Journal of Organometallic Chemistry 690 (2005) 3134–3141 www.elsevier.com/locate/jorganchem New reactivity of Cp02NbH3; Cp0 ¼ g5-C5H4SiMe3. Synthesis, electrosynthesis and reactivity of new carboxylato niobocene complexes Antonio Antiñolo *,a, Santiago Garcı́a-Yuste a, Isabel López-Solera a, Antonio Otero a,*, Juan Carlos Pérez-Flores a, Isabel del Hierro b, Laurent Salvi c, Hélène Cattey c, Yves Mugnier c a b Departamento de Quı́mica Inorgánica, Orgánica y Bioquı́mica y Bioquı́mica, Facultad de Quimica, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain Departamento de Tecnologı́a Quı́mica, Ambiental y de los Materiales, ESCET, Universidad Rey Juan Carlos, 28933 Móstoles (Madrid), Spain c Laboratoire de Synthèse et Electrosynthèse Organométalliques, LSEO UMR 5188 Faculté des Sciences Mirande, 9 Allée Alain Savary, 21000 Dijon, France Received 25 January 2005; revised 5 April 2005; accepted 6 April 2005 Available online 23 May 2005 Abstract A new family of niobium bidentate carboxylato-containing niobocene complexes, mononuclear Cp02 Nbðj2 -O; O0 AOOCðC6 H5 ÞÞ ð3Þ, binuclear ½ðCp02 NbÞ2 ð1; 4-ðj2 -O; O0 AOOCÞ2 ðC6 H4 ÞÞ
ð4Þ and ½ðCp02 NbÞ2 ð1; 3-ðj2 -O; O0 AOOCÞ2 ðC6 H4 ÞÞ
ð5Þ and trinuclear ½ðCp02 NbÞ3 ð1; 3; 5-ðj2 -O; O0 AOOCÞ3 ðC6 H3 ÞÞ
ð6Þ, have been prepared by the reaction of Cp02 NbH3 ð1Þ and the corresponding carboxylic acid, namely (C6H5)COOH, (1,4-COOH)2(C6H4), (1,3-COOH)2(C6H4) and (1,3,5-COOH)3(C6H3). Complexes 3, 4, 5 and 6 have been prepared by an alternative route involving a two-electron reduction of Cp02 NbCl2 ð2Þ in the presence of the appropriate molar ratios of the corresponding carboxylic acids. Furthermore, the reaction of complexes 3, 4 and 6 with 2,6Me2C6H3NC (xylylNC) in the molar ratios 1:1, 1:2 and 1:3, respectively, resulted in opening of the bidentate carboxylato ligand to give the monodentate carboxylato-containing complexes ½Cp02 Nbðj1 -OAOOCðC6 H5 ÞÞðxylylNCÞ
ð7Þ; ½ðCp02 NbðxylylNCÞÞ2 ð1; 4-ðj1 -OAOOCÞ2 ðC6 H4 ÞÞ
ð8Þ and ½ðCp02 NbðxylylNCÞÞ3 ð1; 3; 5-ðj1 -OAOOCÞ3 ðC6 H3 ÞÞ
ð9Þ. Similarly, complex ½ðCp02 Nbðg1 -C; j1 -SACS2 ÞÞ3 ð1; 3; 5-ðj1 -OAOOCÞ3 ðC6 H3 ÞÞ
ð10Þ was prepared by reaction of 6 with the appropriate amount of CS2. Complexes 7, 8 and 9 can be prepared in an alternative way by reaction of ½Cp02 NbðHÞðxylylNCÞ
with the corresponding carboxylic acids. The structures of all complexes have been established by spectroscopic techniques. In addition, the X-ray molecular structure of 4 was determined by a single-crystal X-ray diffraction study.
