Capítulo 1 El Emprendimiento
1.1.2 Evolución del concepto
methane ligands.
Further attempts to promote nucleophilic reactivity of ruthenium-coordinated arenes in a poly(pyrazolyl)borate environment have led to studies on the second generation methylated poly(pyrazolyl)borate and methane derivatives. Treatment of a suspension of [Ru(r|^-C6HJ (3,5-Me^Pz)]} ] [P F j, [8] in tetrahydrofuran with Na[BHJ leads to formation o f a yellow solution which upon evaporation to dryness gives [Ru(r|^- QH?) {r|^-HB(3,5-Me2Pz)3} ], [37] (Figure 4.14), along with a number o f unidentified side products. Purification of [37] is achieved by column chromatography using tetrahydrofuran as the eluent on an alumina column, yielding [37] as a dark orange solid in 68 % yield. The infrared spectrum of [37] contains two strong bands, at 2860 and 2797 cm ' which are assigned to the v(C-Hgndo) and v(C-Hg^J stretches of the cyclohexadienyl ligand (ca. a shift of -103 and +15 cm ' respectively when compared with [23]).
N ucleophilic additions to ruthenium (arene)poly(pyrazolyl)borates and methanes exo
O
N NO
'N N NMë
\ | /
B H Figure 4.14 [Ru(îi'-QH,){r|'-HB(3,5-Me2Pz)3}], [37].The ’H NMR spectrum of [37] at room temperature is shown in Figure 4.15(a). The singlet resonance for the t i-bonded benzene in [8] is replaced by signals for the cyclohexadienyl ligand at 5 2.73 (m), 1.46 (d), 6.10 (t), 5.12 (t), and 2.39 ppm (t). The appearance of the triplet resonances relatively more downfield compared to those displayed by [23], can be attributed to the greater basicity of the [HB(3,5-Me2Pz)3}]‘ ligand. While the multiplet resonance for Hg^do remains unchanged in chemical shift, the doublet resonance due to is displaced upfteld (by 0.61 ppm) with respect to the corresponding resonances for [23]. As has been noted for [23], the pyrazolyl signals in the spectrum are broad, indicative of dynamic NMR processes in operation. The signal at Ô 5.72 ppm {Vyji 21 Hz) is due to H"* and is broad. While the resonance for the methyl group at Ô 2.46 (v,j, 36 Hz) shows considerable broadening, that at 2.25 ppm (v^/% 8 Hz), is much sharper, implying that it is isolated from any changes in the coordination environment at ruthenium. These observations can be usefully employed to assign the
N ucleophilic addition s ta ruth en iu m (aren e)poly(pyrazolyl)borales a n d methanes
re so n an ce s at ô 2.46 and 2.25 ppm to the m ethyl sub stitu en ts at ‘3 ’ and ‘5 ’ p o sitions resp ectiv ely .
(Pz) — Ru BH N N Me, M e
Me
(a)21°C
exo endoMe
(b) -65 " C
T T T T T T T T T TI TTT T T 2 P P MFigure 4.15 V ariable T em p eratu re 'H N M R sp ec tra o f [37] at (a) 21 (b) -65“C.
Nucleophilic additions to ruthenium (arene)poly(pyrazolyl)borates and methanes
While raising the temperature of the NMR probe to 50°C (not shown) leads to a sharpening of the broad resonances (ô 5.72, 2.48 and 2.34 ppm), the lowering of the temperature to -65°C leads to their splitting into two subsets, with integral ratio of 1:2, 5 6.05, 2.27, 2.19 (3H, Pz‘) and 5.61, 2.87, 2.34 (6H, Pz"), Figure 4.15(b).
In an analogous fashion the broad ‘"C NMR signals observed at 20 °C are resolved at low temperature, ô 154.04 C", 143.45 107.92 17.82 Me" 13.27 Me", (Pz’) and 152.27 C", 143.18 C", 108.42 16.04 Me", 13.09 ppm Me", (Pz"). These observations are consistent with the presence of two distinct pyrazolyl environments at low temperatures, as discussed previously.
