Is a polymer semiconductor having a “perfect” regular structure desirable for organic thin film transistors?

This study utilized high temperature NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry to reveal that appreciable amounts of structural defects are present in the diketopyrrolopyrrole (DPP)–quaterthiophene copolymers (PDQT) synthesized by the Stille coupling polymerization with Pd(PPh₃)₂Cl₂, Pd₂(dba)₃/P(o-tol)₃, and Pd(PPh₃)₄ catalyst systems. It was proposed that these structural defects were produced via homocoupling side reactions of the C–Br bonds and the organostannane species. Model Stille coupling reactions further substantiated that the amount of structural defects are catalyst-dependent following the order of Pd(PPh₃)₂Cl₂ > Pd₂(dba)₃/P(o-tol)₃ > Pd(PPh₃)₄. To verify the structural assignments, “perfect” structurally regular PDQT polymers were prepared using Yamamoto coupling polymerization. When compared to the structurally regular polymers, the polymers containing defects exhibited notable redshifts in their absorption spectra. Surprisingly, the “perfect” structurally regular polymers showed poor molecular ordering in thin films and very low charge transport performance as channel semiconductors in organic thin film transistors (OTFTs). On the contrary, all the “defected” polymers exhibited much improved molecular ordering and significantly higher charge carrier mobility.     

Metallacyclic complexes with ortho-silylated triphenylphosphine ligands, LnOs(κ(Si,P)-SiMe2C6H4PPh2), derived from thermal reactions of the coordinatively unsaturated trimethylsilyl, methyl complex, Os(SiMe3)(Me)(CO)(PPh3)2

Reaction between Os(SiCl₃)Cl(CO)(PPh₃)₂ and five equivalents of MeLi produces a colourless intermediate, tentatively formulated as the lithium salt of the six-coordinate, dimethyl, trimethylsilyl-containing complex anion, Li[Os(SiMe₃)(Me)₂(CO)(PPh₃)₂]. Reaction of this material with ethanol releases methane and gives the red, coordinatively unsaturated methyl, trimethylsilyl-containing complex, Os(SiMe₃)(Me)(CO)(PPh₃)₂ (1). An alternative synthesis of 1 is to add one equivalent of MeLi to Os(SiMe₃)Cl(CO)(PPh₃)₂, which in turn is obtained by adding three equivalents of MeLi to Os(SiCl₃)Cl(CO)(PPh₃)₂. Treatment of 1 with p-tolyl lithium, again gives a colourless intermediate which may be Li[Os(SiMe₃)(Me)(p-tolyl)(CO)(PPh₃)₂], and reaction with ethanol gives the red complex, Os(SiMe₃)(p-tolyl)(CO)(PPh₃)₂ (3). Complexes 1 and 3 are readily carbonylated to Os(SiMe₃)(Me)(CO)₂(PPh₃)₂ (2) and Os(SiMe₃)(p-tolyl)(CO)₂(PPh₃)₂ (4), respectively. Heating Os(SiMe₃)Cl(CO)(PPh₃)₂ in molten triphenylphosphine results only in loss of the trimethylsilyl ligand and formation of the previously known complex containing an ortho-metallated triphenylphosphine ligand, Os(κ²(C,P)-C₆H₄PPh₂)Cl(CO)(PPh₃)₂. In contrast, heating the five-coordinate osmium-methyl complex, Os(SiMe₃)(Me)(CO)(PPh₃)₂ (1), in the presence of triphenylphosphine results mainly, not in tetramethylsilane elimination, but in ortho-silylation as well as ortho-metallation of different triphenylphosphine ligands giving, Os(κ²(Si,P)-SiMe₂C₆H₄PPh₂)(κ²(C,P)-C₆H₄PPh₂)(CO)(PPh₃) (5). A byproduct of this reaction is the non-silicon containing di-ortho-metallated complex, Os(κ²(C,P)-C₆H₄PPh₂)₂(CO)(PPh₃) (6). A similar reaction occurs when Os(SiMe₃)(Me)(CO)(PPh₃)₂ (1) is heated in the presence of tri(N-pyrrolyl)phosphine producing Os(κ²(Si,P)-SiMe₂C₆H₄PPh₂)(κ²(C,P)-C₆H₄PPh₂)(CO)[P(NC₄H₄)₃] (7) but a better synthesis of 7 is to treat 5 directly with tri(N-pyrrolyl)phosphine. Heating the six-coordinate complex, Os(SiMe₃)(Me)(CO)₂(PPh₃)₂ (2), gives two complexes both containing ortho-metallated triphenylphosphine, one with loss of the trimethylsilyl ligand, giving the known complex, Os(κ²(C,P)-C₆H₄PPh₂)H(CO)₂(PPh₃), and the other with retention of the trimethylsilyl ligand, giving Os(SiMe₃)(κ²(C,P)-C₆H₄PPh₂)(CO)₂(PPh₃) (8). Crystal structure determinations for 5, 6, 7 and 8 have been obtained.     

