Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.     

Synthesis, characterization and crystal structures of cyclometallated palladium (II) compounds containing difunctional ligands with [P,P], [As,As], [N,N], [P,As], [P,N] and [P,O] donor atoms

Treatment of the chloro-bridged dinuclear complex [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}(μ-Cl)]₂ (1) with homobidentate [P,P], [As,As], [N,N], and heterobidentate [P,As], [P,N] ligands in a 1:1 molar ratio gave the dinuclear complexes [{Pd[3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N](Cl)}₂{μ-L}] (L = Ph₂PC₄H₆(NH)CH₂PPh₂ (2); Ph₂As(CH₂)₂AsPh₂ (3); 1,3-(NH₂CH₂)₂C₆H₄ (4); Ph₂P(CH₂)₂AsPh₂ (5); Ph₂P(CH₂)₂NH₂ (6)), with the bidentate ligands bridging the two cyclometallated fragments.The reaction with the homobidentate ligands in a 1:2 molar ratio in the presence of NaClO₄ afforded the mononuclear compounds [[Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-P,P}][ClO₄] (L = Ph₂PC₄H₆(NH)CH₂PPh₂ (7); (o-Tol)₂P(CH₂)₂P(o-Tol)₂ (8)), [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{Ph₂As(CH₂)₂AsPh₂-As,As}][ClO₄] (9) and [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-N,N}][ClO₄] (L = NH₂(CH₂)₃NH₂ (10); NH₂(C₆H₈)CH₂(C₆H₈)NH₂ (11); 1,3-(NH₂CH₂)₂C₆H₄ (12); 1,3-(NH₂)₂C₅H₃N (13); NH₂(C₆H₄)O(C₆H₄)NH₂ (14); NMe₂(CH₂)₂NMe₂ (15)), in which the chloro ligands are absent and the bidentate ligands are chelated to the palladium atom.Reaction of 1 with Ph₂P(CH₂)₂AsPh₂ in 1:2 molar ratio in acetone in the presence of NH₄PF₆ afforded the analogous mononuclear compound [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{Ph₂P(CH₂)₂AsPh₂-P,As}][PF₆] (16); whereas reaction with Ph₂P(CH₂)₃NH₂ gave [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{Ph₂P(CH₂)₃N(CMe₂)-P,N}][PF₆] (17), derived from intermolecular condensation between the aminophosphine and acetone. Condensation of the NH₂ group was precluded by change of solvent, using dichloromethane.Iminophoshines also reacted with 1 in 1:2 molar ratio in acetone to give a new series of mononuclear cyclometallated complexes: [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-P,N}][ClO₄] (L = Ph₂PC₆H₄C(H)NCy (20); Ph₂PC₆H₄C(H)NC(CH₃)₃ (21); Ph₂PC₆H₄C(H)NNMe₂ (22); Ph₂PC₆H₄C(H)NNHMe (23); Ph₂PC₆H₄C(H)NNHPh (24)). Analogous complexes with a stable P,O-chelate were obtained using bidentate [P,O] donor ligands: [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-P,O}][Cl] (L = 2-(Ph₂P)C₆H₄CHO (25); Ph₂PN(Me)C(O)Me (26)).The crystal structures of compounds 1, 5, 15, 16, 18, 20 have been determined by X-ray crystallography.     

Rhodium(I) complexes with κP coordinated ω-phosphinofunctionalized alkyl phenyl sulfide, sulfoxide and sulfone ligands and their reactions with sodium bis(trimethylsilyl)amide and Ag[BF4]

