Insertion vs Ligand Exchange: Reactivity of Distanna Ansa Half

(3) In recent decades they have proven to be versatile reagents for catalysis, ... in which both rings are linked by a diatomic bridge, serve as a rep...
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Organometallics 2011, 30, 305–312 DOI: 10.1021/om101049d

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Insertion vs Ligand Exchange: Reactivity of Distanna Ansa HalfSandwich Complexes of Molybdenum and Tungsten toward Isocyanide and Phosphine Complexes of Nickel and Palladium Holger Braunschweig,* Rainer D€ orfler, Katrin Gruss, Julia K€ ohler, and Krzysztof Radacki Institut f€ ur Anorganische Chemie, Universit€ at W€ urzburg, Am Hubland, D-97074 W€ urzburg, Germany Received November 8, 2010

Addition of [Ni(CNtBu)4] or [Ni(PEt3)4] to the molybdenum and tungsten distanna ansa half-sandwich complexes [{κ1-SntBu2SntBu2(η5-C5H4)}M(CO)3] (M = Mo, W) leads to carbonyl-isocyanide and carbonyl-phosphine exchange, respectively, resulting in enhanced reactivity toward chalcogen insertion in the case of the isocyanide compounds 8 and 9. Additionally, the first examples of oxidative addition of a half-sandwich ansa bridge toward zerovalent transition metals are presented by preparing the novel 1,3-distanna-2-pallada ansa half-sandwich complexes 17-20 by addition of [Pd(CNtBu)2].

Introduction Ansa-bridged complexes of metallocenes1 and related metalloarene complexes2 are currently in the focus of organometallic chemistry due to their versatile reactivity.3 In recent decades they have proven to be versatile reagents for catalysis, insertion,4 substitution, and ring-opening reactions.5 Here, [2]metallocenophanes and [2]arenocenophanes, in which both rings are linked by a diatomic bridge, serve as a representative example, as they are known to react with zerovalent group 10 metals with oxidative addition to the metal center. In comparison to this, the chemistry of related ansa halfsandwich complexes has not yet drawn as much attention, although they have already proven to be an interesting subclass of metallocenes.6 Their distinct structural feature is a σ-bonded bridge, which links the η5-coordinated cyclopentadienyl ring to the metal center and thus imposes different reactivity patterns and therefore new properties and additional synthetic possibilities in comparison to metallocenophanes. Pannell’s group, for example, reported various examples where ansa half-sandwich complexes undergo ringopening polymerization, yielding organometallic polymers.7 In contrast, the oxidative addition of the ansa bridge to zerovalent metal fragments, which constitutes a typical reactivity pattern for metallocenophanes (vide supra), has not yet been observed for half-sandwich complexes.

Recently, we synthesized the first distannadiyl ansa halfsandwich complexes of molybdenum (3a) and tungsten (3b) from the dimetalated salts Li[(η5-C5H4Li)(CO)3M] (M = Mo (1a), W (1b)) and tBu2(Cl)SnSn(Cl)tBu2 via a double salt elimination metathesis.8 Both compounds can be obtained in good yields and show high thermal stability, despite the high

*To whom correspondence should be addressed. E-mail: h.braunschweig@ mail.uni-wuerzburg.de. (1) (a) Osborne, A. G.; Whitely, R. H. J. Organomet. Chem. 1975, 101, C27. (b) Hultzsch, K. C.; Nelson, J. M.; Lough, A. J.; Manners, I. Organometallics 1995, 14, 5496. (c) Gates, D. P.; Rulkens, R.; Dirk, R.; Nguyen, P.; Pudelski, J. K.; Resendes, R.; Braunschweig, H.; Manners, I. Phosphorus, Sulfur, Silicon Relat. Elem. 1997, 124-125, 561. (d) Braunschweig, H.; von Koblinski, C.; Wang, R. Eur. J. Inorg. Chem. 1999, 6973. (e) Braunschweig, H.; von Koblinski, C.; Mamuti, M.; Englert, U.; Wang, R. Eur. J. Inorg. Chem. 1999, 1899. (f) Braunschweig, H.; Breitling, F. M.; Gullo, E.; Kraft, M. J. Organomet. Chem. 2003, 680, 3142. (g) Schachner, J. A.; Lund, C. L.; Quail, J. W.; M€ uller, J. Organometallics 2005, 24, 785. (h) Lund, C. L.; Schachner, J. A.; Quail, J. W.; M€ uller, J. Organometallics 2006, 25, 5817. (i) Braunschweig, H.; Gross, M.; Radacki, K. Organometallics 2007, 26, 6688. (j) Braunschweig, H.; Gross, M.; Radacki, K.; Rothgaengel, C. Angew. Chem. 2008, 120, 101279; Angew. Chem., Int. Ed. 2008, 47, 9979.

(2) (a) Elschenbroich, C.; Gerson, F. Chimia 1974, 28, 720. (b) Elschenbroich, C.; Hurley, J.; Metz, B.; Massa, W.; Baum, G. Organometallics 1990, 9, 889. (c) Tamm, M.; Kunst, A.; Bannenberg, T.; Herdtweck, E.; Sirsch, P.; Elsevier, C. J.; Ernsting, J. M. Angew. Chem. 2004, 116, 5646; Angew. Chem., Int. Ed. 2004, 43, 5530. (d) Braunschweig, H.; Homberger, M.; Hu, C.; Zheng, X.; Gullo, E.; Clentsmith, G.; Lutz, M. Organometallics 2004, 23, 1968. (e) Braunschweig, H.; Lutz, M.; Radacki, K. Angew. Chem. 2005, 117, 5792; Angew. Chem., Int. Ed. 2005, 44, 5647. (f) Braunschweig, H.; Kupfer, T.; Radacki, K. Angew. Chem. 2007, 119, 1655; Angew. Chem., Int. Ed. 2007, 46, 1630. (g) Tamm, M. Chem. Commun. 2008, 3089. (h) Braunschweig, H.; Kupfer, T.; Lutz, M.; Radacki, K. J. Am. Chem. Soc. 2007, 8893. (i) Adams, C. J.; Braunschweig, H.; Kupfer, T.; Manners, I.; Richardson, R.; Whittell, G. Angew. Chem. 2008, 120, 3886; Angew. Chem., Int. Ed. 2008, 47, 3826. (j) Braunschweig, H.; Kupfer, T. Acc. Chem. Res. 2010, 43, 455. (k) MacLachlan, M. J.; Ginzburg, M.; Coombs, N.; Coyle, T. W.; Raju, N. P.; Greedan, J. E.; Ozin, G. A.; Manners, I. Science 2000, 287, 1460. (l) Chan, W. Y.; Clendennings, S. B.; Berenbaum, A.; Lough, A. J.; Aouba, S.; Ruda, H. E.; Manners, I. J. Am. Chem. Soc. 2005, 127, 1765. (m) Mayer, U. F. J.; Gilroy, J. B.; O0 Hare, D.; Manners, I. J. Am. Chem. Soc. 2009, 131, 14958. (n) Herbert, D. E.; Mayer, U. F. J.; Manners, I. Angew. Chem., Int. Ed. 2007, 46, 5060. (o) Liu, K.; Ho, C.-L.; Aouba, S.; Zhao, Y.-Q.; Lu, Z.-H.; Petrov, S.; Coombs, N.; Dube, P.; Ruda, H. E.; Wong, W.-Y.; Manners, I. Angew. Chem., Int. Ed. 2008, 47, 1255. (p) Tamm, M.; Kunst, A.; Herdtweck, E. Chem. Commun. 2005, 1729. (q) Bagh, B.; Gilroy, J. B.; Staubitz, A.; M€uller, J. J. Am. Chem. Soc. 2010, 132, 1794. (r) Lund, C. L.; Bagh, B.; Quail, J. W.; M€uller, J. Organometallics 2010, 29, 1977. (s) Schachner, J. A.; Trockner, S.; Lund, C. L.; Quail, J. W.; Rehahn, M.; M€uller, J. Organometallics 2007, 26, 4658. (3) (a) Manners, I. Adv. Organomet. Chem. 1995, 37, 131. (b) Nguyen, P.; Gomez-Elipe, P.; Manners, I. Chem. Rev. 1999, 99, 1515. (c) Bellas, V.; Rehahn, M. Angew. Chem. 2007, 119, 5174; Angew. Chem., Int. Ed. 2007, 46, 5082. (4) (a) Finckh, W.; Tang, B. Z.; Lough, A.; Manners, I. Organometallics 1992, 11, 2904. (b) Herberhold, M.; Steffl, U.; Milius, W.; Wrackmeyer, B. Angew. Chem. 1997, 109, 1545. Angew. Chem., Int. Ed. 1997, 36, 1508; (c) Braunschweig, H.; Lutz, M.; Radacki, K. Angew. Chem. 2005, 117, 5792; Angew. Chem., Int. Ed. 2005, 44, 5647. (d) Braunschweig, H.; Lutz, M.; Radacki, K.; Schauml€ offel, A.; Seeler, F.; Unkelbach, C. Organometallics 2006, 25, 4433. (e) Braunschweig, H.; Kupfer, T.; Lutz, M.; Radacki, K.; Seeler, F.; Sigritz, R. Angew. Chem. 2006, 118, 8217; Angew. Chem., Int. Ed. 2006, 45, 8048. (f) Braunschweig, H.; Kupfer, T. Organometallics 2007, 26, 4634.