Group VIII metal phosphine complexes-catalyzed addition of disilanes to allenic compounds: Formation of new organosilicon compounds containing both vinylsilane and allylsilane units

Addition of chloromethyl- and methoxymethyldisilanes, X₃-_mMe_mSiSiMe_n-X₃-_n (X - Cl and OMe;m, n - 0-2), as well as hexamethyldisilane, to allene and 1, 2-butadiene in the presence of Pd(PPh₃)₄ catalyst gave regioselectively new functionalized organosilicon compounds, 2, 3-bis(organosilyl)prop-1-enes and 2, 3-bis(organosilyl)but-1-enes, respectively. Other group VIII metal-phospine complexes also affected the reaction, but results were found to be less satisfactory. Also, the reaction of any unsymmetrical disilane with an allenic compound gave only a single product; e.g., the addition of chloropentamethyldisilane to 1, 2-butadiene in the presence of Pd(PPh₃)₄ gave CH₂-C(SiMe₃)CH(SiMe₂Cl)Me in 93% yield.     

Alkyl- und arylkomplexe des iridiums und rhodiums: XXI. Chelatphosphan-stabilisiertepentakoordinierte organoiridium(I)-komplexe Ir(R)(CO)( chel-P33)

Novel five-coordinate organoiridium(I) complexes of the type Ir(R)(CO)(chel-P₃) (chel-P₃=PhP(CH₂CH₂CH₂PPh₂)₂: R = CH₂CMe₃, CH₂SiMe₃; chel-P₃ = MeP-(CH₂CH₂CH₂PPh₂)₂: R = CH₂SiMe₃; chel-P₃PhP(CH₂CH₂PPh₂)₂; R = CH₂SiMe₃, 4-MeC₆H₄) have been prepared from Ir(R)(CO)(PPh₃)₂ and the respective triphosphine. According to ³¹P NMR, these compounds are stereochemically rigid at normal temperatures. The reaction of Rh(R)(CO)(PPh₃)₂, where R = CH₂CMe₃ or 2-MeC₆H₄, with PhP(CH₂CH₂CH₂PPh₂)₂ yielded the four-coordinate derivatives Rh(CH₂CMe₃)[PhP(CH₂CH₂CH₂PPh₂)₂] and Rh(2-MeC₆H₄)[PhP(CH₂CH₂CH₂PPh₂)₂]), which arealready known from the literature.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)methanide Ligands

