Insertion Reactions in Ta–H and Ta–Me Bonds in Complexes

Article pubs.acs.org/Organometallics

Insertion Reactions in Ta−H and Ta−Me Bonds in Complexes Containing Tridentate κ3O,S,O-Type Ligands § ́ Jacob Fernández-Gallardo,† Á ngel Bajo,† Rosa Fandos,† Antonio Otero,*,‡ Ana Rodrıguez, and María José Ruiz*,† †

Departamento de Quı ́mica Inorgánica, Orgánica y Bioquı ́mica, Universidad de Castilla-La Mancha, Facultad de Ciencias Ambientales y Bioquı ́mica, INAMOL, Avda. Carlos III, s/n 45071 Toledo, Spain ‡ Facultad de Ciencias y Tecnologı ́as Quı ́micas, Campus de Ciudad Real, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain § ETS Ingenieros Industriales, Avda. Camilo José Cela, 3, 13071 Ciudad Real, Spain S Supporting Information *

ABSTRACT: A series of new tantalum complexes containing the κ3O,S,O-type alkoxide ligand from 2,2′-thiodiethanol (tdgolH2) have been synthesized and characterized. The complexes [TaCp*Cl2{[O(CH2)2]2S-κ3O,S,O}] (1) and [TaCp*Me2{[O(CH2)2]2Sκ3O,S,O}] (2) were prepared by reaction of 2,2′-thiodiethanol with [TaCp*X4] (X = Cl, Me). The tantalum dihydride complex [TaCp*H2{[O(CH2)2]2S-κ3O,S,O}] (3) and its analogue containing the 2,2′-thiobis(6-tert-octylphenolate) ligand (4) were synthesized by reaction of the respective dichlorides with 2 equiv of NaBHEt3. In addition, [TaCp*Me(TfO){[O(CH2)2]2S-κ3O,S,O}] (5) and [TaCp*(TfO)2{[O(CH2)2]2S-κ3O,S,O}] (6; TfO = F3COSO2−) were synthesized by reaction of 2 with 1 and 2 equiv of triflic acid, respectively. The reactivity of this family of complexes with nucleophiles was also studied and, as a result, three azatantalacyclopropane complexes (7−9) and the carbene [TaCp*{C(Me)N(H)xylyl-κ1C}(OH){[O(CH2)2]2S-κ3O,S,O}] (10) were characterized. The single-crystal structures of 1 and 6 were determined by Xray diffraction methods.

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INTRODUCTION Multidentate ligands represent a fascinating class of compounds that have been widely used as scaffolds to study basic organometallic transformations due to their versatility and relative ease of modification.1 In recent years our research group has devoted significant attention to the relationship between the structural and electronic properties of multidentate ligands and the reactivity of the metallic center. A wide variety of homo- and heterofunctional multidentate ligands such as κ3O,O,O,2 κ3S,S,S,3 κ3S,O,S,3 and κ3O,S,O4 have been used to tune the reactivity of early transition metals such as tantalum (Figure 1). During the course of our research we discovered interesting differences in the coordination mode of ligands and in the

reactivity of the synthesized complexes. Among the ligands investigated, the bis-alkoxides that incorporate a sulfur donor atom (κ3O,S,O) and substituted aromatic rings proved to be of particular interest due to the significant difference in reactivity found between the derivatives containing alkyl (tbop) and chloro (tbcp) substituents on the aromatic fragments (Figure 2).

Figure 2. Received: December 4, 2012

Figure 1. © XXXX American Chemical Society

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dx.doi.org/10.1021/om3011728 | Organometallics XXXX, XXX, XXX−XXX

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In fact, while the tbcp-containing derivatives reacted with isocyanides to give azatantalacyclopropane complexes, the tbop-containing complexes did not react.4 This observation could indicate a possible influence of the ring substituents on the electronic density on the tantalum center. With this idea in mind, we decided to synthesize complexes bearing aliphatic moieties instead of aromatic ones in order to compare their reactivity with isocyanides. Herein we report the results of our most recent study on the preparation of a series of new alkyl and hydride tantalum−tdgol and −tbop complexes (tdgol = 2,2′-thiodiethanolate, tbop = 2,2′-thiobis(6-tert-octylphenolate)) and a comparative study on the reactivities of the methyl and hydride complexes in isocyanide insertion processes.

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Figure 3. ORTEP drawing of complex 1 (molecule A) with the atomic labeling scheme. Hydrogen atoms are omitted for clarity; thermal ellipsoids are at the 30% probability level. Selected bond lengths (Å) and angles (deg): Ta(1)−Ct(1) = 2.167(6), Ta(1)−S(1) = 2.652(1), Ta(1)−O(1) = 1.934(4), Ta(1)−O(2) = 1.936(4), Ta(1)−Cl(1) = 2.447(16), Ta(1)−Cl(2) = 2.458(17); Ct(1)−Ta(1)−S(1) = 178.28, O(1)−Ta(1)−O(2) = 92.5(2), C(1)−O(1)−Ta(1) = 128.9(4), C(4)−O(2)−Ta(1) = 131.2(4), C(2)−S(1)−C(3) = 102.5(4), C(16)−S(2)−C(17) = 102.1(3), Cl(1)−Ta(1)−Cl(2) = 82.55(6), C(2)−S(1)−Ta(1) = 97.4(2), C(3)−S(1)−Ta(1) = 96.2(2).

RESULTS AND DISCUSSION The first step in our study was to synthesize a series of tantalum compounds containing a pentamethylcyclopentadienyl ring as an ancillary moiety and the ligand 2,2′-thiodiethanolate (tdgol). A general method for the synthesis of alkoxide derivatives of early transition metals is the reaction of the corresponding metal halide precursors with alcohols, normally in the presence of an amine, which facilitates the elimination of HX by formation of the corresponding adduct (NHR3)X. In fact, reaction of [TaCp*Cl4] with 2,2′-thiodiethanol and NEt3 in a 1:1:2 molar ratio gave the corresponding alkoxide complex 1 after the appropriate workup as an air- and moisture-sensitive gray solid (Scheme 1). Scheme 1.

