Tantalum Complexes Containing a Tridentate [NSN]-Type Ligand

ARTICLE pubs.acs.org/Organometallics

Tantalum Complexes Containing a Tridentate [NSN]-Type Ligand: Unusual Reactivity of a Dihydride Complex with an Isocyanide to Give an Azatantallaziridine Moiety Rosa Fandos,† Jacob Fern
andez-Gallardo,† Antonio Otero,*,‡ Ana Rodríguez,§ and María Jos
e Ruiz*,† †

Departamento de Química Inorg
anica, Org
anica y Bioquímica, Universidad de Castilla-La Mancha, Facultad de Ciencias Ambientales y Bioquímica, INAMOL, Avenida Carlos III, s/n 45071 Toledo, Spain ‡ Departamento de Química Inorg
anica, Org
anica y Bioquímica, Universidad de Castilla-La Mancha, Facultad de Químicas, Campus de Ciudad Real, 13071 Ciudad Real, Spain § Departamento de Química Inorg
anica, Org
anica y Bioquímica, Universidad de Castilla-La Mancha, ETS Ingenieros Industriales, Avenida Camilo Jos
e Cela, 3, 13071 Ciudad Real, Spain

bS Supporting Information ABSTRACT: A series of new tantalum complexes containing a [NSN]-type amide ligand (2,20 -diamidophenyl sulfide) have been synthesized and characterized. The complexes [TaCp*Cl2{(N-C6H4)2S-κ3-N,S,N}] (1) and [TaCp*Me2{(N-C6H4)2S-κ3-N,S,N}] (2) were prepared by reaction of 2,20 -diaminophenyl sulfide with [TaCp*Cl4] and [TaCp*Me2Cl2], respectively. In addition, [TaCp*MeCl{(N-C6H4)2S-κ3-N,S,N}] (3) and [TaCp*(H)2{(NC6H4)2S-κ3-N,S,N}] (4) were synthesized by reaction of 1 with AlMe3 and NaBEt3H, respectively. The reactivity of these complexes with nucleophiles and electrophiles was also studied, and complexes [TaCp*(tBuNCH2-κ2-C,N){(N-C6H4)2S-κ3-N,S,N}] (5) and [TaCp*Me{(N-C6H4)2S-κ3-N,S,N}][MeB(C6F5)3] (6) were isolated and characterized. The single-crystal structures of 1 and 4 were determined by X-ray diffraction methods. The NMR chemical shifts of the amidic protons in the complexes allowed us to evaluate the influence that the other ligands in the coordination sphere have on the electronic density of the metal.

’ INTRODUCTION The development of the organometallic chemistry of early transition metals owes much to the evolution of biscyclopentadienyl systems. The wedge-shaped biscyclopentadienylmetal fragments provide geometrically and electronically well-defined pockets, the size and the shape of which are suited for the promotion of various important organic/inorganic reactions. To expand the scope of metallocene chemistry, it is desirable to finely tune the geometry and the electronic richness of reaction sites. The replacement of one cyclopentadienyl group by a geometrically and electronically tunable ancillary ligand enables yet another range of new reactive sites to be created.1 In this context, in recent years transition metal complexes with ligands that contain different donor atoms have been widely investigated. Among them, we chose for this work a ligand that contains two phenyl amido functionalities and a sulfur atom that acts as a bridge between them (2,20 -diamidophenyl sulfide, Scheme 1) for two reasons: first, this [NSN] ligand allows comparisons to be made with the [OSO]-type ligands previously studied by us2 and, second, amide ligands may be bound to the metal in a single or double fashion and the free NH groups offered the possibility of binding other metals to give heterobimetallics.3 In particular, this ligand would be capable of forming strong bonds with early transition metals in their r 2011 American Chemical Society

Scheme 1a

a

Reagents: (i) X = Cl (1), 4 equiv of piperidine. (ii) X = CH3 (2), 2 equiv of nBuLi.

higher oxidation state through the nitrogen atoms, while the sulfur atom would assist the formation of an additional bond to the metal center, thus helping to modulate its electronic density depending on its requirements. We report here the synthesis, characterization, and reactivity of a series of complexes of tantalum with the ligand 2,20 -diamidophenyl sulfide. In addition, we demonstrate that the NMR chemical shifts of the amidic protons in the complexes provide information about the Received: November 17, 2010 Published: February 22, 2011 1551

