Si−Cl Preferential Reactivity in Chlorosilyl ... - ACS Publications

Organometallics 2009, 28, 6975–6980 DOI: 10.1021/om9008026

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M-Cl/Si-Cl Preferential Reactivity in Chlorosilyl-Substituted Cyclopentadienyl Early Transition Metal Complexes in Reactions with Amines: Key to Understanding the Nature of the Final Product Cristina Paniagua,† Marta E. G. Mosquera,†,‡ Heiko Jacobsen,§ Gerardo Jim
enez,*,† and Tom
as Cuenca*,† †

Departamento de Quı´mica Inorg
anica, Universidad de Alcal
a, Campus Universitario, 28871 Alcal
a de Henares. Spain, and §KemKom, 1215 Ursulines Avenue, New Orleans, Louisiana 70116 Received September 14, 2009

The reaction of [Ti(η5-C5Me4SiMe2Cl)Cl3] (1) with 1 equiv of different ethylenediamines, NHR(CH2)2NR0 R00 , regiospecifically affords cyclopentadienyl-silyl-amido derivatives with constrainedgeometry, [Ti{η5-C5Me4SiMe2-κ-N(CH2)2NR0 R00 }Cl2] (R0 =R00 =H, 2a; R0 =H, R00 =Me, 2b; R0 = R00 =Me, 2c) or unstrained structure, [Ti{η5-C5Me4SiMe2NMe(CH2)2-κ-NMe}Cl2] (3). Treatment of 1 with 1.5 equiv of ethylenediamine gives a mixture of 2a and the transient complex [Ti{η5C5Me4SiMe2NH(CH2)2NH2}Cl3] (4), which is transformed into 2a upon addition of a base. The reaction of 1 with N,N,N0 -trimethylethylenediamine permits the synthesis and isolation of the complex [Ti{η5-C5Me4SiMe2NMe(CH2)2NMe2}Cl3] (5). Compound 1 reacts with 0.5 equiv of NH2(CH2)2NH2 to yield a mixture of 2a along with the tethered dinuclear cyclopentadienyl-silyl-amido compound [Ti{η5-C5Me4SiMe2-κ-N(CH2)-}Cl2]2 (6). Currently, there is a continuous and increasing interest in the chemistry of transition metal compounds bearing ancillary polydentate ligands.1-5 Modification of the ligand environment at the metal centers has enabled the preparation of new generations of polymerization catalyst precursors with excellent performance.6-14 Among the multidentate ligands most widely studied, a prominent class consists of bifunctional cyclopentadienyl ligands incorporating neutral or anionic appended donor substituents.15-18 The relevance of this research area is inferred from the numerous reviews of derivatives of this type recently

published.1,3,16,17 This field has largely been stimulated by the remarkable success of the group 4 metal “constrained-geometry” complexes as alternative catalysts to the classical bis(cyclopentadienyl) systems19-22 (MCp2X2) for R-olefin polymerization processes.23,24 One of our ongoing research lines is focused on the development of a new, efficient, and versatile alternative strategy to prepare transition metal complexes containing a bifunctional cyclopentadienyl ligand,25 based on protonolysis reactions of M-Cl and Si-Cl bonds from chlorosilylsubstituted cyclopentadienyl compounds,26-28 in reactions with