Attempts to add CN' and OH to the arene ring in [8] result in extensive degradation of the starting mixed sandwich complex. The fragile nature of the hydrido/m(3,5- dimethylpyrazolyl)borate derivatives has already been commented upon (see Chapter 2). In view of the apparently greater stability of the neutral analogue HC(3,5-Me2Pz)] it was expected that nucleophilic addition to complexes such as [Ru(r|"-C6H6){ic"-HC(3,5- Me2Pz)3}Cl][PFJ [17], [Ru(T|'-l,4-Me2CA){K"-HC(Pz)3)Cl][PFj [18], [Ru()i'-
{ic"-HC(3,5-Me2Pz)3}][PFj2 [19] was possible. In our hands however the parent complexes undergo degradation to yield unidentified products. We believe that this degradation is due to the relatively large size of the nucleohpiles (CN' and OH ) Double nucleophilic addition would be promoted if a hydride source were used. The investigation of such reactions still remains to be explored pending synthesis o f mixed sandwich complexes bearing a neutral tripodal ligand in which the acidic proton is replaced with a protecting group such as a methyl or a pyrazolyl substituent.
Chapter 4: Experimental
4.6
Experimental
Details o f instrumental methods and the starting materials are as described in Section
2.6.
[Ru(ti^C,H ,){k^-HB(Pz)3}] [231
[Ru(ri^-QH6){K^-HB(Pz)3}][PF6] [1] (0.09 g, 0.16 mmol) was suspended in degassed th f
(10 cm^) and treated with Na[BH4] (0.05 g, excess). After stirring for 1 h at room
temperature the solution was filtered through celite to remove any unreacted Na[BHJ. Evaporation of the resulting filtrate to dryness gave [23] as a pale yellow air sensitive residue. Yield: 0.05 g, 0.12 mmol, 75%. (Found: C, 45.52; H, 4.51; N, 20.39. Calc, for CjgHi^NgBiRu;: C, 45.90; H, 4.36; N, 21.41). Mass Spectrum: 393 m/z, [M-//]^. Infrared: v(BH) 2494, v(C H ,„J 2963, v (C H ,J, 2782 cm '.
[Ru(r|^-C,H,CN){K^-HB(Pz)3}] [24]
[Ru(T|'^-C6H6) {K^-HB(Pz)3} ][PFJ [1] (0.05 g, 0.09 mmol) was suspended in degassed th f
and treated with KCN (0.05 g, excess). The mixture was stirred at room temperature for 2 h and then pumped to dryness. Extraction into chloroform followed by filtering through celite and evaporation to dryness gave [24] as an air stable yellow residue. Crystals suitable for x-ray crystallographic study were formed by slow evaporation o f a chloroform solution o f [24]. Yield: 0.033g, 0.079 mmol, 84% (Found: C, 46.1; H, 3.8; N, 23.3. Calc, for Ci^Hi^N^B^Ru,: C, 45.9; H, 3.9; N, 23.5). Mass Spectrum: 419, [M]^ 393 m/z, [M-C7V]". Infrared: v(BH) 2484, v(CN) 2214, v(C-H ,„J 2945 cm '.
C hapter 4: Experimental
[Ru(Ti'-C,H,OH){HB(Pz)J] [25]
[Ru(T|^-C6HJ {ic^-HB(Pz)3}][PFJ [1] (0.050 g, 0.09 mmol) was suspended in degassed
methanol (10 cm^) and treated with methanolic KOH (0.047 g, excess). The mixture was stirred at room temperature for 48 h and then evaporated to dryness. Extraction into th f followed by filtration through celite and evaporation to dryness gave [25] as a yellow material. Yield: 0.031 g, 0.08 mmol, 81%. (Found: C, 43.7; H, 4.1; N, 20.1. Calc, for CjjHiyNgBiOiRu,: C, 44.0; H, 4.2; N, 20.5). Mass Spectrum: [M-077]^ 393 m/z. Infrared: v(BH) 2497, v(OH) 3450 v(C H ,„J 2950 cm '.