2004 Elsevier B.V. All rights reserved. Keywords: Niobocene; Carboxylato; Synthesis; Electrosynthesis 1. Introduction In previous studies we have investigated the chemical behaviour of the trihydride complex Cp02 NbH3 ð1Þ in * Corresponding author. Fax: +34 92 629 5318. E-mail addresses: antonio.antinolo@uclm.es (A. Antiñolo), antonio.otero@uclm.es (A. Otero). 0022-328X/$ - see front matter
2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2005.04.003 great depth. This complex constitutes an interesting example of a trihydride complex that exhibits the phenomenon of exchange coupling [1], with unusual 1 J(H,H) couplings that vary with temperature [2]. In the last 15 years we have focused our attention on the study of the reactivity of 1, e.g., with p-acid ligands to give different families of complexes Cp02 NbHðLÞ; L ¼ p-acid ligand [3], in E–H (E = Si, Ge, H) 3135 A. Antiñolo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141 activation processes [4] and with Lewis acids, such as [M(PPh3)][PF6], M = Cu, Ag, Au to give a broad class of heterobimetallic species [5]. A few years ago, we prepared a formato niobocene complex Cp02 Nbðj2 -O; O0 AOOCHÞ by carbon dioxide insertion into the niobium-hydrogen bond of Cp02 NbH3 . The formato complex could also be obtained from the two-electron reduction of Cp02 NbCl2 in the presence of formic acid [6]. In addition, an acetato-containing complex, namely Cp02 Nbðj2 -O; O0 AOOCMeÞ, was also chemically and electrochemically prepared [6]. Other authors have prepared O-bound carboxylato complexes by the insertion of carbon dioxide into M–C bonds [7]. More recently, electrochemical and spectroscopic studies on dicarboxylato-containing niobocene complexes were carried out [8]. As a continuation of our interest in the chemistry of Cp02 NbH3 , we report here its behaviour towards mono-, bi- and trinuclear aromatic carboxylic acids. These reactions led to the isolation of new carboxylato niobocene complexes, namely Cp02 Nb ðj2 O; O0 AOOCRÞ; ½ðCp02 NbÞ2 ðj2 -O; O0 AOOCÞ2 R
; and ½ðCp02 NbÞ3 ðj2 -O; O0 AOOCÞ3 R
, which can also be formed from the reduction of Cp02 NbCl2 in the presence of the appropriate carboxylic acid. Several aspects concerning the reactivity of these systems are also discussed. 2. Results and discussion We are currently interested in studying the reactivity of Cp 0 NbH3 towards different classes of carboxylic acids. With this aim in mind, four types of carboxylic acid, namely benzoic, (C6H5)COOH, terephthalic, (1,4-COOH)2(C6H4), isophthalic, (1,3-COOH)2(C6H4) and 1,3,5-phenyltricarboxylic, (1,3,5-COOH)3(C6H3), were selected. The standard reaction procedure involved heating at ca. 60 C a stirred THF solution of 1 with the appropriate carboxylic acid. This method allowed the isolation of the carboxylato-containing complexes after an appropriate work-up procedure (Eqs. (1)–(3)). ∆ Cp'2NbH3 + HOOC(C6H5) - 2 H2 ð1Þ O Cp'2Nb C O 3 ∆ 2 Cp'2NbH3 + (1,X-(HOOC)2(C6H4)) - 4 H2 Cp'2Nb ð2Þ O O O C X=4,4 X=3,5 C O NbCp'2 ∆ 3 Cp'2NbH3 + (1,3,5-(HOOC)3(C6H3)) - 6 H2 ' NbCp 2 O C O O ð3Þ C Cp'2Nb C O 6 O O NbCp' 2 The different complexes were isolated as green air-sensitive solids. The evolution of H2 was detected in all of the experiments. Complexes 4, 5 and 6 were isolated as the only carboxylato-containing species even when niobocene:carboxylic acid molar ratios lower than 2:1 or 3:1 were employed, indicating that the formation of either the corresponding binuclear or trinuclear species is thermodynamically favoured. The formation of those complexes could take place through the elimination of H2 and the formation of a very reactive sixteen-electron monohydride niobocene species, which has previously been proposed in several cases [9]. All the complexes described in this work were spectroscopically characterized. The most prominent features in the IR spectra are the CO 2 stretching frequencies of the carboxylato group and our attention was focused upon