Reactions of Titanium Hydrazinediido Complexes with Unsaturated

Organometallics 2009, 28, 4747–4757 DOI: 10.1021/om900428d

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Reactions of Titanium Hydrazinediido Complexes with Unsaturated Organic Substrates Katharina Weitershaus, Julio Lloret Fillol, Hubert Wadepohl, and Lutz H. Gade* Anorganisch-Chemisches Institut, Universit€ at Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany Received May 22, 2009

Reaction of [Cp*Ti(NXylN){N-NPh2}(NHt2Bu)] (1a) with 1 molar equiv of phenylallene resulted in the formation of a mixture of the two metallacyclic compounds [Cp*Ti(NXylN){κ2N(NPh2)C(CHPh)CH2}] (2a and 2b) in a molar ratio of 3:1. Comparison of the 13C and 15N NMR resonances with the computed chemical shifts, along with an X-ray diffraction study of 2a, allowed the assignment of the diastereomers as the cycloadducts derived from a (3,2)-cycloaddition of the allene to the TidN bond. Upon reaction of 1a with phenylisothiocyanate, two complexes were formed in a 3:1 ratio. The major isomer, [Cp*Ti(NXylN){κ2-N(NPh2)C(NPh)S}] (4a), was isolated and identified by X-ray diffraction to result from a [2þ2] cycloaddition of the CdS bond in PhNCS to the TidN bond of the hydrazinediido unit, giving a four-membered metallacyclic ring with an S,N-coordination to the titanium center and an exocyclic CdN double bond. In the minor compound (4b) the two nitrogen atoms of the thiourea unit formed in the cycloaddition are coordinated to the titanium center. Isomerization between the cycloadducts occurs only in the direction 4b f 4a, and crossover experiments indicate a dissociative mechanism (via a retro-cycloaddition) for the rearrangement. The reaction of 1a with PhNCO gave analogous N,O- and N,N-coordinated cycloadducts. Finally, the N,N-dimethyl hydrazinediido complexes reacted unspecifically with most organic azides at ambient temperature. However, complex [Cp*Ti(NXylN){N-NMe2}(dmap)] (1c) underwent a clean and fast reaction with trimethylsilylazide to give the N-silylated η2-hydrazido(1-) titanium azide [Cp*Ti(NXylN)(η2-NMe2-NSiMe3)(N3)] (8), in which the trimethylsilyl group of the azide is transferred to the hydrazido ligand, while the azide is terminally coordinated to the titanium center.

Introduction Despite the first synthesis of a titanium hydrazinediido complex by Wiberg et al. as early as 1978,1 their coordination chemistry and role in catalytic C-N coupling processes have only begun to receive closer attention during the past decade.2-10 This is remarkable in view of the large body of published work on analogous imidotitanium complexes.11,12 *Corresponding author. Fax: (þ49)6221-545-609. E-mail: lutz.gade@ uni-hd.de. (1) Wiberg, N.; Haering, H. W.; Huttner, G.; Friedrich, P. Chem. Ber. 1978, 111, 2708. (2) Selby, J. D.; Schulten, C.; Schwarz, A. D.; Stasch, A.; Clot, E.; Jones, C.; Mountford, P. Chem. Commun. 2008, 5101. (3) Selby, J. D.; Manley, C. D.; Schwarz, A. D.; Clot, E.; Mountford, P. Organometallics 2008, 27, 6479. (4) Clulow, A. J.; Selby, J. D.; Cushion, M. G.; Schwarz, A. D.; Mountford, P. Inorg. Chem. 2008, 47, 12049. (5) Selby, J. D.; Manley, C. D.; Feliz, M.; Schwarz, A. D.; Clot, E.; Mountford, P. Chem. Commun. 2007, 4937. (6) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov, G. I.; Swallow, D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379. (7) Li, Y.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2004, 126, 1794. (8) Banerjee, S.; Odom, A. L. Organometallics 2006, 25, 3099. (9) Patel, S.; Li, Y.; Odom, A. L. Inorg. Chem. 2007, 46, 6373. (10) Thorman, J. L.; Woo, L. K. Inorg. Chem. 2000, 39, 1301. (11) Mountford, P. Chem. Commun. 1997, 2127. (12) Gade, L. H.; Mountford, P. Coord. Chem. Rev. 2001, 216-217, 65. r 2009 American Chemical Society

The focus of the study of the hydrazides of titanium has been their significance as intermediates in hydrohydrazinations of alkynes and related catalytic multicomponent reactions. Mountford and co-workers reported several stoichiometric reactions of unsaturated substrates, such as terminal and internal alkynes, isocyanates, and CO2.2,4-6 They isolated, inter alia, a model system for the postulated intermediate in the hydrohydrazination of terminal alkynes and investigated [2þ2] cycloadditions with isocyanates and CO2. On the other hand, the reaction of a hydrazinediido complex with an internal alkyne indicated reaction patterns involving N-N bond cleavage of the hydrazide. The latter appears to be more pronounced in the reactions of hydrazinediides of the heavier group 4 metal analogues13-15 and opens up the possibility to discover new types of reactions. Recently, we have found that the titanium hydrazinediides [Cp*Ti(NXylN){N-NR1R2}(L)] (R1=R2=Ph and L=NHt2Bu: 1a, R1=Ph, R2=Me and L=py: 1b, or R1=R2=Me and L= dmap: 1c) are very active hydrohydrazination catalysts for (13) Herrmann, H.; Lloret Fillol, J.; Wadepohl, H.; Gade, L. H. Angew. Chem., Int. Ed. 2007, 46, 8426. (14) Herrmann, H.; Lloret Fillol, J.; Gehrmann, T.; Enders, M.; Wadepohl, H.; Gade, L. H. Chem.-Eur. J 2008, 14, 8131. (15) Herrmann, H.; Wadepohl, H.; Gade, L. H. Dalton Trans. 2008, 2111. Published on Web 07/23/2009

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Organometallics, Vol. 28, No. 16, 2009

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Scheme 1. Synthesis of Compounds 2a, 2b, and 3a by [2þ2] Cycloaddition Reaction of Phenylallene to the Hydrazido Moietya

a

Compound 3b in parentheses could not be isolated.

alkynes that operate at ambient temperature.16 The metallacyclic compound [Cp*Ti(NXylN){κ2N(NMe2)C(Ph)CH}], obtained by [2þ2] cycloaddition with phenylacetylene, was sufficiently stable to allow its characterization by NMR spectroscopy in solution. However, in general it proved to be difficult to isolate stable cycloadducts of alkynes with these TidN-NR2 complexes. In this study, we therefore focused our attention on the reactivity of [Cp*Ti(NXylN){N-NR1R2}(L)] (1a,b,c) toward other unsaturated substrates, namely, phenylallene and heteroallene derivatives, such as phenylisothiocyanate, phenylisocyanate, and trimethylsilylazide. In all cases issues of stereo- and regioselectivity in the cycloadditions had to be addressed in the assignment of the molecular structures. DFT-based modeling of the key complexes has been carried out to support the assignment of the characterization data and to provide insight into the bonding situation within the cycloadducts.

Results and Discussion [2þ2] Cycloadditions of Titanium Hydrazinediido Complexes with Phenylallene. Reaction of [Cp*Ti(NXylN){N-NPh2}(NHt2Bu)] (1a)16-18 with 1 molar equiv of phenylallene at room temperature immediately resulted in the formation of a mixture of two metallacyclic compounds, [Cp*Ti(NXylN){κ2N(NPh2)C(CHPh)CH2}] (2a and 2b), in a molar ratio of 3:1, as determined by NMR spectroscopy (Scheme 1). Whereas the elemental analysis of the crystalline mixture of the two isomers confirmed the overall formulation of the product, its two diastereomeric forms proved to be impossible to separate on a preparative scale. It was only by chance that a few single crystals of diastereomer 2a, which were suitable for X-ray diffraction, could be isolated (vide infra). However, we were able to assign the molecular structures of both 2a and 2b unambiguously by NMR spectroscopy. On the basis of the 1H NMR spectra of the product mixture possible regioisomers resulting from a (1,2)-cycloaddition of the allene could be discounted due to the absence of a characteristic dCH2 olefinic set of signals. Furthermore, the 1H NMR spectrum displays two major doublet resonances at 3.11 and 2.17 ppm, which are assigned to the AB system of the CH2 group of the major diastereomer 2a, while a similar set of two signals at 3.01 and 1.77 ppm was assigned to the minor isomer. The 2JH-H coupling constants are very (16) Weitershaus, K.; Wadepohl, H.; Gade, L. H. Organometallics 2009, 28 (12), 3381. (17) Ward, B. D.; Risler, H.; Weitershaus, K.; Bellemin-Laponnaz, S.; Wadepohl, H.; Gade, L. H. Inorg. Chem. 2006, 45, 7777. (18) Weitershaus, K.; Ward, B. D.; Kubiak, R.; M€ uller, C.; Wadepohl, H.; Doye, S.; Gade, L. H. Dalton Trans. 2009, 23, 4586.