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Table 1. Selected Bond Distances and Angles for Compound 1 bond lengths (Å) a

a

bond angles (deg)

Ta(1)-Ct(1)

2.125

Ct(1)-Ta(1)-S(1)

178.75

Ta(1)-S(1) Ta(1)-N(1)

2.599(3) 2.02(1)

N(1)-Ta(1)-N(2) C(2)-S(1)-C(7)

92.6(4) 102.4(6)

Ta(1)-N(2)

2.043(9)

C(1)-N(1)-Ta(1)

131.2(8)

Ta(1)-Cl(1)

2.461(3)

C(12)-N(2)-Ta(1)

128.8(8)

Ta(1)-Cl(2)

2.452(3)

C(1)-N(1)-H(1)

106(1)

N(1)-H(1)

0.89(9)

C(12)-N(2)-H(2)

115(1)

N(2)-H(2)

0.880(9)

Ct: centroid of Cp*.

Scheme 2 Figure 1. ORTEP S,N}] (1).

diagram

of

[TaCp*Cl2{(N-C6H4)2S-κ -N,3

influence that the other ligands in the coordination sphere have on the electronic density of the metal.

’ RESULTS AND DISCUSSION The first step in our study was the synthesis of a series of tantalum compounds containing a pentamethylcyclopentadienyl ring and the ligand 2,20 -diamidophenyl sulfide. The dichloride derivative [TaCp*Cl2{(N-C6H4)2S-κ3-N,S,N}] (1) was prepared by reaction of [TaCp*Cl4] with one equivalent of the diamino precursor in the presence of four equivalents of piperidine in dichloromethane for 16 h (Scheme 1). The high basicity of piperidine prevents the reaction between the free amino ligand and the HCl generated during the reaction by trapping the latter. Complex 1 is soluble in dichloromethane, sparingly soluble in hot toluene and benzene, and insoluble in pentane, diethyl ether, and THF. The 1H NMR spectrum of 1 in C6D6 shows the resonance of the Cp* ligand as a singlet at 1.85 ppm along with four multiplets at 5.96, 6.31, 6.77, and 7.07 ppm (each integrating for 2H), which correspond to the eight protons of the aromatic rings. Furthermore, the most remarkable feature of the spectrum is a singlet at 6.24 ppm (integrating for two protons) that corresponds to the two amidic protons of the bisamido ligand. These protons also give rise to a broad band in the infrared spectrum at 3400 cm-1 due to the vibration of the N-H bonds.4 The molecular structure of 1 was determined by X-ray diffraction (Figure 1). Selected bond lengths and angles are listed in Table 1. The molecular structure of 1 shows a pseudooctahedral geometry around the tantalum atom with the Cp* and the sulfur atom occupying the axial positions and the nitrogen and chlorine atoms lying on the equatorial plane. The tantalum atom is 0.580 Å out of this plane. The Ta(1)-N(1) and Ta(1)-N(2) distances are 2.02(1) and 2.043(9) Å, respectively, and these are within the normal range for sigma bonds in bisarylamido complexes.5-7 The angles C(1)-N(1)-Ta(1) and C(12)N(2)-Ta(1) are 131.2(8)° and 128.8(8)°, respectively, indicating that the nitrogen atom has a hybridization close to sp2 and suggesting a reinforcement of the N-Ta bonds by donation of additional electronic density from the nitrogen to the metal center.5-7 Finally, the Ta(1)-S(1) distance [2.599(3) Å] is longer than a single S-Ta bond8,9 but similar to the values found in many other sulfide linker-containing complexes such as alkoxides2 and thiolates.9

