Tetranuclear Zirconium and Hafnium Polyhydride Complexes

Mar 15, 2013 - Hanna Ebert , Vanessa Timmermann , Tim Oswald , Wolfgang Saak , Marc Schmidtmann , Marion Friedemann , Detlev Haase , and Rüdiger ...
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Tetranuclear Zirconium and Hafnium Polyhydride Complexes Composed of the “CpMH2” Units Shaowei Hu,† Takanori Shima,*,† Yi Luo,*,‡ and Zhaomin Hou*,† †

Organometallic Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan State Key Laboratory of Fine Chemicals and School of Pharmaceutical Science and Technology, Dalian University of Technology, Dalian 116024, People’s Republic of China

‡

S Supporting Information *

ABSTRACT: A series of tetranuclear group 4 transition metal octahydride complexes [(C5Me4R)4M4(μ-H)8] (2-Zr, M = Zr, R = SiMe3; 2-Hf, M = Hf, R = SiMe3; 3, M = Zr, R = Me) were synthesized by the hydrogenolysis of the half-sandwich tris(trimethylsilylmethyl) complexes [(C 5 Me 4 R)M(CH2SiMe3)3] (1-Zr, M = Zr, R = SiMe3; 1-Hf, M = Hf, R = SiMe3; 1-Zr′, M = Zr, R = Me). X-ray diffraction studies revealed that these hydride clusters possess a tetrahedral M4 framework which is connected by two μ3-H and six μ2-H ligands. Such bonding modes have been further clarified by DFT studies. The reaction of 2-Zr with SePPh3 resulted in oxidation of two of the four Zr(III) ions in 2-Zr to Zr(IV) and reduction of SePPh3 to Se2−, yielding the selenium-capped hydride cluster [(C5Me4SiMe3)4Zr4(μ3-Se)(μ-H)8] (4) with release of PPh3.

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(CH2C6H4NMe2-o)2] (R = SiMe3, Me, Et, H)13 could be easily transformed into the corresponding dihydride species “(Cp)LnH2” by hydrogenolysis with H2. The resulting dihydride species showed unique polynuclear structures and reactivities which are different from those of the conventional metallocene hydride complexes bearing two Cp ligands per metal.14−27 During these studies, we became interested in the analogous group 4 metal hydride clusters. In this paper, we report that half-sandwich group 4 metal tris(trimethylsilylmethyl) complexes such as [(C5Me4R)M(CH2SiMe3)3] (M = Zr, Hf; R = SiMe3, Me) can serve as excellent precursors for the synthesis of the tetranuclear zirconium and hafnium polyhydride complexes [(C5Me4R)M(μ-H)2]4, which are formally composed of four “(C5Me4R)MH2” units. DFT studies on a zirconium complex to elucidate the Zr4H8 core structure, as well as a preliminary reactivity study on the Zr hydride cluster, are also reported.

INTRODUCTION Group 4 transition metal hydride complexes have received much interest because of their importance in various chemical transformations.1−5 So far, a large number of group 4 transition metal hydride compounds of the general types [(Cp)2MH2] and [(Cp)2MHX] (Cp = cyclopentadienyl derivatives) bearing two cyclopentadienyl ligands per metal (for example, [Cp*2ZrH2]; Cp* = C5Me5)6 have been reported and extensively studied. In contrast, group 4 metal hydride complexes of the half-sandwich type “[(Cp)MHn]”, which bear one cyclopentadienyl ligand per metal, have hardly been studied, although such complexes are of much interest both structurally and chemically.7 In 1982, Wolczanski and Bercaw reported the first mono-Cpcoordinated zirconium hydride complex, [{Cp*Zr(BH4)H(μH)}2],8 in combination with a tetrahydroborate unit. Since then, several analogous mono-Cp-coordinated group 4 metal hydride complexes, such as [{Cp*Zr(BH4)}2(μ-η2-BH4)(μH)3]2, [{Cp*Zr(BH4)}2(μ-H)(μ-H)3]2,8,9 [(Cp*MCl)(μH)(μ3-H)]4 (M = Zr, Hf),9,10 and [(Cp*Hf)4(μ-C6H8)(μH)6],11 have been reported. However, group 4 metal hydride complexes composed of only the “CpMHn” unit without a third component have not yet been reported. Previous attempts to prepare such half-sandwich hydride complexes by hydrogenolysis of the corresponding half-sandwich alkyl precursors such as [Cp*ZrMe3], [Cp*Zr(CH2Ph)3], [Cp*ZrPh3],8 and [Cp*HfMe3]10 with H2 did not give a structurally characterizable product. We recently found that half-sandwich rare-earth bis(alkyl) complexes such as [(C5Me4SiMe3)Ln(CH2SiMe3)2(THF)] (Ln = Y, Lu, Sc, Gd−Yb), [(C5Me4SiMe3)Ln(CH2C6H4NMe2-o)2] (Ln = La, Ce, Pr, Nd, Sm), 1 2 and [(C 5 Me 4 R)Y© 2013 American Chemical Society

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RESULTS AND DISCUSSION Synthesis and Structure of C5Me4SiMe3-Ligated Tetranuclear Zr and Hf Octahydride Complexes. Hydrogenolysis of the half-sandwich Zr tris(trimethylsilylmethyl) complex [(C5Me4SiMe3)Zr(CH2SiMe3)3] (1-Zr) with H2 (10 atm) in hexane at 80 °C for 1 day afforded the tetranuclear zirconium octahydride complex [(C5Me4SiMe3)4Zr4(μ-H)8] (2-Zr) in 87% yield (Scheme 1). The formation of 2-Zr can be viewed as a result of the hydrogenation of the three alkyl groups in 1-Zr followed by tetramerization of the resulting trihydride species “[Cp′ZrH3]” and liberation of two molecules Received: January 8, 2013 Published: March 15, 2013 2145