similar for both compounds (11.8 Hz for complex 2a and 11.9 Hz for compound 2b). The exocyclic olefinic CH proton deriving from phenylallene is detected at 5.60 ppm for compound 2a and at 5.50 ppm for 2b. These chemical shifts are in agreement with previously reported data for azatitanacyclobutanes.19 A series of ROESY-NMR spectra displayed the crossrelaxation between the exocyclic olefinic proton of 2a with the ortho-protons on the phenyl rings of the NNPh2 fragment as well as a cross-peak between the metalated CH2 unit and the ortho-protons of the xylyl group on the (NXylN) ligand. These intramolecular cross-relaxation patterns are consistent with the molecular structure of 2a, as represented in Scheme 1. The minor isomer of the mixture, compound 2b, was found to possess a very similar NMR chemical shift pattern to complex 2a, suggesting an isomeric structure with similar connectivities. However, ambiguities remained concerning the exact chemical structure of compound 2b, which proved to be an interesting object of study for a combined experimental and theoretical approach. This involved the calculation of the 13C and 15N NMR chemical shifts of 2a along with other diastereomers (DFT GIAO-B3PW91 hybrid functional; see Experimental Section and Supporting Information) based on their DFT-computed structures (B3PW91 with a 6-31G(d) basis set; see the following section). The best fit between experimental and calculated NMR data is found for the isomeric structure 2b depicted in Figure 1, which differs from 2a in the relative orientation of the ancillary amidinate ligand with respect to the TiCCN metallacycle. Four 13C and 15N resonances were found to be particularly diagnostic. The experimentally determined chemical shifts are given in Figure 1 along with the computed data (in parentheses). Both 2a and 2b result from a (3,2)-cycloaddition and are clearly distinguished from potential isomers derived from a (2,3)-cycloaddition (with respect to the TidN bond), one of which is displayed as complex 2c along with its computed chemical shifts. Variable-temperature 1H NMR studies of the mixture of 2a and 2b indicated some exchange broadening at 100 °C; however, thermal decomposition setting in at this temperature precluded the observation of complete coalescence. A 2D exchange spectroscopy experiment (2D-EXSY) performed at 25 °C confirmed the slow interconversion of both diastereomers in solution, which suggests that both compounds may be assumed to be in equilibrium at ambient temperature. (19) Tr€ osch, D. J. M.; Collier, P. E.; Bashall, A.; Gade, L. H.; McPartlin, M.; Mountford, P.; Radojevic, S. Organometallics 2001, 20, 3308.

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Figure 1. Computed molecular structures of possible (3,2)-cycloaddition products to the TidN bond of 1a with phenylallene. Experimental and theoretical NMR data of compounds 2a and 2b and the calculated (2,3)-cycloaddition product 2c (not observed).

Figure 2. Molecular structure of complex 2a. Hydrogen atoms are omitted for clarity and ellipsoids drawn at the 40% probability level. Selected bond lengths (A˚) and angles (deg): Ti-N(1) 2.128(2), Ti-N(2) 2.110(2), Ti-N(3) 1.974(2), Ti-C(14) 2.186(2), Ti-Cent 2.048, N(3)-N(4) 1.411(2), C(13)-C(15) 1.350(3), C(13)-C(14) 1.505(3), C(13)-N(3) 1.394(3), N(1)Ti-N(2) 62.90(7), C(13)-N(3)-Ti 102.3(1), N(3)-Ti-C(14) 65.46(8), N(3)-C(13)-C(14) 102.1(2), C(13)-C(14)-Ti 89.7(1).

As indicated above, it proved possible to obtain single crystals of 2a that were suitable for X-ray diffraction analysis and therefore allowed the confirmation of the structural assignment based on spectroscopic methods. The molecular structure of complex 2a is depicted in Figure 2, along with the


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principal bond lengths and angles. The 2-aminopyrrolinato ligand is symmetrically κ2-coordinated to the titanium atom [Ti-N(1) 2.128(2), Ti-N(2) 2.110(2) A˚; N(1)-Ti-N(2) 62.90(7)°] as found previously for this type of ligands.16-18 In the four-membered metallacycle, generated by a formal [2þ2] (3,2)-cycloaddition of the hydrazinediide and phenylallene, the exocyclic bond C(13)-C(15) clearly has doublebond character [1.350(3) A˚], while the C(13)-C(14) distance [1.505(3) A˚], within the metallacyclic ring, falls in the singlebond range. All other bond lengths and angles are similar to the previously reported metric parameters of cycloaddition products derived from allenes and titanium imido compounds.19 Upon reacting [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b) with phenylallene, two isomeric complexes were formed in a 6:1 ratio (3a,b). From this mixture only the major compound, [Cp*TiN(NXylN){κ2N(N(Ph)Me)C(CHPh)CH2}] (3a), could be isolated in low yield (36%). As for 2a the 13C and 15N NMR spectra along with a 1H ROESY experiment allowed the structural assignment of 3a, which is displayed in Scheme 1. The small amount in which the minor component 3b was formed made a definitive structural assignment impossible. However, it is assumed to be the analogue of the characterized species 2b (Scheme 1). DFT Study of the Cycloaddition Products of the Hydrazinediido Complexes 1a and 1b with Phenylallene. To gain insight into energetics and bonding of the isomers formed in the reaction of phenylallene with the hydrazinediido titanium complexes 1a and 1b, both structures were modeled by DFT using the hybrid functional B3PW91 with a 6-31G(d) basis set for all atoms.20-23 An analysis of the possible reaction products generated by a [2þ2] cycloaddition of the allene to the hydrazido TidN bond revealed four possible isomers, the computed energies and free energies of which (relative to the lowest calculated value) are represented in Table 1. (20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople J. A. Gaussian 03, Revision D.02; Gaussian, Inc.: Wallingford, CT, 2004. (21) (a) Carpenter, J. E.; Weinhold, F. J. Mol. Struct. (THEOCHEM) 1988, 169, 41. (b) Carpenter, J. E. Ph.D. Thesis, University of Wisconsin, Madison, WI, 1987. (c) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211. (d) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 4066. (e) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899. (f ) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1985, 83, 1736. (h) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83, 735. (22) Dennington, R., II; Keith, T.; Millam, J.; Eppinnett, K.; Hovell, W. L.; Gilliland, R. GaussView, Version 3.0; Semichem, Inc.: Shawnee Mission, KS, 2003. (23) (a) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257. (b) Pople, J. A. J. Chem. Phys. 1975, 62, 2921. (c) Francl, M. M.; Petro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654. (d) Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P. V. R. J. Comput. Chem. 1983, 4, 294.

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Table 1. Relative Energies and Free Energies of the Calculated [2þ2] Phenylallene Cycloaddition Isomers

a

The zero point-corrected standard reaction energy and free energy of the [2þ2] cycloaddition products are given in parentheses for the thermodynamic reaction product.

Figure 3. Frontier Kohn-Sham molecular orbitals (NLMOs) of compound 2a.

The DFT-computed energies and Gibbs free energies of the different isomers are in qualitative agreement with the experimentally determined product ratio (the major experimental isomer, “type a”, being lower in energy than the “type b” isomers). The calculated differences in energy and free energy for 2a and 2b of ΔEzp=1.7 kcal 3 mol-1 and ΔG= 1.9 kcal 3 mol-1, respectively, are consistent with a possible equilibrium between them. On the other hand, the isomers derived form a [2þ2] cycloaddition (with 2,3 orientation relative to the TidN bond) are computed to be energetically disfavored by at least 9.6 kcal 3 mol-1, which is consistent with their absence in the product mixtures. In order to obtain some insight into the electronic structure of the metallacycle in complex 2a resulting from the [2þ2] cycloaddition and, in particular, the role of the nitrogen lone pair, the relevant Kohn-Sham molecular orbitals were analyzed.23 The conjugation of the double bond C(13)dC(15) with the lone pair of the hydrazido nitrogen atom N(3) is reflected in three different frontier MOs depicted at the top of Figure 3. The in-phase conjugated HOMO-14 clearly represents the π-bonding interaction between C(15)-C(13)-N(3), while HOMO-10 itself is a nonbonding C(15)-C(13)-N(3) fragment orbital with a node in the central carbon atom. The HOMO of complex 2a is also a π-orbital possessing a node between the C(15)dC(13) and the N. This analysis has been extended by means of an NLMO study

