Novel Knöevenagel-type reaction via titanium enolate derived from Ti(O-i-Pr)4 and diketene

Knöevenagel-type reaction between diketene and aldehydes proceeded in the presence of Ti(O-i-Pr)₄. This reaction proceeded via titanium enolate derived from Ti(O-i-Pr)₄ and diketene. As for the stereoselectivity of the products, E-isomers were produced predominantly in the case of aromatic aldehydes.     

A ferrocenyl-bridged intramolecularly coordinated bis(diorganostannylene): Synthesis, molecular structure and reactivity of [4-t-Bu-2,6-{P(O)(O-i-Pr)2C6H2Sn}C5H4]2Fe

The intramolecularly coordinated heteroleptic stannylene [4-t-Bu-2,6-{P(O)(O-i-Pr)₂}₂C₆H₂]SnCl serves as synthon for the synthesis of the ferrocenyl-bridged bis(diorganostannylene) [4-t-Bu-2,6-{P(O)(O-i-Pr)₂}₂C₆H₂SnC₅H₄]₂Fe (1) which in turn reacts with W(CO)₆ and Cr(CO)₄(C₇H₈) to provide the corresponding transition metal complexes [4-t-Bu-2,6-{P(O)(O-i-Pr)₂}₂C₆H₂Sn{W(CO)₅}C₅H₄]₂Fe (2) and [4-t-Bu-2,6-{P(O)(O-i-Pr)₂}₂C₆H₂SnC₅H₄]₂Fe · Cr(CO)₄ (3), respectively. Reaction of compound 1 with sulphur and atmospheric moisture gave, under partial tin-carbon and oxygen-carbon bond cleavage, a tetranuclear organotin-oxothio cluster 5. All compounds were characterized by ¹H, ¹³C, ³¹P, and ¹¹⁹Sn NMR, and IR spectroscopy, as well as by single-crystal X-ray diffraction analysis. Compounds 1 and 3 were also investigated by Mössbauer spectroscopy. Cyclovoltametric studies reveal the influence of the organostannyl moieties on the redox-behaviour of compounds 1-3 in comparison with unsubstituted ferrocene.     

Formation of azatitanacyclopentanes from ene-imines and a Ti(O-i-Pr)4/2i-PrMgX reagent and their synthetic reactions

ω-Vinylimines reacted with a Ti(O-i-Pr)₄/2i-PrMgX reagent to generate the corresponding azatitanacyclopentanes in quantitative yield, which in turn reacted with H₂O, I₂ and O₂ to give 2-methyl-, 2-iodomethyl-, 2-hydroxymethyl-1-aminocyclic compounds, respectively. The azatitanacyclopentanes thus generated reacted with formaldehyde to afford the corresponding 2,3-annulated pyrrolidines in good yield.     

Synthesis of N-substituted 2-arylpyrroles by the reaction of (η-imine)titanium complexes with 3,3-diethoxypropyne

(η²-Imine)Ti(O-i-Pr)₂ complexes generated from arylaldehyde imines and a divalent titanium reagent, Ti(O-i-Pr)₄/2i-PrMgCl, reacted with 3,3-diethoxypropyne to afford 2-arylpyrroles.     

McMurry coupling of aryl aldehydes and imino pinacol coupling mediated by Ti(O-i-Pr)4/Me3SiCl/Mg reagent

Ti(O-i-Pr)₄/Me₃SiCl/Mg reagent mediated McMurry coupling of aryl aldehydes to biaryl olefins at near room temperature. This low valent titanium (LVT) reagent also mediated the coupling of aldimines to 1,2-diamines (imino pinacol coupling).     

Use of isopropyl alcohol as a solvent in Ti(O-i-Pr)4-catalyzed Knöevenagel reactions

Knöevenagel reactions of aldehydes and ketones with malononitrile, isopropyl cyanoacetate and diisopropyl malonate catalyzed by Ti(O-i-Pr)₄ proceeded smoothly in i-PrOH to give the corresponding reaction products in good to high yield. 3-Substituted coumarins were prepared by the present method.     