these. The usual approach in this respect has been to relate the D values (the  separation between masym ðCO 2 Þ and msym ðCO2 Þ) with the mono- or bidentate character of the ligands [10]. The IR spectra of complexes 3, 4, 5 and 6 showed the masym  ðCO 2 Þ and msym ðCO2 Þ absorptions to have D values of 95, 117, 121 and 74 cm1, respectively, which are consistent with the presence of a bidentate carboxylato ligand[10]. Moreover, the 1H and 13C NMR data confirm the bidentate coordination. In fact, the observation of two and three signals for each cyclopentadienyl ring in the 1H and 13C NMR spectra, respectively, (see Section 4) indicate the presence of a symmetrical environment. In addition, the 13C NMR spectra contain signals for the carboxylato carbon atoms at d 190.1, 205.5, 188.9 and 187.6 for complexes 3, 4, 5 and 6, respectively. In order to confirm the proposed structural disposition for these complexes, the X-ray crystal molecular structure of 4 was determined. The molecular structure and atomic numbering scheme are shown in Fig. 1. Selected bond lengths and angles for 4 are given in Table 1. The structure of 4 consists of a symmetric binuclear niobium complex. The metal atoms are bound to two cyclopentadienyl rings in a g5 mode and to two oxygen atoms from the chelating carboxylato group. The sixmembered aromatic ring and the two carboxylato groups are coplanar, although the niobium atom is out of the plane defined by O1, O2, C1, C2, C3 and C4 (by 0.156(6) Å). The two oxygen atoms of the bidentate carboxylato ligand have similar Nb–O bond distances (2.220(4) and 2.230(4) Å for O1 and O2, respectively) and these values are in reasonable agreement with those 3136 A. Antiñolo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141 Fig. 1. Molecular structure and atom-labelling scheme for complex 4, with thermal ellipsoids at 30% probability. Table 1 Selected bond lengths (Å) and angles () for 4 Nb1–O1 Nb1–O2 O1–C1 O2–C1 C1–C2 2.220(4) 2.230(4) 1.262(7) 1.261(7) 1.501(8) O1–Nb1–O2 C1–O1–Nb1 C1–O2–Nb1 O1–C1–O2 O1–C1–C2 O2–C1–C2 58.9(2) 90.5(4) 90.1(4) 120.3(5) 120.0(6) 119.7(6) reported for the carboxylato ligands [11]. The cyclopentadienyl groups are in a typical eclipsed fashion with respect to each other and the SiMe3 groups are in a trans disposition. Reactions of complexes 3, 4 and 6 with 2,6Me2C6H3NC (xylylNC), in the appropriate molar ratios led to a change from a bidentate to a monodentate carboxylato unit due to coordination of the incoming ligand. These reactions led to the isolation of new complexes after the appropriate work-up procedure (Eqs. (4)–(6)). The same complexes can be prepared in an alternative way by reaction of the complex ½Cp02 NbðHÞðxylylNCÞ
[3] with the appropriate molar ratios of the corresponding carboxylic acids. Finally, complex ½Cp02 Nb ððg1 -C; j1 -SACS2 ÞÞ3 ð1; 3; 5-ðj1 -OAOOCÞ3 ðC6 H3 ÞÞ
ð10Þ was also prepared by the reaction of 6 with CS2. The different monodentate carboxylato-niobocene complexes were isolated as either air-sensitive green (for 7, 8 and 9) or non-air-sensitive brown (for 10) solids. The different complexes were spectroscopically characterized. The IR spectra of complexes 7–10 show the masym ðCO 2Þ and msym ðCO Þ absorptions to have D values of 262, 2 245, 242 and 230 cm1, respectively, which are consistent with the presence of a bidentate carboxylato ligand [10]. In accordance with the lack of symmetry in the proposed structures (see Fig. 2), the 1H and 13C NMR spectra of these complexes show four and five resonances for each cyclopentadienyl ring. The carbon resonances for the carboxylato ligands appear at d 175.6, 174.2, 174.4 and 182.2, respectively, for 7–10. In addition, in these spectra the carbon resonances for the ancillary ligands, namely 2,6-Me2C6H3NC and CS2, appear at d 208.2, 209.9, 212.5 and 250.2, respectively. Cp02 Nbðj2 -O; O0 AOOCðC6 H5 ÞÞ þ xylylNC ! ½Cp02 Nbðj1 -OAOOCðC6 H5 ÞÞðxylylNCÞ
ð4Þ ð7Þ SiMe3 SiMe3 ½ðCp02 NbÞ2 ð1; 4-ðj2 -O; O0 AOOCÞ2 ðC6 H4 ÞÞ