(Figure 3, bottom left) showing that the nitrogen lone pair orbital is delocalized into the titanium atom (10%) and into the π-antibonding orbital of the C(15)dC(13) bond (8%). Furthermore, natural population analysis also suggests the idea of delocalization of the N(3) lone pair into the π-antibonding of the C(15)dC(13) bond, which is reflected in the relatively low negative charge on N(3) (-0.47 e) and the increased partial charge on the C(15) carbon (-0.34 e) of the C(15)-C(13)-N(3) subsystem (Figure 3, bottom right). [2þ2] Cycloaddition of Phenylisothiocyanate to Complexes 1a and 1b. Upon reaction of N,N-diphenyl-substituted hydrazinediido complex [Cp*Ti(NXylN){N-NPh2}(tBuNH2)] (1a) with phenylisothiocyanate, two new compounds were formed in a 3:1 ratio (Scheme 2). Both compounds were separated and isolated by fractional crystallization from a concentrated diethyl ether solution at -18 °C. The crystals of the major isomer in the product mixture, [Cp*Ti(NXylN){κ2-N(NPh2)C(NPh)S}] (4a), were suitable for X-ray diffraction, and its molecular structure is depicted in Figure 4. As a result of a [2þ2] cycloaddition of the CdS bond in PhNCS to the TidN bond of the hydrazinediido unit, a fourmembered metallacyclic ring with a S,N-coordination to the titanium center and an exocyclic CdN double bond [C(13)N(5), 1.280(2) A˚] has been formed. The Ti-S distance [2.398(5) A˚] and the Ti-N(3) bond length [2.010(1) A˚] are in the range reported previously for thiolatotitanium24 and hydrazido(1-)-titanium species.25 The angles within the metallacyclic ring are very similar to those found in the (24) (a) Shaver, A.; McCall, J. M.; Bird, P. H.; Ansari, N. Organometallics 1983, 2, 1894. (b) Alcock, N. W.; Clase, H. J.; Duncalf, D. J.; Hart, S. C.; McCamley, A.; McCormack, P. J.; Taylor, P. C. J. Organomet. Chem. 2000, 605, 45. (c) Muller, E. G.; Watkins, S. F.; Dahl, L. F. J. Organomet. Chem. 1976, 111, 73. (d) Firth, A. V.; Stephan, D. W. Inorg. Chem. 1998, 37, 4732. (e) Kim, J. T.; Park, J. W.; Koo, S. M. Polyhedron 2000, 19, 1139. (f ) Fenwick, A. E.; Fanwick, P. E.; Rothwell, I. P. Organometallics 2003, 22, 535. (25) (a) Latham, I. A.; Leigh, G. J.; Huttner, G.; Jibril, I. J. Chem. Soc., Dalton Trans. 1986, 385. (b) Hughes, D. L.; Jimenez-Tenorio, M.; Leigh, G. J.; Walker, D. G. J. Chem. Soc., Dalton Trans. 1989, 2389. (c) Kim, S.-J.; Jung, I. N.; Yoo, B. R.; Cho, S.; Ko, J.; Kim, S. H.; Kang, S. O. Organometallics 2001, 20, 1501. (d) Yoon, S. C.; Bae, B. A.; Sub, I.-H.; Park, J. T. Organometallics 1999, 18, 2049. (e) Zippel, T.; Amdt, P.; Ohff, A.; Spannenberg, A.; Kempe, R.; Rosenthal, U. Organometallics 1998, 17, 4429. (f ) Hill, J. E.; Fanwick, P. E.; Rothwell, I. P. Inorg. Chem. 1991, 30, 1143. (g) Goetze, B.; Knizek, J.; N€oth, H.; Schnick, W. Eur. J. Inorg. Chem. 2000, 1849.

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structurally characterized phenylallene cycloaddition product (2a), except that the endocyclic angle at S [80.40(5)°] is more acute than the corresponding angle in 2a [C(13)C(14)-Ti, 89.7(1)°], due to the greater Ti-S distance in 4a compared to the corresponding Ti-C bond length in 2a. Whereas the molecular structure of 4a is thus unambiguously established in the solid state, the connectivities in solution of the isomeric metallacyclic compounds 4a and 4b were determined using 15N and 13C NMR spectroscopy (Figure 5). The 15N chemical shift of the nitrogen atom N(5) was found to be particularly characteristic. Coordination to the titanium atom shifted the resonance of this nucleus

Figure 4. Molecular structure of complex 4a. Hydrogen atoms are omitted for clarity and ellipsoids drawn at the 40% probability level. Selected bond lengths (A˚) and angles (deg): TiN(1) 2.136(1), Ti-N(2) 2.063 (1), Ti-N(3) 2.010(1), Ti-S 2.398 (5), Ti-Cent 2.047, N(3)-N(4) 1.409(2), C(13)-S 1.782(1), C(13)-N(5) 1.280(2), C(13)-N(3) 1.374(2), N(1)-Ti-N(2) 64.30(5), N(3)-C(13)-S 104.3(1), C(13)-S-Ti 80.40(5), C(13)-N(3)-Ti 106.50(9), N(3)-Ti-S 68.58(4).


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toward lower field, whereas the nitrogen atoms located in the exocyclic position are observed at significantly higher field. Thus, the N(5) of the major N,S-coordinated product (4a) is detected at 245.1 ppm, while N(3) was found at 266.2 ppm. In contrast, in the minor compound (4b) the two nitrogen atoms are coordinated to the titanium center, and both signals are shifted toward higher frequency (N(3): 281.9 ppm and N(5): 271.1 ppm), which is consistent with the proposed N,N coordination of the thiourea unit formed in the cycloaddition (Figure 5). Another characteristic signal that helps to differentiate between both modes of ligation is the 13C NMR signal of the carbon atom that is located in the metallacycle ring system. This resonance is detected at 154.9 ppm in the major product (4a), whereas the signal belonging to this carbon for the minor product (4b) resonates at 198.1 ppm. These assignments were additionally supported by the calculated DFTGIAO chemical shifts, which were found to be in good agreement with the measured values (Figure 5). The case at

Figure 5. Computed molecular structures of compounds 4a and 4b along with selected experimental and theoretical NMR data of both complexes.

Scheme 2. [2þ2] Cycloaddition Reactions of Phenylisothiocyanate and Phenylisocyanate to the Hydrazinediido Compounds [Cp*Ti(NXylN){N-NPh2}(NHt2Bu)] (1a) and [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b), resulting in the formation of two isomeric metallacyclic compoundsa

a

Compounds in parentheses could not be isolated.

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Scheme 3. Interconversion of 4a and 4b and Their Relative Energies and Free Energies

hand clearly demonstrates the usefulness of DFT methods as an additional tool for the assignment and thus structural elucidation for isomeric complexes in a case in which X-ray data were not available for both species. Finally, we note that by means of a NOESY experiment it was possible to determine the relative disposition of the NXylN amidinato ligand in solution for both compounds 4a and 4b, which was found to be similar to the orientation established in the X-ray diffraction study. The ortho-protons of the NNPh2 fragment display a NOESY cross-peak with the NCH2 protons of the NXylN fragment, while such crossrelaxation is absent for the xylyl group. Both isomers 4a and 4b were stable in solution for weeks at ambient temperature, and no interconversion was observed. However, previous studies had shown that titanium cycloaddition products could undergo retro-cycloaddition.6 Therefore, a solution of the minor isomer (4b) in deuterated benzene was heated to 40 °C and monitored by 1H NMR spectroscopy. A slow transformation of the minor isomer (4b) into the major isomer (4a) was observed with partial degradation of the product. Additionally, heating of the major isomer did not lead to an evolution in the reverse direction. This indicates that the formation of both isomers in the preparation of 4a,b is kinetically controlled, a notion that is also consistent with the thermodynamic data of the isomers computed by DFT methods (ΔEzp(4a-4b) = 5.5 kcal 3 mol-1; ΔG(4a-4b)=5.2 kcal 3 mol-1) and represented in Scheme 3 and Table 2. Upon performing the cycloaddition of PhNCS with [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b), only the major isomer 5a could be isolated (Scheme 2). However, an NMRtube experiment indicated the formation of a minor isomer (∼15%). The connectivity of the major compound was established by 1H-15N HMBC, 1H-13C HMBC, and 1 H-13C HSQC NMR spectroscopy. Compound 5a was found to display very similar 1H, 13C, and 15N NMR spectral patterns to complex 4a, and the structural assignment depicted in Scheme 2 was again backed up by a DFT NMR(GIAO) study. As described above, the isomerization between the cycloadducts occurs only in the direction 4/5b f 4/5a (Scheme 3), which is consistent with the computed free energies. A crossover experiment was carried out to illustrate the nature of the isomerization. By monitoring a mixture of compound 4b and 10 equiv of tolylisothiocyanate by 1H NMR spectroscopy at 40 °C, the formation of the isomer 4a, free phenylisothiocyanate, and a new set of signals assigned to the tolylisothiocyanate-derived analogue of 4a was observed. This indicates a dissociative mechanism (via a retro-cycloaddition) for the rearrangement of 4/5b f 4/5a. However, performing the same experimental procedure with

Figure 6. Molecular structure of complex 7b. Hydrogen atoms are omitted for clarity and ellipsoids drawn at the 40% probability level. Selected bond lengths (A˚) and angles (deg): TiN(1) 2.123(2), Ti-N(2) 2.070(2), Ti-N(3) 2.058(1), Ti-N(4) 1.984(2), Ti-Cent 2.043, N(3)-C(13) 1.397(2), N(4)-C(13) 1.379(2), C(13)-O(1) 1.222(2), N(3)-N(4) 1.391(2), N(1)Ti-N(2) 64.12(6), N(3)-Ti-N(5) 64.62(6), C(13)-N(5)-Ti 94.6(1), C(13)-N(4)-Ti 98.5(1).

compound 4a did not lead to an exchange of the phenylisothiocyanate for the tolylisothiocyanate-derived unit. This demonstrates that 4a is not only thermodynamically more stable than 4b but also kinetically more robust. [2þ2] Cycloadditions of 1a,b and Phenylisocyanate. The reaction of [Cp*Ti(NXylN){N-NPh2}(tBuNH2)] (1a) with PhNCO resulted in the formation of two isomers in a 1:12 ratio. In contrast to the reactions discussed above, all spectroscopic evidence indicates that the major compound formed in this cycloaddition was the N,N-coordinated isomer (6b), which could be separated from the minor component by fractional crystallization and was isolated in an overall yield of 30% (Scheme 2). GIAO-DFT calculations of the 13C and 15N NMR spectroscopic data also corroborate the structural assignment. Heating the major compound to 40 °C did not affect the product, while heating 6b to 70 °C resulted in the formation of a complex product mixture, possibly due to oxo-complex formation, the composition of which could not be established. The analogous [2þ2] cycloaddition of phenylisocyanate to [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b) also gave a mixture of two isomers, compounds 7a and 7b (Scheme 2), which were formed in a 2:1 ratio. In this case the 13C and 15 N NMR data did not allow an unambiguous determination of the structures in solution. However, a partial assignment of the 13C NMR data was possible. For example the resonance of the ring carbon (of the urea unit in the metallacycle) is shifted to lower frequency in the case of the major N,O-coordinated isomer 7a (155.8 ppm) compared to the minor N,N-coordinated isomer 7b, which resonates at 164.4 ppm. The assignment of these resonances is again supported by a GIAO-DFT study (see Supporting Information). Further support for the possible existence of both N,N-bonded isomers (6b and 7b) stems from the related cycloaddition product [Ti{(NPh2)C(O)N(Tol)}(Me4taa)] reported by Mountford and co-workers. For the latter, only the N,N-bonded isomer was observed and isolated.6

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Table 2. Relative Energies and Free Energies of the Calculated [2þ2] Phenylthioisocyanate Cycloaddition Isomers

a The zero point-corrected standard reaction energy and free energy of the [2þ2] cycloaddition products are given in parentheses for the thermodynamic reaction product.

