Ambiphilic Reactivity of a Phosphane-Functionalized

Jan 4, 2010 - Organometallics , 2010, 29 (3), pp 671–675 ... complex [(η7-C7H7)Zr(η5-C5H4PiPr2)] (1) with selenium, [(tht)AuCl] (tht = tetrahydrot...
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Organometallics 2010, 29, 671–675 DOI: 10.1021/om9009763

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Ambiphilic Reactivity of a Phosphane-Functionalized Cycloheptatrienyl-Cyclopentadienyl Zirconium Sandwich Complex Susanne B€ uschel, Constantin Daniliuc, Peter G. Jones, and Matthias Tamm* Institut f€ ur Anorganische und Analytische Chemie, Technische Universit€ at Carolo-Wilhelmina zu Braunschweig, Hagenring 30, 38106 Braunschweig, Germany Received November 9, 2009

The reactions of the phosphane-functionalized cycloheptatrienyl-cyclopentadienyl sandwich complex [(η7-C7H7)Zr(η5-C5H4PiPr2)] (1) with selenium, [(tht)AuCl] (tht = tetrahydrothiophene) and [(η6-C7H8)W(CO)3] (C7H8 = 1,3,5-cycloheptatriene) afford the complexes [(η7-C7H7)Zr{η5-C5H4P(Se)iPr2}] (2), [(1)2AuCl] (3), and [(1)2W(CO)3] (4). Because of the presence of a Lewis basic phosphane moiety and a Lewis acidic zirconium atom, ambiphilic behavior of the metallo ligand 1 is observed, and the structural characterization of the complexes 2-4 reveals intramolecular secondary Zr-Se (2), Zr-Cl (3), and Zr-O (4) interactions, respectively. In addition, 4 displays an agostic C-H 3 3 3 W interaction with one of the cycloheptatrienyl rings.

Introduction Group 4 cycloheptatrienyl-cyclopentadienyl (Cht-Cp) sandwich complexes of the type [(η7-C7H7)M(η5-C5H5)] (M = Ti, Zr, Hf) might be expected to interact with one additional two-electron donor ligand to complete their valence shell and thus comply with the 18-electron rule.1 However, such coordination has never been observed for [(η7-C7H7)Ti(η5C5H5)] (troticene),2 whereas the heavier congeners [(η7C7H7)Zr(η5-C5H5)] (trozircene) and [(η7-C7H7)Hf(η5-C5H5)] (trohafcene) form isolable complexes with phosphanes, isocyanides, and N-heterocyclic carbenes.3,4 Nevertheless, the metal-ligand interaction in these complexes is rather weak, indicating that these 16-electron Cht-Cp complexes do not behave in the same way as complexes containing titanium, zirconium, or hafnium in a lower oxidation state but instead bear a closer resemblance to Lewis acidic MþIV complexes.5 *To whom correspondence should be addressed. E-mail: m.tamm@ tu-bs.de. (1) Mitchell, P. R.; Parish, J. The Eighteen-Electron Rule. J. Chem. Educ. 1969, 46, 811–814. Jensen, W. B. The origin of the 18-electron rule. J. Chem. Educ. 2005, 82, 28. (2) The addition of σ-donor/π-acceptor ligands such as carbon monoxide or isocyanides has only been reported for ansa-Cht-Cp complexes, e.g., for dimethylsila[1]troticenophane (a) Tamm, M.; Kunst, A.; Bannenberg, T.; Herdtweck, E.; Sirsch, P.; Elsevier, C. J.; Ernsting, J. M. Angew. Chem., Int. Ed. 2004, 43, 5530–5534. (b) Tamm, M.; Kunst, A.; Herdtweck, E. Chem. Commun. 2005, 1729–1731. (c) Tamm, M.; Kunst, A.; Bannenberg, T.; Randoll, S.; Jones, P. G. Organometallics 2007, 26, 417– 424. (3) (a) Green, M. L. H.; Walker, N. M. J. Chem. Soc., Chem. Commun. 1989, 1865–1867. (b) Diamond, G. M.; Green, M. L. H.; Mountford, P.; Walker, N. M.; Howard, J. A. K. J. Chem. Soc., Dalton Trans. 1992, 417–422. (4) (a) Tamm, M.; Kunst, A.; Bannenberg, T.; Herdtweck, E.; Schmid, R. Organometallics 2005, 24, 3162–3171. (b) Baker, R. J.; Bannenberg, T.; Kunst, A.; Randoll, S.; Tamm, M. Inorg. Chim. Acta 2006, 359, 4797–4801. (c) B€uschel, S.; Bannenberg, T.; Hrib, C. G.; Gl€ ockner, A.; Jones, P. G.; Tamm, M. J. Organomet. Chem. 2009, 694, 1244–1250. (5) Tamm, M. Chem. Commun. 2008, 3089–3100. r 2010 American Chemical Society