‡Correspondence concerning the crystallography data should be addressed to this author. E-mail: [email protected]. *Corresponding authors. Tel: 34918854765; 34918854655. Fax: 34 918854683. E-mail: [email protected]; [email protected]. (1) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283–315. (2) Adams, J. R.; Bennett, M. A. Adv. Organomet. Chem. 2006, 54, 293–331. (3) Gibson, V. C.; Redshaw, C.; Solan, G. A. Chem. Rev. 2007, 107, 1745–1776. (4) Gendler, S.; Zelikoff, A. L.; Kopilov, J.; Goldberg, I.; Kol, M. J. Am. Chem. Soc. 2008, 130, 2144–2145. (5) Chen, F.; Kapon, M.; Woollins, J. D.; Eisen, M. S. Organometallics 2009, 28, 2391–2400. (6) Brintzinger, H. H.; Fischer, D.; M€ ulhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143–1170. (7) Scollard, J. D.; McConville, D. H.; Payne, N. C.; Vittal, J. J. Macromolecules 1996, 29, 5241–5243. (8) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169–1203. (9) Kaminsky, W. Catal. Today 2000, 62, 23–34. (10) Hustad, P. D.; Tian, J.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 3614–3621. (11) Bolton, P. D.; Mountford, P. Adv. Synth. Catal. 2005, 347, 355–366. (12) Stephan, D. W. Organometallics 2005, 24, 2548–2560. (13) Matsugi, T.; Fujita, T. Chem. Soc. Rev. 2008, 37, 1264–1277. (14) Makio, H.; Fujita, T. Acc. Chem. Res. 2009, 42, 1532–1544. (15) Jutzi, P.; Redeker, T. Eur. J. Inorg. Chem. 1998, 663–674. (16) Butensch€ on, H. Chem. Rev. 2000, 100, 1527–1564. (17) Siemeling, U. Chem. Rev. 2000, 100, 1495–1526. (18) Nabika, M.; Katayama, H.; Watanabe, T.; Kawamura-Kuribayashi, H.; Yanagi, K.; Imai, A. Organometallics 2009, 28, 3785–3792.

(19) Okuda, J.; Eberle, T., Half-Sandwich Complexes as Metallocene Analogues. In Metallocenes; Togni, A. H. R. L., Eds.; Wiley-VCH: New York, 1998; Vol. 1, Chapter 7. (20) Okuda, J. Dalton Trans. 2003, 2367–2378. (21) Braunschweig, H.; Breitling, F. M. Coord. Chem. Rev. 2006, 250, 2691–2720. (22) Cano, J.; Kunz, K. J. Organomet. Chem. 2007, 692, 4411–4423. (23) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587–2598. (24) Chum, P. S.; Kruper, W. J.; Guest, M. J. Adv. Mater. 2000, 12, 1759–1767. (25) Cuenca, T.; Royo, P. Coord. Chem. Rev. 1999, 195, 447–498. (26) Ciruelos, S.; Cuenca, T.; G
omez-Sal, P.; Manzanero, A.; Royo, P. Organometallics 1995, 14, 177–185. (27) Buitrago, O.; Jim
enez, G.; Cuenca, T. J. Organomet. Chem. 2003, 683, 70–76. (28) Alcalde, M. I.; G
omez-Sal, P.; Martı´ n, A.; Royo, P. Organometallics 1998, 17, 1144–1150. (29) Alcalde, M. I.; G
omez-Sal, M. P.; Royo, P. Organometallics 2001, 20, 4623–4631. (30) Buitrago, O.; Mosquera, M. E. G.; Jim
enez, G.; Cuenca, T. Inorg. Chem. 2008, 47, 3940–3942. (31) Gonz
alez-Maupoey, M.; Cuenca, T.; Frutos, L. M.; Casta~ no, O.; Herdtweck, E. Organometallics 2003, 22, 2694–2704. (31) Gonz
alez-Maupoey, M.; Cuenca, T.; Frutos, L. M.; Casta~ no, O.; Herdtweck, E. Organometallics 2003, 22, 2694–2704. (32) Gonz
alez-Maupoey, M.; Cuenca, T. Organometallics 2006, 25, 4358–4365. (33) Alesso, G.; Sanz, M.; Mosquera, M. E. G.; Cuenca, T. Eur. J. Inorg. Chem. 2008, 4638–4649. (34) Buitrago, O.; Jim
enez, G.; Cuenca, T. Doctoral Thesis, University of Alcal
a, 2008.