A study of the coordination chemistry of different bis(diphenylphosphino)methanide ligands [Ph₂PC(X)PPh₂] (X=H, SiMe₃) with Group 4 metallocenes is presented. The paramagnetic complexes [Cp₂Ti{κ²‐P,P‐Ph₂PC(X)PPh₂}] (X=H ( 3 a ), X=SiMe₃ ( 3 b )) have been prepared by the reactions of [(Cp₂TiCl)₂] with [Li{C(X)PPh₂}₂(thf)₃]. Complex 3 b could also be synthesized by reaction of the known titanocene alkyne complex [Cp₂Ti(η²‐Me₃SiC₂SiMe₃)] with Ph₂PC(H)(SiMe₃)PPh₂ ( 2 b ). The heterometallacyclic complex [Cp₂Zr(H){κ²‐P,P‐Ph₂PC(H)PPh₂}] ( 4 aH ) has been prepared by reaction of the Schwartz reagent with [Li{C(H)PPh₂}₂(thf)₃]. Reactions of [Cp₂HfCl₂] with [Li{C(X)PPh₂}₂(thf)₃] gave the highly strained corresponding metallacycles [Cp₂M(Cl){κ²‐P,P‐Ph₂PC(X)PPh₂}] ( 5 aCl and 5 bCl ) in very good yields. Complexes 3 a , 4 aH , and 5 aCl have been characterized by X‐ray crystallography. Complex 3 a has also been characterized by EPR spectroscopy. The structure and bonding of the complexes has been investigated by DFT analysis. Reactions of complexes 4 aH , 5 aCl , and 5 bCl did not give the corresponding more unsaturated heterometallacyclobuta‐2,3‐dienes.     

Synthesis of [TpRu(CO)(PPh3)]2(μ-CHCHCHCHC6H4CHCHCHCH) from Wittig reactions

Treatment of [Ru(CHCHCH₂PPh₃)X(CO)(PPh₃)₂]⁺ (X=Cl, Br) with KTp (Tp=hydridotris(pyrazolyl)borate) and NaBPh₄ produced [TpRu(CHCHCH₂PPh₃)(CO)(PPh₃)]BPh₄. Reaction of RuHCl(CO)(PPh₃)₃ with HCCCH(OEt)₂ produced Ru(CHCHCH(OEt)₂)Cl(CO)(PPh₃)₂, which reacted with KTp to give TpRu(CHCHCHO)(CO)(PPh₃). Treatment of [TpRu(CHCHCH₂PPh₃)(CO)(PPh₃)]BPh₄ with NaN(SiMe₃)₂ and benzaldehyde produced TpRu(CHCHCHCHPh)(CO)(PPh₃). The later complex was also produced when TpRu(CHCHCHO)(CO)(PPh₃) was treated with PhCH₂PPh₃Cl/NaN(SiMe₃)₂. The bimetallic complex [TpRu(CO)(PPh₃)]₂(μ-CHCHCHCHC₆H₄CHCHCHCH) was obtained from the reaction of [TpRu(CHCHCH₂PPh₃)(CO)(PPh₃)]BPh₄ with NaN(SiMe₃)₂ and terephthaldicarboxaldehyde.     

The preparation and catalytic hydroformylation activity of some halocarbonylrhodium(I) complexes containing phosphinoalkylorganosilicon ligands

The synthesis and properties of a series of trans-halocarbonylrhodium(I) complexes containing the phosphinoalkylorganosilicon ligands Me₃SiCH₂PPh₂, Me₃Si(CH₂)₃PPh₂, and PPh₂CH₂(Me)$\text{Si(OSiMe}{}_2\text{)}{}_3\text{O}$ have been investigated. The complexes could be prepared by an exchange reaction involving RhCl(CO)(PPh₃)₂ and the organosilicon ligands or in better yields by the reaction of Rh₂Cl₂(CO)₄ with the ligands. Iodorhodium derivatives were obtained as the exclusive products in the latter reaction if a small amount of LiI was present. The catalytic activity of RhCl(CO)(PPh₂CH₂SiMe₃)₂ was similar to that of RhCl(CO)(PPh₃)₂ in the hydroformylation of hex-1-ene at 100°C and 1000 psi pressure of H₂/CO. The catalytic properties of the iodo derivatives RhI(CO)L₂ [L = Me₃SiCH₂PPh₂, Me₃Si(CH₂)₃PPh₂, and PPh₂CH₂(Me)$\text{Si(OSiMe}{}_2\text{)}{}_3\text{O}$] varied considerably, with RhI(CO)(PPh₂CH₂SiMe₃)₂ producing an unexpectedly low linear/branched aldehyde product ratio.     