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Scheme 1. Synthesis of C5Me4SiMe3-Ligated Tetranuclear Zirconium and Hafnium Octahydride Complexes

of H2. The oxidation state of the four metal centers was reduced from Zr(IV) in 1-Zr to Zr(III) in 2-Zr. Similarly, the hydrogenolysis of [(C5Me4SiMe3)Hf(CH2SiMe3)3] (1-Hf) with H2 (10 atm) in benzene at 90 °C for 4 days gave [(C5Me4SiMe3)4Hf4(μ-H)8] (2-Hf) in 58% isolated yield (Scheme 1). Compounds 2-Zr and 2-Hf are soluble in common organic solvents such as benzene, hexane, THF, and Et2O. Single crystals of 2-Zr and 2-Hf suitable for X-ray structure determinations were obtained by recrystallization from hexane. Both complexes adopted a similar solid structure, and the X-ray structure of 2-Zr is shown in Figure 1. Each Zr atom is bonded to one C5Me4SiMe3 ligand in an η5 bonding mode. There are eight hydride ligands in the tetranuclear Zr framework, two of which are face-capped in a μ3-H fashion and six are edgebridged in a μ2-H form. Unlike the analogous tetranuclear yttrium octahydride complex [(C5Me4SiMe3)4Y4(μ4-H)(μ3H)(μ2-H)6],23 no body-centered interstitial μ4-H ligand was found in the Zr4 tetrahedron cavity in 2-Zr. The short Zr−Zr distances in 2-Zr (3.0670(4)−3.0949(5) Å (average 3.0787 Å)) in comparison with the sum of the atomic radii of Zr (3.10 Å)28 and the diamagnetism of 2-Zr (vide infra) might indicate the existence of Zr−Zr σ interactions. The Zr−Zr distances in 2-Zr fall into a narrow range, in contrast with the case for the analogous mixed chloride/hydride cluster [{Cp*ZrCl(μ-H)(μ3H)}4],9 which adopted a butterfly-like core structure (Zr- - -Zr, 3.2808(4)−5.635 Å). The Zr−μ2-H bond distances (1.79(5)− 2.03(3) Å (average 1.91 Å)) and the Zr−μ3-H bond distances (1.92(7)−2.22(7) Å (average 2.09 Å)) in 2-Zr are comparable to those in [{Cp*ZrCl(μ-H)(μ3-H)}4] (Zr−μ2-H, 1.79(5)− 2.09(6) Å; Zr−μ3-H, 1.96(8)−2.33(5) Å). The 1H NMR spectrum of 2-Zr in C6D6 at room temperature showed a singlet at δ 0.61 (8H) for the hydride ligands, which are shifted significantly to high field in comparison with those in [{Cp*ZrCl(μ-H)(μ3-H)}4] (δ 3.88, 3.50)9 and [{Cp*Zr(BH4)H(μ-H)}2] (δ 1.31).8 The line shape and intensity of the hydride signal in 2-Zr remained unchanged in the temperature range of +80 to −80 °C in toluene-d8 or in THF-d8, suggesting that these hydride ligands are highly fluxional in solution. Complex 2-Hf showed similar behavior in its 1H NMR spectrum. In an attempt to recrystallize 2-Zr from THF, single crystals having a lattice THF molecule (2-Zr·THF) were obtained. An X-ray diffraction study revealed that 2-Zr·THF adopts a tetranuclear structure similar to that of 2-Zr. However, in contrast to 2-Zr, 2-Zr·THF possesses an interstitial μ4-H ligand at the center of the tetrahedron Zr4 cavity (Figure 2), which is similar to the case for the previously reported Y complex [(C5Me4SiMe3)4Y4(μ4-H)(μ3-H)(μ2-H)6].23 Because of disorder problems, further discussion of the Zr4H8 core structure in

Figure 1. (a) X-ray full structure of Zr4H8 in 2-Zr recrystallized from hexane with 30% thermal ellipsoids. (b) Core structure of 2-Zr. Selected bond lengths (Å): Zr1−Zr4, 3.0679(4); Zr1−Zr2, 3.0806(4); Zr1−Zr3, 3.0885(4); Zr2−Zr4, 3.0735(4); Zr2−Zr3, 3.0949(5); Zr3− Zr4, 3.0670(4); Zr1−H1, 1.97(3); Zr1−H4, 1.79(5); Zr1−H6, 1.88(5); Zr1−H7, 2.07; Zr1−H8, 2.22(7); Zr2−H2, 1.92(3); Zr2− H3, 2.00(3); Zr2−H6, 1.87(4); Zr2−H7, 2.16; Zr3−H1, 1.91(3); Zr3−H3, 1.94(3); Zr3−H5, 1.87(6); Zr3−H8, 1.92(7); Zr4−H2, 2.03(3); Zr4−H4, 1.93(5); Zr4−H5, 1.85(5); Zr4−H7, 2.04; Zr4− H8, 2.11(7). The H7 atom was not refined.

