Cationic Five-Coordinate Bis(guanidinato)silicon(IV) Complexes with SiN4 El Skeletons (El=S, Se): "Heterolytic Activation" of S-S and Se-Se Bonds.

The donor-stabilized silylene [iPrNC(NiPr2 )NiPr]2 Si (2) reacts with PhEl-ElPh (El=S, Se) to form the respective cationic five-coordinate bis(guanidinato)silicon(IV) complexes {[iPrNC(NiPr2 )NiPr]2 SiSPh}(+) PhS(-) (4) and {[iPrNC (NiPr2 )NiPr]2 SiSePh}(+) PhSe(-) (5). Compounds 4 and 5 were characterized by crystal structure analyses and NMR spectroscopic studies in the solid state.

Reactivity of the Donor-Stabilized Silylenes [iPrNC(Ph)NiPr]2 Si and [iPrNC(NiPr2 )NiPr]2 Si: Activation of CO2 and CS2.

Activation of CO2 by the bis(amidinato)silylene 1 and the analogous bis(guanidinato)silylene 2 leads to the structurally analogous six-coordinate silicon(IV) complexes 4 (previous work) and 8, respectively, the first silicon compounds with a chelating carbonato ligand. Likewise, CS2 activation by silylene 1 affords the analogous six-coordinate silicon(IV) complex 10, the first silicon compound with a chelating trithiocarbonato ligand. CS2 activation by silylene 2, however, yields the five-coordinate silicon(IV) complex 13 with a carbon-bound CS2 (2-) ligand, which also represents an unprecedented coordination mode in silicon coordination chemistry. Treatment of the dinuclear silicon(IV) complexes 5 and 6 with CO2 also affords the six-coordinate carbonatosilicon(IV) complexes 4 and 8, respectively.

Stable Four-Coordinate Guanidinatosilicon(IV) Complexes with SiN3El Skeletons (El = S, Se, Te) and Si=El Double Bonds.

To get information about the reactivity profile of the donor-stabilized guanidinatosilicon(II) complexes 2 and 3, a series of oxidative addition reactions was studied. Treatment of 2 and 3 with S8, Se, or Te afforded the respective four-coordinate silicon(IV) complexes 8-10 and 12-14, which contain an SiN3 El skeleton (El = S, Se, Te) with an Si=El double bond. Treatment of 2 with N2O yielded the dinuclear four-coordinate silicon(IV) complex 11 with an SiN3O skeleton and a central four-membered Si2O2 ring. Compounds 8-14 exist both in the solid state and in solution. They were characterized by elemental analyses, NMR spectroscopic studies in the solid state and in solution, and crystal structure analyses. The reactivity profile of 2 was compared with that of the structurally related bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) (1), which is three-coordinate in the solid state and four-coordinate in solution (1'). In contrast, as shown by state-of-the-art relativistic DFT analyses and experimental studies, silylene 2 is three-coordinate both in the solid state and solution. The three-coordinate species 2 is 9.3 kcal mol(-1) more stable in benzene than the four-coordinate isomer 2'. The reason for this was studied by bonding analyses of 2 and 2', which were compared with those of 1 and 1'. The gas-phase proton affinities of the relevant species in solution (1' and 2) amount to 288.8 and 273.8 kcal mol(-1), respectively.

High-performance organic thin-film transistors of J-stacked squaraine dyes.

We have synthesized a series of dipolar squaraine dyes that contain dicyanovinyl groups as acceptor and benzannulated five-membered ring heterocycles with alkyl chains of varied length as donor moieties. Based on these squaraines, thin-film transistors (TFT) were fabricated by spin coating and solution shearing. Moreover, with one of these squaraine derivatives vacuum-deposited TFTs were prepared as well. Our detailed studies revealed that the transistor performance of the present series of squaraines is strongly dependent on their structural features as well as on the processing method of thin films. Thus, solution-sheared OTFTs of selenium squaraine bearing dodecyl substituents (denoted as Se-SQ-C12) performed best with a maximum hole mobility of 0.45 cm(2) V(-1) s(-1), which is by far the highest value yet reported for OTFTs based on squaraines. This value was even surpassed by vacuum-deposited thin films of n-butyl-substituted selenium squaraine Se-SQ-C4, the only sublimable compound in this series, exhibiting a record hole mobility of 1.3 cm(2) V(-1) s(-1). Furthermore, we have investigated the morphology of the thin films and the molecular packing of these squaraine dyes by optical spectroscopy, atomic force microscopy, and X-ray diffraction. These studies revealed a relationship between the molecular structure, packing motif, thin-film morphology, and transistor performance of the squaraine dyes. From the supramolecular point of view two packing features discovered in the single crystal structure of Se-SQ-C8 are of particular interest with regard to the structure-functionality relationship: The first is the slipped and antiparallel π-stacking motif which ensures cancellation of the molecules' dipole moments and J-type absorption band formation in thin films. The second is the presence of CN···Se noncovalent bonds which show similarities to the more common halogen-bonding interactions and which interconnect the individual one-dimensional slipped π-stacks, thus leading to two-dimensional percolation pathways along the source-drain direction.

