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Slow hydrolysis of an organozirconium complex: The first polyoxometallic heptanuclear zirconium oxide
Journal of Organometallic Chemistry 775 (2015) 76e79
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Communication
Slow hydrolysis of an organozirconium complex: The first polyoxometallic heptanuclear zirconium oxide Arup Mukherjee a, *, Tamal K. Sen a, Sambath Baskaran b, Chinnappan Sivasankar b, Swadhin K. Mandal a, * a b
Department of Chemical Sciences, Indian Institute of Science Education and Research-Kolkata, Mohanpur 741246, India Catalysis and Energy Laboratory, Department of Chemistry, Pondicherry University, Puducherry 605014, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 July 2014 Received in revised form 11 October 2014 Accepted 16 October 2014 Available online 25 October 2014
Herein we report controlled hydrolysis of an organozirconium trimetallic complex, [Cp*2(Me)Zr(m-O) Zr(NMe2)2(m-O)Zr(Me)Cp*2] (Cp* = h5-C5Me5) by slow hydrolysis pathway inside the glovebox resulting in unexpected formation of the first heptanuclear zirconium complex. The basic core of this zirconium complex is reminiscent of a butterfly like structure. © 2014 Elsevier B.V. All rights reserved.
Keywords: Heptanuclear complex Zirconium Hydrolysis Oxide Density functional theory
Introduction Over the past decades, transition metal oxides have attracted a continual interest not only because of their fascinating structural topologies but also owing to their potential applications in catalysis [1] and zirconium oxides in particular received a special attraction in this regard [2,3]. For example, zirconium dioxide is one of the most studied ceramic materials with multiple material applications. Moreover, zirconium oxides have been used extensively as catalysts for different homogeneous organic transformations [4,5,6,7,8]. The use of multinuclear zirconium oxide might be advantageous with regard to material and catalytic applications compared to their monometallic counterpart. Roesky et al. and others have developed a number of Zr(IV) multinuclear metal complexes which have shown interesting structural geometries [9]. Most of these multinuclear zirconium complexes were synthesized by hydrolytic pathway. Until now there are no reports in the literature available dealing with the heptanuclear Zr(IV) complex. Herein, we report the controlled hydrolysis of a organozirconium trimetallic complex, [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2]
* Corresponding authors. E-mail addresses: [email protected] (A. Mukherjee), swadhin.mandal@iiserkol. ac.in (S.K. Mandal). http://dx.doi.org/10.1016/j.jorganchem.2014.10.022 0022-328X/© 2014 Elsevier B.V. All rights reserved.
resulting the first heptanuclear zirconium cluster [{Cp*Zr(mO)2Zr(m-O)Zr(Cp*)2(m-O)2}2Zr] (1, Cp* ¼ h5-C5Me5). Complex 1 was formed by controlled hydrolysis of the ZreNMe2 and ZreCH3 bonds inside the glovebox. The solid state structure of 1 was established by single crystal X-ray diffraction study. Synthesis of Complex 1 was accomplished in an unprecedented way by reacting the monometallic hydroxide precursor, Cp*2(Me)Zr(OH) with Zr(NMe2)4 under the elimination of HN(SiMe3)2, followed by controlled hydrolysis of the reaction mixture inside a nitrogen filled glovebox, which resulted in the heptanuclear assembly of zirconium ions. Results and discussion A solution of Cp*2(Me)Zr(OH) in toluene was added drop-bydrop to the solution of Zr(NMe2)4 in a 1:1 stoichiometric ratio in toluene at 0 C and stirred at 25 C for 24 h to yield a reaction mixture composed of a trinuclear compound [Cp*2(Me)Zr(m-O) Zr(NMe2)2(m-O)Zr(Me)Cp*2] (2) and unreacted Zr(NMe2)4 (Scheme 1, step A). The 1H NMR spectrum of the reaction mixture confirmed the presence of both 2 and free Zr(NMe2)4 (see Supporting Information). Complex 2 can also be prepared exclusively when the reaction was carried out between Cp*2(Me)Zr(OH) and Zr(NMe2)4 in a 2:1 stoichiometric ratio and has been structurally characterized previously [10]. Upon prolonged standing of this reaction mixture containing 2 and unreacted Zr(NMe2)4 for a month inside the
A. Mukherjee et al. / Journal of Organometallic Chemistry 775 (2015) 76e79
Scheme 1. Formation of the heptanuclear zirconium complex 1.
