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Reactions of Secondary Allylamines with Bis(η5:η1‑pentafulvene)titanium Complexes: Selective Formation of Monoazabutadiene Titanium Complexes by N−H and C−H Bond Activation Manfred Manßen, Iris Töben, Christoph Kahrs, Jens-Henning Bölte, Marc Schmidtmann, and Rüdiger Beckhaus* Institut für Chemie, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Federal Republic of Germany S Supporting Information *

ABSTRACT: The N−H and C−H bond activation reactions at ambient conditions of seven different secondary allyl amines (Aa−g) with bis(η5:η1-pentafulvene)titanium complexes (1) have been investigated. Bis(η5:η1adamantylidenepentafulvene)titanium (1a) reacts with Nallylaniline (Aa), N-allylbenzylamine (Ac), N-allyl-tert-butylamine (Ad), N-allylcyclohexylamine (Ae), and N-allyl-2methylaniline (Af) to give the 1-azabutadiene complexes 2a,c−f with high yields. They are the first complexes of the CH2-terminated monoazadiene RNCHCHCH2. Using bis(η5:η1-di-p-tolylpentafulvene)titanium (1b), which exhibits a less Brønsted basic Cexo center, and Aa, the β-C−H bond activation can be slowed down so much that the agostic interaction between the titanium center and the C−H bond is detectable via NMR measurements at room temperature. In the reactions of the titanium azabutadiene complexes 2a,b and 3a with carbon monoxide a ligand exchange is observed, forming the titanocene dicarbonyls 4a,b.

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INTRODUCTION Bis(η5:η1-pentafulvene)titanium complexes I are efficient reagents for N−H/C−H bond activation reactions1−3 and can, for example, form titanaaziridines II in reactions with secondary amines (Scheme 1).1,2

Scheme 2. Oxidation of Secondary Allylamines to Azabutadienes

Scheme 1. Bis(η5:η1-pentafulvene)titanium Complexes (I), Titanaaziridine (II), and Titanapyrrolidine (III)

Various coordination modes of monoazabutadiene ligands are known.9−16 Group IV metallocene and non-metallocene type complexes are known to exhibit a characteristic envelope structure (Scheme 3).5,17−20 Scheme 3. Selected Structurally Characterized Cyclopentadienyltitanium 1-Azabutadiene Complexes

Aziridines are used in a broad range of ring enlargement reactions with carbonyl compounds, acetylenes, and nitriles.1,2,4,5 In particular, the insertion of C−C double bonds is of great interest toward understanding the hydroaminoalkylation of olefins.1,6−8 However, to the best of our knowledge only one isolated titanapyrrolidine, III, is known.1 Here, we present the formation of monoazadiene titanium complexes by N−H and C−H activation of secondary allylamines (Scheme 2) starting from bis(η5:η1-pentafulvene)titanium complexes. © XXXX American Chemical Society

Received: June 12, 2017

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DOI: 10.1021/acs.organomet.7b00425 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

The titanium azabutadiene complexes 2a−f can be isolated in good yields (64−95%) as intensely colored substances. Whereas the aryl-substituted complexes 2a,b,f are dark petrol blue, the aliphatic derivatives 2c−e are dark red. All azabutadiene complexes can be stored as solids for months under inert conditions without any indication of decomposition, but they decompose immediately in the presence of oxygen or atmospheric moisture. They are only slightly soluble in aliphatic solvents but demonstrate a high solubility in aromatic solvents, which is ideal for purification proposes and subsequent NMR experiments. The smallest possible substitution pattern present at the TiCH2 carbon atom of the azabutadiene unit IV renders compounds 2a,c−f the very first examples of highly reactive titanium monoazabutadiene complexes. The reactivities of 2b and comparable derivatives are much lower.17,18 In addition, owing to spontaneous oligomerization or polymerization, the imines derived from the allyl amines Aa,c−f cannot be used directly as ligands in reductive complexation reactions. In particular, for Ac,e, the C−H bond activation occurs exclusively at the allylic Csp3H2 position. The azabutadiene complexes 2a−f have been fully characterized by NMR measurements (Table 1). The activation

Such monoazadiene complexes V are typically prepared by reductive complexation of the corresponding azadiene ligand. Following this route, only C-substituted azabutadiene complexes are available due to the unavailability of CH2-terminated monoazadienes of type IV.21,22

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RESULTS AND DISCUSSION Bis(η5:η1-adamantylcyclopentadienyl)titanium Azabutadiene Complexes 2a−f. The reactions of the bis(η5:η1adamantylidenepentafulvene)titanium complex 1a with the secondary allylamines Aa−f (Scheme 4) in n-hexane at ambient Scheme 4. Overview of the Secondary Allylamines Aa−g

Table 1. Selected 1H, 13C, and 15N NMR Data (ppm) of 2a− fa 2a 2b 2c 2d 2eb 2fc

temperature are accompanied by an instant color change from blue to an almost black suspension of the monoazabutadiene titanium complexes 2a−f (Scheme 5). Monitoring the reactions with NMR shows that no intermediates or side products are formed during the reaction.

a b

Scheme 5. Reactions of 1a with Secondary Allylamines Aa− fa

a

HCexo

Cexo

Ti-N-CH

Ti-CHx-CH

Ti-CHx

2.06

43.6 42.5, 43.5 44.0 44.0 44.6 44.4

6.45 6.61 6.48 6.63 6.60 6.37

5.36 5.81 5.10 4.89 5.07 5.15

57.3 74.2 61.6 65.5 61.7 61.3

2.50 2.52 2.47 2.44

15

N

248.7 257.0 242.1 259.4 266.7

Conditions unless specified otherwise: C6D6, room temperature. Toluene-d8 and 343 K; cToluene-d8 and 373 K

