Hypercoordinate Organosilicon Complexes of an ONN′O

Cite this:Organometallics 2009, 28, 2, 621-629. Synopsis. Reactions of various organochlorosilanes with the salphen-like tetradentate (ONN′O′) lig...
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Organometallics 2009, 28, 621–629

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Hypercoordinate Organosilicon Complexes of an ONN′O′ Chelating Ligand: Regio- and Diastereoselectivity of Rearrangement Reactions in Si-Salphen Systems Katrin Lippe, Daniela Gerlach, Edwin Kroke, and Jo¨rg Wagler* Institut fu¨r Anorganische Chemie, Technische UniVersita¨t Bergakademie Freiberg, Leipziger Strasse 29, D-09596 Freiberg, Germany ReceiVed October 30, 2008

Reactions of various organochlorosilanes with the salphen-like tetradentate (ONN′O′) ligand o-HOp-MeO-C6H3C(Ph)dN(o-C6H4)NdCHC6H4-o-OH, bearing two chemically and sterically different imine moieties, provided insights into the regio- and diastereoselectivity of various rearrangement reactions. Whereas thermally driven allyl- and UV-induced phenyl-shift reactions from the Si to an imine carbon atom yield one diastereomer, hydride-shift reactions were found to be less diastereoselective; however, only the sterically less demanding salicylaldimine site was attacked in all these rearrangement reactions. Introduction The coordination number of the silicon atom in various silicon complexes1 exerts great influence on both the reactivity and electronic properties2 of these compounds. Examples include a broad range of Si-X bond activation by hypercoordination: e.g., * To whom correspondence should be addressed. Tel.: (+49) 3731 39 3556 or (+49) 3731 39 4343. Fax: (+49) 3731 39 4058. E-mail: [email protected]. (1) Selected reviews on hypercoordinate silicon compounds: (a) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. ReV. 1993, 93, 1371. (b) Tacke, R.; Pu¨lm, M.; Wagner, B. AdV. Organomet. Chem. 1999, 44, 221. (c) Kost, D.; Kalikhman, I. AdV. Organomet. Chem. 2004, 50, 1. (d) Voronkov, M. G.; Trofimova, O. M.; Bolgova, Yu. I.; Chernov, N. F. Russ. Chem. ReV. 2007, 76, 825. Selected recent publications dealing with hypercoordinate silicon compounds: (e) Fester, G. W.; Wagler, J.; Brendler, E.; Bo¨hme, U.; Roewer, G.; Kroke, E. Chem. Eur. J. 2008, 14, 3164. (f) Haga, R.; Burschka, C.; Tacke, R. Organometallics 2008, 27, 4394. (g) Theis, B.; Burschka, C.; Tacke, R. Chem. Eur. J. 2008, 14, 4618. (h) Gonza´lez-Garcı´a, G.; Gutie´rrez, J. A.; Cota, S.; Metz, S.; Bertermann, R.; Burschka, C.; Tacke, R. Z. Anorg. Allg. Chem. 2008, 634, 1281. (i) Negrebetsky, V. V.; Taylor, P. G.; Kramarova, E. P.; Shipov, A. G.; Pogozhikh, S. A.; Ovchinnikov, Yu. E.; Korlyukov, A. A.; Bowden, A.; Bassindale, A. R.; Baukov, Yu. I. J. Organomet. Chem. 2008, 693, 1309. (j) Seiler, O.; Burschka, C.; Fenske, T.; Troegel, D.; Tacke, R. Inorg. Chem. 2007, 46, 5419. (k) Yamamura, M.; Kano, N.; Kawashima, T. J. Organomet. Chem. 2007, 692, 313. (l) Malhotra, R.; Mehta, J.; Puri, J. K. CEJC 2007, 5, 858. (m) Wagler, J.; Roewer, G. Inorg. Chim. Acta 2007, 360, 1717. (n) Gerlach, D.; Brendler, E.; Heine, T.; Wagler, J. Organometallics 2007, 26, 234. (o) Gerlach, D.; Wagler, J. Inorg. Chem. Commun. 2007, 10, 952. (p) Wagler, J.; Gerlach, D.; Roewer, G. Inorg. Chim. Acta 2007, 360, 1935. (q) Sergani, S.; Kalikhman, I.; Yakubovich, S.; Kost, D. Organometallics 2007, 26, 5799. (r) Wagler, J.; Gerlach, D.; Roewer, G. Chem. Heterocycl. Compd. 2006, 42, 1557. (s) Korlyukov, A. A.; Lysenko, K. A.; Antipin, M. Yu.; Shipov, A. G.; Kramarova, E. P.; Murasheva, T. P.; Negrebetskii, V. V.; Ovchinnikov, Yu. E.; Pogozhikh, S. A.; Yakovlev, I. P.; Baukov, Yu. I. Chem. Heterocycl. Compd. 2006, 42, 1592. (t) Voronkov, M. G.; Trofimova, O. M.; Chernov, N. F.; Bolgova, Yu. I.; Albanov, A. I.; Chipanina, N. N.; Zelbst, E. A. Heteroat. Chem. 2006, 17, 567. (u) Maaranen, J.; Andell, O. S.; Vanne, T.; Mutikainen, I. J. Organomet. Chem. 2006, 691, 240. (v) Couzijn, E. P. A.; Ehlers, A. W.; Schakel, M.; Lammertsma, K. J. Am. Chem. Soc. 2006, 128, 13634. (2) (a) Yamamura, M.; Kano, N.; Kawashima, T.; Matsumoto, T.; Harade, J.; Ogawa, K. J. Org. Chem. 2008, 73, 8244. (b) Liu, Y.; Steiner, S. A., III; Spahn, C. W.; Guzei, I. A.; Toulokhonova, I. S.; West, R. Organometallics 2007, 26, 1306. (c) Wagler, J.; Gerlach, D.; Bo¨hme, U.; Roewer, G. Organometallics 2006, 25, 2929. (d) Yamaguchi, S.; Akiyama, S.; Tamao, K. J. Organomet. Chem. 2002, 652, 3. (e) Muguruma, C.; Koga, N.; Hatanaka, Y.; El-Sayed, I.; Mikami, M.; Tanaka, M. J. Phys. Chem. A 2000, 104, 4928. (f) El-Sayed, I.; Hatanaka, Y.; Onozawa, S.; Tanaka, M. J. Am. Chem. Soc. 2001, 123, 3597.