nitrogen filled glovebox, it resulted unexpectedly complex 1 in 27% isolated yield (Scheme 1, step B). Compound 1 is insoluble in npentane but readily dissolves in toluene and THF. Complex 1 is a colorless block shape crystalline solid which was characterized by 1 H, 13C, NMR spectroscopy, and EI mass spectrometry and it is thermally stable. The melting point of 1 exceeds 410 C. The 1H NMR spectrum of 1 in C6D6 exhibited only one singlet at d 1.83 ppm attributed to the proton resonance arising from the Cp* group and this indicates the loss of ZreMe as well as ZreNMe2 resonances observed in 2. The Cp* resonance in 1 is shifted upfield to d 1.83 ppm in case of 1 when compared to that observed for [Cp*2(Me)Zr-(m-O)-Ca(thf)3N(SiMe3)2] (d 1.90 ppm) [11] and [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2] (d 1.93 ppm) [10]. The 13C NMR spectrum of 1 reveals a resonance at d 118.3 ppm, assigned to the Cp* resonance, which was shifted slightly downfield as compared to that of [Cp*2(Me)Zre(m-O)eCa(THF)3N(SiMe3)2] (d 117.4 ppm) [11] and [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2] (d 117.3 ppm) [10]. In the EI mass spectrum of 1, the most intense peak appears at m/z 391(100%) [Mþe{Cp*2Zr(m-O)2Zr(mO)3Zr(Cp*2)Zr(m-O)3Zr(Cp*2)Zr}eC7H8e2H], and the signal at 817 (60%) is assigned to the [Mþe{Cp*2Zr(m-O)2Zr(m-O)3Zr(Cp*2)Zr(mO)2}eCp*eH] fragment.
77
The solid state structure of 1 was established unambiguously by single crystal X-ray diffraction study. To our surprise, the X-ray structure revealed a heptanuclear zirconium complex in which the assembly of seven zirconium has occurred (vide infra). Analytically pure crystals of 1 were obtained from toluene solution at 25 C by slow solvent evaporation technique inside a nitrogen filled glovebox for a month. The structure of 1 was determined by single crystal X-ray diffraction study (Fig. 1a) [12]. Compound 1 crystallizes in the triclinic space group Pı with one molecule in the asymmetric unit. X-ray diffraction study of 1 revealed a heptanuclear complex in which the five zirconium metal atoms [Zr(1), Zr(2), Zr(4), Zr(5) and Zr(6)] define a butterfly shape, with the angle at the hinges of the butterfly being 138.19(11) and 137.61(11) [Zr(2)eO(5)eZr(4) 138.19(11) and Zr(5)eO(8)eZr(6) 137.61(11) , Fig. 1a]. Two of the wingtip zirconium atoms [Zr(2) and Zr(6)] bear four bridging oxygen (meO) atoms. While, other two wingtip zirconium atoms [Zr(4) and Zr(5)] are connected with the Cp* moieties (Fig. 1a). A core structure of the complex 1 is shown in Fig. 1b. The X-ray structural analysis of 1 reveals that the central zirconium, Zr(1) is bonded through four bridging oxygen atoms to the other zirconium ions. The central zirconium ion adopts a distorted tetrahedral geometry. Similarly, the terminal zirconium ions [Zr(3) and Zr(7)] also adopt distorted tetrahedral geometry, considering Cp* as a single coordination site (Fig. 1a). The central zirconiumeoxygen bond distances [Zr(1)eO(3), 1.973(2) Å, Zr(1)eO(4), 1.9486(19) Å, Zr(1)e O(6) 1.971(2), Zr(1)eO(7) 1.944(2) Å] found in 1 are slightly shorter compared to that observed in terminal zirconium ions bound to oxygen center in 1 [Zr(3)eO(1), 2.017(2) Å, Zr(3)eO(2), 2.021(2) Å, Zr(7)eO(9) 2.018(2), Zr(7)eO(10) 2.023(2) Å], but comparable to that observed in a earlier reported related trimetallic complex [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2] (av. ZreO 1.972 Å) [10]. Moreover, the ZreO bond