Furthermore, the dimethyl derivative [TaCp*Me2{(NC6H4)2S-κ3-N,S,N}] (2) was prepared by reaction of [TaCp*Me2Cl2]10 with one equivalent of the lithium salt of the 2,20 diamidophenyl sulfide generated “in situ” (Scheme 1). All our attempts to synthesize compound 2 by reaction between [TaCp*Me4] or [TaCp*Me2Cl2] and the proligand were unsuccessful. At room temperature they do not react at all, and at higher temperatures the tantalum precursors decomposed and the 2,20 -diamidophenyl sulfide was recovered unaltered. Complex 2 is slightly more soluble than complex 1, and it can be dissolved in toluene and dichloromethane but is insoluble in diethyl ether and pentane. We propose for 2 a structure similar to that of 1, as the signal patterns in their NMR spectra are identical, apart from the methyl signals at -0.01 and 27.15 ppm in the 1H and 13C NMR spectra, respectively. The presence of the NH groups was confirmed by infrared spectroscopy on the basis of the broad band at 3390 cm-1. The most remarkable difference observed for complex 2 in comparison to 1 is that the NH proton signal of 2 appears at higher field (6.24 ppm for 1 and 5.53 ppm for 2), indicating a relationship between the position of these protons in the NMR spectra and the electronic density of the metal. Bearing these results in mind, one can infer that the Cl ligands provide less electronic density to the metal center than the methyl ligands, a situation that forces the nitrogen atoms to compensate for this and makes the NH protons more electron deficient. In order to check this supposition, we decided to synthesize a complex with a chloro and a methyl ligand. Thus, the methyl chloro complex [TaCp*MeCl{(N-C6H4)2S-κ3-N,S,N}] (3) was synthesized from the dichloro derivative 1 by reaction with AlMe3, as shown in Scheme 2. Complex 3 was characterized by spectroscopic methods, and the NMR spectra reflect the asymmetry of the molecule, as all protons and carbons (except for those of Cp*) are inequivalent. The 1H NMR spectrum of 3 shows seven multiplets between 6.13 and 7.25 ppm, corresponding to the eight aromatic protons, a singlet at 1.74 ppm integrating for 15 protons due to Cp*, and a signal at 0.53 ppm that integrates for three protons and confirms the presence of only one methyl group in the molecule. The NH 1552

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Scheme 3

Table 2. Selected Bond Distances and Angles for Compound 4 bond lengths (Å)

bond angles (deg)

Ta(1)-Ct(1)a

2.121

Ct(1)-Ta(1)-S(1)

169.02

Ta(1)-S(2)

2.564(3)

N(1)-Ta(1)-N(2)

100.7(4)

Ta(1)-N(1)

2.061(9)

C(6)-S(2)-C(7)

104.0(6)

Ta(1)-N(2)

2.038(9)

C(1)-N(1)-Ta(1)

130.0(8)

Ta(1)-H(101) Ta(1)-H(102)

1.98 1.76

C(12)-N(2)-Ta(1) C(1)-N(1)-H(103)

129.1(8) 115.3(9)

C(12)-N(2)-H(104)

115.0(9)

H(101)-Ta(1)-H(102) a

Figure 2. ORTEP diagram of [TaCp*(H)2{(N-C6H4)2S-κ3-N,S,N}] (4).

Table 3. Selected NMR Signals

76.3(2)

NH

Ct: centroid of Cp*.

protons give rise to a band in the infrared spectrum at 3401 cm-1, and these are inequivalent in the NMR spectrum. One NH proton gives rise to a singlet at 5.81 ppm and the other a signal at 5.94 ppm as a part of one of the multiplets of the aromatic protons (that multiplet is the only one that integrates for two protons). Both protons appear in an intermediate position between those of 1 and 2, thus confirming our supposition and providing a tool to measure the electronic density on the metal. In order to gain further insights into the use of the NH proton NMR signal as a measure of the electronic density of the metal center, we decided to prepare the dihydride complex [TaCp*(H)2{(N-C6H4)2S-κ3-N,S,N}] (4) by reaction of 1 with two equivalents of sodium triethyl borohydride (Scheme 3). There are very few examples of the coexistence of NH groups and hydrides at the same tantalum atom.11 Nevertheless, the two terminal hydride ligands of complex 4 were unequivocally identified by the Ta-H stretching band12 in the infrared spectrum at 1678 cm-1 and the resonance at 8.69 ppm in the 1 H NMR spectrum.13 The NH protons of 4 give rise to one signal at 5.56 ppm. If we consider this signal as a measure of the electronic density that the hydride ligands are able to give to the metal, and we compare it with those of complexes 1, 2, and 3 (Table 3), we can say that, as far as the effect of the electronic density of the tantalum is concerned, the hydride ligands are similar to the methyl ligands. Finally, the 1H NMR spectrum of 4 also contains a singlet at 1.89 ppm due to the Cp* protons and four multiplets at 6.24, 6.41, 6.82, and 7.33 ppm corresponding to the aromatic protons of the tridentate ligand. The molecular structure of 4 was determined by X-ray diffraction (Figure 2), and selected bond distances and angles are summarized in Table 2. It can be seen that, broadly speaking, the structure of 4 is similar to that of 1 (Figure 2). The molecule has a pseudooctahedral geometry with the Cp* and the sulfur atom occupying the axial positions and the nitrogen atoms and the hydride ligands lying on the equatorial plane. The tantalum atom is 0.579 Å out