r 2009 American Chemical Society

Published on Web 11/05/2009

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Paniagua et al. Scheme 1

Scheme 2

protic reagents such as water,29,30 alcohols,31-33 silanols,34 primary monoamines,35-37 and diamines.38-42 We are interested in understanding the pathway following these reactions since it would enable us to attain greater control over such processes. With this idea in mind, we initially studied the behavior that [Nb(η5-C5H4SiMe2Cl)Cl4] features in its reactions with primary mono- and diamines. This study indicated that the reactions specifically proceed with initial aminolysis of a Nb-Cl bond, rendering an amido transient that ultimately gives imido (A) or amido-amino (B) derivatives.42 In contrast, the behavior exhibited by the analogous titanium compound [Ti(η5-C5H4SiMe2Cl)Cl3] in similar aminolysis processes was markedly different. Thus, the parallel reactions with the titanium complex yield the corresponding cyclopentadienyl-amido derivative (C or D) (comparative Ti-Nb experimental observations are shown in Scheme 1). We describe herein our study analyzing the reactivity of the cyclopentadienyl-substituted titanium complex [Ti(η5-C5Me4SiMe2Cl)Cl3] (1), bearing the higher electron-donor permethylated cyclopentadienyl ligand, with different organic ethylenediamines NHR(CH 2)2NR0 R00 . (35) Ciruelos, S.; Cuenca, T.; G
omez, R.; G
omez-Sal, P.; Manzanero, A.; Royo, P. Organometallics 1996, 15, 5577–5585. (36) Alcalde, M. I.; G
omez-Sal, M. P.; Royo, P. Organometallics 1999, 18, 546–554. (37) Arteaga-M€ uller, R.; S
anchez-Nieves, J.; Royo, P.; Mosquera, M. E. G. Polyhedron 2005, 24, 1274–1279. (38) Jim
enez, G.; Rodrı´ guez, E.; G
omez-Sal, P.; Royo, P.; Cuenca, T.; Galakhov, M. Organometallics 2001, 20, 2459–2467. (39) Jim
enez, G.; Royo, P.; Cuenca, T.; Herdtweck, E. Organometallics 2002, 21, 2189–2195. (40) Maestre, M. C.; Tabernero, V.; Mosquera, M. E. G.; Jim
enez, G.; Cuenca, T. Organometallics 2005, 24, 5853–5857. (41) Maestre, M. C.; Paniagua, C.; Herdtweck, E.; Mosquera, M. E. G.; Jim
enez, G.; Cuenca, T. Organometallics 2007, 26, 4243–4251. (42) Maestre, M. C.; Mosquera, M. E. G.; Jacobsen, H.; Jim
enez, G.; Cuenca, T. Organometallics 2008, 27, 839–849.

Results and Discussion Treatment of 1 with an equimolar amount of different ethylenediamines, in aromatic solvents in the presence of 2 equiv of NEt3, gave cyclopentadienyl-silyl-amido derivatives (Scheme 2). When the aminolysis reaction was performed with diamines with at least a primary extreme, NH2(CH2)2NR0 R00 , the constrained-geometry derivatives [Ti{η5-C5Me4SiMe2-κ-N(CH2)2NR0 R00 }Cl2] (R0 = R00 = H, 2a; R0 = H, R00 = Me, 2b; R0 = R00 = Me, 2c43), with the pendant amino functionality weakly interacting with the titanium atom, were obtained. This result coincides with that reached in similar processes with the analogous niobium complex [Nb(η5-C5H4SiMe2Cl)Cl4]. However, when N,N0 -dimethylethylenediamine was used, the reaction yielded the cyclopentadienyl-silyl-amido derivative [Ti{η5-C5Me4SiMe2NMe(CH2)2-κ-NMe}Cl2] (3), featuring an unstrained structure, in sharp contrast to that achieved when the niobium complex [Nb(η5-C5H4SiMe2Cl)Cl4] reacts with the same diamine, where the final product is an amido-amino derivative (Scheme 1), retaining the Si-Cl bond intact. These reactions specifically proceeded with the aminolysis of the Ti-Cl and Si-Cl bonds with concomitant elimination of two HCl molecules. However, whereas the reaction with NHMe(CH2)2NHMe progressed through the deprotonation of both NHMe moieties, generating a strain-free cyclopentadienyl-silyl-amido derivative 3, the reactions with the diamines NH2(CH2)2NR0 R00 , containing at least a primary amine extreme, proceed with double deprotonation of the NH2 functionality, affording the corresponding constrainedgeometry complexes 2. The outcomes observed for compounds 2 are substantially in agreement with those reached in parallel reactions for the congener titanium compound [Ti(η5-C5H4SiMe2Cl)Cl3]. However, whereas in the complexes with the unsubstituted cyclopentadienyl ring the (43) Duplooy, K. E.; Moll, U.; Wocadlo, S.; Massa, W.; Okuda, J. Organometallics 1995, 14, 3129–3131.

