Group 4 Metal Complexes of Chelating ... - ACS Publications

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Group 4 Metal Complexes of Chelating Cyclopentadienyl-ketimide Ligands Miloš Večeřa,†,‡ Vojtech Varga,† Ivana Císařová,‡ Jiří Pinkas,† Pavel Kucharczyk,§ Vladimír Sedlařík,§ and Martin Lamač*,† †

J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences, v.v.i., Dolejškova 2155/3, 18223 Prague 8, Czech Republic ‡ Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, 12840 Prague 2, Czech Republic § Centre of Polymer Systems, University Institute, Tomás ̌ Bat’a University in Zlín, tř. T. Bati 5678, 76001 Zlín, Czech Republic S Supporting Information *

ABSTRACT: A pendant nitrile group attached to the lithium cyclopentadienide moiety in (C5H4CMe2CMe2CN)Li was alkylated using organyl lithium reagents (RLi, R = Ph, t-Bu, Me), giving rise to dianionic cyclopentadienyl-ketimides [C5H4CMe2CMe2C(R)N]Li2, which were subsequently utilized as chelating ligands for the synthesis of group 4 bent metallocene or half-sandwich complexes (12 examples of the types [(η5-C5R′5){η5-C5H4CMe2CMe2C(R)N-κN}MCl], R′ = H or Me, M = Ti, Zr, or Hf, and [{η5-C5H4CMe2CMe2C(R)NκN}TiX2], X = Cl or NMe2, respectively, were prepared and characterized). Consecutive protolysis of the intramolecularly bound ketimide moiety in bent metallocenes afforded pendant imine or cationic iminium moieties, respectively, attached to group 4 organometallic fragments. Selected compounds were used as precatalysts in a preliminary screening for ethylene polymerization activity.

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INTRODUCTION Complexes of group 4 elements containing cyclopentadienyltype ligands have been investigated for several decades with a sustained effort of the scientific community. Up to the present time, part of the research has been aimed at variously functionalized complexes and even at chemical transformations of functional groups attached to such organometallic moieties.1 The attempted modifications of the archetypal cyclopentadienyl ligands were often motivated by a potential improvement of some desired properties of the respective derivatives such as their catalytic or biological activity. 2 Moreover, many interesting findings resulted from such studies, especially from the perspective of fundamental organometallic and coordination chemistry. As a matter of fact, the synthetic accessibility of functionalized group 4 metal complexes is often limited by the reactive nature of these elements, which do not tolerate certain reagents or conditions. In some cases, however, intramolecular reactions of the attached groups with the metal center may be utilized to perform some functional group chemistry directly at the metallocene framework.1a,3 We have recently described the preparation of a series of group 4 bent metallocene complexes with pendant nitrile groups,4 and we studied transformations of such moieties connected to transition metal complexes.5 We have found that under certain conditions an addition of organyl lithium reagent © XXXX American Chemical Society

across the pendant nitrile accompanied by an alkylation at the metal took place. The whole process led to intramolecularly bound ketimide complexes.5a However, the scope of this reaction was limited due to side-reactions at the metal, such as a reductive β-elimination, that was observed when reagents bearing alkyl groups possessing β-hydrogens (e.g., t-Bu) were applied.5b We concluded that for the preparation of Cpketimide complexes in a straightforward fashion it would be more convenient to perform the nitrile alkylation before the ligand transmetalation/coordination step to avoid any undesired reactivity with the metal center.6 By this approach, functionalized cyclopentadienide alkali metal salts would be obtained, which could be utilized for the preparation of a much wider variety of compounds. We were especially considering a possible preparation of titanium half-sandwich complexes that would resemble the constrained-geometry-type cyclopentadienyl-amido complexes (CGCs). These compounds were successfully applied in olefin polymerization catalysis.7 On the other hand, Ti complexes bearing the ketimide monoanionic ligand as a replacement for one cyclopentadienyl ring are also well established as catalyst precursors giving, like the previously Received: January 11, 2016

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DOI: 10.1021/acs.organomet.6b00019 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

spectroscopy in solution suggested a common bent metallocene dichloride structure of pseudo-Cs symmetry for both 2 and 3 with a flexible pendant nitrile side arm, which does not interact with the metal (13C resonances of the CN group at δ 125.3 and 125.8 ppm for 2 and 3, respectively, are in the range typical for free nitriles). The solid-state structure of titanocene 2 was determined by X-ray diffraction, and it confirmed the expected structural features (Figure 1). In contrast to the previously

mentioned CGCs, interesting results in copolymerizations of ethylene with bulkier olefins.8 Herein, we report a new type of versatile, easily accessible bifunctional cyclopentadienyl-ketimide ligands prepared from a readily available nitrile precursor. A series of group 4 element complexes was prepared, and their reactivity comprising the ketimide group protonation was investigated. Performance of the prepared compounds in ethylene polymerization catalysis was evaluated and compared to known related compounds.

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RESULTS AND DISCUSSION Alkylation of the nitrile group in a substituted lithium cyclopentadienide was initially attempted using the previously reported compound A4 and phenyllithium (Scheme 1). A solid Scheme 1. Reaction of Lithium Salt A with PhLi

Figure 1. View of the molecular structure of compound 2 with thermal displacement ellipsoids at the 50% probability level and hydrogen atoms omitted for clarity. Selected distances (Å) and angles (deg): Ti1−Cl1 2.3596(5), Ti1−Cl2 2.3332(5), Ti1−Cg1 (C5H4) 2.1047(7), Ti1−Cg2 (C5Me5) 2.0976(7), C1−C6 1.521(2), C6−C9 1.599(2), C9−C12 1.481(2), C12−N1 1.141(2), Cg1−Ti1−Cg2 131.79(3), Cl1−Ti1−Cl2 93.52(2), C1−C6−C9 106.00(10), C6−C9−C12 107.46(11), C9−C12−N1 176.6(2), C2−C1−C6−C9−76.8(2), C1−C6−C9−C12 178.28(11); Cg denotes the corresponding centroid of the cyclopentadienyl ring.

product was obtained; however, NMR spectroscopy revealed a mixture of two products, which were ascribed to structures B and C (see the Supporting Information for details). Clearly, the major pathway of the reaction led to an abstraction of a proton from the activated methylene group next to the nitrile. Such a reactivity of nitriles was well precedented as described in the literature.9 Another complication was the imide/enamide tautomerism,5a leading to stabilization of the enamide form C. On the basis of these results we decided to modify the parent ligand. We introduced a CMe2 group instead of the CH2 by using isobutyronitrile as the starting material. The nitrile was deprotonated with lithium diisopropylamide, and the lithiated intermediate was reacted in situ with 6,6-dimethylfulvene to afford the lithium salt 1 in a good yield (Scheme 2). With the ligand precursor 1 in hand we first synthesized two bent metallocene dichlorides, 2 and 3, by a reaction with pentamethylcyclopentadienyl titanium or zirconium trichloride, Cp*MCl3 (Scheme 2). These complexes are analogous to the previously reported compounds bearing ligand A.4,5a NMR

reported compound [(η5-C5Me5){η5-C5H4CMe2CH2CN}TiCl2],5a in which the pendant arm points to the opened bent-metallocene wedge, in the structure of 2 it is positioned rather on the side of the organometallic scaffold. Lithium salt 1 was subsequently reacted with organyl lithiums (RLi, R = Ph, t-Bu, Me) in THF according to Scheme 3 to afford dilithium salts 4a−c as highly air- and moisturesensitive solids precipitating directly from the reaction mixtures. These compounds were of a limited stability especially in solution (see below), but in the solid state, it was possible to store samples of these compounds for several days in a glovebox at room temperature without any significant decomposition. Salts 4a−c were characterized only by NMR and IR spectroscopy. In DMSO-d6 solutions,10 two sets of signals, both of them attributable to the products 4a−c, were observed in all cases (see Figures S7−S9 in the Supporting Information). Clearly, the nitrile group in the starting material 1 was converted to the ketimide moiety (13C NMR signals in the range δ 186.6−193.8 ppm vs 127.8 ppm in 1). Varying amounts of a residual THF solvent that was difficult to remove from the solid products were also identified in the spectra. Single imide bands in the IR spectra of solid materials 4a−c were present in the range 1607−1627 cm−1 (cf. the nitrile band at 2248 cm−1 in 1). Unfortunately, attempts to prepare single

Scheme 2. Preparation of Lithium Salt 1 and Related Ti and Zr Metallcoene Complexes with a Pendant Nitrile Group

B


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Organometallics Scheme 3. Preparation of Dilithium Salts 4 and Metallocene Complexes Bearing a Cp-ketimide Ligand

Scheme 4. Anticipated Decomposition Pathway of Dilithium Salts 4 in Solution and Formation of Byproduct 9

crystals of the dilithium salts in order to perform diffraction analysis were not successful (even using other coordinating molecules such as TMEDA in order to prepare corresponding adducts); therefore the real structure of these compounds, also with respect to a suspected aggregation in solution, remains obscured at this point. Nevertheless, dilithium salts 4a−c were successfully used as ligand precursors for the preparation of a series of group 4 metallocene complexes 5−8 (Scheme 3) by simply suspending the corresponding dilithium salt and the respective Cp′MCl3 (Cp′ = η5-C5H5 = Cp or η5-C5Me5 = Cp*; M = Ti, Zr, Hf) precursor in THF. In general, the Cp-ketimide complexes were isolated in a good yield and reasonable purity (>90% by NMR) just by extraction of the crude product into toluene. Recrystallization was viable in most cases, which afforded analytically pure products and crystals suitable for X-ray diffraction; however, yields dropped noticeably and it was usually difficult to recover the remaining product from mother liquors. A partial decomposition of the parent dilithium salt must be, however, taken into account during the preparation of complexes 5−8. Thus, when we attempted the synthesis of an analogue of complexes 5a,b starting from 4c, we have after prolonged crystallization attempts isolated the dimeric imidobridged complex 9 (see the Supporting Information for experimental details and X-ray diffraction analysis of 9)11 as an undesired outcome of the reaction of Cp*TiCl3 with a decomposition product of 4c (Scheme 4). When we reinvestigated the NMR spectra of compounds 4a−c, we were able to identify the major decomposition product [C5H4C(Me)CH2]Li, which was present in all the samples and also some signals of the tentative byproducts Me2C C(R)NHLi. Spectral features of the products 5−8 were in line with the proposed structures. Due to the intramolecularly tethered ketimide moiety and the presence of two differently substituted cyclopentadienyl rings, the molecules possess an inherent chirality at the metal center. This is reflected in the sets of nonequivalent NMR signals of the −CMe2CMe2− linker and of the attached C5H4 ring in both 1H and 13C spectra. The presence of ketimide moieties (the CN signals in the range δC 177.4−189.8 ppm) and the appropriate substituents R (R = Ph, t-Bu, Me) introduced during the preparation of 4a−c were unequivocally evidenced. This evidence was important particularly for compounds 6c and 7c, where the methyl group was present and no sign of an alternative enamide

tautomer was observed (unlike for similar compounds reported previously by our group).5a This was, however, in line with earlier reports describing the preparation of zirconocene ketimide complexes via the lithium azaallyl derivative LiCH2C(t-Bu)NH. IR spectra of all complexes 5−8 displayed medium to strong bands of the CN stretch in the range 1623−1660 cm−1. EI-MS and elemental analysis confirmed the corresponding composition of the products. In addition, solid-state structures were determined by singlecrystal X-ray diffraction for compounds 5a (Figure 2), 5b (Figure 3), 6b (Figure S1 in the Supporting Information), 7b (Figure 4), and 8 (Figure S1 in the Supporting Information).