Novel transition-metal (M=Cr, Mo, W, Fe) carbonyl complexes with bis(guanidinato)silicon(II) ligands.

The donor-stabilized silylene 2 (the first bis(guanidinato)silicon(II) complex) reacts with the transition-metal carbonyl complexes [M(CO)6 ] (M=Cr, Mo, W) to form the respective silylene complexes 7-10. In the reactions with [M(CO)6 ] (M=Cr, Mo, W), the bis(guanidinato)silicon(II) complex 2 behaves totally different compared with the analogous bis(amidinato)silicon(II) complex 1, which reacts with [M(CO)6 ] as a nucleophile to replace only one of the six carbonyl groups. In contrast, the reaction of 2 leads to the novel spirocyclic compounds 7-9 that contain a four-membered SiN2 C ring and a five-membered MSiN2 C ring with a MSi and MN bond (nucleophilic substitution of two carbonyl groups). Compounds 7-10 were characterized by elemental analyses (C, H, N), crystal structure analyses, and NMR spectroscopic studies in the solid state and in solution.

Reactions of the donor-stabilized silylene bis[N,N'-diisopropyl-benzamidinato(-)]silicon(II) with Brønsted acids.

Reaction of the donor-stabilized silylene 1 (which is three-coordinate in the solid state and four-coordinate in solution) with [HMCp(CO)3 ] (M=Mo, W; Cp=cyclopentadienyl) leads to the cationic five-coordinate silicon(IV) complexes 2 and 3, respectively, and reaction of 1 with CH3 COOH yields the neutral six-coordinate silicon(IV) complex 4. Compounds 2-4 were structurally characterized by crystal structure analyses and multinuclear NMR spectroscopic studies in the solid state and in solution. The formation of 2-4 can be formally described in terms of a Brønsted acid/base reaction, coupled with a redox process (Si(II) →Si(IV) , H(+) →H(-) ).

Bis[N,N'-diisopropylbenzamidinato(-)]silicon(II): Lewis acid/base reactions with triorganylboranes.

Reaction of the donor-stabilized silylene 1 (which is three-coordinate in the solid state and four-coordinate in solution) with BEt3 and BPh3 leads to the formation of the Lewis acid/base complexes 2 and 3, respectively, which are the first five-coordinate silicon compounds with an SiB bond. These compounds were structurally characterized by crystal structure analyses and by multinuclear NMR spectroscopic studies in the solid state and in solution. Additionally, the bonding situation in 2 and 3 was analyzed by quantum chemical studies.

Activation of sulfur dioxide by bis[N,N'-diisopropylbenzamidinato(-)]silicon(II): synthesis of neutral six-coordinate silicon(IV) complexes with chelating O,O'-Sulfito or O,O'-dithionito ligands.

The neutral six-coordinate silicon(IV) complexes 2 and 3 (mixture of cis-3 and trans-3) were synthesized by reaction of the donor-stabilized silylene bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) (1) with SO2 . Compounds 2 and 3 are the first silicon(IV) complexes with chelating sulfito or dithionito ligands, and 3 is even the first molecular compound with a chelating dithionito ligand. Compounds 2 and 3 were structurally characterized by crystal structure analyses and multinuclear NMR spectroscopic studies in the solid state and in solution.

The donor-stabilized silylene bis[N,N'-diisopropylbenzamidinato(-)]silicon(II): synthesis, electronic structure, and reactivity.