Figure 2. X-ray structure of the Zr4H8 core in 2-Zr·THF recrystallized from THF with 30% thermal ellipsoids. The hydride ligands H4 and H4* are refined at 25% occupancy due to a disorder problem. Selected bond lengths (Å): Zr−Zr, 3.0748(4)−3.0886(5) (average 3.0794); Zr−μ2-H(2,3), 1.87(3)−1.91(2) (average 1.90); Zr−μ3-H4, 2.13(8)− 2.14(7) (average 2.14), Zr−μ4-H1, 1.8857(3).

2-Zr·THF is not possible. The crystals of 2-Zr obtained from benzene, cyclohexane, and pyridine showed the same structure as that from hexane, without a μ4-H ligand. In view of the general uncertainty in determining the positions of metal2146

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molecular orbitals and the Wiberg bond indexes (WBI) were performed. The HOMOs and LUMOs of 2m and 2m′ are mainly contributed by the Zr 4d orbital with a small amount of hybridization of Zr 5s (Figure 3c,d and Figure S6 in the Supporting Information). The HOMO-16 orbital of 2m′ shows orbital overlap between the 1s orbital of μ4-H and 4d orbitals of Zr atoms (Figure S6). In the frontier orbitals, except for the LUMO of 2m, the contribution from ancillary ligands is negligible. The HOMOs in Figure 3c,d demonstrate Zr−Zr bonding. Unlike the previously reported Lu analogues [(η5C5H4SiH3)4Lu4H8], in which the bridging hydrides play an important role in the Lu···Lu bonding interactions,23 no significant contribution of the 1s orbital of the bridging hydrides is found in the Zr−Zr bonding involved in 2m and 2m′. The computed WBIs also suggest Zr−Zr bonding (average WBIs of 0.724 and 0.676 for Zr−Zr contacts in 2m and 2m′, respectively). The result that the Zr−Zr WBI in 2m is larger than that in 2m′ is in agreement with the shorter average Zr−Zr distance in 2m optimized by DFT(B3LYP) (3.087 Å for 2m and 3.176 Å for 2m′; see Figure 3a,b). Such a discrepancy could be ascribed to the interstitial μ4-H atom, which could increase the electron density in the cavity of 2m′ and therefore weaken the intermetallic bonding. Synthesis and Structure of a Cp*-Ligated Tetranuclear Zr Octahydride Complex. The successful isolation of the C5Me4SiMe3-ligated tetranuclear polyhydride complexes 2Zr and 2-Hf encouraged us to synthesize the analogous hydride complexes bearing a Cp* ligand by similar approaches. The hydrogenolysis of the Cp*-ligated Zr tris((trimethylsilyl)methyl) complex [Cp*Zr(CH2SiMe3)3] (1-Zr′) with H2 (10 atm) in THF (0.06 M) at 80 °C for 18 h afforded the corresponding tetranuclear octahydride complex [Cp*4Zr4(μH)8] (3) in 87% yield (Scheme 2).31 When the reaction was

bound hydride atoms by X-ray diffraction, theoretical calculations were then carried out to further elucidate the Zr−H connections in 2-Zr. DFT Studies on the Zr4H8 Core Structure of 2-Zr. To gain insight into the stable hydride positions of 2-Zr, density functional theory (DFT) computations29 were performed on model compounds of 2-Zr, viz., [(C5H4SiH3)4Zr4H8] (2m includes two μ3-H and six μ2-H atoms; 2m′ includes one μ4-H, one μ3-H, and six μ2-H atoms). Starting from the X-ray crystallographic geometry data of 2-Zr (obtained from hexane) and 2-Zr·THF (obtained from THF), full geometry optimizations were performed. The resulting optimized structures 2m and 2m′ are shown in Figure 3a,b, which reproduced well

Scheme 2. Synthesis of the Cp*-Ligated Zirconium Octahydride Complex 3

Figure 3. (a) DFT(B3LYP)-optimized structure of the Zr4H8 core in [(C5H4SiH3)4Zr4(μ3-H)2(μ-H)6] (2m) based on the X-ray structure of 2-Zr crystallized in hexane. (b) DFT(B3LYP)-optimized structure of the Zr4H8 core in [(C5H4SiH3)4Zr4(μ4-H)(μ3-H)(μ-H)6] (2m′) based on the X-ray structure of 2-Zr crystallized in THF (2-Zr·THF). DFT(B3LYP)-optimized Zr−Zr and Zr−H contacts (Å) in 2m and 2m′ are shown below. Molecular orbital isosurfaces of (c) 2m (HOMO) and (d) 2m′ (HOMO).

conducted in hexane or concentrated THF solutions (0.3 M), the yield of 3 decreased (∼50% by 1H NMR), with increased byproduct (∼50%).32 These results suggest that the formation of the hydride complex 3 is influenced by the reaction conditions. In agreement with these observations, the hydrogenation of [Cp*Zr(CH2Ph)3]8 (10 atm of H2) in toluene at 80 °C gave only a trace amount of 3, but a similar reaction in THF afforded 3 in about 50% yield. The 1H NMR spectrum of 3 recorded at room temperature in C6D6 showed two sharp signals at δ 2.32 (60 H) and 0.79 (8H), which could be assigned to the cyclopentadienyl methyl protons and the hydride ligands, respectively. An X-ray diffraction study revealed that 3 adopted the same Zr4H8 core structure (two μ3-H and six μ2-H atoms) as those of 2Zr and 2-Hf (see the Supporting Information, Figure S4). Reaction of 2-Zr with SePPh3. The reduction of triphenylphosphine chalcogenides EPPh3 (E = S, Se) by early-transition-metal complexes is well-known.33 2-Zr has four Zr(III) metal centers and eight hydride ligands. Both the metal

the overall tetrahedral skeleton of the Zr4H8 core with two μ3-H atoms for 2m and one μ4-H atom for 2m′. The Zr−Zr and Zr−μ3-H distances in 2m are slightly shorter than those in 2m′, but other Zr−H bond lengths of 2m and 2m′ are relatively comparable with each other. Energy comparisons between 2m and 2m′ revealed that 2m is significantly more stable than 2m′ by ca. 17.5 kcal/mol from B3LYP.30 These results are in agreement with the experimental observation that the structure of 2-Zr without an interstitial μ4-H atom is preferred in most cases. For a better understanding of the electronic characters of 2m and 2m′, and the metal−metal interactions, analyses of the 2147