r 2010 American Chemical Society

Published on Web 12/28/2010

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Scheme 1. Synthesis and Reactivity of Distanna Ansa HalfSandwich Complexes

Braunschweig et al. Scheme 2. Oxidative Addition of Distannanes to Pt and Pd

Scheme 3. Ligand Exchange Reactions with Quaternary Nickel Compounds

ring strain in the ansa bridge. Although both complexes are almost identical in their molecular structure, only the tungsten species undergoes insertion into the tin-tin bond when treated with elemental chalcogens, releasing the ring strain almost completely and yielding the 1,3-distanna-2-chalcogena ansa half-sandwich complexes 4a-d (Scheme 1). In this report, we focus on the reactivity of these ansa complexes toward Ni and Pd complexes with isocyanide and phosphine ligands. Low-coordinated zerovalent group 10 complexes, especially of platinum and palladium, are known to undergo various oxidative addition reactions at the metal center.9 This reaction scheme is of major importance for various catalytic transformations in metal-organic chemistry, such as the distannylation of unsaturated C-C bonds10 or the Heck reaction,11 for example. Herberhold et al. reported the insertion of Pt into the tin-tin bond of the distanna[2]ferrocenophane 5 upon treatment with [(Ph3P)2Pt(η2-C2H4)], yielding the 1,3-distanna2-platina[3]ferrocenophane 6.12 The same pattern can be extended to palladium compounds, as shown by Kunai and coworkers, who generated the catalytic intermediate [(SnBu3)2(tOcNC)2Pd] (7) for distannylation reactions by insertion of [Pd(CNtOc)2] into the tin-tin bond of Bu3SnSnBu3.13 Although the use of nickel compounds as catalysts is not as (5) (a) Braunschweig, H.; Dirk, R.; M€ uller, M.; Nguyen, P.; Resendes, R.; Gates, D. P.; Manners, I. Angew. Chem. 1997, 109, 2433; Angew. Chem., Int. Ed. 1997, 36, 2338. (b) Braunschweig, H.; Dirk, R.; Englert, U.; J€ akle, F.; Berenbaum, A.; Green, J. C.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2000, 122, 5765. (c) Braunschweig, H.; Radacki, K.; Rais, D.; Scheschkewitz, D. Angew. Chem. 2005, 117, 5796; Angew. Chem., Int. Ed. 2005, 44, 5651-5654. (d) Bartole-Scott, A.; Braunschweig, H.; Kupfer, T.; Lutz, M.; Manners, I.; Nguyen, T.; Radacki, K.; Seeler, F. Chem. Eur. J. 2006, 12, 1266. (e) Braunschweig, H.; Kupfer, T.; Lutz, M.; Radacki, K.; Seeler, F.; Sigritz, R. Angew. Chem. 2006, 118, 8217; Angew. Chem., Int. Ed. 2006, 45, 8048 (6) (a) Eilbracht, P. Chem. Ber. 1976, 109, 1429. (b) Eilbracht, P. Chem. Ber. 1976, 109, 3136. (c) Crocco, G. L.; Young, C. S.; Lee, K. E.; Gladysz, J. A. Organometallics 1988, 7, 2158. (d) Raith, A.; Altmann, P.; Cokoja, M.; Herrmann, W. A.; K€ uhn, F. E. Coord. Chem. Rev. 2010, 254, 608. (7) (a) Sharma, H. K.; Pannell, K. H. Chem. Commun. 2004, 2556. (b) Sharma, H.; Cervantes-Lee, F.; Pannell, K. H. J. Am. Chem. Soc. 2004, 126, 1326. (c) Sharma, H.; Cervantes-Lee, F.; Pannell, K. H. Organometallics 2007, 25, 3969. (d) Apodaca, P.; Kumar, M.; Cervantes-Lee, F.; Sharma, H.; Pannell, K. H. Organometallics 2008, 27, 3136. (8) Bera, H.; Braunschweig, H.; D€ orfler, R.; Hammond, K.; Oechsner, A.; Radacki, K.; Uttinger, K. Chem. Eur. J. 2009, 15, 12092. (9) Beletskaya, I.; Moberg, C. Chem. Rev. 1999, 99, 3435. (10) Rubina, M.; Rubin, M.; Gevorgyan, V. J. Am. Chem. Soc. 2002, 124, 11566. (11) Heck, R. F.; Nolley, J. P. J. Org. Chem. 1972, 37, 2320. (12) Herberhold, M.; Steffl, U.; Wrackmeyer, B. J. Organomet. Chem. 1999, 577, 76. (13) Yoshida, H.; Tanino, K.; Ohshita, J.; Kunai, A. Angew. Chem., Int. Ed. 2004, 43, 5052.

common as for Pt or Pd complexes, there are some examples where [Ni(COD)2] or [Ni(dppe)2] has been employed for hydro-, carbo-, and silylstannation reactions of alkynes.14 As expected, the molecular structures of 6 and 7 show a square-planar geometry at the metal center (Scheme 2). Since no intermediate was isolated, the geometry of the catalytically active nickel species remains unknown.

Results and Discussion When treated with [(Ph3P)2Pt(η2-C2H4)], both ansa complexes 3a,b show no reaction at ambient temperature or upon heating to 80 °C, which is most likely due to the steric demand of the bulky tert-butyl groups at the tin atoms and the triphenylphosphine ligands at platinum, respectively. Therefore, considering the mainly square-planar geometry at Pt and Pd, the use of less sterically hindered ligands is essential for oxidative addition into the tin-tin bond, when the latter is shielded by large groups at the tin atoms. This problem can be avoided by using tert-butyl isocyanide ligands, which stabilize the complex with a bulky group but do not impose local steric hindrance at the metal center, as the tertbutyl groups reside at the far end of the almost linear tBu-N-C-M moiety. Reactivity toward Nickel Compounds. On treatment with a stoichiometric amount of [Ni(CNtBu)4], both ansa compounds 3a,b react readily at ambient temperature over 18 h. Remarkably, no insertion into the tin-tin bond occurs, but the products 8 and 9 thus obtained exhibit a ligand exchange of the carbonyl trans to the stannyl group by a tertbutyl isocyanide. Analogously, the reaction with [Ni(PEt3)4] leads to the similar compound 10 with a triethylphosphine ligand, but only in the case of the tungsten compound 3b (Scheme 3). Since the treatment of 3a,b with pure tert-butyl isocyanide or triethylphosphine leads to no reaction, it is assumed that the nickel species plays a decisive role in the observed ligand exchange reaction. This was confirmed by the appearance of (14) Shirakawa, E.; Yamamoto, Y.; Nakao, Y.; Oda, S.; Tsuchimoto, T.; Hiyama, T. Angew. Chem., Int. Ed. 2004, 43, 3448.

