Synthesis and Characterization of N-Donor-Functionalized

Article pubs.acs.org/Organometallics

Synthesis and Characterization of N-Donor-Functionalized Enantiomerically Pure Pentadienyl Ligands Derived from (1R)‑(−)Myrtenal Ann Christin Fecker, Bogdan-Florin Crăciun,† Peter Schweyen, Matthias Freytag, Peter G. Jones, and Marc D. Walter* Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany S Supporting Information *

ABSTRACT: A series of enantiomerically pure −SiMe2NR2 (R = Me, Et) substituted pentadienyl ligands were prepared starting from the natural product (1R)-(−)-myrtenal. Deprotonation with a Schlosser superbase yields the corresponding potassium salts, which were characterized by various spectroscopic techniques. In solution these neutral N-donor-substituted pentadienyl systems predominantly adopt a U conformation, but in two cases the rare S conformation was also observed as a minor component in solution. Addition of 18-crown-6 allowed the molecular structures of two of these potassium pentadienyls to be determined by X-ray diffraction. Interestingly, η5 and κN coordination of the pentadienyl system to the [K(18-crown-6)]+ cation was observed. Furthermore, these ligand systems also coordinate to transition metals and form an open titanocene, open vanadocenes, open chromocenes, and half-open trozircenes with [TiCl3(thf)3], [VCl3(thf)3], CrCl2, and [(η7-C7H7)ZrCl(tmeda)], respectively. These complexes were characterized by elemental analyses and various spectroscopic techniques. However, no coordination of the pendant −SiMe2NR2 group to the metal centers was observed. In addition, significant steric crowding in these open metallocenes prevents the formation of isolable CO or PMe3 adducts. This was further corroborated by EPR studies on an open vandadocene, which showed that no adduct formation occurs at ambient temperature in solution, but a weak PMe3 adduct was detected at 26 K.

■

than that of the ground state. 2 NMR spectroscopy or regioselective trimethylsilylation was used to obtain experimental information on the preferred conformation of the alkali-metal pentadienyl anions in solution.1i,3 However, whereas the influence of alkyl and trimethylsilyl groups on the conformation of the pentadienyl anion is now well established, the effect of neutral O- and N-donor functionalization on the structure of their respective lithium salts is still under investigation. In order to close this knowledge gap, Naruta and Maruyama reacted the lithium and potassium pentadienyl complexes [2-RC5H6]M (M = Li, K; R = CH2NMe2, CH2OMe) with Me3EBr (E = Si, Sn),3k but only recently did Layfield and co-workers provide structural insights into related species.3i,j In the course of these studies [(tmeda)Li{1,5-(Me3Si)2-3-(MeOC2H4)C5H4}],3i [(pmdeta)Li{(1,5-R3Si)2C5H5}], and [(pmdeta)Li{(1-R3Si)C5H6}] (R = Me2(NMe2)Si, pmdeta = N,N,N′,N″,N″-pentamethyldiethylenetriamine)3j were prepared and it was demonstrated that the silylated lithium derivatives [(pmdeta)Li{(1,5-R3Si)2C5H5}] and [(pmdeta)Li{(1-R3Si)C5H6}] (R = Me2SiNMe2) adopt W configurations with η1 and η3 coordination of the [(pmdeta)Li]+ cation, respectively, in the solid state and in solution.3j However, the coordination chemistry of these N-donor-functionalized

INTRODUCTION Pentadienyl (Pdl) and heteropentadienyl ligands are an integral part of the organometallic toolbox, and many pentadienyl complexes have been synthesized since 1962.1 One of the most prominent protagonists in this field is Ernst, who showed that pentadienyls can adopt not only several conformations, namely the W, S, and U conformations (Chart 1), but also multiple coordination modes such as η1, η3, and η5.1b−j Nevertheless, most of these investigations have employed alkyl- and trimethylsilylsubstituted derivatives.1b,c,f−h Chart 1

To gain additional insights into the relative stabilities of the W, S, and U conformations, computational and experimental studies were conducted on alkali-metal pentadienyl and silyl-substituted derivatives. Density functional theory (DFT) suggested that the η5-U conformation is the most stable form for the unsubstituted alkali-metal pentadienyls [(C5H7)M] (M = Li−K) in the gas phase and in solution. Nevertheless, for the smallest alkali metal, lithium, the energy of the W conformation is only slightly higher © 2014 American Chemical Society

Received: October 7, 2014 Published: December 22, 2014 146

dx.doi.org/10.1021/om501024j | Organometallics 2015, 34, 146−158

Organometallics

Article

Scheme 1

Tables 1 and 2. The potassium salts 4a−c and 5a−c have been prepared from the chiral 1,3-pentadienes 2a−c and 3a−c, respectively, by deprotonation with the Schlosser base combination of potassium tert-pentoxide (KOtPe) and nbutyllithium (n-BuLi) and have been isolated as extremely pyrophoric yellow powders in excellent yields (Scheme 1). NMR spectra of 4a−c and 5a−c were recorded in thf-d8 solutions. The η5-U conformation is preferred in solution, as shown by NOESY experiments, but we also observe the rare S conformation7 as a minor component in some cases (ratios 1:2.41 and 1:2.36 for 4c′:4c and 5c′:5c, respectively) (Scheme 1). This represents a major difference from the observations by Layfield and coworkers on the N-donor-substituted lithium pentadienyls [(pmdeta)Li{(1,5-R 3 Si) 2 C 5 H 5 }] and [(pmdeta)Li{(1R3Si)2C5H6}] (R = Me2SiNMe2).3j The assignment of the Uand S conformations for 4c/5c and 4c′/5c′, respectively, is further substantiated by the typical cis/trans 3JHH coupling constants between H2 and H3, which are in the range commonly observed in pentadienyl complexes.3b,e,8 In addition, both conformers are in equilibrium with each other, as illustrated by the exchange peaks in the 1H−1H-NOESY NMR spectrum (Chart 2 and Figure 1). To further provide structural insights, 18-crown-6 adducts [K(18-crown-6)][4b] and [K(18-crown-6)][5a] were prepared and single crystals were grown by slow diffusion of pentane into a toluene solution at −30 °C. ORTEP diagrams are shown in Figure 2, and selected bond distances and angles are given in the figure caption. Whereas [K(18-crown-6)][4b] cocrystallizes with two independent molecules and three molecules of C7H8 in the asymmetric unit in the triclinic space group P1, the orthorhombic space group P212121 is found for [K(18-crown6)][5a], which crystallizes “normally” with Z′ = 1 and no solvent

pentadienyl ligands toward metals other than group 1 has yet to be explored. Following an initial report by Salzer on the dimethylnopadienyl ligand (1a),4 we have recently prepared new enantiomerically pure pentadienyl ligands (1b,c) starting from the natural product (1R)-(−)-myrtenal and used them for the synthesis of transition-metal complexes.5 The advantage of these pentadienyl ligands is their high degree of face selectivity on metal coordination, because one side of the ligand systems (cis to the CMe2 bridge) is significantly more sterically crowded than the other (cis to the CH2 bridge). Encouraged by these initial results, we are now extending our studies to N-donor-functionalized chiral pentadienyl ligands and their coordination chemistry, since this might offer an additional site for metal interaction.

■

RESULTS AND DISCUSSION Synthesis and Solution Characterization of N-Donor Functionalized Pentadienyls and Their Potassium Salts. In general, alkylation of pentadienyl anions is not regiospecific and may occur at the 1-, 3-, and 5-positions.3c Nevertheless, silylation of the parent pentadienyl ligand is selective for the chain ends.3f,6 The reaction of 1a−c with ClSiMe2NR2 (R = Me, Et) at −40 °C in tetrahydrofuran proceeds smoothly, and the corresponding 1,3-pentadienes 2a−c and 3a−c are isolated as colorless oils in good yields (Scheme 1; see also the Experimental Section for details). The N-functionalized 1,3-pentadienes are obtained in an s-cis configuration with the exception of 3c/3c*, which is a mixture of s-cis and s-trans isomers (ratio 1.85:1). Both configurations are expected when a Pdl anion in a U configuration reacts with electrophiles.3e,f,k NMR spectroscopic data for 2a−c and 3a−c and their potassium salts are given in 147


Organometallics

Article

Table 1. Spectroscopic Details for Pentadienes 2a−c and Their Potassium Salts 4a−c

a

Because of the low concentration of this isomer, the detection of these resonances was only possible by 1H−13C HSQC/HMBC experiments.

