Structure of polypiperylene chain segments according to high-resolution 13C NMR spectra

The microstructure of stereoregular 1,4-trans-and 1,4-cis-polypiperylenes, as well as polymers prepared from the trans-and cis-piperylene isomers via cationic polymerization in the presence of TiCl₄, was studied by high-resolution ¹³C NMR spectroscopy. Polypiperylene synthesized through the cationic polymerization of the cis isomer had a more diversified morphology of the macromolecular chain, i.e., had higher relative amounts of 1,2-cis-units and combinations of irregular-addition 1,4-trans-units. It was shown that ¹³C NMR spectra give the most comprehensive and independent information on the details of structure of the piperylene macromolecular chain.     

Nature of active centers and stereospecificity of tetravalent titanium benzyl derivatives in polymerization of butadiene

Stereospecificity of tetrabenzyltitanium and its halogeno-derivatives in the polymerization of butadiene has been investigated. The content of 1,2-units decreases while the content of 1,4-cis-units increases in the resulting polybutadiene for the series (C₆H₅CH₂)₄Ti, (C₆H₅CH₂)₃TiCl, (C₆H₅CH₂)₃TiBr, (C₆H₅CH₂)₃Til. Tribenzyltitanium iodide exhibits high stereospecificity for the formation of 1,4-cis-units and their content reaches 94–97%. By determining the number of benzyl groups linked with titanium at different degrees of conversion, it has been shown that the active centre formed from tetrabenzyltitanium contains three benzyl groups and one polymer chain. Two benzyl groups, one iodine atom and one polymer chain are attached to a titanium atom in the active centre for the case of tribenzyltitanium iodide. Electron donors sharply change the stereospecificity of tribenzyltitanium iodide: the content of 1,2-units in the polymer rises to 68%.     

Katalytische isomerisierung von heptenen mit IrX(CO)L2

1-, 2-cis-, 2-trans-, and 3-trans-heptenes (C₇)are isomerized either very slowly or not at all with IrX(CO)L₂ at 80°C in toluene and under N₂. However, under the conditions of hydrogenation fast isomerisation takes place. With IrCl(CO)L₂ as catalyst the rate of isomerisation decreases the order: 1-C₇ ∼ 2-cis-C₇ > 3-trans-C₇ > 2-trans-C₇. This sequence is independent of the ligand L in lrCl(CO)L₂, however, with a particular isomer the rate of isomerisation is a function of L in the order L = PPh₃ > P(C₆H₁₁)3 > P(OPh)₃.     

Influence des interactions attractives non liees sur les stabilites relatives d'ethers et d'acetates d'enol renfermant un groupe styryle

The measure of relative stabilities of β-alcoxystyrene isomers I: C₆H₅-CHCH-OR shows that the trans compound is the most stable when RCH₃ and C₂H₅ and the cis compound is the most stable when Ri-C₃H₇ and t-C₄H₉. The orientation of the OR group can be determined by RMN ¹³C. The stabilities of these molecules are discussed in terms of non bounded attractive interactions. This interpretation is confirmed by the measure of relative stabilities of α-methyl β-alcoxy (and acetoxy)-styrene isomers II: C₆H₅-C(CH3)CH-OR. (RCH₃, C₂H₅ et COCH₃).     

Preparation and protonation of 2-pyrimidyl- and 2-pyrazylpalladium(II) complexes

The oxidative addition of 2-chloropyrimidine or 2-chloropyrazine to [Pd(PPh₃)₄] yields a mixture of trans-[PdCl(C₄H₃N₂-C²)(PPh₃)₂] (I) and [PdCl(μ-C₄H₃N₂-C²,N¹)(PPh₃ (II) (C₄H₃N₂ = 2-pyrimidyl or 2-pyrazyl group). The mononuclear complexes I are quantitatively converted into the binuclear species II upon treatment with H₂O₂. The reaction of II with HCl gives the N-monoprotonated derivatives cis-[PdCl₂(C₄H₄N₂-C²)(PPh₃)] (III), from which the cationic complexes trans-[PdCl(C₄H₄N₂-C²)(L) (L = PPh₃, IV; PMe₂Ph, V; PEt₃, VI) can be prepared by ligand substitution reactions. Reversible proton dissociation occurs in solution for III–VI. The low-temperature ¹H NMR spectra of trans-[PdCl(C₄H₄N₂-C²)(PMe₂Ph)₂]ClO₄ show that the heterocyclic moiety undergoes restricted rotation around the PdC² bond and that the 2-pyrazyl group is protonated predominantly at the N¹ atom. These results and the ¹³C NMR data for the PEt₃ derivatives are interpreted on the basis of a significant d_π → π^★ back-bonding contribution to the palladium—carbon bond of the protonated ligands.     

Ⅱ conjugation in the butadiene

The π electronic delocalization in trans-C4H6 and cis-C4H6 has been investigated in the frame of ab initio valence bond theory with 6-31G basis set. The result shows that the Csp2-Csp2 single bond length (1.506 A) is only about 0.024 A shorter than the Csp3-Csp3 bond, thus the central bond length shortening would be mainly due to π conjugation. The theoretical resonance energies of the trans-C4H6 and cis-C4H6 are 8.48 and 7.44 kcal/mol, respectively.     