Single crystals of the minor diastereomer 7b were obtained from a concentrated diethyl ether solution of the mixture of isomers at room temperature. Its molecular structure is depicted in Figure 6 along with selected bond lengths and angles. The proposed N,N-coordination of the urea unit ligated to the titanium atom is confirmed by an X-ray diffraction study. The exocyclic C(13)-O(1) bond [1.222(2) A˚] is typical for a carbonyl unit. All Ti-nitrogen bonds [TiN, 1.984(2)-2.123(2) A˚] are in the range of amido-type single bonds.26 The bite-angle of the metalated urea unit of 64.62(6)° is similar to that of the 2-aminopyrrolinato ligand [N(1)-Ti-N(2) 64.12(6)°]. Upon heating the mixture of 7a and 7b to 40 °C, the intensity of the signals assigned to the minor isomer decreased, while those of the major isomer grew in intensity. The process was found to be irreversible, and this indicates that the observed product ratio is not thermodynamically controlled. This interpretation is also in agreement with the DFT-computed free energies for the two diastereomeric complexes. Indeed, the DFT energies of the phenylisocyanate derivatives 6 and 7 (Table 3) suggest again kinetic control of the [2þ2] cycloaddition. Notably, the difference in energy/free energy between 6a,b and 7a,b is reduced with respect to the phenylisothiocyanate derivatives (4a,b and 5a, b) ((ΔEzp(6a-6b) = 1.0 kcal 3 mol-1; ΔG = 1.3 kcal 3 mol-1; (ΔEzp(7a-7b): ΔE=1.5 kcal 3 mol-1; ΔG=1.3 kcal 3 mol-1). In other words, the energy differences for the phenylisothiocyanate adducts are more pronounced than that for the corresponding phenylisocyanate derivatives. Reaction of 1a-c with Organic Azides: Isolation of an NSilylated η2-Hydrazido(1-) Titanium Azide. We recently reported the [3þ2] cycloaddition of organic azides, such as trimethylsilylazide and adamantylazide, with a zirconium hydrazinediido complex.27 In this reaction a five-membered {ZrN4} metallacyclic compound was obtained that fragmented upon heating, liberating N2 and generating a side-on bonded diazenide. This reactivity pattern was not observed with the titanium hydrazido complexes discussed in this work. Their reactivity toward azides was found to be strongly dependent on the substitution on Nβ of the hydrazido ligand. Neither [Cp*Ti(NXylN){N-NPh2}(tBuNH2)] (1a) nor (26) (a) Allen, F. H.; Kennard, O. Chem. Des. Automation News 1993, 8, 1–31. (b) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput. Sci. 1996, 36, 746. (27) Gehrmann, T.; Lloret Fillol, J.; Wadepohl, H.; Gade, L. H. Angew. Chem., Int. Ed. 2009, 48, 2152.

Table 3. Relative Energies and Free Energies of the Calculated [2þ2] Phenylisocianate Cycloaddition Isomers

a The zero point-corrected standard reaction energy and free energy of the [2þ2] cycloaddition products are given in parentheses for the thermodynamic reaction product.

[Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b) reacted with aryl, adamantyl, or trimethylsilyl azides at room temperature and formed complex product mixtures at elevated temperatures. Only the N,N-dimethyl hydrazinediido complex [Cp*Ti(NXylN){N-NMe2}(dmap)] (1c) reacted with organic azides at ambient temperature, albeit unspecifically in most cases. However, complex 1c underwent a clean and fast reaction with trimethylsilylazide The reaction product was identified as the N-silylated η2-hydrazido(1-) titanium azide [Cp*Ti(NXylN)(η2-NMe2-NSiMe3)(N3)] (8) (Scheme 4) on the basis of its analytical and spectroscopic data. In particular the intense IR band observed at 2066 cm-1 is characteristic for terminal azides.28 Due to difficulties encountered in the separation of the product from the liberated donor ligand 4-dimethylaminopyridine, the isolation of the pure compound was only achieved in low yield. Single crystals of [Cp*Ti(NXylN)(η2NMe2-NSiMe3)(N3)] (8), which were suitable for X-ray diffraction, were obtained from a concentrated hexane solution at 4 °C. Its molecular structure is depicted in Figure 7 along with selected bond lengths and angles. In complex 8 the trimethylsilyl group of the azide has been transferred to the hydrazido ligand, which is converted to a side-on coordinated hydrazido(-1) ligand, while the azide is terminally coordinated to the titanium center. This ligand is (28) Meyer, K. E.; Walsh, P. J.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 474.

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identification of diastereomeric products the modeling and computation of 13C and 15N NMR data have been of particular importance. The latter especially is thought to gain increasing significance in future studies in this field. Compared to imidotitanium complexes the chemistry of the corresponding hydrazinediides (as well as their heavier group 4 metal analogues) is still comparatively underdeveloped and merits further systematic studies, which are ongoing in our lab.

Experimental Section

Figure 7. Molecular structure of complex 8. Hydrogen atoms are omitted for clarity and ellipsoids drawn at the 40% probability level. Selected bond lengths (A˚) and angles (deg): N(1)Ti 2.145(2), N(2)-Ti 2.213(2), N(3)-Ti 2.176(2), N(4)-Ti 1.951(2), N(3)-N(4) 1.446(2), N(4)-Si(1) 1.758(2), N(5)-Ti 2.088(2), N(5)-N(6) 1.198(2), N(6)-N(7) 1.160(2), Ti-Cent 2.114, N(1)-Ti-(N2) 60.58(5), N(3)-Ti-N(4) 40.55(6), TiN(5)-N(6) 135.91(1), N(5)-N(6)-N(7) 177.3(2). Scheme 4. Reaction of [Cp*Ti(NXylN){N-NMe2}(dmap)] (1c) with Trimethylsilylazide, Resulting in the Formation of a Complex with a Side-on Bonded Hydrazido(-1) Ligand and a Terminal Azide

close to linear [N(5)-N(6)-N(7), 177.3(2)°], in correspondence with the structures of other azido complexes (range 171.0179.6°, mean 177.7° for seven examples in the CSD).26 The angle Ti-N(5)-N(6) was found to be 135.91(1)°, which is similar to the data reported previously for titanium complexes with terminal azide ligands.29 Finally, the side-on coordinated hydrazido(-1) ligand is slightly unsymmetrically bonded to the titanium center, the Ti-N(4) bond [1.951(2) A˚] being shorter than the Ti-N(3) bond [2.176(2) A˚].

Conclusions The aim of this study has been the characterization of [2þ2] cycloadducts that serve as models for intermediates in Ti-catalyzed C-N coupling reactions involving hydrazines as substrates. Whereas the cycloadduct with phenylallene is of direct relevance to the hydrohydrazination of allenes, the reactions with heteroallenes have shed some light on the regiochemistry of such formal cycloaddition steps. In the (29) (a) Carmalt, C. J.; Cowley, A. H.; Culp, R. D.; Jones, R. A.; Sun, Y.-M.; Fitts, B.; Whaley, S.; Roesky, H. W. Inorg. Chem. 1997, 36, 3108. (b) de Gil, E. R.; de Burguera, M.; Rivera, A. V.; Maxfield, P. Acta Crystallogr. (B) 1997, 33, 578. (c) Gross, M. E.; Siegrist, T. Inorg. Chem. 1992, 31, 4898. (d) Honzicek, J.; Vinklarek, J.; Erben, M.; Cisarova, I. Acta Crystallogr. (E) 2004, 60, m1090. (e) Haiges, R.; Boatz, J. A.; Schneider, S.; Schroer, T.; Yousufuddin, M.; Christe, K. O. Angew. Chem., Int. Ed. 2004, 43, 3148.