Diphenylcarbene rhodium complexes: of the halfsandwich type with (η5-C5H4SiMe3)Rh as a molecular unit

The square-planar rhodium(I) complexes trans-[RhCl(=CPh₂)(L)₂] (L = SbiPr₃, PiPr₃, PPh₃) react with LiC₅H₄SiMe₃ to give the halfsandwich type compounds [(η⁵-C₅H₄SiMe₃)Rh(=CPh₂)(L)] 7–9 in good to excellent yields. While the phosphine complexes 8 and 9 are rather inert toward Lewis bases, the stibine derivative 7 reacts with CO, CNtBu and PMe₃ to afford the corresponding substitution products [(η⁵-C₅H₄SiMe₃)Rh(=CPh₂)(L′] 10–12. In contrast, the reaction of 7 with C₂H₄ leads to the displacement of the carbene ligand and to the formation of the ethene complex [(η⁵-C₅H₄SiMe₃)Rh(C₂H₄)(SbiPr₃)] 14 together with the C−C coupling product Ph₂C=CHCH₃13. Upon treatment of 9 (L = PPh₃) with an equimolar amount of HCl, the chloro(hydrido)rhodium(III) compound [{η⁵-C₅H₃)(CHPH₂)(SiMe₃)}RhHCl(PPh₃)] 15 is formed. With an excess of HCl, a mixture of two products is obtained, one of which, with the composition [η⁵-C₅H₄)CHPh₂)RhCl₂(PPH₃)] 17 has been independently prepared from η⁵-C₅H₅)Rh(=CPh₂)(PPh₃] 18 and 2 equiv of HCl.     

Phosphine-mediated diverse reactivity of γ-substituted allenoates with aldehydes: syntheses of highly functionalized chromans and (E,E)-1,3-dienes

As an extension of our previous studies, the phosphine-mediated diverse reactivity of γ-substituted allenoates with aldehydes has been further investigated. Under the catalysis of tris(p-chlorophenyl)phosphine (20 mol %), ethyl 2,3-pentadienoate, namely ethyl γ-methyl allenoate, readily undergoes a formal [4+2] annulation with dual-functional salicylaldehydes, giving highly functionalized chromans in 47-97% yields. This transformation represents a novel reactivity pattern of electron-deficient allenes with aldehydes. Conversely, when the γ substituent in the allenoate changes from methyl to benzyl or the employed phosphine from weakly nucleophilic triarylphosphine to strongly trialkylphosphine, the phosphine-mediated reactivity of γ-substituted allenoates with aldehydes will be steered to a stoichiometric olefination reaction, leading to the highly stereoselective formation of (E,E)-1,3-dienes. Thus, under the mediation of equivalent PPh₃, ethyl γ-benzyl allenoate readily condenses with salicylaldehydes, affording (E,E)-1,3-dienes in 34-84% yields; with strongly nucleophilic 1,3,5-triaza-7-phosphaadamantane (PTA) used instead of PPh₃, ethyl γ-methyl allenoate also gives the corresponding olefination products in 32-73% yields with reactive aromatic aldehydes. On the basis of our previous studies and current work, these chemical transformations of γ-substituted allenoates with aldehydes, as well as their diverse reactivity, have been mechanistically rationalized.     