distances observed in 1 are slightly shorter as compared to that found in [(Cp*ZrC1)3(m-O) (m-OH)4] (av. ZreO 2.179 Å) [13]. The O(3)eZr(1)eO(4) bond angle in 1 is 104.86(9) , which is similar to that observed in case of O(6)eZr(1)e O(7) bond angle [104.56(9) ] in 1. A closer look at Fig. 1b reveals that the O(3)eZr(1)eO(7) and O(4)eZr(1)eO(6) bond angles are 113.70(9) and 113.30(9) , respectively characteristic for the tetrahedral geometry. Furthermore, the O(3)eZr(2)eO(5) and O(6)e Zr(6)eO(8) bond angles [105.38(9) and 105.28(9) , respectively] observed in 1 were higher as compared to that O(4)eZr(4)eO(5) and O(7)eZr(5)eO(8) bond angles [98.12(8) and 99.04(9) ,
Fig. 1. (a) Molecular structure of complex 1. Hydrogen atoms and lattice held toluene molecule have been omitted for the sake of clarity. Selected bond distances (Å) and angles ( ): Zr(1)eO(3) 1.973(2), Zr(1)eO(4) 1.9486(19), Zr(1)eO(6) 1.971(2), Zr(1)eO(7) 1.944(2); O(3)eZr(1)eO(4) 104.86(9), O(6)eZr(1)eO(7) 104.56(9); (b) Core structure of the complex 1.
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A. Mukherjee et al. / Journal of Organometallic Chemistry 775 (2015) 76e79
Fig. 2. (a) HOMO1, (b) HOMO, (c) LUMO, and (d) LUMO þ 1 of 1 with energies 5.27, 5.26, 1.17, and 1.15 eV, respectively, (e) calculated electrostatic potential on the 0.0004 au electron density isosurface. Color ranges from red (negative potential) to blue (positive potential). All hydrogen atoms are omitted for the sake of clarity. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
respectively]. This may be attributed to the fact that Zr(4) and Zr(5) ions are attached to the bulky Cp* groups, which reflects a higher steric demand of Cp* moiety squeezing the other bond angles. To understand the electronic structure and bonding properties of 1, density functional theory calculation was performed using Gaussian 03 package [14]. We have adopted a hybrid B3LYP [15] exchange and a correlation functional with the LANL2DZ [16] basis set. The molecular structure from the X-ray diffraction experiment served as the starting point, nevertheless the structure was fully optimized and the optimized structural parameters were found to be comparable with the experimentally observed data. A closer look at the electronics of the zirconium complex 1 shows some interesting features. The HOMO1 appears to concentrate on the Zr and Cp* part (Fig. 2a). Similarly, the HOMO of 1 is mainly centered on the Zr and Cp* and found to be a bonding combination of p symmetry orbitals of Zr and Cp* (Fig. 2b). The LUMO is mainly located on two Zr centers (Fig. 2c) and the difference in energy between HOMO and LUMO of 1 was computed to be 4.09 eV. The LUMO þ 1 resembles more like HOMO1 of 1 (Fig. 2a and d), with the difference in energy between HOMO1 and LUMO þ 1 computed as 4.12 eV. Moreover, Fig. 2e illustrates that in 1 the negative charge (highlighted by the red color) is localized on the electron-withdrawing oxygen centers, while the positive charge (highlighted by the blue) is localized on the Cp* ring. Conclusion In conclusion, formation of the first heptanuclear zirconium complex 1 has been reported. Synthesis of 1 has been unprecedented but has been found to be reproducible several times. The heptanuclear zirconium complex was formed by controlled hydrolysis of a mixture of Cp*2(Me)Zr(OH) with Zr(NMe2)4 under very low level of moisture inside the nitrogen filled glovebox. The basic core of the zirconium complex 1 is reminiscent of a butterfly like