of the N−H and C−H bonds is realized by protonation of the exocyclic carbon atoms (Cexo) of the pentafulvene ligands in 1a. The 1H NMR signals of the CexoH units are found in the range of 2.06−2.52 ppm and the corresponding 13C carbon signals in the range of 42.5−44.6 ppm. Of high diagnostic value are the 1 H NMR signals of the newly formed cyclopentadienyl ligands. Usually, for highly symmetrical compounds, two to four proton signals are found at room temperature. This is true for the azabutadiene complexes 2a,c,d (1H, 5.16−5.65 ppm). However, for compound 2b eight signals for the cyclopentadienyl ligands (1H, 4.41−6.02 ppm) as well as two signals for the Cexo atoms (13C, 42.5 and 43.5 ppm) are observed due to the newly formed stereocenter in the titanadihydropyrrole ring system. For 2e,f, very broad signals are found at room temperature for the cyclopentadienyl ligands and the protonated Cexo. The same is observed for 2a,c,d if the NMR probe is cooled slowly. At approximately 220 K, 2a,c−f exhibit eight signals for the cyclopentadienyl protons and two signals for the protonated Cexo units. This signal pattern results from the characteristic envelope rearrangement of these diene type complexes, which is inhibited at low temperatures.5,18 In Figure 1 the signal pattern of the adamantylcyclopentadienyl ligands and the protonated Cexo atoms at different temperatures is illustrated for 2e. The signals of the protons of the titanahydropyrrole double bond can be found at around 6.5 ppm (Ti-N-CH, doublet) and

Isolated yields are given. B


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Organometallics

Figure 1. 1H NMR spectra (toluene-d8) of 2e in the region of 2.4−6.8 ppm at different temperatures. Legend: (*) Cp-H; (#) CexoH.

Figure 2. Molecular structure of 2b. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1−N1 2.0397(11), Ti1−C40 2.2827(13), N1−C38 1.3733(17), C1−C6 1.5109(19), C16−C21 1.5081(19), C38−C39 1.367(2), C39−C40 1.4564(19); N1−Ti1−C40 83.06(5), Ct1−Ti1−Ct2 130.08 (Ct1 with C1; Ct2 with C16).

5.2 ppm, whereas the protons of the Ti-CHx unit are masked by the adamantyl signals. The 1H,15N HMBC spectra of compounds 2a−e reveal one signal each for the nitrogen atoms with shifts between 242 and 267 ppm. These shifts are comparable to those of the titanium monoamide complexes, which we reported recently.2 Selected NMR data are summarized in Table 1. The structures of the titanaazabutadiene complexes have been confirmed by a single-crystal X-ray diffraction analysis of compound 2b. Single crystals were obtained from a saturated nhexane solution at room temperature. The molecular structure of 2b (Figure 2) reveals the envelope structure characteristic of titanaazabutadiene complexes. The fold angle of the central five-membered ring system of 44.4° is comparable to those of complexes of this type reported previously.5,18 The contribution of the η4-π bonding mode can be quantified by the difference Δ = (Ti1−C38 + Ti1−C39)/2 − (Ti1−N1 + Ti1−C40)/2 = 0.526 Å. This value differs from those for the η4-bonded azabutadiene complexes23 but is comparable to those for the previously mentioned titanaazabutadiene complexes Va (0.328 Å) and Vb (0.541 Å).18 The Ti−N bond length of 2.0397 Å lies within the range expected for titanium−nitrogen single bonds. The C38−C39 bond length of 1.367 Å matches with a typical Csp2−Csp2 double bond. The bond lengths C1−C6 and C16−C21 (average 1.51 Å) lie within the range of C−C single bonds and further confirm protonation of the Cexo positions. Bis(η5:η1-(di-p-tolylmethyl)cyclopentadienyl)titanium Azabutadiene Complexes 3a,b. The reactions of the bis(η5:η1-di-p-tolylpentafulvene)titanium complex 1b with the secondary allyl amines Aa,b in n-hexane at ambient temperature (Scheme 6) are accompanied by a color change from green to a dark suspension. However, in comparison to the reactions of 1a, the reaction time has to be increased to 72 h, which is explained by the different Brønsted basicities of the pentafulvene ligands we described previously.2 Due to the lower basicity of the Cexo position in the di-p-tolylpentafulvene ligand, the activation of the N-CH2 protons is much slower.

Scheme 6. Reactions of 1b with Secondary Allylamines Aa,b

The titanaazabutadiene complexes 3a,b are isolated in good yields (61−71%). Like the azabutadiene complexes 2a−f, they can be stored as solids for months under inert conditions without any indication of decomposition, but they also decompose immediately in the presence of oxygen or atmospheric moisture. 3a,b have been fully characterized by NMR measurements (Table 2), and the results are very similar to those of the complexes 2a−f. Nevertheless, due to p-tolyl substitution of the Cexo, the 1H and 13C signals of this position are significantly shifted to lower field (e.g., 3a: 1H, 4.72 ppm; 13C, 51.7 ppm). Additionally, the signals of the Ti-CHx protons of the titanahydropyrrole unit can be found at 1.82 ppm (3a) and 1.63 ppm (3b). C


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Organometallics Table 2. Selected 1H, 13C, and 15N NMR Data (ppm) of 3a and ba 3a 3b a

HCexo

Cexo

Ti-N-CH

Ti-CHx-CH

Ti-CHx

Ti-CHx

4.72 4.52, 4.59

51.7 50.0, 51.4

6.39 6.63

5.18 5.69

1.82 1.63

61.7 78.7

15

N

247.7 252.4

Conditions: C6D6, room temperature.

temperature (Scheme 7), an instant color change from almost black to brick red is observed. The titanocene dicarbonyl

Furthermore, due to the slower activation of the N-CH2 protons of the allylamine, it is now possible to identify the monoamide intermediate (i, Figure 3) spectroscopically by

Scheme 7. Reactions of 2a and 3a with Carbon Monoxide

compounds 4a,b have been isolated in moderate yields (45− 79%) and are less reactive toward oxygen or atmospheric moisture than the corresponding titanaazabutadiene complexes. The azabutadiene, which is exchanged during the reaction, cannot be isolated due to its immediate polymerization under the present reaction conditions.21,22 Also, no insertion of carbon monoxide into the titanium−carbon bonds of 2a or 3a is observed. Unlike the titanaazabutadiene complexes 2a−f and 3a,b, the dicarbonyl titanocenes are highly symmetrical (C2v), which manifests the NMR spectra of the two compounds. Here, for each compound only two signals for the cyclopentadienyl ligand protons (4a, 4.68, 4.86 ppm; 4b, 4.39, 4.48 ppm) and one signal for the protonated Cexo unit (4a, 2.63 ppm; 4b, 4.92 ppm) are present. However, the 13C signal for the carbonyl ligand was only found for 4a at 262.9 ppm. Selected NMR data are summarized in Table 3.

