see the Supporting Information for the structures of 1a,d). An X-ray diffraction study showed that the two aminobenzyl ligands in 1b are bonded to the metal center in a chelating fashion through both the benzyl CH2 carbon atom and the amino group. No THF ligand was observed, although these complexes were prepared in a THF solution. The Y-C(benzyl) and Y-N bond lengths in 1b (2.436(4)-2.461(4) (av 2.449) and 2.546(3)-2.559(4) (av 2.553) Å, respectively) are comparable with those in 1a (2.444(2)-2.461(2) (av 2.453) and 2.551(2)-2.568(2) (av 2.560) Å), 1d (2.440(6)-2.453(4) (av 2.446) and 2.514(4)2.543(4) (av 2.526) Å), and [Y(CH2C6H4NMe2-o)3] (2.458(3)2.487(3) (av 2.472) and 2.535(2)-2.609(3) (av 2.566) Å).6 The distances between Y and the C atoms of the C5Me4R ring are 2.645(4)-2.705(5) (av 2.679) Å (1b), 2.662(2)-2.704(2) (av 2.679) Å (1a), and 2.609(6)-2.708(6) (av 2.664) Å (1d); these values are close to those in [Cp*2YCH(SiMe3)2] (2.637(6)2.692(6) (av 2.668) Å) and [Cp*2YN(SiMe3)2] (2.632(7)2.737(7) (av 2.680) Å).8 Whereas the basic structures of 1a,b,d are fixed in the solid state, the benzyl groups display fluxionality in solution.9 The 1H NMR spectrum of 1b in toluene-d8 at room temperature showed one set of broad signals at δ 1.29 (2H) and 1.38 (2H) (benzyl CH2) and another set at δ 2.05 (6H) and 2.26 (6H) (NMe2 groups). When the temperature was lowered to -80 °C, the benzyl -CH2- proton signals at δ 1.29 and 1.38 became split into four doublet signals at δ 1.98, 1.41, 1.37, and 1.19 with geminal coupling (9.2 Hz). The NMe2 signals were similarly split into four broad singlets at δ 2.26, 2.15, 2.12, and 1.71. These observations suggest that complex 1b contains endo- and exo-aminobenzyl ligands at lower temperatures, as observed in the X-ray structure. The low-temperature 1H NMR showed a lower-field shift in the signal for the benzylic -CH2- protons,

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which appeared at δ 1.98 (C10-Haxial: see Figure 1, side view 2), and an upper-field shift of the signal of one of the NMe2 groups, which was observed at δ 1.71 (C18 in Figure 1), probably implying the existence of shielding of the aminobenzyl ligand by the endo-phenyl group. Side view 2 in Figure 1 clearly shows the orientation of the endo-phenyl ring, from which the shielding effect on the NMe2 group (C18) and the benzyl protons (H10a) originates. The distance between the centroid of the endo-phenyl group and C18 is about 3.65 Å. When the temperature was raised to 60 °C, the two sets of peaks merged to form broad singlets at δ 2.23 (12H, NMe2) and 1.35 (4H, CH2), respectively. Similar fluxional behaviors were also observed in the low-temperature 1H NMR spectra of 1a,d.9 Reaction of the C5Me4SiMe3-Ligated Complex [(C5Me4SiMe3)Y (CH2C6H4NMe2-o)2] (1a) with Hydrogen. We previously reported that the tetranuclear polyhydride complex 2 was obtained on hydrogenation of [Cp0 Y(CH2SiMe3)2(THF)] in toluene (Scheme 2).2a,b,3a-3q We therefore investigated the hydrogenation reaction of 1a. The reaction of 1a with H2 (1 atm) at 70-80 °C in C6D6 gave complicated mixtures, but the reaction of 1a with H2 at 30 atm in benzene at 40 °C for 62 h resulted in the formation of the pentanuclear yttrium polyhydride complex [{Cp0 Y(μ-H)2}5] (3) in 64% yield, together with N,N,2-trimethylaniline (Scheme 3). The formation of a tetranuclear species similar to 2 was not observed, probably because of the absence of a THF ligand in 1a. Complex 3 is soluble in common organic solvents such as benzene, hexane, and Et2O. Single crystals of 3 suitable for an X-ray structure determination were obtained by recrystallization from i-Pr2O.10 An X-ray analysis of 3 clearly established that it contains a pentanuclear square-pyramidal Y5 metal core frame (Figure 2); this has one apical yttrium metal atom (Y1) and four basal yttrium metal atoms (Y2-Y5). The Y2-Y5 atoms are almost coplanar to within 0.021 Å. There are seven μ2-H ligands and two μ3-H ligands, together with one square-pyramidal μ5-H ligand (H1) at the center of the four basal yttrium metal atoms. Four μ2-H ligands (H2-H5) bridge the two basal yttrium metal atoms, whereas three other μ2-H ligands (H8-H10) bridge the basal and apical yttrium metal atoms. Two μ3-H ligands (H6 and H7) each bridge two basal and one apical yttrium metal atoms. The lengths of the Y-(μ2-H) bonds (1.95(5)-2.12(5) (av 2.04) Å) and the Y-(μ3-H) bonds (2.14(5)-2.31(5) (av 2.23) Å) in 3 are similar to those in 2 (av 2.170 and 2.346 Å)3e and those in other reported rare-earth hydride complexes,11 whereas the lengths of the Y-(μ5-H) bonds (2.38(5)-2.65(5) (av 2.50) Å) are significantly longer than those of other Y-H bonds. Although there are many examples of syntheses of di-, tri-, tetra-, and hexanuclear rare-earth-metal polyhydride complexes by aggregation of monomeric hydride species, this is the first example of pentanuclear rare-earth-metal polyhydride complexes. The pentanuclear decahydride complex 3 could be formed through a “self-assembly” of five THF-free dihydride species [Cp0 YH2] (A) (Scheme 3). Alternatively, it may also be formed by a combination of a tetranuclear octahydride complex (2-THFfree)3m,o with the THF-free dihydride species [Cp0 YH2] (A). In agreement with this assumption, the hydrogenolysis of the bis(aminobenzyl) complex 1a in presence of 1 equiv of 2-THF-free selectively afforded 3 (Scheme 4). In contrast, only a trace amount of 3 was observed when 2-THF-free and [Cp0 Y(CH2SiMe3)2(THF)] were treated similarly with H2. Whereas the bridging hydrides are fixed in the solid state, rapid site exchange of hydride ligands occurs in solution. The 1H NMR 2514

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Figure 1. ORTEP drawings of 1b (left, side view 1; right, side view 2), with thermal ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Y1-C1, 2.461(4); Y1-C10, 2.436(4); Y1-N1, 2.546(3); Y1-N2, 2.559(4); C1-C2, 1.452(5); N1-C7, 1.468(5); N1-C8, 1.481(5); N1-C9, 1.486(5); C10-C11, 1.479(5); N2-C16, 1.468(5); N2-C17, 1.477(5); N2-C18, 1.502(5); Y1-C5Me5(ring), 2.679(5); Y1-C1-C2, 94.3(3); Y1-C10-C11, 100.0(3); Y1-N1-C7, 92.8(2); Y1-N2-C16, 99.1(3).

Scheme 2

Scheme 3

Figure 2. ORTEP drawing of the core structure of 3 with 30% thermal ellipsoids. Selected bond lengths (Å) and angles (deg): Y1-Y2, 3.3916(11); Y1-Y3, 3.6008(11); Y1-Y4, 3.6856(11); Y1-Y5, 3.5995(12); Y2-Y3, 3.6171(11); Y3-Y4, 3.4940(11); Y4-Y5, 3.4821(11); Y2-Y5, 3.5824(11); Y1-H1, 2.47(5); Y2-H1, 2.38(5); Y3-H1, 2.65(5); Y4-H1, 2.61(5); Y5-H1, 2.41(5); Y2-H2, 2.02(5); Y3-H2, 2.12(5); Y2-H3, 2.05(5); Y5-H3, 2.12(5); Y4-H4, 2.00(5); Y5-H4, 2.10(5); Y3-H5, 2.05(5); Y4-H5, 1.95(5); Y1-H6, 2.28(5); Y3-H6, 2.21(5); Y4-H6, 2.14(5); Y1-H7, 2.31(5); Y4-H7, 2.23(5); Y5-H7, 2.22(5); Y1-H8, 1.98(5); Y5-H8, 1.95(5); Y1-H9, 2.09(4); Y3-H9, 2.04(5); Y1-H10, 2.05(5); Y2-H10, 1.97(5); Y1-H1-Y2, 89(2); Y2-H1-Y3, 92(2); Y3-H1-Y4, 83(1); Y4-H1-Y5, 88(2); Y5-H1-Y2, 97(2); Y1-H1-Y3, 89(2); Y1-H1-Y4, 93(2); Y1H1-Y5, 95(2).