þ 2xylylNC ! ½ðCp02 NbðxylylNCÞÞ2 ð1; 4-ðj1 -OAOOCÞ2 ðC6 H4 ÞÞ
ð8Þ O O O C Nb Nb CNXylyl ! ½ðCp02 NbðxylylNCÞÞ3 ð1; 3; 5-ðj1 -OAOOCÞ3 ðC6 H3 ÞÞ
ð9Þ ð6Þ C C ð5Þ ½ðCp02 NbÞ3 ð1; 3; 5-ðj2 -O; O0 AOOCÞ3 ðC6 H3 ÞÞ
þ 3xylylNC O S S (a) SiMe3 (b) SiMe3 Fig. 2. (a) Proposed structure for complex 7. An analogous structural situation may be displayed for 8 and 9. (b) Analogous trinuclear disposition with an g1-C, j1-S–CS2 ancillary ligand proposed for complex 10. 3137 A. Antiñolo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141 Cl 2.1. Electrochemical studies Cp'2Nb Cp'2NbCl + HOOC(C6H5) O Electrochemical studies on ð2Þ in the presence of the appropriate carboxylic acids were carried out. Rotating disk electrode (RDE) voltammetry was performed on the complex in THF in the presence of 0.2 mol L1 NaBPh4 as a supporting electrolyte. Complex 2 was found to exhibit a reduction wave A and an oxidation wave E 0 (Fig. 3(a)). Wave A corresponds to the one-electron reduction of 2 to give Cp02 NbCl, as mentioned previously [12]. When the process was repeated in the presence of one equivalent of (C6H5)COOH the RDE voltammogram was unchanged; however, when the electrolysis was performed on a carbon gauze electrode at 1.50 V (versus an SCE electrode) corresponding to the plateau of wave A, a quantity of electricity close to two equivalent of electrons per mole of 2 was consumed. The RDE voltammogram of the resulting solution showed one well-defined oxidation wave F 0 at 0.510 V (Fig. 3(b)). This electrogenerated product corresponds to complex 3. The formation of this complex can be rationalized in terms of the following global reaction (Eq. (7)):  HOOCðC6 H5 Þ þ 2e ! ½ðCp02 NbÞ  ðj -O; O AOOCðC6 H5 ÞÞ
þ 1=2H2 þ 2Cl Cl 2Cp'2NbCl + Cp'2Nb O C O ð10Þ O Cp'2NbCl2 + Cp'2Nb C O 3 Cp02 NbCl would react with the carboxylic acid to give a paramagnetic niobium(IV) complex, namely Cp02 NbCl ðj1 -O; O0 AOOCðC6 H5 ÞÞ, with elimination of H2 (Eq. (9)). This intermediate would then be reduced by Cp02 NbCl to give 3 and the regeneration of 2 (yield 50%, Eq. (10)). These results imply that reaction (10) should be markedly faster than reaction (9). In cyclic voltammetry studies, 3 exhibited an F/F 0 reversible system (Fig. 4), which can be described by the following reaction (Eq. (11)): -1e- O Cp'2Nb O Cp'2Nb C - +1e O ð7Þ C O ð11Þ 3' 3 However, under different experimental conditions (i.e., THF/NaBPh4 or THF/Bu4NPF6), the electrooxidation process of 3 at the potential of the wave F 0 leads to partial regeneration of 2 according to the following process (Eq. (12)): When one equivalent of (C6H5)COOH was added to a solution containing Cp02 NbCl (obtained from the oneelectron reduction of 2 in THF in the presence of 0.2 mol L1 NaBPh4), a fast reaction occurred to give 3 and the regeneration of 50% of 2 (identified by its reduction wave A and by ESR spectroscopy). This result explains the consumption of 2 electrons in the electrolysis of 2 in the presence of one equivalent of the acid. These electrochemical results can be rationalized according to the processes represented in the Eqs. (8)–(10): 2Cp02 NbCl2 þ 2e ! 2Cp02 NbCl þ 2Cl ð9Þ O Cp02 NbCl2 Cp02 NbCl2 þ 0 2 + 1/2 H2 C O Cp'2Nb Cp'2NbCl2 + (C6H5)COO- - 1e- + 2 Cl- C O ð12Þ Even when the electrolysis of 3 was carried out a low temperature, the stabilization of 3 0 was not possible. Finally, complexes 4, 5, and 6, with dicarboxylic and tricarboxylic acids, were similarly electrogenerated from Cp02 NbCl2 ð2Þ and the appropriate molar ratios of the carboxylic acids (see Table 2). In cyclic ð8Þ 20 µA c F' E' E (V/ECS) b -1.5 -1 -0.5 0 0.5 A a Fig. 3. RDE voltammogram of (a, m) Cp02 NbCl2 2 in THF containing 0.2 mol L1 of NaBPh4; (b, h) after adding one equivalent of benzoic acid and a 2 e reduction at 1.50 V on carbon electrode (scan rate: 20 mV s1). 