Figure 3. 1H NMR spectrum (C6D6, 1 h after start) of the reaction mixture of 1b and Aa. Significant titanium monoamide i signals are highlighted by colored symbols.

NMR. This observation is in clear contrast to the reaction of 1a. In Figure 3 the signal pattern of the N-CH2−CHCH2 unit is illustrated (in addition to the signals of the two starting materials 1b and Aa) for the reaction of 1b with Aa, which was correlated by 1H,15N HMBC, 1H,13C HMQC, and HMBC spectra. From left to right, the first noticeable signals of i at 5.50− 5.58, 4.89−4.93, and 4.76−4.79 ppm show the characteristic coupling pattern of the −CHCH2 unit with one ddt (CH CH2, 3J = 5.5, 10.5, and 16.5 Hz) and two dd (CHCH2, trans (4.91 ppm), 3J = 16.5 Hz, 2J = 1.9 Hz; cis (4.78 ppm), 3J = 10.5 Hz, 2J = 1.9 Hz). However, the two broad signals of the N-CH2 protons at 4.71 and 3.56 ppm are much more significant for this type of monoamide species. In clear contrast to the allylamine (3.35 ppm),24 these signals are shifted to lower field and are split by 1.2 ppm. This signal pattern is indicative of the strong agostic interaction between the titanium center and one proton of the N-CH2 unit. A comparably strong agostic interaction is observed for titanium isopropyl amides (CpTi(NiPr2)Cl2), resulting in a strong signal splitting of the agostic C−H proton (6.77 ppm) and the nonagostic proton (2.33 ppm).25 However, for i the agostic and nonagostic interactions become observable at the identical carbon center at room temperature, whereas for CpTi(NiPr2)Cl2 two different C−H units are involved, and the rotations of the iPrN moieties about the Ti−N and the N−C bonds have to be frozen out (178 K).25 The C−H bond activation step in i is responsible for the formation of the vinylsubstituted titanaaziridine, which rearranges to 3a,b (Scheme 6). Titanocene Dicarbonyl Complexes 4a,b. In reactions of the titanaazabutadiene complexes 2a and 3a with the strong πacceptor ligand carbon monoxide in n-hexane at ambient

Table 3. Selected 1H and 13C Data (ppm) of 4a and ba 4a 4b a

HCexo

Cexo

CH−Cp

CH−Cp

CO

2.63 4.92

44.4 51.1

4.68, 4.86 4.39, 4.48

91.0, 94.1 91.4, 94.9

262.9

Conditions: C6D6, room temperature.

The IR spectra reveal two signals for the CO bond stretching vibration (4a, 1936, 1837 cm−1; 4b, 1952, 1859 cm−1), which is typical for compounds with C2v symmetry. In comparison to the values reported for titanocene dicarbonyl compounds known in the literature, both are shifted to lower reciprocal wavenumbers with an absolute minimum for 4a, which is an indication of the slightly stronger π back-donation in this case (Table 4).26−32 The structures of the titanocene dicarbonyls 4a,b have been confirmed by single-crystal X-ray diffraction (Figures 4 and 5). Single crystals were obtained from saturated n-hexane solutions at room temperature. Due to the small crystal size (needle shaped) and resulting poor crystallographic data quality of 4b, only the adamantyl structure 4a is discussed in detail. The Ti−CCO bond lengths of both compounds (average 2.02 Å) lie within the expected range for titanocene dicarbonyls. The C−O bond lengths (average D


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Organometallics Table 4. Infrared Carbonyl Stretching Frequencies of Selected Titanocene Dicarbonyl Complexes (cm−1) and C− O Distances (Å) CO 4a 4b Me2Si(C5H4)2Ti(CO)229 Me2Si(C5Me4)2Ti(CO)230 Cp2Ti(CO)226 CpCpCF3Ti(CO)227 CpCp*Ti(CO)227 Cp*2Ti(CO)228

1936, 1952, 1980, 1942, 1975, 1979, 1946, 1940,

1837 1859 1905 1879 1897 1897 1854 1858

C−O 1.1553(14) 1.156(5), 1.159(5) 1.134(9), 1.129(11) 1.148(1)32

1.149 (av)31

Figure 5. Molecular structure of 4b. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1−C41 2.028(6), Ti1− C42 2.007(6), C41−O1 1.156(5), C42−O2 1.159(5), C1−C6 1.522(6), C21−C26 1.508(6); Ti1−C41−O1 176.6(4), Ti1−C42− O2 177.0(4), C41−Ti1−C42 83.6(2), Ct1−Ti1−Ct2 139.89 (Ct1, centroid C1−C5; Ct2, centroid C21−C25).

Scheme 8. Reaction of 2b with Carbon Monoxide and Subsequent Purification

Figure 4. Molecular structure of 4a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1−C16 2.0218(12), C16−O1 1.1553(14), C1−C6 1.5193(14); Ti1−C16−O1 177.95(9), C16−Ti1−C16′ 88.93(6), Ct−Ti1−Ct′ 142.21.