κ3O,S,O ligand is bent and the angles O(1)−Ta(1)−O(2) and C(2)−S(1)−C(3) are 92.5(2) and 102.5(4)°, respectively. The spectroscopic characterization of 1 seems to confirm that the fac disposition of the bis-alkoxide ligand was also present in solution, as shown by the four multiplets that appear in the 1H NMR spectrum at 1.63, 2.63, 4.27, and 4.73 ppm (integrating for 2H each), which correspond with the Cs symmetry of the complex.8 Moreover, in the 13C NMR spectrum of 1, the signal at 38.1 ppm assigned to the carbon atoms bonded to the sulfur is shifted downfield with respect to that of the free ligand, which appears at 34.9 ppm in C6D6. We will find this kind of behavior in all the complexes described in this work (vide infra), and it could confirm a coordination of the sulfur atom to the metal center. However, we cannot definitively discard the possibility of a rapid process of coordination and decoordination of the sulfur atom preserving the Cs symmetry of the system (in other words, a fac κ3O,S,O ↔ κ2O,O equilibrium) but clear evidence of a fluxional process was not observed in VT-NMR experiments. Another well-documented general way to achieve the synthesis of alkoxide derivatives of early transition metals is the reaction of metal alkyl complexes with alcohols to yield the corresponding alkanes and the alkoxide complexes.9 A likely mechanism for the protonolysis of the carbon−metal bond requires initial donation of an oxygen lone pair to the metal center.10 This synthetic methodology was investigated, and the tantalum complex [TaCp*Me4] was reacted with 2,2′thiodiethanol in toluene in a 1:1 ratio at 60 °C for 5 h to render the complex [TaCp*Me2{[O(CH2)2]2S-κ3O,S,O}] (2) as an air- and moisture-sensitive white solid (see Scheme 1). Complex 2 is soluble in common organic solvents such as diethyl ether, dichloromethane, and toluene but is less soluble in pentane. The spectroscopic and analytical data for 2 are consistent with the proposed structural disposition (see Scheme 1). For example, the 1H NMR spectrum shows two singlets at −0.23 and 1.88 ppm, and these are assigned to the methyl groups bonded to the metal center and to the Cp* ligand, respectively. The κ3O,S,O ligand gives rise to several multiplets centered at

a

Legend: (i) for complex 1, 2,2’-thiodiethanol, NEt3, toluene, 60 °C, 3 h; (ii) for complex 2, 2,2’-thiodiethanol, toluene, 50 °C, 5 h.

a

Complex 1 is soluble in toluene, benzene, dichloromethane, and chloroform but is insoluble in pentane. Crystallization of the complex from a saturated solution in dichloromethane at −20 °C gave crystals suitable for X-ray characterization. In this compound the asymmetric unit contains two molecules that correspond to two different orientations of CH2 groups (C1 and C4) of the bis-alkoxide ligand. In both molecules the bisalkoxide ligand is in a fac disposition, with the sulfur atom trans to the Cp* and the oxygen atoms in the same plane as the chloride ligands.2,3 Taking into account the similarity of the two molecules, we will focus the discussion on one of these molecules (see Figure 3). In this molecule the tantalum atom is 0.528 Å out of the equatorial plane defined by O(1), O(2), Cl(1), and Cl(2). The Ta(1)−O(1) and Ta(1)−O(2) distances are 1.934(4) and 1.936(4) Å, respectively, and these values lie within the range found for other alkoxide5 and bis-alkoxide3,4,6 chelate complexes. The Ta(1)−S(1) distance is 2.652(1) Å, which is long for a single bond but shorter than the sum of the van der Waals radii (3.80 Å).7 This distance is consistent with a weak interaction between the metal center and the sulfur, which to some extent compensates for the electronic deficiency of Ta(V).3 Finally, the fac coordination mode means that the B


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1.76, 2.36, 4.22, and 4.32 ppm, which integrate for 2H each and correspond to the aliphatic protons. This pattern implies the fac coordination of the ligand to the metal center with the sulfur atoms located trans to the Cp*. This structural disposition with the tridentate ligand in a fac conformation is similar to that previously observed in a related complex with the diethylene glycolate (digol) ligand.2 An interesting feature of multidentate and alkoxide ligands is their ability to stabilize hydride complexes.11,12 Moreover, mono- and dihydride complexes of niobium and tantalum with ancillary aryloxide ligands have been shown to take part as catalysts in the hydrogenation of unsaturated hydrocarbons.9,13 With this idea in mind, we decided to synthesize the 2,2′thiodiethanolate dihydride tantalum complex 3 and its homologue containing 2,2′-thiobis(6-tert-octylphenolate) 4, which have not been described in our previous work.4 The synthesis was performed by reaction of the respective dichlorido complexes4 with 2 equiv of NaBHEt3 (Scheme 2).

Scheme 3

but is insoluble in pentane. Compound 6 was isolated as a white solid that is less soluble than 5, as it is soluble in dichloromethane, partially soluble in toluene, and insoluble in pentane. This solubility behavior points to the existence of a covalent bond between the triflate moieties and the tantalum center,16 which was confirmed for complex 6 in the solid state by an X-ray diffraction study. The slow cooling of a solution of 6 in dichloromethane down to −20 °C gave rise to crystals suitable for study by X-ray diffraction. The ORTEP diagram and a selection of distances and angles are given in Figure 4.