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Organometallics centers and the hydrides could show a certain reduction potential.34 However, no reaction between 2-Zr and SPPh3 was observed at 80 °C. In contrast, the reaction of 2-Zr with SePPh3 took place rapidly to give the tetranuclear selenide/ hydride complex [{(C5Me4SiMe3)Zr}4(μ3-Se)(μ-H)8] (4) in 76% yield together with PPh3 (Scheme 3). In this reaction, two of the four Zr(III) ions in 2-Zr are oxidized into Zr(IV) and SePPh3 is reduced to Se2− and PPh3. Release of hydrogen was not observed.35

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In summary, tetranuclear zirconium and hafnium polyhydride complexes composed of “CpMH2” units, such as 2-Zr, 2-Hf, and 3, have been synthesized and structurally characterized for the first time by using the half-sandwich tris((trimethylsilyl)methyl) complexes [(C5Me4R)M(CH2SiMe3)3] (M = Zr, Hf; R = SiMe3, Me) as precursors. X-ray diffraction and DFT studies have demonstrated that the group 4 metal hydride clusters prefer formation of a tetrahedral M4H8 core structure without an interstitial μ4-H ligand, in contrast with the case for analogous rare-earth polyhydride complexes such as [(C5Me4SiMe3)4Y4(μ4-H)(μ3-H)(μ2-H)6].23 The reaction of 2-Zr with SePPh3 to give 4 may suggest that the mono-Cpligated group 4 metal hydride complex could serve as a unique building block for the synthesis of molecular hydride clusters with novel structures. Further studies on analogous earlytransition-metal polyhydride complexes are in progress.

Scheme 3. Reaction of 2-Zr with SePPh3

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 Combi-Analyzer (Mbraun) to ensure both were always below 1 ppm. Samples for NMR spectroscopic measurements were prepared by using Schlenk techniques or in the glovebox by use of J. Young valve NMR tubes. 1H and 13C NMR spectra were recorded on JEOLECS400, AL400, and JNM-AL300 spectrometers. Elemental analyses were performed with a MICRO CORDER JM10 instrument. Anhydrous THF, hexane, benzene, Et2O, and toluene were purified by use of a SPS-800 solvent purification system (Mbraun) and dried over fresh Na chips in the glovebox. [Cp′4Y4(μ-H)8(THF)]14,15,26,27 was prepared according to the literature. C5Me4H(SiMe3) and C5Me5H were purchased from Aldrich and Kanto Chemicals and used as received. Other reagents (ZrCl4, HfCl4) were used as received. [(C5Me4SiMe3)Zr(CH2SiMe3)3] (1-Zr). LiC5Me4SiMe3 (963 mg, 4.81 mmol, prepared from the reaction of C5Me4H(SiMe3) with nBuLi in THF) in toluene solution (20 mL) was added to a suspension of ZrCl4 (1.12 g, 4.81 mmol) in toluene (10 mL), and the mixture was refluxed for 1 day, at which point LiCH2SiMe3 (1.36 g, 14.4 mmol) was added. The resulting light yellow solution was left for 1 h. After removal of the solvent under vacuum, the residual pale yellow solid was extracted with hexane and the extract filtered. After reduction of the solution volume under reduced pressure, the pale yellow solution was cooled to −33 °C overnight to give 1-Zr (1.70 g, 3.11 mmol, 65%) as colorless cubic crystals. In a similar manner, [(C5Me5)Zr(CH2SiMe3)3] (1-Zr′) was also synthesized from the reaction of C5Me5Li with ZrCl4 followed by alkylation with LiCH2SiMe3 (62%). Data for 1-Zr are as follows. 1H NMR (C6D6, room temperature): δ 2.06 (s, 6H, C5Me4SiMe3), 1.85 (s, 6H, C5Me4SiMe3), 0.45 (s, 6H, ZrCH2SiMe3), 0.30 (s, 9H, C5Me4SiMe3), 0.28 (s, 27H, ZrCH2SiMe3). 13 C NMR (C6D6, room temperature): δ 127.9 (s, C5Me4SiMe3), 126.3 (s, C5Me4SiMe3), 125.7 (s, ipso-C5Me4SiMe3), 64.4 (s, ZrCH2SiMe3), 15.2 (s, C5Me4SiMe3), 12.3 (s, C5Me4SiMe3), 3.3 (s, ZrCH2SiMe3), 2.1 (s, C5Me4SiMe3). Anal. Calcd for C24H54Si4Zr: C, 52.77; H, 9.96. Found: C, 52.63; H, 9.69. Data for 1-Zr′ are as follows. 1H NMR (C6D6, room temperature): δ 1.84 (s, 15H, C5Me5), 0.35 (s, 6H, ZrCH2SiMe3), 0.26 (s, 27H, ZrCH2SiMe3). [(C5Me4SiMe3)Hf(CH2SiMe3)3] (1-Hf). LiC5Me4SiMe3 (625 mg, 3.12 mmol, prepared from the reaction of C5Me4H(SiMe3) with nBuLi in THF) in toluene solution (5 mL) was added to a suspension of HfCl4 (1.0 g, 3.12 mmol) in toluene (10 mL), and the mixture was refluxed for 1 day, at which point LiCH2SiMe3 (882 mg, 9.37 mmol)

