Synthesis and Reactivity of Group 4 Metal Benzyl Complexes

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Synthesis and Reactivity of Group 4 Metal Benzyl Complexes Supported by Carbazolide-Based PNP Pincer Ligands Gudrun T. Plundrich, Hubert Wadepohl, and Lutz H. Gade* Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany S Supporting Information *

ABSTRACT: This study focuses on the viability of the carbazolebased Cbzdiphos PNP pincer ligand as a stabilizing element for group 4 metal complexes, and both the diphenylphosphino- and diisopropylphosphino-substituted Cbzdiphos protioligands 1PhH and 1iPrH were used. Treatment of the lithiated protioligands with the corresponding chlorido precursor compounds of the metals (titanium, zirconium, and hafnium) afforded the trichlorido complexes [(CbzdiphosiPr)MCl3] 2iPrM and [(CbzdiphosPh)MCl3] 2PhM (M = Ti, Zr, Hf), which were converted to the corresponding iodido complexes [(CbzdiphosiPr)MI3] 3iPrM and [(CbzdiphosPh)MI3] 3PhM (M = Ti, Zr, Hf) by reaction with an excess of trimethylsilyl iodide. Reaction of 2iPrTi and 3PhTi with 1 equiv of dibenzyl magnesium tetrahydrofuran adduct led to the formation of the alkylidene complexes 4iPrTi and 5PhTi, respectively, while the zirconium and hafnium complexes 2iPrZr and 3PhZr/Hf formed the cyclometalated monoalkyl compounds [(CbzdiphosiPrCH)ZrBnCl] 6iPrZr as well as [(CbzdiphosPh-CH)MBnX] 6PhHf (X = Cl) and 7PhZr/Hf (X = I) under analogous reaction conditions. On the other hand, stirring 2PhZr with 0.25 equiv of tetrabenzyl zirconium afforded [(CbzdiphosPh)ZrBnCl2] (8PhZr), which contained the PNP ligand intact, while its alkylation with benzyl potassium led to the formation of the cyclometalated monobenzyl complex [(CbzdiphosPh-CH)ZrBnCl] (6PhZr). The remaining coordination site occupied by the halogenido ligand in the cyclometalated monobenzyl complexes [(Cbzdiphos-CH)MBnX] 6iPrZr, 6PhZr/Hf, and 7PhZr/Hf was readily benzylated by treatment with benzyl potassium to afford the cyclometalated dibenzyl complexes [(Cbzdiphos-CH)MBn2] 9iPrZr and 9PhZr/Hf. Further reaction of 9PhZr with an excess of benzyl potassium led to the formation of the anionic tribenzyl zirconium ate complex [(Cbzdiphos-CH)MBn3]K (10PhZr). Upon heating a solution of 8PhZr in the presence of 1 mol equiv of trimethyl phosphine, one of the ligand methylene groups was deprotonated, yielding the cyclometalated complex [(CbzdiphosPhCH)ZrCl2(PMe3)] 11PhZr. Finally, reaction of 7PhZr with methylene triphenylphosphorane produced the ortho-metalated product [(CbzdiphosPh-CH)Zr(o-C6H4PPh2CH2)I] (12PhZr), which is characterized by a slightly puckered five-membered Zr− C(48)−P(3)−C(49)−C(50) metallacycle.

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by Sacconi et al. in the late 1960s.39 Fryzuk et al. reported the synthesis of a similar PNP ligand with an SiMe2CH2 backbone (B)40 and a number of early transition metal complexes which gave rise to remarkable results in the activation of small molecules.41−46 In 2003 Liang et al. reported the synthesis of a o-phenylene-linked PNP pincer ligand C,47 which was modified by Ozerov et al. in 2004. In the field of early transition metals, studies by Ozerov48−50 and Mindiola50−59 demonstrated that this PNP ligand is particularly suited to stabilize alkyl, alkylidene, and alkylidyne species. Ozerov et al. also described the synthesis of ligand D and its chemistry of the late transition metals. 60−62 Cui, Hou, and co-workers prepared the carbazolide-based PNP ligand (E) with a large bite angle and studied its rare-earth metal complexes.63 Recently, we reported the synthesis of the carbazolide-based PNP pincer ligand Cbzdiphos which bears two methylene diphenylphosphine groups in the wingtip position of the ligand backbone.64 First studies of its application in the coordination

INTRODUCTION The reactivity of a metal complex is decisively influenced by the choice of the appropriate ancillary ligand. This is equally relevant in the development of new molecular catalysts and the stabilization of reactive molecular fragments at the metal with the aim of isolating key active species and intermediates. For low-valent late transition metal complexes, soft phosphines1−4 and N-heterocyclic carbenes5−9 have been employed as kinetically robust anchors within polydentate ligand systems, whereas polydentate amido ligands have found widespread application for complexes of high-valent Lewis-acidic early transition metals.10−13 Amidophosphine ligands combining hard nitrogen and sof t phosphorus donor functionalities have been studied extensively because they combine the achetypal anchor functions for the two regimes of electron-rich and electron-poor metal atoms and thus act as versatile spectator ligands.14−31 In particular, PNP pincers, which constrain metals to certain geometries, have given rise to remarkable results in a variety of chemical transformations.32−38 The first monoanionic class of this ligands (A, Figure 1) with an aliphatic backbone was developed © XXXX American Chemical Society

Received: October 31, 2015

A

DOI: 10.1021/acs.inorgchem.5b02498 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Examples of monoanionic PNP pincer ligands.

Scheme 1. Synthesis of the PNP Protioligand (CbzdiphosiPr)H (1iPrH) and Subsequent Lithiation to 1iPrLi

chemistry of the late transition metals followed.64−66 Herein, we disclose the results of our investigation into the viability of the Cbzdiphos ligand as a stabilizing scaffold for group 4 metal complexes and the way in which its CH activation influences the reactivity of the resulting complexes.

revealed distorted T-shaped coordination geometry with an P(1)−Li−P(2) angle of 157.25(9)°. The coordination of the Cbzdiphos ligands 1iPrH and 1PrH to group 4 metals was accomplished readily via deprotonation and lithiation followed by treatment with the corresponding chlorido precursor compounds of the metals (titanium, zirconium, and hafnium), affording the trichlorido complexes [(CbzdiphosiPr)MCl3] 2iPrM and [(CbzdiphosPh)MCl3] 2PhM (M = Ti, Zr, Hf) in moderate to good yields (Scheme 2). While complexes 2iPrTi/Zr/Hf and 2PhTi/Zr were formed within 1 h at ambient temperature, the conversion to the hafnium complex 2PhHf required elevated temperatures (80 °C). The 31P NMR chemical shifts in the spectra of complexes iPr 2 M [29.7 (Ti), 18.0 (Zr), and 21.6 ppm (Hf)] and 2PhM [18.4 (Ti), 6.7 (Zr), and 13.4 ppm (Hf)] are indicative of the coordination of the wingtip phosphine groups to the metal center. The corresponding protioligands were found to resonate at −2.0 (1iPrH) and −18.5 ppm (1PhH). Single-crystal X-ray structure analyses of the compounds 2iPr/PhTi were carried out to establish their structural details (Figure 3). Whereas the C2-symmetric complex 2iPrTi displayed an almost ideal octahedral coordination around the metal center, the octahedral coordination geometry 2PhTi is slightly distorted due to a bending of the carbazole backbone [P(1)−Ti−P(2) 179.69(2)° (2iPrTi), 170.960(17)° (2PhTi); Cl(3)−Ti−Cl(2) 178.28(2)° (2iPrTi), 175.61(2)° (2PhTi); N(1)−Ti−Cl(1) 179.48(6)° (2iPrTi), 174.84(4)° (2PhTi)]. The molecular structures of complexes 2iPrZr/Hf and 2PhZr/Hf were also determined and found to be very similar to the Cs-symmetric structure of 2PhTi (see the Supporting Information). Reaction of the chlorido complexes 2iPr/PhM with an excess of trimethylsilyl iodide resulted in the formation of the corresponding iodido complexes [(CbzdiphosiPr)MI3] 3iPrM and [(CbzdiphosPh)MI3] 3PhM (M = Ti, Zr, Hf) (Scheme 2, see also Supporting Information) Synthesis and Characterization of Titanium Alkylidene Complexes. Hybrid ligands have been found previously to stabilize group 4 metal−ligand multiple bonds. Complexes 2/3iPr/PhTi turned out to be potential precursors for complexes containing Ti−C multiple bonds:48−50,53,54 Reaction of 2iPrTi

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RESULTS AND DISCUSSION We previously reported the Ph2P-substituted Cbdiphos ligand 1PhH.64 In analogy, in addition to a recently published procedure67 we prepared the diisopropylphosphino-subsitituted ligand (CbzdiphosiPr)H (1iPrH) as depicted in Scheme 1. Reacting 1,8-bis(bromomethyl)-3,6-di-tert-butyl-9H-carbazole with diisopropylphosphine gave the protioligand 1iPrH,67 which could be metalated cleanly using LiHMDS. The resulting lithiated compound was isolated and fully characterized. The molecular structures of 1 iPrH (see Supporting Information) and 1iPrLi. (Figure 2) were established by X-ray diffraction of suitable single crystals. All metric parameters are as expected for carbazole derivatives, and the lithiated species

