Formation and structural characterization of mercury complexes from Te(R)CH2SiMe3 (R = Ph, CH2SiMe3) and HgCl2

The reaction of HgCl₂ and Te(R)CH₂SiMe₃ [R = CH₂SiMe₃ (1), Ph (2)] in ethanol yielded a mononuclear complex [HgCl₂{Te(R)CH₂SiMe₃}₂] (R = Ph, 3a; R = CH₂SiMe₃, 3b). The recrystallization of 3a or 3b from CH₂Cl₂ produced a dinuclear complex [Hg₂Cl₂(μ-Cl)₂{Te(R)CH₂SiMe₃}₂] (R = Ph, 4a; R = CH₂SiMe₃, 4b). When 3a was dissolved in CH₂Cl₂, the solvent quickly removed, and the solid recrystallized from EtOH, a stable ionic [HgCl{Te(Ph)CH₂SiMe₃}₃]Cl·2EtOH (5a·2EtOH) was obtained. Crystals of [HgCl₂{Te(CH₂SiMe)₂}]·2HgCl₂·CH₂Cl₂ (6b·2HgCl₂·CH₂Cl₂) were obtained from the CH₂Cl₂ solution of 3b upon prolonged standing. The complex formation was monitored by ¹²⁵Te-, and ¹⁹⁹Hg NMR spectroscopy, and the crystal structures of the complexes were determined by single crystal X-ray crystallography.     

A highly stereoselective preparation of CF3-substituted 1-aryl-1,2-diphenylethenes: application to the synthesis of panomifene

β-CF₃-α,β-diphenylvinyl sulfide 3a was prepared stereoselectively in 77% yield from the reaction of 2 with phenyllithium at room temperature for 5 h. Oxidation of 3a with MCPBA afforded the corresponding vinyl sulfone 4a, in which (E)-4a can be crystallized in a mixture of CH₂Cl₂ and hexane. The addition-elimination reaction of (E)-4a with phenyllithium having substituents on the benzene ring provided 5a-j in 51-82% yields stereospecifically. Similarly, the treatment of (E)-4a with p-chloroethoxyphenyllithium in the presence of 12-crown-4 (20 mol %) at −10 °C, followed by slowly warming to room temperature, resulted in the formation of the corresponding panomifene precursor 6 in 82% yield.     

Photochemical synthesis of a palladium dichloromethyl complex, {(hexyl)HC(N-methyl-imidazol-2-yl)2}Pd(CHCl2)Cl.: X-ray molecular structures of {(hexyl)HC(N-methylimidazolyl-2-yl)2}Pd(X)Cl, X=Cl, and CHCl2

The reaction of (hexyl)HC(mim)₂ (1, mim=N-methyl-imidazol-2-yl) with (cod)PdMeCl in C₆H₆ yields {(hexyl)HC(mim)₂}Pd(Me)Cl (3). The photochemical reaction of 3 with CH₂Cl₂ at 23 °C in ambient room light yields {(hexyl)HC(mim)₂}Pd(CHCl₂)Cl (4). It is proposed that this reaction proceeds by homolytic scission of the PdMe bond of 3.     

Reactions of novel trifluoromethyl propargylic carbocation with carbon nucleophiles

Trifluoromethyl propargylic carbocation [I] generated from the reaction of 1-amino substituted 3-trifluoromethyl-2-propynyl trimethylsilyl ether 1 with TMSOTf in CH₂Cl₂ at −15 °C, followed by warming to room temperature reacted with 1.2 equiv of substituted benzenes, RMgBr and allylsilane to give the enones 3a-l and 5, respectively. The reaction of [I] with anisole, followed by treatment with Grignard reagents afforded the corresponding allyl amine derivatives 7, which underwent cyclization reaction to give indene derivatives 8 by using 2 equiv of TMSOTf.     

