3463-21-6

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A series of ruthenium(II) polypyridyl complexes, with novel silane functionalisation, [Ru(bipy)2(bipy-sil)](PF6)2 (3), [Ru(bipy-sil)2Cl2] (6), and [Ru(bipy-sil) 2(NCS)2] (7) have been synthesised and tested as chromophores (dyes) in TiO2 and WO3 based dye-sensitised solar cells (DSSCs). The performance of the respective DSSCs were compared to analogous dyes with ionic carboxylate ([Ru(bipy)2(dcbipy)](PF 6)2 (1), [Ru(dcbipy)2Cl2] (4), [Ru(dcbipy)2(NCS)2] (5)) or phosphonate ([Ru(bipy) 2(dpipy)](PF6)2 (2)) linking groups. The covalent silane-metal oxide linkage offers much needed improvement to the operating conditions, and lifetime of DSSCs, in terms of pH range and choice of solvent. UV-Vis spectroscopy of the deep-red solutions showed that the bis-bipy-sil complexes absorbed more visible light than the tris-bipy complex, as indicated by the presence of two absorption bands and higher ε values. The UV-Vis spectrum of (3) contained a single broad absorption at 400-600 nm with: λmax = 457 nm; ε = 10 520 ± 440 L mol -1 cm-1, whereas two intense broad absorption bands were observed for novel bis-bipy-sil complexes (6): 340-370 nm (λ max(1) = 365 nm, ε(1) = 12 716 ± 180 L mol-1 cm-1); and 440-540 nm (λmax(2) = 485 nm, ε(2) = 11 070 ± 150 L mol-1 cm -1), and (7): 340-400 nm (λmax = 371 nm, ε(1) = 20 690 ± 485 L mol-1 cm-1), and 460-530 nm (λmax = 500 nm and ε(2) = 20 750 ± 487 L mol-1 cm-1). The bands in (7) being significantly more defined. A 10-fold improvement in the efficiency of the bipy-sil TiO2-based DSSCs was observed from (3) to (6) to (7). This performance was lower than that of the commercial N3 dye, [Ru(dcbipy) 2(NCS)2] (5), but the current of (7) on WO3, was comparable to that of the carboxylate system (4). There is considerable potential for further improvement by modification of the silyl linker, reducing the long non-conjugated propyl chain between the amide group and the silatrane (bipy-sil), to a short, conjugated link. During an extensive synthetic study, the most promising strategy was identified as direct linkage, the formation of a direct Si-C bond, using butyllithium with 4,4′-dibromo-2,2′- bipyridine and either trimethylsilane or 1-ethoxysilatrane, provided that the product can be captured and stabilised prior to binding to a metal oxide coated DSSC substrate.

Reactions of (triethylstannylthioalkyl)trimethoxysilanes Et 3SnS(CH2)nSi(OMe)3 (n = 1, 2) and (triethylstannylthioalkyl)trialkoxysilatranes Et3Sn(CH2) n Sa [hereinafter Sa = Si(O

Hydrosilylation of (ethoxycarbonyl)acetylene with triethoxysilane was used to obtain triethoxy-(2-ethoxycarbonylvinyl)silane as a mixture of cis and trans isomers. This mixture under the action of the boron trifluoride-ether complex readily converts to a mixture of respective isomers of (2-ethoxycarbonylvinyl)trifluorosilane. trans-Triethoxy(2-ethoxycarbonylvinyl)silane reacts with triethanolamine to give trans-1-(2-ethoxycarbonylvinyl)silatrane in quantitative yield. Transetherification of the isomeric mixture of triethoxy-(2-ethoxycarbonylvinyl)silane with triethanolamine, too, yields trans-1-(2-ethoxycarbonylvinyl)silatrane. Along with this silatrane and ethanol, the latter reaction gives 1-ethoxysilatrane and vinyl acetate.

Novel heterocyclic I-derivatives of silatranes have been obtained. The optimal synthetic method for the indicated compounds is transesterification of tetraethoxysilane by an eqitimolar mixture of triethanolamine and a heterocyclic (or aromatic) hydroxyl-containing compound. 1999 KluwerAcademic/Plenum Publishers.