Figure 2. Molecular structure of (CbzdiphosiPr)Li (1iPrLi) (thermal ellipsoids at 50% probability level). Hydrogen atoms have been omitted for clarity. Selected bond lengths [Angstroms] and angles [degrees] for 1iPrLi: Li−P(1) 2.466(2), Li−P(2) 2.488(2), P(1)−Li− P(2) 157.25(9). B


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Inorganic Chemistry Scheme 2. Synthesis of Cbzdiphos−Halogenido Complexes of the Group 4 Metals (M = Ti, Zr, Hf)

Figure 3. Representation of the molecular structure of 2iPrTi (top) and 2PhTi (bottom) (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond lengths [Angstroms] and angles [degrees] for 2iPrTi: Ti−Cl(1) 2.3246(5), Ti−Cl(2) 2.3257(5), Ti− Cl(3) 2.3230(5), Ti−P(1) 2.5886(5), Ti−P(2) 2.5868(5), Ti−N(1) 2.0100(13), P(1)−Ti−P(2) 179.69(2), N(1)−Ti−Cl(1) 179.48(6), Cl(3)− Ti−Cl(2) 178.28(2). Selected bond lengths [Angstroms] and angles [degrees] for 2PhTi: Ti−Cl(1) 2.3115(11), Ti−Cl(2) 2.2715(9), Ti−Cl(3) 2.3344(9), Ti−P(1) 2.6332(10), Ti−P(2) 2.6173(10), Ti−N(1) 2.0469(16), P(1)−Ti−P(2) 170.960(17), N(1)−Ti−Cl(1) 174.84(4), Cl(3)−Ti− Cl(2) 175.61(2).

and 3PhTi with 1 equiv of dibenzyl magnesium tetrahydrofuran adduct led to the formation of the alkylidene complexes 4iPrTi and 5PhTi, respectively, and elimination of toluene (Scheme 3). The presence of dioxane is important for removing the (Cbzdiphos)Mg species, which is formed as a byproduct during the reaction. The overall symmetry displayed by 4iPrTi and 5PhTi in their 31 1 P, H, and 13C NMR spectra is Cs, rendering the two halves of the pincer ligands equivalent. While the 31P NMR spectrum displays broad singlets at 18.1 (5PhTi) and 26.3 ppm (4iPrTi), the 1H NMR spectra contained the characteristic resonances of the alkylidene ligands. For 5PhTi this appeared as a singlet resonance at 10.54 ppm with a 1JCH coupling constant of 103.5 Hz (detected via 13C labeling), which is representative of an α-H of the terminal alkylidene ligand. This low value of the

Scheme 3. Synthesis of the Titanium Alkylidene Complexes 4iPrTi and 5PhTi

coupling is consistent with an α-agostic interaction in solution. The α-H resonance for 4iPrTi was observed as a singlet at 11.50 ppm. The alkylidene Cα resonances were detected at 298.8 (via C


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Inorganic Chemistry C labeling; 5PhTi) and 288.7 ppm (4iPrTi), which is within the expected range for such ligands.50,68−73 Single crystals of 4iPrTi were grown in Et2O at −40 °C, and the molecular structure is depicted in Figure 4. Complex 4iPrTi possesses a 13

Scheme 4. Synthesis of Benzylated Zirconium and Hafnium Complexes

Figure 4. ORTEP plot of 4iPrTi (thermal ellipsoids at 50% probability). Hydrogen atoms, expect for the α-H on C(36), have been omitted for clarity. Selected bond lengths [Angstroms] and angles [degrees] for 4iPrTi: Ti−Cl 2.3515(11), Ti−P(1) 2.5702(11), Ti−P(2) 2.5669(11), Ti−N(1) 2.063(3), Ti−C(36) 1.918(4), C(36)−C(37) 1.456(6), P(2)−Ti−P(1) 169.26(4), N(1)−Ti−Cl 143.08(9), N(1)−Ti−C(36) 102.76(15), C(36)−Ti−Cl 114.12(13), Ti−C(36)−C(37) 139.5(3), Ti−C(36)−H(36) 107(3).

3.8 ppm (2JPP = 25.5 Hz) (7PhHf)]. In the proton NMR spectra of these compounds only three protons of the ligand methylene groups were observed. One of these signals in each of the spectra [2.50 ppm (2JPH = 7.0 Hz) (6iPrZr); 3.36 (6PhZr); 3.62 (2JPH = 4.4 Hz) (6PhHf); 3.29 (2JPH = 7.0 Hz) (7PhZr); 3.01 (2JPP = 4.9 Hz) (7PhHf)], which was found to couple to no other proton (1H−1H COSY) but to one of the 31P nuclei (1H−31P HMBC), was assigned to the CH-activated methine position. To establish the structural details of the cyclometaled complexes, single-crystal X-ray structure analysis of 7PhZr was carried out. The molecular structure of complex 7PhZr is shown in Figure 5 (left) along with selected bond length and angles. The iodido ligand is disposed trans to the nitrogen anchor of the pincer ligand [N(1)−Zr−I 154.06(8)°], and the benzyl ligand adopts a η3-coordination mode at zirconium [C(49)− C(48)−Zr 80.0(2)°; Zr−C(48) 2.332(4) Å; Zr−C(49) 2.519(4) Å; Zr−C(50) 2.636(4) Å]. The Zr−C(48) bond length of 2.329(4) Å in 7PhZr is within the usual range of zirconium benzyl complexes.76 The most characteristic feature of the molecular structure is the bridging Zr−(μ-CH)−PPh2 moiety, resulting from cyclometalation at one of the ligand methylene groups which is directly bonded to the metal center [Zr−C(15) 2.339(3) Å]. An X-ray diffraction study of 8PhZr established its distorted octahedral coordination geometry. The asymmetric unit of 8PhZr contains two independent molecules (Figure 5) with very similar structural features. The benzyl ligand [Zr−C(48) 2.295(5)/2.338(6) Å] is positioned trans with respect to the nitrogen [N(1)−Zr−C(48) 146.70(17)/146.1(2)°] and coordinated in a η2-mode to zirconium [Zr−C(48)−C(49) 91.9(3)/90.4(4)°, Zr−C(49) 2.763(5)/2.750(6) Å]. Notably, the P(1)−Zr−P(2) angle is distorted from the ideal 180° of a trans orientation to 157.59(4)/154.66(4)°, which is a structural consequence of the tilted arrangement adopted by the carbazole ligand backbone also observed in the halogenido complexes discussed above. The remaining coordination site occupied by the halogenido ligand in the cyclometalated monobenzyl complexes [(Cbzdiphos-CH)MBnX] 6iPrZr, 6PhZr/Hf, and 7PhZr/Hf was readily benzylated by treatment with benzyl potassium to afford the

short TiC(36) bond length of 1.918(4) Å and a Ti−C(36)− C(37) bond angle of 139.5(3)°, which is within the expected range for such alkylidene ligands,68,70−74 especially those the titanium alkylidene complexes [(PNP)Ti(CHR) (OTf)] (PNP = N[2-P(CHMe2)2-4-Me-C6H3)2−], R = tBu, SiMe3) reported by Mindiola and co-workers.50,69,75 Synthesis and Characterization of Zirconium and Hafnium Alkyl Complexes. In contrast to the titanium complexes 2iPrTi and 3PhTi, the zirconium and hafnium complexes 2iPrZr and 3PhZr/Hf reacted with Bn2Mg(THF)2 to form the cyclometalated monoalkyl compounds [(CbzdiphosiPr-CH)ZrBnCl] 6iPrZr as well as [(CbzdiphosPh-CH)HfBnCl] 6PhHf and [(CbzdiphosPh-CH)MBnI] 7PhZr/Hf (M = Zr, Hf), as shown in Scheme 4. Upon treatment of 2PhZr with 1 equiv of Bn2Mg(THF)2 or 2 equiv of KBn in toluene, only incomplete conversion to the cyclometalated species with concomitant formation of side products was observed. On the other hand, reaction of 2PhZr with 0.25 equiv of tetrabenzyl zirconium afforded [(CbzdiphosPh)ZrBnCl2] (8PhZr) within 1 h at room temperature in good yield. This monobenzyl complex [(CbzdiphosPh)ZrBnCl2] (8PhZr) was found to be thermally unstable and decomposed in a nonspecific manner at room temperature within several days but could be stored at −40 °C for weeks. Alkylation of 8PhZr with benzyl potassium led to the formation of the cyclometalated monobenzyl complex [(CbzdiphosPhCH)ZrBnCl] (6PhZr), which was originally obtained by direct reaction of 2PhZr with benzyl transfer reagents. The 31P NMR spectra of the cyclometalated monobenzyl compounds display two phosphorus resonances, indicating the absence of mirror symmetry [1.7, 15.5 ppm (d, 2JPP = 27.3 Hz) (6iPrZr); −13.3, 0.3 ppm; (6PhZr); −20.8, 3.1 ppm (2JPP = 23.9 Hz) (6PhHf); −13.7, 0.1 ppm (2JPP = 28.3 Hz) (7PhZr); −20.7, D