Quantum chemical study of ethylene addition to group-7 oxo complexes MO2(CH3)(CH2) (M = Mn, Tc, Re)

Quantum chemical calculations using DFT at the B3LYP level have been carried out for the reaction of ethylene with the group-7 compounds ReO₂(CH₃)(CH₂) (Re1), TcO₂(CH₃)(CH₂) (Tc1) and MnO₂(CH₃)(CH₂) (Mn1). The calculations suggest rather complex scenarios with numerous pathways, where the initial compounds Re1-Mn1 may either engage in cycloaddition reactions or numerous addition reactions with concomitant hydrogen migration. There are also energetically low-lying rearrangements of the starting compounds to isomers which may react with ethylene yielding further products. The [2 + 2]_Re,C cycloaddition reaction of the starting molecule Re1 is kinetically and thermodynamically favored over the [3 + 2]_C,O and [3 + 2]_O,O cycloadditions. However, the reaction which leads to the most stable product takes place with initial rearrangement to the dioxohydridometallacyclopropane isomer Re1a that adds ethylene with concomitant hydrogen migration yielding Re1a-1. The latter reaction has a slightly higher barrier than the [2 + 2]_Re,C cycloaddition reaction. The direct [3 + 2]_C,O cycloaddition becomes more favorable than the [2 + 2]_M,C reaction for the starting compounds Tc1 and Mn1 of the lighter metals technetium and manganese but the calculations predict that other reactions are kinetically and thermodynamically more favorable than the cycloadditions. The reactions with the lowest activation barriers lead after rearrangement to the ethyl substituted dioxometallacyclopropanes Tc1a-1 and Mn1a-1. The manganese compound exhibits an even more complex reaction scenario than the technetium compounds. The thermodynamically most stable final product of ethylene addition to Mn1 is the ethoxy substituted metallacyclopropane Mn1a-2 which has, however, a high activation barrier.     

Synthesis, structures and preliminary biological screening of bis(diphenyl)chlorotin complexes and adducts: Ph2ClSn-CH2-R-CH2-SnClPh2, R = p-C6H4, CH2CH2

The reaction between ClCH₂-R-CH₂Cl, R = p-C₆H₄, and [Ph₃Sn]⁻Li⁺ yields Ph₃Sn-CH₂-R-CH₂-SnPh₃ (1) in high yield. The related known compound R = CH₂CH₂ (1a) is synthesized by the reaction of the di-Grignard reagent BrMg(CH₂)₄MgBr with two equivalents of Ph₃SnCl. Cleavage of a single Sn-Ph group at each tin centre of both compounds using HCl/Et₂O yields the corresponding bis-chlorostannanes Ph₂ClSn-CH₂-R-CH₂-SnClPh₂, R = (CH₂)₄ (2) and R = C₆H₄ (3), respectively. Compounds 1, 2 and 3 are crystalline solid materials and their single crystal X-ray structures are reported. In the solid state both 2 and 3 form self-assembled ladder structures involving alternating intermolecular Cl-Sn?Cl and Cl?Sn-Cl bonded chains at both ends of the distannanes with 5-coordinate tin atoms. Recrystallization of 3 from CH₂Cl₂ in the presence of DMF yields the bis-DMF adduct (4) in which no self-assembled structures were noted. Evaluation of the chlorostannanes 2 and 3 against a suite of bacteria, Staphylococcus aureus, Escherichia coli and Photobacterium phosphoreum is reported and compared to the related mono-chlorostannanes Ph₂(CH₃)SnCl and Ph₂(PhCH₂)SnCl.     