nucleophile-catalyzed hydrolysis of alkoxysilanes,3 basecatalyzed trans-silylation reactions,4 disproportionation of disilanes,5 ionic dissociation of Si-halogen bonds,6 and even activation of Si-C bonds for allyl shift reactions between allyl silanes and aldehydes,7 Si-C bond cleavage by hydroxylic chelating ligands,8 Pd-catalyzed cross-coupling reactions with arylsilanes,9 ring-opening reactions of silacyclobutanes,10 and the thermal rearrangement of silicon-bound silyl groups.11 Furthermore, the tendency of silanes to increase the coordination (3) (a) Corriu, R. J. P.; Leclercq, D.; Vioux, A.; Pauthe, M.; Phalippou, J. In Ultrastructure Processing of AdVanced Ceramics; Mackenzie, J. D., Ulrich, D. R., Eds.; Wiley: New York, 1988; p 113. (b) Corriu, R. J. P.; Leclercq, D. Angew. Chem., Int. Ed. 1996, 35, 1420. (4) (a) Nahar-Borchert, S.; Kroke, E.; Corriu, R. J. P.; Boury, B.; Riedel, R. J. Organomet. Chem. 2003, 686, 127. (b) Riedel, R.; Kroke, E.; Greiner, A.; Gabriel, A. O.; Ruwisch, L.; Nicolich, J.; Kroll, P. Chem. Mater. 1998, 10, 2964. (5) (a) Trommer, K.; Herzog, U.; Schulze, N.; Roewer, G. Main Group Met. Chem. 2001, 24, 425. (b) Herzog, U.; Schulze, N.; Trommer, K.; Roewer, G. Main Group Met. Chem. 1999, 22, 19. (6) (a) Schley, M.; Wagler, J.; Roewer, G. Z. Anorg. Allg. Chem. 2005, 631, 2914. (b) Wagler, J.; Bo¨hme, U.; Brendler, E.; Roewer, G. Z. Naturforsch. B 2004, 59, 1348. (c) Kalikhman, I.; Krivonos, S.; Lameyer, L.; Stalke, D.; Kost, D. Organometallics 2001, 20, 1053. (d) Kost, D.; Kingston, V.; Gostevskii, B.; Ellern, A.; Stalke, D.; Walfort, B.; Kalikhman, I. Organometallics 2002, 21, 2293. (7) (a) Sato, K.; Kira, M.; Sakurai, H. J. Am. Chem. Soc. 1989, 111, 6429. (b) Aoyama, N.; Hamada, T.; Manabe, K.; Kobayashi, S. J. Org. Chem. 2003, 68, 7329. (c) Kobayashi, S.; Ogawa, C.; Konishi, H.; Sugiura, M. J. Am. Chem. Soc. 2003, 125, 6610. (d) Chemler, S. R.; Roush, W. R. J. Org. Chem. 2003, 68, 1319. (e) Kira, M.; Zhang, L. C.; Kabuto, C.; Sakurai, H. Organometallics 1998, 17, 887. For related reactions see: (f) Yamamura, M.; Kano, N.; Kawashima, T. J. Organomet. Chem. 2007, 692, 313. (g) Kano, N.; Yamamura, M.; Kawashima, T. J. Am. Chem. Soc. 2004, 126, 6250. (8) (a) Richter, I.; Penka, M.; Tacke, R. Organometallics 2002, 21, 3050. (b) Tacke, R.; Heermann, J.; Pu¨lm, M.; Richter, I. Organometallics 1998, 17, 1663. (9) (a) Wolf, C.; Lerebours, R. Org. Lett. 2004, 6, 1147. (b) Seganish, W. M.; DeShong, P. J. Org. Chem. 2004, 69, 1137. (c) Mowery, M. E.; DeShong, P. J. Org. Chem. 1999, 64, 3266. (10) Gostevskii, B.; Kalikhman, I.; Tessier, C. A.; Panzner, M. J.; Youngs, W. J.; Kost, D. Organometallics 2005, 24, 5786. (11) (a) Wagler, J.; Bo¨hme, U.; Roewer, G. Organometallics 2004, 23, 6066. (b) Kummer, D.; Chaudhry, S. C.; Depmeier, W.; Mattern, G. Chem. Ber. 1990, 123, 2241. (12) (a) Wagler, J.; Hill, A. F. Organometallics 2008, 27, 6579. (b) Wagler, J.; Hill, A. F. Organometallics 2007, 26, 3630. (c) Metz, S.; Burschka, C.; Tacke, R. Eur. J. Inorg. Chem. 2008, 4433. (d) Metz, S.; Burschka, C.; Platte, D.; Tacke, R. Angew. Chem., Int. Ed. 2007, 46, 7006.

10.1021/om801049q CCC: $40.75  2009 American Chemical Society Publication on Web 12/19/2008

622 Organometallics, Vol. 28, No. 2, 2009 Scheme 1

Lippe et al. Scheme 3

Scheme 2

Results and Discussion

number of the Si atom may also activate Si-bonded heterocycles.12 However, diminished reactivity due to the higher coordination number of the Si center may also be observed, as shown by Kawashima et al.13 From our investigations of hexa- and pentacoordinate silicon complexes bearing tetradentate ONNO and tridentate ONO′ o-iminomethylphenolato ligands I and II, respectively, we reported UV-initiated rearrangement reactions14 and thermal rearrangement of allyl groups15 (Scheme 1). These shift reactions have been observed with the ONNO tetradentate ligand system I, which generally gives rise to the formation of hexacoordinate silicon complexes. We have also shown that these reactivity patterns may be due to either Si hexacoordination in precursors (or intermediates) or Si pentacoordination in the rearrangement products, since they were not observed in complexes with the related tridentate ONO′ ligand II (Scheme 2).16 The 1,3-shift reactions between the ONNO ligand I and various silanes (Scheme 1) were found to occur with high diastereoselectivity with regard to the relative configuration of the Si atom and the attacked (former imine) C atom in the rearrangement products, and alkyl vs aryl selectivity regarding the UV-initiated Si-C bond cleavage in hexacoordinate diorganosilanes was also observed. However, the symmetric ONNO ligand system I does not allow for regioselectivity studies with respect to two chemically different imine moieties within one tetradentate ligand backbone. Herein we report the synthesis of a new tetradentate (ONN′O′) ligand bearing two chemically and sterically different imine moieties and its reactions with various chlorosilanes. (13) Kobayashi, J.; Ishida, K.; Kawashima, T. Silicon Chem. 2002, 1, 351. (14) Wagler, J.; Doert, Th.; Roewer, G. Angew. Chem., Int. Ed. 2004, 43, 2441. (15) Wagler, J.; Roewer, G. Z. Naturforsch., B 2006, 61, 1406. (16) (a) Wagler, J. Organometallics 2007, 26, 155. (b) Wagler, J.; Brendler, E. Z. Naturforsch., B 2007, 62, 225.

As reported by Atkins et al.,17 the reaction of o-phenylenediamine and 2-hydroxybenzophenones in the presence of triethyl orthoformate and piperidine gives rise to N-(o-aminophenyl)2-hydroxybenzophenoneimines, which can be converted into ONNO ligand systems by a second equivalent of the hydroxybenzophenone and into ONN′O′ ligand systems by reaction with 2-hydroxybenzaldehydes. These procedures allowed the syntheses of compounds 1,18 2, and 3 (Scheme 3). Single-crystal X-ray diffraction analyses of 2 and 3 (Tables 1 and 2) already reveal some differences between these symmetric and nonsymmetric ONNO and ONN′O′ chelators, respectively. In contrast to the ethylene-bridged salen-type ONNO ligands, which often exhibit an inverse symmetric arrangement,19 the rigid o-phenylene bridge of these salphen-type ligands 2 and 3 forces the o-iminomethylphenol moieties to remain in closer proximity to one another. In contrast with the only slight distortions of the two ON chelates out of an idealized tetradentate ONNO plane (together with the almost planar o-phenylenediimine moiety) in some symmetric salicylaldimine-derived salphen ligands,20 the sterically more demanding benzophenoneimine moiety of 2 and 3 forces these ligands to a more pronounced distortion. In the case of the ONNO ligand 2 both benzophenoneimine moieties express the same steric requirements, which results in a C2-symmetric shape of the ligand (straddling a 2-fold axis in the crystal structure, space group P2/c). The noticeably different ON chelates of compound 3 allow for an almost planar ONN′ chelate arrangement of the salicylaldimine moiety together with the benzophenoneimine nitrogen atom, whereas the idealized plane of the hydroxybenzophenoneimine (ON) chelate is still twisted out of the o-phenylenediimine plane as in compound 2. Despite these distortions both compounds maintain the O-H-N hydrogen bridge within each ON chelate. The reaction of 3 with dichlorodiphenylsilane yielded the hexacoordinate Si complex 4 (Scheme 4, Figure 1), which (17) Atkins, R.; Brewer, G.; Kokot, E.; Mockler, G. M.; Sinn, E. Inorg. Chem. 1985, 24, 127. (18) Lippe, K.; Gerlach, D.; Kroke, E.; Wagler, J. Inorg. Chem. Commun. 2008, 11, 492. (19) (a) Darensbourg, D. J.; Billodeaux, D. R. Inorg. Chem. 2005, 44, 1433. (b) Plitt, P.; Pritzkow, H.; Oeser, T.; Kra¨mer, R. J. Inorg. Biochem. 2005, 99, 1230. (20) (a) Kabak, M.; Elmali, A.; Elerman, Y.; Durlu, T. N. J. Mol. Struct. 2000, 553, 187. (b) Kanappan, R.; Tanase, S.; Tooke, D. M.; Spek, A. L.; Mutikainen, I.; Turpeinen, U.; Reedijk, J. Polyhedron 2004, 23, 2285. (c) Elerman, Y.; Elmali, A.; Kabak, M.; Aydin, M.; Peder, M. J. Chem. Crystallogr. 1994, 24, 603.