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Inorganic Chemistry

Figure 5. ORTEP plots of 7PhZr (left) and 8PhZr (right, thermal ellipsoids at 50% probability level). Hydrogen atoms and solvent molecules are omitted for clarity. Only one of the two independent molecules in the asymmetric unit of 8PhZr is shown. Valus in square brackets refer to the second molecule. Selected bond lengths [Angstroms] and angles [degrees] for 7PhZr: Zr−I 2.8319(13), Zr−N(1) 2.125(3), Zr−C(15) 2.339(3), Zr−C(48) 2.332(4), Zr−C(49) 2.519(4), Zr−C(50) 2.636(4), Zr−P(2) 2.7196(14), Zr−P(1) 2.7662(15), C(48)−Zr−C(15) 133.59(12), C(48)− Zr−P(2) 174.14(9), C(48)−Zr−P(1) 85.14(10), C(15)−Zr−P(1) 135.84(9), P(2)−Zr−P(1) 98.67(4), P(2)−Zr−I 86.54(4), P(1)−Zr−I 85.04(3), C(49)−C(48)−Zr 80.0(2), N(1)−Zr−I 154.06(8). Selected bond lengths [Angstroms] and angles [degrees] for 8PhZr: Zr(1)−N(1) 2.224(4) [2.244(5)], Zr(1)−P(1) 2.8736(13) [2.8744(15)], Zr(1)−P(2) 2.7771(12) [2.7646(15)], Zr(1)−Cl(1) 2.4447(11) [2.4388(12)], Zr(1)− Cl(2) 2.4497(11) [2.4507(12)], Zr(1)−C(48) 2.295(5) [2.338(6)], Zr(1)−C(49) 2.763(5) [2.750(6)], N(1)−Zr(1)−C(48) 146.70(17) [146.1(2)], Cl(1)−Zr(1)−Cl(2) 170.12(4) [171.17(5)], P(2)−Zr(1)−P(1) 157.59(4) [154.66(4)], C(49)−C(48)−Zr(1) 91.9(3) [90.4(4)].

cyclometalated dibenzyl complexes 9iPrZr and 9PhZr/Hf (Scheme 5).

protons was observed, and below −60 °C the two protons were found to resonate at 5.2 and 3.7 ppm. From these data an activation barrier ΔGc ≈ 13.5 kJ/mol for the exchange process represented in Figure 6 was determined. We attribute the notable upfield chemical shift of one of the ortho-protons to its spatial arrangement relative to the anisotropy cone of the adjacent benzyl group. Notably, a similar dynamic behavior was not encountered for the corresponding hafnium complex 9PhHf. The solid-state structures of all three complexes 9iPrZr and 9PhZr/Hf were determined by X-ray diffraction and found to display notable differences in the relative arrangements of the two cis-disposed benzyl ligands (Figure 7): The zirconium− carbon bond lengths in 9iPrZr (Figure 5, left) were found to be 2.3010(4) [Zr−C(55)] and 2.3039(15) Å [Zr−C(48)], and the Zr−CH2−Ph bond angles are 98.47(8)° [C(56)−C(55)−Zr] and 100.77(8)° [C(49)−C(48)−Zr], respectively, which is consistent with two η1-coordinated benzyl units. For 9PhZr (Figure 5, middle), on the other hand, one of the benzyl ligands adopts an η3-coordination [Zr−C(48) 2.3236(15) Å, Zr− C(49) 2.597(15) Å, Zr−C(50) 2.8136(15) Å, C(49)−C(48)− Zr 83.18(7)°], while the other one binds in a η2-mode [Zr− C(55) 2.3637(15) Å, Zr−C(56) 2.7268(15) Å, C(56)− C(55)−Zr 87.86(8)°] to zirconium. This is in excellent agreement with the VT-NMR study discussed above, which also suggests a desymmetrization of one of the benzyl units. Finally, in the case of 9PhHf (Figure 5, right) one benzyl ligand is η2-coordinated [Hf−C(55) 2.283(3) Å, Hf−(C56A/C56B) 2.811(5)/2.871(4) Å, C(56A/56B)−C(55)−Hf 98.4(2)/ 93.6(3)°], while the second benzyl unit adopts η1-coordination [C(49)−C(48)−Hf 107.79(15)°]. In contrast to the observations in the formation of the titanium complexes reported in this work as well as previous reports by Ozerov et al. and Mindiola et al. on related PNP

Scheme 5. Synthesis of the Dibenzyl Complexes 9iPrZr and 9PhZr/Hf

As to be expected for these nonsymmetrical complexes, the P NMR spectra display two sets of doublets [−4.0, 10.2 ppm (d, 2JPP = 27.3 Hz) (9iPrZr), −17.3, 3.5 ppm (d, 2JPP = 25.4 Hz) (9PhZr), −26.4, 3.3 ppm (d, 2JPP = 17.1 Hz) (9PhHf)]. Particularly diagnostic for 9iPrZr and 9PhZr/Hf are the proton resonances for the six diastereotopic methylene groups of the two benzyl ligands as well as the α-CH2 units of the ligand. Furthermore, one characteristic signal attributed to methine moiety of the cyclometalated ligand “arm” was observed for all three compounds [3.22 (9iPrZr), 3.45 (9PhZr), 3.76 ppm (9PhHf)]. The zirconium complexes 9iPr/PhZr displayed remarkably high-field-shifted 1H NMR resonances in one of the η3-coordinated benzyl rings at 5.61 (9iPrZr) and 4.94 ppm(9PhZr), which are assigned to the ortho-H atoms. This finding was further investigated by X-ray diffraction analysis (vide infra) as well as variable-temperature 1H NMR spectroscopy (Figure 6). Upon cooling a solution of 9PhZr in toluene-d8 to −50 °C coalescence of the signal assigned to the two ortho31

E


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Inorganic Chemistry

Figure 6. Variable-temperature 1H NMR spectra of complex 9PhZr (399.89 MHz, from −80 to 100 °C in toluene-d8; assignment of Ha and Hb is made random).

Figure 7. ORTEP plots of 9iPrZr (left) as well as 9PhZr (middle) and 9PhHf (right) (thermal ellipsoids at 50% probability level). Hydrogen atoms and disorder in 9PhHf are omitted for clarity. Selected bond lengths [Angstroms] and angles [degrees] for 9iPrZr: Zr−P(1) 2.8232(9), Zr−P(2) 2.7060(8), Zr−N(1) 2.1597(12), Zr−C(15) 2.3621(15), Zr−C(55) 2.3010(14), Zr−C(48) 2.3039(15), P(2)−Zr−P(1) 101.44(3), C(15)−Zr− P(2) 41.13(3), P(2)−Zr−C(48) 88.10(4), C(48)−Zr−P(1) 125.84(3), C(48)−Zr−P(2) 129.10(4), N(1)−Zr−C(48) 92.50(5), N(1)−Zr−C(55) 151.67(4), C(56)−C(55)−Zr 98.47(8), C(49)−C(48)−Zr 100.76(8). Selected bond lengths [Angstroms] and angles [degrees] for 9PhZr: Zr−P(1) 2.7653(12), Zr−P(2) 2.7950(10), Zr−N(1) 2.2069(13), Zr−C(15) 2.3788(14), Zr−(C48) 2.3236(15), Zr−C(49) 2.5937(15), Zr−C(50) 2.8136(15), Zr−C(55) 2.3637(15), Zr−C(56) 2.7268(15), C(48)−Zr−C(55) 98.44(6), C(50)−C(49)−Zr 83.81(7), C(56)−C(55)−Zr 87.86(8), P(1)−Zr−P(2) 100.538(17), C(15)−Zr−P(2) 40.26(3), C(15)−Zr−C(49) 95.99(4), C(48)−Zr−P(1) 83.66(3), C(48)−Zr−P(2) 167.31(3), N(1)−Zr−C(48) 91.15(5), N(1)−Zr−C(55) 144.66(4). Selected bond lengths [Angstroms] and angles [degrees] for 9PhHf: Hf−P(2) 2.8322(6), Hf−P(1) 2.7937(6), Hf−N(1) 2.1298(19), Hf−C(15) 2.293(2), Hf−C(55) 2.283(3), Hf−C(48) 2.253(2), Hf−C(56A/56B) 2.871(4)/2.811(5), P(2)−Hf−P(1) 101.634(17), C(15)−Hf−P(2) 40.38(6), C(48)−Hf−P(2) 138.08(6), C(48)−Hf−P(1) 117.18(6), N(1)−Hf−C(48) 91.90(8), N(1)−Hf−C(55) 150.66(9), C(56A/56B)−C(55)−Hf 98.4(2)/93.6(3), C(49)−C(48)−Hf 107.79(15).

dibenzyl complexes, 9iPrZr and 9PhZr/Hf did not undergo thermally or photolytically induced α-abstraction and subsequent conversion to the corresponding alkylidene complexes.48,49,59 Further reaction of the cyclometalated dibenzyl complex 9PhZr with an excess of benzyl potassium led to the formation of the anionic tribenzyl zirconium ate complex

10PhZr (Scheme 6). The latter could be “conproportionated” with 7PhZr to regenerate the neutral dibenzyl species 9PhZr. An X-ray diffraction study of single-crystalline 10PhZr revealed a polymeric structure in the solid state in which the zirconium atoms are seven-coordinate and bonded to the cyclometalated ligand backbone and three benzyl groups (Figure 8). The anionic zirconium complexes are linked by F


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Inorganic Chemistry

Scheme 6. Reaction of 9PhZr to the Zirconium Ate Complex 10PhZr and Regeneration of 9PhZr upon Reaction of 10PhZr with 7PhZr

Figure 8. ORTEP of 10PhZr (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond lengths [Angstroms] for 10PhZr: Zr(1)···K(1) 4.2938(18), Zr(1)−P(1) 2.8635(10), Zr(1)−P(2) 2.7659(9), Zr(1)−N(1) 2.2957(14), Zr(1)−C(15) 2.3720(17), K(1)−Ph(C49)cent 2.920, K(1)−Ph(C63)cent 2.854, K(1)−Ph(Carb)cent 2.846.