3138 A. Antiñolo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141 F' 5 µA E (V/ECS) -1.1 -0.85 -0.6 -0.35 -0.1 F Fig. 4. Cyclic voltammogram of 3 on carbon electrode in THF containing 0.2 mol L1 of NaBPh4 (scan rate: 100 mV s1; starting potential: 1 V). Table 2 Half-wave potential of the F/F 0 system, obtained on carbon electrode (scan rate: 20 mV s1) in THF/NaBPh4 Complex E1/2 (V) 4 5 6 0.482 0.479 0.456 voltammetry experiments, these complexes also exhibit the reversible F/F 0 system at the potential values indicated in Table 2. solvents were dried over 4 Å molecular sieves and degassed prior to use. Carboxylic acids, namely C6H5(COOH), [1,4-(HOOC)2(C6H4)], [1,3-(HOOC)2(C6H4)], [1,3,5-(HOOC)2(C6H3)], and carbon disulphide were used as purchased from Aldrich. NMR spectra were recorded on a Varian Unity 300 (300 MHz for 1 H, 75 MHz for 13C) spectrometer. Chemical shifts were measured relative to partially deuterated solvent peaks and are reported relative to TMS. IR spectra were recorded on a Perkin–Elmer 883 spectrometer in Nujol mulls over CsI windows. 4.1. Electrochemical experiments 3. Conclusions The interaction of Cp02 NbH3 with carboxylic acids was studied. The liberation of H2 and the subsequent formation of new carboxylato-containing niobocenes, which were alternatively prepared by an electrochemical method, was observed. In addition, the reactivity of these complexes towards xylylNC and CS2 was studied. It was found that a bidentate ! monodentate conversion of the coordination mode of the carboxylato ligand occurred. 4. Experimental General procedures. All reactions were carried out using Schlenk techniques. Oxygen and water were excluded by the use of vacuum lines supplied with purified N2. Toluene was distilled from sodium. Pentane was distilled from sodium/potassium alloy. Diethyl ether and THF were distilled from sodium benzophenone. All solvents were deoxygenated prior to use. Complexes Cp02 NbðHÞ3 and Cp02 NbðHÞðCNð2; 6-Me2 C6 H3 ÞÞ were prepared as described in the literature [2,3]. Deuterated All manipulations were performed using Schlenk techniques in an atmosphere of dry oxygen-free argon gas and using dry solvents. The supporting electrolyte was degassed under vacuum before use and then solubilized at a concentration of 0.2 mol L1. Voltammetric analyses were carried out in a standard three-electrode cell with a Princeton Applied Research, Model 263A. The reference electrode was a saturated calomel electrode (SCE) separated from the solution by a sintered glass disk. The auxiliary electrode was a platinum wire. For all voltammetric measurements, the working electrode was a vitreous carbon electrode (/ = 3 mm). A CTV101 Speed Control unit  ¼ 500 rpmÞ of was used to adjust the rotation speed ðx the EDI101 electrode (Radiometer). In these conditions, when operating in THF, the formal potential for the ferrocene+/ couple is found to be +0.56 V versus SCE. The controlled potential electrolysis was performed with an Amel 552 potentiostat coupled with an Amel 721 electronic integrator. High scale electrolyses were performed in a cell with three compartments separated with fritted glasses of medium porosity. A carbon gauze was used as the working electrode, a platinum plate as the counter-electrode and a saturated calomel electrode as the reference electrode. A. Antiñolo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141 4.2. Synthesis of Cp02 Nb(j2 -O,O0 AOOC(C 6 H5 )) (3) A mixture of Cp02 NbH3 ð1Þ (0.28 g; 0.75 mmol) and the carboxylic acid C6H5(COOH) (0.15 g; 0.75 mmol) was stirred with dry THF (30 mL) at 50 C for 5 h. The solution became dark green in colour and the solvent was evaporated to dryness under vacuum. The dark green oily residue was extracted with hexane (10 mL). The resulting solution was filtered and evaporated to dryness. Complex 3 was isolated as a dark green solid (90% yield): IR (Nujol/PET cm1) ðmCOO asym Þ 1634, 1 H NMR (C6D6): d 0.06 (s, 18H, ðCOO sym Þ 1539. SiMe3), 4.18, 5.69 (4H each a complex signal, C5H4SiMe3), 6.87 (t, 3JH–H = 7.4 Hz, 1H, Hp C6H5), 6.90 (t, 3JH–H = 7.5 Hz, 2H, HmC6H5), 7.78 (d, 3JH–H = 7.5 Hz, 2H, Ho C6H5). 