Reactions of ω-diphenylphosphinofunctionalized alkyl phenyl sulfides Ph₂P(CH₂)_nSPh (n = 1, 1a; 2, 2a; 3, 3a), sulfoxides Ph₂P(CH₂)_nS(O)Ph (n = 1, 1b; 2, 2b; 3, 3b) and sulfones Ph₂P(CH₂)_nS(O)₂Ph (n = 1, 1c; 2, 2c; 3, 3c) with dinuclear chlorido bridged rhodium(I) complexes [(RhL₂)₂(μ-Cl)₂] (L₂ = cycloocta-1.5-diene, cod, 4; bis(diphenylphosphino)ethane, dppe, 5) afforded mononuclear Rh(I) complexes of the type [RhCl{Ph₂P(CH₂)_nS(O)_xPh-κP}(cod)]¹ (n/x = 1/0, 6a; 1/1, 6b; 1/2, 6c; 2/0, 8a; 2/1, 8b; 2/2, 8c; 3/0, 10a; 3/1, 10b; 3/2, 10c) and [RhCl{Ph₂P(CH₂)_nS(O)_xPh-κP}(dppe)] (n/x = 1/0, 7a; 1/1, 7b; 1/2, 7c; 2/0, 9a; 2/1, 9b; 2/2, 9c; 3/0, 11a; 3/1, 11b; 3/2, 11c) having the P^S(O)_x ligands κP coordinated. Addition of Ag[BF₄] to complexes 6-11 in CH₂Cl₂ led with precipitation of AgCl to cationic rhodium complexes of the type [Rh{Ph₂P(CH₂)_nS(O)_xPh-κP,κS/O}L₂][BF₄] having bound the P^S(O)_x ligands bidentately in a κP,κS (13a-18a, 15b-18b) or a κP,κO (13b, 14b, 13c-18c) coordination mode. Unexpectedly, the addition of Ag[BF₄] to 6a in THF afforded the trinuclear cationic rhodium(I) complex [Rh₃(μ-Cl)(μ-Ph₂PCH₂SPh-κP:κS)₄][BF₄]₂·4THF (12·4THF) with a four-membered Rh₃Cl ring as basic framework. Addition of sodium bis(trimethylsilyl)amide to complexes 6-11 led to a selective deprotonation of the carbon atom neighbored to the S(O)_x group (α-C) yielding three different types of organorhodium complexes: a) Organorhodium intramolecular coordination compounds of the type [Rh{CH{S(O)_xPh}CH₂CH₂PPh₂-κC,κP}L₂] (22a-c, 23a-c), b) zwitterionic complexes [Rh{Ph₂PCHS(O)_xPh-κP,κS/O}L₂] having κP,κS (21a, 21b) and κP,κO (20b/c, 21c) coordinated anionic [Ph₂PCHS(O)_xPh] ligands, and c) the dinuclear rhodium(I) complex [{Rh{μ-CH(SPh)PPh₂-κC:κP}(cod)}₂] (19). All complexes were fully characterized spectroscopically and complexes 15b, 15c, 12·4THF and 19·THF additionally by X-ray diffraction analysis. DFT calculations of zwitterionic complexes gave insight into the coordination mode of the [Ph₂PCHS(O)Ph] ligand (κP,κS versus κP,κO).     

New developments in the studies of the reactivity of cyclometallated palladium(II) compounds with homo- ([P,P],[As,As]) and heterobidentate ([P,N],[P,O]) ligands