(Table S1, Supporting Information). In each case the pentadienyl moiety adopts a U configuration, but only for [K(18-crown-6)][5a] does the pentadienyl anion coordinate in an η5 fashion to the [K(18-crown-6)]+ cation. Similar to the case for [K(18-crown-6)][1a]5a the shortest K−C distance of 3.0987(16) Å is observed for the central C3 atom, whereas the other K−C distances become increasingly longer: 3.1804(16) Å (C4), 3.2871(15) Å (C2), 3.2521(17) Å (C5), and 3.4812(16) Å

(C1). However, one notable difference between [K(18-crown6)][1a]5a and [K(18-crown-6)][5a] is the significantly elongated K−C1 and K−C2 distances of 3.4812(16) and 3.2871(15) Å, respectively, in comparison to those in [K(18-crown-6)][1a] (3.1693(18) and 3.1156(16) Å, respectively).5a Simultaneously the K−C4 and K−C5 distances of 3.1804(16) and 3.2521(17) Å in [K(18-crown-6)][5a] are distinctly shorter than those in [K(18-crown-6)][1a] (3.2332(16) and 3.3063(18) Å, respecti148


Organometallics

Article

Table 2. Spectroscopic Details for Pentadienes 3a−c and Their Potassium Salts 5a−c

a

Because of the low concentration of this isomer, the detection of these resonances was only possible by 1H−13C HSQC/HMBC experiments.

vely).5a These differences are probably a consequence of the functionalization of C1 with the bulky SiMe2NEt2 group. In contrast, for [K(18-crown-6)][4b] the coordination of the pentadienyl system to the [K(18-crown-6)]+ cation occurs via the NMe2-donor group: i.e., in a κN fashion. This rather unusual coordination mode may be attributed to the sterically encumbered Ph group at the C2 position of the pentadienyl

anion, which hampers a close approach of 4b to the [K(18crown-6)]+ cation. However, further inspection of the two independent molecules in the asymmetric unit also reveals that these molecules form an intermolecular cation−anion pair, i.e. the [K(18-crown-6)]+ and the pentadienyl fragment of 4b are located in close proximity to each other (Figure S2 in the 149


Organometallics

Article

[K(18-crown-6)][4b]. Therefore, both isomers apparently coexist in benzene solutions for [K(18-crown-6)][4b]. Synthesis of Open Vanadocenes and Chromocenes. With these N-donor-functionalized Pdl ligands in hand, we attempted to stabilize mono(pentadienyl) vanadium(II) and chromium(II) complexes. However, regardless of the ligand ratio only the corresponding open metallocenes could be isolated from the reaction with [VCl3(thf)3] and CrCl2. To ensure complete conversion and good yields, 3 and 2 equiv of the potassium salts were reacted with [VCl3(thf)3] and CrCl2 to yield the corresponding open vanadocene and open chromocene complexes, respectively (Scheme 2). The resulting open metallocenes crystallized from concentrated hexane solutions at −30 °C (Tables S1 and S2 in the Supporting Information). Representative molecular structures of an open vanadocene (6a) and open chromocene (8a) are shown in Figures 3 and 4, respectively, and selected bond distances and angles are given in the figure captions. ORTEP diagrams of the remaining open metallocenes 7a,c, 8c, and 9a,c can be found in the Supporting Information. The introduction of the N-donor functionality in the C1 position has only minor effects on the overall molecular structures in comparison to the case for the non-donor-functionalized compounds. In all cases no coordination of the neutral N-donor functionality to the vanadium or chromium atom was observed, which might be a direct consequence of the severe steric demand of these pentadienyl ligands. We have advanced this argument before, on the basis of our inability to isolate stable CO or PMe3 adducts of the open titanocene, vanadocene, and chromocene bearing the pentadienyl 1a.5 Although the introduction of the −SiMe2NR2 group at the C1 position of the pentadienyl group induces additional steric bulk at the metal center, the averaged M−C bond distances of V−C(av) 2.2540 ± 0.0145 Å and Cr− C(av) 2.2371 ± 0.0409 Å are essentially identical with the 3σ criterion in comparison to those of the unfunctionalized open metallocenes, V−C(av) 2.234 ± 0.032 [2.226 ± 0.028] and Cr− C(av) 2.208 ± 0.016 [2.199 ± 0.023] Å.5a However, these steric

Chart 2

Supporting Information), which apparently provides additional stabilization of the κN coordination mode. Since solution and solid-state properties of a complex may be different, we also recorded NMR spectra of crystalline [K(18crown-6)][4b] in C6D6 solution. However, the resulting 1H NMR spectrum is rather complicated and suggests the presence of two dominant species A and B in solution in a ratio of 3:1. Because of severely overlapping resonances of the bicyclic framework, an unambiguous assignment of the NMR resonances is only possible for the resonances corresponding to the pentadienyl fragment and the respective −SiMe2NMe2 groups of species A and B (see the Experimental Section for details). On the basis of NOESY experiments a U conformation can be unambiguously assigned for A and B, as illustrated for example by an NOE interaction between the H1 and H5 atoms (Chart 3). Nevertheless, there are marked differences between the isomers A and B and their interaction with the [K(18-crown6)]+ cation. The major isomer A shows strong NOE interactions between the protons of Mea and Meb and those of 18-crown-6. In addition, weak NOEs are also found between the protons of 18crown-6 and H1 and H3. Overall, these observations strongly suggest that species A is best described by a η5-U coordination mode as found in [K(18-crown-6)][η5-5a], in which the −SiMe2NEt2 points away from the [K(18-crown-6)]+ cation. In contrast, isomer B exhibits only one strong NOE interaction between the H atoms of 18-crown-6 and of one Me group. The absence of additional interactions between the H atoms of the Pdl moiety and 18-crown-6 strongly suggest a κN coordination mode for isomer B, as was observed in the solid-state structure of

Figure 1. 1H−1H-NOESY NMR spectrum of 4c and 4c′ recorded in thf-d8 at ambient temperature. Labels in italics correspond to the S conformer 4c′. 150


Organometallics

Article

Figure 2. ORTEP diagrams of [K(18-crown-6)][4b] and [K(18-crown-6)][5a] with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg) are as follows. K(18-crown-6)][4b]: K−O(18-C-6) 2.800(2)−2.883(3) [2.785(2)−2.892(2)], K−N 2.962(3) [2.986(3)], C1−C2 1.402(4) [1.384(5)], C2−C3 1.391(5) [1.412(5)], C3−C4 1.444(5) [1.426(3)], C4−C5 1.356(5) [1.353(5)], C1···C5 3.309; C1−C2−C3 130.3(3) [128.9(3)], C2−C3−C4 130.0(3) [130.8(3)], C3−C4−C5 130.5 [130.9(3)]. Values given in brackets correspond to the second molecule in the asymmetric unit. [K(18-crown-6)][5a]: K−O(18-C-6) 2.764(2)-3.0987(16), K−C1 3.4812(16), K−C2 3.2871(15), K−C3 3.0987(16), K−C4 3.1804(16), K−C5 3.2521(17), C1−C2 1.397(2), C2−C3 1.406(2), C3−C4 1.438(2), C4−C5 1.366(2), C1···C5 3.325; C1−C2− C3 128.38(15), C2−C3−C4 130.84(14), C3−C4−C5 131.12(15).