Organosilicon Complexes of an ONN′O′ Ligand

Organometallics, Vol. 28, No. 2, 2009 623

Table 1. Crystal Data and Experimental Parameters for the Crystal Structure Analyses of 2, 4 · CHCl3, 6, and 8aa CCDC no. empirical formula Mw collecn T, K cryst syst space group a, Å b, Å c, Å β, deg V, Å3 Z Fcalcd, Mg/m3 F(000) θmax, deg no. of collected rflns no. of indep rflns no. of indep rflns (I > 2 σ(I)) Rint no. of params GOF R1, wR2 (I > 2σ(I)) R1, wR2 (all data) max, min resid electron dens (e Å-3) a

2

4 · CHCl3

6

8a

659391 C34H28N2O4 528.58 93(2) monoclinic P2/c 12.5225(10) 8.4242(7) 13.9239(10) 112.577(3) 1356.29(18) 2 1.294 556 28.0 16 715 3275 2945 0.0186 185 1.072 0.0357, 0.0952 0.0400, 0.0979 0.342, -0.185

659386 C40H31Cl3N2O3Si 722.11 90(2) monoclinic P21/n 10.8202(11) 25.228(2) 13.0459(12) 104.665(6) 3445.2(6) 4 1.392 1496 26.0 46 978 6761 4361 0.1048 443 1.015 0.0566, 0.1494 0.1055, 0.1700 0.577, -0.660

659388 C36H30N2O3Si 566.71 90(2) orthorhombic Pbca 16.553(1) 14.905(1) 22.785(2) 90 5621.7(7) 8 1.339 2384 25.0 11 865 4949 3590 0.0566 381 0.923 0.0427, 0.0942 0.0813, 0.1025 0.317, -0.520

706853 C40H32N2O4Si 632.77 90(2) orthorhombic Pbca 18.6908(4) 17.3692(4) 19.7167(5) 90 6400.9(3) 8 1.313 2656 40.0 177 492 19 826 15 007 0.0341 426 1.098 0.0389, 0.1098 0.0629, 0.1205 0.696, -0.357

Radiation used: Mo KR, λ ) 0.710 73 Å.

Table 2. Crystal Data and Experimental Parameters for the Crystal Structure Analyses of 3, 5a · CHCl3, and 7 · CHCl3a 5a · CHCl3

7 · CHCl3

659385 C27H22N2O3 422.47 triclinic P1j 8.7939(11) 9.7102(12) 13.0745(13) 83.201(5) 71.011(5) 84.206(5) 1045.9(2) 2 1.341 444 28.0 23 856 4966 3848

659389 C40H31Cl3N2O3Si 722.11 triclinic P1j 10.9840(6) 13.4905(3) 13.6978(3) 119.198(1) 98.988(2) 98.715(2) 1687.93(11) 2 1.421 748 30.0 25 162 9728 7728

659387 C34H27Cl3N2O3Si 646.02 triclinic P1j 10.7243(8) 11.4283(9) 13.9199(10) 95.262(4) 90.622(4) 116.653(4) 1515.7(2) 2 1.415 668 30.0 21 215 8814 6599

0.0243 298 1.081 0.0436, 0.1217 0.0606, 0.1304 0.319, -0.223

0.0234 447 1.334 0.0424, 0.1246 0.0579, 0.1308 0.527, -0.570

0.0456 434 1.058 0.0483, 0.1390 0.0662, 0.1470 0.638, -0.820

3 CCDC no. empirical formula Mw cryst syst space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Fcalcd, Mg/m3 F(000) θmax, deg no. of collected rflns no. of indep rflns no. of indep rflns (I > 2σ(I)) Rint no. of params GOF R1, wR2 (I > 2σ(I)) R1, wR2 (all data) max, min resid electron dens (e Å-3) a

Radiation used: Mo KR, λ ) 0.710 73 Å. T ) 90(2) K.

exhibits a distorted-octahedral coordination sphere about the silicon atom. Although the tetradentate ligand occupies the four equatorial positions and the relative orientation of the two axially Si-bound phenyl groups is very similar to their arrangement in the analogous complex of ligand I, the asymmetric ligand system causes some differences in the Si coordination sphere. Whereas the mirror symmetric molecule I-SiPh221 has bond lengths N-Si ) 1.958(2), Si-O ) 1.763(1), and Si-C ) 1.967(3) and 1.955(3) Å, the Si-N bonds in 4 are somewhat longer (Si1-N1 ) 1.966(2), Si1-N2 ) 1.986(3) Å). The silicon-oxygen bond lengths (Si1-O1 ) 1.758(2), Si1-O2 ) 1.763(2) Å) are (21) Wagler, J.; Bo¨hme, U.; Brendler, E.; Blaurock, S.; Roewer, G. Z. Anorg. Allg. Chem. 2005, 631, 2907.

Figure 1. Molecular structure of 4 in the crystal of 4 · CHCl3 (ORTEP diagram with 50% probability ellipsoids, hydrogen atoms and chloroform molecule omitted, selected atoms labeled).

essentially similar to those in I-SiPh2, and the Si-C bonds appear slightly shorter (Si1-C27 ) 1.960(3), Si1-C33 ) 1.946(3) Å), however, within the limits of their standard errors. In this tetradentate ligand system the salicylaldimine moiety, which forms the shorter silicon-nitrogen bond, would appear to be a better donor. In the 29Si NMR spectrum compound 4 has a signal at -168.7 ppm, which is shifted significantly downfield with respect to the 29Si NMR signal of the structurally related compound I-SiPh2 (-177.6 ppm). The o-phenylene bridge within the ligand system 3 is presumably the major origin of this downfield shift, as it has also been shown for other hypercoordinate silicon complexes that an o-phenylene instead of an ethylene bridge within a five-membered chelate causes a significant shift of the 29 Si NMR signal to lower field.22 In addition to the signal at -168.7 ppm, characteristic of a hexacoordinate Si complex, another (smaller) resonance appears at -37.7 ppm, characteristic (22) One hexacoordinate silicon compound from ref 2c bearing a bidentate ethylene-bridged NN ligand exhibits a 29Si NMR shift of-177.2 ppm, whereas an analogous complex with a phenylene-bridged NN ligand but similar bonding properties around the Si atom1m has a 29Si NMR signal at-165.3 ppm.

624 Organometallics, Vol. 28, No. 2, 2009

Lippe et al.

Scheme 4

Figure 2. Molecular structure of 5a in the crystal of 5a · CHCl3 (ORTEP diagram with 50% probability ellipsoids, most hydrogen atoms and chloroform molecule omitted, selected atoms labeled).