Figure 2. View of the molecular structure of compound 5a with thermal displacement ellipsoids at the 30% probability level and hydrogen atoms omitted for clarity. For selected distances and angles see Table 1.

Selected structural parameters of the metallocene ketimide complexes are given in Table 1. All the structures obtained were racemic mixtures crystallizing in centrosymmetric monoclinic space groups. Slight differences can be found among the derivatives in the conformation of the −CMe2CMe2C(R)N− fragment depending on the central metal atom and on the substituent R. Obviously, in a series of related compounds 5b, 6b, and 8, the Zr and Hf derivatives are structurally closer to each other. A notable parameter for all structures is the angle C12−N1−M, which is in the range 150.2−153.7° throughout the series. This suggests a significant distortion of the ketimide C


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Organometallics

coordination of these ligands (CN−M angles are typically 168−180°; for Ti complexes, see ref 13; for Zr, see refs 12, 13a, 14, and 15). The only exceptions are the compounds in which an increased steric hindrance forces the ketimide moiety to bend from the linear arrangement, such as in Cp2Ti(N CPh2)2,16 or related more sterically crowded complexes.17 Recently, Beckhaus and co-workers reported a doubly tethered Cp-ketimide zirconocene obtained by a nitrile insertion into a bis(η5:η1-pentafulvene)zirconium complex. An even shorter linker in this product caused the CN−Zr angle value to decrease to 124.7°.18 The zirconocene complexes 6a and 6b were studied also for their reactivity with Brønsted acids. A stepwise protonation of the ketimide moiety was performed using a dry HCl solution or the anilinium salt PhNH3Cl (Scheme 5). The reaction with 1 Figure 3. View of the molecular structure of compound 5b with thermal displacement ellipsoids at the 30% probability level and hydrogen atoms omitted for clarity. For selected distances and angles see Table 1; analogous structures of compounds 6b and 8 are depicted in Figure S1 in the Supporting Information.

Scheme 5. Protonation/Deprotonation Reactions of Zirconocene Ketimide Complexes

Figure 4. View of the molecular structure of compound 7b with thermal displacement ellipsoids at the 30% probability level and hydrogen atoms omitted for clarity. For selected distances and angles see Table 1.

moiety from the ideal arrangement for coordination to the group 4 metal. Related group 4 bent-metallocene complexes bearing nontethered ketimide ligands feature a close-to-linear Table 1. Selected Bond Lengths (Å) and Angles (deg) of Metallocene Ketimide Complexes 5a, 5b, 6b, 7b, and 8a M−Cl1 M−N1 M−Cg1 (C5H4) M−Cg2 (Cp* or Cp) C12−N1 Cg1−M−Cg2 N1−M−Cl1 C1−C6−C9 C6−C9−C12 C9−C12−N1 C13−C12−N1 C12−N1−M C2−C1−C6−C9 C1−C6−C9−C12 C9−C12−N1−M a

5a (M = Ti)

5b (M = Ti)

6b (M = Zr)

7b (M = Zr)

8 (M = Hf)

2.4379(5) 1.9682(14) 2.0695(8) 2.0881(8) 1.269(2) 135.45(3) 90.00(4) 114.62(12) 106.19(12) 120.27(14) 117.40(14) 150.16(11) 119.1(2) −54.6(2) −18.5(3)

2.4512(6) 1.891(2) 2.0711(10) 2.1166(9) 1.260(3) 135.05(4) 95.48(5) 113.8(2) 107.0(2) 116.1(2) 117.4(2) 153.65(14) −104.4(2) 46.5(2) 36.4(4)

2.5057(5) 2.011(2) 2.2129(9) 2.2414(8) 1.261(2) 133.78(3) 98.46(4) 114.72(14) 107.69(14) 116.6(2) 117.3(2) 150.75(13) −107.9(2) 50.1(2) 40.0(3)

2.4963(4) 2.0084(12) 2.1976(7) 2.2266(7) 1.263(2) 132.04(3) 99.65(4) 115.32(11) 106.29(11) 116.09(12) 116.68(13) 151.92(11) −109.8(2) 54.2(2) 27.1(3)

2.4740(7) 1.992(2) 2.1947(12) 2.2223(11) 1.262(3) 133.79(5) 97.42(6) 114.6(2) 107.6(2) 116.2(2) 117.8(2) 151.5(2) 108.3(3) −50.6(3) −38.6(5)

Cg denotes the corresponding centroid of the cyclopentadienyl ring. D


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equilibrium observable in the VT NMR experiment (see Figure S14 in the Supporting Information). In contrast to a rather complicated behavior of complexes 10, compounds 11a,b and 13a,b displayed a set of sharp resonances consistent with a pseudo-Cs symmetrical metallocene dichloride with a noncoordinated pendant iminium moiety. Also the observed pair of NH2+ signals in the range 10.99−13.54 ppm clearly indicated the identity of these derivatives. IR spectra of solid materials also suggested the presence of the corresponding functional groups (e.g., the band for the N−H stretch in 10a at 3316 cm−1 vs broad bands for the NH2+ moiety of the iminium salts in the range 2500−2800 cm−1). A successful solid-state structure elucidation of 10a·CH2Cl2 (Figure 5) helped to clarify the constitution of this compound.

equiv of the acid was accompanied by a chloride coordination to the metal. Thus, the zirconocene dichloride complexes with a pendant primary imine group (10a,b) were obtained. An excess of HCl led to the formation of iminium chloride salts 11a,b. These salts usually precipitate from solutions and can be further recrystallized; however, various amounts of the decomposition product 12Zr were detected in the remaining solutions. Even pure compounds 11a,b undergo decomposition in solution over a few days, which seems to be facilitated by the presence of an acidic iminium group. Notably, the described protonation reactions are reversible. By using a stronger base (NEt3 performed well) it was possible to convert iminium salts to free imine compounds or further to the starting ketimide complexes 6a,b. Moreover, an effective and clean pathway for the preparation of complexes 10 is a simple mixing of stoichiometric amounts of the respective complexes 6 and 11 (see the Experimental Section for details). A similar reactivity was expected also for analogous titanocene complexes. However, it was only possible to prepare the iminium hydrochlorides 13a,b starting from 5a,b, respectively (Scheme 6). Despite numerous attempts, we failed Scheme 6. Protonation/Deprotonation Reactions of Titanocene Ketimide Complexes

Figure 5. View of the molecular structure of compound 10a·CH2Cl2 with thermal displacement ellipsoids displayed at the 30% probability level and hydrogen atoms omitted for clarity except for the isotropically refined N-H atom. Selected distances (Å) and angles (deg): Zr1−Cl1 2.5783(7), Zr1−Cl2 2.5597(7), Zr1−N1 2.365(2), Zr1−Cg1 (C5H4) 2.2454(12), Zr1−Cg2 (C5Me5) 2.2722(11), C1− C6 1.523(4), C6−C9 1.574(4), C9−C12 1.524(4), C12−N1 1.276(3), Cg1−Zr1−Cg2 129.10(4), Cl1−Zr1−Cl2 77.20(3), N1− Zr1−Cl2 70.01(5), C12−N1−Zr1 148.1(2), C1−C6−C9 114.7(2), C6−C9−C12 109.2(2), C9−C12−N1 121.7(2), C13−C12−N1 116.6(2), C2−C1−C6−C9 130.4(2), C1−C6−C9−C12−59.3(3), C9−C12−N1−Zr1 7.2(5).

to prepare defined titanium analogues of compounds 10. In some cases a mixture of compounds 5 and 13 was obtained; we therefore propose that this behavior is general for titanium, which does not allow an intramolecular coordination of the primary imine moiety, which is necessary for its stabilization. Spectral properties of compounds 10a,b are quite distinct from their parent ketimide complexes. At room temperature, NMR spectra of both compounds displayed a fluxional behavior (similar observations were made for related compounds5a), which resulted in a set of broad signals that became better resolved at higher temperatures, which could be attributed to the pseudo-Cs symmetrical structure of a zirconocene dichloride with a flexible free imine pendant arm (for VT NMR experiments, see Figures S10−S13 in the Supporting Information). The NH resonances in the 1H NMR spectra at δ 9.28 and 9.69 ppm for compounds 10a and 10b, respectively, are consistent with the primary imine group. At lower temperatures, the signals split into a set characteristic for complexes with an intramolecularly coordinated pendant imine moiety. Moreover, two distinct isomers appeared at low temperature in different ratios for 10a (15:1) and 10b (5:4), which were ascribed to constitutional isomers at the CNH double bond (denoted E- and Z- with respect to the imine proton and the substituted zirconocene moiety).19 In addition, we observed that a mixture of compounds 6b and 10b (excess 6b used for the reaction with 11b) was not forming an equilibrium on the NMR time scale, whereas 10b and 11b were mutually exchanging protons in solution and gave rise to an

The molecule of 10a is chiral, similar to the parent 6a, and the crystal is composed of a racemic mixture giving rise to a monoclinic structure with P21/c symmetry. The pendant primary imine moiety is coordinated to Zr from one side of the bent-metallocene core and adopts exclusively the Econfiguration on the CN bond with the NH hydrogen atom pointing approximately in a perpendicular direction to the plane defined by the atoms Cl1, Cl2, N1, and Zr1 (the angle between the plane and the N−H bond is 105.9°). Notably, the flexible aliphatic tether readily allows various positions of the imine (cf. the difference in the torsion angle C1−C6−C9−C12 for 10a and 6b: − 59.3° vs 50.1°). The Zr1−N1 distance of 2.365(2) Å is significantly longer than in the comparable ketimide complex 6b (2.011(2) Å), which is consistent with an N−Zr coordination bond. To complete the picture of structural diversity of metallocene ketimide protonation products, we also performed a diffraction analysis of iminium chlorides 11b (Figure 6) and 13b (Figure S3 in the Supporting Information). Both structures were solvates with one molecule of chlorinated solvent. The pendant cationic iminium arm in both 11b·CHCl3 and 13b·CH2Cl2 is E


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Organometallics

TiCl2(NMe2)2.20 Surprisingly, however, dilithium salts 4a,b did not react preferably with two chloride ligands in TiCl2(NMe2)2 as was typically observed during preparations of Cp-amide-type complexes.20b,21 Instead, the reaction with 4a afforded exclusively compound 14a, containing both chloro and amido ligands, which was isolated in a crystalline form. Utilization of 4b led to a mixture of compounds 14b and 15 (1:1.4 molar ratio), which were not separated and were used directly in the following reaction. NMR spectra of 14a, 14b, and 15 were again very indicative, reflecting different symmetries adopted by each complex. The former two compounds have a center of chirality at the Ti atom, which resulted, for example, in a set of well-resolved nonequivalent signals for all CMe2 and C5H4 protons observed in 1H spectra. On the other hand, 15 exhibited a set of broad signals in the 1H NMR spectra that were indicative of a fluxional behavior (see Figure S15 in the Supporting Information). At higher temperature, a pseudo-Cs symmetry could be presumed, caused by a rapid conformational change of the pendant tether (could be described also as a six-membered metallacycle). At lower temperature, signals of 15 split into a set characteristic for a chiral molecule similar to 14b; however, the sole source of chirality in this molecule is the twisted tethered arm. In addition to the spectral characterization, the solid-state structure of 14a was elucidated (Figure 7, Table 2). Compound