Single crystals of 4 suitable for X-ray diffraction study were obtained by recrystallization from toluene (Figure 4). However,

Figure 4. X-ray structure of the Zr4SeH8 core in 4 with 30% thermal ellipsoids. The selenium atom is disordered (Se1/Se1A/Se2/Se2A = 33/33/17/17%). Selected bond lengths (Å): Zr−Zr, 3.0509(7)− 3.2078(11) (average 3.1350); Zr−Se, 2.6100(14)−2.7606(14) (average 2.719); Zr−μ2-H, 1.68(4)−1.92(4) (average 1.84).

the selenium atom, which is bonded to three of the four Zr atoms, is disordered over four positions, which were treated with 33/33/17/17% occupancies, respectively. Two possible μ3-H ligands could not be located because of overlap with the disordered μ3-Se ligands. The six μ2-H atoms could be found without a problem. The 1H NMR spectrum of 4 at room temperature showed two sets of signals for the Cp′ ligands in an intensity ratio of 3/ 1. This signal pattern is in agreement with the solid structure where the selenium atom is bonded to three of the four Zr atoms. The eight hydride ligands showed two signals at δ 3.42 (sextet, JHH = 2.9 Hz, 3H) and 1.91 (quartet, JHH = 2.9 Hz, 5H), respectively. The former is assignable to the three μ2-H ligands bonding to the Zr- - -Zr edge of the three “Zr2Se” planes, and the latter could be assigned to the remaining five hydrides (three μ2-H and two μ3-H) bonding to the Zr atoms in the three “Zr3” planes. 2148

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Hz, 3H, μ-H), 2.42 (s, 18H, C5Me4SiMe3), 2.36 (s, 6H, C5Me4SiMe3), 2.27 (s, 18H, C5Me4SiMe3), 2.25 (s, 6H, C5Me4SiMe3), 1.91 (q, JHH = 2.9 Hz, 5H, μ-H), 0.56 (br s, 27H, C5Me4SiMe3), 0.55 (br s, 9H, C5Me4SiMe3). 13C NMR (100 MHz, C6D6, room temperature): δ 125.6 (s, 3 × C5Me4SiMe3), 125.0 (s, C5Me4SiMe3), 123.8 (s, 3 × C5Me4SiMe3), 123.4 (s, C5Me4SiMe3), 114.3 (s, ipso-C5Me4SiMe3), 113.3 (s, ipso-C5Me4SiMe3), 15.9 (s, 3 × C5Me4SiMe3), 15.7 (s, C5Me4SiMe3), 13.0 (s, 3 × C5Me4SiMe3), 12.7 (s, C5Me4SiMe3), 3.1 (s, C5Me4SiMe3), 2.9 (s, C5Me4SiMe3). Anal. Calcd for C48H92Si4Zr4Se: C, 47.05; H, 7.57. Found: C, 47.50; H, 7.45. 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 Bruker SMART APEX diffractrometer with CCD area detector, using graphite-monochromated Mo Kα radiation (λ = 0.71073 A). The determination of crystal class and unit cell parameters was carried out by the SMART program package.36 The raw frame data were processed using SAINT37 and SADABS38 to yield the reflection data file. The structures were solved by using the SHELXTL program.39 Refinements for 2-Zr, 2-Zr·THF, 2-Hf, 3, and 4 were performed on F2 anisotropically for all the non-hydrogen atoms by full-matrix least-squares methods. The analytical scattering factors for neutral atoms were used throughout the analyses. The selenium atom of 4 was disordered, having four orientations (occupancy Se1/ Se1A/Se2/Se2A = 33/33/17/17%). The hydrogen atoms, except those bonded to metals, were placed at calculated positions, which were then refined using a riding model. The metal-bound hydrogen atoms were located on difference Fourier maps, and their positions (except for H7 in 2-Zr) were refined. The metal-bound hydrogen atoms of 2-Zr·THF (from THF) (H4) and 2-Hf (H5, H6) were disordered, which were refined at 25% (H4 in 2-Zr·THF) and 50% occupancy (H5, H6 in 2-Hf). The residual electron densities were of no chemical significance. Crystal data and analysis results are given in the Supporting Information. Computational Details. Due to the large molecular size of 2-Zr, each methyl of the realistic ligand η5-C5Me4SiMe3 (Cp′) was replaced by H and the model complex (C5H4SiH3)4Zr4H8 (2m and 2m′) was used for the calculations by using various density functionals: viz., B3LYP,40 B3PW91,41,41 and M062X.42 In the geometrical optimizations, the 6-31G* basis set was considered for the H and C atoms of the auxiliary π ligand. To get a more accurate core structure, however, 6-31+G** containing one set of p polarization functions were used for the eight hydrogen atoms involved in the core part. The Stuttgart/ Dresden effective potentials as well as the associated valence basis sets43 (4s4p)/[2s2p] and (8s7p6d)/[6s5p3d] were used for Si and Zr atoms, respectively. The basis set of the Si atom was also augmented by one d polarization function (exponent of 0.284).44a We call this basis set “BSI”. Single-point calculations with the larger basis set “BSII” were performed subsequently for the optimized geometries. In BSII, the 6-311++G(3df,2p) basis set was used for the eight core hydrogens. The basis sets for the remaining atoms were the same as those in BSI, but one f polarization function (exponent of 0.875)44b was augmented for Zr atoms. The analyses of electronic structure were carried out through single-point calculations at the level of B3LYP/BSII theory. The energies shown in Table S26 (Supporting Information) were obtained from the single-point calculations. The C1 symmetry point group was used throughout all calculations, and no higher molecular symmetry restriction was imposed. All calculations were carried out utilizing the Gaussian 09 program.45