Chart 3

comparison to those found in the literature for other open vanadocenes and their CO and PMe3 adducts. Nevertheless, at 26 K in frozen pentane solution a very weak coupling can be detected between the unpaired electron located at the V2+ atom and the 31P nucleus (Figure S14 and Table S3 in the Supporting Information). Attempts to construct heterobimetallic complexes via coordination of a further metal atom to the N lone pair have so far been unsuccessful. When 8c was treated with ZnCl2, [FeBr2(dme)], or FeCl2 in THF, no reaction occurred with ZnCl2, whereas Fe2+ was reduced within a few minutes to iron metal. Synthesis of an Open Titanocene and Half-Open Trozircenes. After the successful preparation of open vanadocenes and chromocenes, we also decided to employ these ligands in combination with group 4 elements. Indeed,

effects slightly affect the molecular conformation of these open metallocenes. Complexes 6a and 8a have conformational angles χ of 76 and 79°, respectively, which are considerably smaller than those in the unfunctionalized derivatives.5a The value of 79° for 8a is close to that found in [(η5-1,5-(Me3Si)2C5H5)2Cr].9 The related [(η5-1,5-(Me3Si)2C5H5)2V] exhibits reversible CO adduct formation, as shown by EPR spectroscopy at ambient temperature.9 Therefore, we decided to record the EPR spectrum of 7a in the presence of an excess of PMe3 at ambient temperature and in frozen pentane solution (26 K). At room temperature no adduct formation could be detected, since only the vanadium hyperfine splitting V2+ (I = 7/2), giving rise to the expected eight-line pattern, was detected in the presence or absence of PMe3 (Figure 5). Table 3 gives the parameters derived from the experimental data at ambient temperature in 151


Organometallics

Article

Scheme 2

Figure 3. ORTEP diagram of open vanadocene (6a) with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): C1···C5 3.125, C18···C22 3.131, C1−V 2.253(3), C2−V 2.240(3), C3−V 2.237(3), C4−V 2.269(3), C5−V 2.265(3), C18−V 2.237(3), C19−V 2.252(3), C20−V 2.243(3), C21−V 2.273(3), C22−V 2.271(3), C1−C(5) 3.125, C18−C22 3.131, V−C(av) 2.2540 ± 0.0145, Pdlcent(C1−C5)−Cr 1.666, Pdlcent(C18− C22)−Cr 1.669; C2−C1−Si1 124.9(2), C1−Si1−N1 109.6(2), C2− C1−Si1−N1−46.8(3), C19−C18−Si(2) 122.6(2), C18−Si2−N2 109.8(2), C19−C18−Si2−N2 −48.8(3), conformational angle χ 76, αplanes 9.8, αSi1 −4.8, αH1 −37.1, αC13 8.2, αH3 7.9, αH5 −19.4, αSi2 −7.0, αH18 −33.8, αC30 3.9, αH20 8.1, αH22 −23.9. Angles associated with a negative sign indicate that the group/atom is oriented away from the metal atom, whereas a positive sign specifies that the group/atom points toward the metal.

Figure 4. ORTEP diagram of open chromocene (8a) with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): C1···C5 3.076, C18···C21 3.076, C1−Cr 2.274(2), C2−Cr 2.206(2), C3−Cr 2.180(2), C4−Cr 2.232(2), C5−Cr 2.299(2), C18−Cr 2.255(2), C19−Cr 2.221(2), C20−Cr 2.187(2), C21−Cr 2.231(2), C22−Cr 2.287(2), Cr−C(av) 2.2371 ± 0.0409; Pdlcent(C1−C5)−Cr 1.655, Pdlcent(C18−C22)−Cr 1.654, C2− C1−Si1 124.1(2), C1−Si1−N1 109.3(1), C2−C1−Si1−N1−48.5(3), C19−C18−Si2 121.9(2), C18−Si2−N2 109.1(2), C19−C18−Si2−N2 −50.3(2), conformational angle χ 79, αplanes 8.8. αSi1 −4.5, αH1 −33.5, αC13 6.2, αH3 5.0, αH5 −21.5, αSi2 −6.4, αH18 −36.6, αC30 7.6, αH20 4.5, αH22 −20.6. Angles associated with a negative sign indicate that the group/atom is oriented away from the metal atom, whereas a positive sign specifies that the group/atom points toward the metal.

potassium pentadienide 5a reacts with [TiCl3(thf)3] to yield the open titanocene 10a (Scheme 2). However, this reaction is not as clean as previously observed for [(η5-1a)2Ti],5a and several recrystallizations are required to obtain analytically pure material. Nevertheless, in contrast to the case for [(η5-1a)2Ti]5a we only observed one isomer in solution (Figure 6). Furthermore, longrange interactions between the SiMe2 groups, Mea and Meb, and

the protons H3′ and H9′ on the other pentadienyl ligand unambiguously establish that no κN coordination persists in solution. Crystals of 10a suitable for X-ray diffraction were grown from concentrated hexane solutions at −30 °C (see the Supporting Information for details, Table S2). The molecular structure of 10a is shown in Figure 7, and selected bond distances and angles 152


Organometallics

Article

distances exhibit the typical short−longer−longest pattern usually observed for pentadienyl complexes with metals in high oxidation states. The shortest bond distance is observed between C3 and Zr, while the others are progressively longer. This asymmetry in the Zr−C bonds can be attributed to the contracted Zr(IV) orbitals, reducing the efficient overlap with all carbon atoms.

■

CONCLUSIONS Enantiomerically pure N-donor-functionalized 1,3-pentadienes were readily prepared starting from the natural product (1R)(−)-myrtenal. Deprotonation is accomplished by a Schlosser base combination to yield the pentadienide salts in good yield. NMR spectroscopy on the potassium salts showed that the U conformation is preferred in solution. However, when the C2 position carries an H atom, the rare S conformation also persists in solution, as shown by NOESY spectroscopy. Furthermore, the coordination chemistry of donor-functionalized pentadienyl ligands has also been explored for titanium(II), vanadium(II), chromium(II), and zirconium(IV). The open titanocene, vanadocenes, and chromocenes do not form stable adducts with CO or PMe3; this is a direct consequence of the severe steric demand of these ligand systems. Furthermore, no intramolecular N-donor coordination to these transition-metal atoms was observed. Studies focusing on the construction of chiral constrained-geometry pentadienyl systems and their coordination chemistry are ongoing and will be reported in due course.

Figure 5. X-band EPR spectrum of 7a recorded in pentane solution at ambient temperature. Simulated parameters are given in Table 3

are given in the figure caption. The introduction of the additional N-donor functionality has only a minor influence on the overall structure in comparison to the case for [(η5-1a)2Ti]:5a e.g., the averaged Ti−C distance Ti−C(av) 2.278 ± 0.017 Å is essentially identical with those observed in [(η5-1a)2Ti] of 2.273 ± 0.017 [2.264 ± 0.027] Å.5a However, the conformational angle χ in 10a is slightly reduced to 79° relative to 85° in [(η5-1a)2Ti]. Because of its excellent crystallization properties, the [(η7C7H7)Zr]+ fragment has been used to coordinate various monoanionic ligands.5,13 Furthermore, the Lewis acidity of the Zr atom might also result in an intramolecular coordination of the neutral N-donor side arm to the metal atom, but so far we have been unable to obtain crystalline material in the absence of PMe3. Nevertheless, crystals of the PMe3 adducts 11b,c and 12b,c can readily be obtained from concentrated pentane solutions at −30 °C (see Scheme 3 and Table S3 in the Supporting Information for details), and the molecular structure of 11b is shown in Figure 8, while relevant bond distances and angles are given in the figure caption. The ORTEP diagrams of 11c and 12b,c and relevant structural data are shown in the Supporting Information. It is interesting to compare the metric parameters in 11b to those of [(η7-C7H7)Zr(η5-1b)(PMe3)].5b The steric demand of this ligand system on the [(η7-C7H7)Zr]+ group is quite pronounced: e.g., the C1···C5 distance in 11b (3.25 Å) is larger than that in [(η7-C7H7)Zr(η5-1b)(PMe3)] (3.16 Å).5b Consistently the average Zr−CPdl distances and Pdlcent are elongated by 0.045 and 0.040 Å, respectively. Furthermore, the Zr−CPdl

■

EXPERIMENTAL SECTION

General Considerations. All experiments were carried out under an atmosphere of purified N2, either in a Schlenk apparatus or in a glovebox. The solvents were dried and deoxygenated by distillation under nitrogen atmosphere from sodium benzophenone ketyl (tetrahydrofuran) and by a solvent purification system (toluene, pentane). The following starting materials were prepared according to the literature: potassium pentadienyls 1a−c,5 ClSiMe2NR2 (R = Me,14 Et15), KOtPe,16 [TiCl3(thf)3],17a [VCl3(thf)3],17b and [(η7-C7H7)Zr(tmeda)Cl].13a Other commercial reagents such as n-BuLi, CrCl2, and 18-crown-6 were used as received without further purification. NMR spectra were recorded at 400 MHz (1H) or 101 MHz (13C). All chemical shifts are reported in δ units with reference to the residual protons of the deuterated solvents, which are internal standards, for proton and carbon chemical shifts. Gas chromatography was conducted on an instrument equipped with a 35 m × 0.25 mm glass capillary column coated with Cyclodex-B. Elemental analyses were performed by the analytical facilities at the Institute of Inorganic and Analytical Chemistry at the TU Braunschweig. The X-band EPR spectra were simulated with EasySpin 4.5.0.18 X-ray Diffraction Studies. Data were recorded at 100(2) K on Oxford Diffraction diffractometers using monochromated Mo Kα or mirror-focused Cu Kα radiation (see Tables S1−S3 in the Supporting Information). The structures were refined anisotropically on F2 using the SHELXL-97 program.19 Hydrogens at C1, C3, and C5 of the