Scheme 2

The hydride complexes were isolated as white and light yellow solids, respectively, which are soluble in pentane and toluene, and they were characterized by the usual spectroscopic and analytical techniques. For 3, the signal patterns in 1H, 13C, and HSQC NMR experiments indicate a fac κ3O,S,O coordination of the 2,2′-thiodiethanolate ligand, as shown by the four multiplets that appear in the 1H NMR spectrum at 1.81, 2.26, 4.12, and 4.27 ppm (integrating for 2H each). These multiplets correlate with two signals in 13C NMR at 37.6 and 70.3 ppm. The two terminal hydride ligands give a resonance at 10.07 ppm in the 1H NMR spectrum.11−14 In accordance with these data, a structural disposition similar to that found for the complexes discussed above (Scheme 2) is proposed for complex 3. In the 1H NMR spectrum of 4 the tert-octyl moiety gives rise to one singlet at 0.65 ppm for the terminal methyl groups, one singlet at 1.55 ppm for the methylene fragments, and two singlet signals at 1.19 and 1.21 ppm, which correspond to the inequivalent methyl groups of the tert-octyl moiety, indicating a fac coordination mode of the κ3-tbop ligand to the metal center.4 Finally, the most remarkable feature of the 1H NMR spectrum of complex 4 is that the two terminal hydride ligands give rise to a singlet signal at 12.23 ppm, which is shifted significantly downfield in relation with the corresponding signal in the spectrum of complex 3 (10.07 ppm) but within the wide range for these kinds of ligands.11,15 It is well-known that the Ta−C bonds are reactive toward acidic protons, and when the anion has a coordinative ability, it is possible to stabilize neutral species that, although neutral (or zwitterionic), could retain some reactivity corresponding to a cationic metal fragment.16 With this idea in mind, complex 2 was reacted with 1 and 2 equiv of triflic acid and, as a result, complexes 5 and 6 were formed in a selective way (Scheme 3). The mono-triflate derivative 5 was isolated as a white solid, which is soluble in dichloromethane, toluene, and diethyl ether

Figure 4. ORTEP drawing of complex 6 with the atomic labeling scheme. Hydrogen atoms are omitted for clarity; thermal ellipsoids are at the 30% probability level. Selected bond lengths (Å) and angles (deg): Ta(1)−Ct(1) = 2.168, Ta(1)−S(1) = 2.686(4), Ta(1)−O(1) = 1.915(9), Ta(1)−O(2) = 1.928(8), Ta(1)−O(21) = 2.126(8), Ta(1)−O(31) = 2.154(8); Ct(1)−Ta(1)−S(1) = 178.12, O(1)− Ta(1)−O(2) = 97.2(4), O(21)−Ta(1)−O(31) = 80.1(3), C(1)− O(1)−Ta(1) = 129.6(9), C(4)−O(2)−Ta(1) = 131(1), C(2)−S(1)− C(3) = 103.1(8), S(2)−O(31)−Ta(1) = 139.6(6), S(3)−O(21)− Ta(1) = 148.0(6).

Crystals of 6 are constituted by discrete pseudo-octahedral molecules in which the centroid of the Cp* ligand occupies a coordination position and is bonded to the metal center in a η5 fashion. In addition, the bis-alkoxide ligand is coordinated in a fac mode through the three heteroatoms, with the sulfur atom in a trans disposition in relation to the Cp* and the oxygen atoms lying in the same plane as the triflate ligands, which are in a cis disposition to one another. The tantalum atom is displaced by 0.453 Å out of the plane defined by O(1), O(2), O(21), and O(31) and, as a consequence of the fac coordination mode, the bis-alkoxide ligand is bent, giving rise to a value for the O(1)−Ta(1)−O(2) angle of 97.2(4)° while the C(2)−S(1)−C(3) angle is 103.1(8)°. The spatial configuration of the tdgol ligand produces a long Ta(1)− S(1) distance, 2.686(4) Å,7 but this is enough to justify an interaction between the two atoms. The Ta(1)−O(1) and Ta(1)−O(2) bond distances (1.915(9) and 1.928(8) Å) and C(1)−O(1)−Ta(1) and C(4)−O(2)−Ta(1) angles (129.6(9) C


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confirms the existence of that mirror plane and several singlet signals have been found in the 1H NMR spectra at 2.29 (7), 1.88 (8), and 2.27 ppm (9), respectively, attributable to the equivalent protons of the metallaaziridine fragments. In addition, in the 13C NMR spectra of 7 and 8 the resonances of the azatantalacyclopropane carbon atoms appear at 58.9 (7) and 59.5 ppm (8), respectively, while for 9 this signal is located at 71.9 ppm, which could reinforce the idea of a withdrawal of electrons by the κ3O,S,O ancillary ligand when it contains aromatic rings. Finally, the reaction of 4 with tBuNC gave rise to mixtures even at low temperature, revealing once more its high reactivity. Furthermore, the monotriflate complex 5 reacts with xylyl isocyanide and water to yield the aminocarbene cationic complex 10 (Scheme 5), which was isolated as an air-stable

and 131(1)°) are similar to those found in compound 1 and other related alkoxide-containing complexes3,4,6 and are justified by the π reinforcement of the bonds (vide supra). Furthermore, the triflate ligand Ta−O distances are longer (Ta(1)−O(21) = 2.126(8) Å; Ta(1)−O(31) = 2.154(8) Å), which is consistent with simple tantalum−oxygen bonds.17 Finally, the difference between the S(2)−O(31)−Ta(1) and S(3)−O(21)−Ta(1) angles (8.4°) can be justified by steric requirements.18 The triflate derivatives 5 and 6 were characterized in solution by the usual spectroscopic and analytical techniques. The 1H NMR spectrum of 5 shows two singlets at 0.37 and 1.86 ppm, corresponding to the Me and Cp* ligands, respectively, and eight multiplets, integrating for one proton each. The spectrum indicates the inequivalence of the tridentate ligand protons, which was confirmed by the presence of four signals in the 13 C{1H} NMR spectrum at 36.6, 38.9, 72.9, and 73.5 ppm attributable to the ligand carbon atoms. All of these spectroscopic data, along with the solubility of the compound, confirm that the triflate ligand is covalently bonded to the tantalum atom and generates the asymmetry in the coordination sphere, which produces the spectroscopic inequivalence of the ligand’s methylene groups. In contrast, the bis-triflate complex 6 is symmetric and the methylene groups of the bis-alkoxide ligand give rise to only four multiplets in the 1H NMR spectrum at 1.63, 3.10, 3.92, and 4.75 ppm and two signals in the 13C spectrum at 39.0 and 77.0 ppm. One of the main aims of this study was to compare the reactivity with isocyanides of the complexes bearing methyl or hydride ligands (2−5). In that sense, while the dimethyl complex 2 remained unaltered, the dihydrides 3 and 4 and the methyl triflate derivative 5 showed an interesting reactivity. In fact, complexes 3 and 4 react readily with xylylNC (xylyl = 2,6-dimethylphenyl) or tBuNC to give the corresponding azatantalacyclopropanes 7−9 in quantitative yield (Scheme 4).