of Si compounds bearing a Ph2Si(O-aryl)2 silicon environment. This signal arises from the isomer 4a bearing a tetracoordinate silicon atom. Compounds 4 and 4a coexist in an equilibrium, which can also be monitored by 1H NMR behavior of the signals of the methoxy groups (4, 3.80 ppm, 4a, 3.25 ppm). Upon heating, the intensity of the signals of 4a increases, reverting to the initial ratio (4:4a ) ca. 4:1) after cooling the solution to room temperature. However, equilibration is slow (not fully achieved within 30 min), and therefore, kinetic and thermodynamic investigations of this equilibrium by VT-NMR experiments were undertaken. (Whereas rapid equilibration in systems with bi- and even tridentate chelating ligand systems has been observed,16b,23 sometimes even rapid exchange on the NMR time scale, this equilibration 4 vs 4a seems to be hindered by the rigid π-conjugated tetradentate ligand system.) From VT NMR experiments the thermodynamic parameters ∆H ) -65.3 kJ mol-1 and ∆S ) -209 J mol-1 K-1 were estimated for the transition from the four- to the six-coordinate silicon complex. The above data, which correspond to the formation of two formally dative Si-N bonds, are in accord with the data reported from one of our previous studies (∆H ) -31.5 kJ mol-1 and ∆S ) -116.7 J mol-1 K-1 for the formation of one such bond).23a Upon dissolution of 4 in CDCl3 the equilibrium was established slowly, thus enabling us to also estimate the activation parameters ∆Hq ) 159 kJ mol-1 and ∆Sq ) 205 J mol-1 K-1. (For details see the Supporting Information.) As reported for hexacoordinate diorganosilanes with the symmetric ethylene-bridged tetradentate ONNO ligand I,14 compound 4 can also undergo UV-induced rearrangement of a phenyl group to an imine carbon atom. Irradiation of a suspension of 4 in THF with UV resulted in the diastereoselective formation of 5a (Scheme 4). This isomer was identified as the only product by 29Si NMR spectroscopy of the crude (23) (a) Wagler, J.; Bo¨hme, U.; Brendler, E.; Roewer, G. Organometallics 2005, 24, 1348. (b) Kalikhman, I.; Gostevskii, B.; Botoshansky, M.; Kaftory, M.; Tessier, C. A.; Panzner, M. J.; Youngs, W. J.; Kost, D. Organometallics 2006, 25, 1252. (c) Gostevskii, B.; Silbert, G.; Adear, K.; Sivaramakrishna, A.; Stalke, D.; Deuerlein, S.; Kocher, N.; Voronkov, M. G.; Kalikhman, I.; Kost, D. Organometallics 2005, 24, 2913.

Figure 3. Molecular structure of 6 in the crystal (ORTEP diagram with 50% probability ellipsoids, most hydrogen atoms omitted, selected atoms labeled).

product solution, and its configuration has been proven by single-crystal X-ray diffraction analysis (Figure 2). As found for such UV-initiated rearrangement reactions, the shifted substituent remains on the initial side of the idealized plane with respect to the tetradentate chelate (O1,N1,N2,O2). In the case of the above reaction the phenyl group is selectively shifted to the former salicylaldimine carbon atom C7. Reactions of 3 with both allylphenyldichlorosilane and phenyldichlorosilane24 resulted in the instant formation of rearrangement products bearing pentacoordinate silicon atoms (6 and 7, respectively; Scheme 4). In both cases 29Si NMR spectroscopy of the crude product solution proved the formation of only one silicon complex each. (Within the s/n limits of the spectra obtained, the presence of another isomer up to an amount of 5% with respect to the main product cannot be excluded.) Their crystal structures (Tables 1 and 2) reveal the selective allyl and hydrogen shift to the former salicylaldimine carbon atom C7. In contrast with 5a, which bears the migrated phenyl group on the opposite side of the idealized plane of the tetradentate ligand (anti), the allyl group in 6 is syn to the Si-bonded phenyl group (Figure 3). A possible mechanistic reason for that diastereoselectivity has been discussed previously.15 The hydrosilylation reaction between 3 and phenyldichlorosilane with formation of 7 (Scheme 4) does not allow for (24) Hydrosilylation of imine24a and diazo ligands24b has recently been reported by other groups: (a) Kertsnus-Banchik, E.; Kalikhman, I.; Gostevskii, B.; Deutsch, Z.; Botoshansky, M.; Kost, D. Organometallics 2008, 27, 5285. (b) Yamamura, M.; Kano, N.; Kawashima, T. Tetrahedron Lett. 2007, 48, 4033.

Organosilicon Complexes of an ONN′O′ Ligand Scheme 5

distinction between syn and anti diastereoselectivity of this hydrogen shift reaction. Therefore, ligand 2 was reacted with phenyldichlorosilane under the same conditions (Scheme 5). 29Si NMR spectroscopy of the product mixture revealed the formation of two compounds (8a and 8b) bearing pentacoordinate silicon atoms (δ(29Si) -104.4 and -105.1 ppm, ratio 10:1. Hence, hydrosilylation of 2 appears to be much more diastereoselective than hydrosilylation of the ethylene-bridged ligand I.25) The major product of the 8a/8b mixture was crystallized from acetonitrile. X-ray diffraction analysis (Table 3) revealed the predominant formation of 8a, adding this hydrosilylation to the reactions producing the syn addition products. The molecular structure of 8a is closely related to that of 5a, the major differences being in the torsion of the Si-bound phenyl group due to packing effects and the presence of a second methoxy group at the ligand backbone. Recently, Kost et al. reported the reactions between hypercoordinate chlorosilicon complexes and trimethylsilyl cyanide, which gave rise to the formation of hypercoordinate cyano silicon complexes and such bearing a cyano-functionalized former imine carbon atom (Scheme 6).26 Therefore, we also investigated the cyano functionalization of our ONN′O′ ligand system. Reaction of 3 with triethylamine and chlorotrimethylsilane (TMS-Cl) gave rise to the TMS derivative 9, which was then treated with phenyltrichlorosilane to yield 10 (Scheme 7). Compound 10 has a hexacoordinate silicon atom in the solid state (δiso(29Si) -166.3 ppm) and exhibits poor solubility in chloroform. The Si-Cl bond of 10 can be activated by addition of SnCl4 to 10 in chloroform to yield a solution of 11. The cation of 11 in chloroform has a 29Si NMR signal at -111.3 ppm, which is shifted somewhat upfield with respect to the signals of the other phenylsilicon compounds 5a, 6, 7, and 8a (25) Hydrosilylation experiments have not been reported for ligand system I so far. In test reactions involving I-H2 and PhHSiCl2 (or MeHSiCl2) a striking lack of diastereoselectivity was found: in THF (20 mL) ligand I (1.0 g, 2.1 mmol) and triethylamine (0.80 g, 7.9 mmol) were stirred at 0 °C and phenyldichlorosilane (0.38 g, 2.2 mmol) was added dropwise. After 15 min the reaction mixture was filtered, the hydrochloride precipitate was washed with THF (5 mL), and the volatiles were removed from the filtrate under vacuum to yield a yellow foam. This crude product was dissolved in CDCl3 and analyzed by 29Si NMR (-113.3 and-114.9 ppm), 1H NMR (4.88 and 5.06 ppm for HC(N,Ar,Ph)), and 13C NMR spectroscopy (67.2 and 69.1 ppm for C(N,H,Ph,Ar)) to reveal the hydrosilylation of one imine bond under formation of a mixture of two diastereomeric pentacoordinate silicon complexes in the ratio 3:2. Following the same procedure but using methyldichlorosilane instead of phenyldichlorosilane, two diastereomers formed in the ratio 1:1 with their characteristic NMR shifts for the hydrosilylation products: 29Si-101.6.-102.6 ppm; 13C 66.8, 69.0 ppm; 1H 4.80, 4.94 ppm. In the case of the hydrosilylation reaction with methyltrichlorosilane, the product mixture also contained notable amounts (ca. 8%) of the siliconium chloride (ONNO)SiMe+Cl- (structure and spectroscopic data reported in ref 6b), which can be isolated by dissolving the crude product mixture in toluene (5 mL) to yield this byproduct as a white precipitate. (26) Kalikhman, I.; Gostevskii, B.; Kertsnus, E.; Botoshansky, M.; Tessier, C. A.; Youngs, W. J.; Deuerlein, S.; Stalke, D.; Kost, D. Organometallics 2007, 26, 2652.