CipsoN

1

2

6.24 160.10

3

4

5

6

5.53

5.81

5.56

5.49

7.58

161.70

5.94 159.14

161.70

5.77 159.14

161.70

161.45 CipsoS

122.46

118.48

119.02 119.14

161.45 118.48

117.70

121.77

118.24

of the equatorial plane. The Ta(1)-N(1) and Ta(1)-N(2) distances are 2.061(9) and 2.038(9) Å, respectively, and they are similar to those found in 2 and in other bisarylamido complexes.5-7 The C(1)-N(1)-Ta(1) and C(12)-N(2)Ta(1) angles are 130.0(8)° and 129.1(8)°, indicating, as in the case of 1, hybridization close to sp2 for the nitrogen atom.5-7 The Ta(1)-S(2) distance of 2.564(3) Å confirms the tridentate coordination of the ligand to the metal center. Finally, the Ta(1)-H(101) and Ta(1)-H(102) distances, which were estimated to be 1.98 and 1.76 Å, are within the normal range found in other hydride-amide complexes of tantalum.14,15 The most remarkable feature of the structure is the Ct(1)Ta(1)-S(1) angle. In complex 1 this angle is almost linear [178.75°]—as found in other similar sulfide linker-containing complexes9,16—but in complex 4 the sulfur atom of the tridentate ligand is slightly shifted by the hydrides and the angle diminishes to 169.92°, probably due to the trans influence of the hydrides, causing the amides to deviate greatly from a pseudotrans arrangements; additionally, steric reasons cannot be definitively rule out (Figure 3). It is well known that isocyanides can be inserted into early transition metal-alkyl and metal-amido bonds to give η2iminoacyl and η2-iminocarbamoyl compounds, respectively,17 and these are versatile and potentially useful reagents in many synthetic applications.18,17 Nevertheless, migratory insertion reactions into transition metal hydride bonds, particularly for early transition metals, have hardly been achieved19 despite the importance of the resulting products, which have been used as models for the related hydrogenation of carbon monoxide.20 The reactivity of complexes 2 and 4 with nucleophiles was studied, and differences between these two compounds were 1553

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Scheme 5

Figure 3. Comparison of the angles between complexes 1 and 4.

Scheme 4

found. For example, while complex 2 was unreactive with CO and isocyanides at room temperature, it decomposed at temperatures over 60 °C under all of the conditions assayed. Nevertheless, complex 4 is highly reactive with unsaturated molecules even at room temperature, giving rise to complicated mixtures of products. Fortunately, reaction of 4 with an equivalent of tert-butylisocyanide at low temperature gave the insertion product [TaCp*(tBuNCH2-κ2-C,N){(N-C6H4)2S-κ3-N,S,N}] (5) in 50% yield (Scheme 4). Compound 5 is soluble in all of the common organic solvents and is extremely sensitive to air and moisture. Nevertheless, complex 5 was characterized by spectroscopic methods. The 1H and 13C NMR data for compound 5 point to a κ2-coordination of the generated tantallaziridine moiety. The 1H NMR spectrum contains two doublets at 1.72 and 1.82 ppm (2JH-H = 1.29 Hz), corresponding to the diastereotopic protons of the metallaziridine, for which the carbon signal appears in the 13C NMR spectrum at 65.67 ppm.16,21-23 To the best of our knowledge, this is the first example of a double insertion of an isocyanide into tantalum hydride bonds to give a tantallaziridine. The literature examples of these bonding systems were formed by activation of a CH bond of a methyl substituent on a nitrogen atom in an amide ligand.23 Complex 2 also reacts with one equivalent of B(C6F5)3 to yield the highly unstable cationic complex [TaCp*Me{(NC6H4)2S-κ3-N,S,N}][MeB(C6F5)3] (6) (Scheme 5), which is soluble in THF, chloroform, and diethyl ether but insoluble in toluene and pentane. We propose a reversible interaction of the metal center of the cationic moiety with a molecule of the donor solvent, namely, THF or diethyl ether, to give intermediates that evolve to a mixture of intractable species. This complex was characterized by spectroscopic methods. The 19F spectrum of 6 shows three signals at 133.31, 164.46, and 167.13 ppm, corresponding to the ortho-, para-, and meta-fluorine atoms of the borate unit. The difference of