Figure 6. View of the molecular structure of compound 11b·CHCl3 (only the cation of one of two symmetrically independent molecules is shown; for depictions and geometric parameters of molecule 2 and of the analogous structure of compound 13b·CH2Cl2 see the Supporting Information). Thermal displacement ellipsoids are displayed at the 30% probability level, and hydrogen atoms are omitted for clarity except for the isotropically refined hydrogen atoms of the iminium moiety. Selected distances (Å) and angles (deg): Zr1−Cl1 2.4389(7), Zr1−Cl2 2.4244(6), Zr1−Cg1 (C5H4) 2.2502(12), Zr1−Cg2 (C5Me5) 2.2191(12), C1−C6 1.524(3), C6−C9 1.621(3), C9−C12 1.541(3), C12−N1 1.279(3), Cg1−Zr1−Cg2 130.71(5), Cl1−Zr1− Cl2 97.80(3), C1−C6−C9 106.7(2), C6−C9−C12 108.5(2), C9− C12−N1 116.6(2), C13−C12−N1 114.5(2), C2−C1−C6−C9 84.8(3), C1−C6−C9−C12−175.5(2).

twisted away from the metallocene core, and pairs of molecules are interconnected by hydrogen bonds linking the iminium groups via two chloride anions (see Figure S4 in the Supporting Information). The same structural features were observed for related complexes reported previously.5a The prepared ligand precursors 4a,b were also used for the synthesis of Ti half-sandwich complexes (Scheme 7). The most convenient starting material proved to be the complex


14a crystallized as a racemate in a centrosymmetric structure. The Cp-ketimide ligand in this compound is bonded to Ti in a similar way to that in metallocene 5a. Nevertheless, there are slight differences such as a shorter Ti1−N1 bond in 14a in comparison to 5a (1.8877(10) vs 1.9682(14) Å). Notably, the C12−N1−Ti1 angle is as low as 145.71(8)°. The amide derivatives 14 and 15 immediately served as intermediates for the preparation of dichloride complexes 16a,b (Scheme 7) by chlorination with Me3SiCl. Both compounds were obtained as extremely air- and moisture-sensitive solids that were successfully recrystallized, although only in moderate yields. NMR spectra of both compounds displayed similar features to those of 15. At room temperature, the 1H spectra showed simple sets of signals attributable to complexes with a plane of symmetry. At lower temperature, the signals became broad and finally split into a set of nonequivalent signals (see Figures S17 and S19 in the Supporting Information for 1H VT NMR spectra of 16a and 16b, respectively). For all three related compounds 15, 16a, and 16b we were able to estimate

Scheme 7. Preparation of Ti Half-Sandwich Complexes with Cp-ketimide Ligands

F


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Organometallics Table 2. Selected Bond Lengths (Å) and Angles (deg) of 14a, 16a, and 16ba 14a Ti1−Cl1 Ti1−Cl2 Ti1−N1 Ti1−N2 Ti1−Cg (C5H4) C12−N1 Cl1−Ti1−Cl2 N2−Ti1−Cl1 Cg−Ti1−N1 C1−C6−C9 C6−C9−C12 C9−C12−N1 C13−C12−N1 C12−N1−Ti1 C2−C1−C6−C9 C1−C6−C9−C12 C9−C12−N1−Ti1

2.3296(4) 1.8877(10) 1.8797(10) 2.0172(6) 1.2641(14) 107.35(3) 110.12(4) 113.81(9) 108.57(8) 120.30(10) 118.42(10) 145.71(8) 114.21(12) −54.07(12) −10.1(2)

16a

16b

2.2900(5) 2.2551(5) 1.8618(13)

2.2964(4) 2.2689(4) 1.8421(12)

1.9989(8) 1.268(2) 102.92(2)

2.0031(8) 1.266(2) 102.17(2)

107.05(5) 113.95(13) 108.55(13) 120.07(14) 116.92(14) 146.52(12) 102.5(2) −47.5(2) −10.7(3)

106.82(4) 113.86(11) 106.42(11) 115.70(12) 116.56(12) 150.91(10) −109.7(2) 55.0(2) 8.0(3)

Figure 9. View of the molecular structure of compound 16b (only one of two symmetrically independent molecules is shown; for the depiction of molecule 2 see the Supporting Information). Thermal displacement ellipsoids are displayed at the 30% probability level, and hydrogen atoms are omitted for clarity. For selected distances and angles see Table 2.

171.3° for CpTiCl2[NC(t-Bu)n-Bu].25 The Ti1−N1 distances in the herein described compounds 14a, 16a, and 16b are in the range 1.84−1.89 Å, which is only slightly more than in the aforementioned known complexes (values of 1.83−1.84 Å). The CN distances in the range 1.26−1.27 Å for 14a, 16a, and 16b are comparable to the distances in reference compounds (1.27−1.28 Å). Ethylene Polymerization. A preliminary evaluation of the newly synthesized compounds as catalyst precursors for ethylene polymerization was performed (results are summarized in Table 3). The systems comprising the corresponding

a

Only one of two symmetrically independent molecules is listed; for data of molecule 2 see the Supporting information. Cg denotes the C5H4 centroid.

the thermodynamic parameters for the racemization process based on the line shape analysis using the WINDNMR software.22 The estimated ΔG⧧298 values are increasing in the order 46.6, 50.4, and 60.9 kJ mol−1 for 16a, 16b, and 15, respectively (for details, see the Supporting Information, Figures S16, S18, S20, and Table S2). Both 16a and 16b afforded X-ray quality monocrystals, and their solid-state structures were found to be formed by racemic mixtures of molecules, which was consistent with their spectral behavior (Figures 8 and 9, Table 2). As with the previous

Table 3. Ethylene Polymerizationa


precatalyst

T [°C]/t [min]

Ab

Mw × 10−4

Mw/ Mn

Tm [°C]

3 6a 6b 6b 6c 7a 7b 7b 7b 7c 10a 10b 10b 10b 16a 16b Cp*CptBuZrCl2 CpTi(NCtBu2)Cl2

25/10 25/60 25/60 75/60 25/60 25/60 25/60 50/60 75/20 25/60 25/10 25/10 50/10 75/10 60/10 60/10 25/10 60/10

250 25 25 50 20 140 210 840 3540 100 520 2000 5900 12 230 20 140 13 500 14 000

39.5 n.d. n.d. 19.9 n.d. n.d. 39.8 16.0 19.4 n.d. 54.4 48.0 36.2 15.6 n.d. n.d. 41.5 37.6

3.3 n.d. n.d. 2.3 n.d. n.d. 2.0 2.6 2.8 n.d. 3.7 3.3 3.9 3.7 n.d. n.d. 3.6 3.3

139.1 137.2 n.d. 139.7 137.3 138.7 138.3 139.8 139.4 137.3 137.3 136.9 137.9 138.7 n.d. 134.1 139.6 135.3

Polymerization conditions: cocatalyst MAO, [M] = 5 × 10−6 mol· L−1, Al/Zr = 1000 (mol/mol), for 16a, 16b, and CpTi(NCtBu2)Cl2: Al/Ti = 2000 (mol/mol), pethylene = 3 × 105 Pa, solvent: toluene, total volume 50 mL. bActivity; [A] = kgPE (molM·h·bar)−1. a

compounds, the most pronounced feature of their molecular structures is the deformation of the bound ketimide moiety from the preferable linear coordination mode due to the strain inflicted by the aliphatic tether. The C12−N1−Ti1 angle for 16a and 16b is 146.52(12)° and 150.91(10)°, respectively. Related Ti half-sandwich compounds Cp′TiCl2(NCR1R2) with nontethered ketimide ligands exhibit an arrangement closer to linearity, and the ketimide is tilted in a different direction (typically down from the Cp′ ring, as a result of steric repulsion), cf. the C−N−Ti angle values: 166.4° for Cp*TiCl2(NCt-Bu2),23 170.5° for Cp*TiCl2(NCPh2),24

complex and methylaluminoxane (MAO) as the activator in toluene solution were examined to explore the effect of the present ligands, pendant donor groups, and substituents (both at the auxiliary cyclopentadienyl ligand and at the ketimide moiety). Indeed, the zirconocene complexes with a bound ketimide group are inferior in terms of activity in comparison to simple zirconocene dichlorides (we have chosen G


Article

Organometallics Cp*CptBuZrCl226 as the reference complex with similar steric properties to our compounds; it shall be noted that Cp2ZrCl2 under these conditions gave about an order of magnitude higher activities, which caused problems with the temperature control and reactor fouling). However, related zirconocene ketimide complexes Cp2ZrCl[NC(t-Bu)Ph]14 and Cp2ZrCl[NC(t-Bu)Me]12 were reported to give active systems for ethylene polymerization, although the activities were rather low (32 and 109 kgPE (molZr·h·bar)−1 for the latter mentioned complexes, respectively). The activity of these compounds was explained by a replacement of the ketimide by an alkyl group from MAO in order to create an active site for polymerization. In the case of our compounds, we were curious about the effect of strained coordination of the ketimide. As evident from Table 3, the activities induced by complexes 6 were low even when the polymerization temperature was increased. Substituents R on the ketimide moiety seemed to have a rather negligible effect. Replacement of the Cp* ligand by the unsubstituted Cp in compounds 7 somewhat increased the activities. Even more pronounced was the effect of temperature on the polymerization with 7b, which led to the activity of 3540 kgPE (molZr·h· bar)−1 at 75 °C. Complexes 10 exhibited activities at least an order of magnitude higher than the corresponding ketimide complexes, while 10b outperformed 10a. This is in line with their structure featuring two chloride ligands and a weakly coordinated imine arm. At 75 °C the activity induced by 10b reached the value 12 230 kgPE (molZr·h·bar)−1. Surprisingly, the activity of zirconocene dichloride 3 with a pendant nitrile group was about an order of magnitude lower than that of 10b. Regarding the obtained polymers, they can be in all cases described as linear high-density polyethylenes with unexceptional molecular weights (Mw up to 5.45 × 105) and melting points (in the range 137.2−139.8 °C for zirconocene precatalysts). Molecular weight distributions were somewhat broader for some samples, but no sign of multimodal distribution was observed. In general, at higher temperatures, the same systems gave lower molecular weight polymers. The Ti half-sandwich complexes 16a,b were also tested in ethylene polymerization, but slightly different conditions were applied according to the report using the related complex CpTiCl2(NCt-Bu2) (see Table 3).23 In our hands, the system based on CpTiCl2(NCt-Bu2) was highly active (the activity 14 000 kg PE (mol Zr ·h·bar) −1 was reproducible within ±10%).23,27 In sharp contrast, complexes 16a,b exhibited very low activities. We can speculate that the different arrangement of ketimide moieties with respect to the metal center in our complexes in comparison to the nontethered ketimide in CpTiCl2(NCt-Bu2) led to a reduced electron-donating ability of the ketimides, which in turn destabilized the active species in the course of the polymerization reaction.

pendant iminium salts (for both Ti and Zr compounds). Preliminary evaluation of the zirconocene complexes in ethylene polymerization expectedly revealed higher activities for the dichlorides with pendant donor groups in comparison to the ketimide compounds. A strong influence of polymerization temperature was also noted. On the contrary, the Ti halfsandwich complexes were found to be poorly performing in ethylene polymerization, which was in a striking contrast to related Ti compounds bearing nontethered ketimide ligands. In the following work, we would like to modify the structure of the Cp-ketimide scaffold in order to decrease the strain imposed by the tether on the ketimide moiety.