Bis-aryloxo-functionalized NHC complexes of ytterbium(III): Syntheses and structures of Yb[O-4,6-Bu2-C6H2-2-CH2{C(RNCHCHN)}]2N(Pr)2 (R = Pr, Me)

The transamination of anionic homoleptic amido ytterbium complex, LiYb[N(i-Pr)₂]₄ with aryloxo-functionalized N-heterocyclic carbene (NHC) precursor, HO-4,6-di-^tBu-C₆H₂-2-CH₂{CH[i-Pr-NCHCHN]}Cl (H₂LCl) 1 and HO-4,6-di-^tBu-C₆H₂-2-CH₂{CH[Me-NCHCHN]}Cl (H₂L′Cl) 2, and BuLi in 1:2:1 molar ratio in THF at 0 °C afforded the first bisaryloxo- NHC monoamido ytterbium complexes, L₂Yb [N(i-Pr)₂] 3 and , respectively. The same reactions in the molar ratio of 1:1 without BuLi yields also the complex 3 and 4, not the bis-amido mono aryloxo-NHC complex {LYb[N(i-Pr)₂]₂} and {L′Yb[N(i-Pr)₂]₂}. The in situ low-temperature reaction of 2 with two equivalents of BuLi, followed by addition of one equivalent of YbCl₃ in THF does not afford the expected LYbCl₂, instead, [Li(DME)₃][YbCl₄(DME)] 5 and a dimeric imidazole-aryloxo lithium {[O-4,6-di-^tBu-C₆H₂-2-CH₂{CH(MeNCHCHNH)}]Li(THF)}₂6 which results from the 1,2-benzyl migration in N-heterocyclic carbene, are obtained. Complexes 3, 4, 5 and 6 have been characterized by elemental analysis and X-ray crystallography, and by NMR spectroscopy for 6.     

Ti(II)-mediated domino cyclization of 2-functionalized 1-halo-2,n-enynes (n = 7, 8) to bicyclic compounds

The reaction of 2-functionalized 1-halo-2,n-enynes (n = 7 or 8) with a divalent titanium reagent, Ti(O-i-Pr)₄/2i-PrMgCl, proceeded in a domino fashion to afford bicyclic compounds in good yields.     

Stereoselective synthesis of vinylic (Z)-vic-bis(arylchalcogenides)

Alkyne-titanium complexes 3, readily prepared in situ by the reaction of alkynes with Ti(O-i-Pr)₄/2 i-PrMgCl, react with electrophilic chalcogen species under mild conditions to provide the corresponding addition products in fair to good yields. The obtained vinylic vic-bis(arylchalcogenides) 4 are useful synthetic intermediates for introducing vinyl functions into organic molecules.     

Metal-organic chains constructed from pre-organized N2S2 donor ligands

Three new N₂S₂ donor ligands 1,1′-((2-(2-(phenylthio)phenylthio)phenyl)methylene)bis(3,5-R-1H-pyrazole), R = H (L^H), R = Me (L^Me), R = i-Pr (L^i-Pr) have been prepared and characterized. These bifunctional ligands incorporate two distinct chelate donor systems, by virtue of the presence of bispyrazole and bisthioether functions. The preferred conformation of these ligands is such that the N₂ and S₂ donor moieties may be oriented in opposite directions, thus favoring the formation of molecular chains when treated with AgBF₄. The X-ray structures of Ag(I) complexes show that, depending on the steric hindrance present on the pyrazole rings, these ligands behave as κ⁴-SSNN-μ bridging tetradentate (when R = H), or κ³-SNN-μ bridging tridentate (when R = Me, i-Pr). Interestingly, [Ag(L^H)]BF₄ crystallizes in the chiral space group P4₁, with the molecular chain that is folded around the 4₁ screw axis.     

Mechanistic investigation of the thermal decomposition of Biphen(OPi-Pr)PtEt2: An entrance into C-C single bond activation?