2.67 ppm between the para- and meta-signals indicates the cationic nature of the complex.24 The 1H-13C HSQC NMR spectrum in CDCl3 at room temperature contains a proton signal at 0.53 ppm that correlates with the signal at 57.15 ppm, which corresponds to the carbon of the methyl group bonded to the tantalum atom. The other methyl group in the complex is bonded to the boron atom, and this gives rise to a proton signal at 2.02 ppm, which correlates with the carbon signal at 10.88 ppm. A singlet appears in the low-field region of the 1H spectrum at 7.58 ppm, and this integrates for 2H but does not correlate with any signal in the 13C spectrum. This signal can be assigned to the NH protons, and comparison of the position of this signal with those for the other compounds in this work (Table 3) is indicative of a low electronic density on the tantalum atom, as one would expect given the cationic nature of the complex. In conclusion, a series of new tantalum complexes containing a tridentate amide ligand with a sulfur donor atom have been synthesized and characterized. Additionally, a good relationship was found in the complexes between the electronic density on the metal center and the chemical shifts of the NH moieties of the ligand. The nature of complex 4 must be highlighted due to the unusual coexistence of both hydride ligands and NH groups. Complex 4 reacted with tert-butylisocyanide to give through a double insertion process an interesting azatantallaziridine moiety. Additionally, an electrophilic attack of the Lewis acid B(C6F5)3 into the Ta-Me bond of the neutral dimethyl complex 2 took place, giving rise to a very unstable cationic complex 6.

’ 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*Me2Cl2]10 and [TaCp*Cl4]25 were prepared by literature procedures. The commercially available compounds 2,20 -diaminophenyl sulfide, nBuLi, tBuNC, Et3BHNa, and B(C6F5)3 were used as received from Aldrich. 1H and 13C NMR spectra were recorded on a 400 MHz Advance Bruker 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 4000400 cm-1 on Nicolet Magna-IR 550 and Jasco FT/IR-41100 spectrophotometers. Elemental microanalyses were carried out in the SIDI (Universidad Aut
onoma de Madrid). [TaCp*Cl2{(N-C6H4)2S-κ3-N,S,N}] (1). To a mixture of [TaCp*Cl4] (0.583 g, 1.27 mmol) and 2,20 -diaminophenyl sulfide (0.275 g, 1.27 mmol) were added dichloromethane (25 mL) and piperidine (501 μL, 5.08 mmol). The suspension was stirred for 16 h, and the solvent was removed under vacuum to yield a red solid, which was extracted 10 times with a 3:2 mixture of toluene and dichloromethane (50 mL). The solvent was removed, and the crude product was washed twice with Et2O (20 mL) to yield 0.663 g (87%) of a red powder, which 1554

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Table 4. Crystal Data and Structure Refinement for 1 and 4 1

4

empirical formula

C22H25Cl2N2STa

C22H27N2STa

fw

601.35

532.47

temperature (K)

180(2)

200(2)

wavelength (Å)

0.71073

0.71073

cryst syst

orthorhombic

trigonal

space group

Pbca

P65

a (Å)

14.218(7)

17.864(2)

b (Å) c (Å)

15.612(8) 19.37(1)

17.864(2) 12.492(2)

γ (deg)

120

volume (Å3)

4300(4)

3452.6(7)

Z

8

6

density(calcd) (g/cm3)

1.858

1.537

absorp coeff (mm-1)

5.469

4.873

F(000)

2352

1572

cryst size (mm3) index ranges

0.22  0.17  0.12 -16 e h e 16

0.33  0.22  0.22 -21 e h e 21

-15 e k e 18

-21 e k e 21

reflns collected

-23 e l e 23

-14 e l e 11

24 752

19 026

indep reflns

3771 [R(int) = 0.1185]

3510 [R(int) = 0.1057]

data/restraints/params

3771/0/262

3510/1/240

goodness-of-fit on F2

0.972

0.879

final R indices [I > 2σ(I)]a

R1 = 0.0595, wR2 = 0.1263

R1 = 0.0495, wR2 = 0.0830

R indices (all data)a

R1 = 0.1260, wR2 = 0.1611

largest diff peak and hole (e Å-3)