structure. Further investigation including the scope and mechanism of this reaction are in progress in our laboratory. Acknowledgments SKM thanks financial support from SERB (DST), New Delhi (Grant No. SR/S1/IC-25/2012), India. We thank the NMR and X-ray facilities at IISER-Kolkata. Appendix A. Supplementary material CCDC 933635 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jorganchem.2014.10.022. References [1] (a) B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis with Organometallic Compounds, Wiley-VCH, Weinheim, 1996; (b) J.-M. Basset, B.C. Gates, J.P. Candy, A. Choplin, M. Leconte, F. Quignard, C. Santini, Surface Organometallic Chemistry: Molecular Approaches to Surface Catalysis, Kluwer, Dordrecht drecht, The Netherlands, 1988; (c) H.W. Roesky, I. Haiduc, N.S. Hosmane, Chem. Rev. 103 (2003) 2579e2595. €ger, W. Kowalsky, T. Riedl, A. Kahn, Adv. Mater. [2] (a) J. Meyer, S. Hamwi, M. Kro 24 (2012) 5408e5427; (b) C.N.R. Rao, Annu. Rev. Phys. Chem. 40 (1989) 291e326. [3] R. Nielsen, Zirconium and Zirconium Compounds in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. [4] (a) M. Anpo, T. Nomura, J. Kondo, K. Domen, K.-I. Maruya, T. Onishi, Res. Chem. Intermed. 13 (1990) 195e202; (b) M.-Y. He, J.G. Ekerdt, J. Catal. 90 (1984) 17e23; (c) H. Abe, K.-I. Maruya, K. Domen, T. Onishi, Chem. Lett. (1984) 1875e1878;
A. Mukherjee et al. / Journal of Organometallic Chemistry 775 (2015) 76e79
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(d) Z. Feng, W.S. Postula, C. Erkey, C.V. Philip, A. Akgerman, R.G. Anthony, J. Catal. 148 (1994) 84e90. (a) J. Kondo, K. Domen, T. Onishi, Res. Chem. Intermed. 19 (1993) 521e565; (b) S.-C. Moon, K. Tsuji, T. Nomura, M. Anpo, Chem. Lett. (1994) 2241e2290. (a) T. Yamaguchi, H. Sasaki, K. Tanabe, Chem. Lett. (1973) 1017e1021; (b) S.-C. Moon, M. Fujino, H. Yamashita, M. Anpo, J. Phys. Chem. B 101 (1997) 369e373; (c) A. Satoh, H. Hattori, K. Tanabe, Chem. Lett. (1983) 497e498. K. Kaneda, Y. Kawanishi, S. Teranishi, Chem. Lett. (1984) 1481e1482. (a) G. Kickelbick, U. Schubert, J. Chem. Soc. Dalton Trans. (1999) 1301e1306; (b) G. Kickelbick, P. Wiede, U. Schubert, Inorg. Chim. Acta 284 (1999) 1e131. (a) G. Bai, H.W. Roesky, P. Lobinger, M. Noltemeyer, H.-G. Schmidt, Angew. Chem. 113 (2001) 2214e2217. Angew. Chem. Int. Ed. 40 (2001) 2156e2159; (b) G. Bai, H.W. Roesky, J. Li, T. Labahn, F. Cimpoesu, J. Magull, Organometallics 22 (2003) 3034e3038; (c) G. Bai, D. Vidovic, H.W. Roesky, J. Magull, Polyhedron 23 (2004) 1125e1129; (d) L. Pan, R. Heddy, J. Li, C. Zheng, X.-Y. Huang, X. Tang, L. Kilpatrick, Inorg. Chem. 47 (2008) 5537e5539; (e) Charles E. Runyan Jr., T. Hughbanks, J. Am. Chem. Soc. 116 (1994) 7909e7910; reya, Chem. Commun. (f) V. Guillerm, S. Gross, C. Serre, T. Devic, M. Bauerc, G. Fe 46 (2010) 767e769; (g) M. Fitzgerald, I. Pappas, C. Zheng, Z.-L. Xie, X.-Y. Huang, S. Tao, L. Pan, Dalton Trans. (2009) 6289e6291;
[10] [11]
[12]
[13] [14] [15] [16]
