From Five to Five: Titanium Ketimine Complexes with Monoaza

Article Cite This: Organometallics XXXX, XXX, XXX-XXX

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From Five to Five: Titanium Ketimine Complexes with Monoazabutadiene η4‑Coordination Mode and Hidden η2‑Imine Reactivity Malte Fischer, Marc Schmidtmann, and Rüdiger Beckhaus* Institut für Chemie, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Federal Republic of Germany S Supporting Information *

ABSTRACT: In the reactions of LTiCl3 (L: Cp*, Cp), Mg, and PhN C(p-tolyl)2 (1) the formation of η4-ketimine complexes Cp*Ti(Cl)(η4PhNC(p-tolyl)2) (2a) and CpTi(Cl)(η4-PhNC(p-tolyl)2) (2b) are observed. Their “nonclassic” five-membered titanium monoazabutadiene envelope coordination modes, involving one of the p-tolyl substituents, is confirmed by single crystal X-ray diffraction analysis of 2b. In reactions of 2 with aldehydes, ketones, alkynes, carbodiimides, isocyanates, isothiocyanates, and imines five-membered titanacycles are formed in a regioselective manner. This behavior is in agreement with a hidden η2-imine reactivity. All reaction products are fully characterized, including single crystal X-ray diffraction studies. For the PhCCH insertion products (4b, 4c) the formation of Ti−C(Ph) units are observed. By insertion of the isocyanate CyNCO the formation of a Ti−N bond in 6a is preferred in comparison to the insertion of the isothiocyanate PhNCS, where a Ti−S bond is formed (7a). By reacting 2a with aldimine PhNC(H)(p-tolyl) the nonsymmetric titanaimidazolidine derivative 8a is formed by subsequent ketimine−aldimine coupling. By derivatization of 2a with LiN(Me)Cy the formation of a the titanadihydropyrrole 9a is observed, caused by a 1,3-H-shift. 2 appears to be inert toward a broad range of terminal olefins. Reacting 2a with allyl ethyl ether results in a spontaneous ether cleavage reaction to 10a.

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INTRODUCTION During the last few decades, imines have been used as versatile ligands in organometallic and coordination chemistry. The coordination of such Schiff bases to a metal center enables the synthesis of highly active homogeneous catalysts1 and allows the formation of supramolecular complexes.2,3 In our previous work on the coordination modes of imines to early transition metals like titanium, η1- (I), η2- (II), and η4-coordination modes (III) were observed, as well as various C−C coupling reactions leading to McMurry-type coupling products IV, Aldol-type coupling products V, titanaazavinylidenes VI, and mixed imine amido titaniumcomplexes VII, strongly dependent on the nature of the used imines and the oxidation state of titanium (Scheme 1).4−7 Especially, the until then unknown η4-coordination mode was of great interest and density functional calculations at the M06-2X level of theory supported the formulation of these complexes as “nonclassic” titanaazacyclopentenes (1-aza-2titanacyclopent-4-enes).4 The first examples of fully characterized 1-aza-2-titanacylopent-4-ene complexes of titanium VIII have been reported by Scholz et al. in 1998, obtained by reduction of Cp2TiCl2 or CpTiCl3 with magnesium in the presence of 1-aza-1,3-dienes (Scheme 2; A).8,9 Recent studies in our group demonstrated that 1-aza-2-titanacylopent-4-ene complexes IX can be obtained through N−H and C−H activation of various allylamines featuring the smallest substitution pattern at the carbon atom in the α-position to © XXXX American Chemical Society

Scheme 1. Coordination Modes of Titanium Imine Complexes η1 (I), η2 (II), η4 (III), and Subsequent Titanium Complexes (IV−VII)

the titanium center (Scheme 2; B).10 Another remarkable access to 1-aza-2-titanacylopent-4-ene complexes 2 was achieved by the reductive complexation, using Cp2TiCl2 or Cp*TiCl3 and magnesium in the presence of the ketimine PhNC(p-tolyl)2 1 (Scheme 2; C).4 Such an unusual Received: September 5, 2017

A

DOI: 10.1021/acs.organomet.7b00673 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

corresponding derivative 2b with the less electron-donating cyclopentadienyl ligand using CpTiCl3 as the precursor (Scheme 4).

Scheme 2. Synthesis of 1-Aza-2-titanacyclopent-4-enes

Scheme 4. Formation of 1-Aza-2-titanacylopent-4-ene Complexes 2a and 2b by Reductive Complexation of Ketimine 1

The reactions go hand in hand with a color change from bright orange or yellow to brown. Products which are both highly air- and moisture-sensitive can be obtained in form of dark violet (2a) and dark red (2b) solids in good yields (up to 89%) after purification. 2a and 2b demonstrate only slight solubilities in aliphatic solvents, but high solubilities in aromatic and polar solvents facilitate good purification processes and subsequent NMR experiments. The molecular structure of 2b obtained by single crystal Xray diffraction analysis is shown in Figure 1 and confirms the η4-

monoazadiene substructure with a dearomatized ring was also observed by the Rosenthal group for vinylpyridines in the coordination sphere of low-valent zirconocene complexes.11 To the best of our knowledge, the reactivities of 1-aza-2titanacylopent-4-ene complexes are sparsely investigated. For many years only insertion reactions of carbonyl compounds were reported by Scholz et al., quite limited due to sterically demanding substituents.9 Recent studies on the reactivities of compounds IX show manifold subsequent reactions, facilitated by the lack of additional substituent at the C-terminus.12 Here, we present the synthesis of the new η4-ketimine complex 2b and the unexpected and high reactivities of 2a and 2b, that are best described as nonclassic titanaazabutadienes. We introduce the reactions of those η4-ketimine complexes with various unsaturated substrates summarized in Scheme 3.

Figure 1. Molecular structure of complex 2b. Hydrogen atoms are omitted for clarity (except H25). Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1−N1 1.934(1), Ti1−Cl1 2.312(1), Ti1−C12 2.362(1), Ti1−C20 2.407(1), Ti1−C25 2.254(2), Ti1···H25 2.25, N1−C12 1.390(2), C12−C20 1.426(2), C20−C21 1.445(2), C21−C22 1.363(2), C22− C23 1.428(2), C23−C24 1.366(2), C24−C25 1.429(2), C20−C25 1.432(2), C13−C14 1.398(2), C14−C15 1.391(2); N11−Ti1−Cl1 97.44(4), N1−Ti1−C25 84.82(5), Σ∠C12 (359.7).

Scheme 3. Overview of Investigated Reactions

coordination mode of the imine. The N1−C12 bond length in 2b (1.390(2) Å) is elongated in comparison to the N−C bond length in the ketimine 1 (1.283(1) Å),4 indicating a single bond character,13 while the C12−C20 bond length (1.426(2) Å) is shortened in comparison to that in 1 (1.497(1) Å).4 Additionally, the sum of angles around C12 of approximately 360° indicates its sp2-hybridization. Furthermore, localized carbon−carbon double bonds are found in the former aromatic ring C20−C25 (C21−C22 1.363(2) Å, C23−C24 1.366(2) Å), whereas the C−C distances in the intact aromatic ring C13− C18 are well-balanced. The Ti1−N1 bond length (1.934(1) Å), the Ti1−C25 bond length (2.254(2) Å), as well as the other described bonding parameters are in agreement with 2a and

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RESULTS AND DISCUSSION Synthesis and Characterization of η4-Ketimine Complexes 2a and 2b. As reported previously, complex 2a is prepared by the reaction of Cp*TiCl3 with the corresponding ketimine 1 and magnesium at room temperature using THF as solvent.4 We extended this reaction to synthesize the B


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Organometallics

Unexpectedly, in all cases five-membered titanaazabutadienes 2a and 2b react readily and in a highly selective manner with aldehydes and ketones, in the same manner as three-membered titanaaziridines (XII), to corresponding five-membered titanaoxazolidines 3a−e (Scheme 6). No indication was observed

other 1-aza-2-titanacylopent-4-ene complexes.8,9 The structural data are summarized in Table 1. Table 1. Comparison of the Structural Data of 2a,4 2b, VIIIa,9 and VIIIb9 (Bond Lengths [Å])a Ti1−N1 Ti1−C25 Ti1−C12 Ti1−C20 N1−C12 C12−C20 C20−C25 a

2a

2b

VIIIa

VIIIb

1.941(1) 2.247(2) 2.399 (1) 2.441(2) 1.393(2) 1.425(2) 1.432(2)

1.934(1) 2.254(2) 2.362(2) 2.407(1) 1.390(2) 1.426(2) 1.438(2)

1.902(3) 2.147(3) 2.323(3) 2.374(3) 1.376(4) 1.394(4) 1.449(4)

1.920(1) 2.136(2) 2.332(2) 2.381(1) 1.385(2) 1.386(2) 1.442(2)

Scheme 6. Reactions of 2a and 2b with Carbonyl Compounds

Structures:

The envelope structure of 2b is characteristic of 1-aza-2titanacyclopent-4-ene complexes. The fold angle of the central five-membered ring system of 69.4° is almost the same as in complex 2a (67.4°).4 The difference Δ = [(Ti1−C12 + Ti1− C20)/2 − (Ti1−N1 + Ti1−C25)/2] = 0.291 Å describes the contribution of the η4−π bonding mode. Δ is larger than in other comparable complexes14−16 but in good agreement with 2a (0.326 Å), VIIIa (0.324 Å), and VIIIb (0.328 Å). The low Δvalue also indicates that N1, C12, C20, and C25 lie in a plane. The aforementioned envelope structure goes hand in hand with the envelope rearrangement between isomers prone X and supine XI (Scheme 5), which are inhibited at low temper-

for the formation of seven-membered ring systems XIII, which would have been in accordance with the reactivity of classic monoazabutadiene complexes like VIIIa and VIIIb toward carbonyl compounds. All reactions of 2a and 2b with carbonyl compounds are accompanied by an instant color change to orange or red, and clear solutions are obtained. The titanaoxazolidines 3a−e are obtained in good yields (72−89%) after purification. In comparison to 2a and 2b, complexes 3a−e are less reactive toward oxygen and moisture and can also be stored as solids for months under inert conditions. Cp*-derivatives 3a, 3c, and 3d are well-soluble in aliphatic solvents. Cp-derivatives 3b and 3e are slightly soluble in aliphatic solvents, and all show high solubilities in aromatic and polar solvents. Complexes 3a−e are fully characterized by NMR-experiments. Due to the formation of the titanaoxazolidine moieties, envelope rearrangements as shown in Scheme 5 no longer occur resulting in sharp signals. Titanaoxazolidines 3a and 3b, formed by the insertion of acetone, produce 1H signals at 1.40 and 1.60 ppm and 1.45 and 1.78 for 3a and 3b, respectively, for the two methyl groups at the central five-membered rings, indicating significant different chemical surroundings above and below the central ring systems, which is consistent with their C1 symmetries. The same is true for the signals of the hydrogen atoms localized at the p-tolyl groups. Of high diagnostic value are the 13C signals of the quaternary carbon atoms of the fivemembered ring as well as the results of 15N,1H HMBC NMR experiments which are summarized in Table 2. All values are in good agreement to comparable titanaoxazolidines reported previously.4,5,18 The structures of the titanaoxazolidine complexes 3a−e are furthermore confirmed by means of single-crystal X-ray diffraction of compound 3a. Single crystals were obtained from a saturated n-hexane solution at −26 °C. Complex 3a crystallizes in the monoclinic space group C2/c. The molecular structure (Figure 2) shows a 4-fold coordinated titanium atom in a three-legged piano-stool geometry with Ct−