Scheme 7. Treatment of 8PhZr with Trimethylphosphine Forming 11PhZr

cation−π interactions of the potassium cation and altogether three arene rings, two benzyl units in neighboring complexes, as well an arene ring of the carbazole backbone in one of the complex units. The distance between the potassium cation and the centroid benzene rings is around 2.87 Å, which is similar to previously observed van der Waals-type contacts.77−79 Donor-Induced Hydrogen-Atom Abstraction and Cyclometalation of Dichloro Zirconium Complex 8PhZr. The cyclometalation of the Cbzdiphos ligands could not be controlled in the reactions of the halogenide precursor complexes 2iPr/PhM and 3iPr/PhM (M = Zr, Hf) with dibenzyl magnesium or benzyl potassium and only suppressed via the conproportionation with tetrabenzyl zirconium. This was shown in the synthesis of 8PhZr in which the PNP ligand remained intact, which allowed an attempt to specifically induce the cyclometalation step. Upon heating a solution of 8PhZr in the presence of 1 mol equiv of trimethylphosphine, one of the ligand methylene groups was deprotonated, yielding the cyclometalated complex [(CbzdiphosPh-CH)ZrCl2(PMe3)] 11PhZr and eliminated toluene (Scheme 7). The 1H and 31P{1H} NMR spectra of this complex are consistent with a C1-symmetric structure, as indicated by the presence of three inequivalent phosphorus resonances at −22.1 (dd, 2JP3P1 = 84.1 Hz, 2JP3P2 = 17.0 Hz), −13.8 (dd, 2JP1P2 = 24.6 Hz, 2JP3P2 = 17.0 Hz), and −2.1 (dd, 2JP3P1 = 84.1 Hz, 2JP1P2 = 24.6 Hz), the highly shielded signal being assigned to the coordinated trimethylphosphine group. Single crystals of 11PhZr suitable for X-ray diffraction allowed the elucidation of the details of its molecular structure (Figure 9). As in the other complexes containing the cyclometalated CbzdiphosPh-

CH unit the latter now acts as a tetradentate ligand while the two chlorides and the additional trimethylphosphine complete the 7-fold coordination of the metal center. All bond lengths around the metal center are within the expected range and comparable to those of the related structures discussed above. Synthesis and Characterization of an Ortho-Metalated Methylene Triphenylphosphorane Complex. Reaction of 7PhZr with methylenetriphenylphosphorane produced the ortho-metalated product [(Cbzdiphos Ph -CH)Zr(oC6H4PPh2CH2)I] (12PhZr). Ortho-metalation of methylenetriphenylphosphorane has also been reported for hydride and alkyl complexes of lutetium and yttrium,80−83 but in contrast to lanthanide compounds there are several examples involving group 4 metals in which the methylene carbon is further metalated.84,84,85 Recently, Mindiola reported the synthesis of a κ2-phosphinoalkylidene titanium complex by dehydrogenation and P−C bond activation of H2CPPh3.55 The 31P {1H} NMR spectrum of 12PhZr displays a doublet at 37.0 ppm (3JPP = 32.3 Hz), which assigned to the methylene G


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Inorganic Chemistry

Figure 9. ORTEP plot of 11PhZr (thermal ellipsoids at 50% probability). Hydrogen atoms are omitted for clarity. Selected bond lengths [Angstroms] and angles [degrees] for 11PhZr: Zr−Cl(1) 2.4368(4), Zr−Cl(2) 2.4773(4), Zr−P(1) 2.7868(4), Zr−P(2) 2.6730(4), Zr−P(3) 2.7446(5), Zr−N(1) 2.1698(12), Zr−C(15) 2.3792(16), P(1)−Zr−P(2) 90.924(13), C(15)−Zr−P(2), 41.53(4), C(15)−Zr−P(3) 77.11(4), Cl(2)−Zr−P(3) 78.207(16), Cl(2)−Zr− P(1) 79.998(15), Cl(1)−Zr−Cl(2) 103.464(16), N(1)−Zr−Cl(1) 156.94(4).

Figure 10. ORTEP plot of 12PhZr (thermal ellipsoids at 50% probability). Hydrogen atoms, expect of H(48A) and H(48B), have been omitted for clarity. Selected bond lengths [Angstroms] and angles [degrees] for 12PhZr: Zr−I 2.8368(4), Zr−P(2) 2.7451(9), Zr− P(1) 2.8361(9), Zr−N(1) 2.171(3), Zr−C(15) 2.358(4), Zr−C(48) 2.418(3), Zr−C(50) 2.354(3), P(3)−C(48) 1.755(4), C(48)−Zr− C(50) 73.74(12), N(1)−Zr−I 152.68(8), P(2)−Zr−P(1) 94.09(3), C(15)−Zr−P(2) 40.98(8), C(15)−Zr−C(50) 77.18(2), P(3)− C(48)−Zr 108.47(17).

Scheme 8. Treatment of 7PhZr with Ph3PCH2 Forming 12PhZr

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CONCLUSION In this work we present the results of a first investigation into the coordination chemistry of the recently reported carbazolide-based PNP pincer ligand with early transition metals. The 6-fold-coordinated trihalogenido complexes [(Cbzdiphos)MX3] were shown to be a suitable platform for further transformations. While the reaction of these halogenido complexes with the dibenzylmagnesium tetrahydrofuran adduct gave the monohalogenido alkylidene complexes in the case of titanium, cyclometalation of the ligand is observed for the zirconium and hafnium analogs. In this case, the intramolecular deprotonation of the methylene groups adjacent to the phosphine units appears to be kinetically favored over αhydrogen abstraction leading to alkylidenes. The different behavior of the Ti complex vs its heavier metal analogs may be due to the shorter metal−ligand bonds and the resulting differences in the orientation of the phosphino−methylene units within the coordination sphere. That such interligand interaction may be crucial has been apparent in the reaction of the monobenzyl complex with the externally attacking donor trimethylphosphine which yields the corresponding cyclometalated dichloro complex containing the PMe3 ligand. In contrast to the reactivity of the group 4 metal PNP complexes reported by Ozerov’s and Mindiola’s groups, the presence of αCH2 units adjacent to the phosphine donors becomes the dominating reactive pattern in alkylation reactions as studied in this work.

triphenylphosphorane unit, as well as a doublet of doublets at −6.3 ppm (3JPP = 32.3 Hz, 2JPP = 26.1 Hz) and a doublet at −19.6 ppm (2JPP = 26.1 Hz) for the phosphino groups of the PNP ligand. Diagnostic for the diastereotopic protons of the methylene unit in the activated methylenetriphenylphosphorane are doublets at 1.18 and 1.88 ppm (2JHH = 11.8 Hz) in the 1 H {31P} NMR spectrum, which couple both to one of the 31P nuclei of the (Cbzdiphos) ligand (−6.3 ppm) and that of the phosphorane (37.0 ppm). The signal due to the proton ortho to the metalated position appears as a doublet at 9.25 ppm (3JHH = 7.4 Hz), while the resonance of the metalated carbon atom in the 13C {1H} NMR was observed as a higher order multiplet at 207.3−207.7 ppm. The molecular structure of 12PhZr is given in Figure 10. The most interesting structural feature of the complex is the slightly puckered five-membered Zr−C(48)−P(3)−C(49)−C(50) metallacycle which contains the methylene unit between Zr and P(3) and the ortho-metalated triphenylphosphine moiety. The ylide-C−metal distance of Zr−C(48) = 2.418(3) Å is slightly longer than an average Zr−carbon σ bond and notably greater than the Zr−C(50) bond length for the cyclometalated aryl group [2.354(3) Å]. The C(48)−P(3) bond is elongated [1.755(4) Å] with respect to that in methylenetriphenylphosphorane itself [1.661(8) Å].86 Finally, an interbond angle P(3)−C(48)−Zr of 108.47(17)° is consistent with sp 3 hybridization at the ylide carbon atom.

