Article

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Tetranuclear and Polyhydride Complexes “ ” Composed of the CpMH2 Units Shaowei Hu,† Takanori Shima,*,† Yi Luo,*,‡ and Zhaomin Hou*,†

† 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 μ octahydride complexes [(C5Me4R)4M4( -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 [(C5Me4R)M- (CH2SiMe3)3](1-Zr, M = Zr, R = SiMe3; 1-Hf, M = Hf, R ′ ff = SiMe3; 1-Zr , M = Zr, R = Me). X-ray di raction studies μ μ revealed that these clusters possess a tetrahedral M4 framework which is connected by two 3-H and six 2-H ligands. fi Such bonding modes have been further clari ed by DFT studies. The reaction of 2-Zr with SePPh3 resulted in oxidation of two 2− of the four Zr(III) ions in 2-Zr to Zr(IV) and reduction of SePPh3 to Se , yielding the selenium-capped hydride cluster μ μ [(C5Me4SiMe3)4Zr4( 3-Se)( -H)8](4) with release of PPh3.

13 ■ INTRODUCTION (CH2C6H4NMe2-o)2] (R = SiMe3, Me, Et, H) could be Group 4 transition metal hydride complexes have received easily transformed into the corresponding dihydride species “(Cp)LnH ” by hydrogenolysis with H . The resulting much interest because of their importance in various chemical 2 2 1−5 dihydride species showed unique polynuclear structures and transformations. So far, a large number of group 4 transition reactivities which are different from those of the conventional metal hydride compounds of the general types [(Cp) MH ] 2 2 metallocene hydride complexes bearing two Cp ligands per and [(Cp) MHX] (Cp = cyclopentadienyl derivatives) bearing − 2 metal.14 27 During these studies, we became interested in the two cyclopentadienyl ligands per metal (for example, analogous group 4 metal hydride clusters. In this paper, we [Cp* ZrH ]; Cp* =CMe )6 have been reported and 2 2 5 5 report that half-sandwich group 4 metal tris- extensively studied. In contrast, group 4 metal hydride (trimethylsilylmethyl) complexes such as [(C Me R)M- complexes of the half-sandwich type “[(Cp)MH ]”, which 5 4 n (CH SiMe ) ] (M = Zr, Hf; R = SiMe , Me) can serve as bear one cyclopentadienyl ligand per metal, have hardly been 2 3 3 3 excellent precursors for the synthesis of the tetranuclear studied, although such complexes are of much interest both 7 zirconium and hafnium polyhydride complexes [(C5Me4R)M- structurally and chemically. μ “ ( -H)2]4, which are formally composed of four (C5Me4R)- In 1982, Wolczanski and Bercaw reported the first mono-Cp- ” * μ MH2 units. DFT studies on a zirconium complex to elucidate coordinated zirconium hydride complex, [{Cp Zr(BH4)H( - 8 the Zr4H8 core structure, as well as a preliminary reactivity H)}2], in combination with a tetrahydroborate unit. Since study on the Zr hydride cluster, are also reported. then, several analogous mono-Cp-coordinated group 4 metal * μ η2 μ hydride complexes, such as [{Cp Zr(BH4)}2( - -BH4)( - * μ μ 8,9 * μ ■ RESULTS AND DISCUSSION H)3]2,[{CpZr(BH4)}2( -H)( -H)3]2, [(Cp MCl)( - μ 9,10 * μ μ Synthesis and Structure of C Me SiMe -Ligated H)( 3-H)]4 (M = Zr, Hf), and [(Cp Hf)4( -C6H8)( - 5 4 3 11 Tetranuclear Zr and Hf Octahydride Complexes. Hydro- H)6], have been reported. However, group 4 metal hydride “ ” genolysis of the half-sandwich Zr tris(trimethylsilylmethyl) complexes composed of only the CpMHn unit without a third component have not yet been reported. Previous attempts to complex [(C5Me4SiMe3)Zr(CH2SiMe3)3](1-Zr) with H2 (10 ° ff prepare