Table 3. EPR Data for Selected Open Vanadocenesa

a

compound/host

giso

|Av|/mT

|Ap|/mT

ref

7a/pentane [+PMe3] [(η5-2,4-(Me3C)2C5H5)2V/pentane [(η5-2,4-Me2C5H5)2V]/THF [(η5-1,5-(Me3Si)2C5H5)2V]/toluene [(η5-2,4-Me2C5H5)2V(CO)]/toluene [(η5-2,4-Me2C5H5)2V(PMe3)]/toluene

1.972 [1.972] 1.968 2.001 1.970 1.974 1.985

7.95 [7.95] 6.68 7.72 8.15 7.65 7.78

[−]

this work 10 11 9 12 12

3.27

Recorded in solution at ambient temperature. 153


Organometallics

Article

Figure 6. 1H−1H NOESY NMR spectrum of 10a recorded in C6D6 at ambient temperature featuring NOE interactions between the Mea and Meb protons on the SiMe2 group. Resonances marked with boxes exhibit long-range NOE interactions between the Mea and Meb groups and the protons H3′ and H9′ on the other pentadienyl ring. each case by the Flack parameter. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications nos. CCDC 1025118−1025131 and 1036683. Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/data_request/cif. Special features and exceptions: [K(18-crown-6)][4b] is the only structure that crystallized with solvent, and all three toluene molecules are ordered. The two independent molecules of the complex are related via a pseudoinversion center. In the complex [K(18-crown-6)][5a], one crown ether is disordered over two positions. Suitable restraints were used to improve the stability of the refinement, but the dimensions of disordered groups should always be interpreted with caution. Structures 6a and 8a are isotypic, as are 11b and 12b. Structures 7a and 9c, despite having the same space group, similar cell constants, and imposed 2-fold symmetry, are not isotypic; the molecules are differently oriented, being effectively reversed in direction with respect to the b axis. Structure 7c contains two independent molecules, both with imposed 2-fold symmetry; a leastsquares fit gave a root-mean-square deviation (rmsd) of 0.13 Å (excluding terminal ethyl carbons). The complex [(η5-1b)2Cr] has imposed 2-fold symmetry. The two independent molecules of 8c have an rmsd of 0.23 Å, excluding C30−32 and N2. Complex 9a displays a slightly disordered ethyl group (C18, C19). Standard Procedure for the Aminosilylation. The potassium salts 1a−c were dissolved in THF (150 mL) to form dark red to brown solutions and cooled to −40 °C. After addition of ClSiMe2NR2 (R = Me, Et) the solutions became colorless. After the mixture was stirred for 4 h, the solvent was removed under dynamic vacuum and the glassy residues were extracted with hexanes (100 mL). After filtration, removal of hexanes, and distillation under high vacuum, the products were isolated as highly viscous, colorless oils. Data for 2a are as follows. Yield: 73%. Bp: 71−75 °C (0.01 mmbar). GC/MS: 18.08 min. Anal. Calcd for C17H31NSi (277.53): C, 73.57; H, 11.26. Found: C, 73.12; H, 11.09. Data for 2b are as follows. Yield: 70%. Gentle heating using a heat gun (0.01 mbar). GC/MS: 23.23 min. Anal. Calcd for C22H33NSi (339.60): C, 77.81; H, 9.80. Found: C, 77.66; H, 9.81.

Figure 7. ORTEP diagram of 10a with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): C1···C5 3.18, Ti−C1 2.2635(14), Ti−C2 2.2620(13), Ti−C3 2.2766(13), Ti−C4 2.3031(13), Ti−C5 2.2840(14), Pdlcent(C1−C5)− Ti 1.690, C2−C1−Si 122.95(10), C1−Si−N 111.86(7), C2−C1−Si−N −36.09(14), conformational angle χ 79, αplanes 11.2. αSi −6.0, αH1 −38.0, αC13 10.5, αH3 5.9, αH5 −20.8. pentadienyl ligands were refined freely (but in some cases with C−H distance restraints). Other hydrogens were included as rigid methyl groups allowed to rotate but not tip, or using a riding model starting from calculated positions. The absolute configuration was confirmed in 154


Organometallics

Article

Scheme 3

Data for 5a are as follows. Yield: 74%. Anal. Calcd for C19H34NSiK (343.67): C, 66.40; H, 9.97. Found: C, 65.33; H, 9.68. Data for 5b are as follows. Yield: 70%. Anal. Calcd for C24H36NSiK (405.74): C, 71.05; H, 8.94. Found: C, 70.46; H, 8.92. Data for 5c-U/5c′-S are as follows. Total yield: 65%. Mixture of isomers in U conformation (5c) and S conformation (5c′) in a 2.36:1 ratio. Anal. Calcd for C18H32NSiK (329.64): C, 65.59; H, 9.78. Found: C, 64.68; H, 9.65. Synthesis of [K(18-crown-6)][4b]. A saturated solution of 18crown-6 (33.0 mg, 0.125 mmol) in toluene (0.5 mL) was added to 4b (47.2 mg, 0.125 mmol). A few drops of pentane were carefully layered onto the toluene solution, and slow diffusion at −30 °C overnight resulted in 42.0 mg (0.05 mmol, 43%) of red-orange crystals. Anal. Calcd for C44.5H68NSiKO6 (780.22): C, 68.51; H, 8.79. Found: C, 68.10; H, 8.80. The NMR spectra recorded from crystallized material showed a mixture of two different isomers in a 3:1 ratio. Unfortunately, because of significantly overlapping resonances we only succeeded in unambiguously assigning the resonances of SiMe2, NMe2, and the pentadienyl moiety C1−C5 of the two major isomers A and B. Data for the major isomer A are as follows. 1H NMR (400 MHz, C6D6, 298 K): δ 5.27−5.23 (m, 1 H, H5), 3.94 (“s”, 1 H, H3), 3.81 (“s”, 1 H, H1), 3.02 (s, 18-crown-6), 2.69 (s, 6 H, NMe2), 0.29 (s, 3 H, SiMe2), 0.11 (s, 3 H, SiMe2) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 158.4 (C, C-phenyl), 153.6(C, C2), 149.6 (C, C4), 93.0 (CH, C3), 90.1 (CH, C5), 76.1 (CH, C1), 69.7 (CH2, 18-crown-6), 39.3 (CH3, NMe2), 2.3 (CH3, SiMe2), 2.1 (CH3, SiMe2) ppm. Data for the minor isomer B are as follows. 1H NMR (400 MHz, C6D6, 298 K): δ 4.93 (“d”, 1 H, J = 2.01 Hz, H3), 4.58 (“d”, 1 H, J = 2.26 Hz, H1), 4.09 (“d”, 1 H, J = 2.25 Hz, H5), 3.02 (s, 18-crown-6), 2.35 (s, 6 H, NMe2), 0.63 (s, 3 H, SiMe2), 0.62 (s, 3 H, SiMe2) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 149.4 (C, C-phenyl), 148.7 (C, C2), 147.9 (C, C4), 91.4 (CH, C3), 82.8 (CH, C5), 79.8 (CH, C1), 69.7 (CH2, 18-crown-6), 37.7 (CH3, NMe2), 6.0 (CH3, SiMe2), 4.8 (CH3, SiMe2) ppm. Synthesis of [K(18-crown-6)][5a]. A saturated solution of 18crown-6 (76.9 mg, 0.291 mmol) in toluene (0.5 mL) was added to 5a (100 mg, 0.291 mmol). A few drops of pentane were carefully layered onto the toluene solution, and diffusive mixing at −30 °C overnight resulted in 113 mg (0.186 mmol, 64%) of red-orange crystals. Anal. Calcd for C31H58NSiKO6 (607.99): C, 61.24; H, 9.62. Found: C, 61.30; H, 9.85. 1H NMR (400 MHz, C6D6, 298 K): δ 5.17−5.10 (“s”, 1 H, H5), 3.95−3.93 (“s”, 1 H, H3), 3.79−3.76 (“s”, 1 H, H1), 3.30 (dq, 4 H, J = 6.91 Hz, J = 3.35 Hz, NEt2), 3.19 (s, 24 H, 18-crown-6), 3.02− 2.82 (m, 2 H, H6), 2.51−2.44 (m, 1 H, H8b), 2.35 (s, 3 H, H13), 2.32− 2.26 (“t”, 1 H, J = 5.68 Hz, H9), 1.66 (d, 1 H, J = 7.58, H8a), 1.56 (s, 3 H, H12), 1.43 (s, 3 H, H11), 1.31 (t, 6 H, J = 6.90 Hz, NEt2), 0.65 (s, 3 H, SiMe2), 0.46 (s, 3 H, SiMe2) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 152.2 (C, C4), 149.5 (C, C2), 92.0 (CH, C3), 90.0 (CH, C5), 72.8 (CH, C1), 69.9 (CH2, 18-crown-6), 53.9 (CH, C9), 42.7 (CH, C7), 40.9 (CH2, NEt2), 39.7 (C, C10), 33.7 (CH2, C6), 31.5 (CH2, C8), 28.8 (CH3, C13), 27.8 (CH3, C12), 21.6 (CH3, C11), 16.8 (CH3, NEt2), 4.2 (CH3, SiMe2), 3.5 (CH3, SiMe2) ppm. General Procedure for the Preparation of Open Vanadocenes 6a and 7a,c. [VCl3(thf)3] (124.4 mg, 0.33 mmol) was suspended in THF (ca. 50 mL), and a THF solution of the potassium salts (1 mmol, 3 equiv) dissolved in THF (ca. 20 mL) was slowly added at ambient temperature. Deep green to brown suspensions were formed, and the reaction mixtures were stirred for 4 h at room temperature. The solvent was removed under dynamic vacuum, and the residues were extracted with hexane (10 mL). The extracts were filtered, concentrated to ca. 2