[Ru(Ti'-C,H,D{K'-HB(Pz)J] [26]
[Ru(r)^-C^HJ {K^-HB(Pz);} ][PF^] [1] (0.08 g, 0.16mmol) was treated with Na[BDJ (0.04g, excess) and worked up as described for [23]. Yield: 0.05 g, 0.12 mmol, 77%. Mass Spectrum:
[M-Z)]^, 393
m/z. Infrared: v(BH) 2492,v(CHgndo)
2933,v(CDg^J
2088 cm' .[Ru(ri'-l-'Pr-4-MeC6H5){K'-HB(Pz)3}] [27a] and [27b]
[Ru(r|^-1 -Tr-4-MeC6HJ {ic^-HB(Pz)3} ][PFJ [2] (0.124 g, 0.21 mmol) was suspended in
degassed th f cm^) and treated with Na[BHJ (0.05 g, excess). After stirring for 2 h at room temperature the solution was filtered through celite to remove any unreacted Na[BH4]. Evaporation o f the resulting filtrate to dryness, led to deposition o f a crude
yellow product. Purification by passing a diethylether solution of [27] through an alumina column (mesh 100-250) with subsequent evaporation to dryness o f the eluent resulted in isolation of [27] as a mildly air sensitive solid. The two isomers o f [27], were not separated. Yield: 0.076 g, 0.17 mmol, 82 %. (Found: C, 50.78; H, 5.51; N, 18.53.
C hapter 4: Experimental
Calc, for CigHjsN^jBiRu,: C, 50.79; H, 5.60; N, 18.70). Mass Spectrum: 450 m/z [M]^. Infrared: v(BH) 2452, v(CH,„ J 2922, v (C H ,J 2776 cm '.
IRu(ri'-l-Tr-4-MeC6H4CN){K"-HB(Pz)3}] [28a] and [28b]
[Rii(ri^-l-^Pr-4-MeC6H4){K^-HB(Pz)3}][PF6] [2] (0.134 g, 0.23 mmol) was suspended in degassed th f{\S cm^) and treated with KCN (0.05 g, excess). The mixture was refluxed for 5 days then filtered and evaporated to dryness. Purification was carried out by repeated extraction of the residue with ChCl). The two isomers of [28], were not separated. Yield: 0.067 g, 0.14 mmol, 63 %. (Found: C, 49.57; H, 5.22; N, 20.76. Calc, for C2oH24N7B,RUi: C, 50.03; H, 5.11; N, 20.67). Mass Spectrum: 449 m/z [M-CN]^.
Infrared: v(BH) 2456, v(CHg„jq) 2931, v(CN) 2221 cm*'.
[Ru(T|"-l-'Pr-4 -MeC,H4 0 H){K'-HB(Pz)3}] [29a] and [29b]
[Ru(r|‘^-l-^Pr-4-MeC6H4){K^-HB(Pz)3}][PF6] [2] (0.110 g, 0.19 mmol) was suspended in degassed th f{\5 cm^) and treated with NaOH (0.05 g, excess). The mixture was refluxed for 4 days then filtered and evaporated to dryness. The purification procedure was similar to that for [27]. The two isomers of [29], were not separated. Yield: 0.053 g, 0.11 mmol, 61 %. (Found: C, 49.90; H, 5.30; N, 17.97. Calc, for CigEjsNgBiGjRu,: C, 49.05; H, 5.41; N, 18.06). Mass Spectrum: 449 m/z, [M-O//]^. Infrared: v(BH) 2460, v(CHgndo) 2959, v(OH) ca 3400 cm*'.
[Ru(Ti'-l,4-Me2CA){K'-HB(Pz)3}] [30]
[Ru(r|^-l,4-Me2C6H4){K^-HB(Pz)3}][PF6] [3] (0.121 g, 0.23 mmol) was suspended in degassed th f { \5 cm^) and treated with Na[BH4] (0.05 g, excess). The mixture was