such half-sandwich hydride complexes by hydro- atm) in hexane at 80 C for 1 day a orded the tetranuclear μ genolysis of the corresponding half-sandwich alkyl precursors zirconium octahydride complex [(C5Me4SiMe3)4Zr4( -H)8] * * * 8 (2-Zr) in 87% yield (Scheme 1). The formation of 2-Zr can such as [Cp ZrMe3], [Cp Zr(CH2Ph)3], [Cp ZrPh3], and * 10 be viewed as a result of the hydrogenation of the three alkyl [Cp HfMe3] with H2 did not give a structurally character- izable product. groups in 1-Zr followed by tetramerization of the resulting “ ′ ” We recently found that half-sandwich rare-earth bis(alkyl) trihydride species [Cp ZrH3] and liberation of two molecules complexes such as [(C5Me4SiMe3)Ln(CH2SiMe3)2(THF)] (Ln − = Y, Lu, Sc, Gd Yb), [(C5Me4SiMe3)Ln(CH2C6H4NMe2-o)2] Received: January 8, 2013 12 (Ln=La,Ce,Pr,Nd,Sm), and [(C5Me4R)Y- Published: March 15, 2013

© 2013 American Chemical Society 2145 dx.doi.org/10.1021/om400012a | Organometallics 2013, 32, 2145−2151 Organometallics Article

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

of H2. The 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 μ [(C5Me4SiMe3)4Hf4( -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 η5 to one C5Me4SiMe3 ligand in an bonding mode. There are eight hydride ligands in the tetranuclear Zr framework, two of μ which are face-capped in a 3-H fashion and six are edge- μ bridged in a 2-H form. Unlike the analogous tetranuclear μ μ yttrium octahydride complex [(C5Me4SiMe3)4Y4( 4-H)( 3- μ 23 μ Figure 1. (a) X-ray full structure of Zr4H8 in 2-Zr recrystallized from H)( 2-H)6], no body-centered interstitial 4-H ligand was found in the Zr tetrahedron cavity in 2-Zr. The short Zr−Zr hexane with 30% thermal ellipsoids. (b) Core structure of 2-Zr. 4 Selected bond lengths (Å): Zr1−Zr4, 3.0679(4); Zr1−Zr2, 3.0806(4); distances in 2-Zr (3.0670(4)−3.0949(5) Å (average 3.0787 Å)) − − − − 28 Zr1 Zr3, 3.0885(4); Zr2 Zr4, 3.0735(4); Zr2 Zr3, 3.0949(5); Zr3 in comparison with the sum of the atomic radii of Zr (3.10 Å) Zr4, 3.0670(4); Zr1−H1, 1.97(3); Zr1−H4, 1.79(5); Zr1−H6, and the diamagnetism of 2-Zr (vide infra) might indicate the 1.88(5); Zr1−H7, 2.07; Zr1−H8, 2.22(7); Zr2−H2, 1.92(3); Zr2− existence of Zr−Zr σ interactions. The Zr−Zr distances in 2-Zr H3, 2.00(3); Zr2−H6, 1.87(4); Zr2−H7, 2.16; Zr3−H1, 1.91(3); fall into a narrow range, in contrast with the case for the Zr3−H3, 1.94(3); Zr3−H5, 1.87(6); Zr3−H8, 1.92(7); Zr4−H2, * μ μ − − − − analogous mixed chloride/hydride cluster [{Cp ZrCl( -H)( 3- 2.03(3); Zr4 H4, 1.93(5); Zr4 H5, 1.85(5); Zr4 H7, 2.04; Zr4 9 fl H8, 2.11(7). The H7 atom was not refined. H)}4], which adopted a butter y-like core structure (Zr- - -Zr, − −μ − 3.2808(4) 5.635 Å). The Zr 2-H bond distances (1.79(5) −μ 2.03(3) Å (average 1.91 Å)) and the Zr 3-H bond distances (1.92(7)−2.22(7) Å (average 2.09 Å)) in 2-Zr are comparable * μ μ −μ − to those in [{Cp ZrCl( -H)( 3-H)}4] (Zr 2-H, 1.79(5) −μ − 2.09(6) Å; Zr 3-H, 1.96(8) 2.33(5) Å). 1 The HNMRspectrumof2-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 * μ μ δ comparison with those in [{Cp ZrCl( -H)( 3-H)}4]( 3.88, 9 * μ δ 8 3.50) and [{Cp Zr(BH4)H( -H)}2]( 1.31). 