Organometallics, Vol. 28, No. 2, 2009 625 Table 3. Crystal Data and Experimental Parameters for the Crystal Structure Analyses of 11 · 0.5CHCl3, 12b, and 14 · 2CHCl3a CCDC no. empirical formula Mw cryst syst space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Fcalcd, Mg/m3 F(000) θmax, deg no. of collected rflns no. of indep rflns no. of indep rflns (I > 2σ(I)) Rint no. of params GOF R1, wR2 (I > 2σ(I)) R1, wR2 (all data) max, min resid electron dens (e Å-3) a

11 · 0.5CHCl3

12b

14 · 2CHCl3

659390 C33.5H25.5Cl6.5N2O3SiSn 881.26 triclinic P1j 10.5139(5) 11.3706(5) 15.7917(7) 91.089(3) 107.730(3) 90.590(3) 1797.64(14) 2 1.628 878 35.0 87 854 15 833 11 719

706854 C34H25N3O3Si 551.66 monoclinic P21/c 13.0425(7) 10.0955(5) 20.6130(11) 90 95.221(2) 90 2702.9(2) 4 1.356 1152 27.0 23 869 5894 4076

706855 C40H36Cl6N2O5Si 865.50 triclinic P1j 10.5362(2) 12.6828(3) 15.1854(3) 80.085(1) 80.628(1) 80.941(1) 1954.65(7) 2 1.471 892 25.0 21 696 6648 4860

0.0385 477 1.121 0.0324, 0.0751 0.0648, 0.0862 0.934, -1.151

0.0573 371 1.022 0.0435, 0.0963 0.0752, 0.1057 0.348, -0.392

0.0406 564 1.098 0.0482, 0.1183 0.0755, 0.1279 0.460, -0.514

Radiation used: Mo KR, λ ) 0.710 73 Å. T ) 90(2) K.

Scheme 6

Scheme 7

(δ(29Si) ca. -104 ppm) but clearly indicates pentacoordination of the Si atom. Compound 10 was treated with KCN in CDCl3 in the presence of 18-crown-6 to yield the mixture of diastereomers 12a/12b, which gives rise to two 29Si NMR signals (δ(29Si) -105.1 and -105.9) in the ratio 2:1 (Scheme 8). Hexacoordinate silicon complexes of the type (ONN′O′)Si(R)(CN) were not observed. The regioselective attack of the cyanide at the salicylaldimine carbon atom was concluded from the 13C NMR shifts of the (R,aryl,N,CN) substituted carbon atoms (δ(13C) 47.9 and 48.8 in the ratio 1:2), which are similar to one another and match the chemical shift range for R ) H. One of these diastereomers (12b) crystallized from the chloroform solution (Figure 4). NMR spectroscopy (29Si, 13C, 1H) of this predominant product revealed its purity.

626 Organometallics, Vol. 28, No. 2, 2009 Scheme 8

Scheme 9

To obtain more information about the syn vs anti product selectivity in these reactions with external nucleophiles, 10 was also treated with phenyllithium as a C-nucleophilic reagent (Scheme 9). The product mixture contained both diastereomers 5a and 5b, with the former being the major product (δ(29Si) -104.3 and -104.9 ppm, ratio 2:1). In sharp contrast to the cyanide addition favored in syn fashion, these data suggest the favored formation of the antisubstituted products (referring to the relative positions of the Si-bonded carbon substituent and the carbanionic nucleophile). Furthermore, no indication was found for the formation of 4, which would be inert once it had formed (unless irradiated with UV). This result suggests that the C-nucleophilic attack at complexes such as 10 occurs via direct approach of the C-nucleophile toward the imino carbon atom and not via initial

Figure 4. Molecular structure of 12b in the crystal (ORTEP diagram with 50% probability ellipsoids, most hydrogen atoms omitted, selected atoms labeled).

Lippe et al. Scheme 10

C vs Cl substitution at the silicon atom. The discrepancy between the diastereoselectivities of the aforementioned nucleophilic attacks can be attributed to solvent effects. Whereas the reaction with cyanide was performed in chloroform, phenyllithium was added in THF. Hydrogen bridge donors (such as chloroform and dichloromethane) have already been shown to support ionic dissociation of hexacoordinate silicon compounds.6 Thus, one can expect contributions of pentacoordinate siliconium ions such as 11+ to the overall mechanism of the reaction with cyanide, whereas such ions should play a less pronounced role in thf solution (Scheme 10). In order to obtain structural information about the siliconium ion 11+, its pentachlorostannate salt 11 was prepared by addition of SnCl4 to 10 in chloroform and the structure was determined by X-ray diffraction analysis (Figure 5). As in 5a and related compounds, the Si atom of 11 is situated in a distorted-trigonal-bipyramidal coordination sphere. The pentachlorostannate counterion is not part of the Si coordination sphere; only one of its chlorine atoms points toward the silicon center but remains remote (separation Si1 · · · Cl1 ) 3.901(1) Å). In contrast with the neutral complexes 5a, 6, 7, 8a, and 12b the ONN′O′ ligand is arranged in a different manner in 11. The salicylaldimine N atom occupies an axial position and the benzophenoneimine N atom an equatorial position. For comparison selected bond lengths and angles of the Si coordination spheres of all pentacoordinate Si complexes presented herein are given in Table 4. Whereas 5a and related compounds bear both a short covalent Si1-N1 bond and a much longer (formally dative) Si1-N2 bond, the silicon-nitrogen bond lengths of the cation of 11 are rather similar to one another. Differences between them might be explained by the axial vs equatorial positions of the respective N atom in the Si coordination sphere. For example, Akiba et al. reported NfP π-donation in the equatorial plane of pentacoordinate phosphoranes: the O-P σ* MO of an equatorially situated oxygen atom enhances the equatorial NfP π-interaction.27 The relative proportions of the axial vs equatorial Si-O (1.664(2) and 1.730(2) Å) and Si-N (1.846(2) and 1.937(2) Å) bond lengths in the complex I-SiMe+ 6b are similar to those in the cation 11+. Even the Si-C bond lengths (1.848(3) Å in I-SiMe+) are similar, although 11 bears a silicon-bonded phenyl group. In cation 11+, however, the equatorial angle O1-Si1-N2 (129.7(1)°) is noticeably wider than the analogous angle in the cation I-SiMe+ (115.8(1)°). This significant geometrical difference may be a result of the rigid o-phenylene bridge in the tetradentate ligand backbone of compound 11. In contrast to the case for the hexacoordinate Si compound 4 with a rather planar arrangement of the ONN′O′ ligand, the planes of the ON and O′N′ chelates are folded toward one another in 11+, thus (27) Adachi, T.; Matsukawa, S.; Nakamoto, M.; Kajiyama, K.; Kojima, S.; Yamamoto, Y.; Akiba, K.; Re, S.; Nagase, S. Inorg. Chem. 2006, 45, 7269.

Organosilicon Complexes of an ONN′O′ Ligand

Organometallics, Vol. 28, No. 2, 2009 627

Table 4. Selected Bond Lengths (Å) and Angles (deg) of the Structures of 5a, 6, 7, 8a, 11, 12b, and 14a Si1-C28 Si1-N1 Si1-N2 Si1-O1 Si1-O2 N1-C7 N2-C20 N1-Si1-O2 N2-Si1-O1 N1-Si1-C28 N2-Si1-C28 O1-Si1-C28 O2-Si1-C28 a

5a

6

7

8a

11

12b

14

1.873(2)e 1.760(1)e 2.016(1)a 1.717(1)a 1.702(1)e 1.473(2) 1.318(2) 131.9(1)e 161.1(1)a 116.1(1)e 92.5(1) 99.0(1) 110.9(1)e

1.885(2)e 1.755(1)e 2.040(1)a 1.724(1)a 1.685(1)e 1.479(2) 1.318(2) 127.9(1)e 171.9(1)a 118.0(1)e 91.7(1) 96.4(1) 113.2(1)e

1.872(2)e 1.741(1)e 2.054(1)a 1.708(1)a 1.681(1)e 1.473(2) 1.306(2) 122.0(1)e 177.8(1)a 120.8(1)e 86.9(1) 95.0(1) 115.3(1)e

1.875(1)e 1.759(1)e 2.019(1)a 1.714(1)a 1.701(1)e 1.471(1) 1.314(1) 127.8(1)e 169.4(1)a 117.3(1)e 90.4(1) 99.3(1) 113.6(1)e

1.855(2)e 1.951(1)a 1.855(1)e 1.673(1)e 1.714(1)a 1.293(2) 1.338(2) 169.1(1)a 129.7(1)e 94.3(1) 115.0(1)e 114.9(1)e 95.1(1)

1.865(2)e 1.755(1)e 2.037(2)a 1.722(1)a 1.675(1)e 1.454(2) 1.309(2) 123.3(1)e 174.6(1)a 117.8(1)e 89.8(1) 95.1(1) 117.8(1)e

1.872(3)e 1.746(2)e 2.046(2)a 1.719(2)a 1.687(2)e 1.479(3) 1.312(3) 121.5(1)e 175.9(1)a 119.5(1)e 87.7(1) 96.4(1) 117.0(1)e

Axial and equatorial bonds and angles are indicated by superscript a and e, respectively. For 8a, C20 and C28 are C27 and C35, respectively.