Scheme 5. Prone X and Supine XI Isomer of Monoazabutadiene Complexes

ature.4,17 2b has been fully characterized by NMR spectroscopy. In contrast to 2a, even at a temperature of 193 K the minor isomer is not detectable. The significant chemical shifts of complex 2b are quite similar to those of complex 2a and have already been discussed comprehensively for 2a.4 Details are given in the Supporting Information. Reactivities of 2a and 2b toward Carbonyl Compounds. As mentioned in the Introduction, only very few examples of subsequent reactions of 1-aza-titanacyclopent-4enes are reported. The reactivities of the classic monoazadiene complexes like VIIIa and VIIIb synthesized by Scholz et al. are driven by their reactive metal−carbon bonds. Reactions of VIIIa and VIIIb with carbonyl compounds lead to regioselective insertion of the polar carbon−oxygen bond into the metal−carbon bond under ring expansion to the corresponding seven-membered metallacyclic frameworks.9 Inspired by the structural similarities, we investigated the reactivity of 2a and 2b toward aldehydes and ketones. C


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Organometallics Table 2. Selected 1H, 13C, and 15N NMR Data of 3a−e (ppm) C5H5 3a 3b 3c 3d 3e a

C5Me5

OCq(CH3)2

OCq/OCH

NCq

1.91

1.42, 1.60 1.45, 1.78

96.3 98.0/98.1a 97.3 91.5 91.6

95.8 98.0/98.1a 96.7 95.8 97.6

6.08 1.94 2.03 6.36

Scheme 7. Proposed Mechanism for the Formation of Titanaoxazolidines 3a−e 15

N

302.4 322.0 b b 319.0

Unambiguous assignment not possible. bNot detected.

subsequent reactions with alkynes. The reactions of nonclassic monoazadiene complexes 2a and 2b with alkynes in n-hexane at room temperature are accompanied by instant color changes to clear red (4a), orange (4b), or yellow (4c) solutions (Scheme 8). Five-membered ring systems 4a−c are isolated in moderate

Figure 2. Molecular structure of complex 3a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1− N1 1.949(1), Ti1−Cl1 2.3215(4), Ti−O1 1.823(1), N1−C17 1.503(1), O1−C32 1.452(1), C17−C32 1.612(2); O1−Ti1−N1 82.67(4), Ct−Ti1−Cl1 112.3, Σ∠C17 332.0, Σ∠C32 334.8.

Scheme 8. Reactions of 2a and 2b with Alkynes

Ti−Cl1 and O1−Ti1−N1 bond angles of 112.3 and 82.67(4)°, respectively. The bond lengths of Ti1−O1 (1.823(1) Å) and Ti1−Cl1 (2.3215(4) Å) are typical of single bonds. The Ti1− N1 bond (1.949(1) Å) is slightly shortened in comparison to a Ti−N single bond, indicating pπ−dπ electron donor interactions. In contrast, the newly formed C−C bond C17−C32 (1.612(2) Å) constitutes an elongated single bond (typical C− C single bond length: 1.53 Å).13 The central five-membered ring system is nonplanar due to the sp3-hybridizations of C17 and C32 as indicated by the sum of angles around these atoms of 332.0 and 334.8°, respectively. Furthermore, no localized carbon−carbon double bonds are present in the former coordinating six-membered ring system indicating its aromaticity. We assume this rearomatization of the former six-membered ring, which was bonded via one of the ortho carbon atoms to the Ti center to be the driving force of the unexpected reactivities of complexes 2a and 2b. The proposed reaction mechanism is shown in Scheme 7. Starting from 2a and 2b the ketone coordinates to the metal center (Scheme 7, step a). This coordination of the substrate causes a rearrangement of five-membered ring system XIV to corresponding three-membered titanaaziridine XV (Scheme 7, step b) under rearomatization of the former coordinating ptolyl group. Final insertion of the polar carbon−oxygen double bond into the titanium−carbon bond of XV leads to the formation of isolated complexes 3a−e (Scheme 7, step c) and explains the hidden η2-imine reactivity.4 Reactivities of 2a and 2b toward Alkynes. In order to establish how far the unexpected reactivities of complexes 2a and 2b are extendable to other substrates, we investigated

to good yields (52−87%). Like titanaazaoxazolidines 3a−e, Cp*-substituted derivatives 4a and 4b show higher solubilities in aliphatic solvents than their Cp-substituted congener 4c; all complexes 4a−c demonstrate high solubilities in aliphatic and polar solvents and can be stored for months under inert conditions without any indication of decomposition. The reactions proceed again under preservation of fivemembered ring systems. Additionally, the reactions of 2a and 2b with phenyl acetylene lead to the formation of corresponding titanaazacyclopentene derivatives 4b and 4c under regioselective insertion of the terminal alkyne. In these cases the phenyl substituent is located in α-position to the titanium center which is in accordance with the reactivities of zirconaaziridines19−21 and intermediary formed titanaaziridines.22 Titanaaziridines derived from bis(η5:η1-pentafulvene) titanium complexes react with inverse regioselectivities.18 Complexes 4a and 4c are characterized by X-ray diffraction analysis. The molecular structures of 4a and 4c are shown in Figures 3 and 4, respectively. Complex 4a crystallizes in the monoclinic space group P21/c, and complex 4c crystallizes in the orthorhombic space group D


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4b, and 212.4 ppm 4c). For complex 4a, two doublet signals for the TiCHCH moiety are observed in the 1H NMR spectrum at 7.19 and 7.26 ppm with coupling constants of 11.2 Hz which is characteristic for the ecliptic conformation in 4a. Complexes 4b and 4c each show one singlet signal in the 1H NMR spectra at 7.13 and 7.21 ppm, respectively, for the TiCqCH moieties. The 15N NMR signals of 287.0 (4b) and 301.6 (4c) ppm are in the expected range and in good agreement with other titanaazacylopentene complexes.4,5,18 The results of the NMR measurements are summarized in Table 3. The reactions of alkynes with nonclassic titanaazabutadiene complexes 2a and 2b support the thesis in which 2a and 2b react unexpectedly like three-membered titanaaziridines.

Figure 3. Molecular structure of complex 4a. Hydrogen atoms are omitted for clarity (except H32 and H33). Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1−N1 1.919(3), Ti1−Cl1 2.284(1), Ti1−C33 2.083(4), N1−C17 1.490(4), C17−C32 1.513(5), C32−C33 1.327(5); N1−Ti1−C33 80.8(1), Ct−Ti1−Cl1 116.8, Σ∠C32 360.0, Σ∠C33 360.0.

Table 3. Selected 1H, 13C, and 15N NMR Data of 4a−c (ppm) C5H5 4a 4b 4c a

C5Me5 1.84 1.76

6.13

TiCRCH 203.5/7.19 210.9 212.4

a

TiCRCH

NCq

150.7/7.26 146.4/7.13 144.5/7.21

77.8 72.7 73.0

15

N

b 287.0 301.6

R = H. bNot detected.

Reactivity of 2a and 2b toward Heterocumulenes (XCNR; X = NR, O, S). The reaction chemistry of both classic titanaazabutadiene and titanaaziridine complexes toward heterocumulenes is nearly unexplored. Here we investigate the reactions of the nonclassic titanaazabutadiene complexes 2a and 2b with heterocumulenes such as carbodiimides, isocyanates, and isothiocyanates. The reactions of 2a and 2b with di-p-tolylcarbodiimide in nhexane at room temperature again leads to instant color changes to red (5a) or yellow (5b), and the analyses of the spectroscopic data identify complexes 5a and 5b as titanadiazapentacycles (Scheme 9). Complexes 5a and 5b

Figure 4. Molecular structure of complex 4c. Hydrogen atoms are omitted for clarity (except H27). Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1−N1 1.890(1), Ti1−Cl1 2.2934(4), Ti1−C28 2.101(1), N1−C12 1.499(2), C12−C27 1.520(2), C27−C28 1.344(2); C28−Ti1−N1 83.89(5), Ct−Ti1−Cl1 116.9, Σ∠C27 360.0, Σ∠C28 360.0.

Scheme 9. Reactions of 2a and 2b with Carbodiimides

Pna21. Like 3a, the central titanium atoms are coordinated in a three-legged piano-stool environment surrounded by the η5cyclopentadienyl ligand, the chlorido ligand, and the newly formed bidentate ligand (Ct−Ti1−Cl1:116.8° 4a, 116.9° 4c; N1−Ti1−C33/C28 80.8(1)° 4a, 83.89(5)° 4c). The bond lengths Ti1−Cl1 (2.284(1) Å 4a, 2.2934(4) Å 4c) and Ti1− C33/Ti−C28 (2.083(4) Å 4a, 2.101(1) Å 4c) are typical of single bonds, whereas the bond lengths Ti1−N1 (1.919(3) Å 4a, 1.890(1) Å 4c) are shortened, which is in good agreement with the aforementioned pπ−dπ electron donor interactions. The former triple bonds of the alkynes are elongated to values typical of C(sp2)−C(sp2) double bonds (C32−C33 1.327(5) Å 4a, C27−C28 1.344(2) Å 4c). Due to the rearomatization of the former coordinating aromatic ring systems, no localized double bonds are present in the p-tolyl groups. In both cases, the central titanaazapentene moieties are likewise planar. Compounds 4a−c are fully characterized by NMR analysis, and the spectroscopic data are consistent with the X-ray structures. As for complexes 3a−e, sharp signals are observed due to the loss of envelope rearrangements of the titanaazacyclopentenes 4a−c. Of high diagnostic value are the 13 C chemical shifts of the Ti−C(sp2) moieties because of their significant downfield chemical shifts (203.5 ppm 4a, 210.9 ppm

demonstrate the same solubilities and sensitivities toward air and moisture as titanaoxazolidines 3a−e and titanaazapentenes 4a−c. All are isolated in good yields of 74−84%. As for the previously presented reactions, we propose formal insertion of one CN− double bond of the carbodiimide into a threemembered titanaaziridine as the reaction pathway. The structures of 5a and 5b are confirmed by means of single crystal X-ray diffraction of 5a (Figure 5). Suitable single crystals were obtained from a saturated toluene solution at −26 °C. Complex 5a crystallizes in the monoclinic space group P21/n. The molecular structure also shows the three-legged pianostool geometry. In addition to the η5-Cp* ligand and the chlorido ligand, the coordination environment of the central titanium atom is completed by two Ti−N bonds derived from the former η4-imine ligand and from one nitrogen atom of the E


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Organometallics

NCqN moieties are comparable to those of organic amidines, further supported by the ν̃(CN) stretching frequencies at 1630 (5a) and 1627 (5b) cm−1. The 15N-HMBC spectra of compound 5a reveals two signals for two of the three nitrogen atoms with chemical shifts of 286.1 and 306.7 ppm; the third signal is not detected. The signal at 286.1 ppm can clearly be assigned to the nitrogen atom bearing the phenyl group. Due to the small difference within the 15N chemical shifts of only 20 ppm, indicating similar chemical surrounding, the second signal is assigned to the NCN nitrogen atom. Those shifts are in the same range as those for complexes 3a−e and 4a−c. Selected chemical shifts are summarized in Table 4. After the successful reactions of 2a and 2b with di-ptolylcarbodiimide further reactions with other heterocumulenes were investigated. Because of the so far similar reaction behavior of complexes 2a and 2b, the subsequent reactions were mainly focused on the Cp* congener 2a. The reaction of 2a with cyclohexyl isocyanate in n-hexane at room temperature is accompanied by an immediate color change to orange-red. The analysis of the spectroscopic data identifies the product as the titanadiazapentacycle 6a exhibiting an exocyclic carbonyl function (Scheme 10). Product 6a is formed through formal regioselective insertion of the isocyanate into the aforementioned three-membered titanaaziridine.