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-d , suggesting that these hydride ligands are highly 8 · fluxional in solution. Complex 2-Hf showed similar behavior in Figure 2. X-ray structure of the Zr4H8 core in 2-Zr THF recrystallized 1 from THF with 30% thermal ellipsoids. The hydride ligands H4 and its H NMR spectrum. * fi In an attempt to recrystallize 2-Zr from THF, single crystals H4 are re ned at 25% occupancy due to a disorder problem. Selected bond lengths (Å): Zr−Zr, 3.0748(4)−3.0886(5) (average 3.0794); having a lattice THF molecule (2-Zr·THF) were obtained. An −μ − −μ − Zr 2-H(2,3), 1.87(3) 1.91(2) (average 1.90); Zr 3-H4, 2.13(8) X-ray diffraction study revealed that 2-Zr·THF adopts a −μ 2.14(7) (average 2.14), Zr 4-H1, 1.8857(3). tetranuclear structure similar to that of 2-Zr. However, in · μ contrast to 2-Zr, 2-Zr THF possesses an interstitial 4-H ligand · at the center of the tetrahedron Zr4 cavity (Figure 2), which is 2-Zr THF is not possible. The crystals of 2-Zr obtained from similar to the case for the previously reported Y complex benzene, cyclohexane, and pyridine showed the same structure μ μ μ 23 μ [(C5Me4SiMe3)4Y4( 4-H)( 3-H)( 2-H)6]. Because of disor- as that from hexane, without a 4-H ligand. In view of the der problems, further discussion of the Zr4H8 core structure in general uncertainty in determining the positions of metal-

2146 dx.doi.org/10.1021/om400012a | Organometallics 2013, 32, 2145−2151 Organometallics Article bound hydride atoms by X-ray diffraction, theoretical molecular orbitals and the Wiberg bond indexes (WBI) were calculations were then carried out to further elucidate the performed. The HOMOs and LUMOs of 2m and 2m′ are Zr−H connections in 2-Zr. mainly contributed by the Zr 4d orbital with a small amount of DFT Studies on the Zr4H8 Core Structure of 2-Zr. To hybridization of Zr 5s (Figure 3c,d and Figure S6 in the gain insight into the stable hydride positions of 2-Zr, density Supporting Information). The HOMO-16 orbital of 2m′ shows 29 μ functional theory (DFT) computations were performed on orbital overlap between the 1s orbital of 4-H and 4d orbitals of model compounds of 2-Zr, viz., [(C5H4SiH3)4Zr4H8](2m Zr atoms (Figure S6). In the frontier orbitals, except for the μ μ ′ μ includes two 3-H and six 2-H atoms; 2m includes one 4-H, LUMO of 2m, the contribution from ancillary ligands is μ μ − one 3-H, and six 2-H atoms). Starting from the X-ray negligible. The HOMOs in Figure 3c,d demonstrate Zr Zr crystallographic geometry data of 2-Zr (obtained from hexane) bonding. Unlike the previously reported Lu analogues [(η5- · and 2-Zr THF (obtained from THF), full geometry opti- C5H4SiH3)4Lu4H8], in which the bridging play an mizations were performed. The resulting optimized structures important role in the Lu···Lu bonding interactions,23 no 2m and 2m′ are shown in Figure 3a,b, which reproduced well 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 μ could be ascribed to the interstitial 4-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 Tetranu- clear Zr Octahydride Complex. The successful isolation of the C5Me4SiMe3-ligated tetranuclear polyhydride complexes 2- Zr 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 * μ corresponding tetranuclear octahydride complex [Cp 4Zr4( - 31 H)8](3) in 87% yield (Scheme 2). When the reaction was

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