1.16 Å) lie in the upper range of CO distances (Table 4). This demonstrates the slightly stronger back-donation of the titanium center in 4a,b to the π* orbital of the CO ligands. Whereas in reactions of 2a and 3a with CO the released azabutadiene could not be isolated, in the same reaction with 2b the azabutadiene is stabilized in solution by the additional phenyl group and the titanocene dicarbonyl 4a is formed as before. Nevertheless, the released azabutadiene is still reactive toward atmospheric moisture and a recovery by column chromatography proved to be difficult. Therefore, the azabutadiene was directly reduced by NaBH3CN and the resulting allylamine Ab, which was initially used in the formation of the azabutadiene complex 2b, could be recovered after column chromatography (Scheme 8). Limitation of the N−H/C−H Activation. It was shown that a broad range of allylamines can be converted to monoazabutadienes IV and the corresponding titanium complexes 2a−f and 3a,b. Nevertheless, the sterically demanding 2,6-disubstituted allylaniline Ag shows no formation

of the monoazadiene complexes at room temperature, not even after weeks of reaction (as monitored by NMR). However, at a temperature of 60 °C and reaction times of up to 144 h, instead of the expected H transfer to the Cexo positions of 1a,b, insertion reactions of in situ formed 2,6-dimethyl-N-propylidenebenzenamine33 (double 1,3-H shift)34 are observed. The insertion products 5a,b are obtained in up to quantitative yields in the form of highly reactive solids (Scheme 9). The resulting titanium monoamides 5a,b, exhibiting a σ−πchelating subunit, are comparable to the (η5-Cp)(η5:η5-Fv)TiNR2 monoamide complexes we reported recently.2 Accordingly, the spectroscopic data (eight proton signals for the Cp/ Fv protons, 15N shift, etc.) are quite similar; they are summarized in the Supporting Information.35 The structures of the titanium σ−π-chelating monoamides have been confirmed by single-crystal X-ray diffraction of E


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Organometallics

membered ring with characteristic envelope structure in 2a−f and 3a,b. This activation process represents a novel synthetic route to titanium azabutadiene complexes, which are not substituted at the C terminus. In the case of 1b, the activation of the C−H bond is much slower than the activation of the N− H bond. Therefore, the agostic interaction between the Ti center and the C−H bonds becomes detectable via NMR spectroscopy throughout the reaction time at room temperature. For the sterically more demanding 2,6-dimethyl-Nallylaniline Ag, no N−H/C−H activation is observed. Instead, the titanium monoamides 5a,b are formed after the shift of the allylic double bond and the insertion of the imine into the Ti− Cexo bond. In the reaction of the azabutadiene complexes 2a,b and 3a with carbon monoxide the titanocene dicarbonyls 4a,b are formed. A polymerization of the released azabutadiene can be prevented using the C-substituted azabutadiene complex 2b, and after reduction, the allylaniline Ab can be recovered.

Scheme 9. Reactions of 1a,b with Allylamine Ag

compound 5a (Figure 6). Single crystals were obtained from a saturated n-hexane solution at room temperature.

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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. Solvents and liquid educts were dried according to standard procedures. Solvents were distilled over Na/K alloy and benzophenone under a nitrogen atmosphere. Liquid amines were distilled from CaH2 prior to use. 1H and 13C NMR spectra were recorded on a Bruker AVANCE III 500 spectrometer (1H, 500.1 MHz; 13C, 125.8 MHz; 15N, 50.7 MHz) or a Bruker AVANCE 300 spectrometer (1H, 300.1 MHz). The NMR chemical shifts were referenced to residual protons of the solvent or the internal standard TMS. Given chemical shifts of 15N resulted from 1H,15N 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. Mass spectra were recorded on a Finnigan MAT 95 spectrometer. 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 to be higher in some cases, due to residual traces of n-hexane. Melting points were determined using a “MelTemp” by Laboratory Devices, Cambridge, U.K. The bis(η5,η1-pentafulvene)titanium complexes 1a,b were synthesized according to known procedures.39 Further exact details of the individually synthesized products, crystallographic data, and NMR spectra are given in the Supporting Information. Azabutadiene Complexes 2a−f. [(AdFv)2Ti] (1a) and 1 equiv of the corresponding allylamine were suspended in n-hexane. The reaction mixture was stirred for 16 h at 20 °C, forming a suspension of the titanaazabutadiene complexes 2a−f. The solid was separated, washed with n-hexane, and dried under vacuum. No further purification steps were required. Data for 2a are as follows. Yield: 4.58 g (88%). 1H NMR (C6D6, 500 MHz): δ 1.35−1.95 (m, 30 H, Ti-CH2, Ad-H), 2.06 (m, 2 H, CexoH), 5.33−5.36 (m, 1 H, Ti-CH2-CH), 5.37, 5.44, 5.55, 5.65 (m, 8 H, Cp-H), 6.45 (d, 3JHH = 5.6 Hz, 1 H, Ti-N-CH), 6.65 (m, 2 H, N-ArCHo), 6.93 (m, 1 H, N-Ar-CHp), 7.16 (m, 2 H, N-Ar-CHm) ppm. 13C NMR (C6D6, 125 MHz): δ 28.3, 28.3, 32.0, 32.2, 32.4, 32.4, 38.3, 38.7, 38.9 (Ad-CH/CH2), 43.6 (CexoH), 57.3 (Ti-CH2), 101.3, 104.7, 105.6, 108.0 (CHCp), 112.1 (Ti-CH2-CH), 122.3 (N-Ar-CHp), 122.5 (N-ArCHo), 126.1 (CipsoCp), 128.26 (N-Ar-CHm), 132.2 (Ti-N-CH), 154.2 (N-Ar-CHi) ppm. 15N NMR (C6D6, 51 MHz): δ 248.7 ppm. IR (ATR): ν̃ 3015, 2962, 2897, 2848, 1593, 1528, 1480, 1447, 1352, 1289, 1262, 1170, 1136, 1079, 1061, 1023, 996, 974, 954, 903, 883, 869, 847, 831, 807, 781, 756, 698, 657, 644, 626 cm−1. Mp: 154 °C. Data for 2b are as follows. Yield: 1.38 g (92%). 1H NMR (C6D6, 500 MHz): δ 1.24−2.25 (m, 31 H, Ad-H, Ti-CH-Ph), 2.19 (s, 3 H, NAr-CH3), 4.41, 5.20, 5.33, 5.49, 5.67, 5.81, 6.02 (m, 8 H, Cp-H), 5.81 (m, 1 H, Ti-CH-CH), 6.61 (m, 3 H, Ti-N-CH, N-Ar-CHo), 6.94 (t,

Figure 6. Molecular structure of 5a. Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): Ti1−N1 1.9985(15), Ti1−C6 2.5570(16), N1−C31 1.509(2), C1−C6 1.429(2), C16−C21 1.519(2), C21−C31 1.584(2), C31−C32 1.560(3), C32−C33 1.536(3); Ti1−N1−C31 125.07(10).