Figure 5. Molecular structure of complex 5a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1− N1 1.923(1), Ti1−N2 1.951(1), Ti1−Cl1 2.3083(4), N1−C17 1.496(2), N2−C32 1.415(2), N3−C32 1.273(2), C17−C32 1.540(2); N1−Ti1−N2 85.27(5), Ct−Ti1−Cl1 113.8, Σ∠C32 359.7.

Scheme 10. Reaction of 2a with Cyclohexyl Isocyanate and Phenyl Isothiocyanate

inserted carbodiimide. The Ti1−N1 (1.923(1) Å) and Ti1−N2 (1.951(1) Å) bonds are again shortened due to pπ−dπ electron donor interactions. The N1−C17 (1.496(2) Å) and the N2− C32 (1.415(2) Å) bonds are significantly longer than the exocyclic N3−C32 (1.273(2) Å) bond which is typical of a N(sp2)−C(sp2) double bond.13 The sp2-hybridization of C32 is confirmed by the sum of the angles (359.7°). The newly formed C17−C32 bond (1.540(2) Å) lies in the range of C(sp2)−C(sp3) single bonds (1.51 Å).13 The nonplanarity of the central five-membered titanadiazapentacycle is caused by the sp3-hybridization of the N1, N2, and C17 atoms. As for the other molecular structures presented here, a rearomatization of the former coordinating p-tolyl group to the titanium center leads to average carbon−carbon bond lengths within the aromatic ring between single and double bonds. The solution 1H and 13C NMR spectra of compounds 5a and 5b are in agreement with the X-ray structure of 5a. In particular, the C1 symmetry of both compounds is confirmed by the four inequivalent p-tolyl groups within the molecules. Hence, four signals for the methyl groups are found at higher field (1.83, 1.91, 2.00, and 2.35 ppm 5a; 1.83, 1.84, 1.94, and 2.33 ppm 5b). Of high diagnostic value are the 13C chemical shifts of the quaternary carbon atoms of the central fivemembered rings (95.6 (NCq) and 163.9 (NCN) ppm 5a, 96.9 (NCq) and 163.6 (NCqN) ppm 5b). Whereas the 13C chemical shifts of the NCq moiety bearing the p-tolyl groups are in the same range as in 3a−e, the 13C chemical shifts of the

In contrast, the reaction of complex 2a with phenyl thioisocyanate in n-hexane at room temperature leads to the inverse regioselectivity of the insertion reaction, leading to the formation of titanathiazolidine 7a (Scheme 10). Both complexes 6a and 7a maintain the same solubilities and sensitivities toward air and moisture as the other Cp* derivatives mentioned above and are isolated in good yields of 82 and 92%, respectively.

Table 4. Selected 1H, 13C, and 15N NMR Data of 5a and 5b (ppm) C5H5 5a 5b a

6.09

C5Me5

CH3

NCq

NCN

1.69

1.83, 1.91, 2.00, 2.35

95.6

163.9

1.83, 1.84, 1.94, 2.33

96.9

163.6

15

N

a 286.1 (NPh) 306.7 (NCN)

Not detected. F


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Organometallics

supported by the ν̃(CN) stretching frequency at 1640 cm−1. The 15N-HMBC spectrum of complex 6a shows two characteristic signals at 286.2 and 309.1 ppm, which are in the same range as for the other compounds presented here. The inverse regioselectivity of the reaction between complex 2a and phenyl isothiocyanate, where phenyl isothiocyanate is inserted into the proposed titanaaziridine intermediate, is confirmed by its molecular structure in the solid state (Figure 7). Single crystals of 7a suitable for X-ray diffraction were obtained from a saturated n-hexane solution at 4 °C.

Complexes 6a and 7a are thoroughly characterized by NMR analysis and single-crystal X-ray diffraction. The molecular structure of the titanaimidazolidinone 6a is shown in Figure 6. Suitable single crystals of 6a were obtained from a saturated nhexane solution at 4 °C.

Figure 6. Molecular structure of complex 6a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1− N1 1.907(2), Ti1−N2 1.972(2), Ti1−Cl1 2.3055(6), N1−C17 1.493(3), N2−C32 1.369(3), O1−C32 1.220(2), C17−C32 1.554(3); N1−Ti1−N2 85.28(7), Ct−Ti1−Cl1 114.1, Σ∠C32 359.9, Σ∠N1 359.7, Σ∠N2 358.8.

Figure 7. Molecular structure of complex 7a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1− N1 1.937(1), Ti1−S1 2.3222(4), Ti1−Cl1 2.3003(4), N1−C17 1.483(2), N2−C32 1.270(2), S1−C32 1.782(1), C17−C32 1.547(2); N1−Ti1−S1 84.92(3), Ct−Ti1−Cl1 114.8, Σ∠C32 359.4, Σ∠N1 359.9.

Complex 6a crystallizes in the orthorhombic space group Pna21. The molecular structure shows a three-legged pianostool geometry. In addition to the η5-Cp* and the chlorido ligands, the coordination environment of the central titanium atom is completed by two Ti−N bonds derived from the former η4-imine ligand and from one nitrogen of the isocyanate. The Ti1−Cl1 (2.3055(6) Å), the N1−C17 (1.493(3) Å), the newly formed C17−C32 (1.554(3) Å) bonds are typical of single bonds. The Ti1−N1 (1.907(2) Å) and the Ti1−N2 (1.972(2) Å) bond lengths of the N,N-chelating ligand are significantly shorter than the sum of covalent radii, indicating pπ−dπ electron interactions, which is further confirmed by the trigonal planar coordination environments of N1 (359.7°) and N2 (358.8°). The N2−C32 (1.369(3) Å) and the O1−C32 (1.220(2) Å) bond lengths of the amide group are in good agreement with those of organic γ-lactams. The central fivemembered ring system is almost planar. As expected from the other molecular structures presented here, the reaction is accompanied by the rearomatization of the former coordinating p-tolyl group. The solution NMR measurements of complex 6a are consistent with its structure in the solid state. C1-symmetric complex 6a shows two signals for the methyl groups of the chemically inequivalent p-tolyl groups at 1.95 and 2.25 ppm and distinct signals in the low field for the aromatic hydrogen atoms. The 13C chemical shifts of the carbon atoms within the five-membered titanacycle are again of high diagnostic value and show signals at 94.7 ppm (NCq) and 180.3 (NCO) ppm. The latter signal corresponding to the NCO moiety is observed in the range typical of organic amides, further

Complex 7a crystallizes in the triclinic space group P-1. The central titanium atom exhibits the three-legged piano-stool environment known from 6a, surrounded by the η5-Cp* ligand, the chlorido ligand and the newly formed bidentate ligand (Ct−Ti1−Cl1: 116.8°, N1−Ti1−S1: 84.92(3)°). The Ti1−Cl1 (2.300(3) Å), N1−C17 (1.483(2) Å), and the newly formed C17−C32 (1.547(2) Å) bonds are typical of single bonds. The Ti1−S1 (2.3222(4) Å) bond length is within the sum of covalent radii,23 in accordance with a single bond. As for the other structurally characterized complexes, the Ti1−N1 (1.937(1) Å) bond length, and the sum of angles around N1 (359.9°) indicate a pπ−dπ electron interaction. The exocyclic N2−C32 (1.270(2) Å) bond constitutes a double bond. The sulfur atom is shifted out of the plane of the central fivemembered voiding its planarity. The solution NMR experiments of complex 7a are consistent with its structure in the solid state. The C1-symmetric complex 7a shows two signals for the methyl groups of the chemically inequivalent p-tolyl groups at 1.86 and 2.28 ppm and distinct signals in the low field for the aromatic hydrogen atoms. The 13 C chemical shifts of the quaternary carbon atoms in the fivemembered titanacycle are again of high diagnostic value and show signals at 99.5 ppm (NCq) and 171.8 (SCN) ppm. The signal of the SCN moiety is in the range typical of comparable organic compounds, further supported by the ν̃(CN) stretching frequency at 1606 cm−1. The 15N-HMBC spectrum of complex 7a shows two characteristic signals at 292.1 (NPh) and 337.0 (SCN) ppm. It has the strongest low-field shift among the complexes reported in this work. G


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Organometallics Table 5. Selected 1H, 13C, and 15N NMR Data of 6a and 7a (ppm) C5Me5

CH3

NCq

NCO

6a

1.88

1.95, 2.25

94.7

180.3

7a

1.78

1.86, 2.28

99.5

15

SCN

171.8

286.2 309.1 292.1 336.6

N

(NCO) (NPh) (NPh) (SCN)

Scheme 11. Reaction of 2a with Imines

Selected chemical shifts of complexes 6a and 7a are summarized in Table 5. One can easily envisage that the chelating ligands in complexes 6a and 7a could both have bound either in N,E (E = O, S) or in N,N′ fashion. Consistent with our observations, Gade et al. have reported that starting from half-sandwich titanium hydrazide complexes mixtures of isomeric metallacycles were formed in reactions with isocyanates and isothiocyanates.24 DFT calculations by Gade et al. and related results by Mountford et al. concerning titanium imido chemistry show that both steric and electronic factors must be considered.25,26 Often one isomer appears to be electronically preferred, but steric factors can easily overturn this. Reactivity of 2a toward Imines. Recent results in our group concerning imines in the titanium coordination sphere, highlight the ability of imine coupling reactions in an (e.g., Michael-like or McMurry-like manner).5 Motivated by the high reactivities of complexes 2a and 2b in a titanaaziridine-like fashion toward various multiple bond substrates, we were encouraged to extend the reactions to imines. The reactions of 2a with an aldimine in n-hexane at ambient temperature is accompanied by instant color change to orange and five-membered titanaimidazolidine 8a is isolated in good yield of 88% (Scheme 11). In contrast, no reaction with a ketimine was observed probably due to steric hindrance, even by using more polar solvents or by heating the reaction mixture to 60 °C for several days, resulting only in reisolation of the starting materials. Titanadiazapentacycle 8a shows the same solubility and sensitivity toward air and moisture as the other complexes with a Cp* substituent reported here. The formation of complex 8a through formal insertion of the carbon nitrogen double bond into the titanium carbon bond of the titanaaziridine intermediate is confirmed by the molecular structure of titanadiazapentacycle 8a in the solid state (Figure 8). Single crystals of 8a were obtained from a saturated toluene solution at −26 °C. Titanadiazapentacycle 8a crystallizes in the monoclinic space group P21/c. The central titanium atom exhibits the familiar three-legged piano-stool environment surrounded by the η5Cp* ligand, the chlorido ligand, and the newly formed bidentate ligand (Ct−Ti1−Cl1 110.8°, N1−Ti1−N2 83.40(9)°). The Ti1−Cl1 (2.300(3) Å), N1−C17 (1.483(2)

Figure 8. Molecular structure of complex 8a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1− N1 1.910(2), Ti1−N2 1.924(3), Ti1−Cl1 2.3363(9), N1−C17 1.501(3), N2−C32 1.486(3), C17−C32 1.585(3); N1−Ti1−N2 83.40(9), Ct−Ti1−Cl1 110.8, Σ∠N1 359.9, Σ∠N2 351.8.