Figure 3. (a) DFT(B3LYP)-optimized structure of the Zr4H8 core in μ μ [(C5H4SiH3)4Zr4( 3-H)2( -H)6](2m) based on the X-ray structure of 2-Zr crystallized in hexane. (b) DFT(B3LYP)-optimized structure of conducted in hexane or concentrated THF solutions (0.3 M), μ μ μ ′ 1 the Zr4H8 core in [(C5H4SiH3)4Zr4( 4-H)( 3-H)( -H)6](2m ) based the yield of 3 decreased (∼50% by H NMR), with increased on the X-ray structure of 2-Zr crystallized in THF (2-Zr·THF). ∼ 32 − − byproduct ( 50%). These results suggest that the formation DFT(B3LYP)-optimized Zr Zr and Zr H contacts (Å) in 2m and of the hydride complex 3 is influenced by the reaction 2m′ are shown below. Molecular orbital isosurfaces of (c) 2m ′ conditions. In agreement with these observations, the hydro- (HOMO) and (d) 2m (HOMO). * 8 genation of [Cp Zr(CH2Ph)3] (10 atm of H2) in toluene at 80 °C gave only a trace amount of 3, but a similar reaction in μ ff the overall tetrahedral skeleton of the Zr4H8 core with two 3-H THF a orded 3 in about 50% yield. μ ′ − 1 atoms for 2m and one 4-H atom for 2m . The Zr Zr and The H NMR spectrum of 3 recorded at room temperature −μ ′ δ Zr 3-H distances in 2m are slightly shorter than those in 2m , in C6D6 showed two sharp signals at 2.32 (60 H) and 0.79 but other Zr−H bond lengths of 2m and 2m′ are relatively (8H), which could be assigned to the cyclopentadienyl methyl comparable with each other. Energy comparisons between 2m protons and the hydride ligands, respectively. An X-ray ′ fi ′ ff and 2m revealed that 2m is signi cantly more stable than 2m di raction study revealed that 3 adopted the same Zr4H8 30 μ μ by ca. 17.5 kcal/mol from B3LYP. These results are in core structure (two 3-H and six 2-H atoms) as those of 2- agreement with the experimental observation that the structure Zr and 2-Hf (see the Supporting Information, Figure S4). μ of 2-Zr without an interstitial 4-H atom is preferred in most Reaction of 2-Zr with SePPh3. The reduction of cases. triphenylphosphine chalcogenides EPPh3 (E = S, Se) by For a better understanding of the electronic characters of 2m early-transition-metal complexes is well-known.33 2-Zr has four and 2m′, and the metal−metal interactions, analyses of the Zr(III) metal centers and eight hydride ligands. Both the metal

2147 dx.doi.org/10.1021/om400012a | Organometallics 2013, 32, 2145−2151 Organometallics Article centers and the hydrides could show a certain reduction ■ CONCLUSION 34 potential. However, no reaction between 2-Zr and SPPh3 was In summary, tetranuclear zirconium and hafnium polyhydride observed at 80 °C. In contrast, the reaction of 2-Zr with “ ” complexes composed of CpMH2 units, such as 2-Zr, 2-Hf, SePPh3 took place rapidly to give the tetranuclear selenide/ μ μ and 3, have been synthesized and structurally characterized for hydride complex [{(C5Me4SiMe3)Zr}4( 3-Se)( -H)8](4)in the first time by using the half-sandwich tris((trimethylsilyl)- 76% yield together with PPh3 (Scheme 3). In this reaction, two methyl) complexes [(C5Me4R)M(CH2SiMe3)3] (M = Zr, Hf; R of the four Zr(III) ions in 2-Zr are oxidized into Zr(IV) and ff 2− = SiMe3, Me) as precursors. X-ray di raction and DFT studies SePPh3 is reduced to Se and PPh3. Release of was have demonstrated that the group 4 metal hydride clusters not observed.35 prefer formation of a tetrahedral M4H8 core structure without μ an interstitial 4-H ligand, in contrast with the case for Scheme 3. Reaction of 2-Zr with SePPh3 analogous rare-earth polyhydride complexes such as μ μ μ 23 [(C5Me4SiMe3)4Y4( 4-H)( 3-H)( 2-H)6]. The reaction of 2-Zr with SePPh3 to give 4 may suggest that the mono-Cp- ligated 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 early- transition-metal polyhydride complexes are in progress.