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(h) G. Bai, Q. Ma, H.W. Roesky, D. Vidovic, R. Herbst-Irmer, Chem. Commun. (2003) 898e899. A. Mukherjee, T.K. Sen, S.K. Mandal, B. Maity, D. Koley, RSC Adv. 3 (2013) 1255e1264. A. Mukherjee, S. Nembenna, T.K. Sen, S.P. Sarish, P.K. Ghorai, H. Ott, D. Stalke, S.K. Mandal, H.W. Roesky, Angew. Chem. 123 (2011) 4054e4058. Angew. Chem. Int. Ed. 50 (2011) 3968e3972. Crystal data for 1$C7H8: C87H128O10Zr7, Mw ¼ 1972.44, 0.20 0.13 0.12 mm3 (block shape and colorless), triclinic, space group P1, a ¼ 14.950(2) Å, b ¼ 15.908(3) Å, c ¼ 19.858(3) Å, a ¼ 106.783(3) , b ¼ 93.001(3) , g ¼ 104.136(3) , V ¼ 4346.4(11) nm3, Z ¼ 2, rcalc ¼ 1.507 g/ cm3, m (Mo-Ka) ¼ 0.860 mm1, T ¼ 100(2) K, q range for data collection ( ) ¼ 1.66e27.00, 69,656 reflections measured, 18,922 independent (Rint ¼ 0.0356), R1 ¼ 0.0332 (I > 2s(I)), wR2 ¼ 0.093(all data), residual density peaks 2.803 to e1.130 e Å3. L.M. Babcock, V.W. Day, W.G. Klemperer, J. Chem. Soc. Chem. Commun. (1988) 519e520. M.J. Frish, G.W. Trucks, H.B. Chlegel, et al., GAUSSION 03, Revision C.01, Gaussion, Inc., Wallingford, CT, 2003. A.D. Becke, J. Chem. Phys. 98 (1993) 5648e5652. (a) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270e283; (b) W.R. Wadt, P.J. Hay, J. Chem. Phys. 82 (1985) 284e298; (c) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299e310.
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem
Communication
Slow hydrolysis of an organozirconium complex: The first polyoxometallic heptanuclear zirconium oxide Arup Mukherjee a, *, Tamal K. Sen a, Sambath Baskaran b, Chinnappan Sivasankar b, Swadhin K. Mandal a, * a b
Department of Chemical Sciences, Indian Institute of Science Education and Research-Kolkata, Mohanpur 741246, India Catalysis and Energy Laboratory, Department of Chemistry, Pondicherry University, Puducherry 605014, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 July 2014 Received in revised form 11 October 2014 Accepted 16 October 2014 Available online 25 October 2014
Herein we report controlled hydrolysis of an organozirconium trimetallic complex, [Cp*2(Me)Zr(m-O) Zr(NMe2)2(m-O)Zr(Me)Cp*2] (Cp* = h5-C5Me5) by slow hydrolysis pathway inside the glovebox resulting in unexpected formation of the first heptanuclear zirconium complex. The basic core of this zirconium complex is reminiscent of a butterfly like structure. © 2014 Elsevier B.V. All rights reserved.
Keywords: Heptanuclear complex Zirconium Hydrolysis Oxide Density functional theory
Introduction Over the past decades, transition metal oxides have attracted a continual interest not only because of their fascinating structural topologies but also owing to their potential applications in catalysis [1] and zirconium oxides in particular received a special attraction in this regard [2,3]. For example, zirconium dioxide is one of the most studied ceramic materials with multiple material applications. Moreover, zirconium oxides have been used extensively as catalysts for different homogeneous organic transformations [4,5,6,7,8]. The use of multinuclear zirconium oxide might be advantageous with regard to material and catalytic applications compared to their monometallic counterpart. Roesky et al. and others have developed a number of Zr(IV) multinuclear metal complexes which have shown interesting structural geometries [9]. Most of these multinuclear zirconium complexes were synthesized by hydrolytic pathway. Until now there are no reports in the literature available dealing with the heptanuclear Zr(IV) complex. Herein, we report the controlled hydrolysis of a organozirconium trimetallic complex, [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2]
* Corresponding authors. E-mail addresses: [email protected] (A. Mukherjee), swadhin.mandal@iiserkol. ac.in (S.K. Mandal). http://dx.doi.org/10.1016/j.jorganchem.2014.10.022 0022-328X/© 2014 Elsevier B.V. All rights reserved.