Scheme 5

yellow solid. This reaction probably proceeds by initial displacement of the triflate ligand by the isocyanide, insertion into the C−Ta bond, and subsequent protonation of the generated cationic iminoacyl intermediate.2,20 This kind of reactivity and the resulting chemical stability of the final cationic aminocarbene complex 10 have also been observed by us in some similar series of complexes containing related tridentate ancillary κ3O,S,O ligands bearing aromatic groups.21 In our previous work, we demonstrated that the stability in air was due to the presence of hydrogen bonds between the anion and the cation, a situation that is also plausible in complex 10as suggested by the solubility behavior. In fact, complex 10 is slightly soluble and is stable in apolar solvents such as benzene or toluene but decomposes rapidly when dissolved in CDCl3 and more slowly when the solvent is CD3CN. This behavior reproduces that observed for its tbop and tbcp analogues and can be explained by taking into account that more polar solvents may be able to solvate the ions, thus breaking the proposed hydrogen bonds between the triflate unit and the NH and/or OH groups in the cation fragment and eliminating the claimed stabilization effect.21 Complex 10 was characterized in solution by the usual spectroscopic and analytical techniques. The NH and OH groups give rise to two bands in the IR spectrum at 3156 and 3055 cm−1. The Ta−OH proton appears as a broad singlet at 12.36 ppm in the 1H NMR spectrum, while the NH signal was not detected. The two methyl groups of the xylyl fragment are equivalent and give rise to a broad singlet in the 1H NMR spectrum at 2.07 ppm and to a signal at 18.8 ppm in the 13C NMR spectrum. The spectroscopic characterization of complex 10 was completed with an HSQC experiment, which confirmed that the coordination of the tdgol ligand is fac on the basis of the presence of eight multiplet signals in the 1H NMR spectrum at 4.89, 4.65, 4.40, 3.52, 3.34, 1.97, 1.93, and 1.69 ppm, which correlate with four signals in the 13C NMR spectrum at 73.9, 72.8, 39.8, and 38.3 ppm. Another important correlation was found between a broad singlet at 1.61 ppm

Scheme 4

To the best of our knowledge, only one case of a double insertion of an isocyanide into tantalum−hydride bonds to give an azatantalacyclopropane has been reported to date.11 The rest of the literature examples of complexes bearing an aziridine moiety were formed by activation of a C−H bond of a methyl substituent on a nitrogen atom in an amide ligand.19 The azatantalacyclopropanes 7−9 are extremely sensitive to air and moisture, and all our attempts to isolate them in a pure form were unsuccessful. Nevertheless, they were generated on an NMR tube scale in almost quantitative yield and characterized by spectroscopic methods. The 1H and 13C NMR data for these compounds are consistent with a κ3 coordination of the tridentate κ3O,S,O ligand4 and an azatantalacyclopropane disposition such that a mirror plane divides the molecule into two equivalent fragments (Scheme 4).4,11,20 In fact, the resonance pattern for the alkoxide ligands D