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Scheme 3

Scheme 4

pendant amine function is tightly coordinated to the titanium atom in solution and in the solid state, in the analogous compounds with the tetramethylcyclopentadienyl ligand this group interacts only weakly in solution with the metal center, as judged by its spectroscopic behavior. This feature is explained by the different donor capacity of the cyclopentadienyl ligand in each case. Complexes 2 and 3 were alternatively generated by treating 1 with 3-fold of the corresponding diamine in aromatic solvents and in the absence of NEt3. However, in the case of the ethylenediamine, when the amount of diamine was halved (1(Ti):1.5(diamine)), and the reaction was conducted in a polar chlorinated solvent, the final result was perceptively different. Upon incomplete consumption of 1, a mixture of the constrained-geometry compound 2a and a new cyclopentadienytitanium derivative, [Ti{η5-C5Me4SiMe2NH(CH2)2NH2}Cl2] (4), bearing a noncoordinated pendant ethylenediaminesilyl-substituted cyclopentadienyl ligand, was detected in a spectroscopic molar ratio of ca. 3:1, respectively (Scheme 3). Upon addition of NEt3, compound 4 was quantitatively (as seen by NMR spectroscopy) converted into complex 2a. All attempts, using different Ti: diamine ratios, to isolated 4 in a pure form proved unfruitful, although the structural disposition of this compound could be formulated by spectroscopic analysis of the sample mixture containing both compounds 2a and 4. In trying to clarify the reacting preference of the Ti-Cl and Si-Cl bonds, we explored the reaction of 1 with the N,N,N0 trimethylethylenediamine, which contains a single reacting N-H bond. This reaction specifically proceeds with the aminolysis of the Si-Cl bond, giving the monocyclopentadienyl derivative [Ti{η5-C5Me4SiMe2NMe(CH2)2NMe2}Cl3] (5), revealing therefore that the first step in these processes is the protonolysis of the silicon-chloride bond (Scheme 4). Subsequently, the Ti-Cl bond aminolysis reaction produces the final derivative of the reactions. To prove whether the weaker amino-titanium interaction in solution in these complexes, compared to an analogue with an unmethylated cyclopentadienyl ring, enhanced the reactivity of the NH2 group toward a further intermolecular aminolysis process, we explored the reaction of 1 with 0.5 equiv of diamine. Thereby, the reaction of 1 with 0.5 equiv of ethylenediamine in toluene and in the presence of 2 equiv of

NEt3 afforded a mixture of a new dinuclear derivative, [Ti{η5-C5Me4SiMe2-κ-N(CH2)-}Cl2]2 (6), consisting of two tethered constrained-geometry fragments, and the mononuclear complex 2a, as the major product, as well as some unreacted starting material (Scheme 5). The constrained-geometry complexes with a noncoordinated appended amine group are more easily hydrolyzed than their partners with the cyclopentadienyl ring unsubstituted. In the complexes bearing a permethylated ring the Lewis acidity of the titanium atom decreases, and consequently, the potential coordination of the pendant donor group is weaker, which means that the amine functionality is more available to be involved in hydrolysis.44 The spectroscopic behavior of all these compounds is in agreement with Cs symmetry in solution, according to the proposed structures. The spectroscopic analysis of the chemical shifts in the SiMe2X fragment, for the methyl groups in the 1H NMR spectra and the silicon resonances in the 29Si NMR spectra, provide a suitable means to determine whether the chloride atom remains bonded to silicon or if it has been substituted in these reactions.42,45 The expected NMR resonances are notably influenced by the nature of the X substituent, and upfield shifts are observed when a nitrogen atom interchanges with the chloride atom. Consistently, the corresponding “SiMe2N” resonances for compounds 2-6 appear high-field shifted (δrange ≈ 0.45-0.70 for the methyl protons and δaverage ≈ -16.5 for the silicon atom in the constrainedgeometry complexes 2 and 6 and δrange ≈ 5.5 to -5.6 for the silicon atom in compounds 3-5) compared with the corresponding resonances for the parent compound 1 (δ 0.91 for the methyl protons and δ 15.3 for the silicon atom). In addition, the constrained-geometry nature of complexes 2 and 6 was confirmed by the diagnostic observation of the upfield shifted resonance for the cyclopentadienyl ipso-carbon with respect to the rest of the ring carbon atoms.42,45 The 1H NMR spectra of 2a and 2b (room temperature in CDCl3) feature an easily observed broad signal for amino protons, while the resonance for NH2 protons in the case of 4 appears indistinguishable, although its presence has been confirmed by TOCSY experiments. In the three complexes, the downfield shift observed for amino protons, compared to the corresponding free diamine resonances, indicates that the pendant amino group was interacting in some manner with the titanium atom.46 However, the Cs spectroscopic behavior shown by 2b contrasts with the asymmetric structure found (44) Flores, J. C.; Chien, J. C. W.; Rausch, M. D. Organometallics 1994, 13, 4140–4142. (45) G
omez, R.; G
omez-Sal, P.; del Real, P. A.; Royo, P. J. Organomet. Chem. 1999, 588, 22–27. (46) Fric, H.; Puchberger, M.; Schubert, U. Eur. J. Inorg. Chem. 2007, 376–383.