The new dispirobino and dispiroansa spermine derivatives of cyclotriphosphazenes

In this study, the crystal structures of the dispiroansa spermine derivatives of cyclotriphosphazene are characterised for the first time. The reaction of spiro-, gem-disubstituted cyclotriphosphazene derivatives, N₃P₃Cl₄R₂ [R = NHPh, (HN(CH₂)₃NH)_0.5, (OCH₂C(CH₃)₂CH₂O)_0.5], (1–3), with spermine (4), in aprotic solvents such as CH₂Cl₂ results in a series of dispirobino spermine derivatives of cyclotriphosphazene (5a, 6a, 7), namely spermine bridged compounds. Whereas, in protic solvents such as CHCl₃ give, dispiroansa derivatives (8–10) namely tetracyclic cyclotriphosphazene. The new series of dispirobino and dispiroansa spermine derivatives of cyclotriphosphazene (5a, 6a, 7–10) have been characterised by elemental analysis, mass spectrometry, X-ray (for 5a, 8, 10) and ¹H, ³¹P NMR spectroscopies.     

Mixed-metal single-molecule magnets: Syntheses, structure, and magnetic properties of [Mn8Fe4O12(O2CR)16(H2O)4] (R = CH2Cl, CH2Br, CHCl2)

Three mixed-metal single-molecule magnets containing [Mn₈Fe₄O₁₂]¹⁶⁺ cores are synthesized and characterized. The reaction of FeCl₂·4H₂O with KMnO₄ and RCOOH (R = CH₂Cl, CH₂Br) in H₂O gives [Mn₈Fe₄O₁₂(O₂CR)₁₆(H₂O)₄] (R = CH₂Cl (1), CH₂Br (2)) in yields of 43% and 40%, respectively. Treatment of complex 1 with an excess of CHCl₂COOH in CH₂Cl₂ gives [Mn₈Fe₄O₁₂(O₂CCHCl₂)₁₆(H₂O)₄]·CH₂Cl₂·10H₂O (3·CH₂Cl₂·10H₂O) in a yield of 83%. The X-ray structure analysis reveals that all three complexes consist of a trapped-valence dodecanuclear core comprising 4Mn^III, 4Fe^III, and 4Mn^IV ions. DC magnetic susceptibility and magnetization measurements indicate that all three complexes exhibit intramolecular antiferromagnetic interaction, resulting in an S = 4 ground state. In addition, frequency-dependent out-of-phase AC magnetic susceptibility signals at low temperature for complexes 1, 2, and 3 are indicative of their single-molecule magnetism behavior.     

Reverse Kocheshkov reaction - Redistribution reactions between RSn(OCH2CH2NMe2)2Cl (R = Alk, Ar) and PhSnCl3: Experimental and DFT study

A series of organotin compounds bearing two intramolecular N → Sn coordination bonds RSn(OCH₂CH₂NMe₂)₂Cl (R = Me (4), n-Bu (5), Mes (6)) were synthesized in good yields. These compounds as well as 2 (R = Ph) react with PhSnCl₃ to give redistribution products RPhSnCl₂ and (Me₂NCH₂CH₂O)₂SnCl₂ (3). The direction of redistribution reactions is reverse to Kocheshkov reaction. DFT calculations have shown that the driving force of the reactions is formation of intramolecular N → Sn coordination bonds in (RO)₂SnCl₂ (3), the Lewis acid stronger than RSn(OR)₂Cl (2, 4-6). The mechanism of the redistribution reaction between 2 and PhSnCl₃ consists of two steps: (1) initial exchange of OCH₂CH₂NMe₂ and Cl to give PhSn(OCH₂CH₂NMe₂)Cl₂ (7) followed by (2). Ph and OCH₂CH₂NMe₂ exchange.     

Reactions of Mo(II)-tetraphosphine complex [MoCl2{meso-o-C6H4(PPhCH2CH2PPh2)2}] with a series of small molecules