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EXPERIMENTAL SECTION

Materials and Methods. All manipulations of air- and moisturesensitive materials were performed under an inert atmosphere of dry argon (Argon 5.0 purchased from Messer Group GmbH and dried H


Article

Inorganic Chemistry

HCarb4/5). 13C {1H} NMR (150.90 MHz, C6D6, 296 K): δ (ppm) = 18.1 (s, CH(CH3)2), 18.2 (s, CH(CH3)2), 25.7 (t, J = 7.3 Hz, CH(CH3)2), 30.2 (t, J = 6.3 Hz, CH2), 31.9 (s, C(CH3)3), 34.5 (s, C(CH3)3), 114.5 (s, CCarb4/5), 124.6 (s, CCarb), 126.5 (s, CCarb), 127.6 (t, J = 4.2 Hz, CCarb2/7), 145.5 (s, CCarb), 147.1 (t, J = 3.8 Hz CCarb). 31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (ppm) = 29.7 (s). Anal. Calcd for C34H54Cl3NP2Ti: C, 58.93; H, 7.85, N, 2.02. Found: C, 58.93; H, 7.65; N, 2.01. For the syntheses and characterization data of [(CbzdiphosiPr)ZrCl3] (2iPrZr), [(CbzdiphosiPr)HfCl3] (2iPrHf), [(CbzdiphosPh)TiCl3] (2PhTi), [(CbzdiphosPh)ZrCl3] (2PhZr), and [(CbzdiphosPh)HfCl3] (2PhHf), see the Supporting Information. Synthesis of [(CbzdiphosiPr)TiI3] (3iPrTi). To a solution of [(CbzdiphosiPr)TiCl3] (2iPrTi) (300 mg, 0.433 mmol, 1.0 equiv) in toluene was added trimethylsilyl iodide (346 mg, 246 μL (ρ = 1.406 g· mol−1) 1.73 mmol, 4.0 equiv) at room temperature. After stirring at 60 °C overnight the volatiles were removed under reduced pressure. The residue was washed with cold pentane and dried in vacuo to give [(CbzdiphosiPr)TiI3] (3iPrTi) as a black solid (221 mg, 0.228 mmol, 53%). 1H NMR (600.13 MHz, C6D6, 295 K): δ (ppm) = 1.06−1.09 (m, 12H, CH(CH3)2), 1.35 (s, 18H, C(CH3)3), 1.48−1.51 (m, 12H, CH(CH3)2), 2.56−2.84 (m, 4H, CH(CH3)2), 3.63 (bs, 4H, CH2), 7.01 (s, 2H, HCarb2/7), 7.92 (s, 2H, HCarb4/5). 13C {1H} NMR (150.90 MHz, C6D6, 295 K): δ (ppm) = 20.6 (s, CH(CH3)2), 28.7 (t, J = 5.8 Hz, CH2), 31.8 (s, C(CH3)3), 32.3 (t, J = 6.6 Hz, CH(CH3)2), 34.6 (s, C(CH3)3), 114.4 (s, CCarb4/5), 125.9 (t, J = 3.2 Hz, CCarb2/7), 126.3 (s, CCarb), 127.0 (s, CCarb), 146.7 (t, J = 3.0 Hz, CCarb), 147.9 (s, CCarb).31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (pm) = 46.1 (s). Anal. Calcd for C34H54I3NP2Ti: C, 42.22; H, 5.63; N, 1.45. Found: C, 41.88; H, 6.01; N, 1.35. For the syntheses and characterization data of [(CbzdiphosiPr)ZrI3] (3iPrZr), [(CbzdiphosiPr)HfI3] (3iPrHf), [(CbzdiphosPh)TiI3] (3PhTi), [(CbzdiphosPh)ZrI3] (3PhZr), and [(CbzdiphosPh)HfI3] (3PhHf), see the Supporting Information. Synthesis of [(CbzdiphosiPr)Ti(=CHPh)Cl] (4iPrTi). To a solution of [(CbzdiphosiPr)TiCl3] (2iPrTi) (400 mg, 0.577 mmol, 1.0 equiv) in benzene was added dioxane (111.9 mg, 108.6 μL (ρ = 1.03 g·mol−1), 1.27 mmol, 2.2 equiv) followed by Bn2Mg(THF)2 (222.6 mg, 0.635 mmol, 1.1 equiv) at room temperature. After stirring overnight at ambient temperature, the reaction mixture was filtrated over Celite, the volatiles were removed under reduced pressure, and the residue was dissolved in Et2O or pentane. The solution was stored in a freezer (−40 °C) overnight. The supernatant was decanted, and the crystalline solid was dried under vacuum to afford [(CbzdiphosiPr)Ti( CHPh)Cl] (4iPrTi) as a brown solid (200 mg, 0.281 mmol, 49%). 1 H NMR (600.13 MHz, C6D6, 295 K): δ (ppm) = 0.68 (dd, 3JHP = 14.5 Hz, 2JHH = 7.2 Hz, 6H, CH(CH3)2), 1.08 (dd, 3JHP = 11.1 Hz, 2 JHH = 7.1 Hz, 6H, CH(CH3)2), 1.13 (dd, 3JHP = 13.6 Hz, 2JHH = 7.1 Hz, 6H, CH(CH3)2), 1.34 (dd, 3JHP = 14.5 Hz, 2JHH = 6.9 Hz, 6H, CH(CH 3)2), 1.48 (s, 18 H, C(CH3)3 ), 2.03−2.09 (m, 2H, CH(CH3)2), 2.09−2.15 (m, 2H, CH(CH3)2), 3.00 (d, 2JHH = 12.3 Hz 2H, CHH), 3.81 (d, 2JHH = 14.0 Hz, 2H, CHH), 6.63−6.66 (m, 1H, Hp‑Ph), 6.93−6.96 (m, 2H, Hm‑Ph), 7.02−7.05 (m, 2H, Ho‑Ph), 7.26 (s, 2H, H Carb2/7), 8.16 (s, J = 1.4 Hz, 2H, H Carb4/5), 11.50 (s, 1H, Ti = CHPh). 13C {1H} NMR (150.90 MHz, C6D6, 295 K): δ (ppm) = 17.2 (s, CH(CH3)2), 18.9 (s, CH(CH3)2), 19.2 (s, CH(CH3)2), 19.6 (s, CH(CH3)2), 23.3 (t, J = 5.3 Hz, CH(CH3)2), 25.5 (t, J = 7.6 Hz, CH(CH3)2), 27.0 (bs, CH2), 32.1 (s, C(CH3)3), 34.4 (s, C(CH3)3), 114.4 (s, CCarb4/5), 121.6 (s, CCarb), 124.8 (s, Cp‑Ph), 125.1 (bs, Co‑Ph), 125.8 (s, CCarb2/7), 126.7(s, Cipso‑Ph), 128.5 (s, Cm‑Ph), 142.2 (s, CCarb), 146.6 (t, J = 3.8 Hz, CCarb), 147.0 (m, CCarb), 288.7 (bs, Ti = CHPh). 31 P {1H} NMR (161.89 MHz, C6D6, 295 K): δ (ppm) = 18.4 (bs). For the synthesis and characterization data of [(CbzdiphosPh)Ti = CHPh(I)] (5PhTi) see the Supporting Information. Synthesis of [(CbzdiphosiPr-CH)ZrBnCl] (6iPrZr). To a solution of [(CbzdiphosiPr)ZrCl3] (2iPrZr) (6.00 g, 8.15 mmol, 1.0 equiv) in benzene (80 mL) was added dioxane (1.58 g, 1.5 mL (ρ = 1.03 g· mol−1), 17.9 mmol, 2.2 equiv) followed by Bn2Mg(THF)2 (3.14 g, 8.97 mmol, 1.1 equiv) at room temperature. After stirring overnight at ambient temperature, the reaction mixture was filtrated over Celite, the