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Figure 1. Molecular structure of 9. Ellipsoids are drawn at the 50% probability level. Only one molecule of the elemental cell is shown. Hydrogen atoms and ellipsoids of the tert-butyl groups are omitted for clarity. Selected bond lengths (A˚) and bond and torsion angles (deg): W1-Sn1=2.8685(8), Sn1-Sn2=2.8251(6), C12-Sn2 = 2.190(3), W1-C12 = 2.040(3), C11-N21 = 1.159(4); W1-Sn1-Sn2=82.732(15), C12-Sn2-Sn1=82.53(7); Sn2C12-W1-Sn1 = 18.56(9).

Figure 2. Molecular structure of 10. Ellipsoids are drawn at the 30% probability level. Hydrogen atoms and ellipsoids of the tert-butyl and ethyl groups are omitted for clarity. Selected bond lengths (A˚) and bond and torsion angles (deg): W1-Sn2 = 2.8719(3), Sn1-Sn2=2.8486(3), C12-Sn1=2.1837(19), W1P1 = 2.4483(6); W1-Sn2-Sn1 = 83.211(7), C12-Sn1-Sn2 = 81.22(5); Sn2-W1-C2-Sn1=18.35(7).

Table 1. 119Sn NMR Shifts of Cyclopentadienyl- and MetalBound Stannyl Groups (ppm, in C6D6)

Scheme 4. Insertion Products Obtained by Reaction with Elemental Chalcogens

δ(C-Sn) δ(M-Sn)

3a (Mo)

3b (W)

8 (Mo)

9 (W)

10 (W)

-68 -97

-75 -176

-64 -53

-69 -146

-60 -146

the known compound [(tBuNC)3Ni(CO)] in the reaction mixture,15 a single crystal of which could be isolated. The product was identified by comparison of its elemental cell and diffraction data with those reported in the literature. This suggests a carbonyl/isocyanide ligand exchange reaction between nickel and the group 6 metal atoms. All products have been fully characterized by multinuclear NMR spectroscopy and elemental analysis. The carbonyl exchange effects the appearance of a singlet for the tert-butyl protons of 8 and 9 in the 1H NMR spectra and two multiplets in case of 10 for the ethyl groups, respectively, while all other signals experience a slight downfield shift in comparison to the starting materials. The same effect can be observed in the 119 Sn NMR spectra: while the signals for the cyclopentadienyl-bound stannyl group are in the same region as in the precursor compounds, the metal-bound stannyl groups are shifted by about 30-40 ppm downfield (see Table 1). Nonetheless, all resonances are still deshielded, which indicates acute angles at the tin atoms and, hence, the presence of molecular strain within the ansa bridge. This assumption was confirmed by X-ray diffraction analysis of the tungsten species 9 and 10 (Figures 1 and 2). Both angles at the stannyl groups have not changed significantly in comparison to 3b (Cipso-Sn-Sn and Sn-Sn-W: 3b, 83.29(9) and 82.270(11)°; 9, 82.53(7) and 82.732(15)°; 10, 81.22(5) and 83.211(7)°). As expected, with tBuNC and PEt3 being better σ-donors and weaker π-acceptor ligands than CO, the W-Sn bond in a trans position is shortened by approximately 5 pm with respect to that in the precursor (3a, 2.9222(3) A˚; 9, 2.8685(8) A˚; 10, 2.8719(3) A˚). (15) Imhof, W.; G€ orls, H.; Halbauer, K. Acta Crystallogr., Sect. E 2008, 64, m1000.

Chalcogen Insertion. As mentioned beforehand, the tricarbonyl tungsten compound 3b readily reacts with elemental chalcogens, releasing the ring strain almost completely upon insertion into the tin-tin bond. This reaction could not be carried out for the analogous molybdenum compound, where only decomposition of the starting material 3a was observed. Though the molecular structure changed only slightly, the tBuNC/CO exchange enhances the reactivity toward insertion, which now also can be achieved for molybdenum species (Scheme 4). The 1,3-distanna-2-chalcogena ansa half-sandwich complexes 11-16 were obtained by addition of elemental sulfur, selenium, or tellurium, respectively. As in the case of 3b, reaction times and conditions vary strongly with size and solubility of the elemental chalcogen. While insertion of sulfur occurs rapidly at ambient temperature, heating to reflux in benzene for several hours (13, 3 h; 14, 4 h; 15, 96 h; 16, 72 h) is required for selenium and tellurium. Interestingly, both sulfur compounds 11 and 12 show poor stability in solution, indicated by formation of a brown decomposition product after approximately 30 min in benzene, while 13-16 are stable in solution for several weeks. Further evidence can be obtained from the DSC spectra, which show decomposition prior to melting at 155 (11) and 160 °C (12), while the other products show high melting points as previously

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Figure 3. Molecular structure of 13. Only one molecule of the elemental cell is shown. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms and ellipsoids of the tert-butyl groups are omitted for clarity. Selected bond lengths (A˚) and bond and torsion angles (deg): Mo2-Sn3 = 2.8359(3), C18Sn4 = 2.147(2), Sn3-Se2 = 2.6096(3), Se2-Sn4 = 2.5144(3), Mo2-C17=2.054(3), C17-N27=1.160(3); Mo2-Sn3-Se2= 107.579(9), C18-Sn4-Se2=108.45(6), Sn3-Se2-Sn4=99.194(10); Sn3-Mo2-C18-Sn4=35.20(12).

Figure 4. Molecular structure of 14. Ellipsoids are drawn at the 30% probability level. Hydrogen atoms and ellipsoids of the tert-butyl groups are omitted for clarity. The quality of the crystal data is not good enough for an extensive discussion of geometrical parameters and merely can be used as a confirmation of the overall geometry. As nearly all tert-butyl groups were disordered, they were fitted to idealized geometry.

reported for 4a-d (13, 191 °C, 14, 206 °C; 15, 216 °C; 16, 201 °C). The decrease of ring strain is indicated by the 119Sn{1H} NMR resonances, which show a significant low-field shift for all stannyl moieties, especially for the metal-bound atoms, which are shifted up to 350 ppm. In agreement with this, the insertion evokes a decrease of the J(119Sn,117/119Sn) coupling constants, from 720 and 690 Hz (9) down to 95 Hz in the case of 16. Additionally, the presence of 1J(119Sn,77Se) satellites for 13 and 14 and 1J(119Sn,125Te) coupling for 15 and 16, respectively, confirms the insertion. Final proof for the unstrained conformation is provided by the molecular structures derived from X-ray diffraction analyses for 13-16 (Figures 3-6). All compounds exhibit almost tetrahedral M-Sn-E angles (13, 107.579(9)°, M=Mo, E = Se; 15, 107.55(2)°, M = Mo, E = Te), indicating no pronounced ring strain in the ansa bridge.

Braunschweig et al.

Figure 5. Molecular structure of 15. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms and ellipsoids of the tertbutyl groups are omitted for clarity. Selected bond lengths (A˚) and bond and torsion angles (deg): Mo1-Sn1 = 2.8481(12), C11Sn2=2.141(6), Sn1-Te1=2.8130(10), Te1-Sn2=2.7240(10), Mo1-C1=2.065(8), C1-N1=1.154(10); Mo1-Sn1-Te1= 107.55(2), C11-Sn2-Te1=103.23(19), Sn1-Te1-Sn2=96.76(2); Sn1-Mo1-C11-Sn2=40.9(4).