Scheme 4

spectrum of complex 3 recorded at room temperature in toluened8 showed one broad signal at δ 4.7 that was assigned to hydride ligands. To elucidate this dynamic process, variable-temperature 1 H NMR (300 MHz) measurements were performed for 3 (Figure 3). At 100 °C, signals of the methyl groups bonded to the Cp0 ring carbons and trimethylsilyl groups were observed at δ 2.53 (30H), 2.28 (30H), and 0.42 (45H), and the signals of the hydrides were equivalent at δ 4.60 (10H), appearing as a sextet (JYH = 12.8 Hz). The chemical shift of the hydride ligands is similar to that found in 2 (δ 4.32), whereas the JYH coupling constant (JYH = 12.3 Hz) in 3 is smaller than that in 2 (JHY = 15.3 Hz). When the temperature was lowered, the hydride signals initially

broadened and then split into two broad signals at -20 °C. The signals then narrowed gradually as the temperature was reduced. At -60 °C, two signals of hydrides were observed at δ 5.40 (t, JHY = 35.8 Hz, 4H) and 4.02 (5H). The first signal (δ 5.40) was assigned to the four μ2-H ligands (H2-H5 in Figure 3) bridging between basal yttrium metal atoms, and the second signal (δ 4.02) 2515

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Figure 3. Variable-temperature 1H NMR spectroscopy (300 MHz, toluene-d8) of 3. The asterisk denotes the toluene-d8 signal.

was assigned to a mixture of the two μ3-H (H6 and H7) and three μ2-H (H8-H10) ligands bridging the apical and basal yttrium atoms. No signal corresponding to the μ5-H ligand (H1) was observed. The signals from the directly attached methyl groups and the trimethylsilyl group of the Cp0 moieties were separated in a 4:1 ratio. The pattern of splitting of the resonance signals for the Cp0 ligands is consistent with the X-ray structure (see above), which consisted of a square pyramid of yttrium atoms each coordinated to one Cp0 group. No decomposition or ligand redistribution of 3 was observed in THF-d8, as monitored by 1H NMR; however, dissolution of 3 in THF may afford the THFligated complex [{Cp0 Y(μ-H)2}5(THF)n].12 To explain the absence of the μ5-H signal in the 1H NMR spectra, we recorded the 2H NMR spectrum of [{Cp0 Y(μ-D)2}5] (3-d10) (Figure 4), prepared by the reaction of 1a with D2 (10 atm). At -60 °C in toluene, three broad deuteride signals were observed at δ 5.4, 4.0, and 2.2. The signal at δ 2.2 can be assigned to an interstitial deuteride, such as μ5-D, the hydride analogue of which could not be observed in the 1H NMR spectrum because of an overlap with the Cp0 methyl signals. The chemical shift of this obscured μ5-H signal (δ 2.2) in 3 is similar to the corresponding value for the interstitial μ4-H hydride ligand in the analogous tetranuclear yttrium cyclohexenyl complex [(Cp0 Y)4(η2-C6H9)(μ4-H)(μ3-H)2(μ-H)4] (δ 2.50).3j In the absence of THF, the hydrogenation reaction of 1a afforded the pentanuclear complex 3 exclusively, whereas hydrogenolysis of 1a in a THF solution gave mainly the tetranuclear complex [{Cp0 YH2}4(THF)2] (20 ) (Scheme 5);13 this complex had been previously obtained in more than 70% yield by

hydrogenolysis of [Cp0 Y(CH2SiMe3)2(THF)] with H2.3j,p,q The 1H NMR spectrum of the crude products mainly showed signals for 20 and N,N,2-trimethylaniline. The formation of the tetranuclear yttrium polyhydride 20 by this reaction suggests that the presence of THF interrupts higher aggregation of [Cp0 YH2] units. Reactions of the C5Me4R-Ligated Complex [(C5Me4R)Y (CH2C6H4NMe2-o)2] (R = Me (1b), Et (1c)) with Hydrogen. Next, we examined the hydrogenation reaction of the Cp*-ligated yttrium bis(aminobenzyl) complex [Cp*Y(CH2C6H4NMe2-o)2] (1b). Previously, several mono(Cp*)-ligated dialkyl complexes, such as [Cp*Lu(CH2CMe3)2(THF)], [Cp*Lu(CH2SiMe3){CH(SiMe3)2}(THF)],5 and [Cp*Ln{CH(SiMe3)2}2] (Ln = La, Ce),14 have been reported, but hydrogenolysis of these complexes did not afford isolable hydride species. The reaction of complex 1b with hydrogen (10 atm) in toluene at 60 °C for 2 days gave the partially hydrogenated tetranuclear yttrium hydride/benzyl complex 4 in 75% yield (Scheme 6). Complex 4 did not undergo further hydrogenolysis at higher pressure of H2. Kempe and Trifonov et al. showed that the reactions of (2,6-i-Pr2C6H4)[6-(2,4,6-i-Pr3C6H3)pyridin-2yl]amide (Ap*)-ligated rare-earth-metal dialkyl complexes [Ap*Ln(CH2SiMe3)2(THF)] (Ln = Y, Lu) with either H2 or PhSiH3 provide the partially hydrogenated trinuclear alkyl/ hydrido complexes [(Ap*Ln)3(μ2-H)3(μ3-H)2(CH2SiMe3)(THF)2], which did not show any further reaction with H2 or PhSiH3.4e Complex 4 was found to be insoluble in almost all common organic solvents, such as benzene, THF, and chlorobenzene, 2516

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Figure 4. Variable-temperature 2H NMR spectroscopy (62 MHz, toluene) of 3-d10.

Scheme 5

Scheme 6

thereby hindering its characterization by NMR spectroscopy. Colorless single crystals of 4 suitable for X-ray study were obtained directly from the reaction solution after the hydrogenolysis of 1b in toluene at room temperature for several days. An X-ray analysis (Figure 5) showed that 4 is a tetranuclear polyhydride complex containing six bridging hydrides, two aminobenzyl (-CH2C6H4NMe2) groups, and four Cp* units. A crystallographic inversion center exists at the center of the molecule. Each aminobenzyl ligand bridges two Y atoms. Two of the six hydrido ligands (H1 and H1*) each bridge three Y atoms, whereas the other four hydrido ligands (H2, H3, H2*, and H3*) each bridge two Y atoms. The Y-H bond lengths (1.82(5)-2.29 (5) Å) are comparable with those reported for other rare-earth hydride complexes.11 The Y-CH2 (2.563(6)-2.694(6) (av 2.629) Å) and Y-NMe2 (2.757(5) Å) distances in 4 are significantly longer than those in [Y(CH2C6H4NMe2-o)3] (av 2.472 and 2.566 Å, respectively)6 or in 1b (av 2.449 and 2.553 Å, respectively), whereas the distances between Y atoms and phenyl atoms of the benzyl group (Y2-Cipso = 2.846(6) Å, Y2Cortho = 2.954(5) Å) are comparable with those in [Y(CH2C6H4NMe2-o)3] (range 2.754(3)-2.919(3) Å). The reaction probably proceeds through aggregation of the monohydride/monobenzyl unit [Cp*YH(CH2C6H4NMe2)] and the dihydride unit [Cp*YH2] (A0 ), which gives the insoluble precipitate 4.