Organometallics

Article 1 H NMR (C6D6, room temperature): δ −0.23 (s, 6H, Me-Ta), 1.76 (m, 2H, −SCH2), 1.88 (s, 15H, Cp*), 2.36 (m, 2H, −SCH2), 4.22 (m, 2H, −OCH2), 4.32 (m, 2H, −OCH2). 13C{1H} NMR (C6D6, room temperature): δ 10.7 (Cp*), 31.6 (Me-Ta), 37.4 (−SCH2), 70.8 (−OCH2), 117.9 (Cp*). Anal. Calcd for C16H29Cl2O2STa (466.41): C, 41.20; H, 6.27; S, 6.87. Found: C, 40.96; H, 6.08; S, 7.02. [TaCp*H 2 {[O(CH 2 ) 2 ] 2 S-κ 3 O,S,O}] (3). To a solution of [TaCp*Cl2{[O(CH2)2]2S-κ3O,S,O}] (1; 0.210 g, 0.41 mmol) in pentane/toluene (3/1) (12 mL) at 0 °C was slowly added NaBHEt3 (1 M in toluene; 0.828 mL, 0.82 mmol), and the mixture was stirred for 30 min at 0 °C. The solvent was removed under vacuum, and the resulting solid was extracted with cold pentane (0 °C, 3 × 5 mL). Evaporation of the solvent yielded 0.109 g (60%) of a white solid, which was identified as 3. 1 H NMR (C6D6, room temperature): δ 1.81 (m, 2H, −SCH2), 2.20 (s, 15H, Cp*), 2.26 (m, 2H, −SCH2), 4.12 (m, 2H, −OCH2), 4.27 (m, 2H, −OCH2), 10.07 (s, 2H, Ta-H). 13C{1H} NMR (C6D6, room temperature): δ 11.8 (Cp*), 37.6 (−SCH2), 70.3 (−OCH2), 116.1 (Cp*). Anal. Calcd for C14H25O2STa (438.36): C, 38.36; H, 5.75; S, 7.31. Found: C, 38.30; H, 5.61; S, 7.14. [TaCp*H2(κ3-tbop)] (4). To a solution of [TaCp*Cl2(κ3-tbop)] (0.255 g, 0.31 mmol) in pentane (15 mL) at 0 °C was slowly added NaBHEt3 (1 M in toluene; 0.61 mL, 0.62 mmol), and the mixture was stirred for 60 min at 0 °C. The solvent was removed under vacuum, and the resulting solid was extracted with pentane (2 × 15 mL). Evaporation of the solvent yielded 0.177 g (75%) of a light yellow solid, which was identified as 4. 1 H NMR (C6D6, 293 K): δ 0.65 (s, 18H, 6CH3 tert-octyl), 1.19 (s, 6H, 2CH3 tert-octyl), 1.21 (s, 6H, 2CH3 tert-octyl), 1.55 (s, 4H, 2CH2 tert-octyl), 2.18 (s, 15H, Cp*), 6.68 (d, 3JH−H = 8.66 Hz, 2H, ar), 6.98 (dd, 3JH−H = 8.66 Hz, 4JH−H = 2.22 Hz, 2H, ar), 7.63 (d, 4JH−H = 2.22 Hz, 2H, ar), 12.23 (s, 2H, Ta-H). 13C{1H} NMR (C6D6, room temperature): δ 11.9 (Cp*), 31.5 (CMe2 tert-octyl), 31.9 (CMe3 tertoctyl), 32.2 (CMe3 tert-octyl), 37.9 (CMe2 tert-octyl), 56.7 (CH2 tertoctyl), 118.2 (Cp*), 121.2 (Cipso S), 123.2 (ar), 128.9 (ar), 129.2 (ar), 143.1 (Cipso tert-octyl), 165.4 (Cipso O). Anal. Calcd for C38H57O2STa (758.87): C, 60.14; H, 7.57; S, 4.23. Found: C, 59.84; H, 7.34; S, 4.03. [TaCp*Me(TfO){[O(CH2)2]2S-κ3O,S,O}] (5). To a suspension of [TaCp*Me2{[O(CH2)2]2S-κ3O,S,O}] (2; 0.290 g, 0.61 mmol) in toluene (20 mL) at −78 °C was added triflic acid (55 μL, 0.61 mmol). The mixture was stirred for 10 min at −78 °C and for 1 h at room temperature to give a colorless solution. The solvent was removed under vacuum, and the resulting oil was frozen with liquid nitrogen to give a white solid (0.330 g, 88%), which was characterized as 5. 1 H NMR (C6D6, room temperature): δ 0.37 (s, 3H, Me-Ta), 1.55 (m, 1H, −SCH2), 1.65 (m, 1H, −SCH2), 1.86 (s, 15H, Cp*), 2.13 (m, 1H, −SCH2), 2.78 (m, 1H, −SCH2), 3.37 (m, 1H, −OCH2), 4.36 (m, 1H, −OCH2), 4.60 (m, 1H, −OCH2), 4.79 (m, 1H, −OCH2). 13 C{1H} NMR (C6D6, room temperature): δ 10.4 (Cp*), 36.6 (MeTa), 34.4 (−SCH2), 38.9 (−SCH2), 72.9 (−OCH2), 73.5 (−OCH2), 122.4 (Cp*). Anal. Calcd for C16H26F3O5S2Ta (600.45): C, 32.00; H, 4.36; S, 10.68. Found: C, 31.71; H, 4.16; S, 10.04. [TaCp*(TfO)2{[O(CH2)2]2S-κ3O,S,O}] (6). To a suspension of [TaCp*Me2{[O(CH2)2]2S-κ3O,S,O}] (2; 0.210 g, 0.45 mmol) in toluene (10 mL) was added triflic acid (79.5 μL, 0.90 mmol). The mixture was stirred for 2 h at room temperature to give a suspension. The white solid (0.264 g, 88%) was isolated by filtration, dried under vacuum, and characterized as 6. Single crystals suitable for X-ray diffraction were obtained by crystallization from dichloromethane at −20 °C. 1 H NMR (C6D6, room temperature): δ 1.63 (m, 2H, −SCH2), 1.96 (s, 15H, Cp*), 3.10 (m, 2H, −SCH2), 3.92 (m, 2H, −OCH2), 4.75 (m, 2H, −OCH2). 13C{1H} NMR (C6D6, room temperature): δ 10.4 (Cp*), 39.0 (−SCH2), 77.0 (−OCH2), 119.8 (Cp*). Anal. Calcd for C16H23F6O8S3Ta (734.48): C, 26.16; H, 3.16; S, 13.10. Found: C, 26.21; H, 3.27; S, 12.84. Reaction of [TaCp*H2{[O(CH2)2]2S-κ3O,S,O}] with xylylNC. To a solution of [TaCp*H2{[O(CH2)2]2S-κ3O,S,O}] (0.020 g, 0.05 mmol) in C6D6 was added xylylNC (0.006 g, 0.05 mmol), and the

(integrating for 3H) and a carbon signal at 27.8 ppm, both of which can be assigned to the methyl group inserted into the CN bond (Me−CN(H)). Finally, the carbenic nature of the ligand was confirmed by the presence of a signal in the 13C NMR spectrum at 265.3 ppm, which is typical for this type of ligand.21

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CONCLUSIONS A series of tantalum alkyl and hydride complexes containing a tridentate κ3O,S,O ligand was synthesized, and the reactivity of the resulting compounds toward isocyanides was studied. Thus, a lack of reactivity was observed for the alkyl derivatives, while the mono-triflates reacted with an isocyanide and water to give an aminocarbene species. Even more interesting is the reactivity of the hydride complexes with isocyanides to lead to the corresponding metallaziridines. This way of obtaining azatantalacyclopropane is not general, as only one case was reported previously. All the dihydride complexes that gave insertion reactions contain a tridentate ancillary ligand, which points to a generalization of these kinds of reactivity when the metal is stabilized by the effect of the κ3 ligands. Finally, we have found a difference in stability when the ligand is tbop. This finding reinforces our previous assumption about the influence in reactivity of the substituents in the ancillary κ3O,S,O ligand4 and opens the door to a further study on tuning the reactivity of the metal center through modification of the tridentate ligands.