over Granusic phosphorpentoxide granulate) using standard Schlenk techniques or by working in a glovebox (Unilab-2000, M. Braun). Solvents were predried over molecular sieves and dried over potassium (benzene, dioxane) or CaH2 (dichloromethane, triethylamine) and distilled or dried over activated alumina columns using a solvent purification system (M. Braun SPS 800) and stored over potassium mirrors (expect for dichloromethane, dioxane, and triethylamine, which were stored over molecular sieves) in Teflon valve ampules. Deuterated solvents were purchased from Deutero GmbH, dried over potassium (benzene-d6, toluene-d8), vacuum distilled, degassed by three successive freeze−pump−thaw cycles, and stored over molecular sieves in Teflon valve ampules under argon. Samples for NMR spectroscopy were prepared under argon in 5 mm Wilmad tubes equipped with J. Young Teflon valves. NMR spectra were recorded on Bruker NMR spectrometers (Avance II 400 MHz, Avance III 600 MHz). 1H and 13C {1H} NMR spectra were referenced to residual solvent peaks [C6D6 7.16 (1H) and 128.06 ppm (13C); toluene-d8 2.08 (1H) and 20.43 ppm (13C)].87 31P NMR chemical shifts are reported with respect to external H3PO4. 7Li NMR spectra were referenced to external LiCl. NMR assignments were confirmed by the use of twodimensional 1H−1H, 1H−13C, 1H−31P, and 31P−31P correlation experiments. The appearance of the signals was described using the following abbreviations: s (singlet), d (doublet), dd (doublet of doublet), dt (doublet of triplet), t (triplet), m (multiplet), bs (broad signal). Elemental analyses were recorded by the analytical service of the Heidelberg Chemistry Department using Vario MIKRO cube analytical devices. The ligand (Cbzdiphos Ph )H, 64 1,8-bis(bromomethyl)-3,6-di-tert-butyl-9H-carbazol, 64 diisopropylphosphine,88 benzyl potassium,89 Bn2Mg(THF)2,90 tetrabenzyl zirconium,16 trimethylphosphine,92 and Ph3PCH293 were prepared as described. All other chemicals were purchased from commercial sources and used without purification unless otherwise stated. Synthetic Protocols and Characterization Data. For the syntheses and characterization data of (CbzdiphosiPr)H (1iPrH), see the Supporting Information. Synthesis of (CbzdiphosiPr)Li (1iPrLi). To a solution of the protoligand (CbzdiphosiPr)H (1iPrH) (500 mg, 0.926 mmol, 1.0 equiv) in toluene, LiHMDS (155 mg, 0.926 mmol, 1.0 equiv) was added at room temperature and stirred for 10 min. The solution was concentrated and then placed into a −40 °C freezer. After 12 h the resulting slightly yellow crystals were filtered off and dried under vacuum (420 mg, 0.770 mmol, 83% yield). 1H NMR (600.16 MHz, C6D6, 295 K): δ (ppm) = 0.82 (dd, 3JHP = 14.1 Hz, 3JHH = 7.1 Hz, 12H, CH(CH3)2), 0.94 (dd, 3JHP = 13.0 Hz, 3JHH = 7.1 Hz, 12H, CH(CH3)2), 1.53−1.58 (m, 4H, CH(CH3)2), 1.66 (s, 18H, C(CH3)3), 3.29 (d, 2JHP = 4.0 Hz, 4H, CH2), 7.38 (s, 2H, HCarb2/7), 8.49 (s, 2H, HCarb4/5). 13C {1H} NMR (150.90 MHz, C6D6, 295 K): δ (ppm) = 19.1 (m, CH(CH3)2), 19.6 (m, CH(CH3)2), 22.5 (s, CH(CH3)2), 28.1 (d, 2JHH = 2.6 Hz, CH2), 32.8 (s, C(CH3)3), 34.8 (s, C(CH3)3), 115.2 (s, CCarb4/5), 120.5 (s, CCarb), 123.1 (m, CCarb2/7), 126.4 (s, CCarb), 136.7 (s, CCarb), 149.5 (m, CCarb). 31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (ppm) = 4.7 (q, 1JHP = 77.7 Hz). 7Li {1H} NMR (155.41 MHz, C6D6, 295 K): δ (ppm) = 3.6 (t, 1JLiP = 78.3 Hz). Anal. Calcd for C34H54NP2Li: C, 74.83; H, 9.97; N, 2.57. Found: C, 74.92, H; 10.25; N, 2.53. Synthesis of [(CbzdiphosiPr)TiCl3] (2iPrTi). To a solution of the protioligand (CbzdiphosiPr)H (1iPrH) (2.00 g, 3.71 mmol, 1.0 equiv) in toluene, LiHMDS (0.620 g, 3.71 mmol, 1.0 equiv) was added at room temperature. After stirring for 10 min at ambient temperature, TiCl4(THF)2 (1.24 g, 3.71 mmol, 1.0 equiv) was added in portions. During addition the color of the solution changed to dark blue. The mixture was stirred at room temperature for 1 h. The precipitated LiCl was removed by filtration over Celite, and the volatiles were removed under reduced pressure. The crude product was washed with cold pentane and dried under vacuum to afford [(CbzdiphosiPr)TiCl3] (2iPrTi) as a dark blue solid (1.45 g, 2.09 mmol, 56% yield). 1H NMR (600.16 MHz, C6D6, 295 K): δ (ppm) = 1.00 (dd, 3JHP = 13.9 Hz, 3JHH = 6.8 Hz, 12H, CH(CH3)2), 1.09 (dd, 3JHP = 13.8 Hz, 2JHH = 6.8 Hz, 12H, CH(CH3)2), 1.40 (s, 18H, C(CH3)3), 2.06−2.11 (m, 4H, CH(CH3)2), 3.77 (s, 4H, CH2), 7.23 (s, 2H, HCarb2/7), 8.06 (s, 2H, I


Article

Inorganic Chemistry

P2CH(CH3)2), 0.66−0.68 (m, 4H, P2CH(CH3)2, P2CH(CH3)2), 0.99 (dd, 2JHP = 9.6 Hz, 3JHH = 7.0 Hz, 3H, P1CH(CH3)2), 1.04 (dd, 2JHP = 14.6 Hz, 3JHH = 7.2 Hz, 3H, P1CH(CH3)2), 1.12 (dd, 2JHP = 13.7 Hz, 3 JHH = 7.3 Hz, 3H, P1CH(CH3)2), 1.15−1.21 (m, 6H, P1CH(CH3)2, P2CH(CH3)2), 1.32 (dd, 2JHP = 10.9 Hz, 3JHH = 7.2 Hz, 3H, P2CH(CH3)2), 1.37−1.41 (m, 1H, P2CH(CH3)2), 1.50 (s, 9H, C(CH 3 ) 3 ), 1.55 (s, 9H, C(CH 3 ) 3 ), 2.04−2.09 (m, 1H, P1CH(CH3)2), 2.12 (d, 2JHH = 8.5 Hz, 1H, CHHPh′), 2.20−2.26 (m, 2H, P1CH(CH3)2, CHHPh′′), 2.47 (d, 2JHH = 7.7 Hz, 1H, CHHPh′′), 2.67 (d, 2JHH = 8.7 Hz, 1H, CHHPh′), 3.16−3.25 (m, 3H, CH, CH2), 5.61 (d, 3JHH = 7.3 Hz, 2H, Ho‑Ph′), 6.60 (t, 3JHH = 7.3 Hz, 1H, Hp‑Ph′), 6.65 (d, 3JHH = 7.3 Hz, 2H, Hm‑Ph′), 6.93 (t, 3JHH = 7.4 Hz, 1H, Hp‑Ph″), 7.10 (d, 3JHH = 7.3 Hz, 2H, Ho‑Ph′), 7.23 (t, 3JHH = 7.7 Hz, 2H, Hm‑Ph″), 7.31 (s, 1H, HCarb7), 7.40 (s, 1H, HCarb2)), 7.93 (m, 1H, HCarb5), 8.14 (d, 4JHH = 1.4 Hz, 1H, HCarb4). 13C {1H} NMR (150.90 MHz, C6D6, 295 K): 17.7 (d, J = 5.3 Hz, P1CH(CH3)2), 18.9 (t, J = 5.6 Hz, P1CH(CH3)2), 19.1 (d, J = 3.0 Hz, P1CH(CH3)2), 19.9 (d, J = 4.5 Hz, P1CH(CH3)2), 20.4 (d, J = 6.8 Hz, P2CH(CH3)2), 20.6 (d, J = 4.4 Hz, P2CH(CH3)2), 21.3 (d, J = 1.9 Hz, P2CH(CH3)2), 21.7 (d, J = 7.6 Hz, P2CH(CH3)2), 22.3 (d, J = 6.0 Hz, CH2) 22.5 (d, J = 8.0 Hz, P1CH(CH3)2), 24.9 (d, J = 16.4 Hz, P2CH(CH3)2), 25.5 (s, P2CH(CH3)2), 26.2 (dd, J = 7.7 Hz, J = 5.3 Hz, P1CH(CH3)2), 32.4, 32.5 (s, C(CH3)3), 34.8, 35.0 (s, C(CH3)3), 49.4 (d, J = 46.8 Hz, CH), 68.7 (d, J = 2.1 Hz, CH2Ph”), 69.2 (d, J = 5.6 Hz, CH2Ph′), 110.2 (d, J = 2.0 Hz CCarb5), 110.2 (s, CCarb4), 121.3 (d, J = 0.8 Hz, CCarb), 122.3 (s, Cp‑Ph″), 122.4 (d, J = 1.9 Hz, CCarb), 122.7 (s, Cp‑Ph′), 122.9 (d, J = 1.7 Hz CCarb7), 123.5 (d, J = 7.3 Hz CCarb2), 126.7 (s, Co‑Ph′), 126.9 (s, Co‑Ph″), 127.1 (d, J = 1.2 Hz, CCarb), 128.5 (m, CCarb), 129.5 (s, Cm‑Ph″), 130.7(s, Cm‑Ph′), 137.4 (s, Cipso‑Ph′), 141.9 (m, CCarb), 142.0 (m, CCarb), 144.6 (d, J = 3.7 Hz, CCarb), 145.6 (dd, J = 8.0 Hz, J = 1.7 Hz, CCarb), 146.0 (s, Cipso‑Ph″). 31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (ppm) = −4.0 (d, 2JPP = 19.4 Hz, P2), 10.2 (d, 2JPP = 19.4 Hz, P1). Anal. Calcd for for C48H67NP2Zr: C, 71.07; H, 8.33; N, 1.73. Found: C, 70.52; H, 8.02; N, 1,68. For the syntheses and characterization data of [(CbzdiphosPhCH)ZrBn2] (9PhZr) and [(CbzdiphosPh-CH)HfBn2] (9PhHf), see the Supporting Information. Synthesis of [(CbzdiphosPh-CH)ZrBn3]K (10PhZr). To a solution of [(CbzdiphosPh-CH)ZrBn2] (9PhZr) (200 mg, 0.204 mmol, 1.0 equiv) in benzene was added benzyl potassium (133 mg, 1.019 mmol, 5.0 equiv) at room temperature. After stirring for 4 h at room temperature, the reaction mixture was filtrated over Celite, the volatiles were removed under reduced pressure, and the product was dried in vacuo to afford a brown solid (150 mg, 0.139 mmol, 68%). Due to line broadening an assessment of the 1H and 13C NMR spectra was not assigned. Characterization of the compound was carried out by means of 31P NMR, elemental analysis, and X-ray diffraction analysis. 31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (ppm) = −16.8 (bs, P2), −10.4 (d, 2JPP = 15.7 Hz, P1). Anal. Calcd for C67H66NP2ZrK: C, 74.68; H, 6.17; N, 1.30. Found: C, 74.15; H, 6.31; N, 1.07. Reaction of [(CbzdiphosPh-CH)ZrBn3]K (10PhZr) with [(CbzdiphosPh-CH)ZrBnI] (7PhZr). [(CbzdiphosPh-CH)ZrBn3]K (10PhZr) was dissolved in C6D6, and 1 equiv of 7PhZr was added. 1H and 31P {1H} NMR revealed the resonances of [(CbzdiphosPh-CH)ZrBn2] (9PhZr). Synthesis of [(CbzdiphosPh-CH)ZrCl2(PMe3)] (11PhZr). To a solution of [(CbzdiphosPh)ZrBnCl2] (8PhZr) (400 mg, 0.431 mmol, 1.0 equiv) in toluene was added trimethyl phosphine (32.8 mg, 44.6 μL (ρ = 0.735 g·mol−1) 0.431 mmol, 1.0 equiv) at room temperature. After stirring for 3 h at 80 °C, the reaction mixture was filtrated over Celite and the volatiles were removed under reduced pressure. The crude product was washed with n-pentane and dried under vacuum to afford 10PhZr as an orange solid (340 mg, 0.373 mmol, 86%). 1H NMR (600.13 MHz, C6D6, 295 K): δ (ppm) = 1.01 (d, 2JPH = 7.4 Hz, 9H, P(CH3)3), 1.36 (s, 9H, C(CH3)3), 1.44 (s, 9H, C(CH3)3), 3.94 (t, J = 16.0 Hz, 1H, CHH), 4.10−4.12 (m, 1H, CH), 5.10 (dd, 2JHH = 16.0 Hz, 2JHP = 5.4 Hz, 1H, CHH), 5.91−5.94 (m, 2H, Ho‑Ph(P2)), 6.19−6.22 (m, 2H, Hm‑Ph(P2)), 6.41−6.44 (m, 1H, Hp‑Ph(P2)), 6.67− 6.70 (m, 1H, Hp‑Ph(P1)), 6.75−6.77 (m, 2H, Hm‑Ph′(P1)), 7.00 (s, 1H, HCarb7), 7.04−7.07 (m, 1H, Hp‑Ph′(P1)), 7.11−7.15 (m, 3H, Hp‑Ph′(P2), Hm‑Ph′(P1)), 7.21−7.24 (m, Hm‑Ph′(P2)), 7.44 (s, 1H, HCarb2), 7.62 (s,