On the basis of theoretical calculations, this behavior can be mainly attributed to the strong and appreciably covalent metal-cycloheptatrienyl interaction, which implies that the formal assignment of a -3 charge to the Cht ligand is more justified than the assignment of a þ1 charge.5,6 As a consequence of the Lewis acidity of trozircene and trohafcene, their phosphane-functionalization affords ambiphilic metallo ligands of the type [(η7-C7H7)M(η5-C5H4PR2)] (M = Zr, Hf; R = Ph, iPr) that are capable of developing secondary interactions involving the metal atoms.7 For instance, the diisopropylphosphanyl-functionalized complex [(η7-C7H7)Zr(η5-C5H4PiPr2)] (1) forms a centrosymmetric dimer in the solid state in which the two sandwich units are linked by two comparatively long Zr-P bonds (Scheme 1). In solution, however, monomeric 1 represents the dominating species, and its reaction with [(cod)MCl]2 (M= Rh, Ir; cod=η4-1,5-cyclooctadiene) furnishes the complexes cis-[(1)MCl(cod)], which exhibit intramolecular Zr-Cl contacts in the solid state. In addition, the palladium(0) complex [(1)2Pd] was structurally characterized, revealing the presence of an intramolecular Zr-Pd interaction, which can be formally regarded as a dative Pd0 f ZrþIV bond.7 In continuation of this work, we present herein additional facets of the reactivity of 1; its reactivity toward selenium, gold(I), and tungsten(0) is reported, affording in all cases complexes with unusual secondary interactions involving the zirconium atom.

Results and Discussion The reaction of 1 with gray selenium afforded an orange solid of the composition [(η7-C7H7)Zr(η5-C5H4P(Se)iPr2)] (2) in moderate yield (Scheme 2). The 31P NMR spectrum gave clear evidence for the oxidation of the phosphorus atom (6) Menconi, G.; Kaltsoyannis, N. Organometallics 2005, 24, 1189– 1197. (7) B€ uschel, S.; Jungton, A.-K.; Bannenberg, T.; Randoll, S.; Hrib, C. G.; Jones, P. G.; Tamm, M. Chem.;Eur. J. 2009, 15, 2176–2184. Published on Web 01/04/2010

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Scheme 1. Dimerization of [(η7-C7H7)Zr(η5-C5H4PiPr2)] (1)

Scheme 2. Ambiphilic Reactivity of [(η7-C7H7)Zr(η5-C5H4PiPr2)] (1) Figure 1. ORTEP view of one independent molecule of [(1)Se] (2). Hydrogen atoms are omitted for clarity. Selected bond lengths [A˚] and angles [deg] in molecule 1/molecule 2: ZrSe 2.9498(5)/2.9459(5), Zr-CCht 2.336(4)-2.464(4)/2.328(4)2.459(4), Zr-CCp 2.519(4)-2.583(4)/2.552(4)-2.571(3), P-Se 2.148(1)/2.149(1), C8-P 1.789(4)/1.784(4); Zr-Se-P 84.02(3)/ 83.22(3), C8-P-Se 101.7 (1)/101.8(1).