Figure 8. ORTEP diagram of 11b with thermal displacement parameters drawn at the 50% probability level. Selected bond lengths (Å) and angles (deg): C1···C5 3.25, Zr−C1 2.683(3), Zr−C2 2.592(3), Zr−C3 2.472(3), Zr−C4 2.622(3), Zr−C5 2.755(3), Zr−C(av) 2.6248 ± 0.1058, Zr−P 2.8477(8), Pdlcent(C1−C5)−Zr 2.13, CHTcent(C25− C31)−Zr 1.77, Pdlplane(C1−C5)−Phplane 59, αplanes 40, β 98, γ 112, δ 150, C(2)−C(1)−Si 126.1(2), C(1)−Si−N 110.4(1), C(2)−C(1)− Si−N −41.3(3), αSi −11.3, αH1 −7.2, αPh 1.1, αH3 0.5, αH5 −14.1. Data for 2c are as follows. Yield: 80%. Bp: 67−75 °C (0.03 mbar). GC/MS: 17.36 min. Anal. Calcd for C16H29NSi (263.50): C, 72.93; H, 11.09. Found: C, 72.53; H, 10.97. Data for 3a are as follows. Yield: 82%. Bp: 65−75 °C (0.10 mbar). GC/MS: 19.62 min. Anal. Calcd for C19H35NSi (305.58): C, 74.68; H, 11.54. Found: C, 73.77; H, 11.18. Data for 3b are as follows. Yield: 63%. Gentle heating using a heat gun (0.01 mbar). GC/MS: 24.32 min. Anal. Calcd for C24H37NSi (367.65): C, 78.41; H, 10.14. Found: C, 77.74; H, 10.04. Data for 3c/3c* are as follows. Total yield: 84%. Mixture of s-cis (3c) and s-trans (3c*) isomers in a 1.85:1 ratio. Bp: 55−60 °C (0.01 mbar). GC/MS: 18.88 min (3c) and 19.00 min (3c*). Anal. Calcd for C18H33NSi (291.55): C, 74.15; H, 11.41. Found: C, 73.05; H, 11.46. Standard Procedure for the Synthesis of Potassium Pentadienides 4a−c and 5a−c. At −78 °C n-BuLi (1 equiv) was added to a solution of KOtPe in pentane (200 mL). After the mixture was stirred for 10 min at this temperature, the N-donor-functionalized 1,3-dienes (1 equiv) were added with a syringe and the reaction mixtures were warmed to room temperature. The reaction mixtures were stirred for 12 h at ambient temperature, and the suspension slowly turned yellow. After filtration, the precipitates were washed with pentane (3 × 20 mL) and dried under dynamic vacuum to yield the potassium salts as highly pyrophoric yellow solids. Data for 4a are as follows. Yield: 73%. Anal. Calcd for C17H30NSiK (315.62): C, 64.69; H, 9.58. Found: C, 64.33; H, 9.52. Data for 4b are as follows. Yield: 70%. Anal. Calcd for C22H32NSiK (377.69): C, 69.96; H, 8.54. Found: C, 69.89; H, 8.58. Data for 4c-U/4c′-S are as follows. Total yield: 78%. Mixture of isomers in U conformation (4c) and S conformation (4c′) in a 2.41:1 ratio. Anal. Calcd for C16H28NSiK (301.59): C, 63.72; H, 9.36. Found: C, 63.18; H, 9.33. 155


Organometallics

Article

mL, and stored at −30 °C. The products were obtained as dark green crystals. Data for 6a are as follows. Yield: 46.0 mg (0.076 mmol; 23%). Mp: 207 °C. Anal. Calcd for C34H60N2Si2V (603.98): C, 67.61; H, 10.01; N, 4.64. Found: C, 67.20; H, 9.91; N, 4.74. The EI mass spectrum (70 eV) showed a molecular ion at m/z 603 amu with the following isotopic cluster distribution (in %): 603 (100), 604 (49), 605 (18), 606 (4). Simulated distribution (in %) for C34H60N2Si2V: 603 (100), 604 (50), 605 (19), 606 (5), 607 (1). Data for 7a are as follows. Yield: 60.1 mg (0.091 mmol; 28%). Mp: 163 °C. Anal. Calcd for C38H68N2Si2V (660.09): C, 69.15; H, 10.38; N, 4.24. Found: C, 69.15; H, 10.57; N, 3.99. The EI mass spectrum (70 eV) showed a molecular ion at m/z = 659 amu with the following isotopic cluster distribution (in %): 659 (100), 660 (53), 661 (20), 662 (6). Simulated distribution (in %) for C38H68N2Si2V: 659 (100), 660 (55), 661 (21), 662 (6), 663 (1). Data for 7c are as follows. Yield: 19 mg (0.03 mmol; 9%). Mp: 150 °C. Anal. Calcd for C36H64N2Si2V (632.03): C, 68.41; H, 10.21; N, 4.43. Found: C, 67.99; H, 10.57; N, 4.59. The EI mass spectrum (70 eV) showed a molecular ion at m/z 631 amu with the following isotopic cluster distribution (in %): 631 (100), 632 (50), 633 (18), 634 (5). Simulated distribution (in %) for C36H64N2Si2V: 631 (100), 632 (52), 633 (20), 634 (5), 635 (1). General Procedure for the Preparation of Open Chromocenes 8a−c and 9a,c. CrCl2 (61.5 mg, 0.5 mmol) was suspended in THF (30 mL), and a solution of the potassium salts (1 mmol, 2 equiv), dissolved in THF (5 mL), was added at ambient temperature. The reaction mixture was stirred for 4 h, and the solvent was removed under dynamic vacuum. The residue was extracted with hexane (20 mL) to give deep green solutions that were filtered and concentrated to ca. 2 mL. The solutions were stored at −30 °C to yield deep green crystals. Data for 8a are as follows. Yield: 119 mg (0.197 mmol, 40%). Mp: 178 °C. Anal. Calcd for C34H60N2Si2Cr (605.03): C, 67.50; H, 10.00; N, 4.63. Found: C, 67.87; H, 10.20; N, 4.79. The EI mass spectrum (70 eV) showed a molecular ion at m/z 604 amu with the following isotopic cluster distribution (in %): 602 (5), 603 (3), 604 (100), 605 (60), 606 (25), 607 (8), 608 (1). Simulated distributions (in %) for C34H60CrN2Si2: 602 (5), 603 (3), 604 (100), 605 (61), 606 (27), 607 (8), 608 (2). Data for 8c are as follows. Yield: 99.5 mg (0.172 mmol, 35%). Mp: 151 °C. Anal. Calcd for C32H56N2Si2Cr (576.98): C, 66.61; H, 9.78; N, 4.86. Found: C, 66.42; H, 9.67; N, 4.89. The EI mass spectrum (70 eV) showed a molecular ion at m/z 576 amu with the following isotopic cluster distribution (in %): 574 (6), 575 (3), 576 (100), 577 (57), 578 (24), 579 (8), 580 (1). Simulated distribution (in %) for C32H56CrN2Si2: 574 (5), 575 (2), 576 (100), 577 (59), 578 (26), 579 (8), 580 (2). Data for 9a are as follows. Yield: 178 mg (0.270 mmol, 54%). Mp: 152 °C. Anal. Calcd for C38H68N2Si2Cr (661.14): C, 69.03; H, 10.37; N, 4.24. Found: C, 68.65; H, 10.43; N, 4.03. The EI mass spectrum (70 eV) showed a molecular ion at m/z 660 amu with the following isotopic cluster distribution (in %): 658 (5), 659 (3), 660 (100), 661 (65), 662 (28), 663 (9), 664 (1). Simulated distribution (in %) for C38H68CrN2Si2: 658 (5), 659 (3), 660 (100), 661 (66), 662 (30), 663 (10), 664 (2). Data for 9c are as follows. Yield: 187.5 mg (0.296 mmol, 60%). Mp: 170 °C. Anal. Calcd for C36H64N2Si2Cr (633.09): C, 68.30; H, 10.19; N, 4.42. Found: C, 68.20; H, 10.11; N, 4.33. The EI mass spectrum (70 eV) showed a molecular ion at m/z 632 amu with the following isotopic cluster distribution (in %): 630 (5), 631 (3), 632 (100), 633 (62), 634 (28), 635 (9), 636 (1). Simulated distribution (in %) for C36H64CrN2Si2: 630 (5), 631 (3), 632 (100), 633 (63), 634 (28), 635 (9), 636 (1).