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Figure 1. Molecular structures of 2b, 3, and 6 shown with 30% thermal ellipsoids. Hydrogen atoms are omitted for clarity. Scheme 5

Scheme 6

in the solid state (see Supporting Information), consistent with the ease of amino nitrogen racemization and revealing that in these complexes the amino-titanium interaction is rather weak in solution. The 15N NMR chemical resonances (measured by 1H-15N heteronuclear multiple-bond correlation spectroscopy, HMBC) provide a useful indicator of the bond environment for the different nitrogen functionalities. These studies reveal that the 15N NMR resonances appeared in a characteristic chemical shift range depending on the nature of the nitrogen group: (i) amido-titanium ligands (both in constrainedgeometry 2 and in strain-free complexes 3) at δ > 300; (ii) Si-NR-CH2 moieties at δ < 13; (iii) pendant NR0 R00 groups in the range δ 30-70. The moderate downfield shifted amino nitrogen resonances (CH2NR0 R00 ) in complexes 2 (δ 69.3, 2a; 68.4, 2b; 48.5, 2c) compared to the resonances in the corresponding free amine (δrange = 22-26) corroborate the above-mentioned weak amino titanium interaction in solution.46,47 In contrast, for complex 5 the signal for the nitrogen atom NMe2 appears upfield shifted (δ = 23.7) in the (47) Fric, H.; Puchberger, M.; Schubert, U. J. Sol-Gel Sci. Technol. 2006, 40, 155–162.

normal range of the free amine resonances, indicating a lack of coordination in solution. A remarkable feature of several of the compounds described is their high fluxionality shown in solution, which we have been able to confirm by variable-temperature 1H NMR analysis. Cooling NMR samples of 2b and 4 resulted in a broadening and finally splitting of the resonances corresponding to SiMe2, C5Me4, and CH2 protons. The 1H NMR spectra of the complexes below their coalescence temperatures (228 and 275 K, respectively) show evidence of resonance patterns consistent with C1-symmetry structures. The observed dynamic process of 2b involves exchange between two enantiomeric C1 ground states, resulting from the racemization at the amino nitrogen through a dissociation-inversion-recoordination sequence.38 For compound 4, the fluxional behavior is described as interconversion between two enantiomeric conformations, resulting from flipping the Cp-NH2 linker, once the amino coordination-decoordination process has been frozen out (Scheme 6).38 Single crystals of 2b, 3, and 6 were grown in toluene/hexane solutions at low temperature, and the molecular structure was established by X-ray diffraction studies. Molecular structures

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Scheme 7

are shown in Figure 1, and structural discussion is found in the Supporting Information. In conclusion, new mononuclear cyclopentadienyl-silylamido derivatives, with constrained-geometry 2 or open structures 3, the cyclopentadienyl-silyl-amino 4 and 5, and the dinuclear amido derivative 6 have been reported. Appropriate reaction conditions and synthetic method for the desired compound are summarized in Scheme 7. We propose that the pathway followed for titanium and niobium compounds in reactions of this type is substantially different and is instrumental in determining the different nature of the products obtained in each case. In titanium compounds, the preferential rupture of the Si-Cl bond prevents the formation of amido-amino or imido derivatives, whereas in niobium compounds, the reaction takes place through the initial aminolysis of a Nb-Cl, which rationalizes the generation of the amido derivatives and the subsequent transformation into imido or cyclopentadienyl-silyl-amido complexes.