resulting the first heptanuclear zirconium cluster [{Cp*Zr(mO)2Zr(m-O)Zr(Cp*)2(m-O)2}2Zr] (1, Cp* ¼ h5-C5Me5). Complex 1 was formed by controlled hydrolysis of the ZreNMe2 and ZreCH3 bonds inside the glovebox. The solid state structure of 1 was established by single crystal X-ray diffraction study. Synthesis of Complex 1 was accomplished in an unprecedented way by reacting the monometallic hydroxide precursor, Cp*2(Me)Zr(OH) with Zr(NMe2)4 under the elimination of HN(SiMe3)2, followed by controlled hydrolysis of the reaction mixture inside a nitrogen filled glovebox, which resulted in the heptanuclear assembly of zirconium ions. Results and discussion A solution of Cp*2(Me)Zr(OH) in toluene was added drop-bydrop to the solution of Zr(NMe2)4 in a 1:1 stoichiometric ratio in toluene at 0 C and stirred at 25 C for 24 h to yield a reaction mixture composed of a trinuclear compound [Cp*2(Me)Zr(m-O) Zr(NMe2)2(m-O)Zr(Me)Cp*2] (2) and unreacted Zr(NMe2)4 (Scheme 1, step A). The 1H NMR spectrum of the reaction mixture confirmed the presence of both 2 and free Zr(NMe2)4 (see Supporting Information). Complex 2 can also be prepared exclusively when the reaction was carried out between Cp*2(Me)Zr(OH) and Zr(NMe2)4 in a 2:1 stoichiometric ratio and has been structurally characterized previously [10]. Upon prolonged standing of this reaction mixture containing 2 and unreacted Zr(NMe2)4 for a month inside the
A. Mukherjee et al. / Journal of Organometallic Chemistry 775 (2015) 76e79
Scheme 1. Formation of the heptanuclear zirconium complex 1.
nitrogen filled glovebox, it resulted unexpectedly complex 1 in 27% isolated yield (Scheme 1, step B). Compound 1 is insoluble in npentane but readily dissolves in toluene and THF. Complex 1 is a colorless block shape crystalline solid which was characterized by 1 H, 13C, NMR spectroscopy, and EI mass spectrometry and it is thermally stable. The melting point of 1 exceeds 410 C. The 1H NMR spectrum of 1 in C6D6 exhibited only one singlet at d 1.83 ppm attributed to the proton resonance arising from the Cp* group and this indicates the loss of ZreMe as well as ZreNMe2 resonances observed in 2. The Cp* resonance in 1 is shifted upfield to d 1.83 ppm in case of 1 when compared to that observed for [Cp*2(Me)Zr-(m-O)-Ca(thf)3N(SiMe3)2] (d 1.90 ppm) [11] and [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2] (d 1.93 ppm) [10]. The 13C NMR spectrum of 1 reveals a resonance at d 118.3 ppm, assigned to the Cp* resonance, which was shifted slightly downfield as compared to that of [Cp*2(Me)Zre(m-O)eCa(THF)3N(SiMe3)2] (d 117.4 ppm) [11] and [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2] (d 117.3 ppm) [10]. In the EI mass spectrum of 1, the most intense peak appears at m/z 391(100%) [Mþe{Cp*2Zr(m-O)2Zr(mO)3Zr(Cp*2)Zr(m-O)3Zr(Cp*2)Zr}eC7H8e2H], and the signal at 817 (60%) is assigned to the [Mþe{Cp*2Zr(m-O)2Zr(m-O)3Zr(Cp*2)Zr(mO)2}eCp*eH] fragment.
77
The solid state structure of 1 was established unambiguously by single crystal X-ray diffraction study. To our surprise, the X-ray structure revealed a heptanuclear zirconium complex in which the assembly of seven zirconium has occurred (vide infra). Analytically pure crystals of 1 were obtained from toluene solution at 25 C by slow solvent evaporation technique inside a nitrogen filled glovebox for a month. The structure of 1 was determined by single crystal X-ray diffraction study (Fig. 1a) [12]. Compound 1 crystallizes in the triclinic space group Pı with one molecule in the asymmetric unit. X-ray diffraction study of 1 revealed a heptanuclear complex in which the five zirconium metal atoms [Zr(1), Zr(2), Zr(4), Zr(5) and Zr(6)] define a butterfly shape, with the angle at the