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EXPERIMENTAL SECTION

All syntheses and manipulations with air- and moisture-sensitive compounds were carried out under an argon atmosphere using standard Schlenk techniques or in a Labmaster 130 glovebox (mBraun) under purified nitrogen. All solvents (including deuterated) were appropriately dried: THF, diethyl ether, toluene, benzene-d6, npentane, n-hexane by refluxing with Na/benzophenone ketyl, distilled under argon, and stored over sodium mirror or 4 Å molecular sieves; chloroform, dichloromethane, DMSO-d6 by refluxing with CaH2, then distilled under argon and stored over 4 Å molecular sieves. PhNH3+Cl− was prepared from aniline by addition of 1 M anhydrous HCl solution in Et2O. TiCl2(NMe2)2,20b Cp*Cpt‑BuZrCl2,26 and CpTi(NCt-Bu2)Cl228 were prepared according to reported procedures. Other chemicals were used as received from commercial sources. NMR spectra were measured on a Varian Unity 300 spectrometer at 293 K. Chemical shifts (δ/ppm) are given relative to solvent signals (benzene-d6: δH 7.16, δC 128.00; toluene-d8: δH 2.08, δC 20.43; CDCl3: δH 7.26, δC 77.16; THF-d8 δH 3.58, δC 67.21; DMSO-d6: δH 2.50, δC 39.52). The assignment of NMR signals is based on 1D-NOESY, gCOSY, gHSQC, and gHMBC experiments, wherever possible. EI-MS spectra were obtained on a VG-7070E mass spectrometer at 70 eV. IR spectra were measured on a Nicolet Avatar FTIR spectrometer on Nujol suspensions between KBr plates (prepared in a glovebox) in the range 400−4000 cm−1. Elemental analyses were performed on a FLASH 2000 CHN elemental analyzer (Thermo Scientific). Melting points were determined on a Kofler apparatus, and the values are uncorrected; samples were sealed in glass capillaries under nitrogen. SEC data of polyethylene samples were measured on an Agilent HT GPC 220 chromatograph equipped with built-in dRI and viscosity detectors. Sample concentration was 1.0 mg· mL−1, and all samples were filtered (0.45 μm filter) prior to injection. Separation was performed at 160 °C on a set of two columns (PLGelolexis 13 μm and PLGel-Mixed-B 10 μm) in 1,2,4-trichlorobenzene stabilized by 125 ppm BHT at a flow rate of 1 mL·min−1. Polyethylene molecular weights and distributions were calculated based on a PS calibration (580−6000 000 g·mol−1) using Cirrus software. DSC measurements were performed on a Mettler Toledo Star 1 instrument with both heating and cooling rate 10 °C·min−1 under nitrogen (50 cm3·min−1). Melting temperatures were obtained from the second heating run. Synthesis of (C5H4CMe2CMe2CN)Li (1). A solution of isobutyronitrile (1.01 g, 14.9 mmol) in 10 mL of THF was cooled to −78 °C, and a solution of lithium diisopropylamide (7.3 mL of 2 M LDA in THF/n-heptane/ethylbenzene, 14.6 mmol) was added dropwise with stirring over 30 min. The mixture was allowed to warm to room temperature, stirred for 15 min, and then cooled again to −78 °C, and 6,6-dimethylfulvene (1.72 g, 16.2 mmol) was slowly introduced into the vigorously stirred mixture. Cooling was removed, the red solution was stirred at room temperature for 1 h, and 20 mL of n-hexane was added. A red-brown oil separated, from which a yellow solution was removed. The oily product was triturated with 3 × 20 mL of n-hexane and dried under vacuum to afford 1 as a beige, amorphous solid, which contained some amount of residual THF solvent (typically 90% by NMR); some of them were further recrystallized as indicated below to afford analytically pure products. However, in most cases, yields decreased significantly after the recrystallization step, and it was difficult to obtain further crops of the products from mother liquors. [(η5-C5Me5){η5-C5H4CMe2CMe2C(Ph)N-κN}TiCl] (5a). Synthesized from Cp*TiCl3 (710 mg, 2.45 mmol) and 4a·0.5THF (740 mg, 2.46 mmol) in THF (20 mL), the product was obtained as a red solid. Yield: 980 mg (85%). Crystallization from toluene/n-hexane at −28 °C afforded dark red crystals of 5a (395 mg). Mp: 201−204 °C. I


Article

Organometallics

[(η5-C5Me5){η5-C5H4CMe2CMe2C(Me)N-κN}ZrCl] (6c). Cp*ZrCl3 (333 mg, 1.00 mmol) and 4c·0.6THF (246 mg, 1.00 mmol) in THF (10 mL) were used, and the residue obtained after evaporation of the toluene extract was triturated with 3 × 20 mL of n-hexane. The resulting yellow powder was dried under vacuum. Yield: 352 mg (78%). NMR (C6D6) 1H: δ 0.77 (s, 3 H, CMe2CN), 0.90 (s, 3 H, C5H4CMe2), 0.97 (s, 3 H, CMe2CN), 0.98 (s, 3 H, C5H4CMe2), 1.77 (s, 3 H, C(Me)N), 1.89 (s, 15 H, C5Me5), 4.88, 5.58, 5.93, 6.14 (4 × m, 1 H, C5H4). 13C{1H}: δ 12.3 (C5Me5), 21.7 (CMe2CN), 24.8, 24.9 (C5H4CMe2), 25.2 (CMe2CN), 26.8 (C(Me)N), 42.4, 52.6 (2 × CMe2), 103.1, 111.8, 112.2, 112.3 (4 × C5H4 CH), 119.4 (C5Me5), 142.1 (C5H4 Cipso), 182.7 (CN). IR (Nujol): 1654 (vs, νCN), 1617 (w), 1604 (w), 1495(w), 1442 (m), 1365 (m), 1349 (w), 1222 (w), 1124 (w), 1097 (w), 1082 (w), 1041 (w), 1028 (w), 849 (m), 796 (s), 757 (w), 730 (s), 695 (s), 620 (m), 597 (w), 543 (w) cm−1. EI-MS, m/z (relative abundance): 449 (26, [M]+•), 414 (17, [M − Cl]+), 408 (74, [M − MeCN]+), 393 (100). Anal. Calcd for C23H34NZrCl (451.18): C 61.22, H 7.60, N 3.11. Found: C 61.12, H 7.71, N 3.18. [(η5-C5H5){η5-C5H4CMe2CMe2C(Ph)N-κN}ZrCl] (7a). CpZrCl3 (314 mg, 1.22 mmol) and 4a·0.5THF (368 mg, 1.22 mmol) in THF (10 mL) were used, and the crude product was obtained as an oily residue, which was triturated with 3 × 20 mL of n-hexane to afford an orange powder. Yield: 400 mg (74%). NMR (C6D6) 1H: δ 0.89 (s, 3 H, CMe2CN), 0.94, 0.97 (2 × s, 3 H, C5H4CMe2), 1.10 (s, 3 H, CMe2CN), 5.05, 5.75, 5.83 (3 × m, 1 H, C5H4), 5.94 (s, 5 H, C5H5), 6.35 (m, 1 H, C5H4), 6.98−7.31 (m, 5 H, Ph). 13C{1H}: δ 23.9 (CMe 2 CN), 25.0 (C 5 H 4 CMe 2 ), 25.7 (CMe 2 CN), 26.1 (C5H4CMe2), 43.2, 56.1 (2 × CMe2), 101.5, 107.0, 109.8 (3 × C5H4 CH), 111.2 (C5H5), 116.6 (C5H4 CH), 127.4, 127.9 (2 × Ph CH), 142.3 (Ph Cipso), 144.2 (C5H4 Cipso), 183.9 (CN); a signal due to Ph CH obscured by the solvent signal. IR (Nujol): 1644 (m, νCN), 1619 (m), 1575 (w), 1366 (m), 1230 (w), 1141 (w), 1126 (w), 1114 (w), 1016 (w), 957 (w), 802 (s), 744 (m), 710 (m), 699 (m), 684 (w), 633 (w), 522 (w) cm−1. EI-MS, m/z (relative abundance): 441 (23, [M]+•), 338 (67, [M − PhCN]+), 325 (57), 302 (73), 190 (33, [CpZrCl]+), 77 (100). Anal. Calcd for C23H26NZrCl (443.12): C 62.34, H 5.91, N 3.16. Found: C 62.16, H 6.02, N 3.21. [(η5-C5H5){η5-C5H4CMe2CMe2C(t-Bu)N-κN}ZrCl] (7b). Synthesized from CpZrCl3 (314 mg, 1.22 mmol) and 4b·0.3THF (326 mg, 1.22 mmol) in THF (15 mL), the product was obtained as a yellow solid. Yield: 418 mg (81%). Crystallization from a concentrated toluene solution at −28 °C afforded 7b as a yellow crystalline solid (122 mg). X-ray quality crystals were grown by slow evaporation of a benzene-d6 solution under vacuum. Mp: 110−111 °C. NMR (C6D6) 1 H: δ 0.73 (s, 3 H, CMe2CN), 0.89, 0.95 (2 × s, 3 H, C5H4CMe2), 1.15 (s, 9 H, CMe3), 1.24 (s, 3 H, CMe2CN), 4.93, 5.61, 5.70 (3 × m, 1 H, C5H4), 5.92 (s, 5 H, C5H5), 6.24 (m, 1 H, C5H4). 13C{1H}: δ 22.2 (CMe2CN), 24.7, 26.5 (C5H4CMe2), 28.2 (CMe2CN), 30.1 (CMe3), 43.2 (CMe2), 43.5 (CMe3), 57.3 (CMe2), 100.6, 107.5, 109.6 (3 × C5H4 CH), 110.9 (C5H4 CH), 115.3 (C5H4 CH), 143.7 (C5H4 Cipso), 188.7 (CN). IR (Nujol): 1639 (m, νCN), 1601 (w), 1366 (m), 1212 (w), 1141 (w), 1116 (w), 1040 (w), 1017 (w), 967 (w), 928 (w), 798 (s), 743 (w), 724 (m), 637 (w) cm−1. EI-MS, m/z (relative abundance): 421 (35, [M]+•), 364 (32, [M − t-Bu]+), 338 (88, [M − CN(t-Bu)]+), 325 (82), 302 (100), 190 (52, [CpZrCl]+). Anal. Calcd for C21H30NZrCl (423.13): C 59.61, H 7.15, N 3.31. Found: C 59.78, H 7.24, N 3.45. [(η5-C5H5){η5-C5H4CMe2CMe2C(Me)N-κN}ZrCl] (7c). CpZrCl3 (246 mg, 0.94 mmol) and 4c·0.6THF (232 mg, 0.94 mmol) in THF (10 mL) were used, and the crude product was obtained as an oily solid. Trituration with 2 × 20 mL of n-pentane gave a yellow powder, which was dried under vacuum. Yield: 247 mg (69%). NMR (C6D6) 1H: δ 0.58 (s, 3 H, CMe2CN), 0.82, 0.90 (2 × s, 3 H, C5H4CMe2), 0.92 (s, 3 H, CMe2CN), 1.75 (s, 3 H, C(Me)N), 4.88, 5.61, 5.74 (3 × m, 1 H, C5H4), 5.94 (s, 5 H, C5H5), 6.31 (m, 1 H, C5H4). 13C{1H}: δ 21.7, 24.3 (2 × CMe2CN), 24.5, 25.3 (2 × C5H4CMe2), 26.4 (C(Me)N), 42.2, 55.4 (2 × CMe2), 101.4, 106.9, 109.9 (3 × C5H4 CH), 110.9 (C5H5), 116.3 (C5H4 CH), 143.6 (C5H4 Cipso), 183.0 (CN). IR (Nujol): 1660 (m, νCN), 1630 (w), 1366