because the resonance of the starting material 1, which is accidentally observed at 0.0 ppm, is significantly shifted to lower field by 45.3 ppm and falls in the range expected for compounds containing P(Se) moieties.8 The 13C NMR resonance observed for the isopropyl methyne carbon atoms gives further evidence for the oxidation of the phosphorus atom because this doublet is shifted to lower field (28.7 ppm) and features a larger 1JCP coupling constant of 40.0 Hz than does 1. A similar trend was reported for iPr3P(Se). The 77Se NMR resonance in 2, however, is observed as a doublet at -362.5 ppm with a 1JSeP coupling constant of 573.2 Hz, which is significantly smaller than that found for iPr3P(Se) (713 Hz).9 This pronounced decrease suggests that the selenium atom in 2 is engaged in a secondary interaction with the zirconium atom because a similar decrease of the 77 Se-31P coupling was observed upon formation of Lewis acid/base adducts such as [Ph3P(Se)-AlCl3].10 To unambiguously confirm the presence of a Zr-Se interaction, an X-ray crystal structure determination was (8) (a) McFarlane, W.; Rycroft, D. S. J. Chem. Soc., Chem. Commun. 1972, 902–903. (b) McFarlane, W.; Rycroft, D. S. J. Chem. Soc., Dalton Trans. 1973, 2162–2166. (9) Kuhn, N.; Schumann, H. J. Organomet. Chem. 1986, 304, 181– 193. (10) Burford, N.; Royen, B. W.; Spence, R. E. v. H. J. Chem. Soc., Dalton Trans. 1990, 2111–2117.

performed on single crystals of 2 that were obtained from a saturated toluene solution at -30 °C. 2 crystallizes in the monoclinic space group P21 with two independent molecules in the asymmetric unit. Both molecules display unusual intramolecular selenium-zirconium contacts, affording acute Zr-Se-P angles of 84.02(3)° and 83.22(3)°, together with Zr-Se distances of 2.9498(5) A˚ and 2.9459(5) A˚ that are longer than any other known Zr-Se bonds (Figure 1).11 Despite the apparent weakness of this interaction, the coordination of the Lewis basic chalcogen atom to the Lewis acidic Zr atom leads to a pronounced distortion from an unstrained sandwich structure and the angles between the best Cht and Cp planes deviate by 31.1° (molecule 1) and 32.1° (molecule 2) from an ideally parallel orientation of the two carbocycles. The selenium-phosphorus bond lengths are 2.148(1) and 2.149(1) A˚, which is considerably longer than that observed for the related ferrocene species [Fe(η5C5H4P(Se)iPr2)2] (2.123 A˚)12 but shorter than that reported for the Lewis acid/base adduct [Ph3P(Se)-AlCl3] [2.182(2) A˚, 2.181(2) A˚].10 As described above, the reaction of 1 with [(cod)MCl]2 (M= Rh, Ir; cod = η4-1,5-cyclooctadiene) afforded the complexes cis-[(1)MCl(cod)], which displayed intramolecular Zr-Cl contacts in the solid state. We anticipated that coordination of 1 to a chlorogold complex fragment might result in the formation of a linear complex [(1)AuCl] in which the transarrangement of the phosphane and chloride ligands gives rise to a metallopolymeric material via intermolecular Zr-Cl interaction. Indeed, the reaction of 1 with the Au(I) species (11) The Cambridge Structural Database (CSD version 5.30, 2009) contains 19 structures with Zr-Se distances ranging from 2.478 to 2.809 A˚; for zirconocene-selenium structures, see: (a) Gautheron, B.; Tainturier, G.; Pouly, S. Organometallics 1984, 3, 1495–1499. (b) Broussier, R.; Gobet, Y.; Amardeil, R.; Da Rold, A.; Kubicki, M. M.; Gautheron, B. J. Organomet. Chem. 1993, 445, C4–C5. (c) Howard, W. A.; Parkin, G. J. Am. Chem. Soc. 1994, 116, 606–615. (d) Howard, W. A.; Trnka, T. M.; Parkin, G. Organometallics 1995, 14, 4037–4039. (e) Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg. Chem. 1995, 34, 5900–5909. (f) Howard, W. A.; Parkin, G.; Rheingold, A. Polyhedron 1995, 14, 25–44. (g) Hoskin, A. J.; Stephan, D. W. Organometallics 1999, 18, 2479–2483. (h) Shin, J. H.; Hascall, T.; Parkin, G. Organometallics 1999, 18, 6–9. (i) Sunada, Y.; Hayashi, Y.; Kawaguchi, H.; Tatsumi, K. Inorg. Chem. 2001, 40, 7072– 7078. (j) d'Arbeloff-Wilson, S. E.; Hitchcock, P. B.; Nixon, J. F.; Kawaguchi, H.; Tatsumi, K. J. Organomet. Chem. 2003, 672, 1–10. (12) Necas, M.; Beran, M.; Woollins, J. D.; Novosad, J. Polyhedron 2001, 741–746.