Treatment of the chloro-bridged dinuclear compounds [{Pd[RC₆H₃C(H)NCy-C2,N]}(μ-Cl)]₂ (R = 4-(COH), 1; R = 5-(COH), 2) with bidentate phosphorus or arsenic diphosphines or diarsine ligands in 1:1 molar ratio gave the dinuclear complexes [{Pd[RC₆H₃C(H)NCy-C2,N](Cl)}₂{μ-(o-Tol)₂P(CH₂)₂P(o-Tol)₂}] (R = 4-(COH), 3; R = 5-(COH), 4), [{Pd[RC₆H₃C(H)NCy-C2,N](Cl)}₂{μ-Ph₂PC₄H₂(NH)CH₂PPh₂}] (R = 4-(COH), 5; R = 5-(COH), 6) and [{Pd[RC₆H₃C(H)NCy-C2,N](Cl)}₂{μ-Ph₂As(CH₂)₂AsPh₂}] (R = 4-(COH), 7; R = 5-(COH), 8) with the homobidentate [P,P] and [As,As] ligands in a bridging mode. Treatment of 1 and 2 with the aminophosphine Ph₂P(CH₂)₂NH₂ yields the dinuclear complexes [{Pd[RC₆H₃C(H)NCy-C2,N](Cl)}₂{μ-Ph₂P(CH₂)₂NH₂}] (R = 4-(COH), 9; R = 5-(COH), 10). The analogous reactions carried out in a 1:2 molar ratio, in the presence of NH₄PF₆ or NaClO₄, gave the mononuclear compounds [Pd{RC₆H₃C(H)NCy-C2,N}{(o-Tol)₂P(CH₂)₂P(o-Tol)₂-P,P}][PF₆] (R = 4-(COH), 11; R = 5-(COH), 12), [Pd{RC₆H₃C(H)NCy-C2,N}{Ph₂PC₄H₂(NH)CH₂PPh₂-P,P}][ClO₄] (R = 4-(COH), 13; R = 5-(COH), 14) and [Pd{RC₆H₃C(H)NCy-C2,N}{Ph₂As(CH₂)₂AsPh₂-As,As}][ClO₄](R = 4-(COH), 15; R = 5-(COH), 16), with the [P,P] and [As,As] ligands chelated to the palladium atom.Treatment of 2 with Ph₂P(CH₂)₃NH₂ in a 1:2 molar ratio in acetone in the presence of NH₄PF₆ afforded the mononuclear compound [Pd{5-(COH)C₆H₃C(H)NCy-C2,N}{Ph₂P(CH₂)₃N(Me₂)-P,N}][PF₆], 17, via intermolecular condensation between the aminophosphine and the solvent. Condensation was precluded using toluene as solvent to give [Pd{RC₆H₃C(H)NCy-C2,N}{Ph₂P(CH₂)_nNH₂-P,N}][PF₆], (n = 3, R = 5-(COH), 18; n = 2, R = 4-(COH), 19; n = 2, R = 5-(COH), 20). Treatment of 1 and 2 with Ph₂P(C₆H₄)CHO in a 1:2 molar ratio in the presence of NH₄PF₆ gave the mononuclear complexes [Pd{RC₆H₃C(H)NCy-C2,N}{2-(Ph₂P)C₆H₄CHO-P,O}][PF₆] (R = 4-(COH), 21; R = 5-(COH), 22) with the palladium atom bonded to four different atoms (C, N, P, O) and a chelating [P,O] ligand. The crystal structures of compounds 7, 11, 15 and 21 have been determined by X-ray crystallography.     

Synthesis and characterization of n=5, 6 members of the La4Srn−4TinO3n+2 series with layered structure based upon perovskite

Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La₄Sr_n−4Ti_nO_3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)₅Ti₅O₁₇] and [(La,Sr)₆Ti₆O₂₀] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]_p. The n=5 member is similar to the previously reported n=5 member of other A_nB_nO_3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this A_nB_nO_3n+2 series.     

Preparation, spectroscopic properties of 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) lanthanide complexes and the supramolecular structure of [Nd2L2(NO3)6(H2O)2]·H2O

The reaction of lanthanide nitrate with 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) yields six novel Ln(III) complexes ([Ln₂L₂(NO₃)₆(H₂O)₂]·H₂O) which are characterized by elemental analysis, thermogravimetric analysis (TGA), conductivity measurements, IR, electronic and ¹H NMR spectroscopies. A new quinoxalinedione-based ligand is used as antenna ligand to sensitize the emission of lanthanide cations. The lowest triplet state energy level of the ligand in the nitrate complex matches better to the resonance level of Eu(III) and Sm(III) than Tb(III) and Dy(III) ion. The f-f fluorescence is induced in the Eu³⁺ and Sm³⁺ complexes by exciting into the π-π* absorptions of the ligand in the UV. Furthermore, the crystal structures of a novel binuclear complex [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O has been determined by single-crystal X-ray diffraction. The binuclear [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O complex units are linked by the intermolecular hydrogen bonds and π-π interactions to form a two-dimensional (2-D) layer supramolecule.     