NMR (C6D6) 1H: δ 0.94 (s, 3 H, CMe2CN), 0.96, 1.02 (2 × s, 3 H, C5H4CMe2), 1.10 (s, 3 H, CMe2CN), 1.76 (s, 15 H, C5Me5), 4.50, 5.44, 6.07, 6.17 (4 × m, 1 H, C5H4), 6.97−7.48 (m, 5 H, Ph). 13C{1H}: δ 13.0 (C5Me5), 24.0 (CMe2CN), 24.5 (C5H4CMe2), 25.4 (CMe2CN), 25.5 (C5H4CMe2), 43.4, 55.0 (2 × CMe2), 101.7, 113.2, 113.5, 116.2 (4× C5H4 CH), 121.4 (C5Me5), 127.8 (Ph CH), 140.9 (Ph Cipso), 142.8 (C5H4 Cipso), 177.4 (CN); signals due to 2 × Ph CH obscured by the solvent signal. IR (Nujol): 1635 (s, νCN), 1365 (m), 1233 (w), 1192 (w), 1140 (w), 1115 (w), 1044 (w), 1025 (w), 1001 (w), 955 (m), 869 (w), 855 (w), 814 (m), 802 (s), 781 (m), 758 (m), 730 (w), 704 (m), 613 (w) cm−1. EI-MS, m/z (relative abundance): 469 (49, [M]+•), 434 (7, [M − Cl]+), 365 (76), 330 (100), 321 (95), 218 (98, [Cp*TiCl]+). Anal. Calcd for C28H36NTiCl (469.93): C 71.56, H 7.72, N 2.98. Found: C 71.51, H 7.78, N 3.10. [(η5-C5Me5){η5-C5H4CMe2CMe2C(t-Bu)N-κN}TiCl] (5b). Synthesized from Cp*TiCl3 (591 mg, 2.04 mmol) and 4b·0.3THF (544 mg, 2.04 mmol) in THF (15 mL), the product was obtained as a red solid. Yield: 725 mg (79%). Crystallization from a concentrated toluene solution at −28 °C afforded dark red crystals of 5b (210 mg). Mp: 190−191 °C. NMR (C6D6) 1H: δ 0.62 (s, 3 H, CMe2CN), 0.98, 0.99 (2 × s, 3 H, C5H4CMe2), 1.19 (s, 3 H, CMe2CN), 1.20 (s, 9 H, CMe3), 1.81 (s, 15 H, C5Me5), 4.34, 5.44, 5.80, 6.17 (4 × m, 1 H, C5H4). 13C{1H}: δ 13.1 (C5Me5), 22.0 (CMe2CN), 23.9, 27.2 (C5H4CMe2), 27.8 (CMe2CN), 30.5 (CMe3), 42.6 (CMe2), 44.3 (CMe3), 58.2 (CMe2), 100.8, 112.0, 114.3, 115.9 (4 × C5H4 CH), 120.4 (C5Me5), 143.4 (C5H4 Cipso), 184.1 (CN). IR (Nujol): 1623 (m, νCN), 1559 (w), 1383 (m), 1367 (m), 1212 (w), 1192 (w), 1066 (w), 1042 (w), 971 (w), 864 (w), 849 (w), 823 (w), 807 (s), 773 (w), 724 (w) cm−1. EI-MS, m/z (relative abundance): 449 (6, [M]+•), 415 (21, [M − Cl]+), 393 (28), 367 (48), 331 (100), 218 (94, [Cp*TiCl]+). Anal. Calcd for C26H40NTiCl (449.94): C 69.40, H 8.96, N 3.11. Found: C 69.52, H 8.89, N 3.14. [(η5-C5Me5){η5-C5H4CMe2CMe2C(Ph)N-κN}ZrCl] (6a). This complex was synthesized from Cp*ZrCl3 (1.25 g, 3.77 mmol) and 4a· 0.5THF (1.14 g, 3.78 mmol) in THF (20 mL). The crude product was obtained as an oily solid, which was triturated with 2 × 20 mL of nhexane, and the resulting orange powder was dried under vacuum. Crystallization attempts failed, but the product was of sufficient purity to obtain analytical data. Yield: 1.72 g (89%). NMR (C6D6) 1H: δ 1.02, 1.03 (2 × s, 3 H, C5H4CMe2), 1.05, 1.12 (2 × s, 3 H, CMe2CN), 1.84 (s, 15 H, C5Me5), 4.97, 5.62, 6.03, 6.17 (4 × m, 1 H, C5H4), 6.98−7.37 (m, 5 H, Ph). 13C{1H}: δ 12.3 (C5Me5), 23.9 (CMe2C N), 25.7, 25.8 (2 × C5H4CMe2), 26.3 (CMe2CN), 43.3, 53.1 (2 × CMe2), 103.0, 111.9, 112.3, 112.5 (4 × C5H4 CH), 119.7 (C5Me5), 127.3, 127.5, 127.9 (3 × Ph CH), 142.7 (C5H4 Cipso), 143.4 (Ph Cipso), 184.0 (CN). IR (Nujol): 1643 (m, νCN), 1597 (w), 1365 (s), 1337 (m), 1243 (w), 1140 (w), 1128 (w), 1074 (w), 1025 (w), 1001 (w), 954 (w), 848 (w), 796 (m), 779 (w), 731 (w), 701 (s), 621 (w) cm−1. EI-MS, m/z (relative abundance): 511 (6, [M]+•), 408 (10, [M − PhCN]+), 393 (15), 77 (100, [C6H5]+). Anal. Calcd for C28H36NZrCl (513.25): C 65.52, H 7.07, N 2.73; Found: C 65.47, H 7.11, N 2.84. [(η5-C5Me5){η5-C5H4CMe2CMe2C(t-Bu)N-κN}ZrCl] (6b). Synthesized from Cp*ZrCl3 (665 mg, 2.04 mmol) and 4b·0.3THF (544 mg, 2.04 mmol) in THF (15 mL), the product was obtained as a yellow solid. Crystallization from a concentrated toluene solution at −28 °C afforded yellow crystals of 6b. Yield: 654 mg (65%). Mp: 195−196 °C. NMR (C6D6) 1H: δ 0.84 (s, 3 H, CMe2CN), 0.98, 1.00 (2 × s, 3 H, C5H4CMe2), 1.20 (s, 9 H, CMe3), 1.27 (s, 3 H, CMe2CN), 1.87 (s, 15 H, C5Me5), 4.84, 5.61, 5.84, 6.13 (4 × m, 1 H, C5H4). 13C{1H}: δ 12.3 (C5Me5), 22.0 (CMe2CN), 25.2, 26.5 (C5H4CMe2), 28.8 (CMe2CN), 30.5 (CMe3), 43.2 (CMe2), 44.4 (CMe3), 55.1 (CMe2), 102.5, 111.4, 111.8, 112.7 (4× C5H4 CH), 119.0 (C5Me5), 142.4 (C5H4 Cipso), 189.6 (CN). IR (Nujol): 1632 (s, νCN), 1366 (m), 1401 (w), 1211 (w), 1192 (w), 1041 (w), 968 (w), 856 (m), 852 (w), 810 (w), 796 (s), 713 (w), 635 (w) cm−1. EI-MS, m/z (relative abundance): 491 (15, [M]+•), 456 (6, [M − Cl]+), 434 (21, [M − tBu]+), 408 (61, [M − CN(t-Bu)]+), 393 (79), 365 (60), 91 (100). Anal. Calcd for C26H40NZrCl (493.26): C 63.31, H 8.17, N 2.84. Found: C 63.29, H 8.23, N 2.91. J