Whereas the hydrogenolysis of 1b in toluene gave the insoluble tetranuclear complex 4, the hydrogenolysis of 1b in THF at 9 atm gave the benzene-soluble pentanuclear yttrium polyhydride complex [{Cp*Y(μ-H)2}5(THF)2] (5) in 74% yield as a white solid (Scheme 7). The hydrogenolysis of [(C5Me4Et)Y(CH2C6H4NMe2-o)2] (1c) is solvent dependent. While the hydrogenolysis of 1c in benzene gave soluble products, which were not isolable, the hydrogenolysis of 1c in THF gave the analogous pentanuclear complex [{(C5Me4Et)Y(μ-H)2}5(THF)2] (50 ), which was obtained only in 29% yield because of the high solubility of the product (Scheme 7). Because of the severely disordered structure of 5, an X-ray diffraction study was carried out by using single crystals of 50 . An ORTEP drawing for 50 is shown in Figure 6, with the relevant bond lengths and angles. The basic structural unit of 50 is similar to that of 3, except that 0 5 contains two additional THF ligands because it bears the less sterically demanding C5Me4Et ligands (compared to C5Me4SiMe3 in 3). The basal plane of the pentanuclear squarepyramidal Y5 metal framework is distorted as a result of the coordination of two THF ligands; the Y2-Y5 atoms in 50 are semicoplanar within 0.34 Å, compared with 0.021 Å in 3. The average lengths of the Y-μ2-H bonds (2.02(4)-2.23(5) (av 2.14) Å), the Y-μ3-H bonds (2.03(4)-2.50(5) (av 2.27) Å), 2517

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Figure 5. ORTEP drawing of 4, with thermal ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Y1-Y2, 3.4074(10); Y1-Y1*, 3.7656(13); Y1-N1, 2.757(5); Y1-C3, 2.694(6); Y2-C3, 2.563(6); Y2-C4, 2.846(6); Y2-C5, 2.954(5); Y1-H1, 2.25(6); Y1*-H1, 2.29(5); Y2-H1, 2.25(6); Y1-H2, 2.18(6); Y2-H2,1.82(5); Y2-H3, 2.01(5); Y1*-H3, 2.19(6); C9N1-Y1, 105.8(3); C4-C3-Y1, 107.2(4); C4-C3-Y2, 86.0(4); Y2C3-Y1, 80.76(17).

Scheme 7

and Y-μ5-H bonds (2.11(5)-2.72(4) (av 2.54) Å) in 50 are similar to those in 3 (av Y-μ2-H, 2.04; Y-μ3-H, 2.23; Y-μ5-H, 2.50 Å). The 1H NMR spectrum of 5 recorded at room temperature in toluene-d8 showed one broad signal at δ 4.26, which was assigned to the bridging hydride ligands. To elucidate the dynamic processes in complex 5, variable-temperature 1H NMR (400 MHz) measurements were performed (Figure 7). The results were quite similar to those for the analogous pentanuclear complex 3. At 70 °C, the hydride signals were observed to be equivalent at δ 4.31 (10H), appearing as a sextet (JYH = 12.3 Hz); this suggested that the hydride ligands couple with all five yttrium atoms. The chemical shift, the coupling pattern, and the JYH coupling constant of the hydride ligands were similar to those found in 3 (δ 4.60, sextet (JYH = 12.8 Hz) at 100 °C). When the temperature was decreased, the hydride signals broadened and, at -40 °C, they split into two broad signals. The signals then gradually narrowed as the temperature fell. At -80 °C, two hydride signals were observed at δ 4.68 (t, JHY = 32.8 Hz, 4H) and 4.06 (m, 5H), respectively. The first signal was assigned to the four μ2-H ligands bridging the basal yttrium metal atoms (Y2-Y5; see also Figure 6), and the second was assigned to a mixture of the four μ3-H and one μ2-H ligands bridging between

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Figure 6. ORTEP drawing of the core structure of 50 , with thermal ellipsoids at the 30% probability level. Selected bond lengths (Å) and angles (deg): Y2-O1, 2.421(3); Y4-O2, 2.427(4); Y1-Y2, 3.7481(7); Y1-Y3, 3.6339(7); Y1-Y4, 3.7563(7); Y1-Y5, 3.3142(6); Y2-Y3, 3.4992(7); Y2-Y5, 3.6190(6); Y3-Y4, 3.5064(7); Y4-Y5, 3.5967(8); Y4-H1, 2.19(5); Y5-H1, 2.06(5); Y4-H2, 2.23(4); Y3-H2, 2.02(4); Y3-H3, 2.11(5); Y2-H3, 2.22(5); Y2-H4, 2.22(4); Y5-H4, 2.23(5); Y1-H5, 2.03(4); Y4-H5, 2.28(4); Y5-H5, 2.35(5); Y1-H6, 2.18(5); Y3-H6, 2.23(4); Y4-H6, 2.47(4); Y1-H7, 2.26(4); Y2-H7, 2.50(5); Y3-H7, 2.23(5); Y1-H8, 2.30(5); Y2-H8, 2.04(4); Y5-H8, 2.40(5); Y1-H9, 2.09(5); Y5-H9, 2.07(4); Y1-H10, 2.74(4); Y2-H10, 2.11(5); Y3-H10, 2.61(5); Y4-H10, 2.54(5); Y5-H10, 2.72(4); O1-Y2-Y4, 85.91(8); O2-Y4-Y2, 85.0(1); Y2-Y1-Y4, 76.10(1); Y3-Y1-Y5, 97.68(2); Y5-Y2-Y3, 94.68(1); Y2-Y3-Y4, 82.64(1); Y3-Y4-Y5, 94.95(1); Y2-Y5-Y4, 79.73(1).

the apical (Y1) and basal (Y2-Y5) yttrium atoms. The interstitial hydride signal was obscured by the Cp* methyl signals. In the 2H NMR spectrum of 5-d10,15 measured at -80 °C in toluene, three deuteride signals were observed at δ 4.8, 4.1, and 2.3.9 The signal at δ 2.3 can be assigned to μ5-D. The chemical shift of this obscured μ5-H signal (δ 2.3) in 5 is similar to that in 3 (δ 2.2). Although the dynamic behavior of the hydride ligands in 5 is similar to that of 3, the dynamic behavior of the Cp* methyl signals in 5 shows further signal separation at low temperatures. At 70 °C, a methyl signal was observed at δ 2.29 (75H). At -40 °C, the resonance signal for the Cp* ligands became split in a 1:4 ratio into peaks at δ 2.46 (15H) and 2.34 (60H); a similar pattern was observed at -60 °C. At -80 °C, however, Cp* methyl signals were observed at δ 2.49 (15H), 2.43 (30H), and 2.32 (30H), and the pattern of splitting of the resonance signal for the Cp* ligands was consistent with the X-ray structure (see above). Reaction of the C5Me4H-Ligated Complex [(C5Me4H)Y (CH2C6H4NMe2-o)2] (1d) with Hydrogen. Although we initially expected the sterically less demanding Cp-supported rareearth-metal complexes to afford polyhydride complexes with a higher nuclearity, hydrogenolysis of 1d in THF afforded the tetranuclear yttrium polyhydride complex [{(C5Me4H)Y (μ-H)2}4(THF)4] (6) in 88% yield, with liberation of N,N, 2-trimethylaniline (Scheme 8). On the other hand, the reaction of 1d with H2 in benzene gave a mixture of unidentified products. An X-ray analysis revealed that 6 adopts a tetranuclear structure in which each of the four Y metal centers is attached to a THF ligand (Figure 8). Eight hydride ligands were located by the structural analysis; four of these were μ2-H ligands, and the 2518

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Figure 8. ORTEP drawing of the core structure of 6 with 30% thermal ellipsoids. Selected bond lengths (Å) and angles (deg): Y1-Y100 , 3.3612(9); Y1-Y10 , 3.4088(9); Y1-Y1*, 3.9859(9); Y1-O1, 2.436(3); Y1-H2, 2.13(4); Y1-H3, 2.16(3); Y1-H4, 2.22(3); Y10 H4, 2.22(4); Y100 -H4, 2.27(3); Y1-H2-Y100 , 105(3); Y1-H3-Y10 , 104(2); Y1-H4-Y100 , 97(1); Y1-H4-Y10 , 100(1); Y10 -H4-Y100 , 125(2).

Figure 7. Variable-temperature 400 MHz 1H NMR spectra (toluened8) of 5 showing (a) the hydride resonances and (b) the Cp* resonances.