Preparation of the Open Titanocene [(η5-5a)2Ti] (10a).

[TiCl3(thf)3] (123.5 mg, 0.33 mmol) was dissolved in THF (50 mL). Potassium salt 5a (340.2 mg, 0.99 mmol), dissolved in THF (20 mL), was added. During the addition a green suspension was formed. The reaction mixture was stirred at ambient temperature for 4 h, the solvent was removed under dynamic vacuum, the residue was extracted with hexane (25 mL), and the extract was filtered. The filtrate was concentrated to ca. 1 mL and stored at −30 °C to yield green crystals. However, to obtain analytically pure material three crystallizations from concentrated hexane solutions at −30 °C were required. Yield: 71 mg (0.108 mmol, 33%). Mp: 161 °C. Anal. Calcd for C38H68N2Si2Ti (657.01): C, 69.47; H, 10.43; N, 4.26. Found: C, 69.30; H, 10.30; N, 4.21. The EI mass spectrum (70 eV) showed a molecular ion at m/z 656 amu with the following isotopic cluster distribution (in %): 654 (12), 655 (16), 656 (100), 657 (58), 658 (30), 659 (10), 660 (2). Simulated distribution (in %) for C38H68TiN2Si2: 654 (10), 655 (15), 656 (100), 657 (60), 658 (31), 659 (11), 660 (3). 1H NMR (400 MHz, C6D6, 298 K): δ 6.71 (s, 2 H, H3), 3.24 (t, 2 H, J = 5.56 Hz, H9), 2.93−2.81 (m, 4 H, H6), 2.79−2.61 (m, 8 H, CH2 groups of NEt2), 2.31−2.23 (m 2 H, H8b), 2.17 (s, 6 H, H13), 2.15−2.09 (m, 2 H, H7), 2.02 (d, 2 H, J = 5.56 Hz, H5), 1.72 (s, 6 H, H11), 1.46 (s, 6 H, H12), 0.92 (t, 12 H, J = 6.95 Hz, Me groups of NEt2), −0.11 (s, 6 H, SiMe2 b), −0.48 (s, 6 H, SiMe2, a), −0.66 (d, 2 H, J = 9.35 Hz, H8a), −1.32 (s, 2 H, H1) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 133.6 (C, C4), 123.6 (C, C2), 113.2 (CH, C3), 90.9 (CH, C5), 75.6 (CH, C1), 55.6 (CH, C9), 40.7 (CH, C7), 40.6 (CH2, NEt2), 38.9 (C, C10), 36.5 (CH2, C8), 32.6 (CH2, C6), 27.0 (CH3, C13), 26.4 (CH3, C12), 22.7 (CH3, C11), 15.9 (CH3, NEt2), 2.2 (CH3, SiMe2, b), 1.8 (CH3, SiMe2, a) ppm. General Procedure for the Synthesis of PMe3 Adducts with Half-Open Trozircenes 11b,c and 12b,c. [(η7-C7H7)ZrCl(tmeda)] (100 mg, 0.299 mmol) was dissolved in 10 mL of THF to give a blue solution. Addition of the potassium salts (1 equiv), dissolved in 10 mL of THF, resulted in red-brown suspensions. After the mixture was stirred at ambient temperature for 1 h, the solvent was removed under dynamic vacuum, the residues were extracted with hexane (3 mL), and an excess of PMe3 (4 equiv) was added. On addition of PMe3 the solution changed from dark red to red-orange. The mixtures were stored for 30 min at −30 °C to induce complete precipitation of the product. After separation of the mother liquor, the products were recrystallized from a mixture of hexane (1 mL) and THF (0.5 mL) at −30 °C to give orange crystals. Data for 11b are as follows.

Yield: 90.5 mg (0.152 mmol, 51%). Mp: 152 °C. Anal. Calcd for C32H48NSiPZr (597.03): C, 64.38; H, 8.10; N, 2.35. Found: C, 64.78; H, 7.83; N, 2.72. 1H NMR (400 MHz, C6D6, 298 K): δ 7.29−7.23 (m, 2 H, H14), 6.87−6.81 (m, 3 H, H15 and H16), 4.84 (s, 7 H, CHT), 4.39 (s, 1 H, H3), 3.21 (“d”, 1 H, J = 3.76 Hz, H5), 2.75−2.65 (m, 1 H, H6b), 2.30−2.21 (m, 1 H, H6a), 2.15 (s, 6 H, NMe2), 2.06 (“dt”, 1 H, J = 8.78 Hz and J = 5.90 Hz, H8b), 1.96−1.89 (m, 1 H, H7), 1.78 (s, 1 H, H1), 1.74 (“dt”, 1 H, H9), 1.44 (d, 1 H, J = 8.78 Hz, H8a), 1.11 (s, 3 H, H12), 0.88 (s, 3 H, H11), 0.33 (d, 9 H, JHP = 2.51 Hz, PMe3), 0.19 (s, 3 H, SiMe2), 0.00 (s, 3 H, SiMe2) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 146.3 (C, C13), 138.0 (C, C2), 135.3 (C, C4), 130.0 (2 × CH, C14), 127.4 (2 × CH, C15), 127.3 (CH, C16), 91.9 (CH, C3), 90.5 (CH, C5), 86.9 (CH, C1), 81.5 (CH, CHT), 51.8 (CH, C9), 41.8 (CH, 156


Organometallics

Article

C7), 39.6 (C, C10), 38.2 (2 × CH3, NMe2), 34.0 (CH2, C8), 31.6 (CH2, C6), 26.4 (CH3, C12), 21.5 (CH3, C11), 17.4 (3 × CH3, d, JCP = 3.16 Hz, PMe3), 1.1 (CH3, SiMe2), 0.3 (CH3, SiMe2) ppm. 31P{1H} NMR (162 MHz, C6D6, 298 K): δ −48.9 ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z 519 amu (M+ − PMe3) with the following isotopic cluster distribution (in %): 519 (100), 520 (60), 521 (51), 522 (18), 523 (36), 524 (12), 525 (8), 526 (2). Simulated distribution (in %) for C29H39ZrNSi: 519 (100), 520 (60), 521 (52), 522 (17), 523 (38), 524 (14), 525 (9), 526 (3). Data for 11c are as follows.