Reactions of Mo(II)-tetraphosphine complex [MoCl₂(κ⁴-P4)] (2; P4 = meso-o-C₆H₄(PPhCH₂CH₂PPh₂)₂) with a series of small molecules have been investigated. Thus, treatment of 2 with alkynes RCCR′ (R = Ph, R′ = H; R = p-tolyl, R′ = H; R = Me, R′ = Ph) in benzene or toluene gave neutral mono(alkyne) complexes [MoCl₂(RCCR′)(κ³-P4)] containing tridentate P4 ligand, which were converted to cationic complexes [MoCl(RCCR′)(κ⁴-P4)]Cl having tetradentate P4 ligand upon dissolution into CDCl₃ or CD₂Cl₂. The latter complexes were available directly from the reactions of 2 with the alkynes in CH₂Cl₂. On the other hand, treatment of 2 with 1 equiv. of XyNC (Xy = 2,6-Me₂C₆H₃) afforded a seven-coordinate mono(isocyanide) complex [MoCl₂(XyNC)(κ⁴-P4)] (7), which reacted further with XyNC to give a cationic bis(isocyanide) complex [MoCl(XyNC)₂(κ⁴-P4)]Cl (8). From the reaction of 2 with CO, a mono(carbonyl) complex [MoCl₂(CO)(κ⁴-P4)] (9) was obtained as a sole isolable product. Reaction of 9 with XyNC afforded [MoCl(CO)(XyNC)(κ⁴-P4)]Cl (10a) having a pentagonal-bipyramidal geometry with axial CO and XyNC ligands, whereas that of 7 with CO resulted in the formation of a mixture of 10a and its isomer 10b containing axial CO and Cl ligands. Structures of 7 and 9 as well as [MoCl(XyNC)₂(κ⁴-P4)][PF₆](8′) and [MoCl(CO)(XyNC)(κ⁴-P4)][PF₆] (10a′) derived by the anion metathesis from 8 and 10a, respectively, were determined in detail by the X-ray crystallography.     

The chemistry of niobium and tantalum halides,MX5, with haloacetic acids and their related anhydrides: Anhydride C–H bond activation promoted by MF5

Niobium and tantalum pentahalides, MX₅ (1), react with acetic acid and halo-substituted acetic acids, in 1:1 ratio, to give the dinuclear complexes [MX₄(μ-OOCMe)]₂ [M = Nb, X = Cl, 2a; M = Ta, X = Cl, 2b; Br, 2c] and [MCl₄(μ-OOCR)]₂ [M = Nb, R = CH₂Cl, 4a; CHCl₂, 4c; CCl₃, 4e; CF₃, 4g; CHBr₂, 4i; CH₂I, 4j; M = Ta, R = CH₂Cl, 4b; CHCl₂, 4d; CCl₃, 4f; CF₃, 4h]. The solid state structures of 2b and 4e have been ascertained by X-ray diffraction studies. The reactions of 1 with acetic anhydride and halo-substituted acetic anhydrides result in C–O bond activation and afford 2 and 4, respectively, with concomitant formation of acetyl halides. Moreover, the complexes MCl₅[OC(Cl)Me] [M = Nb, 3a; M = Ta, 3b] have been detected in significant amounts within the mixtures of the reactions of MCl₅ with acetic anhydride. TaI₅ is unreactive, at room temperature, towards both MeCOOH and (MeCO)₂O. MF₅ react with RCOOH (R = Me, CH₂Cl) in 1:1 molar ratio, to afford the ionic compounds [MF₄(RCOOH)₂][MF₆], 5a–d, in high yields. The additions of (RCO)₂O (R = Me, CH₂Cl) to MF₅ give 5, suggesting that anhydride C–H and C–O bonds activation is operative during the course of these reactions.     

Thermal hydrosilylation of olefin with hydrosilane. Preparative and mechanistic aspects