was then slowly added. After removal of the solvent under vacuum, the residual pale yellow solid was extracted with hexane and filtered. After reduction of the solution volume under reduced pressure, the pale yellow solution was cooled to −33 °C overnight to give 1-Hf (1.32 g, 2.08 mmol, 67%) as colorless crystals. Single crystals suitable for X-ray analysis were grown by recrystallization from hexane. 1H NMR (C6D6, room temperature): δ 2.09 (s, 6H, C5Me4SiMe3), 1.88 (s, 6H, C5Me4SiMe3), 0.28 (s, 9H, C5Me4SiMe3), 0.26 (s, 27H, HfCH2SiMe3), −0.04 (s, 6H, HfCH2SiMe3). 13C NMR (C6D6, room temperature): δ 125.8 (s, C5Me4SiMe3), 125.2 (s, C5Me4SiMe3), 117.3 (s, ipsoC5Me4SiMe3), 70.8 (s, HfCH2SiMe3), 14.9 (s, C5Me4SiMe3), 12.0 (s, C5Me4SiMe3), 3.6 (s, HfCH2SiMe3), 2.1 (s, C5Me4SiMe3). Anal. Calcd for C24H54Si4Hf: C, 45.50; H, 8.59. Found: C, 44.89; H, 8.21. [(C5Me4SiMe3)4Zr4(μ-H)8] (2-Zr). A hexane solution (1.5 mL) of 1-Zr (60 mg, 0.11 mmol) in a 10 mL Hiper glass cylinder (TAIATSU TECHNO) was filled with H2 (10 atm). The mixture was stirred at 80 °C for 1 day. The solution color changed to dark green. After removal of the solvent under vacuum, the residual dark green solid was dissolved in hexane and crystallized at −33 °C to give 2-Zr (28 mg, 0.024 mmol, 87%) as a dark green crystal. Single crystals suitable for an X-ray diffraction study were obtained from a concentrated hexane (2-Zr) or THF solution (2-Zr·THF) at room temperature or −33 °C. 1 H NMR (C6D6, room temperature): δ 2.43 (s, 24H, C5Me4SiMe3), 2.33 (s, 24H, C5Me4SiMe3), 0.61 (s, 8H, μ-H), 0.57 (s, 36H, C5Me4SiMe3). 1H NMR (THF-d8, room temperature): δ 2.30 (s, 24H, C5Me4SiMe3), 2.29 (s, 24H, C5Me4SiMe3), 0.47 (s, 8H, μ-H), 0.39 (s, 36H, C5Me4SiMe3). 13C NMR (C6D6, room temperature): δ 125.9 (s, C5Me4SiMe3), 122.6 (s, C5Me4SiMe3), 112.6 (s, ipso-C5Me4SiMe3), 16.5 (s, C5Me4SiMe3), 13.2 (s, C5Me4SiMe3), 3.5 (s, C5Me4SiMe3). IR (Nujol mull): 2953 (s), 2923 (s), 2853 (s), 1462 (m), 1377 (m), 722 (m) cm−1. Anal. Calcd for C48H92Si4Zr4·C6H6: C, 52.96; H, 8.07. Found: C, 53.05; H, 7.85. [(C5Me4SiMe3)4Hf4(μ-H)8] (2-Hf). A C6H6 solution (1.0 mL) of 1Hf (0.509 g, 0.803 mmol) in a 10 mL Hiper glass cylinder (TAIATSU TECHNO) was filled with H2 (10 atm). The mixture was stirred at 90 °C for 4 days. The colorless solution changed to dark green. After removal of the solvent under vacuum, the residual dark green solid was dissolved in THF and crystallized at −33 °C to give 2-Hf (0.174 g, 0.116 mmol, 58%) as a dark green crystal. Single crystals suitable for X-ray diffraction study were obtained from a concentrated THF solution of 2-Hf at room temperature. 1H NMR (C6D6, room temperature): δ 4.86 (s, 8H, μ-H), 2.49 (s, 24H, C5Me4SiMe3), 2.35 (s, 24H, C5Me4SiMe3), 0.36 (s, 36H, C5Me4SiMe3). 13C NMR (C6D6, room temperature): δ 125.3 (s, C5Me4SiMe3), 121.5 (s, C5Me4SiMe3), 111.1 (s, ipso-C5Me 4SiMe3), 17.0 (s, C5Me4SiMe3), 13.4 (s, C5Me4SiMe3), 4.0 (s, C5Me4SiMe3). IR (Nujol mull): 2953 (s), 2923 (s), 2853 (s), 1462 (m), 1377 (m), 847 (m), 722 (m) cm−1. Anal. Calcd for C48H92Si4Hf4: C, 38.55; H, 6.20. Found: C, 38.92; H, 5.95. [(C5Me5)4Zr4(μ-H)8] (3). A THF solution (4 mL) of [(C5Me5)Zr(CH2SiMe3)3] (114 mg, 0.235 mmol) in a 10 mL Hiper glass cylinder (TAIATSU TECHNO) was filled with H2 (10 atm). The mixture was stirred at 80 °C for 18 h. The solution color changed to dark green. After removal of the solvent under vacuum, the residual dark green solid was dissolved in THF and crystallized at −33 °C to give 3 (46 mg, 0.51 mmol, 87%) as a dark green crystal. Single crystals suitable for X-ray diffraction study were obtained from a concentrated THF solution of 3 at −33 °C. 1H NMR (C6D6, room temperature): δ 2.32 (s, 60H, C5Me5), 0.79 (s, 8H, μ-H). 13C NMR (C6D6, room temperature): δ 117.4 (s, C5Me5), 12.7 (s, C5Me5). IR (Nujol mull): 2953 (s), 2923 (s), 2853 (s), 1462 (m), 1377 (m), 722 (m) cm−1. Anal. Calcd for C40H68Zr4: C, 52.57; H, 7.50. Found: C, 52.71; H, 7.31. [(C5Me4SiMe3)4Zr4(μ3-Se)(μ-H)8] (4). 2-Zr (20 mg, 0.017 mmol), SePPh3 (6 mg, 0.018 mmol), and toluene (0.5 mL) were mixed at room temperature and kept at −33 °C for 2 days, which gave brown crystals. After the solvent was removed, the residual crystals were dried under reduced pressure, which afforded 4·C7H8 as brown crystals (16 mg, 0.013 mmol, 76%). Single crystals suitable for an X-ray study were obtained from a concentrated toluene solution of 4 at −33 °C. 1H NMR (400 MHz, C6D6, room temperature): δ 3.42 (sext, JHH = 2.9