Article

Organometallics

15 H, C5Me5), 5.44, 5.55, 6.02, 6.94 (4 × m, 1 H, C5H4), 9.63 (s, 1 H, NH); isomer Z: δ 1.06, 1.20 (2 × s, 3 H, CMe2), 1.35 (s, 9 H, CMe3), 1.55, 1.58 (2 × s, 3 H, CMe2), 2.02 (s, 15 H, C5Me5), 5.08, 5.36, 5.98, 7.01 (4 × m, 1 H, C5H4), 9.38 (s, 1 H, NH). 13C{1H} (298 K): δ 12.7 (C5Me5), 23.9, 26.5 (2 × CMe2), 30.6 (CMe3), 44.4 (CMe3), 124.6 (C5Me5); remaining signals not observed due to line broadening. For 1 H VT NMR of compound 10b, see the Supporting Information. IR (Nujol): 1659 (s, νCN), 1627 (m), 1528 (w), 1407 (w), 1366 (sh) 1308 (w), 1265 (w), 1193 (w), 1156 (w), 1124 (w), 1025 (m), 964 (w), 922 (w), 889 (w), 847 (w), 804 (s), 731 (w), 693 (w), 668 (w) cm−1. Anal. Calcd for C26H41NZrCl2 (529.72): C 58.95, H 7.80, N 2.64. Found: C 58.72, H 7.65, N 2.50. General Procedure for the Synthesis of Iminium Salts. Ketimide complexes 5a/b or 6a/b were dissolved in toluene, and 4−6 molar equiv of HCl (as a 1 M solution in Et2O) was added slowly into a stirred solution of the complex. Within several minutes a precipitate formed. After approximately 1 h stirring the solution was removed from the precipitate and the solids were washed several times with Et2O and n-pentane and dried under vacuum. [(η5-C5Me5){η5-C5H4CMe2CMe2C(Ph)NH2}ZrCl2]+Cl− (11a). Prepared from 6a (400 mg, 0.78 mmol), the product was obtained as a white powder. Yield: 374 mg (82%). NMR (CDCl3) 1H: δ 1.41 (s, 6 H, CMe2CN), 1.56 (s, 6 H, C5H4CMe2), 2.01 (s, 15 H, C5Me5), 5.90, 6.31 (2 × apparent t, JHH = 2.7 Hz, 2 H, C5H4), 7.14−7.59 (m, 5 H, C6H5), 12.05, 13.47 (2 × br s, 1 H, NH2). 13C{1H}: δ 12.7 (C5Me5), 23.5 (C5H4CMe2), 24.6 (CMe2CN), 44.2, 53.1 (2 × CMe2), 110.3, 119.2 (C5H4 CH), 124.9 (C5Me5), 128.4, 128.8, 129.2 (3 × Ph CH), 133.5 (Ph Cipso), 137.6 (C5H4 Cipso), 196.9 (CN). IR (Nujol): 2800−2450 (br sh, νNH), 1659 (s, νCN), 1534 (w), 1493 (m), 1409 (w), 1366 (m), 1306 (w), 1235 (s), 1154 (m), 1141 (m), 1127 (m), 1120 (w), 998 (w), 983 (w), 923 (w), 820 (w), 809 (w), 744 (m), 708 (w), 700 (w), 568 (w) cm−1. Anal. Calcd for C28H38NZrCl3 (586.16): C 57.37, H 6.53, N 2.39. Found: C 57.67, H 6.42, N 2.24. [(η5-C5Me5){η5-C5H4CMe2CMe2C(t-Bu)NH2}ZrCl2]+Cl− (11b). Prepared from 6b (200 mg, 0.41 mmol), the product was obtained as a white powder. Yield: 179 mg (78%). Recrystallization by slow diffusion of Et2O into a CHCl3 solution yielded colorless crystals of 11b·CHCl3 (119 mg) suitable for X-ray diffraction. Mp: 138 °C. NMR (CDCl3) 1 H: δ 1.37 (s, 6 H, CMe2CN), 1.48 (s, 9 H, CMe3), 1.68 (s, 6 H, C5H4CMe2), 2.00 (s, 15 H, C5Me5), 5.90, 6.33 (2 × m, 2 H, C5H4), 11.35, 12.99 (2 × s, 1 H, NH2). 13C{1H}: δ 12.6 (C5Me5), 24.1 (C5H4CMe2), 26.8 (CMe2CN), 31.1 (CMe3), 44.9, 45.0 (2 × CMe2), 55.4 (CMe3), 110.2, 119.3 (C5H4 CH), 124.9 (C5Me5), 137.7 (C5H4 Cipso), 208.7 (CN). IR (Nujol): 2800−2500 (br sh, νNH), (w), 1657 (s, νCN), 1532 (m), 1378 (s), 1232 (w), 1190 (w), 1153 (w), 1126 (m), 1108 (w), 1016 (m), 921 (w), 885 (w), 870 (w), 805 (m), 730 (w), 693 (w), 633 (w), 531 (w) cm−1. Anal. Calcd for C26H42NZrCl3 (566.18): C 55.15, H 7.48, N 2.47. Found: C 55.26, H 7.56, N 2.33. Formation of a decomposition product was observed in solutions of complexes 10 and 11, which was identified as the complex 12Zr: NMR (toluene-d8) 1H: δ 1.77 (s, 15 H, C5Me5), 2.02 (dd, 4JHH = 1.5 and 0.8 Hz, 3 H, CMe), 5.00 (dq, 2JHH = 4JHH = 1.5 Hz, 1 H, CH2), 5.30 (dq, 2JHH = 1.5 Hz, 4JHH = 0.8 Hz, 1 H, CH2), 5.56, 6.09 (2 × apparent t, JHH = 2.8 Hz, 2 H, C5H4). 13C{1H}: δ 12.2 (C5Me5), 21.7 (CMe), 112.2 (C5H4 CH), 113.3 (CH2), 114.4 (C5H4 CH), 123.8 (C5Me5), 133.4 (CCH2), 136.9 (C5H4 Cipso). EI-MS, m/z (relative abundance): 400 (52, [M]+•), 364 (70, [M − HCl]+), 297 (81), 267 (43), 91 (100). [(η5-C5Me5){η5-C5H4CMe2CMe2C(Ph)NH2}TiCl2]+Cl− (13a). This complex was prepared from 5a (160 mg, 0.34 mmol) as a red powder. Yield: 129 mg (70%). NMR (CDCl3) 1H: δ 1.42 (s, 6 H, CMe2CN), 1.58 (s, 6 H, C5H4CMe2), 2.02 (s, 15 H, C5Me5), 5.90, 6.27 (2 × apparent t, JHH = 2.7 Hz, 2 H, C5H4), 7.14−7.48 (m, 5 H, C6H5), 12.34, 13.54 (2 × br s, 1 H, NH2). 13C{1H}: δ 13.8 (C5Me5), 22.8 (C5H4CMe2), 24.5 (CMe2CN), 44.9, 53.6 (2 × CMe2), 112.4, 124.5 (C5H4 CH), 128.4, 128.7, 129.2 (3 × Ph CH), 130.5 (C5Me5), 133.6 (Ph Cipso), 140.5 (C5H4 Cipso), 196.8 (CN). IR (Nujol): 2700 (br, νNH), 1660 (s, νCN), 1534 (m), 1377 (m), 1240 (w), 1153 (w), 1141

(s), 1307 (w), 1237 (m), 1153 (w), 1098 (w), 1016 (w), 982 (w), 892 (w), 850 (w), 799 (s), 728 (m), 689 (w), 623 (w), 504 (w) cm−1. EIMS, m/z (relative abundance): 379 (20, [M]+•), 344 (14, [M − Cl]+), 338 (77, [M − MeCN]+), 325 (65), 302 (80), 190 (82, [CpZrCl]+), 91 (100). Anal. Calcd for C18H24NZrCl (381.05): C 56.73, H 6.35, N 3.68. Found: C 56.88, H 6.51, N 3.51. [(η5-C5Me5){η5-C5H4CMe2CMe2C(t-Bu)N-κN}HfCl] (8). Synthesized from Cp*HfCl3 (686 mg, 1.63 mmol) and 4b·0.3THF (435 mg, 1.63 mmol) in THF (15 mL), the product was isolated as a light yellow solid. Yield: 814 mg (86%). Crystallization by slow evaporation of a concentrated toluene solution under vacuum afforded pale yellow crystals of 8 (310 mg). Mp: 190−191 °C. NMR (C6D6) 1H: δ 0.85 (s, 3 H, CMe2CN), 0.98, 1.02 (2 × s, 3 H, C5H4CMe2), 1.31 (s, 3 H, CMe2CN), 1.21 (s, 9 H, CMe3), 1.91 (s, 15 H, C5Me5), 4.83, 5.64, 5.76, 5.99 (4× m, 1 H, C5H4). 13C{1H}: δ 12.1 (C5Me5), 22.1 (CMe2CN), 25.2, 26.5 (C5H4CMe2), 28.7 (CMe2CN), 30.4 (CMe3), 42.9 (CMe2), 45.2 (CMe3), 55.5 (CMe2), 100.5, 110.2, 110.5, 111.8 (4 × C5H4 CH), 117.6 (C5Me5), 141.8 (C5H4 Cipso), 189.8 (C N). IR (Nujol): 1641 (s, νCN), 1402 (w), 1385 (m), 1366 (m), 1357 (w), 1233 (w), 1212 (w), 1194 (w), 1128 (w), 1062 (w), 1041 (m), 968 (m), 931 (w), 915 (w), 856 (m), 854 (m), 813 (m), 800 (s), 759 (w), 726 (m), 716 (m), 635 (w), 548 (w) cm−1. EI-MS, m/z (relative abundance): 581 (23, [M]+•), 524 (21, [M − t-Bu]+), 498 (54, [M − CN(t-Bu)]+), 483 (91), 455 (93), 57 (100). Anal. Calcd for C26H40NHfCl (580.53): C 53.79, H 6.95, N 2.41. Found: C 53.91, H 7.01, N 2.40. Protonation Reactions of Complexes 6. General Procedures for the Synthesis of Compounds 10. Method A: Ketimide complex 6a or 6b was treated with 1 equiv of PhNH3+Cl− in CH2Cl2. The color of the solution changed within a few minutes from yellow to pale yellow. After 30 min stirring at room temperature all volatiles were removed under vacuum, and the resulting solids were washed quickly with Et2O and n-pentane and dried in vacuo. Method B: Equimolar amounts of ketimide complex 6a or 6b and the corresponding iminium salt (11a or 11b, see below) were dissolved in a small amount of CH2Cl2. After 30 min stirring at room temperature the solution was evaporated under vacuum, giving solid products 10. [(η5-C5Me5){η5-C5H4CMe2CMe2C(Ph)NH}ZrCl2] (10a). Following method A, this complex was synthesized from 6a (1.13 g, 2.19 mmol) and PhNH3+Cl− (284 mg, 2.19 mmol). The product was recrystallized from a concentrated CH2Cl2 solution at −30 °C to give pale yellow crystals (770 mg, 55%). Method B was applied using 6a (355 mg, 0.69 mmol) and 11a (405 mg, 0.69 mmol), affording 10a in virtually quantitative yield. Mp: 110 °C dec. NMR (328 K, CDCl3) 1H: δ 1.26, 1.42 (2 × s, 6 H, CMe2), 1.95 (s, 15 H, C5Me5), 5.95 (br s, 4 H, C5H4), 7.11−7.40 (m, 5 H, Ph), 9.44 (br s, 1 H, NH). 1H (238 K, major isomer E): δ 1.10, 1.15, 1.30, 1.57 (4 × s, 3 H, CMe2), 1.86 (s, 15 H, C5Me5), 5.14, 5.33, 6.05, 7.05 (4 × m, 1 H, C5H4), 7.10−7.44 (m, 5 H, Ph), 9.28 (s, 1 H, NH). 13C{1H} (298 K): δ 12.6 (C5Me5), 25.1 (CMe2), 48.3 (CMe2), 122.0 (C5Me5), 125.3, 128.6, 129.2 (3 × Ph CH), 143.8 (Ph Cipso), 187.7 (CN); signals of C5H4 CH and Cipso not observed due to line broadening. For 1H VT NMR of compound 10a, see the Supporting Information. IR (Nujol): 3316 (m, νNH), 1612 (s, νCN), 1592 (w), 1481 (m), 1418 (m), 1400 (m), 1264 (w), 1238 (w), 1197 (w), 1161 (w), 1142 (w), 1128 (w), 1112 (w), 1053 (w), 1027 (w), 965 (w), 949 (w), 919 (w), 868 (m), 850 (m), 813 (m), 805 (s), 785 (w), 715 (s), 703 (w), 632 (w) cm−1. Anal. Calcd for C28H37NZrCl2·CH2Cl2 (634.63): C 54.88, H 6.19, N 2.21. Found: C 54.56, H 6.10, N 2.15. [(η5-C5Me5){η5-C5H4CMe2CMe2C(t-Bu)NH}ZrCl2] (10b). This complex was synthesized following method B using 6b (300 mg, 0.53 mmol) and 11b (261 mg, 0.53 mmol). Evaporation of the solvent afforded 10b in nearly quantitative yield as a pale yellow solid. Crystallization attempts failed, as they yielded only crystals of 11b (a mixture of 10b and 6b remained in the mother liquor). NMR (323 K, CDCl3) 1H: δ 1.27 (s, 9 H, CMe3), 1.31, 1.46 (2 × s, 6 H, CMe2), 2.02 (s, 15 H, C5Me5), 5.97, 6.12 (2 × br s, 2 H, C5H4), 9.69 (br s, 1 H, NH). 1H (238 K, tentative assignment) isomer E: δ 1.04, 1.06 (2 × s, 3 H, CMe2), 1.37 (s, 9 H, CMe3), 1.44, 1.57 (2 × s, 3 H, CMe2), 1.96 (s, K