The Role of the “Ligand Periphery” in the Coordination of Tripodal Triamidostannates(II) to Iridium: Simple Ligation vs. Cyclometallation

Reaction of the triamidostannates(II) MeSi{SiMe₂N(3,5‐xyl)}₃SnLi(OEt₂) ( 2a ) and MeSi{SiMe₂N(p‐tol)}₃SnLi(OEt₂) ( 2b ) with [IrCl(CO)(PPh₃)₂] gave the Ir^I‐Sn complex [MeSi{SiMe₂N(3,5‐xyl)}₃SnIr(PPh₃)₂(CO)] ( 3a ) for the former. In contrast, for the tolyl stannate CH‐activation occurred to give the Ir^III compound [MeSi{SiMe₂N(p‐tol)}₂{SiMe₂N(2‐C₆H₃‐4‐CH₃)}SnIr(H)(PPh₃)₂(CO)] ( 3b ). The latter is thus avoided by introduction of suitably placed substituents in the peripheral aryl groups of the triamidostannate ligand.     

Silyl‐Phosphino‐Carbene Complexes of Uranium(IV)

Unprecedented silyl‐phosphino‐carbene complexes of uranium(IV) are presented, where before all covalent actinide–carbon double bonds were stabilised by phosphorus(V) substituents or restricted to matrix isolation experiments. Conversion of [U(BIPM^TMS)(Cl)(μ‐Cl)₂Li(THF)₂] ( 1 , BIPM^TMS=C(PPh₂NSiMe₃)₂) into [U(BIPM^TMS)(Cl){CH(Ph)(SiMe₃)}] ( 2 ), and addition of [Li{CH(SiMe₃)(PPh₂)}(THF)]/Me₂NCH₂CH₂NMe₂ (TMEDA) gave [U{C(SiMe₃)(PPh₂)}(BIPM^TMS)(μ‐Cl)Li(TMEDA)(μ‐TMEDA)_0.5]₂ ( 3 ) by α‐hydrogen abstraction. Addition of 2,2,2‐cryptand or two equivalents of 4‐N,N‐dimethylaminopyridine (DMAP) to 3 gave [U{C(SiMe₃)(PPh₂)}(BIPM^TMS)(Cl)][Li(2,2,2‐cryptand)] ( 4 ) or [U{C(SiMe₃)(PPh₂)}(BIPM^TMS)(DMAP)₂] ( 5 ). The characterisation data for 3 – 5 suggest that whilst there is evidence for 3‐centre P?C?U π‐bonding character, the U=C double bond component is dominant in each case. These U=C bonds are the closest to a true uranium alkylidene yet outside of matrix isolation experiments.     

Palladium-catalyzed Suzuki-Miyaura couplings of potassium aryl trifluoroborates with 4-tosyloxycoumarins or 4-tosyloxyquinolin-2(1H)-one

Pd(PPh₃)₄ catalyzed Suzuki-Miyaura cross-coupling reactions of 4-tosyloxycoumarins or 4-tosyloxyquinolin-2(1H)-one with various potassium aryl trifluoroborates afforded the corresponding 4-substituted coumarins or 4-substituted quinolin-2(1H)-ones in good to excellent yield.     

Synthesis and structural characterization of acetatobis(triphenylphosphine)dicarbonylrhenium(I). new car☐ylato derivatives of rhenium(I)

Acetatobis(triphenylphosphine)dicarbonylrhenium (I), (PPh₃)₂(CO)₂Re(O₂CCH₃), has been prepared in a novel way by treating (PPh₃)₂(CO)₂Re(NHCOR) (R = C₆H₅, p-MeC₆H₄) with triethylamine and water in the presence of air. Oxidation of the ethyl group of the tertiary amine is presumably involved in the formation of the acetate ligand. Three-dimensional single-crystal X-ray diffraction analysis shows that the complex is octahedral with the phosphines in trans positions and the acetate ion acting as a chelating ligand. The complex crystallizes in theP2₁/c space group with cell dimensions a = 17.63(2), b = 9.72(1), c = 20.95(2)Å, β = 104°38'(6'), Z = 4. The mean values of bond lengths observed are Re-P 2.415, Re-O 2.21 and Re-(CO) 1.85Å. The same acetate derivative and a series of car?ylato complexes (PPh₃)₂(CO)₂Re(O₂CR') have been obtained from reactions of Re(CO)₂(PPh₃)₃H with car?ylic acids R'COOH (R' = H, CH₃, CH₂Cl, CH₂CH₃, C₆H₅). When trifluoroacetic acid is used, a product of formula (PPh₃)₂(CO)₃Re(OC(O)CF₃) is isolated. The action of neutral ligands L on some of these products gave rise to derivatives of formula (PPh₃)₂(CO)₂(L)Re(OC(O)R') (L = CO, R' = H, CH₃, C₆H₅; L = pMeC₆H₄NC, R' = CH₃), having monodentate car?ylato moieties.     