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EXPERIMENTAL SECTION

General Procedures. The preparation and handling of compounds were performed under a nitrogen atmosphere using standard vacuum line and Schlenk techniques. All solvents were dried and distilled under a nitrogen atmosphere. The compounds [TaCp*Me4],22 [TaCp*Cl4],23 and [TaCp*Cl2(κ3-tbop)]4 were prepared by literature procedures. The commercially available compounds 2,2′-dithioethanol, tBuNC, xylyl-NC, triflic acid, Et3N, and NaBHEt3 (1 M) were used as received from Aldrich. 1H and 13C NMR spectra were recorded on a Bruker 400 MHz Advance Fourier transform spectrometer. Trace amounts of protonated solvents were used as references, and chemical shifts are reported in units of parts per million relative to SiMe4. IR spectra were recorded in the region 4000−400 cm−1 on Nicolet Magna-IR 550 and Jasco FT/IR-41100 spectrophotometers. Elemental microanalyses were carried out at the SIDI (Universidad Autónoma de Madrid, Spain). [TaCp*Cl 2 {[O(CH 2 ) 2 ] 2 S-κ 3 O,S,O}] (1). To a mixture of [TaCp*Cl4] (0.378 g, 0.82 mmol) and 2,2′-thiodiethanol (0.100 g, 0.82 mmol) in toluene (15 mL) at 0 °C was added Et3N (230 μL, 1.65 mmol). The suspension was stirred for 20 min at 0 °C, for 2 h at room temperature, and for 3 h at 60 °C. The suspension was filtered, and the solid was extracted with toluene (10 mL). The solvent was removed under vacuum to yield 0.325 g (78%) of a gray solid, which was identified as 1. Single crystals suitable for X-ray diffraction were obtained by crystallization from dichloromethane. 1 H NMR (C6D6, room temperature): δ 1.63 (m, 2H, −SCH2), 2.09 (s, 15H, Cp*), 2.63 (m, 2H, −SCH2), 4.27 (m, 2H, −OCH2), 4.73 (m, 2H, −OCH2). 13C{1H} NMR (C6D6, room temperature) δ 11.5 (Cp*), 38.1 (−SCH2), 75.1 (−OCH2) 124.9 (Cp*). Anal. Calcd for C14H23Cl2O2STa (507.25): C, 33.15; H, 4.57; S, 6.32. Found: C, 33.61; H, 4.67; S, 6.12. [TaCp*Me 2 {[O(CH 2 ) 2 ] 2 S-κ 3 O,S,O}] (2). To a solution of [TaCp*Me4] (0.102 g, 0.27 mmol) in toluene (10 mL) was added 2,2′-thiodiethanol (0.033 g, 0.27 mmol), and the mixture was stirred for 5 h at 60 °C. The solvent was removed under vacuum, and the resulting solid was dissolved in pentane and kept at −20 °C overnight. The resulting precipitate was isolated by filtration and dried under vacuum to yield 0.076 g (60%) of a white solid, which was identified as 2. E