Å), N2−C32 (1.486(3) Å,) and the newly formed C17−C32 (1.585(3) Å) bonds are typical of single bonds, despite being slightly elongated. The Ti1−N1 (1.937(1) Å) and Ti1−N2 (1.924(3) Å) bond lengths and the sum of angles around N1 (359.9°) and N2 (351.8°) indicate pπ−dπ electron interactions between the titanium and the nitrogen atoms, in good agreement with the other complexes structurally characterized here and in the literature.5,27 The central five-membered ring is not planar, caused by the sp3-hybridizations of C17 and C32. The solution 1H, 13C, and 15N NMR analysis of 8a are in accordance with its solid-state structure. The 1H NMR spectrum shows distinct signals for the methyl groups (1.79, 1.86, and 2.28 ppm) and aromatic hydrogen atoms of the ptolyl groups in agreement with the C1 symmetry of 8a. Notably, 8a shows one signal in the 1H NMR for the ring hydrogen atom at 6.87−6.91 ppm (masked by a multiplet signal) with the corresponding 13 C resonance at 83.9 ppm. In other titanadiazapentacycles (e.g., XVI and XVII; Table 6), the corresponding signals are shifted to lower field (5.88/73.8 ppm XVI,5 4.68/76.3 ppm XVII)5 caused by the different nature of H


Article

Organometallics

nitrogen atom within the five-membered ring system. As a result, the familiar rearomatization of the coordinating sixmembered ring occurs. Complex 9a has been fully characterized by NMR experiments. The 1H NMR spectrum is shown in Figure 9. In contrast to complex 2a (details in the Supporting Information) sharp signals are observed at room temperature as a result of the rearomatization of the coordinating six-membered ring system. From right to left, the first noticeable signals of complex 9a at 2.00 and 2.25 ppm show the methyl groups localized at the aromatic six-membered rings. As expected, the methyl group of the new amido ligand is shifted to lower field at 3.55 ppm. The signal of the CH moiety within the cyclohexyl group at 5.15−5.20 ppm is significantly shifted to lower field, indicating an agostic interactions between the titanium and the β-H of the cyclohexyl moiety.31 Of high diagnostic value are the signals of the new NCH moiety at 5.97 ppm (1H NMR) and 69.0 ppm (13C NMR) which are in good agreement with complexes 8a, XVI, XVII, and XVIII (Table 6) also exhibiting NCH units within the five-membered titanacycles. A clear indication for the formation of complex 9a is the 13C signal of the quaternary aromatic carbon atom localized in α-position to the titanium atom, which at 198.0 ppm is in the same range as that in other complexes having a C(sp2) atom in α-position to titanium (e.g., 4a−c). The 15N-HMBC NMR spectrum of compound 9a shows two signals for the two nitrogen atoms at 237.7 (NCy) and 285.3 (NPh) ppm. They are comparable to complexes reported herein and also to titanium monoamide complexes published recently.32 Limitation in the Reactivity of 2a. Titanaaziridines are considered key intermediates of the titanium-catalyzed hydroaminoalkylation of alkenes.18,33−36 Utilizing the titanaaziridinelike reactivity of 2a and 2b we reacted 2a with various alkenes (e.g., styrene, trimethyl vinyl silane, 1-hexene, and vinyl ethyl ether). In all cases, no reaction occurred, and starting materials were reisolated (Scheme 13).

Table 6. Selected 1H, 13C and 15N NMR Data of 8a, XVI,5 XVII,5 and XVIII27 (ppm)a NCH 7a XVI XVII XVIII a

6.87−6.91/83.9 5.88/73.8

NCq

15

N

87.3

287.9, 327.6

83.4, 84.4

310.1, 324.7

4.68/76.3

Structures:

the ligand systems at the titanium centers. The 13C NMR chemical shift of the quaternary carbon atom of the fivemembered ring in 8a is located at 87.3 ppm and is comparable to that of complex XVII.5 The 15N-HMBC spectrum shows signals for the two nitrogen atoms at 287.9 and 327.6 ppm, both in the expected range. Table 6 summarizes the characteristic NMR spectroscopic data in comparison to XVI, XVII, and Rothwell aryloxide complex XVIII. Whereas complexes XVI, XVII, and XVIII are formed directly through C−C coupling of two imines in the coordination sphere of low-valent titanium, we herein present for the first time the C−C coupling through a subsequent reaction. We assume the formation of a titanaaziridine intermediate through a rearrangement of the titanazabutadiene moiety followed by the regioselective insertion of the polar carbon nitrogen double bond into the reactive titanium−carbon bond of the three-membered titanacycle. To the best of our knowledge, complex 8a represents the first structurally characterized titanadiazapentacyle, derived from a subsequent imine−imine cross-coupling reaction of two different imines. Although imine−imine cross-coupling reactions of different imines are mentioned in the literature,28 the titanium-mediated cross-coupling reactions are consistently dominated by coupling reactions of the same imine.5,27,29,30 Derivatization of 2a Using a Lithium Amide. In all reactions discussed so far, the Cp−Ti−Cl fragment has been preserved. Therefore, the exchange of the chlorido ligand by an amide unit is performed by reaction of 2a with lithium cyclohexyl(methyl)amide. This leads to the expected exchange of the clorido ligand but also goes along with a 1,3-H shift as presented in Scheme 12 to yield complex 9a as a red-brown solid in good yield of 83% after purification. The 1,3-H shift takes place from the ortho carbon atom of the para-tolyl group coordinated to titanium to the carbon atom in α-position to the

Scheme 13. Expected Reactions of 2a with Alkenes

An exception was observed for the reaction of 2a with allyl ethyl ether in n-hexane at ambient temperature. Here, an immediate color change to yellow is observed, and complex 10a is formed as the result of a spontaneous ether cleavage reaction and isolated in good yield of 65% after purification (Scheme 14). Product 10a shows the same solubility and sensitivity toward air and moisture as those of the other complexes with a Cp* substituent reported here. Single crystals suitable for X-ray diffraction were obtained by slow diffusion of allyl ethyl ether into a solution of 2a in nhexane. The molecular structure of complex 10a is shown in Figure 10. Complex 10a crystallizes in the monoclinic space group P21/ n. The central titanium atom is coordinated in a three-legged piano-stool environment (Ct−Ti1−Cl1 110.8°, N1−Ti1−N2

Scheme 12. Reaction of 2a with Lithium Cyclohexyl(methyl)amide

I


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Organometallics

Figure 9. 1H NMR spectrum (500 MHz, C6D6, rt) of complex 9a. Corresponding signals are highlighted by colored symbols.

C35A−C36A (1.407(7) Å), C32−C33 (1.505(2) Å), and the newly formed C17−C32 (1.565(2) Å) bond lengths all lie in the range of single bonds, whereas C33−C34 (1.320(3) Å) clearly shows double-bond character. Compound 10a has also been fully characterized by NMR analysis. The 1H NMR spectrum shows the characteristic coupling pattern of the −CH2−CH3 unit with one triplet (0.94, 3 JH,H = 6.9 Hz, CH2CH3) and two doublets of quartets (3.20, 2 JH,H = 11.1 Hz, 3JH,H = 6.9 Hz; 4.06, 2JH,H = 11.3 Hz, 3JH,H = 6.9 Hz, CH2CH3). Another characteristic coupling pattern is found for the allyl moiety with one ddt (5.53, 3JH,H (trans) = 17.0 Hz, 3JH,H (cis) = 10.7 Hz, 3JH,H = 6.7 Hz, CH2CHCH2), one multiplet (4.57−4.61, CH2CHCH2), and two broad signals (2.58−2.62 and 2.90−294 ppm, CH2CHCH2). The localization of the allyl group directly at the quaternary carbon atom in α-position to the nitrogen is verified by the 1H,13CHMBC contact. To summarize, the reaction of complex 2a with the allyl ethyl ether is the result of a carbon−oxygen bond splitting followed by addition of the alkoxy moiety to the titanium and addition of the corresponding allyl cation to the quaternary carbon atom in α-position to the nitrogen atom.

Scheme 14. Reaction of 2a with Allyl Ethyl Ether

■

CONCLUSION Convenient syntheses of η4-coordinated titanium ketimine complexes 2a and 2b have been established. Due to their fivemembered ring structure, they are best described as nonclassic monoazabutadiene complexes in the solid state and in solution. However, in subsequent reactions with a broad range of unsaturated substrates like carbonyl compounds, alkynes, heterocumulenes, and imines, five-membered titanacycles are formed in a highly regioselective manner (3a−e, 4a−c, 5a,b, 6a, 7a, and 8a). This unexpected reactivity is best described by insertion of the substrate into a three-membered titanaaziridine. The driving force of this reactivity can be explained by the tendency to rearomatize the former coordinating p-tolyl group

Figure 10. Molecular structure of complex 10a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 50% probability level. Selected bond lengths (Å) and angles (deg):Ti1− N1 1.966(1), Ti1−Cl1 2.3427(5), Ti1−O1 1.756(1)), N1−C17 1.517(2), O1−C35A 1.417(4), C35A−C36A 1.407(7), C17−C32 1.565(2), C32−C33 1.505(2), C33−C34 1.320(3); N1−Ti1−O1 110.32(6), Ct−Ti1−Cl1 110.1, Σ∠CN1 359.7.

83.40(9)°). The Ti1−Cl1 (2.3427(5) Å) and N1−C17 (1.517(2) Å) bonds are typical of single bonds. The Ti1−N1 (1.966(1) Å) and the newly formed Ti1−O1 (1.756(1) Å) bonds as well as the sum of angles around N1 (359.7°) indicate pπ−dπ electron interactions. The O1−C35A (1.417(4) Å), J