Figure 6. Molecular structure of 16. Ellipsoids are drawn at the 30% probability level. Hydrogen atoms and ellipsoids of the tert-butyl groups are omitted for clarity. The quality of the crystal data is not good enough for an extensive discussion of geometrical parameters and merely can be used as a confirmation of the overall geometry. As nearly all tert-butyl groups were disordered, they were fitted to idealized geometry.

Reactivity toward Palladium Complexes. The addition of 1 equiv of [Pd(CNtBu)2] to the ansa complexes 3a,b, 8, and 9 leads to an immediate reaction, as indicated by a color change from yellow to dark red. After workup, the palladium insertion products 17-20 could be isolated as bright yellow powders (Scheme 5). All compounds show very good solubility in aliphatic and aromatic solvents, which renders their separation from soluble byproducts somewhat difficult. Additionally, 17-20 exhibit poor stability in solution, resulting in low yields after workup. The NMR data are in full agreement with the proposed structures of the oxidative addition products. Surprisingly, however, only one singlet is observed for both chemically nonequivalent tert-butyl isonitrile ligands at the palladium fragment. As expected, the insertion again leads to a significant low-field shift in the 119Sn{1H} NMR spectrum. The signals of the metal-bound stannyl group lie in the range of those of the chalcogen insertion products, with the peaks of

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Scheme 5. Products from the Oxidative Addition of the Sn-Sn Bond to [Pd(CNtBu)2]

Table 2. 119Sn shifts for the Cyclopentadienyl-Bound Tin Atoms of the Compounds [{K1-SntBu2-E-SntBu2(η5-C5H4)}M(CNtBu)(CO)2], with a tBuNC Ligand (ppm, in C6D6) E M

- (9)

S (12)

Se (14)

Te (16)

Pd (20)

Mo W

-69 -60

49 52

43 47

16 21

144 158

the tungsten compounds, as expected, about 100 ppm upfield compared to those of the corresponding molybdenum species. Interestingly, the cyclopentadienyl-bound tin exhibits a further downfield shift of approximately 100 ppm in comparison to those observed for the chalcogen insertion products. An overview of the 119Sn (C-Sn) shifts of the isonitrile complexes is presented in Table 2. Suitable single crystals for X-ray analysis of 18 and 19 were obtained upon slow evaporation of a saturated pentane solution at 5 °C, confirming the solid-state structures as presented in Figures 7 and 8. The palladium center adopts an almost square-planar coordination geometry, as indicated by the sums of bond angles of 360.16 (19) and 360.14° (20), respectively. As a result, the angles at the tin atoms within the ansa bridge are widened to values almost typical of sp2 hybridization (19, C11-Sn2-Pd1 = 119.43(6)° and Mo1Sn1-Pd1=119.780(8)°; 20, C11-Sn2-Pd1=118.84(6)° and W1-Sn1-Pd1=118.377(6)°), despite the steric hindrance of the bulky tert-butyl groups. This deviation from ideal tetrahedral angles yet again indicates strain within the ansa bridge and could be the reason for the poor stability of the products as well as for the characteristic downfield-shifted 119Sn NMR resonances. In agreement with this, the metal-tin bond (20: W1-Sn1=2.9427(2) A˚) is elongated by over 5 pm in comparison to that in the strained distanna ansa complex 9 (W1-Sn1=2.8685(8) A˚) and almost 10 pm longer than that in the analogous unstrained tellurium insertion product 16 (W1-Sn1=2.8451(8) A˚).

Conclusion In this report we presented the different reactivity of the distanna ansa half-sandwich complexes 3a,b toward zerovalent nickel and palladium complexes. The reaction with [Ni(CNtBu)4] leads to a carbonyl/isocyanide exchange between the metal centers, forming the ansa complexes 8 and 9 with a tert-butyl isocyanide ligand trans to the bridge. The reaction with [Ni(PEt3)4] gives access to the analogous phosphine complex 10. The isocyanide substitution readily enhances the propensity of the distanna bridge toward insertion of

Figure 7. Molecular structure of 19. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms, solvent molecules, and ellipsoids of the tert-butyl groups are omitted for clarity. Selected bond lengths (A˚) and bond and torsion angles (deg): Mo1-Sn1 = 2.9368(4), C11-Sn2 = 2.178(3), Sn1-Pd1 = 2.6659(3), Sn2-Pd1 = 2.5914(3), Mo1-C12 = 2.027(3), Pd1C15 = 2.033(3), Pd1-C16 = 2.038(3); Mo1-Sn1-Pd1 = 118.790(8), C11-Sn2-Pd1 = 119.43(6), C15-Pd1-C16 = 92.15(10), C16-Pd1-Sn2 = 90.72(7), Sn2-Pd1-Sn1 = 86.399(8), Sn1-Pd1-C15 = 90.89(7); Sn1-Mo1-C11Sn2 = 28.49(11).

Figure 8. Molecular structure of 20. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms, solvent molecules, and ellipsoids of the tert-butyl groups are omitted for clarity. Selected bond lengths (A˚) and bond and torsion angles (deg): W1-Sn1=2.9437(2), C11-Sn2=2.175(2), Sn1Pd1=2.6632(2), Sn2-Pd1=2.5879(2), W1-C12=2.021(2), Pd1-C15 =2.020(2), Pd1-C16 =2.035(2); W1-Sn1-Pd1= 118.377(6), C11-Sn2-Pd1 = 118.84(6), C15-Pd1-C16 = 91.47(9), C16-Pd1-Sn2 = 91.10(6), Sn2-Pd1-Sn1 = 86.802(6), Sn1-Pd1-C15=90.77(6); Sn1-W1-C11-Sn2= 29.05(10).

elemental chalcogens, as proven by the synthesis of 11-16. Finally, treatment with [Pd(CNtBu)2] results in the oxidative addition of the tin-tin bond to the palladium atom, yielding the first 1,3-distanna-2-pallada ansa half-sandwich complexes 17-20.

Experimental Section General Considerations. All manipulations were conducted either under an atmosphere of dry argon or in vacuo using standard Schlenk line or glovebox techniques. Solvents (benzene and pentane) were purified by distillation from appropriate drying agents (sodium and sodium potassium alloy) under dry argon, immediately prior to use. C6D6 was degassed by three freezepump-thaw cycles and stored over molecular sieves. IR spectra