volatiles were removed under reduced pressure, and the product was dried in vacuo to afford [(CbzdiphosiPr-CH)ZrBnCl] (6iPrZr) as a red solid (5.00 g, 6.62 mmol, 81%). 1H NMR (600.13 MHz, C6D6, 295 K): δ (ppm) = 0.64 (dd, 2JHP = 15.8 Hz, 3JHH = 7.3 Hz, 3H, P2CH(CH3)2), 0.77 (dd, 2JHP = 11.0 Hz, 3JHH = 7.0 Hz, 3H, P2CH(CH3)2), 0.88−0.93 (m, 1H, P2CH(CH3)2), 1.10−1.12 (m, 6H, P1CH(CH3)2), 1.17 (dd, 2JHP = 11.6 Hz, 3JHH = 7.1 Hz, 3H, P1CH(CH3)2), 1.34−1.42 (m, 9H, P1CH(CH3)2, P2CH(CH3)2), 1.49 (s, 9H, C(CH3)3), 1.53 (s, 9H, C(CH3)3), 2.04−2.10 (m, 1H, P1CH(CH3)2), 2.13−2.19 (m, 1H, P2CH(CH3)2), 2.29−2.35 (m, 1H, P1CH(CH3)2), 2.50 (d, 1H, 2JPH = 7.0 Hz, CH), 2.61 (d, 2JHH = 7.0 Hz, 1H, CHHPh), 2.93 (d, 2JHH = 7.0 Hz, 1H, CHHPh), 3.11 (dd, 2 JPH = 15.1 Hz, 2JHH = 15.9 Hz, 1H, CHH), 3.42 (dd, 2JPH = 3.8 Hz, 2 JHH = 15.8 Hz, 1H, CHH), 6.00 (bs, 2H, HPh′, 6.81 (m, 3H, HPh′), 7.15 (s, 1H, HCarb7), 7.37 (s, 1H, HCarb2)), 7.85 (dd, 4JHP = 1.4 Hz, 4JHH = 1.6 Hz, 1H, HCarb5), 8.10 (d, 4JHH = 1.0 Hz, 1H, HCarb4). 13C {1H} NMR (150.90 MHz, C6D6, 295 K): δ (ppm) = 18.5 (d, J = 3.0 Hz, P1CH(CH3)2), 18.5 (d, J = 2.1 Hz, P1CH(CH3)2/P2CH(CH3)2), 19.21 (t, J = 4.1 Hz, P1CH(CH3)2/P2CH(CH3)2), 19.7 (d, J = 4.5 Hz, P2CH(CH3)2), 19.9 (d, J = 6.6 Hz, P2CH(CH3)2), 20.0 (d, J = 4.3 Hz, P1CH(CH3)2/P2CH(CH3)2), 20.3 (d, J = 5.4 Hz, P1CH(CH3)2/ P2CH(CH3)2), 21.5 (d, J = 4.3 Hz, P1CH(CH3)2/P2CH(CH3)2), 23.8 (d, J = 11.2 Hz, P1CH(CH3)2), 24.5 (d, J = 2.9 Hz, P2CH(CH3)2), 24.8 (d, J = 14.3 Hz, P2CH(CH3)2), 25.1 (d, J = 9.2 Hz, CH2), 26.2 (dd, J = 10.6 Hz, J = 5.3 Hz, P2CH(CH3)2), 32.4, 32.5 (s, C(CH3)3), 34.8, 35.0 (s, C(CH3)3), 50.6 (dd, J = 47.9 Hz, J = 1.5 Hz, CH), 64.8 (dd, J = 10.2 Hz, J = 2.5 Hz, CH2Ph), 110.5 (d, J = 1.9 Hz, CCarb5), 115.3(s, CCarb4), 121.5 (s, CCarb), 212.5 (d, J = 2.0 Hz, CCarb), 122.8 (d, J = 1.1 Hz, CCarb7), 123.5 (d, J = 7.5 Hz, CCarb2), 123.9 (s, CPh′), 126.6 (d, J = 1.2 Hz, CCarb), 128.6 (s, CPh′), 129.5 (d, J = 4.0 Hz, CCarb), 133.2 (s, CPh′), 135.1 (s, CipsoPh′), 141.2 (d, J = 2.2 Hz, CCarb), 142.4 (s, CCarb), 143.8 (d, J = 3.4 Hz, CCarb), 147.3 (dd, J = 1.3 Hz, J = 6.1 Hz, CCarb). 31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (ppm) = 1.7 (d, 2 JPP = 27.3 Hz, P2), 15.5 (d, 2JPP = 27.3 Hz, P1). Anal. Calcd for C41H60ClNP2Zr: C, 65.18; H, 8.00; N, 1.85. Found: C, 65.48; H, 7.82; N, 1.80. For the syntheses and characterization data of [(CbzdiphosPhCH)ZrBnCl] (6PhZr), [(CbzdiphosPh-CH)ZrBnI] (7PhZr), [(Cbzdiphos Ph -CH)HfBnCl] (6 Ph Hf), and [(Cbzdiphos Ph -CH)HfBnI] (7PhHf), see the Supporting Information. Synthesis of [(CbzdiphosPh)ZrBnCl2] (8PhZr). To a solution of [(CbzdiphosPh)ZrCl3 (2PhZr) (2.00 g, 2.29 mmol, 1.0 equiv) in toluene was added tetrabenzylzirconium (0.261 g, 0.573 mmol, 0.25 equiv) at room temperature. The reaction mixture was stirred for 30 min at ambient temperature and filtrated over Celite, and the volatiles were removed under reduced pressure. The crude product was washed with n-hexane and dried under vacuum to afford [(CbzdiphosPh)ZrBnCl2] (8PhZr) as an orange solid (1.70 g, 1.83 mmol, 80%). 1H NMR (600.13 MHz, C6D6, 295 K): δ (ppm) = 1.26 (s, 18H, C(CH3)3), 3.31 (s, 2H, CH2−Ph), 4.03 (bs, 4H, CH2), 6.50−6.51 (m, 3H, HCarb2/7, Hp‑Ph), 6.75−6.77 (m, 2H, HPh), 7.00−7.07 (m, 14H, HPh),), 7.50−7.53 (m, 8H, HPh), 8.03 (s, 2H, CCarb4/5). 13C {1H} NMR (150.90 MHz, C6D6, 295 K): δ (ppm) = 32.0 (s, C(CH3)3), 32.6 (d, J = 10.8 Hz, CH2), 34.4 (s, C(CH3)3), 75.6 (s, CH2−Ph), 115.0 (s, CCarb4/5), 119.8 (s, CCarb), 125.0 (bs, CCarb2/7), 126.7 (s, Cp‑Ph), 128.1 (d, J = 8.2 Hz, CPh), 129.4 (bs, CPh), 130.2 (bs, CPh), 131.7 (t, J = 3.9 Hz, Cipso‑Ph′), 132.7 (bs, Cipso‑Ph), 134.9 (bs, CPh), 137.6 (bs, CPh), 141.9 (s, CCarb), 149.9 (m, CCarb); n.o. CCarb. 31P {1H} NMR (161.88 MHz, C6D6, 296 K): δ (ppm) = 12.8 (bs). Anal. Calcd for C59H67Cl2NP2Zr [M + n-hexane]: C, 69.87; H, 6.66; N, 1.38. Found: C, 70.11; H, 6.59; N, 1.15. The compound was recrystallized from n-hexane. Synthesis of [(CbzdiphosiPr-CH)ZrBn2] (9iPrZr). To a solution of [(CbzdiphosiPr-CH)ZrBnCl] (7iPrZr) (300 mg, 0.397 mmol, 1.0 equiv) in benzene was added benzyl potassium (56.9 mg, 0.437 mmol, 1.1 equiv) in portions at room temperature. After stirring for 1 h at ambient temperature, the reaction mixture was filtrated over Celite, the volatiles were removed under reduced pressure, and the product was dried in vacuo to afford a red solid (220 mg, 0.271 mmol, 68%). 1H NMR (600.13 MHz, C6D6, 295 K): δ (ppm) = 0.54−0.58 (m, 3H, J