Article

Figure 2. ORTEP view of [(1)2AuCl] (3). Hydrogen atoms are omitted for clarity. Selected bond lengths [A˚] and angles [deg]: Au-P1 2.3078(8), Au-P2 2.3110(8), Zr1-Cl 2.7735(8), Zr2-Cl 2.7575(8), Zr1-CCht 2.342(4)-2.448(3), Zr1-CCp 2.541(3)2.566(3), Zr2-CCht 2.347(3)-2.435(3), Zr2-CCp 2.532(3)2. 570(3); P1-Au-P2 172.36(3), Zr1-Cl-Zr2 135.09(3).

[(tht)AuCl] (tht = tetrahydrothiophene) resulted in the formation of a deep-red solid, which is barely soluble in all common solvents. Elemental analysis was in agreement with the expected 1:1 phosphane-gold ratio; the insolubility of this material, however, prevented further spectroscopic characterization. In contrast, a soluble bright-red compound was obtained when [(tht)AuCl] was treated with 2 equiv of 1. Suitable single crystals were isolated from THF/n-hexane solution at -30 °C, and X-ray diffraction analysis confirmed the formation of a 2:1 complex of the formula [(1)2AuCl] (3). The molecular structure is shown in Figure 2, revealing an activation and dissociation of the Au-Cl bond and the presence of a linear diphosphane-gold(I) moiety, which exhibits metal-phosphorus bond lengths of 2.3078(8) A˚ (Au-P1) and 2.3110(8) A˚ (Au-P2) together with a P1-Au-P2 angle of 172.36(3)°. The observation of a linear geometry at the gold atom is in agreement with the predominance of dicoordination among AuI complexes.13 In addition, the dissociation of the chloride ion is supported by its interaction with the zirconium atoms of the two sandwich fragments [Zr1-Cl = 2.7735(8) A˚, Zr2-Cl=2.7575(8) A˚, Zr1-Cl-Zr2=135.09(3)°], whereas the Au-Cl contact distance of 3.086 A˚ clearly exceeds the sum of the covalent radii of these two atoms (Au: 1.36 A˚, Cl: 1.20 A˚),14 excluding any directed Au-Cl bonding interaction. Au-Cl bond activation has also been observed for related zwitterionic Au(I) complexes containing ambiphilic alaneand gallane-phosphane ligands, and for instance, in [(DPA)AuCl] [DPA = Cl-Al{C6H4(o-PiPr2)}2] and [(DPG)AuCl] [DPG = Cl-Ga{C6H4(o-PiPr2)}2] the chloride is completely transferred from gold to the group 13 element.15,16 In contrast, the corresponding borane complex [(DPB)AuCl] [DPB =Ph-B{C6H4(o-PR2)}2, R=Ph, iPr] displays an interaction (13) (a) Caravajal, M. A.; Novoa, J. J.; Alvarez, S. J. Am. Chem. Soc. 2004, 126, 1465–1477. (b) Gimeno, M. C.; Laguna, A. Chem. Rev. 1997, 97, 511–522. (14) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008, 2832–2838. (15) Sircoglou, M.; Bouhadir, G.; Saffon, N.; Miqueu, K.; Bourissou, D. Organometallics 2008, 27, 1675–1678. (16) Sircoglou, M.; Mercy, M.; Saffon, N.; Copple, Y.; Bouhadir, G.; Maron, L.; Bourissou, D. Angew. Chem., Int. Ed. 2009, 48, 3454–3457. (17) Sircoglou, M.; Bontemps, S.; Mercy, M.; Saffon, N.; Takahashi, M.; Bouhadir, G.; Maron, L.; Bourissou, D. Angew. Chem., Int. Ed. 2007, 46, 8583–8586.