Figure 5. Molecular structure of 11 in the crystal of 11 · 0.5CHCl3 (ORTEP diagram with 50% probability ellipsoids, hydrogen atoms and chloroform molecule omitted, selected atoms labeled). Scheme 11

supporting nucleophilic attacks in a syn fashion with respect to the Si-bound phenyl group. Finally, the electron-donating effect of the benzophenonebound methoxy group on the pronounced regioselectivity of above reactions had to be ruled out. Therefore, ligand 13, containing a dimethoxy-substituted salicylaldimine moiety, was prepared in analogy to 3 (Scheme 3) and, in a representative reaction with allylphenyldichlorosilane, also yielded a product (14) which still underlines regioselectivity for reaction at the salicylaldimine carbon atom (Scheme 11). The molecular structure of 14, which has been determined crystallographically (Table 3), is similar to that of its analogue 6 (for bonding parameters see Table 4) and is therefore not further discussed in this context. Compound 14 was isolated in 59% yield. 29Si NMR spectroscopy of the residual product solution provided no evidence for the formation of any pentacoordinate silicon complex other than 14.

Conclusions The tetradentate ligand system of compound 3 enabled us to elucidate both diastereo- and regioselectivity aspects of rearrangement reactions between various silanes and a tetradentate (ONN′O′) diimine donor system. In addition to organylation reactions, we report hydrosilylation of an imine moiety of such

tetradentate ligand systems for the first time.24,25 Generally, the sterically more demanding benzophenoneimine site remains innocent and the salicylaldimine moiety is altered by 1,3-shift reactions such as allyl transfer, hydrosilylation, and UV-induced 1,3-shift of a phenyl group. Whereas these 1,3-shift reactions of the formal Si-bonded anionic nucleophiles “allyl-”, “H-”, and “Ph-” are very diastereoselective in most cases, reactions of the chlorosilicon complex (ONN′O′)SiPhCl with external nucleophiles (PhLi, KCN) are much less diastereoselective; however, regioselective attack of the salicylaldimine carbon atom was also observed for these reactions. Thus, the pronounced diastereoselectivity of the 1,3-shift reactions reported herein points to nonionic transfer mechanisms. Ligand-dependent differences in the diastereoselectivity were found between the ethylene-bridged ligand system I and the o-phenylene-bridged tetradentate ligand systems 2 and 3. Whereas hydrosilylation of I appeared rather nonselective,25 reaction of 2 with phenyldichlorosilane exhibited pronounced diastereoselectivity for the syn product. Allyl shifts and UVinduced 1,3-shifts of an organic substituent, however, occur diastereoselectively in both ethylene- and o-phenylene-bridged ligand systems. Whereas in the latter cases the high diastereoselectivity can be attributed to the predetermined molecular geometry prior to the UV-initiated organyl shift and cyclic transition states involving a hexacoordinate Si atom for the allyl transfer,7,15 the lower diastereoselectivities for the hydride 1,3shift reaction point to a rearrangement at an early stage of complex formation, the further development of which may then be determined by the flexibility of the tetradentate ligand system.

Experimental Section Syntheses were carried out under an inert atmosphere of dry argon using standard Schlenk techniques and dry solvents. 1H, 13C, and 29Si NMR spectra (solution) were recorded on a Bruker DPX 400 spectrometer using TMS as internal standard. 29Si CP/MAS spectra were recorded on a Bruker Avance 400WB spectrometer using a 7 mm rotor with KelF insert. Chemical shifts are also reported with TMS as the reference. Single-crystal X-ray diffraction analyses were carried out on a Bruker-Nonius X8 APEX2 CCD diffractometer using Mo KR radiation (λ ) 0.710 73 Å). The structures were solved with direct methods (all except 11 · 0.5CHCl3) and Patterson methods (11 · 0.5CHCl3) using SHELXS97. Structure refinement by full-matrix least-squares methods (refinement of F2 against all reflections) was carried out with SHELXL-97. All non-hydrogen atoms were anisotropically refined. C-bonded hydrogen atoms were placed in idealized positions and refined isotropically. The O-bonded hydrogen atoms in the structures of 2 and 3 were located on residual electron density maps and isotropically refined without restraints.

628 Organometallics, Vol. 28, No. 2, 2009 Synthesis of Compound 4. To a solution of 3 (4.00 g, 9.50 mmol) and triethylamine (2.29 g, 22.6 mmol) in 40 mL of THF (-10 °C) was added a solution of diphenyldichlorosilane (2.52 g, 9.90 mmol) in THF (10 mL) dropwise with stirring. The mixture was then stored at 8 °C for 2 h, and the triethylamine hydrochloride precipitate was filtered off and washed with 10 mL of THF. From the yellow filtrate the solvent was removed under vacuum and the resulting orange-yellow solid was recrystallized from 15 mL of chloroform. After 1 day the crystalline product 4 · CHCl3 was filtered, washed with chloroform (9 mL), and dried under vacuum. Yield: 4.46 g (6.20 mmol, 65%). 1H NMR (CDCl3): δ 3.79 (s, 3 H, OCH3), 6.00 (d, 1 H, ar, 3JHH ) 9.6 Hz), 6.18 (d, 1 H, ar, 3JHH ) 8.4 Hz), 6.28 (d, 1 H, ar, 3JHH ) 8.8 Hz), 6.35-7.80 (mm, 23 H, ar), 8.46 (s, 1 H, NdCH). 13C NMR (CDCl3): δ 55.5 (OCH3), 104.2, 107.4, 115.6, 116.2, 117.8, 119.3, 122.4, 124.2, 124.7, 125.5, 127.1, 127.5, 128.1, 129.0, 129.9, 133.7, 134.8, 135.3, 136.5, 137.3, 138.6, 138.8, 155.4, 158.2, 164.7, 166.8, 167.1, 168.4. 29Si NMR (CDCl3): δ -168.7. Anal. Found: C, 66.79; H, 4.32; N, 4.15. Calcd for C40H31N2O3SiCl3: C, 66.53; H, 4.33; N, 3.88. Synthesis of Compound 5a by UV Irradiation of 4. A stirred suspension of 4 · CHCl3 (2.42 g, 3.40 mmol) in 130 mL of THF (at 15 °C) was exposed to UV (medium-pressure Hg lamp, λmax 365-436 nm) for 5.5 h. From the resulting clear red solution the solvent was removed under vacuum, and the red solid product was recrystallized from 2 mL of chloroform. The red crystalline product 5a · CHCl3 was filtered, washed with chloroform (2 mL), and dried under vacuum. Yield: 1.32 g (1.80 mmol, 54.5%). 1H NMR (CDCl3): δ 3.93 (s, 3 H, OCH3), 5.91 (d, 1 H, ar, 3JHH ) 8.0 Hz), 6.00 (s, 1 H, NCH), 6.27 (d, 1 H, ar, 3JHH ) 6.8 Hz), 6.38 (d, 1 H, ar, 3JHH ) 8.8 Hz), 6.55 (d, 1 H, ar, 3JHH ) 9.2 Hz), 6.65-7.70 (mm, 22 H, ar). 13C NMR (CDCl3): δ 55.9 (OCH3), 61.9 (NCH), 103.8, 110.1, 112.0, 116.5, 116.9, 119.4, 119.6, 120.5, 126.2, 126.6, 126.7, 127.0, 128.2 (2×), 128.5, 129.0, 129.6, 129.8, 130.4, 130.8, 131.1, 133.1, 133.2, 136.4, 138.7, 143.5, 146.4, 154.6, 159.9, 165.5, 166.6. 29Si NMR (CDCl3): δ -104.2. Anal. Found: C, 66.27; H, 4.52; N, 4.15. Calcd for C40H31N2O3SiCl3: C, 66.53; H, 4.33; N, 3.88. Synthesis of Compounds 5a and 5b using Phenyllithium. To a suspension of 10 · 0.5(toluene) (0.38 g, 0.63 mmol) in 6 mL of THF (stirred at -78 °C) was added a 1.8 M solution of PhLi in cyclohexane/diethyl ether (70/30) (0.35 mL, 0.63 mmol) dropwise. The mixture was warmed to room temperature and was stirred for a further 6 h. From the resulting red solution the solvent was removed under reduced pressure and the crude product was dissolved in CDCl3 for 29Si NMR spectroscopy: δ -104.3 and -104.9 (ratio 2:1). Synthesis of Compound 6. To a -10 °C solution of 3 (0.50 g, 1.2 mmol) and triethylamine (0.29 g, 2.9 mmol) in THF (7 mL) was added a solution of allylphenyldichlorosilane (0.27 g, 1.2 mmol) in THF (3 mL) dropwise with stirring. The orange-red mixture was then stored at 8 °C for 2 h, whereupon the amine hydrochloride precipitate was filtered off and washed with 5 mL of THF. From the orange-red filtrate the solvent was removed under vacuum and the resulting orange-yellow solid was recrystallized from 1.7 mL of chloroform. After 1 day the crystals were filtered, washed with 2 mL of chloroform, and dried under vacuum. Yield: 0.40 g (0.59 mmol, 51%). This product contains 0.9 mol of CHCl3/mol of 6 in the crystals. From the filtrate the solvent was completely removed under vacuum and the solid residue was recrystallized from 0.4 mL of chloroform to yield further product (0.11 g, 0.17 mmol, 14%) with ca. 0.6 mol of CHCl3/mol of 6 in the crystals. The variable chloroform content originates from the simultaneous crystallization of solvent-free crystals of 6 and crystals bearing one molecule of chloroform per molecule of 6. Both compositions were identified by X-ray crystal structure analysis; however, only the crystals of the solvent-free compound were suitable for a satisfactory final structure refinement. 1H NMR (CDCl3): δ 2.77 (m, 2 H,