A convenient and robust synthesis of bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) (1), a donor-stabilized silylene, has been developed (35 g scale). To get further information about the reactivity profile of 1, a series of oxidative addition reactions were studied. Treatment of 1 with PhSe-SePh (Se-Se bond activation), C6F6 (C-F activation), and CO2 (C=O activation/cycloaddition) yielded the neutral six-coordinate silicon(IV) complexes 10, 11, and 13, respectively. Treatment of 1 with N2O resulted in the formation of the dinuclear five-coordinate silicon(IV) complex 12 (oxidative addition/dimerization), which contains a four-membered Si2O2 ring. Compounds 10-13 were characterized by NMR spectroscopic studies in the solid state and in solution and by crystal structure analyses. Silylene 1 is three-coordinate in the solid state (from crystal structure analysis) and exists as the four-coordinate isomer 1' in benzene solution (from computational studies). Based on state-of-the-art relativistic DFT analyses, the four-coordinate species 1' was demonstrated to be the thermodynamically favored isomer in benzene solution (favored by ΔG = 6.6 kcal mol(-1) over the three-coordinate species 1). The reason for this was studied by bonding analyses of 1 and 1'. Furthermore, the (29)Si NMR chemical shifts of 1 and 1' were computed, and in the case of 1' it was analyzed how this NMR spectroscopic parameter is affected by solvation. These studies further supported the assumption that the silylene is four-coordinate in solution.

Diindole-annulated naphthalene diimides: synthesis and optical and electronic properties of syn- and anti-isomers.

Here we report a selective method for the core-extension of naphthalene diimide (NDI) with two annulated indole rings leading to carbazolo[2,3-b]carbazole diimides (CbDIs) with exclusive syn-connectivity based on a regioselective nucleophilic substitution reaction of Br4-NDI with arylamines, followed by palladium-catalyzed intramolecular C-C coupling. The oxygen analogues of anti-CbDIs, namely anti-benzofurobenzofuran diimides (anti-BfDIs), were obtained from 2,6-Br2-NDI and 2-bromophenol. The syn- and anti-isomers of CbDIs were unambiguously characterized by single-crystal X-ray analysis. The optical properties of the present core-enlarged NDIs were studied, revealing clear differences in the absorption characteristics of the syn- and anti-isomers of CbDI, on one hand, and CbDI vs BfDI derivatives, on the other hand. Cyclic voltammetry studies showed that the redox properties are dependent on the substituents at the CbDI-core and oxygen atom containing BfDIs are more prone to reduction than the respective nitrogen analogues CbDIs. Vacuum-processed organic field effect transistors reveal CbDI and BfDI derivatives with n-channel, p-channel, as well as ambient transport characteristics with mobility values up to 0.2 cm(2)/(V s).

Disila-galaxolide and derivatives: synthesis and olfactory characterization of silicon-containing derivatives of the musk odorant galaxolide.

A series of silicon-containing derivatives of the polycyclic musk odorant galaxolide (4 a) was synthesized, that is, disila-galaxolide ((4RS,7SR)-4 b/(4RS,7RS)-4 b), its methylene derivative rac-9, and its nor analogue rac-10. The tricyclic title compounds with their 7,8-dihydro-6,8-disila-6 H-cyclopenta[g]isochromane skeleton were prepared in multistep syntheses by using a cobalt-catalyzed [2+2+2] cycloaddition of the mono- yne H2C=CHCH2 OCH2 C≡CB(pin) (B(pin)=4,4,5,5-tetramethyl-1,3,2-di- oxaborolan-2-yl) with the diynes H2C=C[Si(CH3 )2 C≡CH]2 or H2C- [Si(CH3)2 C≡CH]2 as the key step. Employing [Cr(CO)3 (MeCN)3 ] as an auxiliary, the disila-galaxolide diastereomers (4RS,7SR)-4 b and (4RS,7RS)-4 b could be chromatographically separated through their tricarbonylchromium(0) complexes, followed by oxidative decomplexation. The identity of the title compounds and their precursors was established by elemental analyses and multinuclear NMR spectroscopic studies and in some cases additionally by crystal structure analyses. Compounds (4RS,7SR)-4 b, (4RS,7RS)-4 b, rac-9, and rac-10 were characterized for their olfactory properties, including GC-olfactory studies of the racemic compounds on a chiral stationary phase. As for the parent galaxolide stereoisomers 4 a, only one enantiomer of the silicon compounds (4RS,7SR)-4 b, (4RS,7RS)-4 b, rac-9, and rac-10, smelt upon enantioselective GC-olfactometry, which according to the elution sequence is assumed to be also (4S)-configured as in the case of the galaxolide stereoisomers. The disila-analogues (4S,7R)-4 b and (4S,7S)-4 b were, however, about one order of magnitude less intense in terms of their odor threshold than their parent carbon compounds (4S,7R)-4 a and (4S,7S)-4 a. The introduction of a 7-methylene group in disila-galaxolide (4 b→rac-9) improved the odor threshold by a factor of two. With the novel silicon-containing galaxolide derivatives, the presumed hydrophobic bulk binding pocket of the corresponding musk receptor(s) could be characterized in more detail, which could be useful for the design of novel musk odorants with an improved environmental profile.

