Regioselective Intramolecular Chloride Displacement Leading to Five

Jul 2, 2009 - Evgenia Kertsnus-Banchik , Boris Gostevskii , Mark Botoshansky , Inna Kalikhman , and Daniel Kost. Organometallics 2010 29 (21), 5435-54...
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Organometallics 2009, 28, 4126–4132 DOI: 10.1021/om9002818

Regioselective Intramolecular Chloride Displacement Leading to Five- or Six-Membered Chelate-Ring Closure and Pentacoordinate Silicon Complexes: A Facile Wawzonek Rearrangement† Shiri Yakubovich, Boris Gostevskii, Inna Kalikhman,* and Daniel Kost* Department of Chemistry, Ben Gurion University, Beer-Sheva 84105, Israel Received April 14, 2009

O-Trimethylsilylated hydrazides with Schiff-base derivatives at the terminal nitrogen atoms[RC(OSiMe3)dNNdCR0 R00 ] react with chloro(chloromethyl)dimethylsilane [ClCH2SiMe2Cl] in a regioselective manner, forming either five-membered or zwitterionic six-membered chelate complexes with pentacoordinate silicon. The type of product is determined by the size of the acidsubstituent R: bulky R groups (Ph, t-Bu) lead to exclusive formation of the six-membered product, whereas with the less bulky groups (Me, PhCH2) only the five-membered product is obtained. Upon mild heating, the six-membered chelate complex transforms into its five-membered isomer, through a Wawzonek-type rearrangement. This facile transformation is remarkable in comparison to previously reported Wawzonek reactions that take place only at elevated temperatures.

Introduction Hypercoordinate organosilicon compounds have attracted considerable attention in recent years.1 One effective route leading to O f Si pentacoordinate silicon complexes consists † Dedicated to Prof. Gerhard Roewer on the occasion of his 70th birthday. *To whom correspondence should be addressed. E-mail: kostd@bgu. ac.il; [email protected]. (1) Selected reviews on hypercoordinate silicon compounds: (a) Bassindale, A. R.; Glynn, S. J.; Taylor, P. G. In The Chemistry of Organic Silicon Compounds; Rappoport, Z.; Apeloig, Y., Eds.; Wiley: Chichester, U.K., 1998; Vol. 2, pp 495-511. (b) Chuit, C.; Corriu, R. J. P.; Reye, C. In The Chemistry of Hypervalent Compounds; Akiba, K-y., Ed.; Wiley-VCH: Weinheim, Germany, 1999; pp 81-146. (c) Kira, M.; Zhang, L. C. In The Chemistry of Hypervalent Compounds; Akiba, K-y., Ed.; Wiley-VCH: Weinheim, Germany, 1999; pp 147-169. (d) Voronkov, M. G.; Trofimova, O. M.; Bolgova, N. F.; Chernov, Yu. I. Russ. Chem. Rev. 2007, 76, 825–845. (e) Tacke, R.; P€ ulm, M.; Wagner, B. Adv. Organomet. Chem. 1999, 44, 221– 273. (f) Brook, M. A. Silicon in Organic, Organometallic, and Polymer Chemistry; Wiley: New York, 2000; pp 97-114. (g) Tacke, R.; Seiler, O. In Silicon Chemistry, From the Atom to Extended Systems; Jutzi, P., Schubert, U., Eds.; Wiley-VCH: Weinheim, Germany, 2003; pp 324337. (h) Kost, D.; Kalikhman, I. In The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig Y., Eds.; Wiley: Chichester, 1998; Vol. 2, pp 1339-1445. (2) (a) Onan, K. D.; McPhail, A. T.; Yoder, C. H.; Hillyard, R. W. J. Chem. Soc., Chem. Commun. 1978, 209–210. (b) Hillyard, R. W.; Ryan, C. M; Yoder, C. H. J. Organomet. Chem. 1978, 153, 369–377. (c) Yoder, C. H.; Ryan, C. M; Martin, G. F.; Ho, P. S. J. Organomet. Chem. 1980, 190, 1–7. (3) Kalikhman, I. D.; Albanov, A. I.; Bannikova, O. B.; Belousova, L. I.; Voronkov, M. G.; Pestunovich, V. A.; Shipov, A. G.; Kramarova, E. P.; Baukov, Yu. I. J. Organomet. Chem. 1989, 361, 147–155. (4) Pestunovich, V. A.; Albanov, A. I.; Larin, M. F.; Voronkov, M. G.; Kramarova, E. P.; Baukov, Yu. I. Izv. Akad. Nauk SSSR, Ser. Chim. 1980, 2178–2179. (5) Kalikhman, I. D.; Bannikova, O. B.; Volkova, L. I.; Belousova, L. I.; Yushmanova, T. I.; Lopyrev, V. A.; Vyazankina, O. A.; Vyazankin, N. S.; Pestunovich, V. A. Izv. Akad. Nauk SSSR, Ser. Khim. 1986, 2781– 2783. (6) Albanov, A. I.; Baukov, Yu. I.; Voronkov, M. G.; Kramarova, E. P.; Larin, M. F.; Pestunovich, V. A. Zh. Obshch. Khim. 1983, 53, 246– 248.

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of the reaction of chloro(chloromethyl)dimethylsilane (ClCH2SiMe2Cl, 1) with various N- or O-trimethylsilylamides,2,3 lactams,3,4 acetylacetamide,5 and 2-pyridones,6,7 as shown, for example, in eq 1. The reaction is a two-step process: transsilylation, followed by internal nucleophilic displacement of chloride by nitrogen or oxygen.