■ EXPERIMENTAL SECTION Single crystals of 4 suitable for X-ray diffraction study were All reactions were carried out under a dry and oxygen-free argon obtained by recrystallization from toluene (Figure 4). However, 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 concen- trations 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 JEOL- ECS400, AL400, and JNM-AL300 spectrometers. Elemental analyses were performed with a MICRO CORDER JM10 instrument. fi Anhydrous THF, hexane, benzene, Et2O, and toluene were puri ed by use of a SPS-800 solvent purification system (Mbraun) and dried ′ μ 14,15,26,27 over fresh Na chips in the glovebox. [Cp 4Y4( -H)8(THF)] 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, Figure 4. X-ray structure of the Zr SeH core in 4 with 30% thermal 4 8 4.81 mmol, prepared from the reaction of C5Me4H(SiMe3) with n- ellipsoids. The selenium atom is disordered (Se1/Se1A/Se2/Se2A = BuLi in THF) in toluene solution (20 mL) was added to a suspension 33/33/17/17%). Selected bond lengths (Å): Zr−Zr, 3.0509(7)− of ZrCl4 (1.12 g, 4.81 mmol) in toluene (10 mL), and the mixture was 3.2078(11) (average 3.1350); Zr−Se, 2.6100(14)−2.7606(14) (aver- refluxed for 1 day, at which point LiCH SiMe (1.36 g, 14.4 mmol) −μ − 2 3 age 2.719); Zr 2-H, 1.68(4) 1.92(4) (average 1.84). 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 the selenium atom, which is bonded to three of the four Zr 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- atoms, is disordered over four positions, which were treated ′ with 33/33/17/17% occupancies, respectively. Two possible (CH2SiMe3)3](1-Zr ) was also synthesized from the reaction of μ C5Me5Li with ZrCl4 followed by alkylation with LiCH2SiMe3 (62%). 3-H ligands could not be located because of overlap with the Data for 1-Zr are as follows. 1H NMR (C D , room temperature): δ disordered μ -Se ligands. The six μ -H atoms could be found 6 6 3 2 2.06 (s, 6H, C5Me4SiMe3), 1.85 (s, 6H, C5Me4SiMe3), 0.45 (s, 6H, without a problem. ZrCH2SiMe3), 0.30 (s, 9H, C5Me4SiMe3), 0.28 (s, 27H, ZrCH2SiMe3). The 1H NMR spectrum of 4 at room temperature showed 13C NMR (C D , room temperature): δ 127.9 (s, C Me SiMe ), 126.3 ′ 6 6 5 4 3 two sets of signals for the Cp ligands in an intensity ratio of 3/ (s, C5Me4SiMe3), 125.7 (s, ipso-C5Me4SiMe3), 64.4 (s, ZrCH2SiMe3), 1. This signal pattern is in agreement with the solid structure 15.2 (s, C5Me4SiMe3), 12.3 (s, C5Me4SiMe3), 3.3 (s, ZrCH2SiMe3), 2.1 where the selenium atom is bonded to three of the four Zr (s, C5Me4SiMe3). Anal. Calcd for C24H54Si4Zr: C, 52.77; H, 9.96. δ Found: C, 52.63; H, 9.69. Data for 1-Zr′ are as follows. 1H NMR atoms. The eight hydride ligands showed two signals at 3.42 δ (C6D6, room temperature): 1.84 (s, 15H, C5Me5), 0.35 (s, 6H, (sextet, JHH = 2.9 Hz, 3H) and 1.91 (quartet, JHH = 2.9 Hz, μ ZrCH2SiMe3), 0.26 (s, 27H, ZrCH2SiMe3). 5H), respectively. The former is assignable to the three 2-H [(C Me SiMe )Hf(CH SiMe ) ] (1-Hf). “ ” 5 4 3 2 3 3 LiC5Me4SiMe3 (625 mg, ligands bonding to the Zr- - -Zr edge of the three Zr2Se fi 3.12 mmol, prepared from the reaction of C5Me4H(SiMe3) with n- planes, and the latter could be assigned to the remaining ve BuLi in THF) in toluene solution (5 mL) was added to a suspension μ μ hydrides (three 2-H and two 3-H) bonding to the Zr atoms of HfCl4 (1.0 g, 3.12 mmol) in toluene (10 mL), and the mixture was “ ” fl in the three Zr3 planes. re uxed for 1 day, at which point LiCH2SiMe3 (882 mg, 9.37 mmol)