The Ti1−N1 bond length (1.9985 Å) lies within the expected range for titanium monoamides.2,36 The former Csp2− Csp2 double bond between C32 and C33 is now a single bond with length 1.560 Å, as well as the newly formed bond between C21 and C31 (1.584 Å).37 Along with the single bond N1−C31 (1.509 Å), these bond lengths confirm the shift of the allylic double bond and subsequent insertion of the resulting imine into the Ti−C bond. The Ti1−C6 bond length (2.5570 Å) lies between the bond lengths of the starting material (average 2.315 Å) and the corresponding NHC complex (average 2.688 Å), which we reported recently.38 Furthermore, the C1−C6 bond (1.429 Å) lies between a typical single bond and a double bond.37 Consequently, the coordination of the fulvene ligand is best described as a η5:η1 coordination mode.

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CONCLUSION In conclusion, in addition to the N−H and C−H bond activations of N-methyl- and N-benzylamines, which result in the formation of titanium aziridines, the bis(η5:η1-pentafulvene) titanium complexes 1a,b are capable of activating the allylamines Aa−f under ambient conditions. Here, the olefinic unit leads to a ring extension from a three-membered to a fiveF


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Organometallics 3

JHH = 7.3 Hz, 1 H, Ti-CH-Ar-CHp), 7.01 (d, 3JHH = 8.0 Hz, 2 H, NAr-CHm), 7.11 (d, 3JHH = 7.6 Hz, 2 H, Ti-CH-Ar-CHo), 7.25 (t, 3JHH = 7.7 Hz, 2 H, Ti-CH-Ar-CHm) ppm. 13C NMR (C6D6, 125 MHz): δ 20.9 (CH3), 28.1, 28.2, 28.2, 28.2, 31.8, 32.0, 32.1, 32.2, 32.4, 32.5, 32.5, 32.5, 38.2, 38.4, 38.7, 38.8 (Ad-CH/CH2), 42.5, 43.5 (CexoH), 74.2 (Ti-CH), 99.4, 99.5, 104.5, 104.8, 105.0, 106.6, 108.0, 113.00 (CHCp), 111.3 (Ti-CH-CH), 122.7 (Ti-CH-Ar-CHp), 123.3 (N-ArCHo), 124.6 (Ti-CH-Ar-CHo), 127.2 (CipsoCp), 128.7 (Ti-CH-ArCHm), 129.0 (N-Ar-CHm), 129.5 (Ti-N-CH), 132.5 (N-Ar-Cp), 149.2 (Ti-CH-Ar-Ci), 150.9 (N-Ar-Ci) ppm. 15N NMR (C6D6, 51 MHz): δ 257.0 ppm. IR (ATR): ν̃ 3021, 2918, 2860, 1593, 1509, 1499, 1452, 1418, 1289, 1279, 1262, 1182, 1109, 1074, 1040, 1021, 907, 806, 761, 697, 671 cm−1. Mp: 72 °C dec. Data for 2c are as follows. Yield: 852 mg (64%). 1H NMR (C6D6, 500 MHz): δ 1.44−2.00 (m, 28 H, Ad-H), 1.53 (br. s, 2 H, Ti-CH2), 2.50 (m, 2 H, CexoH), 4.47 (s, 2 H, N-CH2), 5.10 (m, 1 H, Ti-CH2CH), 5.16, 5.31, 5.33, 5.41 (m, 8 H, Cp-H), 6.48 (d, 3JHH = 5.0 Hz, 1 H, Ti-N-CH), 7.07 (m, 3 H, Ar-CH), 7.16 (m, 2 H, Ar-CH) ppm. 13C NMR (C6D6, 125 MHz): δ 28.3, 28.5, 32.4, 32.5, 32.7, 32.8, 38.4, 39.2 (Ad-CH/CH2), 44.0 (CexoH), 61.6 (Ti-CH2), 62.2 (N-CH2), 100.8, 104.6, 105.8, 106.6 (CHCp), 108.0 (Ti-CH2-CH), 123.0 (CipsoCp), 126.8, 127.4, 128.7 (Aryl-CH), 137.75 (Ti-N-CH), 143.3 (N-CH2-ArCi) ppm. 15N NMR (C6D6, 51 MHz): δ 242.1 ppm. IR (ATR): ν̃ 2963, 2899, 2846, 1449, 1259, 1089, 1060, 1015, 863, 791, 731, 701, 643, 601 cm−1. Mp: 86 °C dec. Data for 2d are as follows. Yield: 866 mg (69%). 