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Organometallics

115.9 (C5H5), 123.9 (CHaryl), 125.2 (CHaryl)*, 125.3 (CHaryl)*, 127.4 (Cq,aryl), 128.2 (2 × CHaryl)*, 128.6 (CHaryl)*, 129.1 (2 × CHaryl)*, 129.7 (CHaryl), 130.0 (Cq,aryl), 132.1 (CHaryl), 133.2 (CHaryl), 135.2 (CHaryl), 137.8 (Cq,aryl), 148.7 (Cq,aryl) ppm. * = overlap with C7D8 signal. IR (ATR): ν̃ 3024, 2919, 2857, 1603, 1503, 1484, 1445, 1315, 1297, 1220, 1198, 1179, 1142, 1113, 1068, 1017, 960, 805, 753, 733, 690, 631, 596, 562 cm−1. Mp: 88 °C (dec.). Anal. Calcd for C26H24ClNTi: C, 71.99; H, 5.58; N, 3.23. Found: C, 71.08; H, 6.13; N, 2.84. Titanaoxazolidine Complex 3a. Complex 2a (0.200 g, 0.397 mmol) was suspended in 10 mL of n-hexane, and acetone (0.03 mL, 0.397 mmol) was added to the suspension, resulting in a clear solution and a color change from dark violet to orange. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 3a as an orange solid. No further purification steps are required. Data for 3a are as follows. Yield: 0.198 g (81%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.42 (s, 3H, OCq(CH3)2), 1.60 (s, 3H, OCq(CH3)2), 1.91 (s, 15 H, C5Me5), 2.02 (s, 3H, CH3), 2.23 (s, 3H, CH3), 6.69−6.72 (m, 1H, p-CHPhN), 6.79−6.81 (m, 2H, 2 × oCHarylCH3), 6.91−6.94 (m, 2H, 2 × m-CHPhN), 7.00−7.02 (m, 2H, 2 × o-CHPhN), 7.14−7.16 (m, 2H, 2 × o-CHarylCH3)*, 7.34−7.36 (m, 2H, 2 × m-CHarylCH3), 8.11−8.13 (m, 2H, 2 × m-CHarylCH3) ppm. 13 C NMR (C6D6, 126 MHz, 305 K): δ = 12.3 (C5Me5), 20.8 (CH3), 21.1 (CH3), 29.4 (OCq(CH3)2), 33.2 (OCq(CH3)2), 95.8 (NCq), 96.3 (OCq), 121.9 (2 × o-CHPhN), 124.5 (p-CHPhN), 127.2 (C5Me5), 128.2 (2 × o-CHarylCH3)*, 128.3 (2 × o-CHarylCH3)*, 129.6 (2 × mCHPhN), 130.4 (2 × m-CHarylCH3), 132.2 (2 × m-CHarylCH3), 135.9 (Cq,arylCH3), 137.4 (Cq,arylCH3), 139.5 (p-Cq,arylCH3), 142.3 (pCq,arylCH3), 147.9 (Cq,PhN) ppm. * = overlap with C6D6 signal. 15N NMR (C6D6, 51 MHz, 305 K): δ = 302.4 ppm. IR (ATR): ν̃ 2986, 2917, 2864, 1589, 1485, 1448, 1377, 1361, 1260, 1229, 1172, 1129, 1085, 1008, 983, 941, 899, 862, 825, 807, 790, 772, 746, 724, 694, 678, 618, 607, 570 cm−1. Mp: 129 °C (dec.). Anal. Calcd for C34H40ClNOTi: C, 72.66; H, 7.17; N, 2.49. Found: C, 71.12; H, 7.52; N, 2.43. Titanaoxazolidine Complex 3b. Complex 2b (0.200 g, 0.461 mmol) was suspended in 10 mL of n-hexane, and acetone (0.03 mL, 0.461 mmol) was added to the suspension, resulting in a color change from dark red to orange. The reaction mixture was stirred for 16 h at room temperature. The solid was separated, washed with small amounts of n-hexane (3 × 2 mL), and dried in vacuum to give 3b as a yellow-brown solid. Data for 3b are as follows. Yield: 0.179 g (79%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.45 (s, 3H, OCq(CH3)2), 1.78 (s, 3H, OCq(CH3)2), 2.01 (s, 3H, CH3), 2.20 (s, 3H, CH3), 6.08 (m, 5H, C5H5), 6.71−6.74 (m, 1H, p-CHPhN), 6.78−6.79 (m, 2H, 2 × oCHarylCH3), 6.91−6.95 (m, 2H, 2 × m-CHPhN), 702−7.03 (m, 2H, 2 × o-CHPhN), 7.08−7.10 (m, 2H, 2 × o-CHarylCH3), 7.23−7.25 (m, 2H, 2 × m-CHarylCH3), 8.14−8.16 (m, 2H, 2 × m-CHarylCH3) ppm. 13 C NMR (C6D6, 126 MHz, 305 K): δ = 20.8 (CH3), 21.1 (CH3), 27.2 (OCq(CH3)2), 33.0 (OCq(CH3)2), 98.0 (NCq/OCq), 98.1 (NCq/ OCq), 117.8 (C5H5), 122.2 (2 × o-CHPhN), 125.7 (p-CHPhN), 128.3 (4 × o-CHarylCH3)*, 129.6 (2 × m-CHPhN), 130.1 (2 × mCHarylCH3), 132.8 (2 × m-CHarylCH3), 136.3 (Cq,arylCH3), 137.8 (Cq,arylCH3), 139.2 (p-Cq,arylCH3), 141.2 (p-Cq,arylCH3), 147.9 (Cq,PhN) ppm. * = overlap with C6D6 signal. 15N NMR (C6D6, 51 MHz, 305 K): δ = 322.0 ppm. IR (ATR): ν̃ 3008, 2971, 2923, 1603, 1584, 1510, 1479, 1444, 1380, 1363, 1231, 1198, 1177, 1155, 1132, 1082, 1013, 985, 944, 902, 866, 815, 782, 750, 725, 697, 619, 607, 571 cm−1. Mp: 108 °C (dec.). Anal. Calcd for C29H30ClNOTi: C, 70.81; H, 6.15; N, 2.85. Found: C, 70.14; H, 6.23; N, 2.68. Titanaoxazolidine Complex 3c. Complex 2a (0.200 g, 0.397 mmol) and 4-tert-butylcyclohexanone (0.061 g, 0.397 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to red. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 3c as a red solid. No further purification steps are required. Data for 3c are as follows. Yield: 0.214 g (89%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 0.81 (s, 9H, Cq(CH3)3), 1.22−1.31 (m, 4H, 4 ×

in the reaction products. In contrast to known titanaaziridine complexes employing a bent-metallocene backbone, the hidden η2-imine coordination mode in 2a and 2b causes an even higher reactivity. Thus, in addition to carbonyl compounds and alkynes, the previously mentioned carbodiimides, isocyanates, isothiocyanates, and imines become viable substrates. By using an aldimine, asymmetrically substituted titanaimidazolidine 8a becomes available for the first time through a subsequent ketimine−aldimine coupling reaction. In the reaction of complex 2a with lithium cyclohexyl(methyl) amide a 1,3-H shift occurs in addition to the substitution of the chlorido ligand resulting in the formation of 9a. A limitation of the general reactivity from five-membered to five-membered ring systems was observed by screening the reactivity toward various alkenes. Whereas complex 2a seems to be inert toward a broad range of terminal alkenes, a spontaneous ether cleavage reaction with allyl ethyl ether was observed, and the titanium monoamide 10a could be isolated.

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EXPERIMENTAL SECTION

General Considerations. All reactions were carried out under an inert atmosphere of argon or nitrogen with rigorous exclusion of oxygen and moisture using standard glovebox and Schlenk techniques. The glass equipment was stored in an oven at 120 °C and evacuated prior to use. Solvents and liquid educts were dried according to standard procedures. Solvents were distilled over Na/K alloy with benzophenone under nitrogen atmosphere. The used liquid reactants were distilled from CaH2 prior to use. Ketimine PhNC(p-tolyl)2 1,4 Cp*TiCl3,37 and CpTiCl337 were synthesized according to known procedures. 1H and 13C NMR spectra were recorded on a Bruker AVANCE III 500 spectrometer (1H 500 MHz; 13C 126 MHz; 15N 51 MHz) or a Bruker AVANCE 300 spectrometer (1H 300 MHz). The NMR chemical shifts were referenced to residual protons of the solvent or the internal standard TMS. Given chemical shifts of 15N result from 15N,1H HMBC NMR-experiments with nitromethane as external standard (δ = 378.9 vs NH3). IR spectra were recorded on a Bruker Tensor 27 spectrometer using an attenuated total reflection (ATR) method. Elemental analyses were carried out on a EuroEA 3000 Elemental Analyzer. The carbon value in the elemental analysis is often lowered by carbide formation. The hydrogen value is found in some cases higher, due to residual traces of solvents. Melting points were determined using a “Mel-Temp” by Laboratory Devices, Cambridge, U.K. Further exact details of the individually synthesized products, crystallographic data, and NMR spectra are given in the Supporting Information. Titanaazabutadiene Complexes 2a and 2b. These were prepared according to a slightly modified literature procedure.4 Pentamethylcyclopentadienyltitaniumtrichloride/cyclopentadienyltitaniumtrichloride (2.000 g, 6.910 mmol/2.000 g, 9.120 mmol), ketimine 1 (1.972 g, 6.910 mmol/2.602 g, 9.120 mmol), and magnesium (0.168 g, 6.910 mmol/0.222 g, 9.120 mmol) were dissolved in 40 mL of tetrahydrofuran. After stirring the reaction mixtures for 16 h at room temperature, the solvents were evaporated in vacuum. The residues were dissolved in 20 mL of toluene, filtered, and the precipitates of MgCl2 washed with toluene (3 × 12 mL). The combined filtrates were concentrated in vacuum, and the resulting solids were recrystallized from 20 mL of n-hexane to yield 2a as deep violet plates and 2b as dark red plates. Analytical data of compound 2a is in accordance with the literature (Yield: 2.816 g (81%)).4 Data for 2b are as follows. Yield: 3.519 g (89%). 1H NMR (C7D8, 500 MHz, 213 K): δ = 1.91 (s, 3H, CH3), 2.01 (s, 3H, CH3), 5.50 (s, 5H, C5H5), 6.01−6.02 (m, 1H, CHaryl), 6.29−6.29 (m, 1H, TiCH), 6.38−6.40 (m, 1H, CHaryl), 6.60−6.61 (m, 1H, CHaryl), 6.71−6.79 (m(br), 4H, 4 × CHaryl), 6.88−6.93 (m, 2H, 2 × CHaryl), 7.02−7.07 (m(br), 1H, CHaryl), 7.20−7.36 (m(br), 1H, CHaryl), 7.68−7.69 (m, 1H, CHaryl) ppm. 13CNMR (C7D8, 125 MHz, 213 K): δ = 20.1 (CH3)*, 20.7 (CH3)*, 103.0 (TiCH), 104.3 (Cq,aryl), 108.0 (Cq,aryl), K