Lippe et al. CH2CHdCH2), 3.89 (s, 3 H, OCH3), 4.53 (m, 1 H, NCH), 5.03 (m, 2 H, CH2CHdCH2), 5.74 (m, 1 H, CH2CHdCH2), 5.86 (d, 1 H, ar, 3JHH ) 8.4 Hz), 6.29 (m, 1 H, ar), 6.37 (d, 1 H, ar, 3JHH ) 8.0 Hz), 6.55-7.55 (mm, 18 H, ar). 13C NMR (CDCl3): δ 38.3 (CH2CHdCH2), 55.7 (OCH3), 59.5 (NCH), 104.1, 109.2, 111.1, 116.1, 116.4, 116.8, 119.2, 120.0, 126.5, 127.0, 127.3, 127.5, 127.8, 128.1, 128.4, 128.5, 129.1, 129.4, 129.7, 129.9, 130.5, 130.7, 131.7, 133.1, 135.6, 136.0, 138.8, 145.4, 155.7, 159.0, 164.5, 165.9. 29Si NMR (CDCl3): δ -104.3. Anal. Found: C, 66.04; H, 4.82; N, 4.53. Calcd for 6 · 0.9CHCl3 (C36.9H30.9N2O3SiCl2.7): C, 65.74; H, 4.62; N, 4.16. Synthesis of Compound 7. To a -10 °C solution of 3 (0.50 g, 1.2 mmol) and triethylamine (0.29 g, 2.9 mmol) in THF (7 mL) was added a solution of phenyldichlorosilane (0.22 g, 1.2 mmol) in THF (3 mL) dropwise with stirring. The red mixture was then stored at 8 °C for 2 h, whereupon the amine hydrochloride precipitate was filtered off and washed with 4 mL of THF. From the red filtrate the solvent was removed under vacuum and the resulting orange-yellow solid was recrystallized from a mixture of 1.1 mL of chloroform and 0.1 mL of THF (the product remained dissolved in 1.1 mL of chloroform; crystallization commenced after addition of 0.1 mL of THF). The red crystals (average composition 7 · 0.9CHCl3 · 0.1THF; the THF content became obvious in 1H NMR spectra) were filtered off and dried under vacuum. Yield: 0.54 g (0.84 mmol, 71%). 1H NMR (CDCl3): δ 3.89 (s, 3 H, OCH3), 4.55 (d, 1 H, N-CH2, 2JHH ) 14.0 Hz), 4.71 (d, 1 H, NCH2, 2JHH ) 14.0 Hz), 5.86 (d, 1 H, ar, 3JHH ) 8.4 Hz), 6.27 (m, 1 H, ar), 6.37 (d, 1 H, ar, 3JHH ) 8.4 Hz), 6.60-7.60 (mm, 18 H, ar). 13C NMR (CDCl3): δ 47.8 (NCH2), 55.8 (OCH3), 59.5 (NCH), 104.3, 109.7, 110.7, 116.1, 116.5, 119.6 (2×), 119.9, 126.5, 127.0, 127.3, 128.3, 128.5, 129.1, 129.6, 130.1, 130.5, 132.6, 133.3, 136.0, 138.7, 146.4, 156.4, 159.4, 165.0, 166.1. 29Si NMR (CDCl3) δ -104.4. Anal. Found: C, 63.84; H, 4.41; N, 4.76. Calcd for 7 · 0.9CHCl3 · 0.1THF (C34.3H27.7N2O3.1SiCl2.7): C, 64.24; H, 4.35; N, 4.37. Synthesis of Compound 8a. To a -10 °C cold solution of 2 (3.00 g, 5.68 mmol) and triethylamine (1.80 g, 1.78 mmol) in THF (50 mL) was added phenyldichlorosilane (1.04 g, 5.88 mmol) dropwise with stirring. The orange-red mixture was then stirred at 0 °C for 15 min, whereupon the hydrochloride precipitate was filtered off and washed with 10 mL of THF. From the filtrate most of the solvent was removed under vacuum to leave a red solution (ca. 10 mL), and a 29Si NMR spectrum thereof was recorded (δ -105.1, -105.5; ratio 13:1). Within some hours compound 8a precipitated from this crude product solution as a fine crystalline solid. The mixture was then stored at 8 °C overnight, whereupon the solid product was filtered off, washed with a THF/hexane mixture (4 mL + 4 mL), and dried under vacuum (1.15 g). From the filtrate some more product precipitated at 8 °C within 2 weeks (0.60 g). Yield: 1.75 g (2.77 mmol, 49%). 1H NMR (CDCl3): δ 3.61, 3.92 (2s, 6 H, OCH3), 5.89 (s, 1 H, NCH), 5.93 (m, 1 H, ar), 6.25 (d, 1 H, ar, 4JHH ) 2.0 Hz), 6.28 (d, 1 H, ar, 4JHH ) 2.4 Hz), 6.30-7.70 (mm, 22 H, ar). 13C NMR (CDCl3): δ 55.1, 56.0 (OCH3), 61.4 (NCH), 103.9, 105.7, 105.8, 110.1, 112.0, 116.6, 116.9, 119.4, 123.7, 126.1, 126.7, 127.0, 127.5, 128.1, 128.3, 128.5, 128.6, 128.9, 129.0, 129.3, 129.6, 129.8, 130.4, 133.1, 133.2, 136.4, 144.0, 146.5, 155.8, 159.9, 165.4, 166.6, 172.9. 29Si NMR (CDCl3): δ -104.4. Anal. Found: C, 75.91; H, 5.02; N, 4.40. Calcd for C40H32N2O4Si: C, 75.93; H, 5.10; N, 4.43. Synthesis of Compound 9. To a stirred solution of 3 (0.50 g, 1.2 mmol) and triethylamine (0.36 g, 3.6 mmol) in THF (7 mL) at -10 °C was added a solution of chlorotrimethylsilane (0.39 g, 3.6 mmol) in THF (2 mL) dropwise. This mixture was stored at 8 °C for 2 h, and then the amine hydrochloride precipitate was filtered and washed with THF (4 mL). From the filtrate the solvent was removed under vacuum to yield the crude product 10 as a yellowish oil of sufficient purity for further reaction. 1H NMR (CDCl3): δ -0.07, 0.27 (2s, 18 H, SiMe3), 3.70 (s, 3 H, OCH3), 6.18 (s, 1 H,