13C{1H}NMR (C6D6): d 0.4 (SiMe3), 94.0 (C1, C5H4SiMe3), 104.3, 108.2 (C2–5, exact assignment not possible, C5H4SiMe3), 127.0, 128.0, 132.7 (C6H5), 190.1 (COO). Anal. Calc. for C23H34NbSi2O2: C, 56.56; H, 6.35. Found: C, 56.11; H, 6.19%. 4.3. Synthesis of [(Cp02 Nb)2 (1,4-(j2 -O,O0 AOOC)2 (C 6 H 4 ))] (4), [(Cp02 Nb)2 (1,3-(j2 -O,O0 AOOC)2 (C 6 H 4 ))] (5) and [(Cp02 Nb)3 (1,3,5-(j2 -O,O0 AOOC)3 (C 6 H 3 ))] (6) A mixture of Cp02 NbH3 ð1Þ (0.28 g; 0.75 mmol) and the corresponding carboxylic acid [1,4-(HOOC)2(C6H4)] (0.15 g; 0.75 mmol) was stirred with dry THF (30 mL) at 50 C for 5 h. The solution became dark green in colour and the solvent was evaporated to dryness under vacuum. The dark green oily residue was extracted with hexane (10 mL). The resulting solution was filtered and evaporated to dryness. Complex 4 was isolated as a dark green solid (90% yield). Complexes 5 and 6 were prepared in a similar way.  4: IR (Nujol/PET cm1) mðCOO asym Þ 1646, ðCOOsym Þ 1 1529. H NMR (CO(CD3)2): d 0.03 (s, 36H, SiMe3), 4.52, 5.83 (8 H each a complex signal, C5H4SiMe3), 7.50 (s, 4H, HoC6H4). 13C{1H}NMR (CO(CD3)2): d 0.4 (SiMe3), 96.0 (C1, C5H4SiMe3), 105.1, 108.1 (C2–5, exact assignment not possible, C5H4SiMe3), 128.7 and 135.9 (C6H4), 205.5 (COO). Anal. Calc. for C40H62Nb2Si4O4: C, 54.24; H, 5.65. Found: C, 53.97; H, 5.55%.  5: IR (Nujol/PET cm1) mðCOO asym Þ 1648, ðCOOsym Þ 1 1527. H NMR (C6D6): d 0.00 (s, 36H, SiMe3), 4.12, 5.62 (8 H each a complex signal, C5H4SiMe3), 6.72 (t, 3 JH–H = 8.0 Hz, 1H, Hm C6H4), 7.70 (d, 3JH–H = 7.7 Hz, 2H, HoC6H4), 8.31 (s, 1H, HoC6H4). 13C{1H}NMR (C6D6): d 0.4 (SiMe3), 94.5 (C1, C5H4), 104.6, 107.5 (C2–5, exact assignment not possible, C5H4SiMe3), 127.0, 129.0, 132.2 and 132.5 (C6H4), 188.9 (COO). Anal. Calc. for C40H62Nb2Si4O4: C, 54.24; H, 5.65. Found: C, 54.04; H, 5.55%. 3139  6: IR (Nujol/PET cm1) mðCOO asym Þ 1605, ðCOOsym Þ 1 1531. H NMR (C6D6): d 0.02 (s, 54H, SiMe3), 4.06, 5.58 (12 H each a complex signal, C5H4SiMe3), 8.40 (s, 3H, C6H3). 13C{1H} NMR (C6D6): d 0.3 (SiMe3), 94.5 (C1, C5H4), 104.7, 107.5 (C2–5, exact assignment not possible, C5H4SiMe3), 132.2 and 132.5 (C6H3), 187.6 (COO). Anal. Calc. for C57H100Nb3O6Si6: C, 52.30; H, 6.19. Found: C, 52.12; H, 6.10%. 4.4. Synthesis of [Cp02 Nb(j1 -OAOOC(C 6 H 5 )) (xylylNC)] [(7)] 4.4.1. Method A A mixture of ½Cp02 NbðHÞðxylylNCÞ
(0.75 g; 2.25 mmol) and the carboxylic acid C6H5(COOH) (0.27 g; 2.25 mmol) was stirred with dry THF (30 mL) at room temperature for 3 h. The solution became green in colour and the solvent was evaporated to dryness under vacuum. The green oily residue was extracted with hexane (10 mL). The resulting solution was filtered and evaporated to dryness. Complex 7 was isolated as a green solid (90% yield). 4.4.2. Method B A mixture of Cp02 Nbðj2 -O; O0 AOOCðC6 H5 ÞÞ ð3Þ (0.13 g; 0.75 mmol) and CN(2,6-Me2C6H3) (0.06 g; 0.75mmol) was stirred with dry THF (30 mL) at room temperature for 3 h. The solution became green in colour and the solvent was evaporated to dryness under vacuum. The green oily residue was extracted with hexane (10 mL). The resulting solution was filtered and evaporated to dryness. Complex 7 was isolated as a green solid (82% yield): IR (Nujol/PET cm1) m(C„N) 1  H NMR 2068, ðCOO asym Þ 1712, ðCOOsym Þ 1450. (C6D6): d 0.02 (s, 18H, SiMe3), 2.35 (s, 6H, CN(2,6Me2C6H3)), 4.99, 5.19, 5.57, 5.86 (2 H each a complex signal, C5H4SiMe3), 6.64 (s, 3H, CN(2,6-Me2C6H3)), 7.00 (t, 3JH–H = 7.3 Hz, 2H, Hm C6H5), 7.13 (t, 3 JH–H = 7.3 Hz, 1H, Hp C6H5) 8.14 (d, 3JH–H = 7 Hz, 2H, HoC6H5). 13C{1H}NMR (C6D6): d 0.1 (SiMe3), 19.1 (CN(2,6-Me2C6H3)), 93.9 (C1, C5H4), 96.7, 101.1, 104.2, 109.6 (C2–5, exact assignment not possible, C5H4SiMe3), 126.5, 129.8, 130.3 and 130.7 (CN(2,6Me2C6H3)), 132.9, 133.1 and 135.3 (C6H5), 175.6 (COO), 208.2 (CN(2,6-Me2C6H3)). Anal. Calc. for C32H43NNb2O2Si4: C, 62.04; H, 6.46; N, 2.26. Found: C, 61.89; H, 6.32; N, 2.32%. 4.5. Synthesis of [[(Cp02 Nb(xylylNC))2 (1,4-[(j1 -OA OOC)2 (C 6 H 4 ))] (8) A mixture of ½ðCp02 NbÞ2 ð1; 4-ðj2 -O; O0 AOOCÞ2 ðC6 H4 ÞÞ