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ASSOCIATED CONTENT

S Supporting Information *

Figures, tables, and CIF files giving ORTEP drawings and crystallographic data, atomic coordinates, thermal parameters, and bond distances and angles for 2-Zr (from hexane), 2Zr·THF (from THF), 2-Hf, 3, and 4 and computational details. This material is available free of charge via the Internet at http://pubs.acs.org. 2149

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(18) Takenaka, Y.; Shima, T.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2009, 48, 7888−7891. (19) Yousufuddin, M.; Gutmann, M. J.; Baldamus, J.; Tardif, O.; Hou, Z. J. Am. Chem. Soc. 2008, 130, 3888−3891. (20) Li, X.; Baldamus, J.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2006, 45, 8184−8188. (21) Shima, T.; Hou, Z. J. Am. Chem. Soc. 2006, 128, 8124−8125. (22) Cui, D.; Nishiura, M.; Hou, Z. Macromolecules 2005, 38, 4089− 4095. (23) Luo, Y.; Baldamus, J.; Tardif, O.; Hou, Z. Organometallics 2005, 24, 4362−4366. (24) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 959−962. (25) Tardif, O.; Hashizume, D.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 8080−8081. (26) Cui, D.; Tardif, O.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 1312− 1313. (27) Tardif, O.; Nishiura, M.; Hou, Z. Organometallics 2003, 22, 1171−1174. (28) Slater, J. C. J. Chem. Phys. 1964, 41, 3199−3204. (29) Ohno, K.; Maeda, S. Chem. Phys. Lett. 2004, 384, 277−282. (30) Energy differences calculated by the other functionals are shown in the Supporting Information. (31) The Cp*-ligated hafnium analogue [Cp*4Hf4(μ-H)8] could also be obtained in a similar manner, but harsher conditions (H2 (10 atm), 90 °C, >10 days) were required, and the yield was less than ∼30%. (32) The possible byproduct might be the pentanuclear species “[Cp*5Zr5H10]”. The analogous yttrium pentanuclear polyhydride complex was obtained previously.13 (33) (a) Hoskin, A. J.; Stephan, D. W. Organometallics 1999, 18, 2479−2483. (b) Evans, W. J.; Forrestal, K. J.; Ziller, J. W. J. Am. Chem. Soc. 1998, 120, 9273−9282. (34) For examples of trivalent Zr(III) organometallic compounds, see: (a) Driess, M.; Aust, J.; Merz, K. Eur. J. Inorg. Chem. 2005, 866− 871. (b) Chirik, P. J.; Henling, L. M.; Bercaw, J. E. Organometallics 2001, 20, 534−544. (c) Fryzuk, M. D.; Jafarpour, L.; Rettig, S. J. Organometallics 1999, 18, 4050−4058. (d) Cano, A.; Cuenca, T.; Gómez-Sal, P.; Manzanero, A.; Royo, P. J. Organomet. Chem. 1996, 526, 227−235. (35) The reaction of the yttrium hydride complex [Cp′4Y4(μH)8(THF)] with EPPh3 (E = S, Se) gave [(Cp′Y)4(μ-H)6(μ4-E) (THF)2] with release of H2. More details will be reported elsewhere in due course. (36) SMART Software Users Guide, version 4.21; Bruker AXS: Madison, WI, 1997. (37) SAINT PLUS, version 6.02; Bruker AXS, Madison, WI, 1999. (38) Sheldrick, G. M. SADABS; Bruker AXS, Madison, WI, 1998. (39) Sheldrick, G. M. SHELXTL, version 5.1; Bruker AXS, Madison, WI, 1998. (40) (a) Beck, A. D. J. Chem. Phys. 1993, 98, 5648−5652. (b) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789. (41) Perdew, J. P.; Burke, K.; Wang, Y. Phys. Rev. B 1996, 54, 16533− 16539. (42) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241. (43) Dolg, M.; Stoll, H.; Savin, A.; Preuss, H. Theor. Chim. Acta 1989, 75, 173−194. (b) Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1993, 85, 441−450. (c) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123−141. (d) Bergner, A.; Dolg, M.; Kuechle, W.; Stoll, H.; Preuss, H. Mol. Phys. 1993, 80, 1431−1441. (44) (a) Höllwarth, A.; Böhme, M.; Dapprich, S.; Ehlers, A. W.; Gobbi, A.; Jonas, V.; Köhler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G. Chem. Phys. Lett. 1993, 208, 237−340. (b) Ehlers, A. W.; Böhme, M.; Dapprich, S.; Gobbi, A.; Höllwarth, A.; Jonas, V.; Köhler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G. Chem. Phys. Lett. 1993, 208, 111−114. (45) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (T.S.); [email protected] (Y.L.); [email protected] (Z.H.). Tel: (+81)-48-467-9392. Fax: (+81)-48-462-4665. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Young Scientists (B) (No. 21750068 to T.S.), a Grant-in-Aid for Scientific Research (S) (No. 21225004 to Z.H.) from the JSPS, an Incentive Research Grant from RIKEN, and the National Natural Science Foundation of China (Nos. 21028001 and 21174023). We also thank RICC (RIKEN Integrated Cluster of Clusters) and the Network and Information Center of Dalian University of Technology for computational resources.