Article

Organometallics

1594, 1509, 1490, 1448, 1410, 1315, 1249, 1188, 1154, 1104, 1085, 1045, 1023, 999, 971, 946, 934, 923, 872, 810, 765, 748, 714, 691, 680, 607, 592 cm−1. Mp: 120 °C (dec.). Anal. Calcd for C37H34ClFeNOTi: C, 68.60; H, 5.29; N, 2.16. Found: C, 65.48; H, 5.59; N, 1.87. Titanaazacyclopentene Complex 4a. Complex 2a (0.150 g, 0.298 mmol) was suspended in 10 mL of n-hexane and stirred under acetylene (1 atm), resulting in a color change from dark violet to redbrown. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 4a as a red-brown solid. No further purification steps are required. Data for 4a are as follows. Yield: 0.137 g (87%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.84 (s, 15H, C5Me5), 1.97 (s, 3H, CH3), 2.21 (s, 3H, CH3), 6.66−6.69 (m, 1H, p-CHPhN), 6.88−6.95 (m, 4H, 4 × CHPh), 6.96−6.98 (m, 2H, 2 × o-CHp‑tolylCH3), 7.04−7.06 (m, 2H, 2 × o-CHp‑tolylCH3), 7.19 (d, 3JH,H = 11.2 Hz, 1H, TiCHCH), 7.26 (d, 3 JH,H = 11.2 Hz, 1H, TiCHCH), 7.40−7.42 (m, 2H, 2 × mCHp‑tolylCH3), 7.92−7.94 (m, 2H, 2 × m-CHp‑tolylCH3) ppm. 13C NMR (C6D6, 126 MHz, 305 K): δ = 12.4 (C5Me5), 20.9 (CH3), 21.1 (CH3), 77.8 (NCq), 122.0 (2 × CHaryl), 123.8 (CHaryl), 127.7 (C5Me5), 128.6 (2 × CHaryl), 128.7 (2 × CHaryl), 128.8 (2 × CHaryl), 130.37 (2 × CHaryl), 130.4 (2 × CHaryl), 136.4 (Cq,p‑tolylCH3), 136.5 (Cq,p‑tolylCH3), 141.0 (p-Cq,p‑tolylCH3), 141.1 (p-Cq,p‑tolylCH3), 147.7 (Cq,Ph), 150.7 (TiCHCH), 203.5 (TiCHCH) ppm. IR (ATR): ν̃ 3021, 2963, 2915, 2861m 1590, 1506, 1482, 1446, 1377, 1313, 1261, 1226, 1183, 1159, 1085, 1020, 916, 883, 791, 770, 748, 693, 617, 604, 572 cm−1. Mp: 134 °C (dec.). Anal. Calcd for C33H36ClNTi: C, 74.79; H, 6.85; N, 2.64. Found: C, 71.37; H, 7.20; N, 2.56. Titanaazacyclopentene Complex 4b. Complex 2a (0.150 g, 0.298 mmol) was suspended in 10 mL of n-hexane, and phenylacetylene (0.03 mL, 0.298 mmol) was added to the suspension, resulting in a color change from dark violet to orange. The reaction mixture was stirred for 16 h at room temperature. The solid was separated, washed with small amounts of n-hexane (3 × 2 mL), and dried in vacuum to give 4b as an orange solid. Data for 4b are as follows. Yield: 0.126 g (70%). 1H NMR (C6D6, 500 MHz, 303 K): δ = 1.76 (s, 15H, C5Me5), 1.92 (s, 3H, CH3), 2,24 (s, 3H, CH3), 6.69−6.72 (m, 1H, CHaryl), 6.88−6.93 (m, 4H, 4 × CHaryl), 6.99−7.03 (m, 5H, 5 × CHaryl), 7.08−7.11 (m, 4H, 4 × CHaryl), 7.13 (s, 1H, TiCqCH), 7.53−7.55 (m, 2H, 2 × mCHp‑tolylCH3), 7.83−7.84 (m, 2H, 2 × m-CHp‑tolylCH3) ppm. 13C NMR (C6D6, 126 MHz, 303 K): δ = 12.6 (C5Me5), 20.9 (CH3), 21.1 (CH3), 72.7 (NCq), 124.0 (2 × CHaryl), 124.2 (CHaryl), 125.9 (CHaryl), 127.1 (2 × CHaryl), 128.1 (2 × CHaryl)*, 128.4 (2 × CHaryl)*, 128.65 (C5Me5), 128. 67 (2 × CHaryl), 128.7 (2 × CHaryl), 130.45 (2 × mCHp‑tolylCH3), 130.5 (2 × m-CHp‑tolylCH3), 136.4 (Cq,p‑tolylCH3), 136.7 (Cq,p‑tolylCH3), 141.3 (Cq,aryl), 141.6 (Cq,aryl), 146.4 (TiCqCH), 147.5 (Cq,aryl), 149.1 (Cq,aryl), 210.9 (TiCq) ppm. * = overlap with C6D6 signal. 15N NMR (C6D6, 51 MHz, 303 K): δ = 287.0 ppm. IR (ATR): ν̃ 3053, 3021, 2952, 2914, 2858, 1588, 1556, 1506, 1481, 1441, 1377, 1228, 1179, 1154, 1121, 1092, 1072, 1028, 1005, 918, 903, 877, 854, 843, 816, 783, 760, 737, 722, 700, 624, 587, 571, 560 cm−1. Mp: 206 °C (dec.). Anal. Calcd for C39H40ClNTi: C, 77.29; H, 6.65; N, 2.31. Found: C, 75.43; H, 7.10; N, 2.22. Titanaazacyclopentene Complex 4c. Complex 2b (0.150 g, 0.346 mmol) was suspended in 10 mL of n-hexane, and phenylacetylene (0.04 mL, 0.346 mmol) was added to the suspension, resulting in a color change from dark violet to brownish yellow. The reaction mixture was stirred for 16 h at room temperature. The solid was separated, washed with small amounts of n-hexane (3 × 2 mL), and dried in vacuum to give 4c as a yellow-brown solid. Data for 4c are as follows. Yield: 0.097 g (52%). 1H NMR (C6D6, 500 MHz, 303 K): δ = 1.98 (s, 3H, CH3), 2.21 (s, 3H, CH3), 6.13 (s, 5H, C5H5), 6.67−6.70 (m, 1H, CHaryl), 6.77−6.78 (m, 2H, 2 × CHaryl), 6.87−6.90 (m, 2H, 2 × CHaryl), 6.94−6.96 (m, 2H, 2 × CHaryl), 6.99−7.01 (m, 3H, 3 × CHaryl), 7.04−7.06 (m, 2H, 2 × CHaryl), 7.09−7.12 (m, 2H, 2 × CHaryl), 7.21 (s, 1H, TiCqCH), 7.37−7.39 (m, 2H, 2 × CHaryl), 7.90−7.92 (m, 2H, 2 × CHaryl) ppm. 13 C NMR (C6D6, 126 MHz, 303 K): δ = 20.9 (CH3), 21.1 (CH3), 73.0 (NCq), 117.9 (C5H5), 122.8 (2 × CHaryl), 124.8 (CHaryl), 126.3 (2 × CHaryl), 126.6 (CHaryl), 128.5 (2 × CHaryl), 128.8 (2 × CHaryl), 129.0

CHcy /CH2,cy), 1.40−1.42 (m, 1H, CH2,cy), 1.48−1.51 (m, 1H, CH2,cy), 1.56−1.62 (m, 1H, CH2,cy), 1.94 (s, 15H, C5Me5), 2.03 (s, 3H, CH3), 2.24 (s, 3H, CH3), 2.36−2.39 (m, 1H, CH2,cy), 3.28−3.32 (m, 1H, CH2,cy), 6.67−6.70 (m, 1H, p-CHPhN), 6.85−6.87 (m, 2H, 2 × o-CHarylCH3), 6.90−6.93 (m, 2H, 2 × m-CHPhN), 6.96−6.98 (m, 2H, 2 × o-CHPhN), 7.16−7.18 (m, 2H, 2 × o-CHarylCH3)*, 7.40−7.42 (m, 2H, 2 × m-CHarylCH3), 8.13 (m(br), 2H, 2 × m-CHarylCH3) ppm. 13 C NMR (C6D6, 126 MHz, 305 K): δ = 12.4 (C5Me5), 20.9 (CH3), 21.1 (CH3), 23.1 (CH2,cy), 23.9 (CH2,cy), 27.7 (Cq(CH3)3), 32.4 (Cq(CH3)3), 35.6 (CH2,cy), 39.0 (CH2,cy), 46.9 (CHcy), 96.7 (NCq), 97.3 (OCq), 121.3 (2 × o-CHPhN), 124.3 (p-CHPhN), 127.0 (C5Me5), 128.3 (4 × o-CHarylCH3)*, 129.7 (2 × m-CHPhN), 130.7 (2 × mCHarylCH3), 132.2 (2 × m-CHarylCH3), 135.9 (Cq,arylCH3), 137.3 (Cq,arylCH3), 138.6 (p-Cq,arylCH3), 141.6 (p-Cq,arylCH3), 147.6 (Cq,PhN) ppm. * = overlap with C6D6 signal. IR (ATR): ν̃ 2946, 2864, 1588, 1510, 1481, 1446, 1376, 1364, 1224, 1183, 1155, 1114, 1083, 1051, 1004, 968, 942, 896, 885, 830, 807, 782, 772, 736, 720, 706, 695, 621, 609, 588, 568 cm−1. Mp: 99 °C (dec.). Anal. Calcd for C41H52ClNOTi: C, 74.82; H, 7.96; N, 2.13. Found: C, 74.08; H, 8.74; N, 2.10. Titanaoxazolidine Complex 3d. Complex 2a (0.200 g, 0.397 mmol) and ferrocenecarboxaldehyde (0.085 g, 0.397 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to orange. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 3d as an orange solid. No further purification steps are required. Data for 3d are as follows. Yield: 0.223 g (78%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.86 (s, 3H, CH3), 2.03 (s, 15H, C5Me5), 2.21 (s, 3H, CH3), 3.66−3.67 (m, 1H, FcC5H4), 3.84−3.85 (m, 1H, FcC5H4), 3.93−3.94 (m, 2H, 2 × FcC5H4), 4.10 (s, 5H, FcC5H5), 6.57−6.60 (m, 1H, p-CHPhN), 6.80−6.82 (m, 4H, 2 × o-CHPhN/2 × o-CHarylCH3), 6.86−6.89 (m, 2H, 2 × m-CHPhN), 7.01−7.03 (m, 2H, 2 × o-CHarylCH3), 7.19−7.20 (m, 2H, 2 × m-CHarylCH3), 7.54 (s, 1H, OCH), 7.78−7.79 (m, 2H, 2 × m-CHarylCH3) ppm. 13C NMR (C6D6, 126 MHz, 305 K): δ = 12.4 (C5Me5), 20.9 (CH3), 21.1 (CH3), 67.1 (FcC5H4), 68.1 (FcC5H4), 68.4 (FcC5H4), 69.1 (FcC5H4), 69.5 (FcC5H5), 87.0 (FcCq), 91.5 (OCH), 95.8 (NCq), 120.2 (2 × oCHPhN), 122.9 (p-CHPhN), 127.1 (2 × o-CHarylCH3), 127.9 (C5Me5)*, 128.5 (2 × m-CHPhN), 128.9 (2 × o-CHarylCH3), 129.8 (2 × m-CHarylCH3), 132.4 (2 × m-CHarylCH3), 134.4 (Cq,arylCH3), 136.7 (Cq,arylCH3), 137.1 (p-Cq,arylCH3), 140.0 (p-Cq,arylCH3), 148.8 (Cq,PhN) ppm. * = overlap with C6D6 signal. IR (ATR): ν̃ 2962, 2911, 2860, 1590, 1510, 1484, 1445, 1377, 1308, 1261, 1240, 1184, 1154, 1102, 1084, 1021, 973, 937, 923, 873, 825, 799, 766, 752, 711, 695, 677, 616 cm−1. Mp: 170 °C (dec.). Anal. Calcd for C42H44ClFeNOTi: C, 70.26; H, 6.18; N, 1.95. Found: C, 67.06; H, 6.60; N, 1.83. Titanaoxazolidine Complex 3e. Complex 2b (0.200 g, 0.461 mmol) and ferrocenecarboxaldehyde (0.099 g, 0.461 mmol) were suspended in 10 mL of n-hexane, resulting in a color change from dark red to orange. The reaction mixture was stirred for 16 h at room temperature. The solid was separated, washed with small amounts of n-hexane (3 × 4 mL) and dried in vacuum to give 3e as an orange solid. Data for 3e are as follows. Yield: 0.215 g (72%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.86 (s, 3H, CH3), 2.21 (s, 3H, CH3), 3.66− 3.68 (m, 1H, FcC5H4), 3.79−3.81 (m, 1H, FcC5H4), 3.88−3.90 (m, 1H, FcC5H4), 3.92−3.94 (m, 1H, FcC5H4), 4.16 (s, 5H, FcC5H5), 6.36 (s, 5H, C5H5), 6.57−6.60 (m, 1H, p-CHPhN), 6.73−6.74 (m, 2H, 2 × o-CHPhN), 6.80−6.82 (m, 2H, 2 × o-CHarylCH3), 6.83−6.86 (m, 2H, 2 × m-CHPhN), 6.99−7.01 (m, 2H, 2 × o-CHarylCH3), 7.20−7.22 (m, 2H, 2 × m-CHarylCH3), 7.74−7.75 (m, 2H, 2 × m-CHarylCH3), 8.00 (s, 1H, OCH) ppm. 13C NMR (C6D6, 126 MHz, 305 K): δ = 20.9 (CH3), 21.1 (CH3), 67.3 (FcC5H4), 68.4 (FcC5H4), 68.6 (FcC5H4), 69.2 (FcC5H4), 69.5 (FcC5H5), 85.7 (FcCq), 91.6 (OCH), 97.6 (NCq), 117.9 (C5H5), 120.3 (2 × o-CHPhN), 123.8 (p-CHPhN), 127.2 (2 × oCHarylCH3), 128.4 (2 × m-CHPhN)*, 129.0 (2 × o-CHarylCH3), 129.6 (2 × m-CHarylCH3), 132.2 (2 × m-CHarylCH3), 134.3 (p-Cq,arylCH3), 137.0 (Cq,arylCH3), 137.5 (Cq,arylCH3), 139.3 (p-Cq,arylCH3), 149.6 (Cq,PhN) ppm. * = overlap with C6D6 signal. 15N NMR (C6D6, 51 MHz, 305 K): δ = 319.0 ppm. IR (ATR): ν̃ 3092, 3026, 2921, 2870, L