Biphen(OPi-Pr) and (COD)PtCl₂ give Biphen(OPi-Pr)PtCl₂ which upon treating with ethyl Grignard forms Biphen(OPi-Pr)PtEt₂. The thermal decomposition of Biphen(OPi-Pr)PtEt₂ was investigated in the temperature range of 353-383 K. The clean and quantitative formation of the Pt(Ethene) adduct was observed. X-ray structures of a molecule in the solid state of all three reaction products and two further related complexes with phenyl fingers instead of i-Pr have been determined. For the complexes with i-Pr fingers a decisive deviation from a square plane is observed in contrast to the complexes with phenyl fingers. The P-Pt-P angle increases from about 95° in Biphen(OPi-Pr)PtCl₂ to about 120° in Biphen(OPi-Pr)Pt(Ethene), forcing the bridging C-C single bond of the biphenyl fragment as near as 4.17 Å to the Pt center. No through-space coupling between the bridging C atoms and the Pt center could be observed in ¹³C NMR spectroscopy. No bond lengthening of the bridging C-C single bond in the biphenyl fragment was observed in Biphen(OPi-Pr)Pt(Ethene) in comparison to the precursor complexes. The thermal decomposition of Biphen(OPi-Pr)PtEt₂ can be described by a first-order kinetic and the activation parameters were determined (temperature range: 353-383 K; ΔH^‡ = 173.8 ± 16.2 kJ/mol and ΔS^‡ = 104.7 ± 44.1 J/(mol K)). The reaction kinetics were also measured for perdeuterated ethyl groups yielding in a kinetic isotopic effect of 1.56 ± 0.14 which was almost temperature-independent. Selective deuteration at α and β position of the ethyl group, respectively, showed that β-H elimination takes place fast in comparison to the complete thermolysis. In the temperature range of 333-353 K only a scrambling of the deuterium atoms was found without further decomposition (temperature range: 333-353 K; Δ_scramH^‡ = 76.1 ± 15.2 kJ/mol, Δ_scramS^‡ = −80.7 ± 45.5 J/(mol K) for Biphen(OPi-Pr)PtEt₂-d⁶). The ethene is not lost during the scrambling process. The scrambling process is connected with a primary KIE decisively larger than 1.56. Biphen(OPi-Pr)Pt(Ethene) exchanges the coordinated ethene with ethene in solution as proven by labeling experiments. Both a dissociative and an associative mechanism could be shown to take place as ethene exchange reaction by means of VT¹H NMR spectroscopy via line shape analysis (temperature range: 333-373 K; Δ_assH^‡ = 26.9 ± 29.6 kJ/mol, Δ_assS^‡ = −148.0 ± 87.5 J/(mol K), Δ_dissH^‡ = 86.0 ± 6.5 kJ/mol, Δ_dissS^‡ = 5.4 ± 17.8 J/(mol K)). The Pt(0) complex formed during the dissociative loss of ethene activates several substrates among them: O₂, H₂, H₂SiPh₂ via Si-H activation, MeI presumably via forming a cationic methyl adduct and ethane via C-H activation but it was proven that the bridging C-C single bond of the biphenyl fragment is not even temporarily broken. The materials were characterized by means of ¹H NMR, ¹³C NMR, ³¹P NMR, ¹⁹⁵Pt NMR, EA, MS, IR, X-ray analysis and polarimetric measurement where necessary.     

Catalytic asymmetric Michael reactions of dibenzyl malonate to α,β-unsaturated N-acylpyrroles using a La(O-iPr)3/Ph-linked-BINOL complex

Catalytic asymmetric Michael reactions of a malonate to acyclic α,β-unsaturated N-acylpyrroles as ester equivalent acceptors are described. A La(O-iPr)₃/(S,S)-linked-BINOL complex, which is suitable for Michael addition to cyclic enones, is not suitable for acyclic α,β-unsaturated N-acylpyrroles. A new (S,S)-Ph-linked-BINOL chiral ligand was developed to improve enantioselectivity, and a La(O-iPr)₃/(S,S)-Ph-linked-BINOL complex with the addition of HFIP afforded Michael adducts in good yield and enantioselectivity (up to 96% ee).     