hinges of the butterfly being 138.19(11) and 137.61(11) [Zr(2)eO(5)eZr(4) 138.19(11) and Zr(5)eO(8)eZr(6) 137.61(11) , Fig. 1a]. Two of the wingtip zirconium atoms [Zr(2) and Zr(6)] bear four bridging oxygen (meO) atoms. While, other two wingtip zirconium atoms [Zr(4) and Zr(5)] are connected with the Cp* moieties (Fig. 1a). A core structure of the complex 1 is shown in Fig. 1b. The X-ray structural analysis of 1 reveals that the central zirconium, Zr(1) is bonded through four bridging oxygen atoms to the other zirconium ions. The central zirconium ion adopts a distorted tetrahedral geometry. Similarly, the terminal zirconium ions [Zr(3) and Zr(7)] also adopt distorted tetrahedral geometry, considering Cp* as a single coordination site (Fig. 1a). The central zirconiumeoxygen bond distances [Zr(1)eO(3), 1.973(2) Å, Zr(1)eO(4), 1.9486(19) Å, Zr(1)e O(6) 1.971(2), Zr(1)eO(7) 1.944(2) Å] found in 1 are slightly shorter compared to that observed in terminal zirconium ions bound to oxygen center in 1 [Zr(3)eO(1), 2.017(2) Å, Zr(3)eO(2), 2.021(2) Å, Zr(7)eO(9) 2.018(2), Zr(7)eO(10) 2.023(2) Å], but comparable to that observed in a earlier reported related trimetallic complex [Cp*2(Me)Zr(m-O)Zr(NMe2)2(m-O)Zr(Me)Cp*2] (av. ZreO 1.972 Å) [10]. Moreover, the ZreO bond distances observed in 1 are slightly shorter as compared to that found in [(Cp*ZrC1)3(m-O) (m-OH)4] (av. ZreO 2.179 Å) [13]. The O(3)eZr(1)eO(4) bond angle in 1 is 104.86(9) , which is similar to that observed in case of O(6)eZr(1)e O(7) bond angle [104.56(9) ] in 1. A closer look at Fig. 1b reveals that the O(3)eZr(1)eO(7) and O(4)eZr(1)eO(6) bond angles are 113.70(9) and 113.30(9) , respectively characteristic for the tetrahedral geometry. Furthermore, the O(3)eZr(2)eO(5) and O(6)e Zr(6)eO(8) bond angles [105.38(9) and 105.28(9) , respectively] observed in 1 were higher as compared to that O(4)eZr(4)eO(5) and O(7)eZr(5)eO(8) bond angles [98.12(8) and 99.04(9) ,
Fig. 1. (a) Molecular structure of complex 1. Hydrogen atoms and lattice held toluene molecule have been omitted for the sake of clarity. Selected bond distances (Å) and angles ( ): Zr(1)eO(3) 1.973(2), Zr(1)eO(4) 1.9486(19), Zr(1)eO(6) 1.971(2), Zr(1)eO(7) 1.944(2); O(3)eZr(1)eO(4) 104.86(9), O(6)eZr(1)eO(7) 104.56(9); (b) Core structure of the complex 1.
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Fig. 2. (a) HOMO1, (b) HOMO, (c) LUMO, and (d) LUMO þ 1 of 1 with energies 5.27, 5.26, 1.17, and 1.15 eV, respectively, (e) calculated electrostatic potential on the 0.0004 au electron density isosurface. Color ranges from red (negative potential) to blue (positive potential). All hydrogen atoms are omitted for the sake of clarity. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
respectively]. This may be attributed to the fact that Zr(4) and Zr(5) ions are attached to the bulky Cp* groups, which reflects a higher steric demand of Cp* moiety squeezing the other bond angles. To understand the electronic structure and bonding properties of 1, density functional theory calculation was performed using Gaussian 03 package [14]. We have adopted a hybrid B3LYP [15] exchange and a correlation functional with the LANL2DZ [16] basis set. The molecular structure from the X-ray diffraction experiment served as the starting point, nevertheless the structure was fully optimized and the optimized structural parameters were found to be comparable with the experimentally observed data. A closer look at the electronics of the zirconium complex 1 shows some interesting features. The HOMO1 appears to concentrate on the Zr and Cp* part (Fig. 2a). Similarly, the HOMO of 1 is mainly centered on the Zr and Cp* and found to be a bonding combination of p symmetry