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Organometallics (2 × CHaryl), 129.1 (2 × CHaryl), 129.9 (2 × CHaryl), 130.3 (2 × CHaryl), 136.7 (Cq,p‑tolylCH3), 136.9 (Cq,p‑tolylCH3), 140.86 (Cq,aryl), 140.9 (Cq,aryl), 144.5 (TiCqCH), 146.8 (Cq,aryl), 147.0 (Cq,aryl), 212.4 (TiCq) ppm. 15N NMR (C6D6, 51 MHz, 303 K): δ = 301.6 ppm. IR (ATR): ν̃ 3050, 3023, 2954, 2916, 2862, 1590, 1572, 1554, 1506, 1485, 1440, 1297, 1243, 1184, 1143, 1110, 1086, 1071 1031, 1010, 920, 905, 876, 852, 815, 756, 725, 715, 700, 687, 624, 581, 564 cm−1. Mp: 133 °C (dec.). Anal. Calcd for C34H30ClNTi: C, 76.20; H, 5.64; N, 2.61. Found: C, 71.29; H, 5.66; N, 2.37. Titanadiazacyclopentane Complex 5a. Complex 2a (0.150 g, 0.298 mmol) and 1,3-di-p-tolylcarbodiimide (0.066 g, 0.298 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to red-brown. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 5a as a red-brown solid. No further purification steps are required. Data for 5a are as follows. Yield: 0.161 g (74%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.69 (s, 15H, C5Me5), 1.83 (s, 3H, CH3), 1.91 (s, 3H, CH3), 2.00 (s, 3H, CH3), 2.35 (s, 3H, CH3), 6.30 (m(br), 2H, 2 × CHp‑tolyl), 6.45−6.47 (m, 2H, 2 × CHp‑tolyl), 6.49−6.51 (m, 2H, 2 × CHp‑tolyl), 6.57−6.59 (m, 2H, 2 × CHp‑tolyl), 6.64−6.67 (m, 1H, CHPh), 6.80−6.86 (m, 4H, 2 × CHp‑tolyl, 2 × CHPh), 7.14−7.16 (m, 2H, 2 × CHPh)*, 7.29−7.31 (m, 2H, 2 × CHp‑tolyl), 7.76−7.78 (m, 2H, 2 × CHp‑tolyl), 8.28−8.29 (m, 2H, 2 × CHp‑tolyl) ppm. 13C NMR (C6D6, 126 MHz, 305 K): δ = 12.5 (C5Me5), 20.8 (CH3), 20.85 (CH3), 20.9 (CH3), 21.3 (CH3), 95.6 (NCq), 120.6 (2 × CHaryl), 124.48 (2 × CHaryl), 124.5 (2 × CHaryl), 124.8 (CHaryl), 128.0 (2 × CHaryl)*, 128.28 (2 × CHaryl)*, 128.3 (2 × CHaryl)*, 128.4 (2 × CHaryl), 128.6 (2 × CHaryl), 129.4 (Cq,aryl), 129.6 (C5Me5), 131.0 (2 × CHaryl), 131.2 (2 × CHaryl), 134.6 (Cq,aryl), 136.1 (Cq,aryl), 137.3 (Cq,aryl), 140.4 (Cq,aryl), 140.9 (Cq,aryl), 146.4 (Cq,aryl), 146.7 (Cq,aryl), 147.7 (Cq,aryl), 163.9 (NCqN) ppm. * = overlap with C6D6 signal. IR (ATR): ν̃ 3021, 2993, 2919, 2860, 1630 (NCN), 1605, 1574, 1504, 1485, 1449, 1378, 1236, 1186, 1143, 1106, 1085, 1025, 990, 955, 919, 884, 849, 816, 798, 775, 755, 7337, 715, 696, 681, 641, 603, 570 cm−1. Mp: 189 °C (dec.). Anal. Calcd for C46H48ClN3Ti: C, 76.08; H, 6.66; N, 5.79. Found: C, 75.26; H, 6.68; N, 5.67. Titanadiazacyclopentane Complex 5b. Complex 2b (0.200 g, 0.461 mmol) and 1,3-di-p-tolylcarbodiimide (0.102 g, 0.461 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to yellow. The reaction mixture was stirred for 16 h at room temperature. The solid was separated, washed with small amounts of n-hexane (3 × 2 mL), and dried in vacuum to give 5b as a yellow-brown solid. Data for 5b are as follows. Yield: 0.253 g (84%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.83 (s, 3H, CH3), 1.84 (s, 3H, CH3), 1.94 (s, 3H, CH3), 2.33 (s, 3H, CH3), 6.09 (s, 5H, C5H5), 6.43−6.44 (m, 2H, 2 × CHaryl), 6.62−6.64 (m, 3H, 3 × CHaryl), 6.71−6.72 (m, 2H, 2 × oCHPhN), 6.83−6.88 (m, 5H, 2 × o-CHp‑tolylCH3, 3 × CHAryl), 7.00− 7.03 (m, 3H, 3 × CHaryl), 7.24−7.25 (m, 2H, 2 × o-CHp‑tolylCH3), 7.90−7.92 (m, 2H, 2 × m-CHp‑tolylCH3), 8.16−8.18 (m, 2H, 2 × mCHp‑tolylCH3) ppm. 13C NMR (C6D6, 126 MHz, 305 K): δ = 20.7 (CH3), 20.8 (CH3), 20.9 (CH3), 21.2 (CH3), 96.9 (NCq), 118.9 (C5H5), 121.3 (2 × CHaryl), 121.8 (2 × CHaryl), 124.9 (CHaryl), 128.4 (2 × CHaryl), 128.65 (6 × CHaryl), 128.7 (4 × CHaryl), 130.8 (mCHp‑tolylCH3), 131.0 (m-CHp‑tolylCH3), 131.1 (Cq,p‑tolylCH3), 134.5 (Cq,p‑tolylCH3), 136.7 (Cq,p‑tolylCH3), 137.6 (Cq,p‑tolylCH3), 138.9 (Cq,aryl), 140.3 (Cq,aryl), 145.6 (Cq,aryl), 147.1 (Cq,aryl), 149.5 (Cq,aryl), 163.6 (NCN) ppm. 15N NMR (C6D6, 51 MHz, 303 K): δ = 286.1 (NPh), 306.7 (NCN) ppm. IR (ATR): ν̃ 3024, 2918, 2863, 1627 (NCN), 1602, 1504, 1485, 1446, 1310, 1255, 1228, 1188, 1140, 1107, 1081, 1011, 999, 954, 925, 885, 813, 778, 757, 739, 709, 695, 679, 640, 602, 571 cm−1. Mp: 118 °C (dec.). Anal. Calcd for C41H38ClN3Ti: C, 75.06; H, 5.84; N, 6.40. Found: C, 72.43; H, 6.08; N, 6.06. Titanaoxazolidinone Complex 6a. Complex 2a (0.150 g, 0.298 mmol) and cyclohexyl isocyanate (0.04 mL, 0.298 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to orange-red. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum

gave 6a as an orange-red solid. No further purification steps are required. Data for 6a are as follows. Yield: 0.153 g (82%). 1H NMR (C6D6, 500 MHz, 299 K): δ = 1.11−1.18 (m, 3H, CH2,cy), 1.45−1.49 (m, 1H, CH2,cy), 1.57−1.60 (m, 1H, CH2,cy), 1.66−1.67 (m, 1H, CH2,cy), 1.73− 1.75 (m, 1H, CH2,cy), 1.88 (s, 15H, C5Me5), 1.95 (s, 3H, CH3), 2.25 (s, 3H, CH3), 2.29−2.32 (m, 1H, CH2,cy), 2.40−2.47 (m, 1H, CH2,cy), 2.64−2.71 (m, 1H, CH2,cy), 3.19−3.24 (m, 1H, CHcy), 6.69−6.72 (m, 1H, p-CHPhN), 6.78−6.81 (m, 2H, 2 × m-CHPhN), 6.89−6.91 (m, 4H, 2 × m-CHPhN, 2 × o-CHp‑tolylCH3), 7.16−7.19 (m, 2H, 2 × oCHp‑tolylCH3)*, 7.63−7.64 (m, 2H, 2 × m-CHp‑tolylCH3), 7.99−8.01 (m, 2H, 2 × m-CHp‑tolylCH3) ppm. 13C NMR (C6D6, 126 MHz, 299 K): δ = 12.6 (C5Me5), 21.0 (CH3), 21.2 (CH3), 26.1 (CH2,cy), 26.9 (CH2,cy), 27.6 (CH2,cy), 28.6 (CH2,cy), 31.7 (CH2,cy), 62.0 (CHcy), 94.7 (NCq), 125.8 (p-CHPhN), 126.0 (2 × CHaryl), 128.2 (2 × CHaryl)*, 128.4 (2 × CHaryl), 128.5 (2 × CHaryl), 129.7 (C5Me5), 131.0 (2 × mCHp‑tolylCH3), 131.1 (2 × m-CHp‑tolylCH3), 136.5 (p-Cq,p‑tolylCH3), 137.3 (p-Cq,p‑tolylCH3), 138.9 (Cq,p‑tolylCH3), 139.7 (Cq,p‑tolylCH3), 145.3 (Cq,Ph), 180.3 (NCO) ppm. * = overlap with C6D6 signal. 15 N NMR (C6D6, 51 MHz, 299 K): δ = 286.2 (NCO), 309.1 (NPh) ppm. IR (ATR): ν̃ 2978, 2921, 2848, 1640 (NCO), 1589, 1510, 1484, 1447, 1377, 1369, 1254, 1241, 1211, 1187, 1154, 1069, 1032, 1005, 970, 921, 905, 893, 875, 856, 838, 822, 807, 790, 769, 741, 705, 693, 613, 591, 565 cm−1. Mp: 150 °C (dec.). Anal. Calcd for C38H45ClN2OTi: C, 72.55; H, 7.21; N, 4.45. Found: C, 72.69; H, 7.38; N, 4.44. Titanathiazolidine Complex 7a. Complex 2a (0.150 g, 0.298 mmol) and phenyl isothiocyanate (0.04 mL, 0.298 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to yellow. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 7a as a yellow-brown solid. No further purification steps are required. Data for 7a are as follows. Yield: 0.176 g (92%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.78 (s, 15H, C5Me5), 1.86 (s, 3H, CH3), 2.28 (s, 3H, CH3), 6.61−6.64 (m, 1H, p-CHPhN), 6.78−6.82 (m, 1H, CHPhNC), 6.84−6.89 (m, 4H, 2 × m-CHPhN, 2 × o-CHp‑tolylCH3), 7.03−7.07 (m, 4H, 4 × CHPhNC), 7.17−7.18 (m, 2H, 2 × oCHp‑tolylCH3)*, 7.33−7.34 (m, 2H, 2 × o-CHPhN), 7.86−7.87 (m, 2H, 2 × m-CHp‑tolylCH3), 7.90−7.91 (m, 2H, 2 × m-CHp‑tolylCH3) ppm. 13 C NMR (C6D6, 126 MHz, 305 K): δ = 12.8 (C5Me5), 21.0 (CH3), 21.2 (CH3), 99.5 (NCq), 119.8 (2 × CHPhNC), 122.4 (2 × oCHPhN), 124.0 (CHPhNC), 125.0 (p-CHPhN), 128.2 (2 × oCHp‑tolylCH3)*, 128.5 (2 × o-CHp‑tolylCH3), 129.0 (2 × CHPhNC), 129.6 (2 × m-CHPhN), 130.4 (C5Me5), 130.9 (2 × o-CHp‑tolylCH3), 131.6 (2 × o-CHp‑tolylCH3), 136.7 (Cq,p‑tolylCH3), 137.3 (Cq,p‑tolylCH3), 139.2 (p-Cq,p‑tolylCH3), 141.3 (p-Cq,p‑tolylCH3), 142.7 (Cq,PhN), 151.3 (Cq,PhNC), 171.8 (SCN) ppm. * = overlap with C6D6 signal. 15N NMR (C6D6, 51 MHz, 305 K): δ = 292.1 (NPh), 336.6 (SCN) ppm. IR (ATR): ν̃ 3056, 3027, 2976, 2954, 2917, 2861, 1606 (SC N), 1589, 1508, 1482, 1447, 1376, 1228, 1214, 1185, 1157, 1077, 1015, 995, 944, 920, 911, 883, 854, 811, 787, 768, 751, 692, 626, 614, 599, 576, 557 cm−1. Mp: 167 °C (dec.). Anal. Calcd for C38H39ClN2STi: C, 71.41; H, 6.15; N, 4.38; S, 5.02. Found: C, 72.70; H, 6.57; N, 4.63; S, 4.65. Titanadiazacyclopentane Complex 8a. Complex 2a (0.200 g, 0.397 mmol) and N-phenyl-1-(p-tolyl)methanimine (0.077 g, 0.397 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to orange. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 8a as an orange solid. No further purification steps are required. Data for 8a are as follows. Yield: 0.245 g (88%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.69 (s, 15H, C5Me5), 1.79 (s, 3H, CH3), 1.86 (s, 3H, CH3), 2.28 (s, 3H, CH3), 6.54−6.56 (m, 2H, 2 × CHaryl), 6.62−6.65 (m, 1H, CHaryl), 6.67−6.69 (m, 2H, 2 × CHaryl), 6.70−6.73 (m, 1H, CHaryl), 6.79−6.84 (m, 1H, CHaryl), 6.87−6.91 (m, 5H, NCH, 4 × CHaryl), 6.97−6.99 (m, 3H, 3 × CHaryl), 7.04−7.11 (m, 2H, 2 × CHaryl), 7.19−7.20 (m, 1H, CHaryl), 7.25 (m(br), 1H, CHaryl), 7.56 (m(br), 2H, 2 × CHaryl), 7.84−7.86 (m, 2H, 2 × CHaryl) ppm. 13C M