The reaction of trichlorosilane (1a) at 250 °C with cycloalkenes, such as cyclopentene (2a), cyclohexene (2b), cycloheptene (2c), and cyclooctene (2d), gave cycloalkyltrichlorosilanes [C_nH_2n−1SiCl₃: n = 5 (3a), 6 (3b), 7 (3c), 8 (3d)] within 6 h in excellent yields (97-98%), but the similar reactions using methyldichlorosilane (1b) instead of 1a required a longer reaction time of 40 h and afforded cycloalkyl(methyl)dichlorosilanes [C_nH_2n−1SiMeCl₂: n = 5 (3e), 6 (3f), 7 (3g), 8 (3h)] in 88-92% yields with 4-8% recovery of reactant 2. In large (2, 0.29 mol)-scale preparations, the reactions of 2a and 2b with 1a (0.58 mol) under the same condition gave 3a and 3b in 95% and 94% isolated yields, respectively. The relative reactivity of four hydrosilanes [HSiCl_3−mMe_m: m = 0-3] in the reaction with 2a indicates that as the number of chlorine-substituent(s) on the silicon increases the rate of the reaction decreases in the following order: n = 3 > 2 > 1 ? 0. In the reaction with 1a, the relative reactivity of four cycloalkenes (ring size = 5-8) decreases in the following order: 2d > 2a > 2c > 2b. Meanwhile linear alkenes like 1-hexene undergo two reactions of self-isomerization and hydrosilylation with hydrosilane to give a mixture of the three isomers (1-, 2-, and 3-silylated hexanes). In this reaction, the reactivity of the terminal 1-hexene is higher than the internal 2- and 3-hexene. The redistribution of hydrosilane 1 and the polymerization of olefin 2 occurred rarely under the thermal reaction condition.     

Branched and dendritic metallo-carbosiloxanes with OCH2PPh2MLn end-grafted units

A straightforward method for the preparation of metallo carbosiloxanes of type Si(OCH₂CH₂CH₂SiMe₂[OCH₂PPh₂M(CO)_n])₄ (n = 3, M = Ni, 7a; n = 4, M = Fe, 7b; n = 5: M = Mo, 7c; M = W, 7d), Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₄ (8) and Me₂Si(OCH₂CH₂CH₂SiMe[OCH₂PPh₂Ni(CO)₃]₂)₂ (11) is described. The reaction of Si(OCH₂CH₂CH₂SiMeXCl)₄ (1: X = Me, 2: X = Cl) or Me₂Si(OCH₂CH₂CH₂SiMeCl₂)₂ (9) with HOCH₂PPh₂ (3) produces Si(OCH₂CH₂CH₂SiMe₂(OCH₂PPh₂))₄ (4), Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₄ (5) or Me₂Si(OCH₂CH₂CH₂SiMe(OCH₂PPh₂)₂)₂ (10) in presence of DABCO. Treatment of the latter molecules with Ni(CO)₄ (6a), Fe₂(CO)₉ (6b), M(CO)₅(Thf) (6c: M = Mo; 6d: M = W), respectively, gives the title compounds 7a-7d, 8 and 11 in which the PPh₂ groups are datively bound to a 16-valence-electron metal carbonyl fragment.The formation of analytical pure and uniform branched and dendritic metallo carbosiloxanes is based on elemental analysis, and IR, ¹H, ¹³C{¹H}, ²⁹Si{¹H} and ³¹P{¹H} NMR spectroscopic studies. In addition, ESI-TOF mass spectrometric studies were carried out.     

Reactions of ruthenium benzylidenes with H2O to give benzaldehyde and (aqua)ruthenium complex

The second generation of Grubbs type catalyst, (PCy₃)(H₂IMes)Cl₂RuCHPh (1) undergoes the Cl replacement with CH₃CN to give cationic ruthenium carbene complexes, [(RCN)₃(H₂IMes)RuCHPh](OTf)₂ (2, R = CH₃ (a), Ph (b)) in the presence of AgOTf. The reaction of 2a with H₂O in the presence of CH₃CN gives (aqua)ruthenium complex, [Ru(H₂IMes)(NCCH₃) ₄(H₂O)](OTf)₂ (3) and benzaldehyde. Benzaldehyde is also observed in the reaction of 1 with H₂O. Plausible reaction pathways are suggested for the degradation of ruthenium benzylidenes to give benzaldehyde on the basis of the isotope labeling experiments.     