Experimental Section All manipulations were performed under argon using Schlenk, high-vacuum line techniques or in a glovebox, model HE-63. C, H, and N microanalyses were performed on a PerkinElmer 240B and/or Heraeus CHN-O-Rapid microanalyzer. NMR spectra, at 25 °C, were recorded on a Bruker AV400 (1H NMR at 400 MHz, 13C NMR at 100.6 MHz, 29Si NMR at 79.5 MHz, 15N NMR at 40.5 MHz). Synthesis of [Ti{η5-C5Me4SiMe2-K-N(CH2)2NH2}Cl2] (2a). A toluene solution (10 mL) of NH2(CH2)2NH2 (0.09 mL, 1.36 mmol) and NEt3 (0.38 mL, 2.72 mmol) was added to a dark red solution of 1 (0.50 g, 1.36 mmol) in toluene (30 mL) at room temperature. The color of the reaction mixture immediately changed to yellowish-brown. The reaction mixture was stirred for 2 h, the white solid formed was collected by filtration, and the volatiles were removed under vacuum. The residue was washed with n-hexane (30 mL) and extracted into toluene (2  20 mL). The resulting solution was concentrated to ca. half volume and cooled to -20 °C to afford 2a in 72.2% yield (0.35 g, 0.98 mmol). Anal. Calcd for C13H24Cl2N2SiTi: C, 43.95; H, 6.82; N, 7.89. Found: C, 44.09; H, 6.81; N, 7.43. 1H NMR (400 MHz, CDCl3): δ 0.49 (s, 6H, SiMe2), 2.07, 2.16 (s, 2  6H, C5Me4), 3.33 (m, 2H, CH2NH2), 3.72 (t, J = 6 Hz, 2H, TiNCH2), 3.97 (brm, 2H,