Organometallics

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NMR (C6D6, 126 MHz, 305 K): δ = 12.1 (C5Me5), 20.8 (CH3), 21.0 (CH3), 21.1 (CH3), 83.9 (NCH), 87.3 (NCq), 121.4 (CHaryl), 123.9 (CHaryl), 124.7 (2 × CHaryl), 126.5 (2 × CHaryl), 127.15 (2 × CHaryl), 127.2 (C5Me5), 128.0 (2 × CHaryl)*, 128.4 (2 × CHaryl)*, 129.3 (2 × CHaryl), 129.4 (2 × CHaryl), 129.7 (2 × CHaryl), 132.0 (2 × CHaryl), 132.6 (2 × CHaryl), 135.6 (Cq,aryl), 135.8 (Cq,aryl), 137.6 (Cq,aryl), 138.3 (Cq,aryl), 139.2 (Cq,aryl), 142.5 (Cq,aryl), 146.8 (Cq,aryl), 151.1 (Cq,aryl) ppm. * = overlap with C6D6 signal. 15N NMR (C6D6, 51 MHz, 305 K): δ = 287.9 (NPh), 327.6 (NPh) ppm. IR (ATR): ν̃ 3029, 2982, 2912, 2868, 1589, 1511, 1481, 1449, 1377, 1339, 1305, 1260, 1235, 1211, 1179, 1119, 1082, 1022, 998, 970, 929, 909, 891, 876, 825, 779, 766, 739, 696, 668, 636, 617, 566 cm−1. Mp: 116 °C (dec.). Anal. Calcd for C45H47ClN2Ti: C, 77.30; H, 6.78; N, 4.01. Found: C, 78.84; H, 7.07; N, 4.25. Titanamonoamide Complex 9a. Complex 2a (0.500 g, 0.992 mmol) and lithium cyclohexyl methyl amide (0.118 g, 0.992 mmol) were dissolved in 20 mL of tetrahydrofuran. After stirring the reaction mixture for 16 h at room temperature, the solvent was evaporated in vacuum. The residue was dissolved in 20 mL of toluene, filtered, and the precipitate of LiCl washed with toluene (3 × 10 mL). The combined filtrates were evaporated in vacuum to give 9a as a redbrown solid. Data for 9a are as follows. Yield: 0.480 g (83%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 1.37−1.67 (m, 6H, 3 × CH2,Cy), 1.75 (s, 15H, C5Me5), 1.80−1.86 (m, 2H, CH2,Cy), 2.00 (s, 3H, CH3,p‑Tol), 2.06− 2.12 (m, 2H, CH2,Cy), 2.25 (s, 3H, CH3), 3.55 (s, 3H, NCH3), 5.15− 5.20 (m, 1H, CHCy), 5.97 (s, 1H, NCH), 6.56−6.58 (m, 2H, 2 × oCHPhN), 6.61−6.64 (m 1H, p-CHPhN), 6.78−6.79 (m, 1H, CHAryl), 6.85−6.86 (m, 1H, TiCq,ArCHAryl), 6.92−6.95 (m, 3H, 2 × oCHp‑TolCH3, CHAryl), 7.01−7.04 (m, 2H, 2 × m-CHPhN), 7.33−7.35 (m, 2H, 2 × m-CHp‑TolCH3) ppm. 13C NMR (C6D6, 126 MHz, 305 K): δ = 11.8 (C5Me5), 21.1 (CH3,p‑Tol), 21.5 (CH3), 26.4 (CH2,Cy), 26.6 (CH2,Cy), 26.7 (CH2,Cy), 31.6 (CH2,Cy), 32.0 (CH2,Cy), 38.8 (NCH3), 65.8 (CHCy), 69.0 (NCH), 118.1 (2 × o-CHPhN), 120.1 (pCHPhN), 123.0 (C5Me5), 126.76 (CHAryl), 126.8 (CHAryl), 129.15 (2 × m-CHp‑TolCH3), 129.2 (2 × m-CHPhN), 129.3 (2 × o-CHp‑TolCH3), 132.5 (TiCq,ArCH), 132.7 (TiCq,ArCq,Ar), 135.8 (Cq,p‑TolCH3), 143.0 (Cq,ArCH), 148.2 (TiCq,ArCq,ArCH3), 149.8 (Cq,PhN), 198.0 (TiCq,Ar) ppm. 15N NMR (C6D6, 51 MHz, 305 K): δ = 237.7 (NCy), 285.3 (NPh) ppm. IR (ATR): ν̃ 2920, 2953, 1603, 1501, 1448, 1376, 1313, 1295, 1259, 1177, 1090, 1068, 1020, 993, 935, 916, 785, 768, 747, 711, 691, 617, 565 cm−1. Mp: 74 °C (dec.). Anal. Calcd for C38H48N2Ti: C, 78.60; H, 8.33; N, 4.82. Found: C, 72.69; H, 7.38; N, 4.44. Titanamonoamide Complex 10a. Complex 2a (0.150 g, 0.298 mmol) and allyl ethyl ether (0.03 mL, 0.298 mmol) were suspended in 10 mL of n-hexane, resulting in a clear solution and a color change from dark violet to yellow. The reaction mixture was stirred for 16 h at room temperature. Solvent removal in high vacuum gave 10a as a yellow solid. Data for 10a are as follows. Yield: 0.114 g (65%). 1H NMR (C6D6, 500 MHz, 305 K): δ = 0.94 (t, 3JH,H = 6.9 Hz, 3H, CH2CH3), 1.65 (s, 15H, C5Me5), 2.14 (s, 3H, CH3), 2.25 (s, 3H, CH3), 2.58−2.62 (m, 1H, CH2CHCH2), 2.90−2.94 (m, 1H, CH2CHCH2), 3.20 (dq, 2 JH,H = 11.1 Hz, 3JH,H = 6.9 Hz, 1H, CH2CH3), 4.06 (dq, 2JH,H = 11.3 Hz, 3JH,H = 6.9 Hz, 1H, CH2CH3), 4.57−4.61 (m, 2H, CH2CH CH2), 5.53 (ddt, 3JH,H = 17.0 Hz, 3JH,H = 10.7 Hz, 3JH,H = 6.7 Hz, 1H, CH2CHCH2), 6.86−7.00 (m, 3H, 3 × CHPh), 7.06−7.08 (m, 4H, 2 × CHPh, 2 × CHp‑tolyl), 7.11−7.13 (m, 2H, 2 × CHp‑tolyl), 7.54−7.56 (m, 2H, 2 × CHp‑tolyl), 7.68−7.69 (m, 2H, 2 × CHp‑tolyl) ppm. 13C NMR (C6D6, 126 MHz, 305 K): δ = 11.5 (C5Me5), 17.5 (CH2CH3), 21.0 (CH3), 21.1 (CH3), 48.1 (CH2CHCH2), 73.4 (CH2CH3), 79.0 (NCq), 116.3 (CH2CHCH2), 124.7 (C5Me5), 125.8 (p-CHPhN), 127.9 (2 × CHPh), 128.0 (2 × CHPh), 128.1 (2 × CHp‑tolyl), 128.7 (2 × CHp‑tolyl), 130.7 (4 × CHp‑tolyl), 135.3 (Cq,p‑tolyl), 135.9 (Cq,p‑tolyl), 136.7 (CH2CHCH2), 144.6 (Cq,Ph), 146.7 (Cq,p‑tolyl), 149.8 (Cq,p‑tolyl) ppm. IR (ATR): ν̃ 2920, 2853, 1603, 1501, 1448, 1376, 1313, 1295, 1259, 1177, 1090, 1068, 1020, 993, 935, 916, 785, 768, 747, 711, 691, 617, 565 cm−1. Mp: 141 °C (dec.). Anal. Calcd for C36H44ClNOTi: C, 73.28; H, 7.52; N, 2.37. Found: C, 70.60; H, 7.59; N, 2.26.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00673. Crystallographic parameters for compounds 2b, 3a, 4a, 4c, 5a, 6a, 7a, 8a, and 10a; 1H and 13C NMR spectra of all compounds (PDF) Accession Codes

CCDC 1571204−1571212 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Web: https:// www.uni-oldenburg.de/ac-beckhaus/. ORCID

Rüdiger Beckhaus: 0000-0003-3697-0378 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We kindly thank Friederike Kirschner for the Table of Contents drawing. REFERENCES

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