1H NMR (C6D6, 500 MHz): δ 1.16 (s, 9 H, N-C-CH3), 1.41 (d, 3JHH = 9.8 Hz, 2 H, TiCH2), 1.45.-2.10 (m, 28 H, Ad-H), 2.52 (m, 2 H, CexoH), 4.89 (m, 1 H, Ti-CH2-CH), 5.22, 5.50 (m, 8 H, Cp-H), 6.63 (d, 3JHH = 5.4 Hz, 1 H, Ti-N-CH) ppm. 13C NMR (C6D6, 125 MHz): δ 28.3, 28.5, 32.5, 32.6, 32.8, 38.4, 39.2, 39.2, 39.2 (Ad-CH/CH2), 32.57 (N-C-CH3), 44.0 (CexoH), 59.2 (Ti-N-C), 65.5 (Ti-CH2), 99.5, 103.0, 106.4, 107.4 (CHCp), 101.3 (Ti-CH2-CH), 122.0 (CipsoCp), 130.4 (Ti-N-CH) ppm. 15 N NMR (C6D6, 51 MHz): δ 259.4 ppm. IR (ATR): ν̃ 2899, 2847, 1639, 1505, 1467, 1449, 1355, 1260, 1201, 1098, 1060, 1034, 954, 852, 791, 778, 723, 684, 642 cm−1. Mp: 75 °C dec. Data for 2e are as follows. Yield: 1.25 g (95%). 1H NMR (toluened8, 500 MHz, 343 K): δ 1.03−2.11 (m, 40 H, Ad-H, Cy-H, Ti-CH2), 2.47 (m, 2 H, CexoH), 3.23 (m, 1H, Ti-N-CHCy), 5.07 (m, 1 H, TiCH2-CH), 5.17, 5.31, 5.41 (m, 8 H, Cp-H), 6.60 (d, 3JHH = 5.0 Hz, 1 H, Ti-N-CH) ppm. 13C NMR (toluene-d8, 125 MHz, 343 K): δ 26.9, 27.5, 28.9, 29.0, 33.0, 33.0, 33.2, 33.5, 36.8, 39.0, 39.7, 39.7 (Ad-CH/ CH2, Cy-CH/CH2), 44.6 (CexoH), 61.7 (Ti-CH2), 66.1 (Ti-N-CHCy), 100.7, 103.3, 106.4, 107.0 (CHCp), 106.7 (Ti-CH2-CH), 123.1 (CipsoCp), 132.2 (Ti-N-CH) ppm. 15N NMR (C6D6, 51 MHz): δ 266.7 ppm. IR (ATR): ν̃ 2960, 2899, 2847, 1509, 1447, 1260, 1225, 1177, 1098, 1061, 1018, 880, 865, 814, 792, 736, 703, 659 cm−1. Mp: 96 °C dec. Data for 2f are as follows. Yield: 269 mg (80%). 1H NMR (toluened8, 500 MHz, 373 K): δ 1.39−2.11 (m, 30 H, Ad-H, Ti-CH2), 2.16 (s, 3 H, N-Ar-CH3), 2.44 (m, 2 H, CexoH), 5.13−5.17 (m, 1 H, Ti-CH2CH), 5.29, 5.39, 5.42, 5.49 (m, 8 H, Cp-H), 6.37 (m, 1 H, Ti-N-CH), 6.50 (m, 1 H, Ar-CH), 6.84−6.87 (m, 2 H, Ar-CH), 7.02 (m, 2 H, ArCH) ppm. 13C NMR (toluene-d8, 125 MHz, 373 K): δ 19.1 (N-ArCH3), 28.7, 28.8, 32.8, 32.9, 33.0, 33.2, 38.7, 39.4, 39.5 (Ad-CH/CH2), 44.4 (CexoH), 61.3 (Ti-CH2), 101.1, 105.9, 107.3, 109.6 (CHCp), 123.6, 125.9, 126.7, 131.3 (N-Ar-CH), 125.7 (CipsoCp), 131.1 (N-Ar-Co), 135.0 (Ti-N-CH), 153.8 (N-Ar-Ci) ppm. IR (ATR): ν̃ 2898, 2846, 1519, 1478, 1448, 1376, 1281, 1266, 1183, 1118, 1100, 1077, 1060, 1034, 900, 879, 861, 838, 822, 800, 786, 753, 723 cm−1. Mp: 180 °C. Anal. Calcd for C40H49NTi: C, 81.20; H, 8.35; N, 2.37. Found: C, 82.62; H, 8.57; N, 2.32. Azabutadiene Complexes 3a,b. [((p-Tol)2Fv)2Ti] (1b) and 1 equiv of the corresponding allylamine were suspended in n-hexane. The reaction mixture was stirred for 72 h at 20 °C, forming suspensions of the titanaazabutadiene complexes 3a,b. The solid was separated, washed with n-hexane, and dried under vacuum. No further purification steps were required. Data for 3a are as follows. Yield: 1.89 g (61%). 1H NMR (C6D6, 500 MHz): δ 1.82 (d, 3JHH = 8.0 Hz, 2 H, Ti-CH2), 2.04, 2.08 (s, 12 H,