A variant of this reaction with O-trimethylsilylated (N,Ndimethyl)hydrazides (2)8-10 has been reported and is shown in eq 2.10-13 In this case, a highly regioselective reaction was observed: the conformational preference of the intermediates (3, 4) determined the structure of the end products, a five-membered neutral oxygen-coordinated chelate (5) or a six-membered zwitterionic oxygen-coordinated chelate (6), (7) Voronkov, M. G.; Pestunovich, V. A.; Baukov, Yu. I. Metalloorganicheskaya Khim., 1991, 4, 1210-27. Translation: Organomet. Chem. 1991, 4, 593-603. (8) Kost, D.; Kalikhman, I. Acc. Chem. Res. 2009, 42, 303–314. (9) Kost, D.; Kalikhman, I. Adv. Organomet. Chem. 2004, 50, 1–106. (10) Kalikhman, I. D.; Pestunovich, V. A.; Gostevskii, B. A.; Bannikova, O. B.; Voronkov, M. G. J. Organomet. Chem. 1988, 338, 169–180. (11) Macharashvili, A. A.; Shklover, V. E; Struchkov, Yu. T.; Gostevskii, B. A; Kalikhman, I. D.; Bannikova, O. B.; Voronkov, M. G.; Pestunovich, V. A. J. Organomet. Chem. 1988, 356, 23–30. (12) Macharashvili, A. A.; Shklover, V. E.; Struchkov, Yu. T.; Voronkov, M. G.; Gostevsky, B. A.; Kalikhman, I. D.; Bannikova, O. B.; Pestunovich, V. A. J. Organomet. Chem. 1988, 340, 23–29. (13) Kalikhman, I. D.; Bannikova, O. B.; Pestunovich, V. A.; Voronkov, M. G. Dokl. Akad. Nauk SSSR 1986, 287, 870–873. r 2009 American Chemical Society

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respectively. In view of the diversity in structure, geometry, and reactions of hydrazide-derived silicon complexes,8,9 it was interesting to compare the behavior of another group of ligand precursors, namely the O-(trimethylsilyl)N-alkylideneaminoimidates (7), with previous results. Complexes derived from 7 differ in many structural and reactivity aspects from those derived from 2, and hence a comparison of the reactions of 7 and 2 with 1 is warranted. For example, compounds 2 differ from 7 in their reaction with XSiCl3, forming N-Si-coordinated neutral hexacoordinate silicon dichelates, in comparison with 7, that tend to release a halide anion and form pentacoordinate siliconium ions.14-16 The present paper describes the reactions of 1 with various compounds 7 and discusses the regioselectivity of these reactions. The results demonstrate the versatility and flexibility usually found in hypercoordinate silicon compounds.8

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Table 1. Selected 1H, 13C, and 29Si NMR Spectral Data for 7, 9, and 10a compound

δ29Si

δ13C CH2

δ1H CH2

δ29Si (7x)b

9a -36.3 41.4 2.69 19.7 9b -35.7 40.6 2.95 19.8 9c -30.6 35.9 2.95 21.7 9d -32.2 41.8 2.92 20.7 9e -34.3 42.6 2.85 20.6 9f -34.9 41.4 2.81 20.2 10g -3.3 49.2 4.28 17.6 10h -1.83 48.0 4.20 18.1 10i -6.3 48.7 4.30 18.2 10j 10.3 46.4 4.19 16.1 9h -36.8 44.4 3.06 9i -37.2 43.2 3.03 9j -39.9 38.1 2.86 a In CDCl3 at 298 K. The data for 9h-j correspond to the Wawzonek rearrangement products. b 7x refers to 7a-j, according to row index.

Results and Discussion O-(Trimethylsilyl)N-alkylideneaminoimidates (7a-j) were prepared as described previously.14-16 Compounds 7a-j react with chloro(chloromethyl)dimethylsilane (1) in chloroform solution in a regioselective manner, to form two different product types (9 or 10, eq 3). Like in the dimethylaminocoordinated series 2,10-13 the product type, either formation of a five-membered (9) or six-membered (10) chelate ring, is determined by the nature of the acid-hydrazide residue R: Bulky R groups [t-butyl (7j) and phenyl (7g-i)] form only the six-membered chelate (10g-j), while the relatively small methyl or benzyl groups (7a-f) form exclusively the fivemembered chelate products (9a-f).

The evidence for the structural assignment of the products 9 and 10 comes from NMR spectra and crystal structures. (14) Kalikhman, I.; Gostevskii, B.; Girshberg, O.; Sivaramakrishna, A.; Kocher, N.; Stalke, D.; Kost, D. J. Organomet. Chem. 2003, 686, 202–214. (15) Kalikhman, I.; Gostevskii, B.; Girshberg, O.; Krivonos, S.; Kost, D. Organometallics 2002, 21, 2551–2554. (16) Kertsnus-Banchik, E.; Kalikhman, I.; Gostevskii, B.; Deutsch, Z.; Botoshansky, M.; Kost, D. Organometallics 2008, 27, 5285–5294.

Figure 1. Temperature dependence of the 29Si NMR chemical shifts for 9b, 9d, 10g, and 10j in CDCl3 solutions.