Five-coordinate silicon(II) compounds with Si-M bonds (M = Cr, Mo, W, Fe): Bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) as a ligand in transition-metal complexes.

Reaction of the donor-stabilized silylene 1 with [Cr(CO)6], [Mo(CO)6], [W(CO)6], or [Fe(CO)5] leads to the formation of the transition-metal silylene complexes 2-5, which contain five-coordinate silicon(II) moieties with Si-M bonds (M = Cr, Mo, W, Fe). These compounds were characterized by NMR spectroscopic studies in the solid state and in solution and by crystal structure analyses. These experimental investigations were complemented by computational studies to gain insight into the bonding situation of 2-5. The nature of the Si-M bonds is best described as a single bond.

Neutral six-coordinate and cationic five-coordinate silicon(IV) complexes with two bidentate monoanionic N,S-pyridine-2-thiolato(-) ligands.

A series of neutral six-coordinate silicon(IV) complexes (4-11) with two bidentate monoanionic N,S-pyridine-2-thiolato ligands and two monodentate ligands R(1) and R(2) was synthesized (4, R(1) = R(2) = Cl; 5, R(1) = Ph, R(2) = Cl; 6, R(1) = Ph, R(2) = F; 7, R(1) = Ph, R(2) = Br; 8, R(1) = Ph, R(2) = N3; 9, R(1) = Ph, R(2) = NCO; 10, R(1) = Ph, R(2) = NCS; 11, R(1) = Me, R(2) = Cl). In addition, the related ionic compound 12 was synthesized, which contains a cationic five-coordinate silicon(IV) complex with two bidentate monoanionic N,S-pyridine-2-thiolato ligands and one phenyl group (counterion: I(-)). Compounds 4-12 were characterized by elemental analyses, NMR spectroscopic studies in the solid state and in solution, and crystal structure analyses (except 7). These structural investigations were performed with a special emphasis on the sophisticated stereochemistry of these compounds. These experimental investigations were complemented by computational studies, including bonding analyses based on relativistic density functional theory.

Stable five-coordinate silicon(IV) complexes with SiN4 X skeletons (X = S, Se, Te) and Si=X double bonds.

Silylenes: Reaction of the donor-stabilized silylene 1 with elemental sulfur, selenium, or tellurium led to the formation of 2 a-c [SiN(4)X skeletons (X = S, Se, Te)], the first stable five-coordinate silicon(IV) compounds with silicon-chalcogen double bonds (see figure).

Zwitterionic and anionic multinuclear pentacoordinate silicon(IV) complexes with bridging (R,R)-tartrato(4-) ligands and SiO5 skeletons: synthesis and reactivity in aqueous solution.

Two nutrients in one molecule: A zwitterionic λ(5)Si,λ(5)Si'-disilicate (1) was synthesized and characterized. It contains ligands that exclusively derive from natural products ((R,R)-tartaric acid, choline). Hydrolysis of 1 yields 2, which shows a remarkable kinetic stability in water. Upon dissolution of 1 and 2 in water, the nutrients choline and orthosilicic acid are formed by hydrolysis.

Disila-analogues of the synthetic retinoids EC23 and TTNN: synthesis, structure and biological evaluation.

Silicon chemistry offers the potential to tune the effects of biologically active organic molecules. Subtle changes in the molecular backbone caused by the exchange of a carbon atom for a silicon atom (sila-substitution) can significantly alter the biological properties. In this study, the biological effects of a two-fold sila-substitution in the synthetic retinoids EC23 (4-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-ylethynyl)benzoic acid (4a)) and TTNN (6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-2-naphthoic acid (7a)) as well as their corresponding analogues with an indane instead of a 1,2,3,4-tetrahydronaphthalene skeleton (compounds 5a and 8a) were investigated. Two-fold C/Si exchange in 4a, 5a, 7a and 8a leads to the silicon-analogues disila-EC23 (4b), 5b, disila-TTNN (7b) and 8b, which contain a 1,2,3,4-tetrahydro-1,4-disilanaphthalene (4b, 7b) or 1,3-disilaindane skeleton (5b, 8b). Exchange of the SiCH(2)Si moiety of 5b for an SiOSi fragment leads to the disiloxane 6 (2-oxa-1,3-disilaindane skeleton). The EC23 derivative 5a, the TTNN derivative 8a and the silicon-containing analogues 4b, 5b, 6, 7b and 8b were synthesised, and the biological properties of the C/Si pairs 4a/4b, 5a/5b, 7a/7b and 8a/8b and compound 6 were evaluated in vivo using RAR isotype-selective reporter cells. EC23 (4a) and its derivatives disila-EC23 (4b), 5a, 5b and 6 are very potent RAR agonists, which are even more potent than the powerful reference compound TTNPB. Disila-substitution of EC23 (4a) and 5a leads to a moderate decrease in RARα activation, whereas the RARß,γ activation is almost not affected. In contrast, two-fold C/Si exchange in the weak retinoid agonist TTNN (7a) and 8a resulted in considerably different effects: a significant increase (7a→7b) and almost no change (8a→8b) in transcription activation potential for all three RAR isotypes. Disila-TTNN (7b) can be regarded as a powerful RARß,γ-selective retinoid.