ð4Þ (0.13 g; 0.75 mmol) and (CN(2,6Me2C6H3)) (0.19 g; 1.50 mmol) was stirred with dry THF (30 mL) at room temperature for 3 h. The solution became green in colour and the solvent was evaporated 3140 A. Antiñolo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141 to dryness under vacuum. The green oily residue was extracted with hexane (10 mL). The resulting solution was filtered and evaporated to dryness. Complex 8 was isolated as a green solid (82% yield): IR (Nujol/PET  cm1) m(CN) 2062, ðCOO asym Þ 1698, ðCOOsym Þ 1453. 1 H NMR (CO(CD3)2): d 0.12 (s, 36H, SiMe3), 2.23 (s, 12H, CN(2,6-Me2C6H3)), 5.21, 5.45, 5.55, 5.95 (4H, each a complex signal, C5H4SiMe3), 6.80 (s, 6H, CN(2,6-Me2C6H3)), 8.19 (s, 4H, C6H4). 13C{1H}NMR (CO(CD3)2): d 0.3 (SiMe3), 19.2 (CN(2,6-Me2C6H3)), 94.9, 97.2, 101.7, 110.3 (C2–5, exact assignment not possible, C5H4SiMe3), 104.7 (C1, C5H4), 128.6, 128.7, 128.9 and 129.7 (C6H4), 127.2, 130.2, 133.4 and 138.9 (CN(2,6-Me2C6H3)), 174.2 (COO), 209.9 (CN(2,6Me2C6H3)). Anal. Calc. for C58H80N2Nb2O4Si4: C, 60.00; H, 6.38; N, 2.69. Found: C, 59.56; H, 6.09; N, 2.41%. 4.6. Synthesis of [(Cp02 Nb(xylylNC))3 (1,3,5-(j1 -O,OOC)3 (C 6 H 3 ))] (9) A mixture of ½ðCp02 NbÞ3 ð1; 3; 5-ðj2 -O; O0 AOOCÞ3 ðC6 H3 ÞÞ
ð6Þ (0.16 g; 0.75 mmol) and CN(2,6-Me2C6H3) (0.29 g; 2.25 mmol) was stirred with dry THF (30 mL) at room temperature for 3 h. The solution became green in colour and the solvent was evaporated to dryness under vacuum. The green oily residue was extracted with hexane (10 mL). The resulting solution was filtered and evaporated to dryness. Complex 9 was isolated as a green solid (87% yield): IR (Nujol/PET cm1) m(C„N) 1  H NMR 2046, ðCOO asym Þ 1629, ðCOOsym Þ 1387. (C6D6): d 0.10 (s, 54H, SiMe3), 2.43 (s, 18H, CN(2,6Me2C6H3)), 5.05, 5.21, 5.51, 5.73 (6H, each a complex signal, C5H4SiMe3), 6.80 (m, 9H, CN(2,6-Me2C6H3)), 8.82 (s, 3H, C6H3). 13C{1H} NMR (C6D6): d 0.3 (SiMe3), 19.4 (CN(2,6-Me2C6H3)), 93.9, 96.6, 100.8, 109.9 (C2–5, exact assignment not possible, C5H4SiMe3), 104.6 (C1, C5H4), 127.5 and 129.2 (C6H3), 133.1, 133.6 and 137.3 (CN(2,6-Me2C6H3)), 174.4 (COO), 212.5 (CN(2,6-Me2C6H3)). Anal. Calc. for C84H127N3Nb3O6Si6: C, 59.25; H, 6.35; N, 2.82. Found: C, 59.43; H, 6.55; N, 2.71%. 4.7. Synthesis of [(Cp02 Nb(g1 -C,j1 -SACS 2 ))3 (1,3,5(j1 -OAOOC)3 (C 6 H 3 ))] (10) A mixture of [(Nb(g5-C5H4SiMe3)2)3(1,3,5-(j2-O,O– OOC)3(C6H3))] (6) (0.16 g; 0.75 mmol) and an equimolecular quantity of CS2 (0.14 mL; 2.25 mmol) was stirred with dry THF (30 mL) at room temperature for 3 h. The solution became green in colour and the solvent was evaporated to dryness under vacuum. The green oily residue was extracted with hexane (10 mL). The resulting solution was filtered and evaporated to dryness. Complex 10 was isolated as a brown solid (70% yield): IR  (Nujol/PET cm1) mðCOO asym Þ 1638, ðCOOsym Þ 1408, (C@S) 1151. 1H NMR (C6D6): 0.06 (s, 54H, SiMe3), 5.91, 6.20, 6.28, 6.44 (6 H each a complex signal, C5H4SiMe3), 8.83 (s, 3H, C6H3). 13C{1H}NMR (C6D6): d 0.2 (SiMe3), 94.5 (C1, C5H4), 102.3, 104.7, 106.8, 107.5 (C2–5, exact assignment not possible, C5H4SiMe3), 134.0 (C6H3), 136.9 (C6H5), 182.2 (COO), 250.2 (CS2). Anal. Calc. for C60H100Nb3O6S6Si6: C, 48.00; H, 1.93. Found: C, 48.43; H, 2.10%. 