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were recorded as solutions between KBr plates on a Bruker Vector 22 FT-IR spectrometer or as solids on a Bruker Alpha FT-IR spectrometer. 1H, 13C{1H}, 31P{1H}, and 119Sn{1H} NMR spectra were acquired as stated on a Bruker Avance 300 NMR spectrometer at 300.1, 75.5, 121.5, and 111.9 MHz or a Bruker Avance NMR spectrometer at 500.1, 125.5, 202.5, and 181.5 MHz, respectively, and referenced to external TMS, 85% H3PO4 (31P), or SnMe4 (119Sn). Microanalyses for C, H, and N were performed by Mrs. L. Michels and Mrs. S. Timmroth (University of W€ urzburg) on a Vario Micro Cube instrument (Elementar Analysensysteme). Melting points were measured on a Mettler Toledo DSC823 instrument. Starting materials were prepared according to literature procedures: [{κ1-SntBu2SntBu2(η5C5H4)}M(CO)3] (M = Mo, W), [Ni(CNtBu)4],16 [Ni(PEt3)4],17 [Pd[CNtBu)2].18 [{K1-SntBu2SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (8). A solution of 200 mg (0.28 mmol) of [{κ1-SntBu2SntBu2(η5-C5H4)}Mo(CO)3] (3a) in 7 mL of benzene was treated with 121 mg (0.31 mmol, 1.1 equiv) of [Ni(CNtBu)4] and was stirred at ambient temperature for 18 h. The solvent was evaporated in vacuo, and the residue was purified by chromatography on Alumina V, using pentane as eluent. Yield: 169 mg (0.22 mmol, 78%). Yellow solid. Mp: 161 °C. 1H NMR (500.1 MHz, C6D6): δ 5.63 (m, 2 H, C5H4), 5.08 (m, 2 H, C5H4), 1.75 (s, 18 H, 3JSnH = 68.7, 66.5 Hz, SntBu2), 1.44 (s, 18 H, 3JSnH = 63.8, 61.1 Hz, SntBu2), 0.98 (s, 9 H, CNtBu) ppm. 13C NMR (125.8 MHz, C6D6): δ = 231.1 (s, CO), 202.9 (s, MoCNtBu), 98.0 (s, 2JSnC = 24 Hz, C5H4), 92.8 (s, 2JSnC = 14 Hz, C5H4), 58.2 (s, CNC(CH3)3), 34.8 (s, 2JSnC = 8 Hz, SnC(CH3)3), 33.1 (s, SnC(CH3)3), 32.7 (s, 2JSnC = 13 Hz, SnC(CH3)3), 31.4 (s, SnC(CH3)3), 30.7 (s, CNC(CH3)3) ppm. 119Sn NMR (186.5 MHz, C6D6): δ -53 (s, MoSn), -64 (s, CSn) ppm. IR (hexanes): ν~ 2095 (w, CN), 1914 (w, CO), 1860 (m, CO) cm-1. Anal. Calcd for C28H49MoNO2Sn2 (765.05 g mol-1): C, 43.95; H, 6.45; N, 1.83. Found: C, 43.89; H, 6.72; N, 2.06. [{K1-SntBu2SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (9). The synthesis was similar to the procedure above, using 200 mg (0.25 mmol) of [{κ1-SntBu2SntBu2(η5-C5H4)}W(CO)3] (3b) and 100 mg (0.27 mmol, 1.1 equiv) of [Ni(CNtBu)4] in 7 mL of benzene. Single crystals suitable for X-ray analysis were obtained by recrystallization from pentane and slow evaporation. Yield: 100 mg (0.12 mmol, 47%). Yellow solid. Mp: 168 °C. 1H NMR (300.1 MHz, C6D6): δ 5.63 (m, 2 H, C5H4), 5.00 (m, 2 H, C5H4), 1.74 (s, 18 H, 3JSnH = 68.7, 66.1 Hz, tBu2), 1.44 (s, 18 H, 3JSnH = 63.3, 60.5 Hz, tBu2), 1.00 (s, 9 H, CNtBu) ppm. 13C NMR (75.5 MHz, C6D6): δ 220.7 (s, CO), 202.9 (s, MoCNtBu), 96.4 (s, C5H4), 91.3 (s, C5H4), 58.5 (s, CNC(CH3)3), 35.0 (s, SnC(CH3)3), 32.6 (s, SnC(CH3)3), 31.8 (s, SnC(CH3)3), 31.7 (s, SnC(CH3)3), 31.0 (s, CNC(CH3)3) ppm. 119 Sn{1H} NMR (111.9 MHz, C6D6): δ -69 (s, 1JSnSn = 720, 695 Hz, CSn), -146 (s, 1JSnSn = 720, 695 Hz, 1JWSn = 200 Hz, WSn) ppm. IR: ν~ 2094 (w, CN), 1909 (w, CO), 1857 (m, CO) cm-1. Anal. Calcd for C28H49NO2Sn2W (852.95 g mol-1): C, 39.42; H, 5.79; N, 1.64. Found: C, 39.55; H, 5.74; N, 1.84. [{K1-SntBu2SntBu2(η5-C5H4)}W(PEt3)(CO)2] (10). A 145 mg portion (0.27 mmol, 1.25 equiv) of Ni(PEt3)4 was added to a solution of 174 mg (0.22 mmol) [{κ1-SntBu2SntBu2(η5-C5H4)}W(CO)3] (3b) in 7 mL of benzene, and the reaction mixture was stirred for 18 h at ambient temperature. The solvent was evaporated in vacuo, and the residue was isolated by chromatography on Alumina III, using hexane as eluent. The crude product was recrystallized from pentane at -60 °C. Yield: 36 mg (0.040 mmol, 19%). Yellow solid. Mp: 222 °C. 1H NMR (500. 1 MHz, C6D6): δ 5.67 (m, 2 H, C5H4), 4.72 (m, 2 H, C5H4), 1.80 (s, 18 H, 3JSnH = 65.4 Hz, tBu2), 1.50 (s, 18 H, 3JSnH = 60.2 Hz, (16) Behrens, H.; Meyer, K. Z. Naturforsch., B: Chem Sci. 1966, 21, 489. (17) Ittel, S. D.; Berke, H.; Dietrich, H.; Lambrecht, J.; H€arter, P.; Opitz, J.; Springer, W. Inorg. Synth. 1990, 28, 98. (18) Otsuka, S.; Nakamura, A.; Tatsuno, Y. J. Am. Chem. Soc. 1969, 91, 6994.