All manipulations of air- and moisture-sensitive species were performed under an atmosphere of argon using standard Schlenk and glovebox techniques. Solvents were predried over molecular sieves and dried over Na/K alloy (pentane, diethyl ether), Na (toluene), or K (THF, hexane), distilled, and stored over potassium mirrors (pentane, hexane, diethyl ether, and toluene) in Teflon valve ampules. Deuterated solvents were dried over K (benzene-d6, toluene-d8) or CaH2 (dichloromethane-d2), vacuum distilled, and stored under argon in Teflon valve ampules. The ligand HNXylN and the hydrazido compounds [Cp*Ti(NXylN){N-NPh2}(tBuNH2)] (1a), [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b), and [Cp*Ti(NXylN){N-NMe2}(dmap)] (1c) were prepared as we described previously.16-18 All other reagents were purchased from commercial suppliers. Samples for NMR spectroscopy were prepared under argon in 5 mm Wilmad tubes equipped with J. Young Teflon valves. NMR spectra were recorded on Bruker Avance II 400 or Bruker Avance III 600 NMR spectrometers. NMR spectra are quoted in ppm and were referenced internally relative to the residual protio-solvent (1H) or solvent (13C) resonances or externally to Si(CH3)4 (29Si) and NH3(l) (15N). Whenever necessary, NMR assignments were confirmed by the use of two-dimensional 1H-1H or 1H-13C correlation experiments. 15N NMR data were obtained by two-dimensional 1 H correlated experiments or by direct detection using a cryogenically cooled direct-detection NMR probe (QNP CryoProbe). Microanalyses were performed by the analytical services in the Chemistry Department of the Universit€ at Heidelberg. IR spectra were recorded on a Varian 3100 Exalibur spectrometer as KBr pellets. Infrared data are quoted in cm-1. [Cp*Ti(NXylN){K2N(NPh2)C(CHPh)CH2}] (2a,b). To a solution of [Cp*Ti(NXylN){N-N(Ph)2}(tBuNH2)] (1a) (216 mg, 0.34 mmol) in toluene (3 mL) was added a solution of phenylallene (40 mg, 0.34 mmol) in toluene (1 mL), leading to an immediate change of color from green to deep red. After stirring the reaction mixture at room temperature for 1 h all volatiles were removed in vacuo. The residue was dissolved in pentane, and a mixture of [Cp*Ti(NXylN){κ2N(NPh2)C(CHPh)CH2}] (2a and 2b) in a 3:1 ratio crystallized as red powder at -18 °C (130 mg, 0.20 mmol, 60%). Single crystals of the major isomer (2a) were received from a concentrated pentane solution at -18 °C. 2a: 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 1.36-1.31 (m, 2 H, NCH2CH2), 1.73 (s, 15 H, C5Me5), 2.16 (s, 6 H, C6H3Me2), 2.17 (sh, 1 H, TiCH2C), 2.27-2.21 (m, 1 H, NCCH2), 2.48-2.42 (m, 1 H, NCCH2), 3.11 (d, 2JH-H = 11.8 Hz, 1 H, TiCH2C), 3.20-3.15 (m, 1 H, NCH2), 3.433.39 (m, 1 H, NCH2), 5.60 (s, 1 H, TiCH2C(CHPh)), 6.57 (s, 1 H, para-C6H3Me2), 6.62 (s, 2 H, ortho-C6H3Me2), 6.83 (tr, 3JH-H= 7.3 Hz, 1 H, para-Ph,), 6.88-6.79 (br m, 2 H, para-NPh2), 7.127.06 (m, 6 H, meta-NPh2 and meta-Ph), 7.41-7.35 (br m, 4 H, ortho-NPh2), 7.48 (d, 3JH-H=7.6 Hz, 2 H, ortho-Ph) ppm. 13 C{1H} NMR (150.9 MHz, benzene-d6, 295 K): δ 12.0 (C5Me5), 21.6 (C6H3Me2), 23.3 (NCH2CH2), 30.9 (NCCH2), 53.1 (NCH2), 65.3 (TiCH2C), 90.4 (TiCH2C(CHPh)), 120.6 (ortho-C6H3Me2), 122.7 (para-Ph), 124.5 (para-C6H3Me2), 126.0 (C5Me5), 128.0 (ortho- and meta-Ph, overlapping with benzene-d6), 128.9 (orthoNPh2), 129.0 (para-NPh2), 138.4 (meta-C6H3Me2), 141.2 (ipsoPh), 146.4 (ipso-NPh2), 147.1 (TiCH2C), 148.6 (ipso-C6H3Me2), 171.0 (NCN) ppm, (meta-NPh2) not obsd. 15N NMR (60.8 MHz,

Article benzene-d6, 295 K): δ 187.3 (NCN-Xyl), 194.5 (NCN-Xyl), 293.5 (N(NPh2)) ppm, (N(NPh2)) not obsd. IR (KBr, cm-1) mixture of both isomers: 3016 (w), 2949 (w), 2910 (m), 2856 (m), 1586 (s), 1488 (s), 1377 (m), 1291 (s). Anal. Found (calcd for C43H48N4Ti) mixture of both isomers: C, 76.8 (77.2); H, 7.4 (7.2); N, 8.1 (8.4). 2b: 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 1.6-1.56 (m, 2 H, NCH2CH2), 1.77 (s, 15 H, C5Me5), 1.77 (1 H, TiCH2C, overlapping with C5Me5), 1.80-1.77 (m, 1 H, NCCH2, overlapping with C5Me5 and TiCH2C), 2.13 (s, 6 H, C6H3Me2), 2.27-2.12 (m, 1 H, NCCH2, overlapping with NCCH2 of the major isomer), 3.01 (d, 2JH-H =11.9 Hz, 1 H, TiCCH2), 3.103.05 (m, 1 H, NCH2), 3.22-3.16 (1 H, NCH2, overlapping with NCH2 of the major isomer), 5.50 (s, 1 H, TiCH2C(CHPh)), 6.46 (s, 2 H, ortho-C6H3Me2), 6.48 (s, 1 H, para-C6H3Me2), 6.916.88 (m, 1 H, para-Ph), 6.88-6.79 (br m, 2 H, para-NPh2, overlapping with para-NPh2 of the major isomer), 7.12-7.06 (m, 4 H, meta-NPh2, overlapping with meta-NPh2 and meta-Ph of the major isomer), 7.15 (m, 2 H, meta-Ph), 7.41-7.35 (m, 4 H, ortho-NPh2, overlapping with ortho-NPh2 of the major isomer), 7.53 (d, 3JH-H =10.3 Hz, 2 H, ortho-Ph) ppm. 13C{1H} NMR (150.9 MHz, benzene-d6, 295 K): δ 12.2 (C5Me5), 21.5 (C6H3Me2), 24.6 (NCH2CH2), 29.3 (NCCH2), 51.7 (NCH2), 64.9 (TiCH2), 90.9 (TiCH2C(CHPh)), 120.4 (ortho-C6H3Me2), 122.8 ( para-Ph), 123.8 (para-C6H3Me2), 125.9 (C5Me5), 128.0 (ortho-Ph), 129.2 (ortho-NPh2, meta-NPh2, meta-Ph, or para-NPh2), 129.3 (ortho-NPh2, meta-NPh2, meta-Ph, or paraNPh2), 129.5 (ortho-NPh2, meta-NPh2, meta-Ph, or para-NPh2), 141.0 (ipso-Ph), 147.4 (TiCH2C), 148.0 (ipso-NPh2), 148.6 (ipsoC6H3Me2), 172.2 (NCN) ppm. 15N NMR (60.8 MHz, benzene-d6, 295 K): δ 194.0 (NCN-Xyl), 282.7 (N(NPh2)) ppm, (NCN-Xyl), (N(NPh2)) not obsd. [Cp*Ti(NXylN){K2N(N(Ph)Me)C(CHPh)CH2}] (3a). To a solution of [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (361 mg, 0.63 mmol) in toluene (5 mL) was added a solution of phenylallene (74 mg, 0.63 mmol) in toluene (1 mL), leading to an immediate change of color from red to deep red. After stirring the reaction mixture for 1 h at room temperature all volatiles were removed in vacuo. The residue was washed with pentane, and the supernatant solution was removed by filtration from the insoluble residue. The solid was dried in vacuo to yield the product as a deep red powder (136 mg, 0.22 mmol, 36%). 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 1.03 (m, 1 H, NCH2CH2), 1.27 (m, 1 H, NCH2CH2), 1.85 (s, 15 H, C5Me5), 2.12 (m, 1 H, NCCH2), 2.17 (s, 6 H, C6H3Me2), 2.30 (m, 1 H, NCCH2), 2.44 (d, 2JH-H =5.9 Hz, 1 H, TiCH2C), 2.88 (m, 1 H, NCH2), 3.09 (s, 6 H, N(Ph)Me), 3.27 (br m, 1 H, TiCH2C), 3.34 (m, 1 H, NCH2), 5.52 (s, 1 H, TiCH2C(CHPh)), 6.57 (s, 1 H, para-C6H3Me2), 6.61 (s, 2 H, ortho-C6H3Me2), 6.70 (m, 1 H, para-N(Ph)Me), 6.78 (m, 2 H, ortho-N(Ph)Me), 6.91 (m, 2 H, meta-N(Ph)Me), 7.15 (m, 1 H, para-NPh, overlapping with benzene-d6), 7.25 (m, 2 H, meta-NPh), 7.59 (d, 3 JH-H=6.7 Hz, 2 H, ortho-NPh) ppm. 13C{1H} NMR (150.8 MHz, benzene-d6, 295 K): δ 12.2 (C5Me5), 21.6 (C6H3Me2), 23.1 (NCH2CH2), 30.4 (NCCH2), 41.1 (N(Ph)Me), 53.6 (NCH2), 67.4 (TiCH2C), 89.3 (br, TiCH2C(CHPh)), 112.9 (ortho-N(Ph)Me), 117.2 ( para-N(Ph)Me), 120.8 (ortho-C6H3Me2), 122.7 (meta-N(Ph)Me), 124.5 ( para-C6H3Me2), 125.3 (C5Me5), 126.5 (ortho-NPh), 128.0 (meta-NPh, overlapping with benzene-d6), 129.3 ( para-NPh), 138.2 (meta-C6H3Me2), 141.8 (TiCH2C(CHPh)), 149.1 (ipso-C6H3Me2), 150.3 (ispo-N(Ph)Me), 152.2 (ipso-NPh), 171.2 (NCN) ppm. 15N NMR (60.8 MHz, benzened6, 295 K): δ 106.0 (N(Ph)Me), 185.9 (NCN-Xyl), 301.9 (NN(Ph)Me) ppm; (NCN-Xyl) not obsd. IR (KBr, cm-1): 2952 (w), 2910 (m), 2854 (w), 1593 (s), 1577 (s), 1561 (s), 1525 (s), 1497 (m), 1441 (m), 1375 (w), 1320 (w), 1293 (m), 1186 (m), 1162 (m), 1150 (m), 1096 (m), 1029 (m), 1012 (m), 834 (w), 815 (m), 785 (s), 743 (m), 693 (s). Anal. Found (calcd for C38H46N4Ti): C, 74.6 (75.2); H, 7.7 (7.6); N, 9.0 (9.2). [Cp*Ti(NXylN){K2N(NPh2)CN(Ph)S}] (4a) and [Cp*Ti(NXylN){κ2N(NPh2)-C(S)N(Ph)}] (4b). To a solution of [Cp*Ti(NXylN){N-N(Ph)2}(tBuNH2)] (1a) (371 mg, 0.59 mmol) in toluene (5 mL)