Single metal four-electron reduction by U(ii) and masked “U(ii)” compounds

The redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)]₂[{((Me₃Si)₂N)₃U}₂(μ-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(η²-C₂Ph₂){N(SiMe₃)₂}₃], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)₂{N(SiMe₃)₂}₃], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe₃)₂}₃], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N₂Ph₂){N(SiMe₃)₂}₃], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a “clear-cut” single metal four-electron transfer in f-element chemistry.

Both a masked and the actual complex [U(ii){N(SiMe₃)₂}₃]⁺ effect the reduction of azobenzene to yield a U(vi) bis-imido species providing the first example of a “clear-cut” metal centred four-electron reduction in f-element chemistry.     

Synthesis of silylene–propenylene oligomers via catalytic polycondensation of diallyldiorganosilanes

Acyclic diene polycondensation (ADP) of diallyldiorganosilanes (CH₂CHCH₂)₂SiR₂ (where R = Me, Ph), in the presence of various ruthenium and rhodium complexes, led predominantly to linear silylene–propenylene oligomers. Ruthenium catalysts (e.g. RuCl₂(PPh₃)₃, RuHCl(CO)(PPh₃)₃, and RuCl(SiMe₃)(CO)(PPh₃)₂) were found to be more efficient than the rhodium ones. The reaction proceeds via preliminary catalytic isomerization of allylsilane to silyl-1-propenes followed by their oligococondensation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3299–3304, 1997     

PPh4{MoNCI3[N(SiMe3)2]}, ein Nitrido-Amido-Komplex von MoIybdän(VI)

Inhaltsübersicht. PPh₄{MoNCl₃[N(SiMe₃)₂]} entsteht aus PPh₄[MoNCl₄] und N,N,N′-Tris-(trimethylsilyl)benzamidin in siedendem Dichlormethan in Form bernsteinfarbener Kristalle, die wir IR-spektroskopisch und durch eine röntgenographische Strukturanalyse charakterisiert haben. Raumgruppe P2₁/n, Z = 4, R = 4,3% für 5168 unabhängige beobachtete Reflexe. Die Gitterkonstanten betragen für ?65°C: A = 918,9; b = 2850,5; c = 1353,9 pm; β = 107,51°. Die Verbindung besteht aus PPh₄⁺-Ionen und Anionen [MoNCl₃[N(SiMe₃)₂]}^–, in denen das Molybdänatom verzerrt tetragonal-pyramidal von dem Nitridoliganden in Apical-Position (r MoN = 165 pm), von drei Chloratomen und von dem N-Atom des Bis(trimethylsilyl)amido-Liganden (r MoN = 194 pm) umgeben ist. Das N-Atom des Amido-Liganden besitzt eine planare Umgebung. PPh₄{MoNCl₃[N(SiMe₃)₂]}, a Nitrido Amido Complex of Molybdenum (VI) PPh₄{MoNCl₃[N(SiMe₃)₂}] has been prepared by the reaction of PPh₄[MoNCl₄] with N,N,N′-Tris(trimethylsilyl)benzamidine in boiling dichloromethane, forming amber coloured crystals, which were characterized by their IR spectrum as well as by an X-ray structure determination. Space group P2₁/n, Z = 4, R = 0.043 for 5168 observed independent reflexions. The lattice dimensions are at ?65°C: A = 918.9; b = 2850.5; c = 1353.9 pm; β = 107.51°. The compound consists of PPh₄⁺ ions and anions {MoNCl₃[N(SiMe₃)₂]}^– in which the complex molybdenum anion forms a distorted tetragonal pyramid with the nitrido ligand (r MoN 165 pm) in the apical position and the chlorine atoms along with the nitrogen atom of the amido ligand (r MoN 194 pm) in the basical positions. The N atom of the amido ligand has a planar geometry.     