A novel route to tetraethoxysilane and other silicon alkoxides is described, from amorphous silica (SiO2·H2O) as the raw material. The reaction of amorphous silica with triethanolamine is enhanced by using an alkali metal hydroxide catalyst, to form a range of triethanolamine-substituted silatrane species. These can undergo alkoxide exchange in acidic alcohols to form alkoxysilatranes, tetraalkoxysilanes, hexaalkoxydisiloxanes and higher siloxanes. Reaction of triethanolamine-substituted silatranes with acetic anhydride produces acetoxysilatrane. Products were identified by multinuclear (1H, 13C and 29Si) magnetic resonance spectroscopy, electrospray mass spectrometry or high-resolution gas chromatography electron impact mass spectrometry.

New convenient methods of sila- and germatranes synthesis from ethoxy- and tetraorganylsilanes and -germanes have been elaborated. The reaction of ethoxysilanes with boratrane in the presence of catalytic amounts of metal alcoholates has been investigated. Dimethylformamide (DMF) as a solvent and NaOEt as a catalyst used instead of xylene and Al(Oi-Pr)3 were found to give better yields. The possibility of using alkoxy-, aminosilanes, tetraethoxygermane and even tetraorganylsilanes in this reaction leading to the corresponding atranes with good yields has been demonstrated. Triethanolamine in the presence of catalytic amounts of base or CsF easily substitutes furyl-, dihydrofuryl-, dihydropyranyl- and thienyl groups in tris- and tetraheterylsilanes, leading to organylsilatranes with good to excellent yields.

The Si-C bond in 1-organylsilatranes is cleaved by bromine or iodine chloride to yield 1-bromo- or 1-chlorosilatrane respectively. In the presence of Et2O or THF and under the action of dioxane dibromide, 1-halosilatranes are formed together with 1-alkoxy- and 1-(ω-haloalkoxy)silatranes.

The electronic structure of 1-halosilatranes is discussed.Some new preparative methods based on hetero- and homo-lytic reactions of the silatrane and the Si- and C-substituted silatranes with halogenating reagents are described and also synthetic routes to 1-halosilatranes from certain organotrialkoxy- and organotrichlorosilanes.The electrophilic reactions of 1-iodosilatrane with ethers and esters, carbonyl compounds, alkoxysilanes and siloxanes, terminal alkynes and organomercurials have been studied

A 300-MHz (1)H-NMR conformational analysis study of a set of pentacoordinated silicon compounds (silatranes) and their tetracoordinated counterparts is presented.The solution conformation of the silatranes shows a close resemblance to known X-ray structures, although the silatrane conformation was found to depend upon the solvrnt polarity.Comparison of the conformation of a 2-methoxyethoxy fragment in the tetra-and pentacoordinated systems showed the existence of conformational transmission, similar to that known for phosphorus compounds.Enhanced electrostatic repulsion between the vicinal oxygens in the 2-methoxyethoxy fragment produces a trans conformation around the C-C bond in the pentacoordinated silatranes.The conformational transmission effect is smaller in silatranes than in phosphorus compounds, due to a relatively weak fifth bond.

The relative reaction rates of several silatranes (derivatives of 2,8,9-trioxa-5-aza-1-silatricyclo1,5>undecane) and HgCl2 in acetone-d6 to yield the corresponding organomercury compound are of the order of e.g., 5 * 10-1 1 mol-1 sec-1 or slightly less, a rate that is unexpectedly high compared to the essentially inert parent organotrialkoxysilanes.Thus, the apical Si-C bond of the silatrane is extraordinarily susceptible to direct electrophilic attack by mercury(II).The rates decrease in the order CH2=CH, C6H5, p-ClC6H4 > CH3 > CH3CH2, CH3CH2CH2 > C6H11, ClCH2, Cl2CH, CH3CH2O.The effects of varying the solvent and the counterions are noted, and the probable mechanism is discussed.

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