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was added phenylisothiocyanate (71 μL, 0.59 mmol) in toluene (1 mL), leading to an immediate change of color from green to deep brown. The reaction mixture was stirred for 1 h at room temperature before all volatiles were removed in vacuo. The residue was washed with diethyl ether, yielding a microcrystalline solid of a mixture of two isomers, [Cp*Ti(NXylN){κ2N(NPh2)CN(Ph)S}] (4a) and [Cp*Ti(NXylN){κ2N(NPh2)C(S)N(Ph)}] (4b), in a 3:1 ratio. Suitable crystals for X-ray diffraction of the major isomer (4a) were obtained from a concentrated diethyl ether solution at -18 °C (150 mg, 40% yield). The supernatant solution was removed by filtration. The minor isomer (4b) was isolated by evaporation of the supernatant solution (50 mg, 13% yield). [Cp*Ti(NXylN){K2N(NPh2)CN(Ph)S}] (4a). 1H NMR (600.1 MHz benzene-d6, 295 K): δ 1.07-1.01 (m, 1 H, NCH2CH2), 1.40-1.34 (m, 1 H, NCH2CH2), 1.71 (s, 15 H, C5Me5), 2.16 (s, 6 H, C6H3Me2), 2.24-2.20 (m, 1 H, NCCH2), 2.42-2.36 (m, 1 H, NCCH2), 3.56-3.52 (m, 1 H, NCH2), 3.76-3.72 (m, 1 H, NCH2), 6.56 (s, 1 H, para-C6H3Me2), 6.58 (tr, 3JH-H =7.2 Hz, 1 H, para-NPh2), 6.82 (s, 2 H, ortho-C6H3Me2), 6.93-6.88 (m, 2 H, meta-NPh2 and m, 1 H, para-NPh), 6.96 (tr, 3JH-H=7.3 Hz, 1 H, para-NPh2), 7.10 (d, 3JH-H = 8.2 Hz, 2 H, ortho-NPh2), 7.19-7.16 (m, 2 H, meta-NPh), 7.23-7.20 (m, 2 H, meta-NPh2), 7.36 (d, 3JH-H = 7.8 Hz, 2 H, ortho-NPh), 7.69 (d, 3JH-H = 7.9 Hz, 2 H, ortho-NPh2) ppm. 13C{1H} NMR (150.9 MHz, benzene-d6, 295 K): δ 12.4 (C5Me5), 21.5 (C6H3Me2), 22.8 (NCH2CH2), 30.5 (NCCH2), 54.1 (NCH2), 114.2 (ortho-NPh2), 118.3 (para-NPh2), 120.7 (ortho-C6H3Me2), 122.5 (para-NPh), 123.6 (para-NPh2), 124.2 (ortho-NPh), 124.7 (ortho-NPh2), 125.2 (para-C6H3Me2), 128.4 (meta-NPh), 128.7 (meta-NPh2), 128.9 (meta-NPh2), 129.9 (C5Me5), 138.4 (meta-C6H3Me2), 146.8 (ipso-NPh2), 146.9 (ipso-NPh2), 147.2 (ipso-C6H3Me2), 149.5 (ipso-NPh), 154.9 (NCS), 168.6 (NCN) ppm. 15N NMR (60.8 MHz, benzene-d6, 295 K): δ 126.9 (NPh2), 193.2 (NCNXyl), 201.1 (NCN-Xyl), 245.1 (NPh), 266.2 (TiNCS) ppm. IR (KBr, cm-1): 3058 (w), 2911 (w), 2869 (w), 1598 (s), 1588 (s), 1555 (s), 1525 (s), 1491 (s), 1328 (m), 1316 (m), 1294 (m), 1262 (m), 1162 (m), 1098 (m), 1023 (m). Anal. Found (calcd for C41H45N5STi) mixture of both isomers: C, 71.2 (71.6); H, 6.7 (6.6); N, 10.1 (10.2). [Cp*Ti(NXylN){K2N(NPh2)C(S)N(Ph)}] (4b). 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 1.01-0.94 (m, 1 H, NCH2CH2), 1.35-1.28 (m, 1 H, NCH2CH2), 1.63 (s, 15 H, C5Me5), 2.031.98 (m, 1 H, NCCH2), 2.06 (s, 6 H, C6H3Me2), 2.16-2.10 (m, 1 H, NCCH2), 3.54-3.50 (m, 1 H, NCH2), 3.61-3.57 (m, 1 H, NCH2), 6.58 (tr, 3JH-H=7.2 Hz, 1 H, para-NPh2), 6.62 (s, 1 H, para-C6H3Me2), 6.70 (s, 2 H, ortho-C6H3Me2), 7.00-6.94 (m, 4 H, para-NPh2, meta-NPh, and para-NPh), 7.16-7.13 (m, 2 H, meta-NPh2 overlapping with benzene-d6), 7.24-7.21 (m, 2 H, meta-NPh2), 7.62 (d, 3JH-H = 8.0 Hz, 2 H, ortho-NPh), 7.82 (d, 3JH-H = 7.9 Hz, 2 H, ortho-NPh2) ppm. 13C{1H} NMR (150.9 MHz, benzene-d6, 295 K): δ 12.4 (C5Me5), 21.2 (C6H3Me2), 22.6 (NCH2CH2), 29.7 (NCCH2), 55.0 (NCH2), 113.9 (para-NPh2), 118.0 (ortho-NPh2), 123.5 (ortho-C6H3Me2), 123.8 (para-NPh2, meta-NPh or para-NPh), 124.4 (para-NPh2, meta-NPh or para-NPh), 125.9 (ortho-NPh2), 126.0 (orthoNPh), 127.1 (para-C6H3Me2), 127.5 (meta-NPh2), 128.0 (paraNPh2, meta-NPh, or para-NPh, overlapping with benzene-d6), 128.9 (C5Me5), 129.7 (meta-NPh2), 138.8 (meta-C6H3Me2), 146.5 (ipso-NPh2), 147.0 (ipso-NPh2), 148.2 (ipso-C6H3Me2), 149.7 (ipso-NPh), 172.1 (NCN), 198.1 (NCS) ppm. 15N NMR (60.8 MHz, benzene-d6, 295 K): δ 126.7 (NPh2), 194.8 (NCNXyl), 200.4 (NCN-Xyl), 271.7 (N(Ph)), 283.9 (N(NPh2)) ppm. IR (KBr, cm-1): 3055 (w), 3031 (w), 2962 (m), 2911 (m), 2861 (m), 1590 (s), 1525 (s), 1492 (s), 1292 (S), 1223 (s), 1184 (s), 1095 (m), 1025 (m). [Cp*Ti(NXylN){K2N(N(Ph)Me)CN(Ph)S}] (5a). To a solution of [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b) (387 mg, 0.68 mmol) in toluene (5 mL) was added phenylisothiocyanate (81 μL, 0.67 mmol) in toluene (1 mL), leading to an immediate change of color from red to deep brown. The reaction mixture was