Scheme 8

other four were μ3-H ligands. No μ4-H hydrogen ligand at the interstitial position was observed. The Y-H bonding mode of 6 is similar to that of bis(THF)-coordinated yttrium polyhydride complex 20 ,3j,p,q in contrast with that of THF-free or mono(THF)-coordinated yttrium polyhydride complexes, such as 2-THF free3m or 2,3q which contain a μ4-H ligand. The Y4 tetrahedron is highly distorted with both long (3.9859(9) Å) and short (3.3612(9) and 3.4088(9) Å) Y-Y distances. The Y-H bond distances for the μ2-H and μ3-H ligands (range 2.13(4)-2.27(3) Å) were comparable with those found in other yttrium hydride complexes. Complex 6 changed when heated in a benzene solution at 50 °C for several hours,16 whereas a THF solution of 6 was thermally stable, even after 1 day at 60 °C. This suggests that the four THF ligands in 6 are dissociatively labile and could thereby provide reactive metal sites. In the 1H NMR spectrum of 6 in toluene-d8 at room temperature, a broad signal assignable to

bridging hydride ligands was observed at δ 3.70.9 At -40 °C, two hydride signals, in a 4H:4H ratio, were observed at δ 4.20 (t, JHY = 30.8 Hz) and 2.97 (m), respectively. The triplet signal was assigned to four edge-bridging μ2-hydride moieties, and the multiplet signal was assigned to face-bridging μ3-hydride moieties. Reaction of Bis(aminobenzyl) Complex [(C5Me4R)Y (CH2C6H4NMe2-o)2] with PhSiH3. It is well-known that rare-earth-metal hydrides can be synthesized by the reaction of alkyl complexes with H2 or PhSiH3.17 Because we showed that several yttrium bis(aminobenzyl) complexes reacted with H2 to give multinuclear polyhydride complexes, we expected to obtain similar polyhydride complexes by reaction with PhSiH3. Whereas the reactions of 1a,c,d with PhSiH3 gave mixtures of unidentifiable products, the reaction of 1b with 3 equiv of PhSiH3 in benzene at 70 °C for 1 day gave the corresponding hexanuclear hydride complex {[Cp*Y(μ-H)2]6} (7) in 35% isolated yield, together with N,N-dimethyl-2-[(phenylsilyl)methyl]aniline (2-Me2NC6H4CH2SiH2Ph; Scheme 9). Other byproducts could not be characterized. Complex 7 showed a relatively low solubility in common organic solvents, such as hexane, benzene, and toluene, permitting the oily amine to be readily separated from the complex by washing with toluene. Complex 7 was thermally stable and showed no decomposition on heating in THF at 80 °C for 1 day or in toluene at 120 °C for 12 h. No mono(Cp*)-ligated yttrium dihydride species have been reported previously. The only example of a structurally characterized mono(Cp*)-ligated dihydride species is the SmIII/K heterometallic complex [Cp*Sm(μ-H)2]6[(μ-H)K(THF)2]3.3r The molecular structure of 7 was determined by X-ray analysis, as shown in Figure 9. Complex 7 has a hexameric structure in which the six yttrium atoms form a distorted-octahedral core with Y-Y distances ranging from 3.542(2) to 3.816(3) Å (av 3.621 Å). The molecule contains 12 hydrido ligands: 1 interstitial μ6-H ligand, 8 face-capping μ3-H ligands, and 3 edge-bridging μ2-H hydrogen atoms (each bridging hydrido ligand was refined at 75% occupancy as a result of a disorder 2519

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Organometallics Scheme 9

Figure 9. ORTEP drawing of the core structure of 7, with thermal ellipsoids at the 30% probability level. The H3 atom was refined at 75% occupancy. Selected bond lengths (Å) and angles (deg): Y1-Y2, 3.542(2); Y1-Y1*, 3.714(2), 3.816(3); Y1-H1, 2.27(4); Y1*-H1, 2.31(7); Y2-H1, 2.29(6); Y1-H2, 2.40(7); Y2-H2, 2.00(7); Y1-H3, 2.26(5); Y2-H3, 2.59(6); Y1-H4, 2.38(7); Y2*-H4, 2.3(1); Y1-H5, 2.663(1); Y2-H5, 2.341(2); Y1*-Y1-Y1*, 90.00(3); Y1-Y1*-Y1*, 90.00(3); Y1-Y2-Y1*, 63.18(4); Y2-Y1-Y1*, 58.50(4); Y2-Y1*Y1, 58.32(4).

problem). The Y-(μ2-H) bond lengths (2.26(5), 2.59(6) Å) and the Y-(μ3-H) bond lengths (2.00(7)-2.40(7) Å) in complex 7 are longer than those reported for other Y-H bonds. The interstitial H5 atom is formally bonded to all six yttrium atoms in a distorted-octahedral form in which the axial Y2-H5 and Y2*-H5 bonds are much shorter (2.341(2) Å) than the equatorial Y1-H5 and Y1*-H5 bonds (2.663(1) Å), probably due to the μ2-bridging hydride ligands (H3, H3*) between Y1(Y1*) and Y2(Y2*). Previously, Takats et al. have shown that the tris(pyrazolyl)borate (Tp)-ligated hexanuclear lutetium polyhydride complex [{(Tp)LuH2}6] possesses 12 bridging hydride ligands, consisting of 1 μ6-H, 8 μ3-H, and 3 μ2-H ligands;4c this is the same coordination mode as that present in 7. The 1H NMR spectrum of 7 in toluene-d8 at room temperature showed one singlet peak at δ 2.28 for Cp* (90H) and a broad peak at δ 4.19 for bridging hydride ligands, whereas at 110 °C, a septet signal at δ 4.00 (JYH = 10.0 Hz, 12H) was observed. This coupling pattern suggests that each hydrido ligand couples with six yttrium atoms and that all the hydrido ligands are equivalent on the NMR time scale. The coupling constant JYH (10.0 Hz) for the bridging hydride ligands in complex 7 is the smallest reported value for any yttrium hydrido complex, suggesting that there is a close relationship between the value of JYH and the nuclearity of the complex. When the nuclearity increases, the value of JYH decreases (cf. mononuclear [Cp0 2YH(THF)],18 75 Hz; dinuclear [Cp*2YH]2,19 32 Hz, tetranuclear 2, 15.3 Hz; pentanuclear 3, 12.8 Hz; pentanuclear 5, 12.3 Hz; hexanuclear 7, 10.0 Hz). When the temperature was lowered to -20 °C, a single signal for the 11

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hydride ligands (8 μ3-H and 3 μ2-H ligands) was observed at δ 4.18 (septet, JYH = 10.8 Hz, 11H), whereas no signal was observed for the μ6-H ligand, presumably because of an overlap with the signal for Cp* or the remaining methyl proton of toluene-d8. The signal at δ 4.18 remained essentially constant, even at -80 °C, suggesting that all the μ3-H and μ2-H ligands are equivalent on the NMR time scale and that exchange between μ3-H and μ2-H ligands is rapid.

’ CONCLUSIONS A new series of tetra-, penta-, and hexanuclear yttrium polyhydride complexes have been successfully synthesized from the THF-free mono(cyclopentadienyl)-ligated yttrium bis(aminobenzyl) precursors [(C5Me4R)Y(CH2C6H4NMe2-o)2] (R = SiMe3 (1a), Me (1b), Et (1c), H (1d)). The structures of these complexes are dependent on the ligand size, the reaction solvent, and the source of hydride used in the synthesis. Scheme 10 summarizes the results. The reaction of 1a with H2 in THF afforded the tetranuclear yttrium polyhydride complex 20 . In contrast, the reaction of 1a with H2 in benzene gave the pentanuclear yttrium polyhydride complex 3. The reaction of 1b with H2 in toluene gave the insoluble tetranuclear yttrium hydride/ benzyl complex 4. Complex 4 did not undergo further hydrogenation because of its low solubility, whereas 1b reacted with H2 in THF solution to give the THF-coordinated pentanuclear polyhydride complex 5. Although the reaction of 1c with hydrogen in benzene gave no isolable products, a similar hydrogenolysis in THF afforded the pentanuclear analogue 50 , the crystal of which is suitable for X-ray study. Hydrogenolysis of the sterically less demanding C5Me4H-ligated complex 1d with H2 in THF gave the tetranuclear polyhydride 6. A polyhydride cluster complex with a greater nuclearity was obtained by the reaction of 1b with PhSiH3 in benzene; this afforded the hexanuclear polyhydride complex 7, while the other hydride precursors 1a,c,d did not afford isolable products. The ease of formation of the yttrium polyhydride complexes 3-7 in these reactions suggests that the cyclopentadienyl-ligated THF-free rare-earth-metal bis(aminobenzyl) complexes [(C5Me4R)Y(CH2C6H4NMe2-o)2] could serve as useful precursors for the synthesis of various polyhydride complexes with a range of nuclearities, a reaction that cannot be achieved by using the Cp0 -ligated yttrium mono(THF)-coordinated bis(trimethylsilylmethyl) precursor [Cp0 Y(CH2SiMe3)2 (THF)]. Further studies on the reactivities of the yttrium polyhydride complexes and syntheses of new series of rare-earth-metal polyhydride complexes with other metal centers are now in progress. ’ EXPERIMENTAL SECTION General Procedures. 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 (4A 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 concentrations in the glovebox atmosphere were monitored by an O2/H2O CombiAnalyzer (Mbraun) to ensure both were always 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. 2520

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Scheme 10. Summary of the Reactions of Half-Sandwich Bis(aminobenzyl) Complexes 1a-d with H2 and PhSiH3 in Different Solventsa

a

The Cp ligands in the products have been omitted for clarity.