4.8. X-ray Structure determination for compound 4 Intensity data for compound 4 were collected on a NONIUS-MACH3 diffractometer equipped with a graphite monochromator (Mo Ka radiation, k = 0.71073 Å) using an x/2h scan technique. The final unit cell parameters were determined from 25 wellcentered reflections and refined by least-squares method. Absorption correction was made. The crystal data and details of the data collection and structure analysis are summarized in Table 3. The structure was solved by direct methods using 2 SHELXS computer program [13] and refined on F by full-matrix least-squares (SHELXL-97) [14]. All nonhydrogen atoms were refined with anisotropic thermal parameters for all compounds. The hydrogen atoms were included in calculated positions and were refined with an overall isotropic temperature factor using a riding model. Weights were optimized in the final cycles. Table 3 Crystal data and structure refinement for 4 C40H56Nb2O4Si4 889.03 200(2) Triclinic P 1 Formula Fw T (K) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) a () b () c () V (Å3) Z Dc (g cm3) l (mm1) F(0 0 0) Crystal dimensions (mm) h Range () Index ranges 7.470(1) 10.763(1) 14.456(1) 103.33(1) 96.92(1) 91.48(1) 1121.0(2) 1 1.332 0.653 466 0.2 · 0.2 · 0.3 2.14 to 28.11 9 6 h 6 9, 14 6 k 6 13, 0 6 l 6 19 Number of reflections measured 5611 Number of independent reflections 5401 Number of observed reflections 3071 Goodness-of-fit on F2 0.987 Final R indices [I > 2r(I)] R1 = 0.0649, wR2 = 0.1287 Largest difference peak and hole (e Å3) 0.761/0.765 R = RiF |  |F i/R|F |; wR ¼ ½R½wðF 2  F 2 Þ2
=R½wðF 2 Þ2

0.5 . 1 o c o 2 o c o A. Antiñolo et al. / Journal of Organometallic Chemistry 690 (2005) 3134–3141 C16 and C17 are in disordered positions (0.54 and 0.63 population, respectively). Crystallographic data for the structural analysis of 4 have been deposited with the Cambridge Crystallographic Data Centre, CCDC Number 256606. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc. cam.ac.uk or http://www.ccdc.cam.ac.uk). Acknowledgements We gratefully acknowledge financial support from the Dirección General de Investigación Cientı́fica, Spain (MEC, Grant No. BQU2002-04638-CO2-02) and the Junta de Comunidades de Castilla-La Mancha (Grant Nos, PAC-02-003, GC-02-010 and PAI-02-016). References [1] A. Antiñolo, F. Carrillo-Hermosilla, B. Chaudret, M. Fajardo, J. Fernandez-Baeza, M. Lanfranchi, H.-H. Limbach, M. Maurer, A. Otero, M.A. Pellinghelli, Inorg. Chem. 35 (1996) 7873. [2] A. Antiñolo, B. Chaudret, G. Commenges, M. Fajardo, F. Jalon, R.H. Morris, A. Otero, C.T. Schweltzer, J. Chem. Soc., Chem. Commun. (1988) 1210. [3] A. Antinolo, F. Carrillo-Hermosilla, M. Fajardo, S. GarciaYuste, A. Otero, S. Camanyes, F. Maseras, M. Moreno, A. Lledos, J.M. Lluch, J. Am. Chem. Soc. 119 (1997) 6107. 3141 [4] A. Antinolo, F. Carrillo-Hermosilla, A. Castel, M. Fajardo, J. Fernandez-Baeza, M. Lanfranchi, A. Otero, M.A. Pellinghelli, G. Rima, J. Satge, E. Villasenor, Organometallics 17 (1998) 1523. [5] A. Antinolo, F. Carrillo-Hermosilla, B. Chaudret, M. Fajardo, S. Garcia-Yuste, F.J. Lahoz, M. Lanfranchi, J.A. Lopez, A. Otero, M.A. Pellinghelli, Organometallics 14 (1995) 1297. [6] A. Antinolo, M. Fajardo, S. Garcia-Yuste, I. del Hierro, A. Otero, S. Elrami, Y. Mourad, Y. Mugnier, J. Chem. Soc., Dalton Trans. (1995) 3409. [7] (a) D.J. Darensbourg, M. Pala, J. Am. Chem. Soc. 107 (1985) 5687; (b) D.J. Darensbourg, R.K. Hanckel, C.G. Bauch, M. Pala, D. Simmons, J.N. White, J. Am. Chem. Soc. 107 (1985) 7463; (c) D.J. Darensbourg, H.P. Wiegreffe, P.H. Wiegreffe, J. Am. Chem. Soc. 112 (1990) 9252; (d) B.P. Sullivan, T.J. Meyer, Organometallics 5 (1986) 1500. [8] D. Lucas, T.Z. Modarres, Y. Mugnier, A. Antinolo, A. Otero, M. Fajardo, J. Organomet. Chem. 629 (2001) 54. [9] A. Antinolo, F. Carrillo-Hermosilla, M. Fajardo, S. GarciaYuste, A. Otero, J. Organomet. Chem. 482 (1994) 93. [10] G.B. Deacon, R.J. Phillips, Coord. Chem. Rev. 33 (1980) 227. [11] A.A. Pasynskii, Y.V. Skiripkin, I.L. Emerenko, V.T. Kalinnikov, G.G. Aleksandrov, Y.T. Struchkov, J. Organomet. Chem. 165 (1979) 39. [12] (a) H. Nabaoui, A. Fakhr, Y. Mugnier, A. Antinolo, M. Fajardo, A. Otero, P. Royo, J. Organomet. Chem. 338 (1988) C17–C20; (b) D. Lucas, Y. Mugnier, A. Antinolo, A. Otero, M. Fajardo, J. Organomet. Chem. 435 (1992) C3–C7. [13] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467. [14] G.M. Sheldrick, Program for the Refinement of Crystal Structures from Diffraction Data, University of Göttingen, Göttingen, Germany, 1997.