Organosilicon Complexes of an ONN′O′ Ligand ar), 6.25 (d, 1 H, ar, 3JHH ) 8.4 Hz), 6.78 (m, 1 H, ar), 6.85-7.75 (mm, 13 H, ar), 8.58 (s, 1 H, NdCH). 13C NMR (CDCl3): δ 0.0, 0.3 (SiMe3), 55.0 (OCH3), 104.7, 105.1, 119.3, 119.5, 120.8, 121.4, 121.6, 123.8, 125.4, 127.6, 127.9, 128.1, 128.6, 129.8, 130.8, 131.8, 132.9, 140.5, 142.8, 145.3, 154.1, 155.6, 155.8, 160.6. 29Si NMR (CDCl3) δ 19.1, 20.9. Synthesis of Compound 10. Compound 9 (prepared according to the above procedure) was dissolved in toluene (15 mL), and phenyltrichlorosilane (0.26 g, 1.2 mmol) was added dropwise. The mixture was then heated to reflux for 1 h and cooled to room temperature, and the resulting precipitate (10 · 0.5(toluene)) was filtered, washed with toluene (6 mL), and dried under vacuum. Yield: 0.59 g (1.0 mmol, 83%). 1H NMR (d6-DMSO): δ 3.90 (s, 3 H, OCH3), 6.35 (d, 1 H, ar, 3JHH ) 8.4 Hz), 6.51 (d, 1 H, ar, 4JHH ) 1.2 Hz), 6.53 (d, 1 H, ar, 4JHH ) 1.6 Hz), 6.75-8.10 (mm, 18 H, ar), 9.78 (s, 1 H, NdCH). 13C NMR (d6-DMSO): δ 56.4 (OCH3), 104.1, 109.6, 114.1, 118.2, 118.4, 120.2, 120.7, 123.4, 125.4, 126.2, 126.5, 128.2, 128.4, 128.5, 128.9, 129.0, 129.4, 129.5, 131.1, 133.5, 134.2, 135.3, 135.7, 138.8, 149.9, 160.6, 161.3, 164.1, 167.9, 171.1. 29 Si NMR (d6-DMSO): δ -167.9. 29Si NMR (CP/MAS): δiso -167.7. Anal. Found: C, 72.31; H, 5.04; N, 4.88. Calcd for C36.5H29N2O3SiCl: C, 72.20; H, 4.81; N, 4.61. Synthesis of Compound 11. 10 · 0.5(toluene) (0.42 g, 0.70 mmol) was stirred in chloroform (10 mL), and tin tetrachloride (0.20 g, 0.77 mmol) was added, whereupon the initial suspension turned into a clear solution. From the crude solution a 29Si NMR spectrum was recorded: δ -111.3. From this solution 11 · 0.5CHCl3 crystallized. After storage at room temperature (1 week) and at 8 °C (another 1 week) the yellow crystals were separated from the solution by decantation, washed with chloroform (1 mL), and briefly dried under vacuum. Yield: 0.42 g (0.48 mmol, 68%). Anal. Found: C, 45.49; H, 2.90; N, 3.19. Calcd for C36.5H29N2O3SiCl: C, 45.66; H, 2.92; N, 3.18. Synthesis of Compound 12b. To a suspension of 10 · 0.5(toluene) (2.1 g, 4.0 mmol) and potassium cyanide (0.30 g, 4.6 mmol) in chloroform (10 mL) was added 18-crown-6 (100 mg), and the mixture was stirred at room temperature for 24 h. The resulting (almost clear) orange-red solution was then filtered through diatomaceous earth and stored at 8 °C for 2 days. Within this time orange crystals of 12b formed, which were then filtered off, washed with a chloroform/hexane mixture (1 mL + 1 mL; 1 mL + 2 mL), and dried under vacuum (0.75 g). Upon storage at -20 °C more crystalline product 12b formed (0.38 g). Yield: 1.13 g (2.05 mmol,

Organometallics, Vol. 28, No. 2, 2009 629 51%). From the filtrate a 29Si NMR spectrum was recorded, which revealed the presence of 12b and 12a in the approximate ratio 1:1 (δ -105.1 and -105.9, respectively). Data for 12b are as follows. 1 H NMR (CDCl3): δ 3.87 (s, 3H, OCH3), 5.35 (s, 1H, NCH), 5.87 (d, 1H, 8.0 Hz), 6.37 (m, 1H), 6.42 (dd, 1H, 9.0 Hz, 2.6 Hz), 6.64 (d, 1H, 2.6 Hz), 6.8-7.6 (m, 17 H). 13C NMR (CDCl3): δ 48.9 (C(H,CN,aryl,aryl)), 55.8 (OCH3), 104.7, 109.9, 110.7, 115.6, 118.4, 120.5, 120.8, 120.9, 123.4, 126.5, 126.8, 127.4, 127.7, 129.2, 129.5, 130.1, 130.2, 131.0, 132.3, 133.7, 135.2, 137.0, 142.9, 156.7, 159.2, 160.4, 166.0, 166.2. 29Si NMR (CDCl3): δ -105.1. Anal. Found: C, 74.19; H, 4.60; N, 7.64. Calcd for C34H25N3O3Si: C, 74.03; H, 4.57; N, 7.62. Synthesis of Compound 14. At -10 °C ligand 13 (0.80 g, 1.65 mmol) was stirred in a solution of triethylamine (0.50 g, 4.95 mmol) in THF (10 mL), and allylphenyldichlorosilane (0.37 g, 1.70 mmol) was added dropwise. After 30 min the solvent was completely removed under reduced pressure and the solid was recrystallized from chloroform (10 mL). Yield: 0.84 g (0.97 mmol, 59%) of 14 · 2CHCl3. (From the remaining solution a 29Si NMR spectrum was recorded, which revealed only one signal in the range -80 to -120 ppm (-103.9) characteristic of compound 14.) 1H NMR (CDCl3): δ 2.65-2.85 (m, 2 H, allyl), 3.78, 3.87, 3.89 (3s, 9 H, OCH3), 4.85-5.15 (mm, 3 H, allyl, NCH), 5.7-5.9 (mm, 2 H, allyl, aryl), 6.1-7.6 (mm, 18 H, aryl). 13C NMR (CDCl3): δ 38.7 (CH2), 50.6 (C(H,allyl,aryl,aryl)), 55.3, 55.6 (OCH3), 90.7, 97.7, 104.3, 109.0, 111.6, 112.3, 115.7, 116.2, 116.2, 119.8, 127.0, 127.2, 128.4, 129.1, 129.4, 129.6, 129.9, 130.4, 131.7, 133.1, 135.9, 136.1, 138.9, 145.8, 156.3, 157.6, 158.9, 160.3, 164.2, 165.8. 29Si NMR (CDCl3): δ -103.9. Anal. Found: C, 56.50; H, 4.41; N, 3.35. Calcd for C40H36N2O5SiCl6: C, 55.51; H, 4.19; N, 3.24.

Acknowledgment. This work was financially supported by the German Chemical Industry Fund. Supporting Information Available: CIF files giving crystallographic data for 2, 3, 4 · CHCl3, 5a · CHCl3, 6, 7 · CHCl3, 8a, 11 · 0.5CHCl3, 12b, and 14 and figures and text giving ORTEP diagrams of 2, 3, 7, 8a and 14, experimental details of ligand syntheses (including NMR spectroscopic data), and details of the equilibrium between complexes 4 and 4a. This material is available free of charge via the Internet at http://pubs.acs.org. OM801049Q