First examples of η1-ligated halogenophosphaalkenes. Crystal structures of trans-[RhCl(PPh3)2{η1-PXC(SiMe3)2}] (X = F or Cl)

Syntheses and single crystal X-ray diffraction studies of the η¹-halogenophosphaalkene complexes trans-[RhCl(PPh₃)₂{η¹-PXC(SiMe₃)₂}] (X = F, Cl) are reported.     

An evaluation of silica-supported catalysts for the reaction between ethanol and polymethylhydrogensiloxane

Catalysis of the reaction between Me₃SiO[Si(H)Me)O]_nSiMe₃ (n ≈ 50) and ethanol by silica-supported rhodium and iridium catalysts has been investigated. Donor groups in the anchored ligands were PPh₂, S^?, or C₅H₄^?. The rhodium-PPh₂ system showed marked inhibition by dihydrogen. The supported iridium catalysts all showed high activity which declined rapidly during successive cycles of re-use, but the iridium-PPh₂ catalyst was the least affected. In every case, the separated liquid products showed activity as homogeneous catalysts, indicating that leaching of the metal from the support was occurring. That ligand was also being leached was shown by labelling with tritium. The results demonstrate the necessity to test supported catalysts through more than one cycle.     

Synthesis of C3-substituted enantiopure 2-(p-tolylsulfinyl)-furans: the sulfoxide group as a chiral inductor for furan dienes as precursors of a wide variety of chiral intermediates

(−)-(1R,2S,5R)-Menthyl (S_S)-p-toluenesulfinate and its enantiomer are a common source for a chiral sulfoxide group in organic synthesis, by means of nucleophilic substitution. The replacement of the menthyloxy group, with complete inversion of configuration at the sulfur center of the chiral sulfoxide, allows the inclusion of this organic function into numerous substrates, with defined stereochemistry and high enantiomeric purity. Nine C3-substituted, enantiomerically pure, 2-sulfinylfurans were prepared by this synthetic methodology with moderate to high yields. These enantiopure C3-substituted 2-sulfinylfurans can be used as chiral dienes for [4+3] cycloaddition reactions and in other chemical transformations, in which π-facial selectivity should be induced in order to obtain enantioselective reactions.     

Transition-metal complexes of two valence tautomers of a bulky phenoxide, 2,6-Bu-t2-4-MeC6H2O− (ArO−); preparation and crystal and molecular structure of a phenoxytitanium(III) and a cyclohexadienonylrhodium(I) complex, [Ti(η-C5H5)2 OAr] and [Rh(ArO-η5)(PPh3)2]

The 2,6-di-t-butyl-4-methylphenoxo ligand (ArO^?) is ambidentate, giving rise to the O-bonded 15-electron d¹ [Ti(η-C₅H₅)₂OAr] and the η⁵ -[C(2)-C(6)]-bonded 18-electron d⁸ complex [Rh(ArO-η⁵)(PPh₃)₂], obtained from [{Ti(η-C₅H₅)₂Cl}₂]-LiO Ar and [Rh{N(SiMe₃)₂}(PPh₃)₂]-ArOH, respectively; the average TiC(η) distance is 2.362(10) Å, TiO 1.892(2) Å, and O:C(of Ar) 1.352(3) Å, and TiOC 142.3(2)°; in the Rh^I complex, C(2)C(6) are coplanar (with CC(av.) 1.38(2) Å). C(1)O 1.28 Å, and Rh to C(2) C(6) bond lengthsare in the range 2.19–2.65 Å.