R1 = 0.0892, wR2 = 0.0927 -0.029(17)

absolute struct param 2.272 and -3.192

1.172 and -0.898

)

R = ∑ Fo| - |Fc|/∑|Fo|. wR = {∑w(Fo2 - Fc2)2/∑w(Fo2)2}1/2. GOF = {∑[w((Fo2 - Fc2)2)/(n - p)}1/2, where n = number of reflections and p = total number of parameters refined. a

was identified as 1. Single crystals suitable for X-ray diffraction were obtained by crystallization from toluene. 1 H NMR (C6D6, rt): δ 1.87 (s, 15H, Cp*), 5.96 (m, 2H, 6-C6H4), 6.24 (s, 2H, NH), 6.31 (m, 2H, 4-C6H4), 6.77 (m, 2H, 5-C6H4), 7.07 (m, 2H, 3-C6H4). 13C{1H} NMR (C6D6, rt): δ 11.39 (Cp*), 117.03 (6-C6H4), 120.21 (4-C6H4), 122.21 (Cp*), 122.46 (CipsoS), 130.31 (5-C6H4), 132.06 (3-C6H4), 160.10 (CipsoN). IR bands (cm-1): 3407 (m, N-H), 1302 (s, C-N). Anal. Calcd for C22H25Cl2N2STa 3 1/ 2Et2O: C, 45.15; H, 4.74; N, 4.39. Found: C, 45.27; H, 4.57; N, 4.64. [TaCp*Me2{(N-C6H4)2S-κ3-N,S,N}] (2). nBuLi (1.6 M in hexane, 2.63 mL, 4.20 mmol) was slowly added dropwise to a solution of 2,20 diaminophenyl sulfide (0.456 g, 2.10 mmol) in Et2O (30 mL) at 0 °C. The mixture was stirred for 1 h at 0 °C. The solvents were removed under vacuum, and [TaCp*Me2Cl2] (0.888 g, 2.10 mmol) and toluene (30 mL) were added to the deep green solid. The mixture was heated at 90 °C and stirred for 3 h, filtered while hot, and washed four times with hot toluene (15 mL) and twice with Et2O (10 mL) to yield 0.620 g (52%) of an orange solid, which was identified as 2. 1 H NMR (C6D6, rt): δ -0.01 (s, 6H, Me), 1.61 (s, 15H, Cp*), 5.53 (s, 2H, NH), 6.11 (m, 2H, 6-C6H4), 6.41 (m, 2H, 4-C6H4), 6.82 (m, 2H, 5-C6H4), 7.31 (m, 2H, 3-C6H4). 13C{1H} NMR (C6D6, rt): δ 10.48 (Cp*), 27.15 (Me), 115.85 (6-C6H4), 117.08 (4-C6H4), 118.48 (CipsoS), 119.62 (Cp*), 130.20 (5-C6H4), 132.18 (3-C6H4), 161.70 (CipsoN). IR bands (cm-1): 3390 (m, N-H), 1296 (s, C-N). Anal. Calcd for C24H31N2STa: C, 51.43; H, 5.57; N, 5.00. Found: C, 51.21; H, 5.46; N, 4.84.