2148 dx.doi.org/10.1021/om400012a | Organometallics 2013, 32, 2145−2151 Organometallics Article μ was then slowly added. After removal of the solvent under vacuum, the Hz, 3H, -H), 2.42 (s, 18H, C5Me4SiMe3), 2.36 (s, 6H, C5Me4SiMe3), fi residual pale yellow solid was extracted with hexane and ltered. After 2.27 (s, 18H, C5Me4SiMe3), 2.25 (s, 6H, C5Me4SiMe3), 1.91 (q, JHH = μ reduction of the solution volume under reduced pressure, the pale 2.9 Hz, 5H, -H), 0.56 (br s, 27H, C5Me4SiMe3), 0.55 (br s, 9H, − ° 13 δ yellow solution was cooled to 33 C overnight to give 1-Hf (1.32 g, C5Me4SiMe3). C NMR (100 MHz, C6D6, room temperature): × × 2.08 mmol, 67%) as colorless crystals. Single crystals suitable for X-ray 125.6 (s, 3 C5Me4SiMe3), 125.0 (s, C5Me4SiMe3), 123.8 (s, 3 1 analysis were grown by recrystallization from hexane. H NMR (C6D6, C5Me4SiMe3), 123.4 (s, C5Me4SiMe3), 114.3 (s, ipso-C5Me4SiMe3), δ × room temperature): 2.09 (s, 6H, C5Me4SiMe3), 1.88 (s, 6H, 113.3 (s, ipso-C5Me4SiMe3), 15.9 (s, 3 C5Me4SiMe3), 15.7 (s, × C5Me4SiMe3), 0.28 (s, 9H, C5Me4SiMe3), 0.26 (s, 27H, HfCH2SiMe3), C5Me4SiMe3), 13.0 (s, 3 C5Me4SiMe3), 12.7 (s, C5Me4SiMe3), 3.1 (s, − 13 δ 0.04 (s, 6H, HfCH2SiMe3). C NMR (C6D6, room temperature): C5Me4SiMe3), 2.9 (s, C5Me4SiMe3). Anal. Calcd for C48H92Si4Zr4Se: 125.8 (s, C5Me4SiMe3), 125.2 (s, C5Me4SiMe3), 117.3 (s, ipso- C, 47.05; H, 7.57. Found: C, 47.50; H, 7.45. C5Me4SiMe3), 70.8 (s, HfCH2SiMe3), 14.9 (s, C5Me4SiMe3), 12.0 (s, X-ray Crystallographic Studies. Crystals for X-ray analysis were C5Me4SiMe3), 3.6 (s, HfCH2SiMe3), 2.1 (s, C5Me4SiMe3). Anal. Calcd obtained as described in the preparations. The crystals were for C24H54Si4Hf: C, 45.50; H, 8.59. Found: C, 44.89; H, 8.21. manipulated in the glovebox under a microscope in the glovebox μ [(C5Me4SiMe3)4Zr4( -H)8] (2-Zr). A hexane solution (1.5 mL) of and were sealed in thin-walled glass capillaries. Data collections were 1-Zr (60 mg, 0.11 mmol) in a 10 mL Hiper glass cylinder (TAIATSU performed at −100 °C on Bruker SMART APEX diffractrometer with fi α TECHNO) was lled with H2 (10 atm). The mixture was stirred at 80 CCD area detector, using graphite-monochromated Mo K radiation °C for 1 day. The solution color changed to dark green. After removal (λ = 0.71073 A). The determination of crystal class and unit cell of the solvent under vacuum, the residual dark green solid was parameters was carried out by the SMART program package.36 The dissolved in hexane and crystallized at −33 °C to give 2-Zr (28 mg, raw frame data were processed using SAINT37 and SADABS38 to yield 0.024 mmol, 87%) as a dark green crystal. Single crystals suitable for the reflection data file. The structures were solved by using the an X-ray diffraction study were obtained from a concentrated hexane SHELXTL program.39 Refinements for 2-Zr, 2-Zr·THF, 2-Hf, 3, and (2-Zr) or THF solution (2-Zr·THF) at room temperature or −33 °C. 4 were performed on F2 anisotropically for all the non-hydrogen atoms 1 δ H NMR (C6D6, room temperature): 2.43 (s, 24H, C5Me4SiMe3), by full-matrix least-squares methods. The analytical scattering factors μ 2.33 (s, 24H, C5Me4SiMe3), 0.61 (s, 8H, -H), 0.57 (s, 36H, for neutral atoms were used throughout the analyses. The selenium 1 δ C5Me4SiMe3). H NMR (THF-d8, room temperature): 2.30 (s, 24H, atom of 4 was disordered, having four orientations (occupancy Se1/ μ C5Me4SiMe3), 2.29 (s, 24H, C5Me4SiMe3), 0.47 (s, 8H, -H), 0.39 (s, Se1A/Se2/Se2A = 33/33/17/17%). The hydrogen atoms, except 13 δ 36H, C5Me4SiMe3). C NMR (C6D6, room temperature): 125.9 (s, those bonded to metals, were placed at calculated positions, which C Me SiMe ), 