Preparation, crystal structure, and spectroscopic, chemical, and electrochemical properties of (2E,4E)-4-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1,3-butadiene compared with those of (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene

Wittig reaction of 3-[4-(dimethylamino)phenyl]propanal (5) with (3-guaiazulenylmethyl)triphenylphosphonium bromide (4) in ethanol containing NaOEt at 25 °C for 24 h under argon gives the title (2E,4E)-1,3-butadiene derivative 6E in 19% isolated yield. Spectroscopic properties, crystal structure, and electrochemical behavior of the obtained new extended π-electron system 6E, compared with those of the previously reported (E)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)ethylene (12), are documented. Furthermore, reaction of 6E with 1,1,2,2-tetracyanoethylene (TCNE) in benzene at 25 °C for 24 h under argon affords a new Diels-Alder adduct 8 in 59% isolated yield. Along with spectroscopic properties of the [π4+π2] cycloaddition product 8, the crystal structure, possessing a cis-3,6-substituted 1,1,2,2-tetracyano-4-cyclohexene unit, is shown. Moreover, reaction of 6E with (E)-1,2-dicyanoethylene (DCNE) under the same reaction conditions as the above gives no product; however, this reaction in p-xylene at reflux temperature (138 °C) for four days under argon affords a new Diels-Alder adduct 9 in 54% isolated yield. Although reaction of 6E with DCNE in toluene at reflux temperature (110 °C) for four days under argon provides 9 very slightly, reaction of 6E with dimethyl acetylenedicarboxylate (DMAD) in toluene at reflux temperature for two days under argon yields a new Diels-Alder adduct 10, in 58% isolated yield, which upon oxidation with MnO₂ in CH₂Cl₂ at 25 °C for 1 h gives 11, converting a (CH₃)₂N-4″ into CH₃NH-4″ group, in 37% isolated yield. The crystal structure of 11 supports the molecular structure 10 possessing a partial structure cis-3,6-substituted 1,2-dimethoxycarbonyl-1,4-cyclohexadiene. The title basic studies on the above are reported in detail.     

Oxime-substituted NCN-pincer palladium and platinum halide polymers through non-covalent hydrogen bonding (NCN = [C6H2(CH2NMe2)2-2,6])

The oxime-substituted NCN-pincer molecules HONCH-1-C₆H₃(CH₂NMe₂)₂-3,5 (2a) and HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 (2b) were accessible by treatment of the benzaldehydes H(O)C-4-C₆H₃(CH₂NMe₂)₂-3,5 (1a) and H(O)C-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 (1b) with an excess of hydroxylamine. In the solid state both compounds are forming polymers with intermolecular O-H?N connectivities between the Me₂NCH₂ substituents and the oxime entity of further molecules of 2a and 2b, respectively. Characteristic for 2a and 2b is a helically arrangement involving a crystallographic 2₁ screw axis of the HONCH-1-C₆H₃(CH₂NMe₂)₂-3,5 and HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6-Br-1 building blocks.The reaction of 2b with equimolar amounts of [Pd₂(dba)₃ · CHCl₃] (3) (dba = dibenzylidene acetone) or [Pt(tol)₂(SEt₂)]₂ (4) (tol = 4-tolyl) gave by an oxidative addition of the C-Br unit to M coordination polymers with a [(HONCH-4-C₆H₂(CH₂NMe₂)₂-2,6)MBr] repeating unit (5: M = Pd, 6: M = Pt). Complexes 5 and 6 are in the solid state linear hydrogen-bridged polymers with O-H?Br contacts between the oxime entities and the metal-bonded bromide.     