Alkyl and dialkylammonium tetrafluoroborate catalyzed cis-trans isomerization of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane

Alkyl and dialkylammonium tetrafluoroborate promoted cis-trans isomerization of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane (1) in DMSO-d₆ were studied. The isomerization equilibrium constant K are within the range of 3.74-3.30 from 22 to 47 °C. Thermodynamic parameters of ΔH° and ΔS° for the isomerization were −0.95 kcal/mol and −0.59 cal/mol-K respectively. The isomerization rate is first order in [cis-1] and second order in [R_nNH_4−nBF₄]. Both components of R_nNH_4−n⁺ and BF₄⁻ are essential for the catalytic cis-trans isomerization. The catalytic strength follows the decreasing order of ⁺H₃N(CH₂)₆NH₃⁺>n-C₈H₁₇NH₃⁺>n-C₁₆H₃₃NH₃⁺>Me₃CNH₃⁺>PhCH₂NH₃⁺>Et₂NH₂⁺?Ph₂CHNH₃⁺, Et₃NH⁺. Inversion region was observed in the plot of ln(k_f/T) versus (1/T) with the ceiling located at around 38 °C. The positive activation enthalpy of 9 kcal/mol was estimated at 22-32 °C. The activation enthalpy turns to be slightly negative at T>38 °C.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

Synthesis, characterization and intercalation property of layered zirconium benzylamino-N,N-dimethylphosphonate phosphate materials

Layered zirconium benzylamino-N,N-dimethylphosphonate phosphate (ZBMPA) was prepared by the reaction of zirconyl chloride with benzylamino-N,N-dimethylphosphonic acid (H₂BMPA) and phosphoric acid in the presence of hydrofluoric acid. The intercalation of n-alkylamines (n-butylamine, n-heptylamine and n-decylamine) into ZBMPA was primarily investigated at room temperature. These materials were characterized by elemental analysis, ICP, XRD, SEM, FT-IR, Raman spectra, TG and DSC. The composition of ZBMPA is Zr(HPO₄)(C₆H₅CH₂N(CH₂PO₃)₂)_0.5 · 2.0H₂O. The interlayer distance of ZBMPA, n-butylamine, n-heptylamine and n-decylamine intercalation compounds is 2.03, 2.58, 2.52 and 3.17 nm, respectively. ZBMPA and the n-alkylamine intercalation compounds are different in the morphology and vibration spectra. Thermogravimetries of all materials obtained reveal three step mass losses at temperatures of up to 1000 °C. These results indicate that n-alkylamines are intercalated into the galleries of host ZBMPA.     

Phase equilibria and crystal chemistry of the R-Cu-Ti-O systems (R=lanthanides and Y)

As part of the study of interaction of the Ba₂RCu₃O_6+z (R=lanthanides and Y) superconductor with SrTiO₃ buffer, phase equilibria of the subsystem, R₂O₃-TiO₂-CuO (R=Nd, Y, and Yb), have been investigated in air at 960 °C. While the phase relationships of the two phase diagrams with smaller R (Y and Yb) are similar, substantial differences were found in the Nd₂O₃-TiO₂-CuO system, partly due to different phase formation in the binary R₂O₃-TiO₂ and R₂O₃-CuO systems. R₂CuTiO₆ and R₂Cu₉Ti₁₂O₃₆ were the only ternary phases established in all the three diagrams. R₂Cu₉Ti₁₂O₃₆ belongs to the perovskite-related [AC₃](B₄)O₁₂ family which is cubic Im3. Depending on the size of R³⁺, R₂CuTiO₆ crystallizes in two crystal systems: Pnma (R=La-Gd), and P6₃cm (R=Dy-Lu). The structure and crystal chemistry of the Pnma series of R₂CuTiO₆ (R=La, Nd, Sm, Eu, and Gd) are discussed in detail in this paper. Patterns for selected members of R₂CuTiO₆ have also been prepared and submitted for inclusion in the Powder Diffraction File (PDF).     

A simple and efficient biphasic method for the preparation of 4-nitrophenyl N-methyl- and N-alkylcarbamates

Treatment of 4-nitrophenyl chloroformate with alkylammonium hydrochloride salts and solid anhydrous Na₂CO₃ in either CH₂Cl₂ or CH₃CN gave 4-nitrophenyl N-methylcarbamate and other N-alkylcarbamate analogues in excellent yields. Of particular interest is the observation that 4-nitrophenyl N-methylcarbamate, a safer alternative to the highly toxic methyl isocyanate, is obtained in quantitative yield (?95% pure as determined by ¹H NMR) after simple filtration and solvent evaporation.     