NH2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 1.8 (SiMe2), 13.0, 15.5 (C5Me4), 43.7 (CH2NH2), 57.2 (TiNCH2), 103.1 (CipsoC5Me4), 135.9, 137.7 (C5Me4). 29Si NMR (79.5 MHz, CDCl3): δ -16.2 (SiMe2). 15N NMR (40.5 MHz, CDCl3): δ 69.3 (CH2NH2), 312.9 (TiNCH2). Synthesis of [Ti{η5-C5Me4SiMe2-K-N(CH2)2NHMe}Cl2] (2b). A method similar to that described for 2a was adopted by using NH2(CH2)2NHMe (0.12 mL, 1.36 mmol) to give 2b as a reddish-brown solid. Yield: 87% (0.44 g, 1.18 mmol). Anal. Calcd for C14H26Cl2N2SiTi: C, 45.53; H, 7.11; N, 7.59. Found: C, 45.21; H, 6.96; N, 7.02. 1H NMR (400 MHz, CDCl3): δ 0.47 (s, 6H, SiMe2), 2.08, 2.14 (s, 2  6H, C5Me4), 2.83 (s, 3H, NHMe), 3.18 (m, 2H, CH2NHMe), 3.60 (brm, 1H, NHMe), 3.67 (t, J = 6 Hz, 2H, TiNCH2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 1.6 (SiMe2), 13.0, 15.7 (C5Me4), 38.8 (NHMe), 52.8 (CH2NHMe), 54.5 (TiNCH2), 102.9 (Cipso-C5Me4), 135.5, 137.3 (C5Me4). 29Si NMR (79.5 MHz, CDCl3): δ -16.6 (SiMe2). 15N NMR (40.5 MHz, CDCl3): δ 68.4 (CH2NHMe), 304.5 (TiNCH2). Synthesis of [Ti{η5-C5Me4SiMe2-K-N(CH2)2NMe2}Cl2] (2c). A method similar to that described for 2a was adopted by using NH2(CH2)2NMe2 (0.16 mL, 1.36 mmol) to give 2c as a yellowish-brown solid. Yield: 83% (0.43 g, 1.13 mmol). Anal. Calcd for C15H28Cl2N2SiTi: C, 47.00; H, 7.35; N, 7.31. Found: C, 47.23; H, 7.36; N, 6.85. 1H NMR (400 MHz, CDCl3): δ 0.53 (s, 6H, SiMe2), 2.05, 2.18 (s, 2  6H, C5Me4), 2.47 (s, 6H, NMe2), 2.93 (m, 2H, CH2NMe2), 3.81 (t, J = 6 Hz, 2H, TiNCH2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 2.1 (SiMe2), 13.1, 15.7 (C5Me4), 41.2 (NMe2), 53.5 (TiNCH2), 60.7 (CH2NMe2), 105.2 (CipsoC5Me4), 128.3, 137.3 (C5Me4). 29Si NMR (79.5 MHz, CDCl3): δ -17.2 (SiMe2). 15N NMR (40.5 MHz, CDCl3): δ 48.5 (CH2NMe2), 313.8 (TiNCH2). Synthesis of [Ti{η5-C5Me4SiMe2NMe(CH2)2-K-NMe}Cl2] (3). A solution of NHMe(CH2)2NHMe (0.58 mL, 5.44 mmol) in toluene (10 mL) was added to a stirred solution of [Ti(η5C5Me4SiMe2Cl)Cl3] (1.00 g, 2.72 mmol) in toluene (35 mL) at room temperature. After the reaction mixture was stirred for 4 h, the solid formed was collected by filtration, and the solvent was completely removed under reduced pressure to give a yellow residue. The residue was washed with cold n-hexane (2  10 mL) and dissolved in a minimum amount of toluene/hexane. The chilled solution (-20 °C) afforded bright yellow crystals. Yield: 89% (0.93 g, 2.42 mmol). Anal. Calcd for C15H28Cl2N2SiTi: C, 47.00; H, 7.38; N, 7.31. Found: C, 46.93; H, 7.18; N, 6.76. 1H NMR (400 MHz, CDCl3): δ 0.46 (s, 6H, SiMe2), 2.13, 2.20 (s,

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2  6H, C5Me4), 2.61 (s, 3H, SiNMe), 2.95 (m, 2H, SiNCH2), 3.64 (s, 3H, TiNMe), 4.02 (m, 2H, TiNCH2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 1.5 (SiMe2), 13.1, 16.0 (C5Me4), 38.2 (SiNMe), 44.9 (TiNMe), 51.5 (SiNCH2), 65.5 (TiNCH2), 124.0 (Cipso-C5Me4), 135.3, 136.2 (C5Me4). 29Si NMR (79.5 MHz, CDCl3): δ -5.6 (SiMe2). 15N NMR (40.5 MHz, CDCl3): δ 11.4 (SiNCH2), 314.5 (TiNCH2). Synthesis of [Ti{η5-C5Me4SiMe2NH(CH2)2NH2}Cl2] (4). NH2(CH2)2NH2 (0.08 mL, 1.22 mmol) in dichloromethane (10 mL) was added to a stirred solution of [Ti(η5-C5Me4SiMe2Cl)Cl3] (0.30 g, 0.82 mmol) in dichloromethane (20 mL) at room temperature. After the reaction mixture was stirred for 1 h, the solid formed was collected by filtration and the solvent was completely removed. The brown solid obtained was a mixture of 2a and 4 in a ratio 3:1. 4: 1H NMR (400 MHz, CDCl3): δ 0.67 (brs, 6H, SiMe2), 1.72 (brt, 1H, SiNH), 2.21, 2.45 (s, 2  6H, C5Me4), 3.06, 3.20 (m, 2  2H, CH2), 4.10 (vbrm, 2H, NH2). 13 C{1H} NMR (100.6 MHz, CDCl3): δ 0.8 (SiMe2), 13.5, 19.1 (C5Me4), 42.9, 47.0 (CH2), 108.1, 140.5, 148.2 (C5Me4). 29Si NMR (79.5 MHz, CDCl3): δ 5.5 (SiMe2). Synthesis of [Ti{η5-C5Me4SiMe2NMe(CH2)2NMe2}Cl2] (5). A solution of NHMe(CH2)2NMe2 (0.22 mL, 1.63 mmol) in toluene (10 mL) at room temperature was added to a dark red solution of [Ti(η5-C5Me4SiMe2Cl)Cl3] (0.30 g, 0.82 mmol) in toluene (20 mL) at room temperature. The reaction mixture was stirred for 2 h, the solid formed was collected by filtration, and the solvent was completely removed. The resulting solid was washed with cold n-hexane (2  10 mL) to give 5. Yield: 59.8% (0.21 g, 0.49 mmol). Anal. Calcd for C16H31Cl3N2SiTi: C, 44.30; H, 7.22; N, 6.46. Found: C, 44.63; H, 7.08; N, 6.76. 1H NMR (400 MHz, CDCl3): δ 0.49 (s, 6H, SiMe2), 2.17 (s, 6H, NMe2), 2.32, 2.51 (s, 2  6H, C5Me4), 2.47 (s, 3H, SiNMe), 2.27 (m, 2H, CH2NMe2), 2.79 (m, 2H, SiNCH2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 2.4 (SiMe2), 13.5, 16.7 (C5Me4), 34.90 (SiNMe), 45.3 (NMe2), 48.4 (SiNCH2), 58.9 (CH2NMe2), 142.2, 143.0, 144.8