Ar-CH3), 4.72 (s, 2 H, CexoH), 5.18 (m, 1 H, Ti-CH2-CH), 5.12, 5.21, 5.41, 5.56 (m, 8 H, Cp-H), 6.39 (d, 3JHH = 5.4 Hz, 1 H, Ti-N-CH), 6.75 (d, 3JHH = 7.8 Hz, 2 H, N-Ar-CHo), 6.86 (d, 3JHH = 7.8 Hz, 4 H, Ar-CH), 6.91−6.95 (m, 6 H, N-Ar-CHp, Ar-CH), 6.99 (d, 3JHH = 7.9 Hz, 4 H, Ar-CH), 7.08 (d, 3JHH = 7.9 Hz, 4 H, Ar-CH), 7.14 (m, 2 H, N-Ar-CHm) ppm. 13C NMR (C6D6, 125 MHz): δ 20.8, 20.8 (Ar-CH3), 51.7 (CexoH), 61.7 (Ti-CH2) 100.4, 106.3, 107.9, 109.5 (CHCp), 110.5 (Ti-CH2-CH), 122.4 (N-Ar-CHp), 122.7 (N-Ar-CHo), 124.2 (CipsoCp), 128.4 (N-Ar-CHm), 128.8, 129.0, 129.2, 129.3 (Ar-CH), 131.9 (Ti-NCH), 135.3, 134.8 (Ar-Cp), 141.9, 143.5 (Ar-Ci), 153.5 (N-Ar-Ci) ppm. 15 N NMR (C6D6, 51 MHz): δ 247.7 ppm. IR (ATR): ν̃ 3018, 2918, 2857, 2390, 2286, 1591, 1573, 1509, 1480, 1447, 1413, 1378, 1289, 1278, 1185, 1170, 1110, 1040, 1021, 904, 878, 849, 804, 757, 698, 645 cm−1. Mp: 98 °C dec. Anal. Calcd for C49H47NTi: C, 83.34; H, 6.79; N, 2.01. Found: C, 83.09; H, 7.83; N, 2.04. Data for 3b are as follows. Yield: 550 mg (71%). 1H NMR (C6D6, 500 MHz): δ 1.63 (d, 3JHH = 8.3 Hz, 1 H, Ti-CH), 1.99, 2.04, 2.06, 2.08, 2.26 (s, 15 H, Aryl-CH3), 4.52, 4.59 (s, 2 H, CexoH), 4.74, 4.81, 5.04, 5.14, 5.58, 5.60, 5.72, 5.88 (Cp-H), 5.69 (dd, 3JHH = 8.3 Hz, 3JHH = 5.7 Hz, 1 H, Ti-CH-CH), 6.35 (d, 3JHH = 7.6 Hz, 2 H, Ti-CH-ArCHo), 6.63 (d, 3JHH = 6.0 Hz, 1 H, Ti-N-CH), 6.78−6.82 (m, 4 H, ArCH), 6.84−6.90 (m, 8 H, Ar-CH), 6.92−6.95 (m, 3 H, Ar-CH), 7.02− 7.05 (m, 6 H, Ar-CH), 7.21 (t, 3JHH = 7.7 Hz, 2 H, Ti-CH-Ar-CHm) ppm. 13C NMR (C6D6, 125 MHz): δ 20.9, 20.9, 20.9, 21.0, 21.0 (ArCH3), 50.0, 51.4 (CexoH), 78.7 (Ti-CH), 97.5, 103.3, 104.5, 107.3, 107.9, 108.6, 110.0, 112.8 (CHCp), 109.9 (Ti-CH-CH), 122.4 (CipsoCp), 122.9, 123.6, 125.2, 128.5, 128.6, 129.0, 129.1, 129.2, 129.3, 129.3, 129.6, 129.7, (Ar-CH), 129.8 (Ti-N-CH) 132.7, 135.3, 135.5, 135.9, 136.2, 141.0, 142.2, 144.3, 144.4, 148.2 151.1 (Ar-C) ppm. 15N NMR (C6D6, 51 MHz): δ 252.4 ppm. IR (ATR): ν̃ 3020, 2918, 2858, 1593, 1498, 1488, 1453, 1419, 1289, 1279, 1179, 1109, 1075, 1055, 1040, 1021, 907, 881, 821, 806, 761, 744, 698, 971, 645 cm−1. Mp: 168 °C. Anal. Calcd for C56H53NTi: C, 85.37; H, 6.78; N, 1.78. Found: C, 83.60; H, 7.93; N, 1.43. Titanocene Dicarbonyl 4a. A 250 mg portion (0.43 mmol) of compound 2a was suspended in 5 mL of n-hexane. The reaction mixture was stirred under CO (1 atm) for 16 h at 20 °C, forming a red suspension of 4a. The solid was separated, washed with n-hexane, and dried under vacuum. Yield: 172 mg (79%). 1H NMR (C6D6, 500 MHz): δ 1.44−2.03 (m, 28 H, Ad-H), 2.63 (m, 2 H, CexoH), 4.68, 4.86 (m, 8 H, Cp-H) ppm. 13C NMR (C6D6, 125 MHz): δ 28.3, 28.3, 32.5, 33.1, 38.3, 39.3 (Ad-CH/CH2), 44.4 (CexoH), 91.0, 94.1 (CHCp), 117.5 (CipsoCp), 262.9 (CO) ppm. IR (ATR): ν̃ 2903, 2881, 2849, 1936, 1837, 1449, 1100, 1030, 859, 809 cm−1. Mp: 137 °C. MS (LIFDI): m/ z (%) 502.40 (100) [M]+. Anal. Calcd for C32H38O2Ti: C, 76.48; H, 7.62. Found: C, 76.64; H, 8.47. Titanocene Dicarbonyl 4b. A 250 mg portion (0.36 mmol) of compound 3a was suspended in 5 mL of n-hexane. The reaction mixture was stirred under CO (1 atm) for 16 h at 20 °C, forming a red suspension of 4b. The solid was separated, washed with n-hexane, and dried under vacuum. Yield: 91 mg (45%). 1H NMR (C6D6, 500 MHz): δ 2.10 (s, 12 H, Ar-CH3), 4.39, 4.48 (m, 8 H, Cp-H), 4.92 (CexoH), 6.93 (d, 3JHH = 7.9 Hz, 8 H, Ar-CH), 7.10 (d, 3JHH = 8.0 Hz, 8 H, ArH) ppm. 13C NMR (C6D6, 125 MHz): δ 21.0, (Ar-CH3), 51.1 (CexoH), 91.4, 94.9 (CHCp), 115.6 (CipsoCp), 129.0, 129.1, 135.8 (ArCH), 135.8, 143.6 (Ar-C) ppm. IR (ATR): ν̃ 3091, 3022, 2960, 2919, 2861, 1952, 1881, 1859, 1601, 1575, 1509, 1453, 1407, 1261, 1184, 1108, 1068, 1033, 1022, 870, 845, 824, 817, 806, 757, 694, 661, 577, 558 cm−1. Mp: 170 °C. Anal. Calcd for C42H38OTi: C, 81.02; H, 6.15. Found: C, 82.42; H, 6.79. Amine Ab. A 250 mg portion (0.37 mmol) of compound 2b was suspended in 5 mL of n-hexane. The reaction mixture was stirred under CO (1 atm) for 16 h at 20 °C, forming a red suspension of 4a. The solid was separated. A 10 mL portion of methanol, 57 mg (0.90 mmol) of sodium cyanoborohydride, and 61 mg (0.45 mmol) of zinc chloride were added to the resulting solution, and the reaction mixture was stirred for 16 h at 20 °C. Subsequently, the solution was quenched with water and extracted three times. After column chromatography compound Ab could be isolated as a colorless solid. 1H NMR (CDCl3, 300 MHz): δ 2.21 (s, 3 H, Ar-CH3), 3.87 (dd, 3JHH = 1.4 Hz, 3JHH = G