Ru-catalyzed enantioselective preparation of methyl (R)-o-chloromandelate and its application in the synthesis of (S)-Clopidogrel

The preparation of methyl (R)-o-chloromandelate via Ru-catalyzed asymmetric hydrogenation and transfer hydrogenation was investigated. With Ru-(R,R)-2,4,6-triisopropyl C₆H₂SO₂-DPEN as the catalyst and HCOOH-Et₃N azeotrope as the hydrogen donor, up to 92% ee was obtained in an optional condition. The synthesis of (S)-Clopidogrel was also studied.     

Crystallization and melting behaviors of polystyrene-b-poly(ethylene-co-butene) block copolymers

Non-isothermal and isothermal crystallization behaviors of polystyrene-b-poly(ethylene-co-butene) (PSt-b-PEB) block copolymers with different compositions and chain lengths were investigated by differential scanning calorimetry (DSC). The results show that crystallization of PEB block is strongly dependent on the composition. Crystallization temperature (T_c), melting temperature (T_m) and fusion enthalpy (ΔH_f) increase rapidly with PEB volume fraction (V_E) for block copolymers with V_E below 50%, but there is little change when PEB block becomes the major component. Glass transition temperature (T_g) of the PSt block and order-disorder transition temperature (T_ODT) of block copolymers also have a weak effect. The isothermal crystallization kinetics results show that Avrami exponent (n) was strongly dependent on the composition and crystallization temperature. For the block copolymers with V_E below 38.7 vol%, the values of n vary between 0.9 and 1.3, indicating that crystallization is confined. For the PSt-b-PEB block copolymers with V_E higher than 50%, fractionated crystallization behavior is usually observed. A two-step isothermal crystallization procedure is applied to these block copolymers. It is found that breakout crystallization occurs at higher T_c, but confined at lower T_c. Two overlapped melting peaks are observed for the block copolymers with fractionated crystallization behavior after two-step crystallization, and only the higher melting peak corresponding to breakout crystallization can be used to derive equilibrium melting temperature.     

Synthesis, structural and larvicidal studies of some triorganotin 2-(p-chlorophenyl)-3-methylbutyrates

A series of triorganotin 2-(p-chlorophenyl)-3-methylbutyrates, (R₃SnO₂CCH(CH(CH₃)₂)C₆H₄Cl-4), where R = methyl, ethyl, n-propyl, n-butyl, phenyl and cyclo-hexyl, have been synthesized. Elemental analyses, Mössbauer, Infrared and NMR spectroscopies have been used to characterize their structures. Based on the spectroscopic results, all the complexes with the exception of the tricyclohexyl compound were found to be five-coordinated in the solid state while the tricyclohexyltin derivative was determined to be four-coordinated. Structural assignments based on spectroscopic data are supported by the crystallographic results of four of the triorganotin butyrates (trimethyl-, tri-n-propyl-, tri-n-butyl- and tricyclohexyltin 2-(p-chlorophenyl)-3-methylbutyrate). Multinuclear NMR spectroscopy studies indicated that all the complexes were tetrahedral in solution. Larvicidal activities of the complexes were evaluated against the 2nd instar stage of the Anopheles stephensi, Aedes aegypti and Culex pipiens quinquefasciatus mosquitoes. The toxicity data indicate that there does not appear to be any significant differences of the compounds towards the different mosquito species based on their averaged toxicity values. In addition, the toxicity of the triorganotin compounds towards the mosquito larvae was concluded to be dependent on both the compound and the species of mosquito larvae.     

Visible light-induced magnetization change of the cyano-bridged 3d-4f heterobimetallic

A visible light-induced magnetization change of the 3d-4f heterometallic, [Nd(DMF)₄(H₂O)₃(μ-NC)Co(CN)₅]·H₂O (DMF=N,N-dimethylformamide), is observed and described. The plots of χ_MT versus T of the complex showed that the χ_MT values, after visible light illumination, were enhanced by about 25% as compared to before irradiation in the temperature range of 5-40 K.     