Anhydrous THF, Et2O, hexane, benzene, and toluene were purified by use of a SPS-800 solvent purification system (Mbraun) and dried over fresh Na chips in the glovebox. [{Cp0 Y(μ-H)2}4(THF)n]2a,b,3o-3q (Cp0 = η5-C5Me4SiMe3; n = 0 (2-THF free), 1 (2), 2 (20 )), LiCH2C6H4NMe2-o,20 and [Y(CH2C6H4NMe2-o)3]7c were prepared according to the literature, and 2-THF free, 2, and 20 were stored at -33 °C in the glovebox. C5Me4H(SiMe3), C5Me5H, and C5Me4H2 were purchased from Aldrich and used as received. Other reagents were used as received. [(C5Me4SiMe3)Y(CH2C6H4NMe2-o)2] (1a). A THF solution (1 mL) of trimethyl(2,3,4,5-tetramethyl-2,4-cyclopentadienyl)silane (97 mg, 0.50 mmol) was added to a THF solution (5 mL) of [Y(CH2C6H4NMe2-o)3] (246 mg, 0.50 mmol) at room temperature in a Schlenk tube with a Teflon stopcock. This tube was taken outside and heated to 70 °C for 12 h. The solvent was removed under reduced pressure. The residue was dissolved in hexane and was cooled to -30 °C to afford pale yellow crystals of 1a (179 mg, 0.32 mmol, 65%), which were suitable for X-ray analysis. 1H NMR (C6D6, 60 °C): 7.07 (d, JHH = 7.7 Hz, 2H, aryl), 6.96 (t, JHH = 7.7 Hz, 2H, aryl), 6.66-6.75 (m, 4H, aryl), 2.27 (s, 12H, NMe2), 1.83 (s, 12H, C5Me4SiMe3), 1.45 (s, 4H, CH2), 0.38 (s, 9H, SiMe3). 1H NMR (toluene-d8, -80 °C): 7.19 (d, JHH = 7.4 Hz, 1H, aryl), 7.08 (m, 1H, aryl), 6.94 (m, 2H, aryl), 6.70 (m, 3H, aryl), 6.45 (d, JHH = 7.8 Hz, 1H, aryl), 2.18 (s, 6H, NMe2), 2.08 (s, 3H, C5Me4SiMe3), 2.03 (s, 3H, NMe2), 1.98 (obscured by C5Me4SiMe3, 1H, CH2), 1.95 (s, 3H, C5Me4SiMe3), 1.76 (s, 3H, C5Me4SiMe3), 1.63 (s, 3H, NMe2), 1.47 (s, 3H, C5Me4SiMe3), 1.33 (m, 2H, CH2), 1.13 (d, JHH = 9.1 Hz, 1H, CH2). 13C NMR (C6D6, 60 °C): 144.7, 142.2, 130.2, 127.4, 127.2, 123.8 (s, aryl), 119.7 (s, C5Me4SiMe3), 118.4 (s, C5Me4SiMe3), 114.2 (s, C5Me4SiMe3), 45.8 (NMe2), 43.9 (d, JCY = 31.2 Hz, CH2), 14.4 (s, C5Me4SiMe3), 11.6 (s, C5Me4SiMe3), 3.2 (s, C5Me4SiMe3). Anal. Calcd for C30H45N2SiY: C, 65.43; H, 8.24; N, 5.09. Found: C, 64.91; H, 8.13; N, 4.85. [(C5Me5)Y(CH2C6H4NMe2-o)2] (1b). A THF solution (5 mL) of pentamethylcyclopentadiene (409 mg, 3.0 mmol) was added to a THF

solution (10 mL) of [Y(CH2C6H4NMe2-o)3] (1.48 g, 3.0 mmol) at room temperature in a Schlenk tube with a Teflon stopcock. This tube was taken outside and was heated to 70 °C for 12 h. The solvent was removed under reduced pressure. The residue was washed with ether and dissolved in toluene. The solution was concentrated and was cooled to -30 °C to give yellow prismatic crystals of 1b (1.01 g, 2.05 mmol, 68%). Recrystallization from benzene solution gave single crystals suitable for X-ray analysis. 1H NMR (C6D6, 60 °C): 7.08 (d, JHH = 7.0 Hz, 2H, aryl), 6.97 (t, JHH = 7.7 Hz, 2H, aryl), 6.65-6.75 (m, 4H, aryl), 2.23 (s, 12H, NMe2), 1.82 (s, 15H, C5Me5), 1.41 (s, 4H, CH2). 1H NMR (toluene-d8, -80 °C): 7.28 (d, JHH = 7.6 Hz, 1H, aryl), 7.16 (s, 1H, aryl), 7.12 (t, JHH = 7.6 Hz, 1H, aryl), 7.02 (m, 1H, aryl), 6.75 (m, 3H, aryl), 6.51 (d, JHH = 7.8 Hz, 1H, aryl), 2.26 (s, 3H, NMe2), 2.15 (s, 3H, NMe2), 2.12 (s, 3H, NMe2), 1.98 (d, JHH = 9.2 Hz, 1H, CH2), 1.89 (s, 15H, C5Me5), 1.71 (s, 3H, NMe2), 1.41 (d, JHH = 9.2 Hz, 1H, CH2), 1.37 (d, JHH = 9.2 Hz, 1H, CH2), 1.19 (d, JHH = 9.2 Hz, 1H, CH2). 13 C NMR (C6D6, 60 °C): 144.8 (d, JCY = 1.9 Hz), 141.6, 129.9, 127.4, 119.3, 118.7, 117.8 (aromatics and Cp ring carbons), 45.3 (br, NMe2), 43.0 (d, JCY = 29.9 Hz, CH2), 11.0 (C5Me5). Anal. Calcd for C28H39N2Y: C, 68.28; H, 7.98; N, 5.69. Found: C, 68.32; H, 7.89; N, 5.60. [(C5Me4Et)Y(CH2C6H4NMe2-o)2] (1c). A THF solution (2 mL) of ethyltetramethylcyclopentadiene (630 mg, 4.2 mmol) was added to a THF solution (20 mL) of [Y(CH2C6H4NMe2-o)3] (2.0 g, 4.1 mmol) at room temperature in a Schlenk tube with a Teflon stopcock. This tube was taken outside and was heated to 70 °C for 18 h. The solvent was removed under reduced pressure to give a brown oil. The residue was washed with hexane and dissolved in 5 mL of toluene. The solution was filtered and removed under reduced pressure. The residue was washed with Et2O and dried under reduced pressure, which gave a yellow powder of 1c (0.950 g, 1.87 mmol, 46%). 1H NMR (C6D6, 80 °C): 7.07 (d, JHH = 7.5 Hz, 2H, aryl), 6.96 (t, JHH = 7.5 Hz, 2H, aryl), 6.74 (d, JHH = 7.5 Hz, 2H, aryl), 6.68 (t, JHH = 7.5 Hz, 2H, aryl), 2.26 (s, 12H, NMe2), 2.26 (obscured by NMe2, 2H, C5Me4Et), 1.88 (s, 6H, C5Me4Et), 1.80 (s, 6H, C5Me4Et), 1.41 (s, 4H, CH2), 0.97 (t, JHH = 7.5 Hz, 3H, 2521

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Table 1. Summary of Crystallographic Data 1a

1b

1d

3

50

4

6

7

formula

C30H45N2SiY C28H39N2Y

C27H37N2Y

C60H115Si5Y5 3 C6H14O C58H90N2Y4

C63H111O2Y5 C52H92O4Y4

C60H102Y6 3 2(C7H8)

formula wt

550.68

492.52

478.50

1523.69

1170.96

1345.07

1136.90

1541.14

cryst syst

triclinic

monoclinic

monoclinic

monoclinic

monoclinic

monoclinic

orthorhombic monoclinic

space group

P1

P21/c

P21/c

C2/c

P21/n

P21/n

I222

C2/m

a, Å

10.5186(9)

17.721(4)

15.734(3)

22.478(4)

11.319(3)

22.782(2)

12.371(2)

19.503(5)

b, Å

10.5728(9)

9.126(2)

10.181(2)

17.705(3)

20.477(5)

13.2011(11) 15.336(3)

17.833(5)

c, Å

13.7075(11)

18.273(5)

31.279(6)

41.032(6)

11.759(3)

24.695(2)

12.969(4)

R, deg β, deg

91.798(2) 95.2210(10)

118.803(4)

95.408(3)

104.887(3)

98.145(4)

114.8100(10)

γ, deg

105.4200(10)

V, Å3

1461.0(2)

2589.4(11)

4988.1(18)

15782(4)

2698.1(12)