Substituted lithiumtrimethylsiloxysilanides LiSiRR′(OSiMe3) - Investigations of their synthesis, stability and reactivity

The reactions of the trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-h: R′ = Ph, 1a: R = H, 1b: R = Me, 1c: R = Et, 1d: R = ⁱPr, 1e: R = ^tBu, 1f: R = Ph, 1g: R = 2,4,6-Me₃C₆H₂ (Mes), 1h: R = 2,4,6-(Me₂CH)₃C₆H₂ (Tip); 1i: R = R′ = Mes) with lithium metal in tetrahydrofuran (THF) at −78 °C and in a mixture of THF/diethyl ether/n-pentane in a volume ratio 4:1:1 at −110 °C lead to mixtures of numerous compounds. Dependent on the substituents silyllithium derivatives (Me₃SiO)RR′SiLi (2b-i), Me₃SiO(RR′Si)₂Li (3a-g), Me₃SiRR′SiLi (4a-h), (LiO)RR′SiLi (12e, 12g-i), trisiloxanes (Me₃SiO)₂SiRR′ (5a-i) and trimethylsiloxydisilanes (6f^∗, 6h^∗, 6i^∗) are formed. All silyllithium compounds were trapped with Me₃SiCl or HMe₂SiCl resulting in the following products: (Me₃SiO)RR′SiSiMe₂R″ (6b-i: R″ = Me, 7c-i: R″ = H), Me₃SiO(RR′Si)₂SiMe₂R″ (8a-g: R″ = Me, 9a-g: R″ = H), Me₃SiRR′SiSiMe₂R″ (10a-h: R″ = Me, 11a-h: R″ = H) and (HMe₂SiO)RR′SiSiMe₂H (13e, 13g-i). The stability of trimethylsiloxysilyllithiums 2 depends on the substituents and on the temperature. (Me₃SiO)Mes₂SiLi (2i) is the most stable compound due to the high steric shielding of the silicon centre. The trimethylsiloxysilyllithiums 2a-g undergo partially self-condensation to afford the corresponding trimethylsiloxydisilanyllithiums Me₃SiO(RR′Si)₂Li (3a-g). (Me₃)Si-O bond cleavage was observed for 2e and 2g-i. The relatively stable trimethylsiloxysilyllithiums 2f, 2g and 2i react with n-butyllithium under nucleophilic butylation to give the n-butyl-substituted silyllithiums ⁿBuRR′SiLi (15g, 15f, 15i), which were trapped with Me₃SiCl. By reaction of 2g and 2i with 2,3-dimethylbuta-1,3-diene the corresponding 1,1-diarylsilacyclopentenes 17g and 17i are obtained.X-ray studies of 17g revealed a folded silacyclopentene ring with the silicon atom located 0.5 Å above the mean plane formed by the four carbon ring atoms.     

Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re2(CO)8(CH3CN)2]: Molecular structures of [Re2(CO)8(C14H10N4)] and [Re2(CO)8(C14H10N4)Re2(CO)8]

The reaction of the labile compound [Re₂(CO)₈(CH₃CN)₂] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re₂(CO)₈(C₁₄H₁₀N₄)] (1 and 2), and the complex [Re₂(CO)₈(C₁₄H₁₀N₄)Re₂(CO)₈] (3). In 1, the ligand is σ,σ′-N,N′-coordinated to a Re(CO)₃ fragment through pyridine and pyrazine to form a five-membered chelate ring. A seven-membered ring is obtained for isomer 2 by N-coordination of the 2-pyridyl groups while the pyrazine ring remains uncoordinated. For 2, isomers 2a and 2b are found in a dynamic equilibrium ratio [2a]/[2b]  =  7 in solution, detected by ¹H NMR (−50 °C, CD₃COCD₃), coalescence being observed above room temperature. The ligand in 3 behaves as an 8e-donor bridge bonding two Re(CO)₃ fragments through two (σ,σ′-N,N′) interactions. When the reaction was carried out in refluxing tetrahydrofuran, complex [Re₂(CO)₆(C₁₄H₁₀N₄)₂] (4) was obtained in addition to compounds 1-3. The dinuclear rhenium derivative 4 contains two units of the organic ligand σ,σ′-N,N′-coordinated in a chelate form to each rhenium core. The X-ray crystal structures for 1 and 3 are reported.     