Bis[N,N'-diisopropylbenzamidinato(-)]silicon(II): a silicon(II) compound with both a bidentate and a monodentate amidinato ligand.

Well looked-after: reductive HCl elimination of the λ(6)-silicon(IV) complex 1 leads to the λ(3)-silicon(II) species 2, a novel type of donor-stabilized silylene. Reaction of 2 with [W(CO)(6)] and with I(2) yields the λ(5)-silicon(II) complex 3 and the λ(6)-silicon(IV) complex 4, respectively.

Neutral pentacoordinate halogeno- and pseudohalogenosilicon(IV) complexes with an SiSONCX skeleton (X=F, Cl, Br, I, N, C): synthesis and structural characterization in the solid state and in solution.

A series of neutral pentacoordinate silicon(IV) complexes with an SiSONCX skeleton (X=F, Cl, Br, I, N, or C) was synthesized and structurally characterized by multinuclear solution-state and solid-state NMR spectroscopy and single-crystal X-ray diffraction. These compounds contain an identical tridentate dianionic S,N,O ligand, a monodentate (pseudo)halogeno ligand (F, Cl, Br, I, NCS, N(3), or CN), and a monodentate organyl ligand (methyl, phenyl, 4-(trifluoromethyl)phenyl, or pentafluorophenyl). For most of these compounds, a dynamic equilibrium between the pentacoordinate silicon(IV) complex and two isomeric tetracoordinate silicon species in solution was observed. Most surprisingly, comparison of two series of analogous compounds containing fluoro, chloro, bromo, or iodo ligands demonstrated that pentacoordination in these series of silicon(IV) complexes is favored in the rank order I approximately Br>Cl>F; i.e., increasing the softness of the halogeno ligand favors pentacoordination.

Neutral penta- and hexacoordinate silicon(IV) complexes containing two bidentate ligands derived from the alpha-amino acids (S)-alanine, (S)-phenylalanine, and (S)-tert-leucine.

The neutral hexacoordinate silicon(IV) complex 6 (SiO(2)N(4) skeleton) and the neutral pentacoordinate silicon(IV) complexes 7-11 (SiO(2)N(2)C skeletons) were synthesized from Si(NCO)(4) and RSi(NCO)(3) (R = Me, Ph), respectively. The compounds were structurally characterized by solid-state NMR spectroscopy (6-11), solution NMR spectroscopy (6 and 10), and single-crystal X-ray diffraction (8 and 11 were studied as the solvates 8 x CH(3)CN and 11 x C(5)H(12) x 0.5 CH(3)CN, respectively). The silicon(IV) complexes 6 (octahedral Si-coordination polyhedron) and 7-11 (trigonal-bipyramidal Si-coordination polyhedra) each contain two bidentate ligands derived from an alpha-amino acid: (S)-alanine, (S)-phenylalanine, or (S)-tert-leucine. The deprotonated amino acids act as monoanionic (6) or as mono- and dianionic ligands (7-11). The experimental investigations were complemented by computational studies of the stereoisomers of 6 and 7.

Neutral pentacoordinate silicon(IV) complexes with silicon-chalcogen (S, Se, Te) bonds.

The neutral pentacoordinate silicon(IV) complexes 1 (SiS2ONC skeleton), 2 (SiSeSONC), 3 (SiTeSONC), 6/9 (SiSe2O2C), 7 (SiSe2S2C), and 8/10 (SiSe4C) were synthesized and structurally characterized by using single-crystal X-ray diffraction and multinuclear solid-state and solution-state (except for 6-9) NMR spectroscopy. With the synthesis of compounds 1-3 and 6-10, it has been demonstrated that pentacoordinate silicon compounds with soft chalcogen ligand atoms (S, Se, Te) can be stable in the solid state and in solution.