6741.4(10)

3200.8(10)

3769.7(18)

Z

2

4

8

8

2

4

2

2

16.871(3)

123.307(4)

Dcalcd, g/cm3

1.252

1.263

1.274

1.283

1.441

1.325

1.180

1.358

temp, K

173(2)

173(2)

173(2)

173(2)

173(2)

173(2)

173(2)

173(2)

μ, mm-1(MoKR)

2.056

2.269

2.353

3.747

4.297

4.293

3.623

4.601

2θmax no. of rflnscollected

50.0 6878

50.0 12 549

52.0 25 337

55.0 48 463

52.0 15 079

55.0 40 851

55.0 10 051

49.2 7348

no. of indep rflns (Rint) 5024 (0.0154) 4544 (0.0839) 9808 (0.1084) 17 800 (0.1819)

5286 (0.0843) 15 070

R1 (I > 2σ(I))

0.0307

0.0452

0.0631

0.0529

0.0447

0.0492

3590 (0.0471) 3248 (0.0521) 0.0358

0.1031

wR2 (I > 2σ(I))

0.0789

0.0568

0.0946

0.0573

0.0820

0.1126

0.0680

0.2014

no. of params

318

289

541

709

316

618

152

218

GOF

1.033

0.842

1.004

0.582

0.988

0.900

0.862

1.052

Flack param

C5Me4Et). 13C NMR (C6D6, 60 °C): 144.9, 141.6, 129.9, 127.4 (s, aryl), 124.3 (s, C5Me4Et), 119.3, 118.7 (s, aryl), 118.0, 117.1 (s, C5Me4Et), 45.3 (NMe2), 43.0 (d, JYC = 29.6 Hz, CH2), 19.6, 15.8 (C5Me4Et), 11.0, 10.9 (C5Me4Et). Anal. Calcd for C29H41N2Y: C, 68.76; H, 8.16; N, 5.53. Found: C, 68.71; H, 8.07; N, 5.86. [(C5Me4H)Y(CH2C6H4NMe2-o)2] (1d). A THF solution (5 mL) of tetramethylcyclopentadiene (367 mg, 3 mmol) was added to a THF solution (10 mL) of [Y(CH2C6H4NMe2-o)3] (1.48 g, 3 mmol) at room temperature in a Schlenk tube with a Teflon stopcock. This tube was taken outside and was heated to 70 °C for 6 h. The solvent was removed under reduced pressure to give a red oil. The residue was dissolved in 5 mL of toluene. The solution was concentrated and was cooled to -30 °C to give yellow prismatic crystals of 1d (0.75 g, 1.57 mmol, 52%), which were suitable for X-ray analysis. 1H NMR (toluene-d8, 60 °C): 6.90-7.09 (m, 4H, aryl), 6.64-6.75 (m, 4H, aryl), 5.08 (s, 1H, C5Me4H), 2.30 (s, 12H, NMe2), 2.04 (s, 6H, C5Me4H), 1.68 (s, 6H, C5Me4H), 1.33 (s, 4H, CH2). 1H NMR (toluene-d8, -80 °C): 7.20 (d, JHH = 7.4 Hz, 1H, aryl), 7.02 (m, 1H, aryl), 6.94 (m, 2H, aryl), 6.72 (m, 3H, aryl), 6.44 (d, JHH = 7.9 Hz, 1H, aryl), 4.96 (s, 1H, C5Me4H), 2.23 (s, 6H, NMe2), 2.17 (s, 6H, C5Me4H), 2.06 (s, 3H, NMe2), 1.87 (obscured by C5Me4H, 1H, CH2), 1.83 (s, 3H, C5Me4H), 1.69 (s, 3H, NMe2), 1.33 (s, 3H, C5Me4H), 1.33 (obscured by C5Me4H, 2H, CH2), 0.87 (d, JHH = 8.8 Hz, 1H, CH2). 13C NMR (C6D6, room temperature): 144.0, 140.5, 129.73, 129.71, 127.4, 119.2, 118.9, 111.6 (d, JCY = 1.9 Hz) (aromatics and Cp ring carbons), 45.4 (NMe2), 44.9, 43.1 (d, JY-C = 29.2 Hz, CH2), 13.5, 11.2, 10.4 (C5Me4H). Anal. Calcd for C27H37N2Y: C, 67.77; H, 7.79; N, 5.85. Found: C, 67.76; H, 7.74; N, 5.63. [{(C5Me4SiMe3)Y(μ-H)2}5] (3). (a) A benzene solution (2.0 mL) of 1a (304 mg, 0.552 mmol) in a 10 mL Hiper Glass Cylinder (TAIATSU TECHNO) was filled with H2 (30 atm). The mixture was stirred at 40 °C for 62 h. After removal of the solvent by slow evaporation, the resulting pale yellow residue was crystallized with hexane, which gave 3 as a colorless crystal (100 mg, 0.0704 mmol, 64%).

0.045(9)

(b) A benzene solution (1.0 mL) of [{(C5Me4SiMe3)Y(μ-H)2}4] (21 mg, 0.018 mmol) and 1a (11 mg, 0.020 mmol) in a 10 mL Hiper Glass Cylinder (TAIATSU TECHNO) was filled with H2 (30 atm). The mixture was stirred at 50 °C for 15 h. After removal of the solvent by slow evaporation, the resulting pale yellow residue was washed with hexane, which gave 3 as a white powder (21 mg, 0.015 mmol, 83%). Single crystals suitable for X-ray analysis were grown by recrystallization from i Pr2O at room temperature. 1H NMR (toluene-d8, 100 °C): 4.60 (sextet, JHY = 12.8 Hz, 10H, μ-H), 2.53 (s, 30H, C5Me4SiMe3), 2.28 (s, 30H, C5Me4SiMe3), 0.42 (s, 45H, C5Me4SiMe3). 1H NMR (400 MHz, toluene-d8, -60 °C, δ/ppm): 5.40 (t, JHY = 35.8 Hz, 4H, μ2-H), 4.02 (m, 5H, μ3-H), 2.55 (s, 24H, C5Me4SiMe3), 2.42 (s, 6H, C5Me4SiMe3), 2.22 (s, 24H, C5Me4SiMe3), 2.18 (s, 6H, C5Me4SiMe3), 0.52 (s, 9H, C5Me4SiMe3), 0.44 (s, 36H, C5Me4SiMe3). 13C NMR (C6D6, room temperature): 129.2 (s, C5Me4SiMe3), 125.0 (s, C5Me4SiMe3), 117.1 (s, ipso-C5Me4SiMe3), 16.5 (s, C5Me4SiMe3), 12.8 (s, C5Me4SiMe3), 2.4 (s, C5Me4SiMe3). Anal. Calcd for C60H115Si5Y5: C, 50.69; H, 8.16. Found: C, 51.05; H, 8.15. [(C5Me5)2Y2(μ-CH2C6H4NMe2-o)(μ-H)3]2 (4). A toluene solution (2 mL) of 1b (76 mg, 0.15 mmol) in a 10 mL Hiper Glass Cylinder (TAIATSU TECHNO) was filled with H2 (10 atm). The mixture was stirred at 60 °C for 2 days. During the reaction a white solid precipitated. After the reaction, the precipitate was washed with toluene and dried under reduced pressure, which gave 4 as a white powder (33 mg, 0.028 mmol, 75%). This compound was insoluble in toluene, chlorobenzene, or THF. Single crystals suitable for X-ray analysis were obtained directly from the reaction mixture without stirring the solution. Anal. Calcd for C58H90N2Y4: C, 59.47; H, 7.75; N, 2.39. Found: C, 59.38; H, 7.72; N, 2.26. [{(C5Me5)Y(μ-H)2}5(THF)2] (5). A THF solution (2 mL) of 1b (201 mg, 0.408 mmol) in a 10 mL Hiper Glass Cylinder (TAIATSU TECHNO) was filled with H2 (9 atm). The mixture was stirred at 60 °C for 2 days. During the reaction a white solid precipitated. After removal of the solvent under vacuum, the resulting pale yellow residue was washed with hexane and dried under reduced pressure, which gave 5 as a 2522