[TaCp*MeCl{(N-C6H4)2S-κ3-N,S,N}] (3). AlMe3 (2 M in heptanes, 211 μL, 0.42 mmol) was added dropwise to a suspension of [TaCp*Cl2{(N-C6H4)2S-κ3-N,S,N}] (1) (0.254 g, 0.42 mmol) in toluene. The orange suspension was stirred for 2 h at room temperature, and the solvent was removed to yield an orange, oily solid, which was washed four times with pentane (5 mL) to give 0.134 g (55%) of an orange solid, which was identified as 3. 1 H NMR (C6D6, rt): δ 0.53 (s, 3H, Me), 1.73 (s, 15H, Cp*), 5.81 (s, 1H, NH), 5.94 (m, 2H, NH, 6-C6H4), 6.13 (m, 1H, 60 -C6H4), 6.33 (m, 1H, 4-C6H4), 6.39 (m, 1H, 40 -C6H4), 6.75 (m, 1H, 5-C6H4), 6.83 (m, 1H, 50 -C6H4), 7.17 (m, 1H, 3-C6H4), 7.25 (m, 1H, 30 -C6H4). 13 C{1H} NMR (C6D6, rt): δ 10.91 (Cp*), 31.53 (Me), 116.95 (6C6H4), 117.18 (60 -C6H4), 119.02 (CipsoS), 119.14 (C0 ipsoS), 119.65 (Cp*), 128.27 (4-C6H4), 130.23 (40 -C6H4), 131.99 (5-C6H4), 132.21 (50 -C6H4), 134.11 (3-C6H4), 134.98 (30 -C6H4), 159.14 (CipsoN), 161.45 (C0 ipsoN). IR bands (cm-1): 3401 (m, N-H), 1299 (s, CN). Anal. Calcd for C23H28ClN2STa: C, 47.55; H, 4.86; N, 4.82. Found: C, 47.75; H, 4.81; N, 4.76. [TaCp*(H)2{(N-C6H4)2S-κ3-N,S,N}] (4). BEt3HNa (1 M in toluene, 778 μL, 0.78 mmol) was added dropwise to a suspension of [TaCp*Cl2{(N-C6H4)2S-κ3-N,S,N}] (1) (0.234 g, 0.38 mmol) in pentane/toluene (2.5:1, 28 mL). The resulting yellow suspension was stirred at room temperature for 3 h, and the solvents were removed under vacuum to yield a yellow solid, which was extracted four times with Et2O (10 mL). The slow evaporation of the solvent under vacuum yielded 0.127 g (61%) of a yellow microcrystalline solid, which was 1555