Yield: 95.1 mg (0.173 mmol, 58%). Mp: 118 °C. Anal. Calcd for C28H48NPSiZr (548.98): C, 61.26; H, 8.81; N, 2.55. Found: C, 61.10; H, 8.99; N, 2.57. 1H NMR (400 MHz, C6D6, 298 K): δ 5.04 (dd, 1 H, J = 18.57 Hz, J = 8.78 Hz, H2), 4.80 (s, 7 H, CHT), 4.25 (d, 1 H, J = 8.53 Hz, H3), 2.91 (“dq”, 5 H, J = 6.99 and 0.63 Hz, CH2 groups of NEt2 and H5), 2.69−2.61 (m, 1 H, H6), 2.33−2.25 (m, 1 H, H6), 2.25−2.20 (m, 1 H, H8b), 2.08 (d, 1 H, J = 19.06 Hz, H1), 2.06−2.00 (“septet”, 1 H, H7), 1.90 (dt, 1 H, J = 5.65 Hz and J = 1.25 Hz, H9), 1.58 (d, 1 H, J = 8.78 Hz, H8a), 1.25 (s, 3 H, H12), 1.02 (t, 6 H, J = 6.90 Hz, Me groups of NEt2), 0.93 (s, 3 H, H11), 0.65 (d, 9 H, JHP = 2.76 Hz, PMe3), 0.45 (s. 3H, SiMe2), 0.29 (s, 3 H, SiMe2) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 137.1 (C, C4), 114.9 (CH, C2), 91.1 (CH, C5), 88.9 (CH, C3), 83.1 (CH, C1), 80.7 (CH, CHT), 51.1 (CH, C9), 41.7 (CH, C7), 40.6 (2 × CH2, NEt2), 39.9 (C, C10), 33.3 (CH2, C8), 31.4 (CH2, C6), 26.4 (CH3, C12), 21.2 (CH3, 11), 17.9 (3 × CH3, JCP = 5.02 Hz, PMe3), 16.3 (2 × CH3, NEt2), −0.1 (CH3, SiMe2), −1.1 (CH3, SiMe2) ppm. 31P{1H} NMR (162 MHz, C6D6, 298 K): δ −46.8 ppm.

Yield: 85.2 mg (0.164 mmol, 55%). Mp: 142 °C. Anal. Calcd for C26H44NSiPZr (520.93): C, 59.95; H, 8.51; N, 2.69. Found: C, 59.72; H, 8.44; N, 2.83. 1H NMR (400 MHz, C6D6, 298 K): δ 4.94 (dd, 1 H, J = 18.32 Hz and J = 8.78 Hz, H2), 4.76 (s, 7 H, CHT), 4.29 (d, 1 H, J = 8.78 Hz, H3), 2.82 (brs, 1 H, H5), 2.69−2.62 (m, 1 H, H6b), 2.54 (s, 6 H, NMe2), 2.34−2.26 (m, 1 H, H6a), 2.26−2.18 (m, 1 H, H8b), 2.07−2.00 (m, 1 H, H7), 2.04 (“d”, 1 H, J = 18.32 Hz, H1), 1.90 (“dt”, 1 H, H9), 1.58 (d, 1 H, J = 8.78 Hz, H8a), 1.26 (s, 3 H, H12), 0.94 (s, 3 H, H11), 0.65 (d, 9 H, JHP = 2.01 Hz, PMe3), 0.41 (s, 3 H, SiMe2), 0.25 (s, 3 H, SiMe2) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 136.4 (C, C4), 114.0 (CH, C2), 91.9 (CH, C5), 88.8 (CH, C3), 80.9 (CH, C1), 80.6 (CH, CHT), 51.0 (CH, C9), 41.8 (CH, C7), 40.0 (C, C10), 38.6 (2 × CH3, NMe2), 33.2 (CH2, C8), 31.3 (CH2, C6), 26.4 (CH3, C12), 21.3 (CH3, C11), 17.6 (3 × CH3, d, JCP = 2.06 Hz, PMe3), −1.6 (CH3, SiMe2), −2.4 (CH3, SiMe2) ppm. 31P{1H} NMR (162 MHz, C6D6, 298 K): δ −48.9 ppm. Data for 12b are as follows.

■

ASSOCIATED CONTENT

■

AUTHOR INFORMATION

S Supporting Information *

Tables, figures, and CIF files giving crystallographic data for [K(18-crown-6)][4b](C7H8)2, [K(18-crown-6)][5a], 6a, 7a,c, 8a,c, 9a,c, 10a, 11b,c, 12b,c, and [(η5-1b)2Cr], synthetic details for [(η5-1b)2Cr], and low-temperature EPR study on 7a. This material is available free of charge via the Internet at http://pubs. acs.org. Corresponding Author

*E-mail for M.D.W.: [email protected]. Present Address †

Faculty of Chemistry, Alexandru Ioan Cuza University of Iaşi, 11, Carol 1, 700506 Iaşi, Romania. Author Contributions Yield: 90.6 mg (0.145 mmol, 48%). Mp: 180 °C. Anal. Calcd for C34H52NPSiZr (625.08): C, 65.33; H, 8.34; N, 2.24. Found: C, 64.95; H, 8.41; N, 2.52. 1H NMR (400 MHz, C6D6, 298 K): δ 7.44−7.39 (m, 2 H, H14), 7.01−6.96 (m, 3 H, H15 and H16), 5.01 (s, 7 H, CHT), 4.48 (s, 1 H, H3), 3.40 (“d”, 1 H, J = 4.26 Hz, H5), 2.86−2.79 (m, 1 H, H6b),2.69 (dq, 4 H, J = 14.51 Hz and J = 7.15 Hz, CH2 groups of NEt2), 2.44−2.36 (m, 1 H, H6a), 2.19 (“dt”, 1 H, J = 8.78 Hz and J = 5.90 Hz, H8b), 2.05(“septet”, 1 H, H7), 1.96 (s, 1 H, H1), 1.87 (“dt”, 1 H, J = 5.65 Hz and J = 1.25 Hz, H9), 1.57 (d, 1 H, J = 9.03 Hz, H8a), 1.23 (s, 3 H, H12), 1.01 (s, 3 H, H11), 0.90 (t, 6 H, J = 7.03 Hz, Me groups of NEt2), 0.47 (d, 9 H, JHP = 2.51 Hz, PMe3), 0.44 (s, 3 H, SiMe2), 0.03 (s, 3 H, SiMe2) ppm. 13C{1H} NMR (101 MHz, C6D6, 298 K): δ 146.1 (C, C13), 138.6 (C, C2), 135.9 (C, C4), 130.2 (2 × CH, C14), 127.4 (2 × CH, C15), 127.3 (CH, C16), 92.2 (CH, C3), 90.1 (CH, C5), 87.8 (CH, C1), 81.7 (CH, CHT), 51.8 (CH, C9), 41.8 (CH, C7), 40.6 (2 × CH2, NEt2), 39.6 (C, C10), 34.0 (CH2, C8), 31.7 (CH2, C6), 26.4 (CH3, C12), 21.4 (CH3, C11), 17.3 (3 × CH3, d, JCP = 3.16 Hz, PMe3), 16.1 (2 × CH3, NEt2), 2.3 (CH3, SiMe2), 1.1 (CH3, SiMe2) ppm. 31P{1H} NMR (162 MHz, C6D6, 298 K): δ = −51.0 ppm. The EI mass spectrum (70 eV) showed a molecular ion at m/z 547 amu (M+ − PMe3) with the following isotopic cluster distribution (in %): 547 (100), 548 (63), 549 (51), 550 (20), 551 (36), 552 (14), 553 (5), 554 (1). Simulated distribution (in %) for C31H43ZrNSi, 547 (100), 548 (63), 549 (54), 550 (18), 551 (38), 552 (38), 553 (14), 553 (9). 554 (3). Data for 12c are as follows.