Organometallics

Article

immediate formation of the insertion compound 7 in almost quantitative yield was determined by NMR. 1 H NMR (C6D6, room temperature): δ 1.87 (s, 15H, Cp*), 2.12 (m, 2H, −SCH2), 2.26 (s, 6H, Me-xyl), 2.29 (s, 2H, CH2-Ta), 2.51 (m, 2H, −SCH2), 4.34 (m, 4H, −OCH2), 6.91 (t, 3JH−H = 7.57 Hz, 1H, ar), 7.08 (d, 3JH−H = 7.57 Hz, 2H, ar). 13C{1H} NMR (C6D6, room temperature): δ 10.4 (Cp*), 18.4 (Me-xyl), 39.5 (−SCH2), 58.9 (CH2Ta), 73.3 (−OCH2), 117.7 (Cp*), 122.7 (ar), 128.2 (ar), 132.6 (CipsoN), 153.6 (Cipso-Me). Reaction of [TaCp*H2{[O(CH2)2]2S-κ3O,S,O}] with tBuNC. To a solution of [TaCp*H2{[O(CH2)2]2S-κ3O,S,O}] (0.013 g, 0.03 mmol) in C6D6 was added tBuNC (3.4 μL, 0.03 mmol), and the immediate formation of the insertion compound 8 in almost quantitative yield was determined by NMR. 1 H NMR (C6D6, room temperature): δ 1.87 (s, 9H, tBu), 1.88 (s, 2H, CH2-Ta), 1.93 (s, 15H, Cp*), 1.99 (m, 2H, −SCH2), 2.65 (m, 2H, −SCH2), 4.28 (m, 2H, −OCH2), 4.58 (m, 2H, −OCH2). 13C{1H} NMR (C6D6, room temperature): δ 10.8 (Cp*), 29.9 (Me3C), 40.3 (−SCH2), 50.4 (Me3C), 59.5 (CH2-Ta), 72.6 (−OCH2), 116.9 (Cp*). Reaction of [TaCp*H2(κ3-tbop)] with xylylNC. To a solution of [TaCp*H2(κ3-tbop)] (0.020 g, 0.03 mmol) in C6D6 was added xylylNC (0.003 g, 0.03 mmol), and the immediate formation of the insertion compound 9 in almost quantitative yield was determined by NMR. 1 H NMR (C6D6, 293 K): δ 0.70 (s, 18H, 6CH3 tert-octyl), 1.31 (s, 6H, 2CH3 tert-octyl), 1.34 (s, 6H, 2CH3 tert-octyl), 1.61 (dd, 2JH−H = 14.54 Hz, 4H, CH2 tert-octyl), 1.89 (s, 15H, Cp*), 2.19 (s, 6H, Mexyl), 2.27 (s, 2H, CH2-Ta), 6.68 (d, 3JH−H = 8.66 Hz, 2H, ar), 6.90 (t, 1H, 3JH−H = 7.56 Hz, ar), 6.98 (d, 3JH−H = 7.56 Hz, 2H, ar), 7.06 (dd, 3 JH−H = 8.64 Hz, 4JH−H = 2.28 Hz, 2H, ar), 7.82 (d, 4JH−H = 2.28 Hz, 2H, ar). 13C{1H} NMR (C6D6, room temperature): δ 10.0 (Cp*), 16.9 (Me-xylyl), 30.8 (CMe2 tert-octyl), 31.6 (CMe3 tert-octyl), 32.1 (CMe3 tert-octyl), 37.7 (CMe2 tert-octyl), 56.9 (CH2 tert-octyl), 71.9 (CH2Ta), 118.7 (Cp*), 121.1 (Cipso-S), 123.7 (ar), 128.7 (ar), 133.6 (ar), 134.5 (Cipso-N), 139.7 (Cipso tert-octyl), 152.3 (Cipso-Me), 166.2 (CipsoO). [TaCp*{C(Me)N(H)xylyl-κ1C}(OH){[O(CH2)2]2S-κ3O,S,O}] (10). To a mixture of [TaCp*Me(TfO){[O(CH2)2]2S-κ3O,S,O}] (5; 0.281 g, 0.47 mmol) and xylylNC (0.061 g, 0.47 mmol) was added toluene (10 mL). The solution was stirred at room temperature for 1 h, and then 1 equiv of water (8.5 μL, 0.47 mmol) was added. The mixture was stirred at room temperature for 15 h, the solvent was removed under vacuum, and the residue was washed with cold pentane to yield a yellow solid (0.139 g, 40%), which was identified as 10. 1 H NMR (C6D6, room temperature): δ 1.61 (br, 3H, CH3CN), 1.81 (s, 15H, Cp*), 1.69 (m, 1H, −SCH2), 1.93 (m, 1H, −SCH2), 1.97 (m, 1H, −SCH2), 2.07 (br, 6H, CH3-xylyl), 3.34 (m, 1H, −SCH2), 3.52 (m, 1H, −OCH2), 4.40 (m, 1H, −OCH2), 4.65 (m, 1H, −OCH2), 4.89 (m, 1H, −OCH2), 6.98 (m, br, 3H, xylyl), 12.36 (br, 1H, Ta-OH). 13C{1H} NMR (C6D6, room temperature): δ 10.7 (Cp*), 18.8 (CH3-xylyl), 27.8 (CH3CN), 38.3 (−SCH2), 39.8 (−SCH2), 72.8 (−OCH2), 73.9 (−OCH2), 122.3 (Cp*), 128.2, 128.9, 133.3, 137.5 (ar), 265.3 (CN). IR ν (cm−1): 1453 (s, CN), 3055 (m, Ta-OH), 3156 (m, NH). Anal. Calcd for C25H37F3O6S2Ta (749.64): C, 40.06; H, 4.97; S, 8.55. Found: C, 40.19; H, 5.10; S, 8.76. X-ray Structure Determination for 1 and 6. Data were collected on a Bruker X8 APEX 2 CCD-based diffractometer, equipped with a graphite-monochromated Mo Kα radiation source (λ = 0.71073 Å). The crystal data, data collection, structural solution, and refinement parameters are summarized in the Supporting Information. Data were integrated using SAINT,24 and an absorption correction was performed with the program SADABS.25 A successful solution by direct methods provided most non-hydrogen atoms from the E map. The remaining non-hydrogen atoms were located in the alternating series of least-squares cycles and difference Fourier maps.26 All non-hydrogen atoms were refined with anisotropic displacement coefficients, and all hydrogen atoms were included in the structure factor calculations at idealized positions and were allowed to ride on the neighboring atoms with relative isotropic displacement coefficients.

For compound 6, the triflate ligands in the structure are disordered over two positions in a ratio of approximately 50:50.

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ASSOCIATED CONTENT

S Supporting Information *

Tables and CIF files giving details of structural data collection, refinement, atom coordinates, anisotropic displacement parameters, and bond lengths and angles for complexes 1 and 6. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*A.O.: fax, (internat.) +34-926295318; e-mail, Antonio.Otero@ uclm.es. M.J.R.: e-mail, [email protected] Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the Ministerio de Economiá y Competitividad (MINECO) of Spain for financial support (Grant Nos. CTQ2011-22578/BQU, Consolider Ingenio 2010 ORFEO CSD-2007-00006) and for a fellowship (J.F.-G., Grant No. AP2005-4738).

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ABBREVIATIONS tdgol = 2,2′-thiodiethanolate; tbop = 2,2′-thiobis(6-tertoctylphenolate); xylyl = 2,6-dimethylphenyl; Ct = centroid of Cp*