Braunschweig et al. tBu2), 1.49-1.44 (m, 6 H, CH2), 0.85-0.75 (m, 9 H, CH3) ppm. C{1H} NMR (125.8 MHz, C6D6): δ 226.2 (d, 2JPC = 17 Hz, CO), 94.9 (s, C5H4), 91.1 (s, C5H4), 35.2 (s, SnC(CH3)3), 32.7 (s, SnC(CH3)3), 31.9 (s, SnC(CH3)3), 31.6 (s, SnC(CH3)3), 22.5 (d, 1JPC = 31 Hz, CH2CH3), 8.4 (d, 2JPC = 2 Hz, CH2CH3) ppm. 31P{1H} NMR (202.5 MHz, C6D6): δ 15.6 (s, 1JWP = 280 Hz, 2JSnP = 95 Hz, 3JSnP = 28 Hz) ppm. 119Sn{1H} NMR (186.5 MHz, C6D6): δ -60 (s, 3JSnP = 28 Hz, CSn), -146 (s, 2JSnP = 97 Hz, WSn) ppm. Not all couplings could be detected, due to the poor quality of the spectra and/or signal overlaps. IR: ν~ 1883 (w, CO), 1817 (m, CO) cm-1. Anal. Calcd: for C29H55O2PSn2W (887.98 g mol-1): C, 39.23; H, 6.24. Found: C, 39.60; H, 6.37. [{K1-SntBu2-S-SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (11). A solution of 57 mg (75 μmol) of [{κ1-SntBu2SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (8) in 0.7 mL of C6D6 was treated with an excess of sulfur, which yielded in an immediate color change from yellow to orange. The solvent was evaporated in vacuo, and the residue was purified by chromatography on silica, using dichloromethane for elution. Yield: 22 mg (28 μmol, 37%). Yellow solid. Mp: 155 °C dec. 1H NMR (300.1 MHz, C6D6): δ 5.35 (m, 2 H, C5H4), 5.04 (m, 2 H, C5H4), 1.77 (s, 18 H, 3JSnH = 71.8, 68.6 Hz, tBu2), 1.39 (s, 18 H, 3JSnH = 78.6, 75.1 Hz, tBu2), 0.96 (s, 9 H, CNtBu) ppm. 13C{1H} NMR (125.8 MHz, C6D6): δ 230.9 (s, CO), 104.9 (s, Cipso), 94.7 (s, C5H4), 93.4 (s, C5H4), 58.6 (s, CNC(CH3)3), 38.3 (s, SnC(CH3)3), 33.5 (s, SnC(CH3)3), 32.6 (s, SnC(CH3)3), 31.4 (s, SnC(CH3)3), 30.5 (s, CNC(CH3)3) ppm. 119Sn{1H} NMR (111.9 MHz, C6D6): δ 299 (s, 2JSnSn = 185 Hz, MoSn), 49 (s, 2JSnSn = 185 Hz, CSn) ppm. Not all couplings could be detected, due to the poor quality of the spectra and/or signal overlaps. IR: ν~ 2117 (w, CN), 1929 (w, CO), 1858 (m, CO) cm-1. Anal. Calcd for C28H49MoNO2SSn2 (797. 12 g mol-1): C, 42.19; H, 6.20; N, 1.76; S, 4.02. Found: C, 41.27; H, 6.13; N, 1.73; S, 3.65. [{K1-SntBu2-S-SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (12). This complex was prepared analogously to 11 using 64 mg (75 μmol) of [{κ1-SntBu2SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (9) in 0.7 mL of C6D6. Yield: 39 mg (44 μmol, 59%). Yellow solid. Mp: 159 °C dec. 1H NMR (500.1 MHz, C6D6): δ 5.36 (m, 2 H, C5H4), 5.00 (m, 2 H, C5H4), 1.77 (s, 18 H, 3JSnH = 71.3, 68.2 Hz, tBu2), 1.38 (s, 18 H, 3JSnH = 79.1, 75.5 Hz, tBu2), 0.98 (s, 9 H, CNtBu) ppm. 13 C{1H} NMR (125.8 MHz, C6D6): δ 220.3 (s, CO), 158.5 (s, CNC(CH3)3), 102.1 (s, Cipso), 92.9 (s, 2JSnC = 31 Hz, C5H4), 92.7 (s, 3JSnC = 26 Hz, C5H4), 58.8 (s, CNC(CH3)3), 37.5 (s, 1JSnC = 263, 251 Hz, SnC(CH3)3), 33.7 (s, 1JSnC = 406, 388 Hz, SnC(CH3)3), 32.7 (s, SnC(CH3)3), 31.4 (s, SnC(CH3)3), 30.7 (s, CNC(CH3)3) ppm. 119Sn{1H} NMR (111.9 MHz, C6D6): δ 193 (s, 1JWSn = 341 Hz, 2JSnSn = 178 Hz, MoSn), 52 (s, 2JSnSn = 178 Hz, CSn) ppm. Not all couplings could be detected, due to the poor quality of the spectra and/or signal overlaps. IR: ν~ 2107 (w, CN), 1923 (w, CO), 1849 (m, CO) cm-1. Anal. Calcd for C28H49NO2SSn2W (885.02 g mol-1): C, 38.00; H, 5.58; N, 1.58; S, 3.62. Found: C, 38.01; H, 5.70; N, 1.45; S, 3.31. General Procedure for the Insertion of Elemental Selenium and Tellurium. A solution of [{κ1-SntBu2SntBu2(η5-C5H4)}M(CNtBu)(CO)2] (M = Mo (8), W (9)) in C6D6 was treated with an excess of gray selenium and tellurium, respectively, and the mixture was heated as stated until complete product formation was detected by NMR spectroscopy. The solvent was removed in vacuo, and the residue was suspended in 10 mL of hexane. The suspension was filtered over Celite to remove remaining chalcogen, and the solvent was removed under reduced pressure. [{K1-SntBu2-Se-SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (13). This complex was prepared from 57 mg (75 μmol) of [{κ1SntBu2SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (8) in 0.7 mL of C6D6 heated to 80 °C for 3 h. Yield: 33 mg (39 μmol, 52%). Yellow solid. Mp: 191 °C. 1H NMR (300.1 MHz, C6D6): δ 5.37 (m, 2 H, C5H4), 5.06 (m, 2 H, C5H4), 1.75 (s, 18 H, 3JSnH = 71.7, 68.5 Hz, tBu2), 1.38 (s, 18 H, 3JSnH = 78.9, 75.4 Hz, tBu2), 0.96 13

Article (s, 9 H, CNtBu) ppm. 13C{1H} NMR (125.8 MHz, C6D6): δ 230.9 (s, CO), 106.2 (s, Cipso), 94.9 (s, C5H4), 93.5 (s, C5H4), 58.7 (s, CNC(CH3)3), 37.5 (s, SnC(CH3)3), 33.3 (s, SnC(CH3)3), 32.8 (s, SnC(CH3)3), 31.5 (s, SnC(CH3)3), 30.4 (s, CNC(CH3)3) ppm. 119 Sn{1H} NMR (111.9 MHz, C6D6): δ 290 (s, 1JSnSe = 932 Hz, 2 JSnSn = 163 Hz, MoSn), 43 (s, 1JSnSe = 1405 Hz, 2JSnSn = 163 Hz, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR: ν~ 2108 (w, CN), 1922 (w, CO), 1853 (m, CO) cm-1. Anal. Calcd for C28H49MoNO2SeSn2 (844.01 g mol-1): C, 38.85; H, 5.85; N, 1.66. Found: C, 40.20; H, 5.94; N, 1.84. [{K1-SntBu2-Se-SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (14). This complex was prepared from 64 mg (75 μmol) of [{κ1SntBu2SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (9) in 0.7 mL of C6D6 with 4 h of heating at 80 °C. Yield: 11 mg (12 μmol, 17%). Yellow solid. Mp: 206 °C. 1H NMR (300.1 MHz, C6D6): δ 5.37 (m, 2 H, C5H4), 5.02 (m, 2 H, C5H4), 1.76 (s, 18 H, 3JSnH = 71.2, 68.1 Hz, tBu2), 1.37 (s, 18 H, 3JSnH = 79.3, 75.8 Hz, tBu2), 0.97 (s, 9 H, CNtBu) ppm. 13C{1H} NMR (125.8 MHz, C6D6): δ 220.4 (s, CO), 103.3 (s, Cipso), 93.1 (s, C5H4), 92.9 (s, C5H4), 58.8 (s, CNC(CH3)3), 36.7 (s, SnC(CH3)3), 33.5 (s, SnC(CH3)3), 32.9 (s, SnC(CH3)3), 31.5 (s, SnC(CH3)3), 30.7 (s, CNC(CH3)3) ppm. 119 Sn{1H} NMR (111.9 MHz, C6D6): δ 184 (s, 1JSnSe = 918 Hz, 1 JSnW = 340 Hz, 2JSnSn = 155 Hz, WSn), 47 (s, 1JSnSe = 1429 Hz, 2JSnSn = 155 Hz, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR: ν~ 2105 (w, CN), 1916 (w, CO), 1846 (m, CO) cm-1. Anal. Calcd for C28H49MoNO2Sn2W (931.91 g mol-1): C, 36.09; H, 5.30; N, 1.50. Found: C, 36.44; H, 5.46; N, 1.55. [{K1-SntBu2-Te-SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (15). This complex was prepared from 57 mg (75 μmol) of [{κ1SntBu2SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (8) in 0.7 mL of C6D6 heated to 80 °C for 4 days. Yield: 22 mg (25 μmol, 33%). Yellow solid. Mp: 216 °C. 1H NMR (300.1 MHz, C6D6): δ 5.41 (m, 2 H, C5H4), 5.10 (m, 2 H, C5H4), 1.73 (s, 18 H, 3JSnH = 71.5, 68.4 Hz, tBu2), 1.38 (s, 18 H, 3JSnH = 79.0, 75.5 Hz, tBu2), 0.96 (s, 9 H, CNtBu) ppm. 13C{1H} NMR (125.8 MHz, C6D6): δ 231.2 (s, CO), 109.0 (s, Cipso), 95.6 (s, C5H4), 93.5 (s, C5H4), 58.7 (s, CNC(CH3)3), 35.6 (s, SnC(CH3)3), 33.3 (s, SnC(CH3)3), 32.7 (s, SnC(CH3)3), 31.6 (s, SnC(CH3)3), 30.5 (s, CNC(CH3)3) ppm. 119 Sn{1H} NMR (111.9 MHz, C6D6): δ 255 (s, 1JSnTe = 2150 Hz, 2JSnSn = 102 Hz, MoSn), 16 (s, 1JSnTe = 3635 Hz, 2 JSnSn = 102 Hz, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR: ν~ 2111 (w, CN), 1923 (w, CO), 1853 (m, CO) cm-1. Anal. Calcd for C28H49MoNO2TeSn2 (892.65 g mol-1): C, 37.67; H, 5.53; N, 1.57. Found: C, 38.42; H, 5.82; N, 1.82. [{K1-SntBu2-Te-SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (16). This complex was prepared from 64 mg (75 μmol) of [{κ1SntBu2SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (9) in 0.7 mL of C6D6 with 3 days of heating at 80 °C. Yield: 43 mg (44 μmol, 58%). Yellow solid. Mp: 201 °C. 1H NMR (300.1 MHz, C6D6): δ 5.39 (m, 2 H, C5H4), 5.08 (m, 2 H, C5H4), 1.73 (s, 18 H, 3JSnH = 71.0, 67.9 Hz, tBu2), 1.37 (s, 18 H, 3JSnH = 79.4, 76.0 Hz, tBu2), 0.98 (s, 9 H, CNtBu) ppm. 13C{1H} NMR (125.8 MHz, C6D6): δ 220.6 (s, CO), 105.7 (s, Cipso), 93.9 (s, C5H4), 93.0 (s, C5H4), 58.9 (s, CNC(CH3)3), 34.9 (s, SnC(CH3)3), 33.3 (s, SnC(CH3)3), 32.9 (s, SnC(CH3)3), 31.6 (s, SnC(CH3)3), 30.8 (s, CNC(CH3)3) ppm. 119Sn{1H} NMR (111.9 MHz, C6D6): δ 152 (s, 1JSnTe = 2130 Hz, 1JSnW = 335 Hz, 2JSnSn = 95 Hz, WSn), 21 (s, 1JSnTe = 3700 Hz, 2JSnSn = 95 Hz, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR: ν~ 2102 (w, CN), 1916 (w, CO), 1844 (m, CO) cm-1. Anal. Calcd for C28H49MoNO2Sn2W (980.55 g mol-1): C, 34.29; H, 5.04; N, 1.43. Found: C, 34.95; H, 5.19; N, 1.63. [{K1-SntBu2-{Pd(CNtBu)2}-SntBu2(η5-C5H4)}Mo(CO)3] (17). A solution of 53 mg (75 μmol) of [{κ1-SntBu2SntBu2(η5-C5H4)}Mo(CO)3] (3a) in 0.5 mL of toluene was treated with 21 mg (75 μmol) of [Pd(CNtBu)2] in 2.5 mL of toluene at -78 °C. After the mixture was warmed to ambient temperature, the solvent