In Table 1 are listed selected 1H, 13C, and 29Si NMR data for 9a-f and 10g-j with unique features enabling unambiguous characterization of 9 and 10: the 29Si chemical shifts of 9a-f fall in the range -30.6 to -36.3 ppm, and the corresponding 29Si shifts of 10g-j are in the range -6.3 to þ10.3 ppm at 298 K. The chemical shifts are temperature dependent: a plot of the 29Si chemical shifts of 10g, 10j and 9b, 9d as a function of temperature is shown in Figure 1. It is apparent from Figure 1 that the temperature dependencies of 9 and 10 are opposite to each other. In 10g and 10j the 29Si resonance changes to high field as the temperature increases. This temperature dependence suggests an increase in the coordination number or strength with increasing temperature, a phenomenon reported previously in the case of solventdriven ionic dissociation in hexacoordinate,17 as well as in pentacoordinate,18-21 silicon complexes. It is thus likely, in analogy with the previous reports, that the temperature dependence is associated with the ionic dissociation shown (17) Kost, D.; Kingston, V.; Gostevskii, B.; Ellern, A.; Stalke, D.; Walfort, B.; Kalikhman, I. Organometallics 2002, 21, 2293–2305. (18) Bassindale, A. R.; Borbaruah, M. J. Chem. Soc., Chem. Commun. 1991, 1501–1503. (19) Sidorkin, V. F.; Vladimirov, V. V.; Voronkov, M. G.; Pestunovoch, V. A. THEOCHEM 1991, 74, 1–9. (20) Kummer, D.; Chaudhry, S. H.; Seifert, J.; Deppisch, B.; Mattern, G. J. Organomet. Chem. 1990, 382, 345–359. (21) Kummer, D.; Abdel Halim, S. H.; Kuhs, W.; Mattern, G. J. Organomet. Chem. 1993, 446, 51–65.

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Figure 2. Molecular structure in the crystal of 9c at the 50% probability level. Only the hydrazonic and methylene hydrogen atoms are shown.

Yakubovich et al.

molecular geometries of these products in the solid state are depicted in Figures 2-4, and selected bond lengths and angles are listed in Table 2. The data in Table 2 support the coordination scheme of 10 suggested by structure IV, namely, the coordination of chloride to silicon: the Si-Cl bond in 10i is 0.114 A˚ longer than that in 9c, explaining why this bond is so much easier to dissociate than the latter. Conversely, the apical Si-O bonds in these two crystals have the opposite trend, 1.875 A˚ in 10i and 1.990 A˚ in 9c, in agreement with a more advanced position along a hypothetical nucleophilic-substitution reaction coordinate, whereby oxygen displaces chloride.1a The other bond lengths in the vicinity of silicon are essentially equal in the two crystal structures, emphasizing the significance of the differences in Si-O and Si-Cl bond lengths.

in eq 4: I-IV represent canonical structures describing collectively the charge distribution in the zwitterionic compounds 10.22 The final step (IV f V) represents a real ionic dissociation, which must be associated with a downfield shift of the 29Si resonance (change from pentato tetracoordinated silicon). Because the observed downfield shift takes place when the temperature is decreased, it represents, in analogy with similar dissociation of hexacoordinate compounds,17 a solvent driven ionic dissociation, resulting from effective solvation of chloride by the hydrogen-bond donor solvent, chloroform, at low temperature.

Figure 3. Molecular structure in the crystal of 9d at the 50% probability level. Hydrogen atoms are omitted.

In contrast to 10, the 29Si chemical shifts of 9 (9b and 9d shown in Figure 1) are barely temperature dependent and in opposite direction relative to 10 (Figure 1). In compounds 9 increasing the temperature results in weaker coordination of the carbonyl oxygen to silicon, as one might expect intuitively. The next two columns in Table 1 list the 13C and 1H NMR chemical shifts for the CH2 groups. Again, there are distinct chemical-shift regions characteristic of compounds 9 and 10. The Table also lists the 29Si chemical shifts for the starting materials 7, for comparison. The structures of 9 and 10 were further confirmed by single crystal X-ray diffraction analyses of three representative compounds of the two series: 9c and 9d, and 10i. The (22) For a more detailed analysis of charge distribution based on amide-imide C-N and C-O bond lengths in a similar system see: Kalikhman, I.; Krivonos, S.; Lameyer, L.; Stalke, D.; Kost, D. Organometallics 2001, 20, 1053–1055. The available crystallographic bond lengths are listed in Table 2.

Figure 4. Molecular structure in the crystal of 10i at the 50% probability level. Hydrogen atoms are omitted.

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Table 2. Selected Crystallographic Bond Lengths and Angles for 9c, 9d, and 10i 9c Si-O(1) Si-Cl(1) Si-C(11) Si-C(2) O(1)-C(1) N(1)-C(1) N(1)-C(2) C(11A)-Si-C(11) C(11)-Si-C(2) C(11)-Si-O(1) C(2)-Si-O(1) C(11)-Si-Cl(1) C(2)-Si-Cl(1) O(1)-Si-Cl(1) C(1)-O(1)-Si C(1)-N(1)-N(2) C(1)-N(1)-C(2)

9d 1.9897(15) 2.2793(3) 1.8601(16) 1.909(2) 1.265(2) 1.336(3) 1.463(5) 120.45(10) 119.62(5) 90.60(6) 83.14(8) 93.59(5) 88.41(7) 171.55(5) 113.75(13) 118.04(16) 117.04(16)