dx.doi.org/10.1021/om1012055 |Organometallics 2011, 30, 2513–2524

Organometallics white powder (77 mg, 0.0604 mmol, 74%). 1H NMR (C6D6, 60 °C): 4.31 (sextet, JHY = 12.3 Hz, 10H, μ-H), 3.63 (s, 8H, THF), 2.31 (s, 75H, C5Me5), 1.41 (s, 8H, THF). 1H NMR (toluene-d8, -80 °C): 4.68 (t, JHY = 32.8 Hz, 4H, μ-H), 4.06 (m, 5H, μ3-H), 3.52 (s, 8H, THF), 2.50 (s, 15H, C5Me5), 2.43 (s, 30H, C5Me5), 2.32 (s, 30H, C5Me5), 2.32 (μ 4-H, obscured by C5Me 5), 1.13 (s, 8H, THF). 13C NMR (C6D 6, 60 °C): 119.2 (s, C5Me 5), 70.9 (s, THF), 25.6 (s, THF), 12.4 (s, C5 Me5). Anal. Calcd for C58H101O2Y5: C, 54.62; H, 7.99. Found: C, 55.29; H, 8.16. [{(C5Me4Et)Y(μ-H)2}5(THF)2] (50 ). A THF solution (2 mL) of 1c (920 mg, 0.408 mmol) in a 10 mL Hiper Glass Cylinder (TAIATSU TECHNO) was filled with H2 (10 atm). The mixture was stirred at 50 °C for 3 days. After removal of the solvent under vacuum, the resulting pale yellow residue was washed with hexane and crystallized in Et2O, which gave 50 as a white crystalline solid (140 mg, 0.104 mmol, 29%). Single crystals of 50 suitable for X-ray analysis were grown by recrystallization from iPr2O at room temperature. 1H NMR (C6D6, 80 °C): 4.31 (sextet, JHY = 12.0 Hz, 10H, μ-H), 3.64 (s, 8H, THF), 2.87 (q, JHH = 7.3 Hz, 10H, C5Me4Et), 2.35 (s, 30H, C5Me4Et), 2.31 (s, 30H, C5Me4Et), 1.46 (s, 8H, THF), 1.17 (t, JHH = 7.3 Hz, 15H, C5Me4Et). 13 C NMR (C6D6, 80 °C): 126.0 (s, C5Me4Et), 119.4 (s, C5Me4Et), 118.7 (s, C5Me4Et), 70.6 (s, THF), 25.7 (s, THF), 20.8 (s, C5Me4Et), 15.9 (s, C5Me4Et), 12.4 (s, C5Me4Et), 12.2 (s, C5Me4Et). Anal. Calcd for C63H111O2Y5: C, 56.25; H, 8.32. Found: C, 57.01; H, 8.04. [{(C5Me4H)Y(μ-H)2}4(THF)4] (6). A THF solution (3 mL) of 1d (1.00 g, 2.09 mmol) in a 10 mL Hiper Glass Cylinder (TAIATSU TECHNO) was filled with H2 (10 atm). The mixture was stirred at room temperature for 1 week. During the reaction a white solid precipitated. After removal of the solvent under vacuum, the resulting pale yellow residue was washed with hexane and dried under reduced pressure, which gave 6 as a white powder (520 mg, 0.458 mmol, 88%). Single crystals suitable for X-ray analysis were grown by recrystallization from toluene/THF at -33 °C. 1H NMR (C6D6, room temperature): 6.26 (s, 4H, C5Me4H), 3.88 (s, 16H, THF), 3.78 (br s, 8H, μ-H), 2.42 (s, 24H, C5Me4H), 2.19 (s, 24H, C5Me4H), 1.52 (s, 16H, THF). 1H NMR (toluene-d8, -40 °C): 6.50 (s, 4H, C5Me4H), 4.20 (t, JHY = 30.8 Hz, 4H, μ-H), 3.94 (s, 16H, THF), 2.97 (m, 4H, μ3-H), 2.48 (s, 24H, C5Me4H), 2.11 (s, 24H, C5Me4H), 1.53 (s, 16H, THF). 13C NMR (C6D6, room temperature): 118.6 (s, C5Me4H), 117.7 (s, C5Me4H), 107.6 (s, C5Me4H), 71.1 (s, THF), 25.7 (s, THF), 14.4 (s, C5Me4H), 11.9 (s, C5Me4H). Anal. Calcd for C52H92O4Y4: C, 54.91; H, 8.16. Found: C, 54.58; H, 7.41. [(C5Me5)Y(μ-H)2]6 (7). A benzene solution (2 mL) of phenylsilane (974 mg, 9 mmol) was added to a benzene solution (20 mL) of 1b (1.478 g, 3 mmol) at room temperature in a Schlenk tube with a Teflon stopcock. This tube was taken outside and heated to 70 °C for 24 h. During the reaction a crystalline powder precipitated. The crystalline powder was collected on a filter and washed with toluene. The collected crystalline powder was recrystallized from a hot toluene solution to give 7 3 2C7H8 as colorless crystals, which were suitable for X-ray analysis. After the crystals were dried under vacuum, 7 3 1.5(toluene) was isolated as a white powder (262 mg, 35%). 1H NMR (toluene-d8, room temperature): 4.19 (br s, 12H, μ-H), 2.28 (s, 90H, C5Me5). 1H NMR (toluene-d8, 110 °C): 4.03 (septet, JY-H = 10.0 Hz, 12H, H), 2.25 (s, 90H, C5Me5). 1H NMR (toluene-d8, -20 °C): 4.16 (septet, JHY = 10.7 Hz, 11H, H), 2.27 (s, 90H, C5Me5). 13C NMR (toluene-d8, room temperature): 119.5 (s, C5Me5), 12.6 (s, C5Me5). Anal. Calcd for C63.5H106Y6 (6 3 0.5(toluene)): C, 54.36; H, 7.62. Found: C, 54.47; H, 7.41. The volatiles of the reaction solution were removed under reduced pressure, and subsequent extraction with hexane gave o-PhSiH2 1 CH2C6H4NMe2 as a colorless oil. H NMR (C6D6, room temperature): 7.52-7.54 (m, 2H, aryl), 7.16-7.18 (m, 3H, aryl), 6.93-7.10 (m, 2H, aryl), 6.89-6.95 (m, 2H, aryl), 4.64 (t, JHH = 3.5 Hz, 2H, SiH2), 2.35 (t, JHH = 3.5 Hz, 2H, CH2), 2.29 (s, 6H, NMe2).

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X-ray Crystallographic Studies. Crystals for X-ray analysis were obtained as described in the preparations. The crystals were manipulated in the glovebox under a microscope in the glovebox and were sealed in thin-walled glass capillaries. Data collections were performed at -100 °C on a Bruker SMART APEX diffractometer with CCD area detector using graphite-monochromated Mo KR radiation (λ = 0.710 73 A). The determination of crystal class and unit cell parameters was carried out by the SMART program package.21 The raw frame data were processed using SAINT22 and SADABS23 to yield the reflection data file. The structures were solved by using the SHELXTL program.24 Refinement for 1a,b,d, 3, 4, 50 , 6, and 7 was performed on F2 anisotropically for the non-hydrogen atoms by full-matrix least-squares methods. The analytical scattering factors for neutral atoms were used throughout the analysis. For 50 , disorder at the C5Me4Et ligand on Y4 was refined with a ratio of 66:34. The metal-bound hydrogen atoms in 3, 4, 50 , 6, and 7 were located by difference Fourier synthesis, and their coordinates and isotropic parameters were refined. Disorder at the H3 atom in 7 was refined at 75% occupancy. Other hydrogen atoms were placed at calculated positions and were included in the structure calculation without further refinement of the parameters. The residual electron densities were of no chemical significance. Crystal data and analysis results are given in Table 1.

’ ASSOCIATED CONTENT

bS

Supporting Information. Figures, tables, and CIF files giving details of the VT-1H NMR experiments of 1a,b,d, VT-2H NMR spectra of 5-d10, VT-1H NMR experiment of 6, atomic coordinates and thermal parameters, bond lengths and angles, and structural refinement details, and ORTEP drawings of 1a,b, d, 3, 4, 50 , 6, and 7 with full numbering schemes. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Tel: (þ81)-48-467-9393. Fax: (þ81)48-462-4665.