Synthesis and characterization of a tetraruthenium butterfly cluster containing a quadruply-bridging ligand derived from an N,N′-dipyrid-2-ylurea

The tetraruthenium cluster complex [Ru₄(μ₄-κ⁴-dmpu)(CO)₁₀], H₂dmpu = N,N′-bis(6-methylpyrid-2-yl)urea, has been prepared by treating [Ru₃(CO)₁₂] with H₂dmpu in toluene at reflux temperature. An X-ray diffraction study has determined that this cluster has a butterfly metallic skeleton hold up by a doubly-deprotonated N,N′-bis(6-methylpyrid-2-yl)urea ligand (dmpu). This ligand has the pyridine N atoms attached to the wing-tip Ru atoms and the amido N atoms spanning Ru-Ru wing-edges, in such a way that the cluster has C₂ symmetry. The donor atoms of doubly-deprotonated N,N′-dipyrid-2-ylureas seem to be appropriately arranged to hold butterfly tetranuclear clusters.     

Stereoselective radical cyclizations of N-(2-halobenzoyl)-cyclic ketene-N,X(X=O, S)-acetals

2-Alkyloxazolines and 2-alkylthiazolines react with 2-halobenzoyl chlorides to form N-(2-halobenzoyl)-cyclic ketene-N,O-acetals and N-(2-halobenzoyl)-cyclic ketene-N,S-acetals in excellent yields, respectively. These ketene acetals readily undergo stereocontrolled aryl radical cyclizations to afford the central six-membered rings of substituted-2,3,10,10α-tetrahydrooxazolo[3,2-b]isoquinolin-5-ones and their 2,3,10,10α-tetrahydrothiazolo[3,2-b]isoquinolin-5-one analogs. The tertiary N,O- and N,S-radicals formed upon aryl radical reaction at the ketene-N,X(X=O, S)-acetal double bond appear to have reasonable stability. The stereoselectivity in hydrogen abstractions by these intermediate radicals from both Bu₃SnH and (Me₃Si)₃SiH was investigated. The N,S-heterocyclic fused ring products may have potential medical value.     

Catalytic photocarboxylation of 1,1-diphenylethylene with N,N,N′,N′-tetramethylbenzidine and carbon dioxide

Photocarboxylation of 1,1-diphenylethylene with N,N,N′,N′-tetramethylbenzidine (TMB) in MeCN under bubbling of CO₂ proceeded with high catalytic efficiency, giving 3,3-diphenylacrylic acid (DPA) and 3-hydroxy-3,3-diphenylpropionic acid (20). The turnover number (TON=(DPA+20)/TMB) reached 17. Similarly, 1-phenyl-1-cyclohexene yielded cis-2-acetamido-2-phenylcyclohexanecarboxylic acid with TON 5.9. As compared with related N,N-dimethylaniline derivatives, TMB is more resistant to photodecomposition, has the much larger absorbance in the S₀→S₁ transition, and has the lower quenching efficiency by CO₂. Probably these factors are partly responsible for the high TON observed for TMB.     

Synthesis and structural characterization of enantiopure exo and endo six-membered oxazoline-derived palladacycles

Direct palladation of (S)-4-benzyl-2-methyl-2-oxazoline (1) and (S)-2-benzyl-4-tert-butyl-2-oxazoline (2) using Pd(OAc)₂ in MeCN afforded the corresponding μ-acetato-dimeric complexes with six-membered exo and endo palladacycles, respectively. The same complexes were obtained by reacting coordination complexes Pd(1)₂(OAc)₂ and Pd(2)₂(OAc)₂ with Pd(OAc)₂ in MeCN. Metalation of (S)-2,4-dibenzyl-2-oxazoline (3) with Pd(OAc)₂ in AcOH, MeCN or CH₂Cl₂ resulted in the regiospecific formation of the six-membered endo palladacycle. The obtained μ-acetato-dimeric complexes were converted to the corresponding μ-chloro-dimeric derivatives 7, 11 and 13 by treatment with LiCl in acetone. The mononuclear PPh₃ adducts 8, 12 and 14 were obtained by reacting dimers 7, 11 and 13 with PPh₃ in benzene. NMR spectroscopy data supported the proposed structures of all complexes and suggested that exo and endo palladacycles in 8 and 12 have rigid boat conformations in CHCl₃. The X-ray crystal structures of the μ-acetato dimer 6 with the exo palladacycle and the PPh₃ adduct 14 with the endo metalacycle revealed boat conformation of both palladacycles and chiral twisted conformations δ(S) and λ(S), respectively, of the oxazoline rings in the solid state.