10i

Bond Lengths (A˚) Si-O(1) 1.987(2) Si-Cl(1) 2.319(16) Si-C(12) 1.854(4) Si-C(10) 1.888(3) O(1)-C(1) 1.267(4) N(1)-C(1) 1.324(4) N(1)-C(10) 1.463(4) Bond Angles (deg.) C(12)-Si-C(14) 118.77(18) C(10)-Si-C(12) 122.99(17) O(1)-Si-C(12) 89.76(15) 83.02(13) O(1)-Si-C(10) Cl(1)-Si-C(12) 93.96(15) Cl(1)-Si-C(10) 87.47(12) Cl(1)-Si-O(1) 170.33(8) Si-O(1)-Cl(1) 112.87(17) N(2)-N(1)-C(1) 121.4(2) C(1)-N(1)-C(10) 116.1(2)

Formation of 9 and 10 follows roughly the steric bulk of the R residue, in analogy with the reaction 2 f 5 and 68-10 (eq 2). The imidate-nitrogen atom in 8-E, whose electron lone pair is nearest to the chloromethyl-carbon atom, attacks carbon and displaces chloride resulting in 9, whereas attack of the imino-nitrogen in 8-Z, that is now nearest to chloromethyl-carbon, produces 10 (eq 3). The intermediates 8-E and 8-Z were not isolated. However, they could be observed during NMR monitoring of the progress of the reaction: when 7h and 1 are dissolved in CD2Cl2 at 260 K in an NMR tube, the 29Si NMR spectrum taken immediately after dissolution features, in addition to signals of the reactants, Me3SiCl and a sharp singlet at 0.72 ppm, attributed to the intermediate 8h-Z. Upon gradual warming, a small but significant, nearly linear, shift of the silicon resonance to lower field is observed (Figure 5). This suggests that the imino-nitrogen in 8h-Z, that is near the silicon atom, loosely coordinates to the essentially tetracoordinate silicon at lower temperatures, resulting in a higher field silicon resonance. At 290 K and above, the internal displacement reaction (8h-Z f 10h) commences, with the gradual appearance of the signal due to 10h and the disappearance of that of 8h-Z. In this case the bulk of the phenyl group causes exclusive formation of the Z-conformer (assigned by the temperature dependence of its 29Si NMR signal) and consequent regiospecific formation of 10h. When the imidate R group is less bulky, like methyl in 7a-c and benzyl in 7d-f, both the E- and Z-conformers of 8 (δ29Si 13.1-14.1 and -1.2 - þ3.5 ppm, respectively) are formed initially (at 260 K) but subsequently give rise to only one cyclic product, 9. This is very likely a manifestation of the Curtin-Hammett principle,23 in which two interconvertible isomers produce predominantly only the one product, which is formed more rapidly from either isomer, consuming both of the equilibrating intermediate isomers. This condition prevails as long as the E-Z isomerization of 8 is faster than either of the reactions 8-E f 9 or 8-Z f 10, and does not necessarily imply rapid E-Z isomerization. An alternative pathway, in which 10 may rearrange to 9, is discussed below. (23) (a) Curtin, D. Y. Recent Chem. Prog. 1954, 15, 111–128. (b) Seeman, J. I. Chem. Rev. 1983, 83, 83–134.

Si-O(1) Si-Cl(1) Si-C(12) Si-C(2) O(1)-C(6) N(1)-C(6) N(2)-C(2)

1.8748(16) 2.3930(9) 1.859(2) 1.906(2) 1.301(3) 1.295(3) 1.484(3)

C(12)-Si-C(14) C(12)-Si-O(1) C(14)-Si-O(1) C(12)-Si-C(2) C(14)-Si-C(2) O(1)-Si-C(2) C(12)-Si-Cl(1) C(14)-Si-Cl(1) O(1)-Si-Cl(1) N(1)-N(2)-C(2)

Figure 5. Temperature dependence of the shift for the intermediate 8h-Z.

122.26(12) 89.38(9) 92.87(10) 121.65(11) 116.07(11) 86.41(8) 89.84(8) 92.68(9) 173.88(6) 116.90(16)

29

Si NMR chemical

The present results are further complicated by the observation that compounds 10, with their six-membered chelate ring, readily undergo a Wawzonek-type rearrangement to 9, their isomer with a five-membered chelate ring (eq 3).24 A similar Wawzonek rearrangement was reported previously in the dimethylamino-coordinated complexes 6, transforming to 5 (eq 2).10 However, while the latter rearrangement required heating of the neat solid to its melting temperature or prolonged boiling in solution, the present reaction takes place under mild conditions, and is essentially complete after ∼2 h boiling in chloroform solution. This is not only in contrast with the analogous rearrangement (eq 2), but also with the original report by Wawzonek on the rearrangement of ylides (eq 5), which took place at 180-182 °C.24 It appears that the sp2-hybridized immonium nitrogen atom in 10 forms a better leaving group relative to the dimethylammoniumnitrogen in the otherwise similar 6, resulting in a faster rearrangement. Compounds 10 do not have sharp melting points, presumably because they undergo the rearrangement during measurement: the solid begins to melt and quickly (24) (a) Wawzonek, S.; Yeakey, E. J. Am. Chem. Soc. 1960, 82, 5718– 5721. (b) McKillip, W. J.; Sedor, E. A.; Culbertson, B. M.; Wawzonek, S. Chem. Rev. 1973, 73, 255–281.