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REFERENCES

(1) Crabtree, R. H. New J. Chem. 2011, 35, 18. (2) Bo, C.; Fandos, R.; Feliz, M.; Hernández, C.; Otero, A.; Rodrı ́guez, A.; Ruiz, M. J.; Pastor, C. Organometallics 2006, 25, 3336. (3) Fandos, R.; Hernández, C.; López-Solera, I.; Otero, A.; Rodrı ́guez, A.; Ruiz, M. J.; Terreros, P. Organometallics 2000, 19, 5318. (4) (a) Fandos, R.; Fernández-Gallardo, J.; López-Solera, M. I.; Otero, A.; Rodrı ́guez, A.; Ruiz, M. J.; Terreros, P. Organometallics 2008, 27, 4803. (b) Fernández-Gallardo, J.; Bellarosa, L.; Ujaque, G.; Lledós, A.; Ruiz, M. J.; Fandos, R.; Otero, A. Organometallics 2012, 31, 7052. (5) de Castro, I.; Galakhov, M. V.; Gómez, M.; Gómez-Sal, P.; Martín, A.; Royo, P. J. Organomet. Chem. 1996, 514, 51. (6) Tonks, I. A.; Henling, L. M.; Day, M. W.; Bercaw, J. E. Inorg. Chem. 2009, 48, 5096. (7) (a) Schrock, R. R.; Wesolek, M.; Liu, A. H.; Wallace, K. C.; Dewan, J. C. Inorg. Chem. 1988, 27, 2050. (b) Tatsumi, K.; Matsubara, I.; Inoue, Y.; Nakamura, A.; Miki, K.; Kasai, N. J. Am. Chem. Soc. 1989, 111, 7767. (c) Koo, S.-M.; Bergero, R.; Salifoglou, A.; Coucouvanis, D. Inorg. Chem. 1990, 29, 4844. (d) Tatsumi, K.; Inoue, Y.; Kawaguchi, H.; Koshada, M.; Nakamura, A.; Cramer, R. E.; VanDoorne, W.; Taogoshi, G. J.; Richmann, P. N. Organometallics 1993, 12, 352. (e) Fandos, R.; Hernández, C.; Otero, A.; Rodrı ́guez, A.; Ruiz, M. J.; Terreros, P. Eur. J. Inorg. Chem. 2003, 493. (8) A mer coordination implies only two multiplets integrating to 4H each. (9) Bradley, D. C.; Mehrotra, R. C.; Singh, A.; Rothwell, I. P. Alkoxo and Aryloxo Derivatives of Metals; Academic Press: London, 2001. (10) Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of OrganoZirconium and Hafnium Compounds; Ellis Horwood Limited, Halsted Press: New York, 1986. (11) Fandos, R.; Fernández-Gallardo, J.; Otero, A.; Rodrı ́guez, A.; Ruiz, M. J. Organometallics 2011, 30, 1551. (12) (a) Clark, J. R.; Fanwick, P. E.; Rothwell, I. P. J. Chem. Soc., Chem. Commun. 1993, 1233. (b) Clark, J. R.; Fanwick, P. E.; Rothwell, F


Organometallics

Article

I. P. Organometallics 1996, 15, 3232. (c) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. Organometallics 2005, 24, 5759. (13) (a) Rothwell, I. P. J. Chem. Soc., Chem. Commun. 1997, 1331. (b) Mulford, D. R.; Clark, J. R.; Schweiger, S. W.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1999, 18, 4448. (c) Parkin, B. C.; Clark, J. R.; Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1995, 14, 3002. (d) Visciglio, V. M.; Clark, J. R.; Nguyen, M. T.; Mulford, D. R.; Fanwick, P. E.; Rothwell, I. P. J. Am. Chem. Soc. 1997, 119, 3490. (e) Thorn, M. G.; Moses, J. E.; Fanwick, P. E.; Rothwell, I. P. Dalton Trans. 2000, 2659. (14) Burckhardt, U.; Casty, G. L.; Gavenois, J.; Tilley, T. D. Organometallics 2002, 21, 3108. (15) (a) Mayer, J M.; Curtis, C J; Bercaw, J E. J. Am. Chem. Soc. 1983, 105, 2651. (b) Mayer, J. M.; Bercaw, J. E. J. Am. Chem. Soc. 1982, 104, 2157. (16) Lawrance, G. A. Chem. Rev. 1986, 86, 17. (17) (a) Conde, A.; Fandos, R.; Otero, A.; Rodríguez, A. Organometallics 2007, 26, 1568. (b) Conde, A.; Fandos, R.; Otero, A.; Rodríguez, A. Organometallics 2008, 27, 6090. (c) Conde, A.; Fandos, R.; Otero, A.; Rodríguez, A. Organometallics 2009, 28, 5505. (d) Gavenonis, J.; Tilley, T. D. Organometallics 2002, 21, 5549. (18) Evans, D. A.; Scheidt, K. A.; Fandrick, K. R.; Lam, H. W.; Wu, H. J. J. Am. Chem. Soc. 2003, 125, 10780. (19) (a) Abbenhuis, H. C. L.; Grove, D. M.; Van Mier, G. P. M.; Spek, A. L.; Van Koten, G. Recl. Trav. Chim. Pays-Bas 1990, 109, 361. (b) Abbenhuis, H. C. L.; Van Belzen, R.; Grove, D. M.; Klomp, A. J. A.; Van Mier, G. P. M.; Spek, A. L.; Van Koten, G. Organometallics 1993, 12, 210. (c) Abbenhuis, H. C. L.; Feiken, N.; Haarman, H. F.; Grove, D. M.; Horn, E.; Spek, A. L.; Pfeffer, M.; van Koten, G. Organometallics 1993, 12, 2227. (d) de Castro, I.; Galakhov, M. V.; Gómez, M.; Gómez-Sal, P.; Royo, P. Organometallics 1996, 15, 1362. (e) Rietveld, M. H. P.; Lohner, P.; Nijkamp, M. G.; Grove, D. M.; Veldman, N.; Spek, A. L.; Pfeffer, M.; Van Koten, G. Chem. Eur. J. 1997, 3, 817. (20) Galakhov, M. V.; Gómez, M.; Jiménez, G.; Royo, P.; Pellinghelli, M. A.; Tiripicchio, A. Organometallics 1995, 14, 1901. (21) Fandos, R.; Fernández-Gallardo, J.; Otero, A.; Rodrı ́guez, A.; Ruiz, M. J. Organometallics 2010, 29, 5834. (22) Sanner, R. D.; Carter, S. T.; Burton, W. J. J. Organomet. Chem. 1982, 240, 157. (23) Burt, R. J.; Chatt, J.; Leigh, G. J.; Teuben, J. H.; Westerhof, A. J. Organomet. Chem. 1977, 129, C33. (24) SAINT+ v7.12a: Area-Detector Integration Program; BrukerNonius AXS, Madison, WI, 2004. (25) Sheldrick, G. M. SADABS version 2004/1: A Program for Empirical Absorption Correction; University of Göttingen, Göttingen, Germany, 2004. (26) SHELXTL-NT version 6.12: Structure Determination Package; Bruker-Nonius AXS, Madison, WI, 2001.

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Insertion Reactions in Ta–H and Ta–Me Bonds in Complexes

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