Reactions of trimethylsiloxychlorosilanes with lithium metal - On the mechanism of the formation of trimethylsiloxysilyllithium compounds LiSiRR’(OSiMe3)

The reaction pathway for the formation of the trimethylsiloxysilyllithium compounds (Me₃SiO)RR′SiLi (2a: R = Et, 2b: R = ⁱPr, 2c: R = 2,4,6-Me₃C₆H₂ (Mes); 2a-c: R′ = Ph; 2d: R = R′ = Mes) starting from the conversion of the corresponding trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-d) in the presence of excess lithium in a mixture of THF/diethyl ether/n-pentane at −110 °C was investigated.The trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a: R = Et, 1b: R = ⁱPr, 1c: R = Mes) react with lithium to give initially the trimethylsiloxysilyllithium compounds (Me₃SiO)RPhSiLi (2a-c). These siloxysilyllithiums 2 couple partially with more trimethylsiloxychlorosilanes 1 to produce the siloxydisilanes (Me₃SiO)RPhSi-SiPhR(OSiMe₃) (Ia-c), and they undergo bimolecular self-condensation affording the trimethylsiloxydisilanyllithium compounds (Me₃SiO)RPhSi-RPhSiLi (3a-c). The siloxydisilanes I are cleaved by excess of lithium to give the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2). In the case of the two trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a: R = Et, 3b: R = ⁱPr) a reaction with more trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a, 1b) takes place under formation of siloxytrisilanes (Me₃SiO)RPhSi-RPhSi-SiPhR(OSiMe₃) (IIa: R = Et, IIb: R = ⁱPr) which are cleaved by lithium to yield the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2a, 2b) and the trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a, 3b). The dimesityl-trimethylsiloxy-silyllithium (Me₃SiO)Mes₂SiLi (2d) was obtained directly by reaction of the trimethylsiloxychlorosilane (Me₃SiO)Mes₂SiCl (1d) and lithium without formation of the siloxydisilane intermediate. Both silyllithium compounds 2 and 3 were trapped with HMe₂SiCl giving the products (Me₃SiO)RR′Si-SiMe₂H and (Me₃SiO)RPhSi-RPhSi-SiMe₂H.     

Chemically modified oximato complexes of titanium(IV) isopropoxide as new precursors for the sol-gel preparation of nano-sized titania: Crystal and molecular structure of [Ti{ONC10H16}4·2CH2Cl2]

Reactions of [Ti(OPrⁱ)₄] with various oximes, in anhydrous refluxing benzene yielded complexes of the type [Ti{OPrⁱ}_4−n{L}_n], where, n = 1-4 and LH = (CH₃)₂CNOH (1-4), C₉H₁₆CNOH (5-8) and C₉H₁₈CNOH (9-12). The compounds were characterized by elemental analyses, molecular weight measurements, FAB-mass, FT-IR and NMR (¹H, ¹³C{¹H}) spectral studies. The FAB-mass spectra of mono- (1), and di- (2), (6), (10) substituted products indicate their dimeric nature and that of tri- (3) and tetra- (4), (8) substituted derivatives suggest their monomeric nature. Crystal and molecular structure of [Ti{ONC₁₀H₁₆}₄·2CH₂Cl₂] (8A) suggests that the oximato ligands bind the metal in a dihapto η²-(N, O) manner, leading to the formation of an eight coordinated species. Thermogravimetric curves of (3), (6) and (10) exhibit multi-step decomposition with the formation of TiO₂ as the final product in each case, at 900 °C. Low temperature (∼600 °C) sol-gel transformations of (2), (3), (4), (6), (7) and (8) yielded nano-sized titania (a), (b), (c), (d), (e) and (f), respectively. Formation of anatase phase in all the titania samples was confirmed by powder XRD patterns, FT-IR and Raman spectroscopy. SEM images of (a), (b), (c), (d), (e) and (f) exhibit formation of nano-grains with agglomer like surface morphologies. Compositions of all the titania samples were investigated by EDX analyses. The absorption spectra of the two representative samples, (a) and (f) indicate an energy band gap of 3.17 eV and 3.75 eV, respectively.