Article

Inorganic Chemistry 1H, HCarb5), 7.78−7.81 (m, 2H, Ho‑Ph′(P2)), 7.84−7.87 (m, 2H, Ho‑Ph(P1)), 7.97 (s, 1H, HCarb4),8.27−8.30 (m, 2H, Ho‑Ph′(P1)). 13C {1H} NMR (150.90 MHz, C6D6, 295 K): δ (ppm) 12.7 (d, J = 17.4 Hz, P(CH3)3), 32.3, 32.4 (s, C(CH3)3), 33.5 (d, J = 14.1 Hz, CH2), 34.8, 34.9 (s, C(CH3)3), 57.4 (d, J = 55.0 Hz, CH), 111.2 (d, J = 1.6 Hz, CCarb5), 115.6 (s, CCarb4), 120.5 (s, CCarb7), 122.3 (d, J = 1.4 Hz, CCarb), 122.5 (d, J = 2.2 Hz, CCarb), 123.8 (d, J = 8.7 Hz, CCarb2), 123.8 (d, J = 3.3 Hz, CCarb2), 127.0 (d, J = 1.2 Hz, CCarb), 127.2 (d, J = 9.5 Hz, Cm‑Ph(P2)), 128.4 (d, J = 9.3 Hz, Cm‑Ph′(P2)), 128.5 (d, J = 8.4 Hz, Cm‑Ph′(P1)), 128.7 (d, J = 2.3 Hz, Cp‑Ph(P2)), 128.9 (d, J = 9.1 Hz, Cm‑Ph(P1)), 129.3 (d, J = 1.7 Hz, Cp‑Ph′(P2)), 129.9 (d, J = 1.4 Hz, Cp‑Ph(P1)), 130.1 (dd, J = 13.1 Hz, J = 1.3 Hz, Cipso‑Ph), 130.4 (d, J = 1.9 Hz, Cp‑Ph′(P1)), 133.2 (d, J = 9.9 Hz, Cp‑Ph(P2)), 133.4 (d, J = 18.4 Hz, Cipso‑Ph), 133.7 (d, J = 11.5 Hz, Co‑Ph(P1)), 134.4 (d, J = 12.7 Hz, Co‑Ph′(P2)), 134.5 (d, J = 25.5 Hz, Cipso‑Ph), 135.2 (d, J = 23.5 Hz, Cipso‑Ph), 135.3 (d, J = 12.1 Hz, Co‑Ph′(P1)), 137.4 (dd, J = 25.7 Hz, J = 3.7 Hz, CCarb), 142.6 (d, J = 2.2 Hz, CCarb), 142.8 (s, CCarb), 145.5 (dd, J = 3.9 Hz, J = 1.6 Hz, CCarb), 145.7 (d, J = 4.1 Hz, CCarb). 31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (ppm) = −22.1 (dd, 2JP3P1 = 84.1 Hz, 2JP3P2 = 17.0 Hz, PMe3), −13.8 (dd, 2JP1P2 = 24.6 Hz, 2JP3P2 = 17.0 Hz, P2), −2.1 (dd, 2JP3P1 = 84.1 Hz, 2JP1P2 = 24.6 Hz, P1). Anal. Calcd for C49H54Cl2NP3Zr: C, 64.53; H, 5.97; N, 1.54. Found: C, 64.79; H, 5.67; N, 1.75. Synthesis of [(CbzdiphosPh-CH)Zr(o-C6H4PPh2CH2)I] (12PhZr). To a solution of [(CbzdiphosPh-CH)ZrBnI] (7PhZr) (400 mg, 0.0.407 mmol, 1.0 equiv) in toluene was added methylenetriphenylphosphorane (112.5 mg, 0.407 mmol, 1.0 equiv) at room temperature. After stirring overnight at 60 °C, the reaction mixture was filtrated over Celite and the volatiles were removed under reduced pressure. The residue was redissolved in toluene, and the solution was stored in a freezer (−40 °C) overnight. The supernatant was decanted, and the solid was dried under vacuum to afford product as a red solid (330 mg, 0.285 mmol, 70%). 1H NMR (600.13 MHz, C6D6, 295 K): δ (ppm) = 1.55−1.21 (m, 1H, CHH = P3), 1.27 (s, 9H, C(CH3)3), 1.51 (s, 9H, C(CH3)3), 1.86−1.91 (m, 1H, CHH = P3), 3.76−3.89 (m, 2H, CHH), 4.33 (s, 1H, CHP1), 6.22−6.25 (m, 3H, HPh), 6.34−6.38 (m, 2H, HPh), 6.40−6.43 (m, 1H, HPh), 6.35−6.59 (m, 2H, HPh), 6.73−6.77 (m, 3H, HPh), 6.79−6.91 (m, 7H, HPh, HCarb7, H2), 6.96−6.99 (m, 2H, HPh), 7.00−7.04 (m, 1H, H3), 7.05−7.10 (m, 1H, HPh), 7.11−7.16 (m, 3H, HPh), 7.20 (s, 1H, HCarb2), 7.27−7.31 (m, 3H, HPh, HCarb4), 7.37−7.38 (m, 1H, HPh), 7.60 (s, 1H, HCarb5), 8.10−8.13 (m, 2H, HPh), 8.16− 8.20 (m, 2H, HPh), 8.38−8.43 (m, 2H, HPh), 9.25 (d, 2JHH = 7.4 Hz, 1H, H5). 13C {1H} NMR (150.90 MHz, C6D6, 295 K) δ (ppm) = 29.2 (dd, J = 35.5 Hz, J = 7.5 Hz, CH2 = P3), 32.5, 32.5 (s, C(CH3)3), 33.7 (d, J = 7.9 Hz, CH2), 34.7, 34.7 (s, C(CH3)3), 64.5 (d, J = 50.4 Hz, CH), 110.0 (s, CCarb5), 115.4 (s, CCarb7), 122.5 (d, J = 7.9 Hz, CCarb2), 132.2 (s, CCarb), 125.5 (d, J = 7.9 Hz, CCarb4), 127.1 (d, J = 7.9 Hz, CPh), 128.1−128.9 (m, CPh), 129.5−129.6 (m, CPh), 130.2 (s, CPh), 130.6−130.8 (m, (d, CPh), 131.3 (s, CPh), 132.2 (d, J = 10.5 Hz, CPh), 133.2 (d, J = 10.7 Hz, CPh), 133.4 (d, J = 20.1 Hz, CPh), 133.7 (d, J = 11.8 Hz, CPh), 133.9−134.2 (m, CPh), 134.6 (d, J = 14.2 Hz, CPh), 137.5−137.8 (m, CCarb/Cipso‑Ph), 138.2 (d, J = 18.7 Hz, CCarb/Cipso‑Ph), 140.2 (140.7 (s, CCarb), 142.2 (d, J = 1.0 Hz, CCarb), 142.3 (d, J = 24.0 Hz, C5), 143.7 (d, J = 5.1 Hz, CCarb), 145.7 (m, CCarb), 207.3−207.7 (m, Zr−C6). 31P {1H} NMR (242.94 MHz, C6D6, 295 K): δ (ppm) = −19.9 (d, 2JP1P2 = 26.1 Hz, P2), −6.3 (dd, 2JP1P2 = 26.1 Hz, 2JP3P2 = 32.2 Hz, P1) and 37.0 (d, 2JP3P1 = 32.3 Hz, P3). Anal. Calcd: C, 66.88; H, 5.27; N, 1.20. Found: C, 66.39; H, 5.51; N, 1.24.

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selected bond parameters; details of the crystal structure determinations; 1H, 13C, and 31P NMR spectra of the compounds (PDF) (CIF)

AUTHOR INFORMATION

Corresponding Author

*Fax: +49-6221-545609. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to Jonas C. Ott and Lukas Lohmeyer for experimental support. We thank the University of Heidelberg for funding.

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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.inorgchem.5b02498. Syntheses and characterization data of 1iPrH, 2iPrZr/Hf, 2PhTi/Hf/Zr, 3iPrZr/Hf, 3PhTi/Zr/Hf, 5PhTi, 6PhZr/Hf, 7PhZr, and 9PhZr/Hf; figures of the molecular structure of ligand 1iPrH and complexes 2Zr/Hf and 3iPrZr and K


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