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stirred for 1 h at room temperature before all volatiles were removed in vacuo. The residue was washed with diethyl ether, yielding a microcrystalline solid of [Cp*Ti(NXylN){κ2N(N(Ph)Me)CN(Ph)S}] (5a) (212 mg, 0.34 mmol, 50%). 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 0.75-0.67 (m, 1 H, NCH2CH2), 1.32-1.24 (m, 1 H, NCH2CH2), 1.85 (s, 15 H, C5Me5), 2.12 (s, 6 H, C6H3Me2), 2.19-2.11 (m, 1 H, NCCH2), 2.31-2.25 (m, 1 H, NCCH2), 3.27-3.23 (m, 1 H, NCH2), 3.32 (s, 3 H, N(Ph)Me), 3.42-3.37 (m, 1 H, NCH2), 6.52 (s, 1 H, para-C6H3Me2), 6.62-6.57 (m, 1 H, para-N(Ph)Me), 6.71 (d, 3JH-H = 8.0 Hz, 2 H, ortho-N(Ph)Me), 6.73 (s, 2 H, ortho-C6H3Me2), 6.90 (tr, 3 JH-H = 7.0 Hz, 1 H, para-NPh), 7.04-7.01 (m, 2 H, metaN(Ph)Me), 7.20-7.17 (m, 2 H, meta-NPh), 7.38 (d, 3JH-H = 7.6 Hz, 2 H, ortho-NPh) ppm. 13C{1H} NMR (150.9 MHz, benzene-d6, 295 K): δ 12.6 (C5Me5), 21.5 (C6H3Me2), 22.5 (NCH2CH2), 30.5 (NCCH2), 42.0 (N(Ph)Me), 53.7 (NCH2), 112.3 (ortho-N(Ph)Me), 116.6 (para-N(Ph)Me), 120.2 (orthoC6H3Me2), 122.4 (para-NPh), 124.2 (ortho-NPh), 124.9 (paraC6H3Me2), 128.0 (meta-NPh, overlapping with benzene-d6), 128.8 (meta-N(Ph)Me), 129.5 (C5Me5), 138.4 (meta-C6H3Me2), 147.2 (ispo-C6H3Me2), 149.6 (ispo-NPh), 150.2 (ipso-N(Ph)Me), 153.1 (NCS), 168.7 (NCN) ppm. 15N NMR (60.8 MHz, benzened6, 295 K): δ 192.8 (NCN-Xyl), 242.4 (NPh), 272.8 (TiNCS) ppm, (NCN-Xyl), (N(Ph)Me) not obsd. IR (KBr, cm-1): 2949 (m), 2911 (m), 2862 (m), 1596 (s), 1566 (s), 1525 (s), 1497 (s), 1375 (w), 1318 (w), 1292 (m), 1191 (w), 1099 (m), 1026 (w), 993 (w), 918 (w), 787 (w), 760 (m), 745 (m), 693 (s). Anal. Found (calcd for C36H38N5STi): C, 68.4 (69.1); H, 6.9 (6.9); N, 10.9 (11.2). [Cp*Ti(NXylN){K2N(NPh2)C(O)N(Ph)}] (6b). To a solution of [Cp*Ti(NXylN){N-N(Ph)2}(tBuNH2)] (1a) (440 mg, 0.70 mmol) in toluene (5 mL) was added phenylisocyanate (76 μL, 0.70 mmol) in toluene (1 mL), leading to an immediate change of color from green to deep brown. The reaction mixture was stirred for 1 h at room temperature before all volatiles were removed in vacuo. The residue was suspended in diethyl ether, and supernatant solution was removed by filtration. The residue was dried in vacuo, yielding a dark brown microcrystalline solid of [Cp*Ti(NXylN){κ2N(NPh2)C(O)N(Ph)}] (6b) (150 mg, 0.22 mmol, 31%). 1H NMR (600.1 MHz, CD2Cl2, 295 K): δ 1.181.24 (m, 1 H, NCH2CH2), 1.77-1.84 (m, 1 H, NCH2CH2, overlapping with C5Me5), 1.81 (s, 15 H, C5Me5), 2.02-2.09 (m, 1 H, NCCH2), 2.23 (s, 6 H, C6H3Me2), 2.61-2.67 (m, 1 H, NCCH2), 3.60-3.65 (m, 1 H, NCH2), 4.00-4.04 (m, 1 H, NCH2), 6.54 (s, 1 H, para-C6H3Me2), 6.63 (d, 3JH-H = 10.0 Hz, 2 H, ortho-Ph), 6.77 (s, 2 H, ortho-C6H3Me2), 6.93-6.97 (m, 3 H, meta- and para-Ph), 7.07 (d, 3JH-H=8.2 Hz, ortho-Ph), 7.12 - 7.18 (m, 4 H, meta-, para- and para-Ph), 7.36-7.39 (m, 2 H, meta-Ph), 7.43-7.45 (m, 2 H, ortho-Ph) ppm. 13C{1H} NMR (150.9 MHz, CD2Cl2, 295 K): δ 12.8 (C5Me5), 21.5 (C6H3Me2), 23.1 (NCH2CH2), 29.8 (NCCH2), 55.1 (NCH2), 113.4 (orthoPh), 122.4 (meta-Ph or para-Ph), 123.2 (ortho-C6H3Me2), 124.0 (ortho-Ph), 124.4 (meta-Ph or para-Ph), 124.8 (meta-Ph or paraPh), 125.7 (ortho-Ph), 126.6 (para-C6H3Me2), 128.2 (meta- or para-Ph), 128.7 (meta- or para-Ph), 129.4 (C5Me5), 129.5 (metaPh) 139.0 (meta-C6H3Me2), 147.4 (ispo-C6H3Me2 and ipso-Ph), 147.9 (ipso-Ph), 149.1 (ipso-Ph), 166.9 (NCO), 171.4 (NCN) ppm. 15N NMR (60.8 MHz, CD2Cl2, 295 K): δ 192.9 (NCNXyl), 242.4 (NPh), 253.9 (NNPh2) ppm, (NCN-Xyl), (NNPh2) not obs. IR (KBr, cm-1): 3059 (w), 3030 (w), 2949 (w), 2913 (w), 2873 (w), 1659 (s), 1588 (s), 1527 (s), 1493 (s), 1481 (s), 1330 (m), 1314 (s), 1301 (m), 1190 (s), 1181 (s), 1096 (w), 1026 (w), 985 (m), 767 (m), 743 (m), 704 (s), 695 (s). Anal. Found (calcd for C41H45N5OTi): C, 73.7 (73.3); H, 6.8 (6.8); N, 9.9 (10.4). [Cp*Ti(NXylN){K2N(N(Ph)Me)CN(Ph)O}] (7a) and [Cp*Ti(NXylN){κ2N(N(Ph)Me)-C(O)N(Ph)}] (7b). To a solution of [Cp*Ti(NXylN){N-N(Ph)Me}(py)] (1b) (494 mg, 0.87 mmol) in toluene (5 mL) was added phenylisocyanate (94 μL, 0.87 mmol) in toluene (1 mL), leading to an immediate change of color from red to deep brown. The reaction mixture was stirred for 1 h at room temperature before all volatiles were removed in vacuo.

Weitershaus et al. The residue was dissolved in diethyl ether, and a microcrystalline solid of both compounds 7a and 7b in a 2:1 ratio was obtained at -18 °C. The supernatant solution was removed by filtration, and the residue was dried in vacuo (yield: 344 mg, 0.55 mmol, 65%). Single crystals of [Cp*Ti(NXylN){κ2N(N(Ph)Me)C(O)N(Ph)}] (7b) could be obtained from a concentrated diethyl ether solution at -18 °C. [Cp*Ti(NXylN){K2N(N(Ph)Me)CN(Ph)O}] (7a). 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 1.04-0.98 (m, 1 H, NCH2CH2), 1.31-1.25 (m, 1 H, NCH2CH2), 1.85 (s, 15 H, C5Me5), 2.21-2.10 (m, 2 H, NCCH2), 2.21 (s, 6 H, C6H3Me2), 3.22-3.19 (m, 1 H, NCH2), 3.48 (s, 3 H, N(Ph)Me), 3.52-3.48 (m, 1 H, NCH2), 6.60 (s, 1 H, para-C6H3Me2), 6.85 (tr, 3JH-H= 7.1 Hz, 1 H, para-NPh), 6.92 (s, 2 H, ortho-C6H3Me2), 6.95 (tr, 3 JH-H=7.3 Hz, 1 H, para-N(Ph)Me), 7.38-7.31 (m, 4 H, metaN(Ph)Me and meta-NPh), 7.41-7.40 (m, 2 H, ortho-NPh), 8.04 (d, 3JH-H =7.6 Hz, 2 H, ortho-N(Ph)Me) ppm. 13C{1H} NMR (150.9 MHz, benzene-d6, 295 K): δ 12.2 (C5Me5), 21.5 (C6H3Me2), 23.4 (NCH2CH2), 29.1 (NCCH2), 41.6 (N(Ph)Me), 54.6 (NCH2), 114.0 (ortho-NPh), 116.8 (para-NPh), 120.9 (orthoC6H3Me2), 121.3 (ortho-N(Ph)Me), 121.6 (para-N(Ph)Me), 125.6 (para-C6H3Me2), 129.0 and 128.5 (meta-N(Ph)Me and meta-NPh, overlapping with benzene-d6), 130.2 (C5Me5), 138.6 (meta-C6H3Me2), 147.5 (ipso-N(Ph)Me), 149.4 (ipso-C6H3Me2), 153.3 (ipso-NPh), 155.8 (NCO), 170.5 (NCN) ppm. 15N NMR (60.8 MHz, benzene-d6, 295 K): δ 192.6 (NCN-Xyl), 221.6 (N(N(Ph)Me) ppm, (N(N(Ph)Me), (NPh), (NCN-Xyl) not obs. IR (KBr, cm-1) mixture of both isomers: 2965 (w), 2911 (m), 2860 (w), 1657 (s), 1596 (s), 1530 (s), 1498 (s), 1445 (s), 1376 (m), 1309 (s), 1299 (s), 1183 (m), 1103 (m). Anal. Found (calcd for C36H43N5OTi) mixture of both isomers: C, 70.7 (70.9); H, 7.2 (7.1); N, 11.3 (11.5). [Cp*Ti(NXylN){K2N(N(Ph)Me)C(O)N(Ph)}] (7b). 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 1.29-1.26 (m, 2 H, NCH2CH2), 1.79 (s, 15 H, C5Me5), 1.90-1.84 (m, 1 H, NCCH2), 2.02 (s, 6 H, C6H3Me2), 2.32-2.23 (m, 1 H, NCCH2), 3.16 (s, 3 H, N(Ph)Me), 3.18-3.12 (m, 1 H, NCH2), 3.51-3.46 (m, 1 H, NCH2), 6.57 (s, 2 H, ortho-C6H3Me2), 6.66-6.57 (m, 2 H, paraN(Ph)Me and para-C6H3Me2), 6.65 (m, 2 H, ortho-N(Ph)Me), 6.95 (tr, 3JH-H = 7.2 Hz, 1 H, para-NPh), 7.05-7.02 (m, 2 H, meta-N(Ph)Me), 7.21-7.19 (m, 2 H, meta-NPh), 7.55 (d, 3 JH-H=7.1 Hz, 2 H, ortho-NPh) ppm. 13C NMR (150.9 MHz, benzene-d6, 295 K): δ 12.2 (C5Me5), 21.2 (C6H3Me2), 22.2 (NCH2CH2), 29.3 (NCCH2), 54.8 (NCH2), 65.9 (N(Ph)Me), 114.9 (ortho-N(Ph)Me), 116.5 (meta-N(Ph)Me), 120.5 (metaNPh), 121.3 (para-NPh), 123.1 (ortho- or para-C6H3Me2), 123.7 (ortho-NPh), 126.6 (ortho- or para-C6H3Me2), 128.0 (C5Me5, overlapping with benzene-d6), 128.8 (para-N(Ph)Me), 138.6 (meta-C6H3Me2), 147.9 (ipso-C6H3Me2), 149.4 (ipso-NPh), 164.4 (NCO), 171.2 (NCN) ppm, (ipso-N(Ph)Me) not obsd. 15 N NMR (60.8 MHz, benzene-d6, 295 K): δ 190.9 (NCN-Xyl), 267.3 (N(N(Ph)Me), (N(N(Ph)Me), (NPh), (NCN-Xyl) not obsd. [Cp*Ti(NXylN)(η2-NMe2-NSiMe3)(N3)] (8). To a solution of [Cp*Ti(NXylN){N-NMe2}(dmap)] (1c) (495 mg, 0.9 mmol) in hexane (5 mL) was added slowly a solution of trimethylsilylazide (73 μL, 0.9 mmol) in hexane (5 mL), leading to an immediate change of color from red to bright orange. After half an hour stirring at room temperature all volatiles were removed in vacuo and the residue was dissolved in pentane. The supernatant solution was removed by filtration from the undissolved dmap, and the product was obtained by crystallization at 4 °C (yield: 40 mg, 0.07 mmol, 8%). Single crystals were obtained from a concentrated hexane solution at 4 °C. 1H NMR (600.1 MHz, benzene-d6, 295 K): δ 0.30 (s, 9 H, SiMe3), 1.61-1.51 (m, 2 H, NCH2CH2), 1.97 (s, 15 H, C5Me5), 2.08-2.01 (m, 1 H, NCCH2), 2.28 (s, 6 H, C6H3Me2), 2.33-2.26 (m, 1 H, NCCH2, overlapping with C6H3Me2), 2.55 (s, 3 H, NMe2), 2.82 (s, 3 H, NMe2), 3.623.55 (m, 1 H, NCH2), 3.83-3.79 (m, 1 H, NCH2), 6.53 (s, 2 H, para-C6H3Me2), 6.56 (s, 1 H, ortho-C6H3Me2) ppm. 13C{1H}