Paniagua et al. (C5Me4). 29Si NMR (79.5 MHz, CDCl3): δ -3.30 (SiMe2). 15N NMR (40.5 MHz, CDCl3): δ 13.5 (SiNMe), 23.7 (NMe2). Synthesis of [Ti{η5-C5Me4SiMe2-K-N(CH2)-}Cl2]2 (6). A toluene solution (10 mL) of NH2(CH2)2NH2 (0.09 mL, 1.36 mmol) and NEt3 (0.76 mL, 5.44 mmol) was added to a dark red solution of [Ti(η5-C5Me4SiMe2Cl)Cl3] (1.00 g, 2.72 mmol) in toluene (50 mL) at room temperature. The reaction mixture was stirred for 2 h, the white solid formed was collected by filtration, and the volatiles were removed under vacuum. The residue was washed with n-hexane (30 mL) and extracted into toluene (2  15 mL), and the resulting solution was cooled to -20 °C to afford 6 as yellow microcrystals. Yield: 11.0% (0.10 g, 0.15 mmol). Anal. Calcd for C24H40Cl4N2Si2Ti2: C, 44.31; H, 6.21; N, 4.30. Found: C, 44.53; H, 6.18; N, 4.76. 1H NMR (400 MHz, CDCl3): δ 0.69 (s, 12H, SiMe2), 2.12, 2.22 (s, 2  12H, C5Me4), 4.13 (s, 4H, CH2). 13C{1H} NMR (100.6 MHz, CDCl3): δ 2.8 (SiMe2), 13.0, 16.1 (C5Me4), 54.5 (CH2), 103.5 (Cipso-C5Me4), 136.0, 141.5 (C5Me4). 29Si NMR (79.5 MHz, CDCl3): δ -15.8 (SiMe2). 15N NMR (40.5 MHz, CDCl3): δ 347.5 (TiNCH2).

Acknowledgment. Financial support for this research by Direcci
on General de Investigaci
on Cientı´ fica y T
ecnica (Project MAT2007-60997) and Comunidad Aut
onoma de Madrid (Project S-0505-PPQ/0328-02) is gratefully acknowledged. C.P.P. acknowledges Comunidad Aut
onoma de Madrid for a fellowship. Supporting Information Available: X-ray diffraction studies, tables of crystallographic data, including fractional coordinates, bond lengths and angles, anisotropic displacement parameters, and hydrogen atom coordinates in CIF format of complexes 2b, 3, and 6. This material is available free of charge via the Internet at http://pubs.acs.org.