Enantio- and diastereoselective construction of vicinal quaternary and tertiary carbon centers by catalytic Michael reaction of α-substituted β-keto esters to cyclic enones

A catalytic enantio- and diastereoselective Michael reaction was achieved to construct vicinal quaternary and tertiary carbon centers in one step. Using 5 mol % of La(O-i-Pr)₃ and 10 mol % of a new N-linked-BINOL type ligand, the reaction of α-substituted β-keto esters to cyclic enones provided the corresponding Michael adducts in up to quantitative yield with a diastereomeric ratio up to 86/14 and enantiomeric excess up to 86% for the major isomer. An alternative catalyst preparation method using La(OTf)₃ instead of La(O-i-Pr)₃ was also examined.     

Crystal structure of [Pd(P(i-Pr)3)2(acac)]BF4

A single crystal X-ray diffraction study is carried out for [Pd(P(i-Pr)₃)₂(acac)]BF₄, T = 150(2) K. Crystal data: a = 10.2935(4) ?, b = 11.3591(5) ?, c = 13.8728(6) ?, α = 89.154(2)°, β = 68.448(1)°, γ = 85.032(1)°, P-1 space group, V = 1502.75(11) ?³, Z = 2, d _x = 1.354 g/cm³.     

Chelating Phosphorus–An O,C, O-Coordinating Pincer-Type Ligand Coordinating PIII and PV Centres

The sequence of reactions of the phosphorus-containing aryllithium compound 5-t-Bu-1,3-[(P(O)(O-i-Pr)₂]₂C₆H₂Li (ArLi) with Ph₂PCl, KMnO₄, elemental sulfur and elemental selenium, respectively, gave the aryldiphenylphosphane chalcogenides 5-t-Bu-1,3-[(P(O)(O-i-Pr)₂]₂C₆H₂P(E)Ph₂ ( 1 , E=O; 2 , E=S; 3 , E=Se). Compound 1 partially hydrolysed giving [5-t-Bu-1-{(P(O)(O-i-Pr)₂}-3-{(P(O)(OH)₂}C₆H₂]P(O)Ph₂ ( 4 ). The reaction of ArLi with PhPCl₂ provided the benzoxaphosphaphosphole [1(P), 3(P)-P(O)(O-i-Pr)OPPh-6-t-Bu-4-P(O)(O-i-Pr)₂]C₆H₂P ( 5i ) as a mixture of the two diastereomers. The oxidation of 5i with elemental sulfur gave the benzoxaphosphaphosphole sulfide [1(P), 3(P)-P(O)(O-i-Pr)OP(S)Ph-6-t-Bu-4-P(O)(O-i-Pr)₂]C₆H₂ ( 5 ) as pair of enantiomers P1(R), P3(S)/P1(S), P3(R) of the diastereomer (RS/SR)- 5 ( 5b ). The aryldiphenylphosphane 5-t-Bu-1,3-[(P(O)(O-i-Pr)₂]₂C₆H₂PPh₂ ( 6 ) was obtained from the reaction of the corresponding aryldiphenylphosphane sulfide 2 with either sodium hydride, NaH, or disodium iron tetracarbonyl, Na₂Fe(CO)₄. The oxidation of the aryldiphenylphosphane 6 with elemental iodine and subsequent hydrolysis yielded the aryldiphenyldioxaphosphorane 9-t-Bu-2,6-(OH)-4,4-Ph₂-3,5-O₂-2,6-P₂-4λ⁵-P-[5.3.1.0]-undeca-1(10),7(11),8-triene ( 7 ). Both of its diastereomers, (RR/SS)- 7 ( 7a ) and (RS/SR)- 7 ( 7b ), were separated as their chloroform and i-propanol solvates, 7a ⋅2CHCl₃ and 7b ⋅i-PrOH, respectively. DFT calculations accompanied the experimental work.     