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Table 4. Details of the Crystal Structure Determinations of the Complexes 2a, 4a, 7b, and 8

formula cryst syst space group a/A˚ b/A˚ c/A˚ β/deg V/A˚3 Z Mr F000 dc/Mg 3 m-3 μ(Mo KR) /mm-1 max., min. transmn factors θ range/deg index ranges (indep set) h,k,l reflns measd unique [Rint] obsd [I g 2σ(I)] params refined GooF on F2 R indices [F > 4σ(F)] R(F), wR(F2) R indices (all data) R(F), wR(F2) largest residual peaks/e 3 A˚-3

2a

4a

C43H48N4Ti monoclinic C2/c 38.976(5) 10.178(1) 20.072(3) 114.283(2) 7258(2) 8 668.75 2848 1.224 0.271 0.7456, 0.6898 2.0 to 26.4 -48 ... 44, 0 ... 12, 0 ... 25 67 378 7421 [0.0861] 5085 449 1.029 0.0411, 0.0821 0.0805, 0.0992 0.299, -0.357

C41H45N5STi monoclinic P21/n 12.5567(11) 18.8324(17) 15.3320(14) 95.934(2) 3606.2(6) 4 687.78 1456 1.267 0.332 0.7464, 0.7031 2.0 to 32.3 -18 ... 18, 0 ... 28, 0 ... 22 87 398 12171 [0.0389] 9722 440 1.112 0.0431, 0.1124 0.0611, 0.1262 0.640, -0.281

NMR (150.9 MHz, benzene-d6, 295 K): δ 4.1 (SiMe3), 12.7 (C5Me5), 21.7 (C6H3Me2), 24.3 (NCH2CH2), 30.1 (NCCH2), 52.8 (NMe2), 52.9 (NCH2), 53.9 (NMe2), 120.2 (ortho-C6H3Me2), 122.5 (para-C6H3Me2), 125.0 (C5Me5), 138.0 (meta-C6H3Me2), 150.6 (ipso-C6H3Me2), 172.8 (NCN) ppm. 29Si (79.5 MHz, benzene-d6, 295 K): δ 4.39 (SiMe3) ppm. IR (KBr, cm-1): 2951 (m), 2911 (m), 2858 (m), 2066 (s), 1619 (sh), 1599 (m), 1532 (m), 1353 (m), 1248 (m). Anal. Found (calcd for C27H45N7SiTi þ DMAP): C, 61.6 (61.3); H, 8.3 (8.3); N, 18.4 (18.9)..

Computational Studies All molecular structures were optimized using the B3PW91 hybrid functional with a 6-31G(d) basis set21 for all atoms using the GAUSSIAN03 program package.20 The natural population analyses were performed with the NBO 3.0 facilities,23 and all the orbital visualizations have been obtained with the GaussView program.22 The molecular systems were optimized using X-ray diffraction data as input. Stationary points were verified by frequency analysis. Theoretical NMR Shifts. All the structures used for the NMR calculations have been carried out from DFT-optimized structures with the B3PW91 hybrid functional with a 6-31G(d) basis set for all atoms with the GAUSSIAN03 program package: NMR calculations have been performed with GIAO-B3PW91 hybrid functional30 with a 6-311þþG(2d, 2p) basis set for N, a 6-311þþG(d,p) basis set for S, O, C, H, and a 6-311þþG(2df,2p) basis set for Ti.31 The 15N NMR shifts have been calibrated by linear regression between all the available experimental data and the chemical shifts obtained from the Gaussian output (see Supporting Information). (30) (a) McWeeny, R. Phys. Rev. 1926, 126, 1028. (b) Ditchfield, R. Mol. Phys. 1974, 27, 789. (c) Dodds, J. L.; McWeeny, R.; Sadlej, A. J. Mol. Phys. 1980, 41, 1419. (d) Wolinski, K.; Hilton, J. F.; Pulay, P. J. Am. Chem. Soc. 1990, 112, 8251. (31) (a) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650. (b) Blaudeau, J.-P.; McGrath, M. P.; Curtiss, L. A.; Radom, L. J. Chem. Phys. 1997, 107, 5016. (c) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639.

7b C36H43N5OTi orthorhombic Pbca 16.971(2) 15.809(2) 23.901(2) 6412(1) 8 609.65 2592 1.263 0.303 0.7464, 0.6713 2.0 to 30.0 0 ... 23, -22 ... 0, -33 ... 0 121 656 9383 [0.0553] 6762 396 1.136 0.0448, 0.1048 0.0813, 0.1376 0.532, -0.370

8 C27H45N7SiTi monoclinic P21/c 12.007(2) 16.755(3) 14.366(2) 91.997(3) 2888.2(8) 4 543.69 1168 1.250 0.366 0.7461, 0.6867 1.7 to 30.6 -48 ... 44, 0 ... 12, 0 ... 25 70 475 8869 [0.0881] 5933 337 1.066 0.0476, 0.1134 0.0807, 0.1245 0.495, -0.374

X-ray Crystal Structure Determinations. Crystal data and details of the structure determinations are listed in Table 4. Intensity data were collected at low temperature with a Bruker AXS Smart 1000 CCD diffractometer (Mo KR radiation, graphite monochromator, λ=0.71073 A˚). Data were corrected for air and detector absorption and Lorentz and polarization effects;32 absorption by the crystal was treated with a semiempirical multiscan method.33 The structures were solved by the heavy atom method combined with structure expansion by direct methods applied to difference structure factors (complexes 2a, 4a, and 8)35 or by conventional direct methods (complex 7b)36,37 and refined by full-matrix least-squares methods based on F2 against all unique reflections.37,38 All non-hydrogen atoms were given anisotropic displacement parameters. Hydrogen atoms were generally placed at calculated positions and refined with a riding model. When justified by the quality of the data, the positions of some hydrogen atoms (those on C(14) and C(15) in complex 2a) were taken from difference Fourier syntheses and refined.

Acknowledgment. We thank the Deutsche Forschungsgemeinschaft for funding (SFB 623) and the EU for a Marie Curie postdoctoral fellowship (to J.L.F.). Supporting Information Available: Crystallographic information in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org. (32) SAINT; Bruker AXS, 2007. (33) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. (34) Sheldrick, G. M. SADABS; Bruker AXS, 2004-2008. (35) Beurskens, P. T. In Crystallographic Computing 3; Sheldrick, G. M., Kr€uger, C., Goddard R., Eds.; Clarendon Press: Oxford, UK, 1985; p 216. Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Smits, J. M. M.; Garcia-Granda, S.; Gould, R. O. DIRDIF-2008; Radboud University, Nijmegen, The Netherlands, 2008. (36) Sheldrick, G. M. SHELXS-97; University of G€ottingen: Germany, 1997. (37) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (38) Sheldrick, G. M. SHELXL-97; University of G€ottingen, 1997.

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