122.6 (s, C Me SiMe ), 112.6 (s, ipso-C Me SiMe ), were then refined using a riding model. The metal-bound hydrogen 5 4 3 5 4 3 5 4 3 ff 16.5 (s, C5Me4SiMe3), 13.2 (s, C5Me4SiMe3), 3.5 (s, C5Me4SiMe3). IR atoms were located on di erence Fourier maps, and their positions (Nujol mull): 2953 (s), 2923 (s), 2853 (s), 1462 (m), 1377 (m), 722 (except for H7 in 2-Zr) were refined. The metal-bound hydrogen −1 · · (m) cm . Anal. Calcd for C48H92Si4Zr4 C6H6: C, 52.96; H, 8.07. atoms of 2-Zr THF (from THF) (H4) and 2-Hf (H5, H6) were Found: C, 53.05; H, 7.85. disordered, which were refined at 25% (H4 in 2-Zr·THF) and 50% μ [(C5Me4SiMe3)4Hf4( -H)8] (2-Hf). AC6H6 solution (1.0 mL) of 1- occupancy (H5, H6 in 2-Hf). The residual electron densities were of Hf (0.509 g, 0.803 mmol) in a 10 mL Hiper glass cylinder (TAIATSU no chemical significance. Crystal data and analysis results are given in fi TECHNO) was lled with H2 (10 atm). The mixture was stirred at 90 the Supporting Information. °C for 4 days. The colorless solution changed to dark green. After Computational Details. Due to the large molecular size of 2-Zr, η5 ′ removal of the solvent under vacuum, the residual dark green solid was each methyl of the realistic ligand -C5Me4SiMe3 (Cp ) was replaced ′ dissolved in THF and crystallized at −33 °C to give 2-Hf (0.174 g, by H and the model complex (C5H4SiH3)4Zr4H8 (2m and 2m ) was 0.116 mmol, 58%) as a dark green crystal. Single crystals suitable for used for the calculations by using various density functionals: viz., 40 41,41 42 X-ray diffraction study were obtained from a concentrated THF B3LYP, B3PW91, and M062X. In the geometrical optimiza- 1 tions, the 6-31G* basis set was considered for the H and C atoms of solution of 2-Hf at room temperature. H NMR (C6D6, room δ μ the auxiliary π ligand. To get a more accurate core structure, however, temperature): 4.86 (s, 8H, -H), 2.49 (s, 24H, C5Me4SiMe3), 2.35 (s, 13 6-31+G** containing one set of p polarization functions were used for 24H, C5Me4SiMe3), 0.36 (s, 36H, C5Me4SiMe3). C NMR (C6D6, δ the eight hydrogen atoms involved in the core part. The Stuttgart/ room temperature): 125.3 (s, C5Me4SiMe3), 121.5 (s, C5Me4SiMe3), Dresden effective potentials as well as the associated valence basis 111.1 (s, ipso-C5Me4SiMe3), 17.0 (s, C5Me4SiMe3), 13.4 (s, sets43 (4s4p)/[2s2p] and (8s7p6d)/[6s5p3d] were used for Si and Zr 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. 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 Calcd for C48H92Si4Hf4: C, 38.55; H, 6.20. Found: C, 38.92; H, 5.95. μ basis set “BSI”. Single-point calculations with the larger basis set “BSII” [(C5Me5)4Zr4( -H)8] (3). A THF solution (4 mL) of [(C5Me5)Zr- were performed subsequently for the optimized geometries. In BSII, (CH2SiMe3)3] (114 mg, 0.235 mmol) in a 10 mL Hiper glass cylinder fi the 6-311++G(3df,2p) basis set was used for the eight core . (TAIATSU TECHNO) was lled with H2 (10 atm). The mixture was ° The basis sets for the remaining atoms were the same as those in BSI, stirred at 80 C for 18 h. The solution color changed to dark green. 