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was evaporated and 0.5 mL of hexane was added to the residue, which resulted in a yellow solid and an orange solution. The solid was filtered off, washed with ice-cold hexane (3  0.5 mL), and evaporated to dryness. Yield: 16 mg (16 μmol, 22%). Yellow solid. Mp: 70 °C dec. 1H NMR (300.1 MHz, C6D6): δ 5.83 (br m, 2 H, C5H4), 5.01 (m, 2 H, C5H4), 1.80 (s, 18 H, 3JSnH = 61.4, 58.8 Hz, SntBu2), 1.50 (s, 18 H, SntBu2), 0.97 (s, 18 H, PdCNtBu) ppm. 13C{1H} NMR (75.5 MHz, C6D6): δ 225.9 (s, CO), 118.0 (s, Cipso), 98.3 (s, C5H4), 92.3 (s., C5H4), 56.2 (s, PdCNC(CH3)3), 36.0 (br s, SnC(CH3)3), 33.4 (br s, SnC(CH3)3), 31.6 (s., SnC(CH3)3), 30.6 (s, SnC(CH3)3), 29.7 (br s, PdCNC(CH3)3) ppm. 119Sn{1H} NMR (111.9 MHz, C6D6): δ 254 (s, 2JSnSn = 162 Hz, MoSn), 127 (s, 2JSnSn = 162 Hz, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR (hexane): ν~ 2158 (w, CN), 2139 (w, CN), 1976 (m, CO), 1905 (w, CO), 1881 (m, CO) cm-1. Elemental analysis for C34H58MoN2O3PdSn2 (982.62 g mol-1) was not carried out due to the poor stability of the product. [{K1-SntBu2-{Pd(CNtBu)2}-SntBu2(η5-C5H4)}W(CO)3] (18). This complex was prepared analogously to 17, from 120 mg (150 μmol) of [{κ1-SntBu2SntBu2(η5-C5H4)}W(CO)3] (3b) in 2 mL of toluene and 41 mg (150 μmol) of [Pd(CNtBu)2] in 7 mL of toluene at -78 °C. Yield: 63 mg (59 μmol, 39%). Yellow solid. Mp: 86 °C dec. 1H NMR (300.1 MHz, C6D6): δ 5.85 (br m, 2 H, C5H4), 5.00 (m, 2 H, C5H4), 1.81 (s, 18 H, 3JSnH = 61.0, 58.5 Hz, SntBu2), 1.49 (s, 18 H, 3JSnH = 57.8, 55.9 Hz, SntBu2), 0.96 (s, 18 H, PdCNtBu) ppm. 13C{1H} NMR (75.5 MHz, C6D6): δ 224.8 (s, CO), 115.3 (s, Cipso), 97.2 (s, C5H4), 91.7 (s, C5H4), 56.6 (s, PdCNC(CH3)3), 36.2 (br s, SnC(CH3)3), 33.4 (s, SnC(CH3)3), 33.4 (br s, SnC(CH3)3), 32.2 (s, SnC(CH3)3), 29.7 (br s, PdCNC(CH3)3), ppm. 119Sn{1H} NMR (111.9 MHz, C6D6): δ 167 (s, 2JSnSn = 205 Hz, 1JWSn = 98 Hz, WSn), 139 (s, 2JSnSn = 205 Hz, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR (hexane): ν~ 2158 (w, CN), 2139 (w, CN), 1973 (m, CO), 1899 (w, CO), 1876 (m, CO) cm-1. Elemental analysis for C34H58N2O3PdSn2W (1070.52 g mol-1) was not carried out due to the poor stability of the product. [{K1-SntBu2-{Pd(CNtBu)2}-SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (19). This complex was prepared by a procedure similar to that for 17, from a solution of 30 mg (39 μmol) of [{κ1SntBu2SntBu2(η5-C5H4)}Mo(CNtBu)(CO)2] (8) in 0.5 mL of toluene and 11 mg (39 μmol) of [Pd(CNtBu)2] in 2.5 mL of toluene at -78 °C. Yield: 19 mg (18 μmol, 47%). Yellow solid. Mp: 123 °C dec. 1H NMR (500.1 MHz, C6D6): δ 5.92 (br m, 2 H, C5H4), 5.25 (m, 2 H, C5H4), 1.94 (s, 18 H, 3JSnH = 56.8, 54.7 Hz, SntBu2), 1.60 (s, 18 H, 3JSnH = 55.5, 53.8 Hz, SntBu2), 1.09 (s, 9 H, CNtBu), 0.99 (s, 18 H, PdCNtBu) ppm. 13C{1H} NMR (125.8 MHz, C6D6): δ 184.1 (s, MoCNtBu), 115.1 (s, Cipso), 96.3 (s, C5H4), 92.6 (br s, C5H4), 58.0 (s, PdCNC(CH3)3), 56.2 (s, MoCNC(CH3)3), 36.4 (br s, SnC(CH3)3), 33.6 (br s, SnC(CH3)3), 31.2 (s, 2  SnC(CH3)3), 31.1 (s, CNC(CH3)3), 29.6 (br s, PdCNC(CH3)3), ppm. 119Sn{1H} NMR (186.5 MHz, C6D6): δ 259 (s, 2JSnSn = 230 Hz, MoSn), 144 (s, 2JSnSn = 230 Hz, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR (hexane): ν~ 2152 (w, CN), 2132 (w, CN), 1905 (w, CO), 1851 (m, CO) cm-1. Elemental analysis for C38H67MoN3O2PdSn2 (1037.74 g mol-1) was not carried out due to the poor stability of the product. [{K1-SntBu2-{Pd(CNtBu)2}-SntBu2(η5-C5H 4)}W(CNtBu)(CO)2] (20). This complex was prepared by a procedure similar to that for 17, from 85 mg (100 μmol) of [{κ1-SntBu2SntBu2(η5-C5H4)}W(CNtBu)(CO)2] (9) in 1.5 mL of toluene and 28 mg (100 μmol) of [Pd(CNtBu)2] in 5 mL of toluene at -78 °C. Yield: 40 mg (36 μmol, 36%). Yellow solid. Mp: 90 °C dec. 1H NMR (500.1 MHz, C6D6): δ 5.95 (br m, 2 H, C5H4), 5.23 (m, 2 H, C5H4), 1.93 (s, 18 H, 3JSnH = 56.7, 54.6 Hz, SntBu2), 1.60 (s, 18 H, 3JSnH = 53.7 Hz, SntBu2), 1.14 (s, 9 H, CNtBu), 0.99