orbitals of Zr and Cp* (Fig. 2b). The LUMO is mainly located on two Zr centers (Fig. 2c) and the difference in energy between HOMO and LUMO of 1 was computed to be 4.09 eV. The LUMO þ 1 resembles more like HOMO1 of 1 (Fig. 2a and d), with the difference in energy between HOMO1 and LUMO þ 1 computed as 4.12 eV. Moreover, Fig. 2e illustrates that in 1 the negative charge (highlighted by the red color) is localized on the electron-withdrawing oxygen centers, while the positive charge (highlighted by the blue) is localized on the Cp* ring. Conclusion In conclusion, formation of the first heptanuclear zirconium complex 1 has been reported. Synthesis of 1 has been unprecedented but has been found to be reproducible several times. The heptanuclear zirconium complex was formed by controlled hydrolysis of a mixture of Cp*2(Me)Zr(OH) with Zr(NMe2)4 under very low level of moisture inside the nitrogen filled glovebox. The basic core of the zirconium complex 1 is reminiscent of a butterfly like
structure. Further investigation including the scope and mechanism of this reaction are in progress in our laboratory. Acknowledgments SKM thanks financial support from SERB (DST), New Delhi (Grant No. SR/S1/IC-25/2012), India. We thank the NMR and X-ray facilities at IISER-Kolkata. Appendix A. Supplementary material CCDC 933635 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jorganchem.2014.10.022. References [1] (a) B. Cornils, W.A. Herrmann, Applied Homogeneous Catalysis with Organometallic Compounds, Wiley-VCH, Weinheim, 1996; (b) J.-M. Basset, B.C. Gates, J.P. Candy, A. Choplin, M. Leconte, F. Quignard, C. Santini, Surface Organometallic Chemistry: Molecular Approaches to Surface Catalysis, Kluwer, Dordrecht drecht, The Netherlands, 1988; (c) H.W. Roesky, I. Haiduc, N.S. Hosmane, Chem. Rev. 103 (2003) 2579e2595. €ger, W. Kowalsky, T. Riedl, A. Kahn, Adv. Mater. [2] (a) J. Meyer, S. Hamwi, M. Kro 24 (2012) 5408e5427; (b) C.N.R. Rao, Annu. Rev. Phys. Chem. 40 (1989) 291e326. [3] R. Nielsen, Zirconium and Zirconium Compounds in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. [4] (a) M. Anpo, T. Nomura, J. Kondo, K. Domen, K.-I. Maruya, T. Onishi, Res. Chem. Intermed. 13 (1990) 195e202; (b) M.-Y. He, J.G. Ekerdt, J. Catal. 90 (1984) 17e23; (c) H. Abe, K.-I. Maruya, K. Domen, T. Onishi, Chem. Lett. (1984) 1875e1878;
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(h) G. Bai, Q. Ma, H.W. Roesky, D. Vidovic, R. Herbst-Irmer, Chem. Commun. (2003) 898e899. A. Mukherjee, T.K. Sen, S.K. Mandal, B. Maity, D. Koley, RSC Adv. 3 (2013) 1255e1264. A. Mukherjee, S. Nembenna, T.K. Sen, S.P. Sarish, P.K. Ghorai, H. Ott, D. Stalke, S.K. Mandal, H.W. Roesky, Angew. Chem. 123 (2011) 4054e4058. Angew. Chem. Int. Ed. 50 (2011) 3968e3972. Crystal data for 1$C7H8: C87H128O10Zr7, Mw ¼ 1972.44, 0.20 0.13 0.12 mm3 (block shape and colorless), triclinic, space group P1, a ¼ 14.950(2) Å, b ¼ 15.908(3) Å, c ¼ 19.858(3) Å, a ¼ 106.783(3) , b ¼ 93.001(3) , g ¼ 104.136(3) , V ¼ 4346.4(11) nm3, Z ¼ 2, rcalc ¼ 1.507 g/ cm3, m (Mo-Ka) ¼ 0.860 mm1, T ¼ 100(2) K, q range for data collection ( ) ¼ 1.66e27.00, 69,656 reflections measured, 18,922 independent (Rint ¼ 0.0356), R1 ¼ 0.0332 (I > 2s(I)), wR2 ¼ 0.093(all data), residual density peaks 2.803 to e1.130 e Å3. L.M. Babcock, V.W. Day, W.G. Klemperer, J. Chem. Soc. Chem. Commun. (1988) 519e520. M.J. Frish, G.W. Trucks, H.B. Chlegel, et al., GAUSSION 03, Revision C.01, Gaussion, Inc., Wallingford, CT, 2003. A.D. Becke, J. Chem. Phys. 98 (1993) 5648e5652. (a) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270e283; (b) W.R. Wadt, P.J. Hay, J. Chem. Phys. 82 (1985) 284e298; (c) P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 299e310.