Article

Organometallics

(br s, 3 H, CMe2), 3.23 (br s, 12H, NMe2), 5.26, 5.49, 5.91, 6.02 (4 × br s, 1 H, C5H4). 13C{1H}: δ 23.4, 24.7, 26.2, 27.2 (4 × br s, CMe2), 30.3 (CMe3), 41.4 (CMe2), 42.5 (CMe3), 49.2 (NMe2), 62.4 (CMe2), 108.1, 108.5 (2 × br s, C5H4 CH), 137.4 (C5H4 Cipso), 186.1 (CN). [{η5-C5H4CMe2CMe2C(Ph)N-κN}TiCl2] (16a). To a solution of 14a (200 mg, 0.53 mmol) in toluene (10 mL) was added Me3SiCl (0.4 mL, 3.18 mmol) with stirring at room temperature. The color of the mixture changed immediately from red to deep green-brown. After 1 h, the solution was filtered and all volatiles were removed under reduced pressure. The solid residue was washed with n-pentane and dried under vacuum to give 16a as a dark brown solid. Yield: 153 mg (78%). Recrystallization by slow diffusion of n-pentane into a toluene solution afforded deep brown crystals (101 mg) suitable for X-ray diffraction. Mp: 161−162 °C. NMR (toluene-d8) 1H: δ 0.82 (s, 6 H, C5H4CMe2), 0.91 (s, 6 H, CMe2CN), 5.53, 6.33 (2 × apparent t, JHH = 2.7 Hz, 2 H, C5H4), 6.94−7.10 (m, 5 H, Ph). 13C{1H}: δ 24.6 (C5H4CMe2), 25.3 (CMe2CN), 41.7, 65.7 (2 × CMe2), 117.2, 118.0 (2 × C5H4 CH), 127.8, 128.4, 129.8 (3× Ph CH), 136.7 (Ph Cipso), 143.2 (C5H4 Cipso), 195.0 (CN). IR (Nujol): 1609 (vs, νCN), 1400 (w), 1379 (s), 1241 (w), 1234 (w), 1188 (w), 1140 (w), 1126 (w), 1112 (w), 1048 (w), 1001 (w), 958 (w), 938 (w), 900 (w), 828 (s), 793 (m), 773 (m), 738 (m), 711 (m), 697 (m), 549 (w), 485 (w), 444 (w), 410 (w) cm−1. EIMS, m/z (relative abundance): 369 (13, [M]+•), 333 (100, [M − HCl]+), 106 (100). Anal. Calcd for C16H25NTiCl2 (370.16): C 58.40, H 5.72, N 3.78. Found: C 58.65, H 5.77, N 3.43. [{η5-C5H4CMe2CMe2C(t-Bu)N-κN}TiCl2] (16b). This compound was synthesized in the same manner as 16a using the mixture 15a/b (840 mg, 2.32 mmol of “Ti”) directly from the described experiment and Me3SiCl (1.5 mL, 11.8 mmol) and was obtained as a deep brown solid. Yield: 528 mg (65% based on TiCl2(NMe2)2). Recrystallization by slow diffusion of n-pentane into a toluene solution afforded deep brown crystals (385 mg) suitable for X-ray diffraction. Mp: 150 °C. NMR (toluene-d8) 1H: δ 0.75 (s, 6 H, C5H4CMe2), 0.95 (s, 6 H, CMe2CN), 1.02 (s, 9 H, tBu), 5.38 (br s, 2 H, C5H4), 6.30 (apparent t, JHH = 2.7 Hz, 2 H, C5H4). 13C{1H}: δ 24.6 (2× CMe2) 29.0 (CMe3), 42.5 (CMe2), 44.0 (CMe3), 67.0 (CMe2), 116.4, 117.5 (2× C5H4 CH), 142.0 (C5H4 Cipso), 202.8 (CN). IR (Nujol): 1599 (vs, νCN), 1392 (w), 1380 (m), 1372 (m), 1366 (m), 1215 (w), 1193 (w), 1126 (w), 1047 (w), 971 (m), 926 (w), 916 (w), 894 (w), 880 (w), 817 (s), 748 (m), 643 (w), 559 (w), 484 (w) cm−1. EI-MS, m/z (relative abundance): 349 (11, [M]+•), 313 (100, [M − HCl]+), 188 (100). Anal. Calcd for C16H25NTiCl2 (350.17): C 54.88, H 7.20, N 4.00. Found: C 54.92, H 7.05, N 3.88. Polymerization Experiments. The polymerizations were performed at constant ethylene pressure (3 × 105 Pa) in a 250 mL Büchi glass double-jacketed autoclave equipped with a magnetic stirrer (at 800 rpm). The hot autoclave was evacuated three times, filled with argon, and charged with toluene and a solution of methylaluminoxane (10 wt % in toluene). After 15 min stirring at the appropriate pressure of ethylene and temperature the reactor was vented and the polymerization was started by injecting the desired amount of catalyst precursor (stock solution in toluene) under a stream of ethylene and immediately pressurized to 3 × 105 Pa. The final volume of the polymerization solution was 50 mL, and [Zr] = 5.0 × 10−6 mol L−1 for all experiments. The autoclave temperature was kept constant during the reaction by using an external Pt100 sensor connected to a Julabo F31-C bath. The consumption of ethylene was followed in each experiment using a calibrated mass flow meter (Bronkhorst, ELFLOW), which was controlled by a Bronkhorst High-Tech modular digital readout and control system. After the appropriate time, the reactor was vented and the residual mixture in the autoclave was quenched with 80 mL of a 10% solution of HCl in ethanol. The precipitated polyethylene was stirred for 1 h, filtered off on a glass frit, rinsed repeatedly with ethanol and acetone, and dried under vacuum to constant weight. Xray Crystallography. Crystals suitable for single-crystal X-ray diffraction analysis were selected directly from the recrystallized materials obtained either as described above (2: dark red plate, 0.45 × 0.40 × 0.22 mm3; 5a: dark red prism, 0.61 × 0.54 × 0.38 mm3; 5b: red prism, 0.32 × 0.16 × 0.16 mm3; 8: yellow fragment, 0.22 × 0.15 × 0.15

(w), 1129 (w), 1063 (w), 1026 (w), 924 (w), 897 (w), 879 (w), 831 (w), 818 (w), 811 (w), 783 (w), 744 (m), 733 (m), 708 (m), 700 (w), 660 (w), 568 (w) cm−1. Anal. Calcd for C28H38NTiCl3 (542.84): C 61.95, H 7.06, N 2.58. Found: C 62.13, H 7.26, N 2.46. [(η5-C5Me5){η5-C5H4CMe2CMe2C(t-Bu)NH2}TiCl2]+Cl− (13b). This complex was prepared from 5b (200 mg, 0.44 mmol) as a red powder. Yield: 154 mg (66%). Recrystallization by slow diffusion of Et2O into a CH2Cl2 solution yielded red crystals of 13b·CH2Cl2 (96 mg) suitable for X-ray diffraction. Mp: 138 °C. NMR (CDCl3) 1H: δ 1.38 (s, 6 H, CMe2CN), 1.53 (s, 9 H, CMe3), 1.71 (s, 6 H, C5H4CMe2), 2.03 (s, 15 H, C5Me5), 5.95, 6.32 (2 × m, 2 H, C5H4), 10.99, 13.28 (2 × s, 1 H, NH2). 13C{1H}: δ 13.8 (C5Me5), 23.5 (C5H4CMe2), 26.8 (CMe2C N), 31.2 (CMe3), 44.9, 45.8 (2 × CMe2), 55.8 (CMe3), 112.1, 125.1 (C5H4 CH), 130.8 (C5Me5), 139.7 (C5H4 Cipso), 209.1 (CN). IR (Nujol): 2800−2500 (br sh, νNH), 1657 (s, νCN), 1527 (w), 1383 (s), 1266 (w), 1191 (w), 1156 (w), 1157 (w), 1124 (m), 1106 (w), 1015 (m), 920 (w), 889 (w), 870 (w), 829 (m), 731 (w), 692 (w), 631 (w), 537 (w) cm−1. Anal. Calcd for C26H42NTiCl3 (522.86): C 59.72, H 8.10, N 2.68. Found: C 59.80, H 8.12, N 2.58. Compounds 13 slowly decomposed in solution to produce compound 12Ti (Ti analogue to 12Zr) as observed by NMR. Data for 12Ti: NMR (CDCl3) 1H: δ 2.05 (s, 15 H, C5Me5), 2.07 (dd, 4JHH = 1.5 and 0.9 Hz, 3 H, CMe), 5.18 (dq, 2JHH = 4JHH = 1.5 Hz, 1 H,  CH2), 5.37 (dq, 2JHH = 1.5 Hz, 4JHH = 0.9 Hz, 1 H, CH2), 5.96, 6.27 (2 × apparent t, JHH = 2.8 Hz, 2 H, C5H4). 13C{1H}: δ 13.6 (C5Me5), 21.5 (CMe), 114.3 (C5H4 CH), 115.3 (CH2), 119.8 (C5H4 CH), 129.7 (C5Me5), 136.3 (C5H4Cipso), 137.2 (CCH2). Preparation of Titanium Half-Sandwich Complexes. Equimolar amounts of TiCl2(NMe2)2 and dilithium salt 4a or 4b were mixed and dissolved in THF upon cooling the mixture to −78 °C. The solution was stirred, allowed to warm slowly to room temperature, and kept at these conditions for 12 h. All volatiles were removed under reduced pressure, and the residue was extracted with toluene. Evaporation of the extract afforded the product 14a or 14b+15, respectively. [{η5-C5H4CMe2CMe2C(Ph)N-κN}TiCl(NMe2)] (14a). Synthesized from TiCl2(NMe2)2 (250 mg, 1.21 mmol) and 4a (320 mg, 1.21 mmol), compound 14a was obtained as the sole product in the form of a red oil, which solidified upon standing overnight into a red solid. Yield: 412 mg (90%). Recrystallization was performed by slow evaporation of the solvent from a toluene solution under vacuum, which afforded red crystals (221 mg) suitable for X-ray diffraction. Mp: 140 °C. NMR (C6D6) 1H: δ 0.74, 1.04 (2 × s, 3 H, CMe2CN), 1.00, 1.02 (2 × s, 3 H, C5H4CMe2), 3.20 (s, 6H, NMe2), 5.52, 5.64, 6.04, 6.61 (4 × m, 1 H, C5H4), 7.14−7.25 (m, 5 H, C6H5). 13C{1H}: δ 24.3 (CMe 2 CN), 24.5 (C 5 H 4 CMe 2 ), 24.9 (CMe 2 CN), 25.7 (C5H4CMe2), 40.9 (CMe2), 47.0 (NMe2), 61.8 (CMe2), 110.6, 112.4, 113.8, 115.6 (4 × C5H4 CH), 127.3, 128.1, 128.2 (3 × Ph CH), 139.2 (C5H4 Cipso), 140.5 (Ph Cipso), 185.8 (CN). IR (Nujol): 1635 (vs, νCN), 1422 (w), 1366 (m), 1245 (w), 1148 (w), 1128 (w), 1051 (w), 955 (w), 920 (m), 864 (w), 819 (w), 810 (w), 788 (w), 728 (w), 712 (w), 697 (w), 646 (w), 621 (w), 584 (w) cm−1. EI-MS, m/z (relative abundance): 378 (26, [M]+•), 333 (82, [M − NMe2]+), 275 (83, [M − PhCN]+), 106 (100). Anal. Calcd for C20H27N2TiCl (378.79): C 63.41, H 7.19, N 7.40. Found: C 63.36, H 7.08, N 7.52. When the precursor 4b (710 mg, 2.90 mmol) was reacted with TiCl2(NMe2)2 (600 mg, 2.90 mmol), a mixture of two compounds, 14b and 15 (molar ratio 1:1.4 identified by NMR), was obtained in the form of a red oil (yield: 840 mg). This mixture was directly used for the preparation of 16b. [{η5 -C 5 H 4 CMe 2 CMe 2 C(t-Bu)N-κN}TiCl(NMe 2 )] (14b). NMR (C6D6) 1H: δ 0.55 (s, 3 H, CMe2CN), 0.85, 0.95 (2 × s, 3 H, C5H4CMe2), 1.15 (s, 9 H, CMe3), 1.16 (s, 3 H, CMe2CN), 3.09 (s, 6H, NMe2), 5.29, 5.39, 5.95, 6.47 (4 × m, 1 H, C5H4). 13C{1H}: δ 22.7 (CMe2CN), 24.4, 25.7 (C5H4CMe2), 26.7 (CMe2CN), 29.6 (CMe3), 41.8 (CMe2), 43.4 (CMe3), 46.7 (NMe2), 63.2 (CMe2), 110.5, 111.7, 112.7, 115.0 (4 × C5H4 CH), 138.1 (C5H4 Cipso), 191.3 (C N). [{η5-C5H4CMe2CMe2C(t-Bu)N-κN}Ti(NMe2)2] (15). NMR (C6D6) 1 H: δ 0.79, 0.98, 1.09 (3 × br s, 3 H, CMe2), 1.25 (s, 9 H, CMe3), 1.30 L