Transesterifications mediated by t-BuNH2

A mild protocol for transesterification of simple esters is described. The method is based on the use of t-BuNH₂/ROH (R = Me, Et, i-Pr, t-Bu) with or without LiBr. The scope of the procedure was explored for aliphatic and aromatic esters. The protocol is particularly useful when going from higher to lower hindered esters and harsh reaction conditions are needed for the reversal process. A rationalization of the mechanism is presented. The scope and limitation of this transformation are also described.     

Synthesis and Characterization of a New Layered Aluminophosphate [Al3P4O16][(CH3)2NHCH2CH2NH(CH3)2][H3O]

A new layered aluminophosphate, denoted AlPO-CJ12, has been synthesized in the system Al(OPrⁱ)₃-H₃PO₄-tetramethylethylenediamine-triethyleneglycol and its structure solved by single-crystal X-ray diffraction analysis. It is further characterized by X-ray powder diffraction, ICP, TG, DTA, and elemental analyses. The compound has an empirical formula of [Al₃P₄O₁₆][(CH₃)₂NHCH₂CH₂NH(CH₃)₂][H₃O], and crystallizes in the triclinic space group P-1 (No. 2) with a=8.9907(6) Å b=9.8359(6) Å, c=14.5566(8) Å, α=75.872(3)°, β=88.616(3)°, γ=63.404(3)°, Z=2, R₁=0.0451, and wR₂=0.1094. The alternation of tetrahedral AlO₄ and PO₃ (=O) units forms a sheet structure with a 4×6×8 network. The inorganic layers stacked in an AAAA sequence are held together by the protonated organic amine and water molecules. The co-templating role of the water molecules is studied by the calculation of the nonbonding host-guest interaction energies through a computational simulation.     

Controlled radical polymerization of alkyl acrylates and styrene using a half-sandwich molybdenum(III) complex containing diazadiene ligands

The half-sandwich molybdenum(III) complex CpMoCl₂(ⁱPr₂-dad) (ⁱPr₂-dad=ⁱPr-NCH-CHN-ⁱPr) proved to be an effective metal catalyst for the controlled radical polymerization of methyl acrylate, butyl acrylate, and styrene. In conjunction with an alkyl iodide [R-I: CH₃CH(COOEt)I] as an initiator and in the presence or absence of Al(O-i-Pr)₃ as a co-catalyst, the molybdenum-based system gave polymers with narrow molecular weight distributions. The in situ addition of styrene to a macroinitiator of poly(methylacrylate) afforded an AB-type block copolymer.     

A one-pot method to prepare the carbene complex [TpRhCl2(CHNiPr2)] from [TpRh(CO)2], CHCl3, and NHiPr2

The complex [Tp^Me₂,ClRh(CO)₂] reacts with chloroform to give quantitatively the rhodium(III) complex [Tp^Me₂,ClRhCl(CHCl₂)(CO)] resulting from the oxidative addition of a C-Cl bond. Further reaction with diisopropylamine gives the aminocarbene complex [Tp^Me₂,ClRhCl₂(CHNiPr₂)], whose X-ray crystal structure has been solved. Addition of an excess of diisopropylamine to [Tp^Me₂,ClRh(CO)₂] in chloroform provides directly [Tp^Me₂,ClRhCl₂(CHNiPr₂)].     

Synthesis and molecular structures of heptafluoroisopropylated fullerenes: C60(i-C3F7)8, C60(i-C3F7)6, and C60(CF3)2(i-C3F7)2

One isomer of C₆₀(i-C₃F₇)₈, three isomers of C₆₀(i-C₃F₇)₆, and the first mixed perfluoroalkylated fullerene, C₆₀(CF₃)₂(i-C₃F₇)₂, have been isolated by HPLC from a mixture prepared by reaction of C₆₀ with heptafluoroisopropyl iodide in a glass ampoule at 260-290 °C. The molecular structures of the four new compounds have been determined by means of X-ray single crystal diffraction partially also by use of synchrotron radiation. Theoretical calculations at the DFT level of theory have been employed to rationalize the energetics of isomers and of C₆₀-R_f binding.