44b After removal of the solvent under vacuum, the residual dark green but one f polarization function (exponent of 0.875) was augmented solid was dissolved in THF and crystallized at −33 °C to give 3 (46 for Zr atoms. The analyses of electronic structure were carried out mg, 0.51 mmol, 87%) as a dark green crystal. Single crystals suitable through single-point calculations at the level of B3LYP/BSII theory. for X-ray diffraction study were obtained from a concentrated THF The energies shown in Table S26 (Supporting Information) were − ° 1 δ obtained from the single-point calculations. The C symmetry point solution of 3 at 33 C. H NMR (C6D6, room temperature): 2.32 1 μ 13 group was used throughout all calculations, and no higher molecular (s, 60H, C5Me5), 0.79 (s, 8H, -H). C NMR (C6D6, room δ symmetry restriction was imposed. All calculations were carried out temperature): 117.4 (s, C5Me5), 12.7 (s, C5Me5). IR (Nujol mull): 45 2953 (s), 2923 (s), 2853 (s), 1462 (m), 1377 (m), 722 (m) cm−1. utilizing the Gaussian 09 program. Anal. Calcd for C40H68Zr4: C, 52.57; H, 7.50. Found: C, 52.71; H, 7.31. ■ ASSOCIATED CONTENT μ μ [(C5Me4SiMe3)4Zr4( 3-Se)( -H)8] (4). 2-Zr (20 mg, 0.017 mmol), *S Supporting Information SePPh3 (6 mg, 0.018 mmol), and toluene (0.5 mL) were mixed at Figures, tables, and CIF files giving ORTEP drawings and room temperature and kept at −33 °C for 2 days, which gave brown crystals. After the solvent was removed, the residual crystals were dried crystallographic data, atomic coordinates, thermal parameters, ff · and bond distances and angles for 2-Zr (from hexane), 2- under reduced pressure, which a orded 4 C7H8 as brown crystals (16 · mg, 0.013 mmol, 76%). Single crystals suitable for an X-ray study were Zr THF (from THF), 2-Hf, 3, and 4 and computational details. obtained from a concentrated toluene solution of 4 at −33 °C. 1H This material is available free of charge via the Internet at δ NMR (400 MHz, C6D6, room temperature): 3.42 (sext, JHH = 2.9 http://pubs.acs.org.

2149 dx.doi.org/10.1021/om400012a | Organometallics 2013, 32, 2145−2151 Organometallics Article ■ AUTHOR INFORMATION (18) Takenaka, Y.; Shima, T.; Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2009, 48, 7888−7891. Corresponding Author (19) Yousufuddin, M.; Gutmann, M. J.; Baldamus, J.; Tardif, O.; *E-mail: [email protected] (T.S.); [email protected] Hou, Z. J. Am. Chem. Soc. 2008, 130, 3888−3891. (Y.L.); [email protected] (Z.H.). Tel: (+81)-48-467-9392. Fax: (20) Li, X.; Baldamus, J.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. (+81)-48-462-4665. 2006, 45, 8184−8188. (21) Shima, T.; Hou, Z. J. Am. Chem. Soc. 2006, 128, 8124−8125. Notes (22) Cui, D.; Nishiura, M.; Hou, Z. Macromolecules 2005, 38, 4089− The authors declare no competing financial interest. 4095. (23) Luo, Y.; Baldamus, J.; Tardif, O.; Hou, Z. Organometallics 2005, ■ ACKNOWLEDGMENTS 24, 4362−4366. (24) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, This work was supported by a Grant-in-Aid for Young 959−962. Scientists (B) (No. 21750068 to T.S.), a Grant-in-Aid for (25) Tardif, O.; Hashizume, D.; Hou, Z. J. Am. Chem. Soc. 2004, 126, Scientific Research (S) (No. 21225004 to Z.H.) from the JSPS, 8080−8081. an Incentive Research Grant from RIKEN, and the National (26) Cui, D.; Tardif, O.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 1312− Natural Science Foundation of China (Nos. 21028001 and 1313. (27) Tardif, O.; Nishiura, M.; Hou, Z. Organometallics 2003, 22, 21174023). We also thank RICC (RIKEN Integrated Cluster of − Clusters) and the Network and Information Center of Dalian 1171 1174. (28) Slater, J. C. J. Chem. Phys. 1964, 41, 3199−3204. University of Technology for computational resources. (29) Ohno, K.; Maeda, S. Chem. Phys. Lett. 2004, 384, 277−282. (30) Energy differences calculated by the other functionals are shown ■ REFERENCES in the Supporting Information. 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2151 dx.doi.org/10.1021/om400012a | Organometallics 2013, 32, 2145−2151