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between the electron rich Au(I) atom and the Lewis acidic boron atom17 and such metal-boron bonds are commonly observed for late-transition metal complexes containing ambiphilic borane-phosphane ligands.18 Finally, it should be emphasized that the related trimetallic Au(I) complex [{(η7-C7H7)Ti(η5-C5H4PPh2)}2AuCl] features a trigonal-planar geometry about the gold atom, and in agreement with the previously reported reactivity of troticenylphosphanes,5,7 no secondary interactions involving the titanium atoms have been observed.19 Pentacoordinate tungsten(0) complexes of the type mer, trans-[(R3P)2W(CO)3] (R = cyclohexyl, iPr) are among the most prominent transition metal phosphane complexes.20 In these formally 16-electron species, the sixth coordination site at the tungsten atom is saturated by an agostic C-H interaction with the phosphorus substituents. Because of the Lewis acidity of the tungsten atom, such compounds have the ability to reversibly or irreversibly bind small molecules such as dihydrogen or dinitrogen.21 Likewise, the reaction of 2 equiv of 1 with the tungsten(0) precursor fac-[(η6-C7H8)W(CO)3] (C7H8 = 1,3,5-cycloheptatriene) should furnish mer, trans-[(1)2W(CO)3] (4); the IR spectrum of the resulting deep-purple-blue compound exhibits three CO absorption bands at 1924, 1863, and 1793 cm-1, in agreement with a meridional arrangement of the carbonyl ligands (Scheme 2). The lowest IR stretching frequency at 1793 cm-1 might indicate an isocarbonyl interaction,22 which is indeed confirmed by an X-ray crystal structure determination. The molecular structure of 4 is shown in Figure 3, revealing the expected meridional arrangement of the CO ligands and the trans-orientation of the phosphane ligands, which affords a distorted square-pyramidal geometry about the tungsten atom. The oxygen atom of the apical carbonyl group undergoes a secondary interaction with one of the Lewis acidic ZrþIV atoms. Such isocarbonyl interactions are well-known for group 4 and 5 metals in a high oxidation state although the majority of complexes exhibiting this kind of interaction consist of an anionic mono- or polynuclear transition metal carbonylate,23 and examples involving neutral species are rare.24 As expected, the apical carbonyl ligand displays the lowest C-O bond order, and the C37-O1 bond length of 1.197(2) A˚ is significantly longer than observed for the trans-oriented CO groups [C38-O2 = 1.153(2) A˚, C39-O3 1.154(2) A˚]. Accordingly, the W-C37 bond length [1.891(2) A˚] is considerably shorter than the W-C38 [2.025(2) A˚] and W-C39 bonds [2.009(2) A˚]. The Zr2-O1 (18) (a) Bontemps, S.; Gornitzka, H.; Bouhadir, G.; Miqueu, K.; Bourissou, D. Angew. Chem., Int. Ed. 2006, 45, 1611–1614. (b) Bontemps, S.; Bouhadir, G.; Miqueu, K.; Bourissou, D. J. Am. Chem. Soc. 2006, 128, 12056–12057. (c) Bebbington, M. W. P.; Bouhadir, G.; Bourissou, D. Eur. J. Org. Chem. 2007, 4483–4486. (d) Bontemps, S.; Sircoglou, M.; Bouhadir, G.; Puschmann, H.; Howard, J. A. K.; Dyer, P. W.; Miqueu, K.; Bourissou, D. Chem.;Eur. J. 2008, 14, 731–740. (19) Mohapatra, S.; B€ uschel, S.; Daniliuc, C.-G.; Jones, P. G.; Tamm, M. J. Am. Chem. Soc. 2009, 131, 17014-17023. (20) Kubas, G. J., Metal Dihydrogen and σ-Bond Complexes; Structure, Theory, and Reactivity; Kluwer Academic/Plenum Publishers: New York, 2001. (21) (a) Kubas, G. J. J. Chem. Soc., Chem. Commun. 1980, 61–62. (b) Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. J.; Wasserman, H. J. J. Am. Chem. Soc. 1984, 106, 451–452. (c) Wasserman, H. J.; Kubas, G. J.; Ryan, R. R. J. Am. Chem. Soc. 1986, 108, 2294–2301. (d) Butts, M. D.; Bryan, J. C.; Luo, X.-L.; Kubas, G. J. Inorg. Chem. 1997, 36, 3341–3353. (22) de la Cruz, C.; Sheppard, N. J. Mol. Struct. 1990, 224, 141–161. (23) Horwitz, C. P.; Shriver, D. F. Adv. Organomet. Chem. 1984, 23, 219–305. (24) Shriver, D. F.; Alich, A. Inorg. Chem. 1972, 11, 2984–2989.