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(s, 18 H, PdCNtBu) ppm. 13C{1H} NMR (125.8 MHz, C6D6): δ 112.2 (s, Cipso), 95.1 (s, C5H4), 92.1 (br s, C5H4), 58.4 (s, PdCNC(CH3)3), 56.2 (s, WCNC(CH3)3), 36.5 (br s, SnC(CH3)3), 33.5 (br s, SnC(CH3)3), 31.9 (s, SnC(CH3)3), 31.4 (s, SnC(CH3)3), 31.4 (s, WCNC(CH3)3), 29.7 (br s, PdC(CH3)3), ppm. 119Sn{1H} NMR (186.5 MHz, C6D6): δ 159 (s, WSn), 156 (s, CSn) ppm. Not all couplings could be detected due to the poor quality of the spectra and/or signal overlaps. IR (hexane): ν~ 2153 (w, CN), 2134 (w, CN), 1898 (w, CO), 1847 (m, CO) cm-1. Elemental analysis for C38H67N3O2PdSn2W (1125.64 g mol-1) was not carried out due to the poor stability of the product. Crystal Structure Determinations. The crystal data of 9, 10, 13-16, 19, and 20 were collected with a Bruker X8 Apex-2 (9, 13, 15, 19, 20) or a D8 Apex-1 (10, 14, 16) diffractometer with CCD area detector and multilayer mirror or graphite-monochromated Mo KR radiation, respectively. The structures were solved using direct methods, refined with the Shelx software package,19 and expanded using Fourier techniques. All nonhydrogen atoms were refined anisotropically. Hydrogen atoms were assigned idealized positions and were included in structure factor calculations. Crystal data for 9: C28H49NO2Sn2W, Mr = 852.91, yellow block, 0.19  0.17  0.09 mm3, triclinic space group P1, a = 10.953(3) A˚, b = 14.230(4) A˚, c = 22.311(6) A˚, R = 85.601(10)°, β = 80.273(11)°, γ = 71.190(9)°, V = 3243.3(16) A˚3, Z = 4, Fcalcd = 1.747 g cm-3, μ = 5.088 mm-1, F(000) = 1656, T = 100(2) K, R1 = 0.0208, wR2 = 0.0698, 17 645 independent reflections (2θ e 61.08°) and 643 parameters. Crystal data for 10: C29H55O2PSn2W, Mr = 887.93, colorless plate, 0.02  0.08  0.47 mm3, monoclinic space group P21/c, a = 18.1230(19) A˚, b = 11.6141(12) A˚, c = 16.1766(17) A˚, R = 90.00°, β = 93.124(2)°, γ = 90.00°, V = 3399.8(6)A˚3, Z = 4, Fcalcd = 1.735 g cm-3, μ = 4.902 mm-1, F(000) = 1736, T = 173(2) K, R1 = 0.0219, wR2 = 0.0472, 6841 independent reflections (2θ e 52.46°) and 366 parameters. Crystal data for 13: C28H49MoNO2SeSn2, Mr = 843.96, colorless block, 0.27  0.24  0.08 mm3, monoclinic space group P21/ n, a = 18.7809(6) A˚, b = 12.3651(4) A˚, c = 30.3829(11) A˚, β = 102.9040(10)°, V = 6877.6(4) A˚3, Z = 8, Fcalcd = 1.630 g cm-3, μ = 2.881 mm-1, F(000) = 3328, T = 100(2) K, R1 = 0.0352, wR2 = 0.0529, 16 900 independent reflections (2θ e 56.64°) and 656 parameters. Crystal data for 14: C28H49NO2SeSn2W, Mr=931.87, yellow plate, 0.31  0.18  0.05 mm3, monoclinic space group P21/c, (19) Sheldrick, G. Acta Crystallogr., Sect. A 2008, 64, 112.

Braunschweig et al. a = 15.445(2) A˚, b = 12.3236(17) A˚, c = 18.898(3) A˚, R=90.00°, β = 102.354(2)°, γ=90.00°, V=3513.7(8)A˚3, Z= 4, Fcalcd = 1.762 g cm-3, μ=5.734 mm-1, F(000) = 1792, T= 174(2) K, R1=0.0462, wR2=0.0756, 8769 independent reflections (2θ e 56.72°) and 353 parameters. Crystal data for 15: C28H49MoNO2Sn2Te, Mr = 892.60, colorless block, 0.36  0.32  0.20 mm3, monoclinic space group P21/c, a=15.314(6) A˚, b=12.144(4) A˚, c=19.069(7) A˚, R = 90.00°, β = 99.575(19)°, γ = 90.00°, V = 3497(2) A˚3, Z = 4, Fcalcd = 1.695 g cm-3, μ = 2.610 mm-1, F(000) = 1736, T = 100(2) K, R1 = 0.0779, wR2 = 0.1122, 7698 independent reflections (2θ e 54.52°) and 316 parameters. Crystal data for 16: C28H49NO2Sn2TeW, Mr = 980.51, yellow plate, 0.21  0.1  0.035 mm3, monoclinic space group P21/c, a = 15.576(4) A˚, b = 12.399(3) A˚, c = 19.125(5) A˚, R = 90.00°, β = 102.502(4)°, γ = 90.00°, V = 3605.8(16)A˚3, Z = 4, Fcalcd = 1.806 g cm-3, μ = 5.371 mm-1, F(000) = 1864, T = 173(2) K, R1 = 0.0560, wR2 = 0.1051, 8979 independent reflections (2θ e 56.64°) and 404 parameters. Crystal data for 19: C44H73MoN3O2PdSn2, Mr = 1115.77, yellow block, 0.18  0.14  0.09 mm3, monoclinic space group P21/n, a = 11.8836(11) A˚, b = 23.225(2) A˚, c = 17.7910(16) A˚, β = 92.918(2)°, V = 4903.8(8) A˚3, Z = 4, Fcalcd = 1.511 g cm-3, μ = 1.652 mm-1, F(000) = 2248, T = 100(2) K, R1 = 0.0307, wR2 = 0.0645, 14 718 independent reflections (2θ e 56.66°) and 522 parameters. Crystal data for 20: C45H75N3O2PdSn2W, Mr = 1217.71, orange block, 0.17  0.09  0.08 mm3, monoclinic space group P21/n, a = 12.0560(5) A˚, b = 23.2372(9) A˚, c = 17.7022(7) A˚, β = 93.083(2)°, V = 4952.1(3) A˚3, Z = 4, Fcalcd = 1.633 g cm-3, μ = 3.705 mm-1, F(000) = 2408, T = 100(2) K, R1 = 0.0200, wR2 = 0.0461, 12 322 independent reflections (2θ e 56.66°) and 507 parameters. Crystallographic data have been deposited with the Cambridge Crystallographic Data Center as Supplementary Publication Nos. CCDC 795142-795149. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgment. We thank the DFG for financial support. Supporting Information Available: CIF files giving crystal data for 9, 10, 13-16, 19, and 20. This material is available free of charge via the Internet at http://pubs.acs.org.