’ ACKNOWLEDGMENT This work was supported by a Grant-in-Aid for Young Scientists (B) (No. 21750068 to T.S. and No. 22750062 to M.N.) and a Grant-in-Aid for Scientific Research (S) (No. 21225004 to Z.H.) from the JSPS. ’ REFERENCES (1) Selected reviews:(a) Edelmann, F. T. In Comprehensive Organometallic Chemistry III; Crabtree, R. H., Mingos, M. P., Eds.; Elsevier: Oxford, U.K., 2007; Vol. 4, pp 1-190. (b) Okuda, J. Dalton Trans. 2003, 2367. (c) Molander, G. A.; Romero, J. A. C. Chem. Rev. 2002, 102, 2161. (d) Hou, Z.; Wakatsuki, Y. Coord. Chem. Rev. 2002, 231, 1.(e) Hou, Z.; Wakatsuki, Y. In Science of Synthesis; Imamoto, T., Noyori, R., Eds.; Thieme: Stuttgart, Germany, 2002; Vol. 2, pp 849-942. (f) Hoskin, A. J.; Stephan, D. W. Coord. Chem. Rev. 2002, 233-234, 107. (g) Ephritikhine, M. Chem. Rev. 1997, 97, 2193. (h) Schumann, H.; MeeseMarktscheffel, J. A.; Esser, L. Chem. Rev. 1995, 95, 865. (2) Recent reviews:(a) Hou, Z.; Nishiura, M.; Shima, T. Eur. J. Inorg. Chem. 2007, 2535. (b) Nishiura, M.; Hou, Z. Nature Chem. 2010, 2, 257. (c) Cheng, J.; Saliu, K.; Ferguson, M. J.; McDonald, R.; Takats, J. J. Organomet. Chem. 2010, 695, 2696. (3) For Cp-ligated rare-earth polyhydrides, see:(a) Nishiura, M.; Baldamus, J.; Shima, T.; Mori, K.; Hou, Z. Chem. Eur. J. 2010in press. (b) Stewart, T.; Nishiura, M.; Konno, Y.; Hou, Z.; McIntyre, G. J.; Bau, R. 2523

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Organometallics Inorg. Chim. Acta 2010, 363, 562. (c) Shima, T.; Hou, Z. Dalton Trans. 2010, 39, 6858. (d) Takenaka, Y.; Shima, T.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2009, 48, 7888. (e) Yousufuddin, M.; Gutmann, M. J.; Baldamus, J.; Tardif, O.; Hou, Z.; Mason, S. A.; McIntyre, G. J.; Bau, R. J. Am. Chem. Soc. 2008, 130, 3888. (f) Luo, Y.; Hou, Z. J. Phys. Chem. C 2008, 112, 635. (g) Luo, Y.; Hou, Z. Organometallics 2007, 26, 2941. (h) Yousufuddin, M.; Baldamus, J.; Tardif, O.; Hou, Z.; Mason, S. A.; McIntyre, G. J.; Bau, R. Physica B 2006, 385-386, 231. (i) Shima, T.; Hou, Z. J. Am. Chem. Soc. 2006, 128, 8124. (j) Li, X.; Baldamus, J.; Nishiura, M.; Tardif, O.; Hou, Z. Angew. Chem., Int. Ed. 2006, 45, 8184. (k) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 959. (l) Cui, D.; Nishiura, M.; Hou, Z. Macromolecules 2005, 38, 4089. (m) Luo, Y.; Baldamus, J.; Tardif, O.; Hou, Z. Organometallics 2005, 24, 4362. (n) Tardif, O.; Hashizume, D.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 8080. (o) Cui, D.; Tardif, O.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 1312. (p) Hultzsch, K.; Voth, P.; Spaniol, T. P.; Okuda, J. Z. Anorg. Allg. Chem. 2003, 629, 1272. (q) Tardif, O.; Nishiura, M.; Hou, Z. Organometallics 2003, 22, 1171. (r) Hou, Z.; Zhang, Y.; Tardif, O.; Wakatsuki, Y. J. Am. Chem. Soc. 2001, 123, 9216. (4) For non-Cp-ligated rare-earth polyhydrides, see:(a) Cheng, J.; Shima, T.; Hou, Z. Angew. Chem., Int. Ed. 2010in press. (b) Cheng, J.; Ferguson, M. J.; Takats, J. J. Am. Chem. Soc. 2010, 132, 2. (c) Cheng, J.; Saliu, K.; Kiel, G. Y.; Ferguson, M. J.; McDonald, R.; Takats, J. Angew. Chem., Int. Ed. 2008, 47, 4910. (d) Ohashi, M.; Konkol, M.; Rosal, I. D.; Poteau, R.; Maron, L.; Okuda, J. J. Am. Chem. Soc. 2008, 130, 6920. (e) Lyubov, D. M.; D€oring, C.; Fukin, G. K.; Cherkasov, A. V.; Shavyrin, A. S.; Kempe, R.; Trifonov, A. A. Organometallics 2008, 27, 2905. (5) van der Heijden, H.; Pasman, P.; de Boer, E. J. M.; Schaverien, C. J.; Orpen, A. G. Organometallics 1989, 8, 1459. (6) Harder, S. Organometallics 2005, 24, 373. (7) For the preparation of related THF-free rare earth aminobenzyl complexes, see:(a) Li, X.; Nishiura, M.; Mori, K.; Mashiko, T.; Hou, Z. Chem. Commun. 2007, 4137. (b) Jaroschik, F.; Shima, T.; Li, X.; Mori, K.; Ricard, L. X.; Goff, L.; Nief, F.; Hou, Z. Organometallics 2007, 26, 5654. (c) Zhang, W.; Nishiura, M.; Mashiko, T.; Hou, Z. Chem. Eur. J. 2008, 14, 2167. (d) Zhang, W.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2008, 47, 9700. (e) Nishiura, M.; Mashiko, T.; Hou, Z. Chem. Commun. 2008, 2019. (f) Zhang, L.; Nishiura, M.; Yuki, M.; Luo, Y.; Hou, Z. Angew. Chem., Int. Ed. 2008, 47, 2642. (8) den Haan, K. H.; de Boer, J. L.; Teuben, J. H.; Spek, A. L.; KojicProdic, B.; Hays, G. R.; Huis, R. Organometallics 1986, 5, 1726. (9) See the Supporting Information for details. (10) A high-quality single crystal suitable for X-ray structure determination was not obtained from benzene, hexane, or Et2O. (11) (a) Arndt, S.; Voth, P.; Spaniol, T. P.; Okuda, J. Organometallics 2000, 19, 4690. (b) Tardif, O.; Nishiura, M.; Hou, Z. Tetrahedron 2003, 59, 10525. (12) 1H NMR of [{Cp0 Y(μ-H)2}5(THF)n] (C6D6, 60 °C): δ 4.44 (quint, JHY =12.5 Hz, 10 H, μ-H), 3.76 (s, 4-8H, THF), 2.53 (s, 30H, C5Me4SiMe3), 2.29 (s, 30H, C5Me4 SiMe3), 1.57 (s, 4-8H, THF), 0.45 (s, 45H, C5Me4SiMe3). (13) The isolated yield of 20 was 22%, due to the difficulty of the separation of 20 from N,N,2-trimethylaniline. (14) (a) van der Heijden, H.; Schaverien, C. J.; Orpen, A. G. Organometallics 1989, 8, 255. (b) Heeres, H. J.; Meetsma, A.; Teuben, J. H.; Rogers, R. D. Organometallics 1989, 8, 2637. (15) {[Cp*Y(μ-D)2]5(THF)2} (5-d10) was synthesized by treatment of 1b with D2 (10 atm) in THF (47% yield). (16) The 1H NMR spectrum of 6 changed after heating for a few hours; however, we were unable to obtain any structural information. 1H NMR (C6D6, room temperature): δ 6.55 (s, 2H, C5Me4H), 6.40 (s, 2 H, C5Me4H), 3.59 (s, 16H, THF), 3.32 (br s, 7-8 H, μ-H), 2.443 (s, 12H, C5Me4H), 2.437 (s, 12H, C5Me4H), 2.38 (s, 12H, C5Me4H), 2.29 (s, 12H, C5Me4H), 1.42 (s, 16H, THF). (17) (a) Voskoboynikov, A. Z.; Parshina, I. N.; Shestakova, A. K.; Butin, K. P.; Beletskaya, I. P.; Kuz’mina, L. G.; Howard, J. A. K. Organometallics 1997, 16, 4041. (b) Castillo, I.; Tilley, T. D. Organometallics 2001, 20, 5598.

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(18) Takenaka, Y.; Hou, Z. Organometallics 2009, 28, 5196. (19) den Haan, K. H.; Wielstra, Y.; Teuben, J. H. Organometallics 1987, 6, 2053. (20) Manzer, L. E. J. Am. Chem. Soc. 1978, 100, 8068. (21) SMART Software Users Guide, version 4.21; Bruker AXS, Inc., Madison, WI, 1997. (22) SAINT PLUS, version 6.02; Bruker AXS, Inc., Madison, WI, 1999. (23) Sheldrick, G. M. SADABS; Bruker AXS, Inc., Madison, WI, 1998. (24) Sheldrick, G. M. SHELXTL, version 5.1; Bruker AXS, Inc., Madison, WI, 1998.

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