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Organometallics identified as 4. Single crystals suitable for X-ray diffraction were obtained by crystallization from Et2O at -20 °C. 1 H NMR (C6D6, rt): δ 1.89 (s, 15H, Cp*), 5.56 (s, 2H, NH), 6.24 (m, 2H, 6-C6H4), 6.41 (m, 2H, 4-C6H4), 6.82 (m, 2H, 5-C6H4), 7.33 (m, 2H, 3-C6H4), 8.69 (s, 2H, H-Ta). 13C{1H} NMR (C6D6, rt): δ 10.48 (Cp*), 115.85 (6-C6H4), 117.8 (4-C6H4), 118.48 (CipsoS), 119.62 (Cp*), 130.20 (5-C6H4), 132.18 (3-C6H4), 161.70 (CipsoN). IR bands (cm-1): 3390 (m, N-H), 1678 (m, Ta-H), 1298 (m, C-N). Anal. Calcd for C22H27N2STa: C, 49.62; H, 5.11; N, 5.26. Found: C, 49.60; H, 5.52; N, 5.31. [TaCp*( tBuNCH2-κ2-C,N){(N-C6H4)2S-κ3-N,S,N}] (5). tBuNC (26 μL, 0.23 mmol) was added to a solution of [TaCp*(H)2{(N-C6H4)2S-κ3N,S,N}] (4) (0.122 g, 0.23 mmol) in CH2Cl2 (10 mL) at -98 °C. The mixture was allowed to reach room temperature over 1 h. After 15 min at room temperature the solvent was evaporated and the solid was extracted with pentane (5 mL). Evaporation of the pentane gave an orange, oily solid, which was characterized as 5 (0.071 g, 50%). 1 H NMR (CD2Cl2, rt): δ 1.01 (s, 9H, tBu), 1.72 (d, 2JH-H =1.29 Hz, 1H, Ta-CH2), 1.82 (d, 2JH-H =1.29 Hz, 1H, Ta-CH2), 2.11 (s, 15H, Cp*), 5.49 (s, 1H, NH), 5.77 (s, 1H, NH), 6.37 (m, 1H, 6-C6H4), 6.46 (m, 1H, 4-C6H4), 6.54 (m, 1H, 60 -C6H4), 6.59 (m, 1H, 40 -C6H4), 6.98 (m, 1H, 5-C6H4), 7.06 (m, 1H, 50 -C6H4), 7.25 (m, 1H, 3-C6H4), 7.41 (m, 1H, 30 -C6H4). 13C{1H} NMR (CD2Cl2, rt): δ 11.23 (Cp*), 30.55 (Me), 58.47 (CMe3), 65.67 (CH2), 115.26 (6-C6H4), 116.27 (60 -C6H4), 117.70 (CipsoS), 118.24 (C0 ipsoS), 118.64 (Cp*), 117.07 (4-C6H4), 117.32 (40 -C6H4), 130.08 (5-C6H4), 130.41 (50 -C6H4), 132.21 (3-C6H4), 133.49 (30 -C6H4), 159.14 (CipsoN), 161.45 (C0 ipsoN). IR bands (cm-1): 3403 (m, N-H), 1298 (m, C-N), 1268 (m, C-N). Anal. Calcd for C27H36N3STa: C, 52.68; H, 5.89; N, 6.83. Found: C, 52.60; H, 5.72; N, 6.71. [TaCp*Me{(N-C6H4)2S-κ3-N,S,N}][MeB(C6F5)3] (6). Diethyl ether (15 mL) was added to a mixture of [TaCp*Me2{(N-C6H4)2S-κ3-N,S, N}] (2) (0.328 g, 0.58 mmol) and B(C6F5)3 (0.299 g, 0.58 mmol). The mixture was stirred for 1 h at room temperature, and the solvent was evaporated. The crude product was washed with cool toluene (2 mL) to yield a red oil, which was washed with pentane at -98 °C under vigorous stirring to yield, after filtration and drying, 0.402 g (64%) of an orange solid, which was identified as 6. 1 H NMR (CDCl3, rt): δ 0.52 (s, 3H, Me-Ta), 2.02 (s, 3H, Me-B) 2.28 (s, 15H, Cp*), 6.65 (m, 2H, 6-C6H4), 7.11 (m, 2H, 4-C6H4), 7.38 (m, 2H, 5-C6H4), 7.58 (s, 1H, NH), 7.76 (m, 1H, 3-C6H4). 13C{1H} NMR (CDCl3, rt): δ 10.88 (Me-B), 11.13 (Cp*), 57.15 (Me-Ta), 120.57 (6C6H4), 121.77 (CipsoS), 118.95 (Cp*), 124.26 (4-C6H4), 131.86 (5C6H4), 132.88 (3-C6H4), 161.70 (CipsoN). 19F NMR (CDCl3, rt): δ 133.21 (m, 6F, o-F), 164.46 (m, 3F, p-F), 167.13 (m, 6F, m-F). IR bands (cm-1): 3396 (m, N-H), 1300 (m, C-N). Anal. Calcd for C42H31BF15N2STa: C, 47.03; H, 2.91; N, 2.61. Found: C, 46.96; H, 2.85; N, 2.61. Structure Determination of 1 and 4. Single crystals suitable for X-ray diffraction were obtained by crystallization from toluene (compound 1) and Et2O (compound 4) at -20 °C. Data were collected on a Bruker X8 APEX II CCD-based diffractometer, equipped with a graphite-monochromated Mo KR radiation source (λ = 0.71073 Å). The crystal data, data collection, structural solution, and refinement parameters are summarized in Table 4. Data were integrated using SAINT,26 and an absorption correction was performed with the program SADABS.27 The structure was solved by direct methods using SHELXTL28 and refined by full-matrix least-squares methods based on F2. All non-hydrogen atoms were refined with anisotropic thermal parameters. For compound 1, hydrogen atoms were placed using a “riding model” and included in the refinement at calculated positions, except the H1 atom, which was found in the Fourier map. For compound 4, one void appears in the lattice (about 115 Å3 per asymmetric unit), and this probably contains very disordered Et2O solvent molecules,

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which could not be resolved. Refinement included application of the squeeze procedure29 to model this diffuse electron density. The initial positions of the hydrogen atoms (Ta-H and N-H) appeared clearly in the Fourier map, but they could not be refined and had to be fixed in the refinement. The rest of the hydrogen atoms were placed using a “riding model” and were included in the refinement at calculated positions.

’ ASSOCIATED CONTENT

bS

Supporting Information. Full experiments details, spectroscopic data, and CIF files giving details of data collection, refinement, atom coordinates, anisotropic displacement parameters, and bond lengths and angles for complexes 1 and 4. This material is available free of charge via the Internet at http://pubs. acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT We gratefully acknowledge the Ministerio de Ciencia e Innovaci
on of Spain for financial support (Grant Nos. CTQ2008-00318/BQU, Consolider Ingenio 2010 ORFEO CSD2007-00006) and also for a fellowship (Jacob Fern
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