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Table 3. Crystallographic Data and Experimental Parameters for the Structure Analyses of 9c, 9d, and 10i

CCDC number empirical formula form mass, g mol-1 collection T, K cryst. syst. space group a, A˚ b, A˚ c, A˚ R, deg β, deg γ, deg V, A˚3 Z F calcd, Mg/m3 F (000) θ range, deg no. of coll. reflns no. of indep reflns Rint no. of reflns used no. of params Goof R1 wR2[I > 2σI)] R1 wR2 (all data) max./min res electron dens (eA˚-3)

9c

9d

10i

727601 C12H15ClN2OSi 266.80 120(2) orthorhombic Pnma 19.307(5) 6.9388(17) 10.358(2) 90 90 90 1387.7 (6) 4 1.277 560 2.11-29.02 7205 1966 0.0297 1966 101 0.961 0.0370 0.0851 0.0448 0.0896 0.387 -0.332

727602 C14H21ClN2OSi 296.88 200(2) triclinic P1 9.111(4) 10.417(4) 10.811(4) 99.269(8) 109.036(6) 115.209(7) 821.8(6) 2 1.190 316 2.13-26.55 4696 3293 0.0382 3293 234 0.975 0.0570 0.1463 0.0764 0.1585 0.551 -0.411

727603 C17H25ClN2OSi 336.94 200(2) monoclinic P2(1)/c 9.372(3) 9.856(3) 19.824(6) 90 103.430(5) 90 1781.0(9) 4 1.257 752 2.11-25.09 8931 3157 0.0459 3157 201 1.030 0.0436 0.1046 0.0624 0.1166 0.368 -0.239

transforms to a semisolid, which then melts completely at a higher temperature.

ing that the sp2-hybridized immonium nitrogen is a good leaving group supporting the rearrangement.

Experimental Section

The observation of the Wawzonek rearrangement that converts 10 to 9 may indicate that formation of only one product (9) from the reaction of 7a-f with 1 (see above), presumably through two intermediates 8E, 8Z (eq 3), results from a rapid rearrangement of 10 to 9. However, this possibility, that both 9d and 10d are formed simultaneously from 8d-E and 8d-Z, respectively, and that 10d rapidly undergoes the Wawzonek rearrangement to form 9d, seems unlikely since no trace of 10d was observed even as low as 260 K, whereas the Wawzonek rearrangement is known to take place at elevated temperatures.24 Compounds 9 that were obtained by the Wawzonek reaction from their isomeric 10 (9h-j), are listed separately in Table 1. Compound 9h was characterized by elemental analysis and the various NMR spectra; 9i and 9j were identified by their NMR spectral analogy with 9a-f and 9h.

Conclusion The reaction of chloro(chloromethyl)dimethylsilane with various O-trimethylsilylated ketoneimine derivatives of hydrazides was studied. The reaction proceeded regioselectively in two different pathways, depending on the acidresidue R of the hydrazide: with bulky R groups (Ph, t-Bu) a pentacoordinate silicon complex with a six-membered chelate ring was formed, while with smaller R (Me, CH2Ph), a five-membered chelate was obtained. Upon mild warming, the six-membered chelate complex transformed to the five-membered-ring compound in a remarkably facile Wawzonek-type rearrangement, suggest-

The reactions were carried out under dry argon using Schlenk techniques. Solvents were dried and purified by standard methods. NMR spectra were recorded on a Bruker Avance DMX-500 spectrometer operating at 500.13, 125.76, and 99.36 MHz, respectively, for 1H, 13C, and 29Si spectra. Unless stated, all NMR spectra were measured at 298 K. Melting points were measured in sealed capillaries using a Buchi melting point instrument and are uncorrected. Elemental analyses were performed by Mikroanalytisches Laboratorium Beller, G€ ottingen, Germany. Compounds 7c,25 7d,15 7f-h, and 7j16 were described previously. Single crystal X-ray diffraction measurements were performed on a Bruker Smart Apex on D8-Goniometer. Crystallographic details are listed in Table 3. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre. The CCDC numbers are listed in Table 3. N-Isopropylideneimino-O-(trimethylsilyl)acetimidate (7a). A solution of acethydrazide 10.5 g (142 mmol) in 40 mL of acetone was refluxed for 1 h. The volatiles were removed under reduced pressure (0.5 mmHg), leaving a white solid residue. The solid was dissolved in 150 mL of dry diethyl ether and 14.2 g (140 mmol) of Et3N was added. To this solution, 15.2 g (140 mmol) of Me3SiCl was added dropwise over 30 min, followed by 4 h of reflux. After cooling to room temperature the solid Et3NHCl was filtered off under argon and washed twice with diethyl ether (2  20 mL). The filtrate and washings were combined and the solvent was removed under reduced pressure, followed by distillation. The fraction boiling at 32-34 °C/0.2 mmHg was collected, 21.9 g (84% yield). 1H NMR (CDCl3): δ 0.21 (s, 9H, Si(CH3)3), 1.86, 1.91, 1.96 (25) Gostevskii, B.; Kalikhman, I.; Tessier, C. A.; Panzner, M. J.; Youngs, W. J.; Kost, D. Organometallics 2005, 24, 5786–5788.