Organometallics

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5.8 Hz, 2 H, N-CH2-CH), 6.28 (dt, 3JHH = 15.9 Hz, 3JHH = 5.8 Hz, 1 H, N-CH2-CH), 6.52−6.61 (m, 3 H, N-CH2-CHCH, Ar-CH), 6.93−6.99 (m, 2 H, Ar-CH), 7.13−7.35 (m, 5 H, Ar-CH) ppm. Monoamide 5a. A 500 mg portion (1.13 mmol) of [(AdFv)2Ti] (1a) and 181 mg (1.13 mmol) of N-allyl-2,6-dimethylaniline (Ag) were suspended in 7 mL of n-hexane. The reaction mixture was stirred for 96 h at 60 °C, forming a dark solution of complex 5a. The solvent was removed in vacuo. Yield: quantitative. 1H NMR (C6D6, 500 MHz): δ 0.36 (t, 3JHH = 7.4 Hz, 3 H, N-CH-CH2-CH3), 1.58−3.19 (m, 30 H, Ad-H, N-CH-CH2-CH3), 1.99 (s, N-Ar-CH3), 2.22 (s, 3 H, NAr-CH3), 3.77 (m, 1 H, N-CH-CH2-CH3), 3.81, 4.14, 5.08, 5.18, 5.79, 6.49, 7.22 (m, 8 H, Cp/Fv-H), 6.85−6.99 (m, 3 H, N-Ar-CH) ppm. 13 C NMR (C6D6, 125 MHz): δ 16.0 (N-CH-CH2-CH3), 18.1, 23.7 (NAr-CH3), 24.5, 28.1, 28.3, 28.9, 30.0, 34.0, 34.1, 35.4, 35.4, 35.8, 35.9, 36.3, 37.2, 37.7, 38.5, 39.0, 39.1, 44.8, 46.4 (Ad-CH/CH2, N-CH-CH2CH3), 50.8 (CexoCp), 92.9 (N-CH-CH2-CH3), 98.6, 100.0, 101.4, 102.0, 106.2, 109.2, 112.1, 120.9 (CHCp/Fv), 117.2 (CexoFv), 123.2 (CipsoCp), 123.3, 128.7 (N-Ar-CH), 132.0, 132.4 (N-Ar-Co), 137.8 (CipsoFv), 160.1 (N-Ar-Ci) ppm. 15N NMR (C6D6, 51 MHz): δ 269.81 ppm. IR (ATR): ν̃ 2902, 2848, 1464, 1411, 1260, 1182, 1093, 1041, 949, 894, 797, 765, 750, 729, 684, 664, 579 cm−1. Mp: 180 °C. Anal. Calcd for C41H51NTi: C, 81.30; H, 8.49; N, 2.31. Found: C, 78.19; H, 8.93; N, 2.31. Monoamide 5b. A 250 mg (0.44 mmol) portion of [((pTol)2Fv)2Ti] (1b) and 71 mg (0.44 mmol) of N-allyl-2,6-dimethylaniline (Ag) were suspended in 7 mL of n-hexane. The reaction mixture was stirred for 144 h at 60 °C, forming a dark solution of complex 5b. The solid was separated, washed with n-hexane, and dried under vacuum. No further purification steps were required. Yield: 186 mg (58%). 1H NMR (C6D6, 500 MHz): δ 0.10 (t, 3JHH = 7.4 Hz, 3 H, NCH-CH2-CH3), 1.15−1.22, 1.47−1.55 (m, 2 H, N-CH-CH2-CH3), 1.35, 2.05, 2.11, 2.17, 2.23, 2.28, (s, 18 H, Ar-CH3), 3.42, 4.36, 4.60, 4.93, 5.07, 5.16, 5.85, 7.01 (m, 8 H, Cp/Fv-H), 5.61 (d, 3JHH = 6.9 Hz, 1 H, N-CH-CH2−CH3), 6.78−6.83 (m, 6 H, Ar-CH), 7.01 (m, 1 H, Ar-CH), 7.07 (d, 3JHH = 8.1 Hz, 2 H, Ar-CH), 7.18 (m, 2 H, Ar-CH), 7.49 (d, 3JHH = 8.2 Hz, 2 H, Ar-CH), 7.58 (d, 3JHH = 8.1 Hz, 2 H, ArCH), 7.69 (m, 1 H, Ar-CH), 8.02 (d, 3JHH = 8.1 Hz, 2 H, Ar-CH), 8.63 (m, 1 H, Ar-CH) ppm. 13C NMR (C6D6, 125 MHz): δ 13.6, 18.9, 20.4, 20.9, 20.9, 21.1, 21.3 (Ar-CH3), 30.7 (N-CH-CH2-CH3), 60.1 (CexoCp), 93.8 (N-CH-CH2-CH3), 100.7, 105.4, 106.5, 107.5, 108.2, 110.6, 115.3, 126.0 (CHCp/Fv), 113.8 (CexoFv), 123.9, 128.9, 129.2, 129.3, 129.8 (Ar-CH), 132.5, 134.5, 134.6, 135.5, 136.0, 136.7, 142.4, 143.2, 143.7, 146.6 (Ar-C), 143.4 (CipsoFv), 160.4 (N-Ar-Ci) ppm. IR (ATR): ν̃ 3019, 2977, 2951, 2918, 2872, 1508, 1466, 1412, 1372, 1351, 1261, 1174, 1099, 1052, 1043, 1023, 984, 889, 869, 856, 833, 814, 804, 780, 763, 740, 695, 652, 581, 567 cm−1. Mp: 230 °C dec. Anal. Calcd for C41H51NTi: C, 84.39; H, 7.08; N, 1.93. Found: C, 84.38; H, 7.22; N, 1.64.

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AUTHOR INFORMATION

Corresponding Author

*R.B.: 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 Leoni Fritsche and Malena Hillje for fruitful technical support. REFERENCES

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00425. Crystallographic parameters for compounds 2b, 4a,b, and 5a; 1H and 13C NMR spectra of all compounds. (PDF) Accession Codes

CCDC 1554944−1554947 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. H


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