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oxidative addition reaction M þ C-H f C-M-H,26 and their structural disparity persuasively illustrates the relatively shallow potential energy surface with regard to structural changes within the agostic M-H-C moiety.20

Conclusion

Figure 3. ORTEP view of [(1)2W(CO)3] (4). Hydrogen atoms except for H1 are omitted for clarity. Selected bond lengths [A˚] and angles [deg]: W-P1 2.4823(5), W-P2 2.5154(5), W-C37 1.891(2), W-C38 2.025(2), W-C39 2.009(2), W-H1 2.42(2), W-C1 2.726(3), W-Zr1 3.3856(2), C37-O1 1.197(2), C38O2 1.153(2), C39-O3 1.154(2), Zr2-O1 2.404(1), Zr1-CCht 2.341(2)-2.390(2), Zr1-CCp 2.461(2)-2.519(2), Zr2-CCht 2.322(2)-2.435(2), Zr2-CCp 2.525(2)-2. 609(2); W-C37-O1 171.8(2), W-C38-O2 175.7(2), W-C39-O3 177.5(2), P1W-P2 160.70(2), Zr2-O1-C37 131.7(1).

distance of 2.404(1) A˚ indicates an only weak interaction, and the Zr2-O1-C37 moiety is strongly bent [131.7(1)°], whereas the W-C37-O1 axis [171.8(2)°] is close to linearity. These structural features are in good agreement with those found for related isocarbonyl species.22,23,25 The intramolecular isocarbonyl interaction in 4 induces a significant deformation of the square-pyramidal geometry about the tungsten atom with the P1-W-P2 angle of 160.70(2)°, indicating a strong deviation from an ideal trans-orientation. This provides a wide open vacant coordination site trans to the apical CO group, which is accessed by an agostic C-H bond of one of the cycloheptatrienyl rings. The W-H1 and W-C1 distances of 2.42(2) and 2.726(3) A˚ fall in the range that has been observed for related complexes of the type mer, trans-[(R3P)2W(CO)3], e.g., W-H = 2.27 A˚ and W-C = 2.945(6) A˚ for R = cyclohexyl and W-C = 3.027(10) A˚ for R = isopropyl,21c and the obtuse W-H1-C1 angle of 101.7(15)° is in accord with the structural features expected for C-H 3 3 3 M agostic interactions.20 The hydrogen H1 lies 0.14(2) A˚ outside the plane of the seven-membered ring displaced away from the Zr atom, in contrast to all other ring H atoms, which are displaced by 0.03-0.12 A˚ toward the Zr atom. Slightly different structural parameters are observed for a polymorphic but twinned (and therefore less precisely determined) form of 4, which exhibits W-H1 and W-C1 distances of 2.19 and 2.776(8) A˚ and a W-H1-C1 angle of 119° (see Supporting Information). However, the relevant H atom could not be refined freely in the second polymorph and its bond lengths and angles should therefore be interpreted with caution. These two structures can nonetheless be regarded as snapshots along the trajectory for the (25) (a) Marsella, J. A.; Huffman, J. C.; Caulton, K. G.; Longato, B.; Norton, J. R. J. Am. Chem. Soc. 1982, 104, 6360–6368. (b) Merola, J. S.; Gentile, R. A.; Ansel, G. B.; Modrick, M. A.; Zenta, S. Organometallics 1982, 1, 1731–1733. (c) Sartain, W. J.; Seleque, J. P. Organometallics 1984, 3, 1922–1924. (c) Tilley, T. D.; Anderson, R. A. J. Chem. Soc. Chem. Commun. 1981, 985–986. (d) Hamilton, D. M.; Willis, W. S.; Stucky, G. D. J. Am. Chem. Soc. 1981, 103, 4255–4256. (e) Boncella, J. M.; Andersen, R. A. Inorg. Chem. 1984, 23, 432–437. (f) Schneider, M.; Weiss, E. J. Organomet. Chem. 1976, 121, 365–371.

This contribution gives further evidence for the ambiphilic behavior of phosphane-functionalized Cht-Cp zirconium sandwich complexes such as [(η7-C7H7)Zr(η5-C5H4PiPr2)] (1). In all cases, intramolecular rather than intermolecular secondary interactions are observed, even at the expense of severe structural distortion, as in the selenium compound [(η7-C7H7)Zr{η5-C5H4P(Se)iPr2}] (2). The secondary Zr-Cl and Zr-O interactions in [(1)2AuCl] (3) and [(1)2W(CO)3] (4) suggest that the reactivity of transition metal complexes is significantly affected by the presence of Lewis acidic sandwich moieties containing zirconium in the formal þIV oxidation state. Upon employing metallo ligands such as 1 in homogeneous transition metal catalysis, similar interactions will certainly also have considerable impact on substrate activation and transformation, and this potential will be further exploited.