Article (3s, 9H, CCH3). 13C NMR (CDCl3): δ 0.00 (Si(CH3)3), 15.53, 18.06 (C(CH3)2), 24.90 (OCCH3), 161.96, 164.14 (CdN). 29Si NMR (CDCl3): δ 19.58. N-Cyclopentylideneimino-O-(trimethylsilyl)acetimidate (7b). Compound 7b was prepared as described for 7a, from acethydrazide 8.0 g (110 mmol), 9.6 mL (110 mmol) of cyclopentanone, 11.1 g (110 mmol) of Et3N, and 12.0 g (110 mmol) of Me3SiCl with one exception: the first step was done in 50 mL of methanol as solvent. The fraction boiling at 65 °C/0.6 mmHg was collected, 18 g (79% yield). 1H NMR (CDCl3): δ 0.21 (s, 9H, Si(CH3)3), 1.68 (m, 4H, (CH2)2), 2.34 (m, 4H, (CH2)2), 1.95 (s, 3H, CCH3). 13C NMR (CDCl3): δ 0.01 (Si(CH3)3), 15.59 (CCH3), 24.56, 24.72, 29.79, 33.01 (CH2)4, 164.19 (OCdN), 175.45 (NdC(CH2)4). 29Si NMR (CDCl3): δ 19.68. Anal. Calcd. for C10H20N2OSi: C, 56.56; H, 9.49; N, 13.19. Found: C, 56.84; H, 9.67; N, 12.79. N-(3-Pentylideneimino)-O-(trimethylsilyl)phenylacetimidate (7e). Compound 7e was prepared as described for 7a, from phenylacethydrazide (8.9 g, 59 mmol), 90 mL of anhydrous 3pentanone, 6.0 g (59 mmol) of Et3N, and 6.44 g (59 mmol) of Me3SiCl. The fraction boiling at 102-105 °C/0.02 mmHg was collected, 13.6 g (78% yield). 1H NMR (CDCl3): δ 0.38 (s, 9H, Si(CH3)3), 1.11 (t, 3J=7.6 Hz, 3H, CH2CH3), 1.29 (t, 3J=7.6 Hz, 3H, CH2CH3), 2.45 (q, 3J=7.6 Hz, 2H, CH2CH3), 2.50 (q, 3J= 7.6 Hz, 2H, CH2CH3), 4.02 (s, 2H, PhCH2), 7.39 (m, 5H, Ph). 13 C NMR (CDCl3): δ 0.09 (Si(CH3)3), 10.72, 10.86 (2CH2CH3), 24.33, 29.46 (2CH2CH3), 35.86 (PhCH2), 126.03, 128.13, 129.05, 136.98 (Ph), 164.68 (OCdN), 170.89 (NdCMe2). 29Si NMR (CDCl3): δ 20.60. Anal. Calcd. for C16H26N2OSi: C, 66.16; H, 9.02; N, 9.64. Found: C, 65.98; H, 9.10; N, 9.68. N-(Cycloheptylideneimino)-O-(trimethylsilyl)benzimidate (7i). Compound 7i was prepared as described for 7b, from 6.81 g (0.05 mol) of benzhydrazide, 5.61 g (0.05 mol) of cycloheptanone, 50 mL MeOH, 5.1 g (0.05 mol) of Et3N, and 5.43 g (0.05 mol) of Me3SiCl. The fraction boiling at 140-145 °C at 0.02 mmHg was collected, 11.5 g (76% yield). 1H NMR (CDCl3): δ 0.43 (s, 9H, CH3), 1.64-1.79 (m, 8H, (CH2)4), 2.67 (t, 3J=7.3 Hz, 2H, NdC(CH2)2), 2.85 (t, 3J=7.3 Hz, 2H, NdC(CH2)2), 7.34-8.16 (m, 5H, C6H5). 13C NMR (CDCl3): δ 2.00 (Si(CH3)3), 24.92, 26.94, 30.22(2), 31.58, 36.69 ((CH2)6), 127.29, 127.79, 129.88, 134.34 (C6H5), 153.69 (CdNN), 172.39 (OCdN). 29Si NMR (CDCl3): δ 18.23. Anal. Calcd. for C17H26N2OSi: C, 67.50; H, 8.66; N, 9.26. Found: C, 67.42; H, 8.43; N, 9.16. Chlorodimethyl[N-(isopropylideneimino)acetamidomethyl]silane (9a). A mixture of 0.79 g (4.2 mmol) of 7a and 0.61 g (4.3 mmol) of ClCH2SiMe2Cl (1) in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) and the yellow solid residue was washed with 5 mL of n-hexane. Yield: 0.76 g. (95%). Mp. 178-179 °C. 1H NMR (CDCl3): δ 0.42 (s, 6H, Si(CH3)2), 1.79 (s, 3H, C(CH3)2), 1.81 (s, 3H, C(CH3)2), 1.97 (s, 3H, OCCH3), 2.67 (s, 2H, NCH2). 13C NMR (CDCl3): δ 6.94 (s, 6H, Si(CH3)2), 16.59, 19.47 (C(CH3)2), 24.70 (OCCH3), 41.42 (CH2), 170.69 (NdC), 177.55 (CdO). 29Si NMR (CDCl3): δ -36.32. Chlorodimethyl[N-(cyclopentylideneimino)acetamidomethyl]silane (9b). A mixture of 0.78 g (3.7 mmol) of 7b and 0.55 g (3.9 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) and the oily brown residue was washed with 5 mL of diethyl ether. 1H NMR (CDCl3): δ 0.55 (s, 6H, Si(CH3)2), 2.04 (s, 3H, OCCH3), 1.76-1.83 (m, 4H, (CH2)2), 2.37-2.46 (m, 4H, (CH2)2), 2.91 (s, 2H, NCH2). 13C NMR (CDCl3): δ 7.12 (Si(CH3)2), 17.23 (OCCH3), 23.92, 25.06, 31.28, 34.58 (CH2)4, 40.95 (NCH2), 172.72 (CdN), 183.95 (CdO). 29Si NMR (CDCl3): δ -35.71. Chlorodimethyl[N-(benzylideneimino)acetamidomethyl]silane (9c). A mixture of 0.84 g (3.6 mmol) of 7c and 0.52 g (3.6 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 30 min. The volatiles were removed under reduced pressure (0.1 mmHg) and the residue was washed with 5 mL of n-hexane.