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the TU Braunschweig through the “Zukunftsfonds” and by the Deutsche Forschungsgemeinschaft (DFG) through the Emmy-Noether program (WA 2513/2).

■

REFERENCES

(1) (a) Mahler, J. E.; Pettit, R. J. Am. Chem. Soc. 1962, 84, 1511. (b) Ernst, R. D. Struct. Bonding (Berlin) 1984, 57, 1. (c) Ernst, R. D. Acc. Chem. Res. 1985, 18, 56. (d) Kreiter, C. G. Adv. Organomet. Chem. 1986, 26, 297. (e) Powell, P. Adv. Organomet. Chem. 1986, 26, 125. (f) Ernst, R. D. Chem. Rev. 1988, 88, 1255. (g) Ernst, R. D. Comments Inorg. Chem. 1999, 21, 285. (h) Stahl, L.; Ernst, R. D. Adv. Organomet. Chem. 2007, 55, 137. (i) Yasuda, H.; Nakamura, A. J. Organomet. Chem. 1985, 285, 15. (j) de la Cruz Cruz, J. I.; Juárez-Saavedra, P.; Paz-Michel, B.; LeyvaRamirez, M. A.; Rajapakshe, A.; Vannucci, A. K.; Lichtenberger, D. L.; Paz-Sandoval, M. A. Organometallics 2014, 33, 278. (2) Cerpa, E.; Tenorio, F. J.; Contreras, M.; Villanueva, M.; Beltran, H. I.; Heine, T.; Donald, K. J.; Merino, G. Organometallics 2008, 27, 827.

157


Organometallics

Article

(3) (a) Heiszwolf, G. J.; Kloosterziel, H. Recl. Trav. Chim. Pays-Bas 1967, 86, 807. (b) Kloosterziel, H.; van Drunen, J. A. A. Recl. Trav. Chim. Pays-Bas 1970, 89, 270. (c) Yasuda, H.; Ohnuma, Y.; Yamauchi, M.; Tani, H.; Nakamura, A. Bull. Chem. Soc. Jpn. 1979, 52, 2036. (d) Yasuda, H.; Yamauchi, M.; Nakamura, A.; Sei, T.; Kai, Y.; Yasuoka, N.; Kasai, N. Bull. Chem. Soc. Jpn. 1980, 53, 1089. (e) Yasuda, H.; Yamauchi, M.; Ohnuma, Y.; Nakamura, A. Bull. Chem. Soc. Jpn. 1981, 54, 1481. (f) Yasuda, H.; Nishi, T.; Lee, K.; Nakamura, A. Organometallics 1983, 2, 21. (g) Schlosser, M.; Staehle, M. Angew. Chem. 1982, 94, 142. (h) Schlosser, M.; Lehmann, R.; Jenny, T. J. Organomet. Chem. 1990, 389, 149. (i) Solomon, S. A.; Bickelhaupt, F. M.; Layfield, R. A.; Nilsson, M.; Poater, J.; Solà, M. Chem. Commun. 2011, 47, 6162. (j) Day, B. M.; Clayden, J.; Layfield, R. A. Organometallics 2013, 32, 4448. (k) Naruta, Y.; Nishigaichi, Y.; Maruyama, K. J. Org. Chem. 1991, 56, 2011. (4) Bosch, H. W.; Hund, H.-U.; Nietlispach, D.; Salzer, A. Organometallics 1992, 11, 2087. (5) (a) Fecker, A. C.; Glöckner, A.; Daniliuc, C. G.; Freytag, M.; Jones, P. G.; Walter, M. D. Organometallics 2013, 32, 874. (b) Fecker, A. C.; Crăciun, B.-F.; Freytag, M.; Jones, P. G.; Walter, M. D. Organometallics 2014, 33, 3792. (6) Seyferth, D.; Pornet, J. J. Org. Chem. 1980, 45, 1721. (7) (a) Stahl, L.; Hutchinson, J. P.; Wilson, D. R.; Ernst, R. D. J. Am. Chem. Soc. 1985, 107, 5016. (b) Adams, R. D.; Babin, J. E.; Tasi, M.; Wolfe, T. A. J. Am. Chem. Soc. 1988, 110, 7093. (c) Wooster, T. T.; Geiger, W. E.; Ernst, R. D. Organometallics 1995, 14, 3455. (d) Stahl, L.; Zahn, T.; Ziegler, M. L.; Ernst, R. D. Inorg. Chim. Acta 1999, 288, 154. (e) Seyferth, D.; Anderson, L. L.; Villafane, F.; Davis, W. M. J. Am. Chem. Soc. 1992, 114, 4594. (8) Bates, R. B.; Gosselink, D. W.; Kaczynski, J. A. Tetrahedron Lett. 1967, 205. (9) Köhler, F. H.; Mölle, R.; Strauss, W.; Weber, B.; Gedridge, R. W.; Basta, R.; Trakarnpruk, W.; Tomaszewski, R.; Arif, A. M.; Ernst, R. D. Organometallics 2003, 22, 1923. (10) Reiners, M.; Baabe, D.; Schweyen, P.; Freytag, M.; Jones, P. G.; Walter, M. D. Inorg. Chim. Acta 2014, 422, 167. (11) Ernst, R. D.; Liu, J. Z.; Wilson, D. R. J. Organomet. Chem. 1983, 250, 257. (12) Newbound, T. D.; Rheingold, A. L.; Ernst, R. D. Organometallics 1992, 11, 1693. (13) (a) Glöckner, A.; Bannenberg, T.; Tamm, M.; Arif, A. M.; Ernst, R. D. Organometallics 2009, 28, 5866. (b) Glöckner, A.; Tamm, M.; Arif, A. M.; Ernst, R. D. Organometallics 2009, 28, 7041. (c) Glöckner, A.; Arif, A. M.; Ernst, R. D.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Inorg. Chim. Acta 2010, 364, 23. (d) Glöckner, A.; Bannenberg, T.; Büschel, S.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Chem. Eur. J. 2011, 17, 6118. (e) Glöckner, A.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Inorg. Chem. 2012, 51, 4368. (f) Glöckner, A.; Bannenberg, T.; Ibrom, K.; Daniliuc, C. G.; Freytag, M.; Jones, P. G.; Walter, M. D.; Tamm, M. Organometallics 2012, 31, 4480. (g) Glöckner, A.; Bauer, H.; Maekawa, M.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Sun, Y.; Sitzmann, H.; Tamm, M.; Walter, M. D. Dalton Trans. 2012, 41, 6614. (h) Glöckner, A.; Cui, P.; Chen, Y.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. New J. Chem. 2012, 36, 1392. (i) Glöckner, A.; Daniliuc, C. G.; Freytag, M.; Jones, P. G.; Tamm, M. Chem. Commun. 2012, 48, 6598. (j) Glöckner, A.; Kronig, S.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. J. Organomet. Chem. 2012, 723, 181. (k) Glöckner, A.; Tamm, M. Chem. Soc. Rev. 2013, 42, 128. (l) Kreye, M.; Glöckner, A.; Daniliuc, C. G.; Freytag, M.; Jones, P. G.; Tamm, M.; Walter, M. D. Dalton Trans. 2013, 42, 2192. (m) Bauer, H.; Glöckner, A.; Tagne Kuate, A. C.; Schäfer, S.; Sun, Y.; Freytag, M.; Tamm, M.; Walter, M. D.; Sitzmann, H. Dalton Trans. 2014, 43, 15818. (14) Washburne, S. S.; Peterson, W. R., Jr. J. Organomet. Chem. 1970, 21, 59. (15) Wannagat, U.; Schreiner, G. Monatsh. Chem. 1965, 96, 1889. (16) Lochmann, L.; Trekoval, J. J. Organomet. Chem. 1987, 326, 1. (17) (a) Jones, N. A.; Liddle, S. T.; Wilson, C.; Arnold, P. L. Organometallics 2007, 26, 755. (b) Manzer, L. E. Inorg. Synth. 1982, 21, 135. (18) Stoll, S.; Schweiger, A. J. Magn. Reson. 2006, 178, 42.

(19) (a) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structure from Diffraction Data; University of Gö ttingen, Göttingen, Germany, 1997. (b) Sheldrick, G. Acta Crystallogr., Sect. A 2008, A64, 112.

158


Synthesis and Characterization of N-Donor-Functionalized

Recommend Documents