Experimental Section General Methods. All operations were performed in a glovebox in a dry argon atmosphere (MBraun 200B) or on a highvacuum line using Schlenk techniques. All solvents were purified by a solvent purification system from MBraun GmbH and stored over molecular sieves (4 A˚) prior to use. The 1H, 13C, and 31P NMR spectra were recorded on Bruker DPX 200 (200 MHz), Bruker AV 300 (300 MHz), and Bruker DRX 400 (400 MHz) devices. The chemical shifts are expressed in parts per million (ppm) with tetramethylsilane (TMS) as an internal standard. Coupling constants (J) are reported in hertz (Hz), and splitting patterns are indicated as s (singlet), d (doublet), t (triplet), q (quartet), vq (virtual quartet), m (multiplet), sept (septet), and br (broad). Elemental analysis (C, H, N) succeeded by combustion and gas chromatographic analysis with an Elementar varioMICRO. The starting materials were obtained either from Aldrich or Alfa Aesar and were used without further purification. The following compounds were synthesized according to reported methods: [(η7-C7H7)Zr(η5-C5H4PiPr2)] (1)7, [(η6-C7H8)W(CO)3],27 [(tht)AuCl].28 The reactions involving gold complexes were performed by carefully excluding any source of light. Synthesis of [(η7-C7H7)Zr(η5-C5H4P(Se)iPr2)] (2). In a Schlenk flask were placed 20 mg (0.25 mmol) of Se in 10 mL of toluene. Compound 2 was dissolved in toluene and added at room temperature while stirring. A color change from deep purple to amber was observed. After 3 h, the solution was filtered through a plug of celite to remove any unreacted selenium. The solvent was removed in high vacuum, and the remaining solid was washed with hexane. 2 was obtained in moderate yields as an orange solid (45.3 mg, 0.10 mmol, 41%). Anal. Calcd for C18H25PSeZr (442.6): C 48.85, H 5.69. Found C 47.97, H 5.66. 1H NMR (300 MHz, THF-d8): δ 5.82 (m, 4 H, C5H4), 4.67 (s, 7 H, C7H7), 2.47 (sept d, 2 H, 1JHP = 11.2 Hz, CHMe2), 1.34 (dd, 6 H, 1JHP = 11.2 Hz, 3JHH = 4.1 Hz, CH3), 1.28 (dd, 6 H, 1JHP = 11.4 Hz, 3JHH = 3.9 Hz, CH3). 13 C{1H}-NMR (75 MHz, THF-d8): δ 112.7 (br s, i-C5H4), 106.0 (d, 2 JCP = 10.6 Hz, R-C5H4), 101.8 (d, 3JCP = 10.0 Hz, β-C5H4), 81.7 (s, C7H7), 28.7 (d, 1JCP = 40.0 Hz, CHMe2), 17.9 (m, CH3). 31P{1H}-NMR (121 MHz, THF-d8): δ 45.3 (s, 77Se satellites, (26) Crabtree, R. H.; Holt, E. M.; Lavin, M.; Morehouse, S. M. Inorg. Chem. 1985, 24, 1986–1992. (27) Kubas, G. J. Inorg. Synth. 1990, 28, 1. (28) Us on, R.; Laguna, A.; Laguna, R. Inorg. Synth. 1989, 27, 85.