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A single crystal for X-ray analysis was grown from THF. Yield: 0.95 g (99%). Mp. 183-184 °C. 1H NMR (CDCl3): δ 0.67 (s, 6H, Si(CH3)2), 2.48 (s, 3H, OCCH3), 2.95 (s, 2H, CH2), 7.44-7.72 (m, Ph), 8.00 (s, CH). 13C NMR (CDCl3): δ 6.86 (Si(CH3)2), 17.94 (OCCH3), 35.42 (CH2), 127.68, 128.87, 130.92, 133.16 (Ph), 146.41 (NdC), 175.49 (CdO). 29Si NMR (CDCl3): δ -30.59. Anal. Calcd. for C12H17ClN2OSi: C, 53.62; H, 6.37; N, 10.42. Found: C, 53.60; H, 6.40; N, 10.48. Chlorodimethyl[N-(isopropylideneimino)phenylacetamidomethyl]silane (9d). A mixture of 0.52 g (2.0 mmol) of 7d and 0.28 g (2.0 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) and the residue was washed with 5 mL of n-hexane. A single crystal for X-ray analysis was grown from a mixture of chloroform and n-hexane. Yield: 0.51 g (86%). Mp. 93-96 °C. 1H NMR (CDCl3): δ 0.73 (s, 6H, Si(CH3)2), 1.48 (s, 3H, C(CH3)2), 2.11 (s, 3H, C(CH3)2), 2.92 (s, 2H, NCH2), 3.70 (s, 2H, PhCH2), 7.20-7.38 (m, 5H, Ph). 13C NMR (CDCl3): δ 7.05 (Si(CH3)2), 18.89, 24.65 (C(CH3)2), 37.01 (PhCH2), 41.82 (NCH2), 127.24, 128.32, 128.53, 132.86 (Ph), 171.23 (NdC), 179.12 (CdO). 29Si NMR (CDCl3): δ -34.06. Anal. Calcd. for C14H21ClN2OSi: C, 56.64; H, 7.13; N, 9.44. Found: C, 56.50; H, 7.10; N, 9.45. Chlorodimethyl[N-(3-pentylideneimino)phenylacetamidomethyl]silane (9e). A mixture of 0.81 g (2.8 mmol) of 7e and 0.42 g (2.9 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg), and the resulting yellow oily residue was washed with 5 mL of n-hexane. Yield: 0.67 g (91%). 1H NMR (CDCl3): δ 0.67 (s, 6H, Si(CH3)2), 0.77 (t, 3J = 7.6 Hz, 3H, CH2CH3), 1.10 (t, 3J = 7.6 Hz, 3H, CH2CH3), 1.80 (q, 3J = 7.6 Hz, 2H, CH2CH3), 2.30 (q, 3J=7.6 Hz, 2H, CH2CH3), 2.82 (s, 2H, NCH2), 3.59 (s, 2H, PhCH2), 7.08-7.27 (m, 5H, Ph). 13C NMR (CDCl3): δ 7.18 (Si(CH3)2), 9.79, 10.13 (CH2CH3), 24.67, 28.44 (CH2CH3), 37.04 (PhCH2), 42.73 (NCH2), 127.34, 128.77, 129.00, 133.06 (Ph), 171.66 (NdC), 185.56 (CdO). 29Si NMR (CDCl3): δ -34.32. Chlorodimethyl[N-(cycloheptylideneimino)phenylacetamidomethyl]silane (9f). A mixture of 0.99 g (3.1 mmol) of 7f and 0.45 g (3.1 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) leaving a colorless oily residue. Yield: 0.69 g (63%). 1H NMR (CDCl3): δ 0.59 (s, 6H, CH3), 1.27, 1.35, 1.49, 1.54, 1.90, 2.44 (6m, 12H, CH2), 2.81 (s, 2H, NCH2), 3.56 (s, 2H, PhCH2), 7.03-7.23 (m, 5H, Ph). 13C NMR (CDCl3): δ 7.02 (CH3), 23.65, 26.07, 29.07, 30.05, 31.88, 36.61 (CH2)6, 36.76 (PhCH2), 41.39 (NCH2), 171.33 (CdN), 186.82 (CdO). 29Si NMR (CDCl3): δ -34.93. Anal. Calcd. for C18H27ClN2OSi: C, 61.60; H, 7.75; N, 7.98. Found: C, 61.76; H, 7.69; N, 8.03. Chlorodimethyl[N-(cyclohexylideneimino)benzamidomethyl]silane (9h). Compound 9h was obtained by Wawzonek rearrangement: a chloroform solution of 10h (1.05 g, 3.25 mmol) was kept at reflux temperature for 2 h, followed by removal of volatiles under reduced pressure. The solid residue was washed twice with n-hexane. The yield is quantitative, mp. 94 °C (dec). 1 H NMR (CDCl3): δ 0.69 (s, 6H, CH3), 1.37-1.62, (m, 6H, (CH2)3), 2.12 (t, 3J = 6.5 Hz, 2H, NdC(CH2)2), 2.31 (t, 3J = 6.5 Hz, 2H, NdC(CH2)2), 3.06 (s, 2H, NCH2), 7.34-7.65 (m, Ph). 13 C NMR (CDCl3): δ 7.27 (CH3), 24.40, 25.91, 26.57, 29.70, 35.22 ((CH2)5), 44.42 (NCH2), 127.81, 128.24, 129.48, 132.31 (Ph), 166.97 (NdC(CH2)5), 182.67 (OCdN). 29Si NMR (CDCl3): δ -36.8. Anal. Calcd. for C16H23ClN2OSi: C, 59.51; H, 7.18; N, 8.68. Found: C, 59.71; H, 6.98; N, 8.60. [N-Benzimidato(cyclopentylideneimmoniummethyl)-O,C]chlorodimethylsilicate (10 g). A mixture of 0.92 g (3.4 mmol) of 7g and 0.49 g (3.4 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) and the yellow solid residue was washed with 5 mL of n-hexane. Yield: 0.93 g (90%). Mp. 102 °C (dec). 1H NMR (CDCl3): δ 0.49 (s, 6H, CH3), 1.73-1.84 (m, 4H,