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REFERENCES

(1) Hoskin, A. J.; Stephan, D. W. Coord. Chem. Rev. 2002, 233−234, 107−129. (2) Bochmann, M. In Comprehensive Organometallic Chemistry III; Mingos, D. M. P., Crabtree, R. H. Eds.; Elsevier Science: Amsterdam, 2007; Vol. 4. (3) Wolczanski, P. T.; Bercaw, J. E. Acc. Chem. Res. 1980, 13, 121− 127. (4) Tilley, T. D. Acc. Chem. Res. 1993, 26, 22−29. (5) Ballmann, J.; Munhá, R. F.; Fryzuk, M. D. Chem. Commun. 2010, 46, 1013−1025. (6) Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. Soc. 1976, 98, 6733−6735. (7) For examples of other d transition metal half-sandwich hydride complexes, see: (a) Gross, C. L.; Girolami, G. S. Organometallics 2007, 26, 160−166. (b) Suzuki, H.; Kakigano, T.; Tada, K.; Igarashi, M.; Matsubara, K.; Inagaki, A.; Oshima, M.; Takao, T. Bull. Chem. Soc. Jpn. 2005, 78, 67−87. (c) Ohki, Y.; Uehara, N.; Suzuki, H. Organometallics 2003, 22, 59−64. (d) Suzuki, H. Eur. J. Chem. 2002, 1009−1023. (e) Ohki, Y.; Uehara, N.; Suzuki, H. Angew. Chem., Int. Ed. 2002, 41, 4085−4087. (f) Ohki, Y.; Suzuki, H. Angew. Chem., Int. Ed. 2000, 39, 3120−3122. (g) Gross, C. L.; Wilson, S. R.; Girolami, G. S. J. Am. Chem. Soc. 1994, 116, 10294−10295. (h) Kersten, J. L.; Rheingold, A. L.; Theopold, K. H.; Casey, C. P.; Widenhoefer, R. A.; Hop, C. E. C. A. Angew. Chem., Int. Ed. Engl. 1992, 32, 1341−1343. (i) Herrmann, W. A.; Okuda, J. Angew. Chem., Int. Ed. Engl. 1986, 25, 1092−1093. (j) Okuda, J.; Murray, R. C.; Dewan, J. C.; Schrock, R. R. Organometallics 1986, 5, 1681−1690. (k) Gilbert, T. M.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1985, 107, 3508−3516. (8) Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982, 1, 793− 799. (9) Liu, F.-C.; Chu, Y.-J.; Yang, C.-C.; Lee, G.-H.; Peng, S.-M. Organometallics 2010, 29, 2685−2692. (10) Booij, M.; Blenkers, J.; Sinnema, J. C. M.; Meetsma, A.; van Bolhuis, F.; Teuben, J. H. Organometallics 1988, 7, 1029−1032. (11) Visser, C.; van den Hende, J. R.; Meetsma, A.; Hessen, B. Organometallics 2003, 22, 615−617. (12) Nishiura, M.; Baldamus, J.; Shima, T.; Mori, K.; Hou, Z. Chem. Eur. J. 2011, 17, 5033−5044. (13) Shima, T.; Nishiura, M.; Hou, Z. Organometallics 2011, 30, 2513−2524. (14) Nishiura, M.; Hou, Z. Nat. Chem. 2010, 2, 257−268. (15) Hou, Z.; Nishiura, M.; Shima, T. Eur. J. Inorg. Chem. 2007, 2535−2545. (16) Cheng, J.; Shima, T.; Hou, Z. Angew. Chem., Int. Ed. 2011, 50, 1857−1860. (17) Shima, T.; Hou, Z. Dalton Trans. 2010, 39, 6858−6863. 2150

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Article

P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö .; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.1; Gaussian, Inc., Wallingford, CT, 2009.

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