Article JSeP =573.2 Hz). 77Se{1H}-NMR (57 MHz, THF-d8): δ (ppm)= -362.5 (d, 1JSeP = 573.2 Hz). Synthesis of [(1)2AuCl] (3). First, 45 mg (0.14 mmol) of [(tht)AuCl] were dissolved in 5 mL of THF and cooled to -78 °C. To this solution, 100 mg (0.28 mmol) of 2 in 6 mL of THF (0 °C) were added dropwise. The reaction mixture was slowly allowed to warm to room temperature, and the bright-red solution was filtered over a plug of celite. The solvent was removed in high vacuum, and compound 3 was obtained as a red solid in good yield (94 mg, 0.98 mmol, 71%). An analytically pure sample was obtained by recrystallizing 3 from a THF/n-hexane solution at -30 °C. Anal. Calcd for C36H50AuClP2Zr2: C, 45.06; H 5.25. Found: C 44.98, H 5.37. 1H NMR (300 MHz, THF-d8): δ 4.81 (br, 4 H, C5H4), 4.67 (br, 4 H, C5H4), 4.53 (s, 14 H, C7H7), 2.51 (m, 4 H, CHMe2), 1.40 (m, 24 H, CH3). 13C NMR (75 MHz, THF-d8): δ 108.4 (br d, 2JCP =5.9 Hz, R-C5H4), 101.2 (d, 3JCP= 4.6 Hz, β-C5H4), 82.2 (C7H7), 32.5 (br, CHMe2), 20.7 (br, CH3), 20.1 (br, CH3). 31P NMR (121 MHz, THF-d8): δ 56.0 (s). Synthesis of [(1)2W(CO)3] (4). First, 76 mg (0.20 mmol) of [(η6-C7H8)W(CO)3] were dissolved in 8 mL of n-hexane and 2 mL of toluene. To this deep-red solution 2 equiv of 2 (150 mg, 0.40 mmol), dissolved in 16 mL of a hexane/toluene mixture (4:1), were added. The reaction mixture was stirred for 5 h at ambient temperature. During this time, a deep-purple solid formed. The supernatant was decanted, the solid washed several times with n-hexane, and dried in high vacuum. Compound 4 was obtained as a fine, blue-purple solid in good yield (126 mg, 0.12 mmol, 60%). Crystals suitable for X-ray crystallography were obtained either by diffusion of n-hexane into a saturated solution of 4 in toluene or by cooling a saturated solution of 4 in toluene to -30 °C. Anal. Calcd for C39H50O3P2WZr2: C, 47.08; H 5.06. Found: C 46.93, H 5.15. IR ν(CtO)/cm-1: 1924, 1863, 1793. 1H NMR (300 MHz, C6D6): δ 5.65 (m, 4 H, C5H4), 5.53 (m, 4 H, C5H4), 5.08 (s, 14 H, C7H7), 2.47 (br m, 4 H, CHMe2), 1.23 (br dd, 12 H, CH3). 13C NMR (75 MHz, C6D6): δ 224.0 (CO), 215.1 (br, CO), 113.0 (br, i-C5H4), 105.2 (br, R-C5H4), 104.2 (br, β-C5H4), 79.6 (C7H7), 29.6 (CHMe2), 19.6 (br, CH3), 19.1 (br, CH3). 31P NMR (121 MHz, C6D6): δ 30.1 (br s, 183W satellites, 1JPW = 248.4 Hz).

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(29) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112–122.

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Table 1. Crystallographic Data

empirical formula a (A˚) b (A˚) c (A˚) R (deg) β (deg) γ (deg) V (A˚3) Z formula weight space group T (°C) λ (A˚) Dcalcd (g cm-3) μ (mm-1) Flack parameter R(Fo) Rw(Fo2)

2

3

4

C18H25PSeZr 10.0011(2) 12.1287(4) 14.5060(4) 90 102.074(2) 90 1720.66(8) 4 442.53 P21 -173 0.71073 1.708 2.839 0.008(5) 0.0293 0.0427

C36H50AuClP2Zr2 11.2225(10) 11.2225(10) 28.1700(3) 90 90 90 3547.8(6) 4 959.56 P41 -140 0.71073 1.796 4.891 -0.003(2) 0.0238 0.0454

C39H50O3P2WZr2 10.8096(3) 11.7868(2) 16.4711(3) 94.885(2) 107.504(2) 110.107(2) 1837.31(7) 2 995.02 P1 -173 0.71073 1.799 3.803 0.0186 0.0326

X-ray Crystal Structure Determinations. Data were recorded on area detectors (Oxford Diffraction Xcalibur and Bruker Smart) at low temperature. Absorption corrections were performed on the basis of multiscans. Structures were refined anisotropically using the program SHELXL-97.29 In the compounds 2, 3, and 4, the hydrogen atoms of the five- and seven-membered rings were refined freely but with appropriate restraints (e.g., to C-H distances). The hydrogen atoms of the methyl groups were refined using rigid groups, other H atoms were included using a riding model. Both 3 and 4 have one disordered isopropyl group. Numerical details are summarized in Table 1.

Acknowledgment. This work was supported by the Deutsche Forschungsgemeinschaft (DFG) through grant Ta 189/5-3. Supporting Information Available: Full details of the X-ray crystal structure determination of a polymorphic but twinned form of 4; CIF files for each of the crystal structures. This material is available free of charge via the Internet at http:// pubs.acs.org.