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(CH2)2), 2.77-2.92 (m, 4H, (CH2)2), 4.05 (s, 2H, NCH2), 7.127.27, 7.69-7.70 (m, Ph). 13C NMR (CDCl3): δ 1.49 (CH3), 23.90, 24.31, 34.21, 34.81 ((CH2)4), 48.16 (NCH2), 127.44, 127.78, 129.82, 132.22 (Ph), 161.06 (NdC(CH2)4), 188.47 (OCdN). 29Si NMR (CDCl3): δ -4.02. Anal. Calcd. for C15H21ClN2OSi: C, 58.33; H, 6.85; N, 9.07. Found: C, 58.12; H, 6.74; N, 8.87. [N-Benzimidato(cyclohexylideneimmoniummethyl)-O,C]chlorodimethylsilicate (10 h). A mixture of 1.15 g (4.0 mmol) of 7h and 0.59 g (4.1 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) and the yellow oily residue was washed with 5 mL of n-hexane. Yield: 1.05 g (81%). 1H NMR (CDCl3): δ 0.65 (s, 6H, CH3), 1.28-2.22 (m, 6H, (CH2)3), 2.96 (m, 4H, NdC(CH2)2), 4.33 (s, 2H, NCH2), 7.27-7.85 (m, Ph). 13 C NMR (CDCl3): δ 2.20 (CH3), 23.40, 25.69, 26.25, 31.53, 31.82 ((CH2)5), 48.01 (NCH2), 127.80, 128.22, 129.24, 132.59 (Ph), 162.65 (NdC(CH2)5), 180.34 (OCdN). 29Si NMR (CDCl3): δ -1.83. Anal. Calcd. for C16H23ClN2OSi: C, 59.51; H, 7.18; N, 8.68. Found: C, 59.67; H, 7.02; N, 8.56. [N-Benzimidato(cycloheptylideneimmoniummethyl)-O,C]chlorodimethylsilicate (10i). A mixture of 1.15 g (1.8 mmol) of 7i and 0.28 g (2.0 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) and the yellow solid residue was washed with 5 mL of n-hexane. Yield: 0.55 g (92%). Mp. 140143 °C. 1H NMR (CDCl3): δ 0.68 (s, 6H, CH3), 1.32-2.48 (m, 8H, (CH2)4), 3.04 (br, 4H, (CH2)2), 4.31 (s, 2H, NCH2), 7.377.96 (m, Ph). 13C NMR (CDCl3): δ 2.90 (CH3), 24.32, 24.38,

Yakubovich et al. 28.47, 28.58, 34.04, 34.31 ((CH2)6), 48.71 (NCH2), 127.88, 128.28, 130.47, 132.59 (Ph), 162.57 (NdC(CH2)6), 181.97 (OCdN). 29Si NMR (CDCl3): δ -6.30. Anal. Calcd. for C17H25ClN2OSi: C, 60.60; H, 7.48; N, 8.31. Found: C, 60.70; H, 7.41; N, 8.40. Chlorodimethyl[N-pivaloimidato(isopropylideneimmoniummethyl)-O,C]silicate (10j). A mixture of 0.48 g (2.1 mmol) of 7j and 0.30 g (2.1 mmol) of 1 in 5 mL of chloroform was stirred at room temperature for 1 h. The volatiles were removed under reduced pressure (0.1 mmHg) and the yellow solid residue was washed with 5 mL of n-hexane. Yield: 0.52 g (94%). Mp. 103-105 °C. 1H NMR (CDCl3): δ 0.48 (s, 6H, Si(CH3)2), 1.03 (s, 9H, C(CH3)3), 2.40 (s, 3H, C(CH3)2), 2.63 (s, 3H, C(CH3)2), 4.18 (s, 2H, NCH2). 13C NMR (CDCl3): δ 0.32 (Si(CH3)2), 23.83, 23.96 (C(CH3)2), 26.79 (C(CH3)3), 38.09 (C(CH3)3), 46.41 (NCH2), 173.60 (NdC(CH3)2), 176.40 (OCdN). 29Si NMR (CDCl3): δ 10.73. Anal. Calcd. for C11H23ClN2OSi: C, 50.26; H, 8.82; N, 10.68. Found: C, 50.15; H, 8.67; N, 10.67.

Acknowledgment. Financial support by the Israel Science Foundation, Grant No. ISF-139/05, is gratefully acknowledged. Supporting Information Available: 1H, 13C, and 29Si NMR spectra for compounds 7a, 9a, 9b, and 9e. Crystallographic data for 9c, 9d, and 10i in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.