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Organometallics mm3; 10a·CH2Cl2: pale yellow prism, 0.48 × 0.33 × 0.20 mm3; 11b· CHCl3: colorless plate, 0.62 × 0.23 × 0.20 mm3; 13b·CH2Cl2: red prism, 0.47 × 0.38 × 0.33 mm3; 14a: red prism, 0.45 × 0.44 × 0.28 mm3; 16a: green-brown bar, 0.45 × 0.15 × 0.11 mm3; 16b: greenbrown plate, 0.48 × 0.38 × 0.34 mm3) or as follows: by slow evaporation of a toluene solution under vacuum (6b: yellow prism, 0.32 × 0.29 × 0.28 mm3), by the same method using a benzene-d6 solution (7b: yellow prism, 0.56 × 0.27 × 0.20 mm3), or by a slow diffusion of n-hexane into a toluene solution at 4 °C (9: dark redbrown rhombohedron, 0.52 × 0.41 × 0.26 mm3). Diffraction data were collected on a Bruker Apex II diffractometer equipped with a Cryostream Cooler (Oxford Cryosystems) at 150(1) K using graphitemonochromatized Mo Kα radiation (λ = 0.710 73 Å) and analyzed with the Bruker SAINT program package.29 Data for all compounds were corrected for absorption using a multiscan method incorporated in the diffractometer software. The structures were solved by direct methods (SHELXS-9730) and refined by full-matrix least-squares routine based on F2 (SHELXL-9730). Non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were included in their calculated positions and treated as riding atoms with Uiso(H) assigned to a multiple of Ueq of their bonding carbon atom except for hydrogen atoms of the imine/iminium moieties in the structures of 10a·CH2Cl2, 11b·CHCl3, and 13b·CH2Cl2, which were localized on a difference Fourier map and isotropically refined. The structure of compound 9 was refined with two equally occupied disordered positions of the N−C(Me)CMe2 moiety and disordered Cp* rings with occupancies 0.155:0.845 (see Figure S2 in the Supporting Information). Selected crystallographic data for all compounds are given in Table S1 in the Supporting Information. Geometric parameters and structural drawings were obtained with a recent version of the Platon program.31

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08531S) and the Ministry of Education, Youth, and Sports of the Czech Republic (project no. LO1504) is acknowledged.

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(1) Reviews: (a) Pinkas, J.; Lamač, M. Coord. Chem. Rev. 2015, 296, 45−90. (b) Erker, G. Organometallics 2011, 30, 358−368. (c) Erker, G.; Kehr, G.; Fröhlich, R. Coord. Chem. Rev. 2006, 250, 36−46. (d) Erker, G. Polyhedron 2005, 24, 1289−1297. (e) Erker, G.; Kehr, G.; Fröhlich, R. J. Organomet. Chem. 2004, 689, 1402−1412. (2) Selected examples: (a) Allen, O. R.; Croll, L.; Gott, A. L.; Knox, R. J.; McGowan, P. C. Organometallics 2004, 23, 288−292. (b) Causey, P. W.; Baird, M. C.; Cole, S. P. C. Organometallics 2004, 23, 4486− 4494. (c) Strohfeldt, K.; Tacke, M. Chem. Soc. Rev. 2008, 37, 1174− 1187. (d) Gansäuer, A.; Winkler, I.; Worgull, D.; Lauterbach, T.; Franke, D.; Selig, A.; Wagner, L.; Prokop, A. Chem. - Eur. J. 2008, 14, 4160−4163. (e) Gansäuer, A.; Winkler, I.; Worgull, D.; Franke, D.; Lauterbach, T.; Okkel, A.; Nieger, M. Organometallics 2008, 27, 5699− 5707. (f) Mijatović, S.; Bulatović, M.; Mojić, M.; Stošić-Grujičić, S.; Miljković, D.; Maksimović-Ivanić, D.; Gómez-Ruiz, S.; Pinkas, J.; Horácě k, M.; Kaluđerović, G. N. J. Organomet. Chem. 2014, 751, 361− 367. (g) Hodík, T.; Lamač, M.; Št’astná, L. C.; Karban, J.; Koubková, L.; Hrstka, R.; Cı ́sařová, I.; Pinkas, J. Organometallics 2014, 33, 2059− 2070. (h) Ceballos-Torres, J.; Prashar, S.; Fajardo, M.; Chicca, A.; Gertsch, J.; Pinar, A. B.; Gómez-Ruiz, S. Organometallics 2015, 34, 2522−2532. (3) Recent examples from our laboratory: (a) Lamač, M.; Horácě k, M.; Kubišta, J.; Pinkas, J. Inorg. Chim. Acta 2011, 373, 291−294. (b) Strašaḱ , T.; Sýkora, J.; Lamač, M.; Kubišta, J.; Horácě k, M.; Gyepes, R.; Pinkas, J. Organometallics 2013, 32, 4122−4129. (4) Pinkas, J.; Gyepes, R.; Kubišta, J.; Horácě k, M.; Lamač, M. J. Organomet. Chem. 2011, 696, 2364−2372. (5) (a) Pinkas, J.; Císařová, I.; Kubišta, J.; Horácě k, M.; Lamač, M. Dalton Trans. 2013, 42, 7101−7110. (b) Horácě k, M.; Gyepes, R.; Císařová, I.; Pinkas, J.; Kubišta, J.; Lamač, M. J. Organomet. Chem. 2015, 787, 56−64. (c) Thiel, I.; Lamač, M.; Jiao, H.; Spannenberg, A.; Hapke, M. Organometallics 2013, 32, 3415−3418. (6) Erker, G.; Kehr, G.; Fröhlich, R. Organometallics 2007, 27, 3−14. (7) Reviews: (a) Braunschweig, H.; Breitling, F. M. Coord. Chem. Rev. 2006, 250, 2691−2720. (b) Rodrigues, A.-S.; Carpentier, J.-F. Coord. Chem. Rev. 2008, 252, 2137−2154. (c) Klosin, J.; Fontaine, P. P.; Figueroa, R. Acc. Chem. Res. 2015, 48, 2004−2016. (d) Okuda, J. Dalton Trans. 2003, 2367−2378. (8) Reviews: (a) Ferreira, M. J.; Martins, A. M. Coord. Chem. Rev. 2006, 250, 118−132. (b) Nomura, K. Dalton Trans. 2009, 8811−8823. (c) Nomura, K.; Liu, J. Y. Dalton Trans. 2011, 40, 7666−7682. (9) (a) Boche, G. Angew. Chem., Int. Ed. Engl. 1989, 28, 277−297. (b) Croisat, D.; Seydenpenne, J.; Strzalko, T.; Wartski, L.; Corset, J.; Froment, F. J. Org. Chem. 1992, 57, 6435−6447. (c) Carlier, P. R.; Lucht, B. L.; Collum, D. B. J. Am. Chem. Soc. 1994, 116, 11602−11603. (d) Carlier, P. R.; Lo, C. W. S. J. Am. Chem. Soc. 2000, 122, 12819− 12823. (10) Compounds 4a−c exhibit limited solubility in THF. For the use of DMSO-d6 in NMR spectroscopy of alkali metal cyclopentadienides, amides, and related compounds, see: Tay, B. Y.; Wang, C.; Stubbs, L. P.; Jacob, C.; van Meurs, M. J. Organomet. Chem. 2011, 696, 3431− 3435. (11) Structures of similar imido-bridged dimers are known: (a) Vroegop, C. T.; Teuben, J. H.; Bolhuis, F.; Vanderlinden, J. G. M. J. Chem. Soc., Chem. Commun. 1983, 550−552. (b) Grigsby, W. J.; Olmstead, M. M.; Power, P. P. J. Organomet. Chem. 1996, 513, 173− 180. (c) Lancaster, S. J.; Al-Benna, S.; Thornton-Pett, M.; Bochmann, M. Organometallics 2000, 19, 1599−1608. (d) Ascenso, J. R.; de Azevedo, C. G.; Dias, A. R.; Duarte, M. T.; Eleuterio, I.; Ferreira, M. J.; Gomes, P. T.; Martins, A. M. J. Organomet. Chem. 2001, 632, 17−26. (e) Tsurugi, H.; Nagae, H.; Mashima, K. Chem. Commun. 2011, 47, 5620−5622. (12) Armstrong, D. R.; Henderson, K. W.; Little, I.; Jenny, C.; Kennedy, A. R.; McKeown, A. E.; Mulvey, R. E. Organometallics 2000, 19, 4369−4375.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00019. Further experimental details; tables of crystallographic data for all structures and depictions of structures 6b, 8, 9, 11b (symmetrically independent molecule 2), 13b, 16b (molecule 2); 1H NMR spectra of compounds 1, 4a−c; VT 1H NMR spectra for compounds 10a, 10b, 14b/15, 16a, 16b; and corresponding Eyring plots and extracted thermodynamic parameters (PDF) Crystallographic data in CIF format (which have also been deposited at the Cambridge Crystallographic Data Centre under CCDC reference numbers 1430842− 1430854 and can be obtained free of charge via www. ccdc.cam.ac.uk/data_request/cif) for compounds 2, 5a, 5b, 6b, 7b, 8, 9, 10a·CH2Cl2, 11b·CHCl3, 13b·CH2Cl2, 14a, 16a, 16b (ZIP)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +420 26605 3735. Fax: +420 28658 2307. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. Róbert Gyepes for X-ray data processing, Dr. Lidmila Petrusová for the determination of melting points, and Dr. Jiřı ́ Kubišta for EI-MS measurements. Financial support from the Czech Science Foundation (project no. GA14M


Article

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