Organometallic formate complexes of platinum(II)

The compounds trans-[Pt(OCHO)R(PPh₃)₂] (R = C₆Cl₅; 2,3,4,6-C₆HCl₄; 2,3,4,5-C₆HCl₄; 2,5-C₆H₃Cl₂) have been prepared by treatment of [PtIR(PPh₃)₂] with AgClO₄ followed by reaction with NaOCHO in methanol. The cis isomers have been obtained by the direct reaction of HCO₂H with compounds containing PtHg bonds. For these and the analogous compounds containing C₆F₅ ligands, the dependence of J(³¹P¹⁹⁵Pt) on R has been studied, and the effects of cis-R shown to be in the opposite direction from those of trans-R ligands.     

Synthesis and crystal structure of the double cluster [Cp3Fe4(CO)4(C5H4)]2(p-C6H4)

[Cp₄Fe₄(CO)₄] (1) reacts with p-BrC₆H₄Li and MeOH in sequence to afford the functionalized cluster [Cp₃Fe₄(CO)₄(C₅H₄-p-C₆H₄Br)] (2), while the reaction of 2 with n-BuLi and MeOH produces [Cp₂Fe₄(CO)₄(C₅H₄Bu)(C₅H₄-p-C₆H₄Br)] (3). The double cluster [Cp₃Fe₄(CO)₄(C₅H₄)]₂(p-C₆H₄) (4) has been prepared by treatment of [Cp₄Fe₄(CO)₄] with p-C₆H₄Li₂ and MeOH in sequence. The electrochemistry of 2 and 4, as well as the crystal structure of 4 have been investigated.     

Transition metal derivatives of arenediazonium ions: XIV. Reactions of arenediazomolybdenum(II) complexes with neutral and anionic Lewis bases

The reactions of arenediazomolybdenum(II) complexes such as [(η-C₅H₅)Mo(N₂C₆H₄CH₃-p)I₂]₂, (η-C₅H₅)Mo(CO species with neutral and anionic monodentate or chelating ligands have been investigated. The new arenediazo complexes isolated from these reactions include neutral species such as (η-C₅H₅)Mo(PPh₃)(N₂C₆H₄CH₃-p)I₂ and (η-C₅H₅)Mo(N₂C₆H₄CH₃-p) cations of the type [η-C₅H₅)Mo(bipy)(N₂C₆H₄CH₃-p)I]⁺ and the anion [(η-C₅H₅)Mo(N₂C₆H₄CH₃-p)I₃]^?. The structures of the new complexes are discussed.     

ω-Bromoalkapolyenylmethyl ketones-II : Use of 5-bromo-3-penten-2-one ethylene ketal as a c5-synthon

The preparation of the phosphonium salt and the dimethyl-phosphonate of (E)-5-bromo-3-penten-2-one ethylene ketal, 6 and 7, is described. These C₅-isoprenoid synthons were condensed with several aldehydes and ketones giving mixtures of the corresponding E and Z-olefination products. Reaction of the anion of the phosphonate derivative with β-ionone gave 9-cis and 9-trans-β-C₁₈-tetraenone ketals, 13 and 14, which by subsequent hydrolysis afforded 9-cis and 9-tras-β-C₁₈-tetraenones, 15 and 16. A C₈-isoprenoid synthon is also described.     

cis-Enhanced cyclopropanation catalysts: reaction chemistry of three isomers of Rh2[N(C6H5)COCH3]4

The catalytic activities of three structural isomers of Rh₂[N(C₆H₅)COCH₃]₄ in cyclopropanation reactions were surveyed. These studies showed cis cyclopropanation selectivity with bulky alkenes for 2,2-cis- and 2,2-trans-Rh₂[N(C₆H₅)COCH₃]₄.     

Synthesis of binuclear rhodacarboranes from 1,4-and 1,3-C6H4(CH2-9-C2H2B9H9-7,8-nido]2 2− dianions and (Ph3P)3RhCl

1,4- and 1,3-C₆H₄(CH₂-9-C₂H₂B₉H₉-7,8-nido]₂ ^2? dianions obtained fromnido-7,8-dicarbollide ion and 1,4-bis(bromomethyl)- and 1,3-bis(bromomethyl)benzenes react with (Ph₃P)₃RhCl to give binuclear rhodacarboranes, 1,4- and 1,3-[3,3-(Ph₃P)₂-3-H-3,1,2-RhC₂B₉H₁₀-4-CH₂]₂C₆H4.     

Über die Einwirkung metallorganischer Verbindungen auf p-Chinole. VI

Zusammenfassung Es wird die Addition von C₆H₅MgBr und C₆H₅Li an das 4-Methyl-p-chinol (I) und 2,4,6-Trimethyl-p-chinol (II), die zur erwarteten Bildung hydroaromatischer Verbindungen führt, beschrieben. C₆H₅Li reagiert mit I und II vorwiegend unter 1,2-Addition, während sich C₆H₅MgBr an I 1,2-und 1,4-, an II ausschließlich 1,4-addiert. Die erhaltenen hydroaromatischen Verbindungen, ihre Beständigkeit und ihre Umwandlungs-produkte sind von Interesse für die Beurteilung des Mechanismus der Umsetzung metallorganischer Verbindungen mit Chinolacetaten.     

1,2- and 1,7-Dicarba-closo-dodecarborane(12)platinum(II) complexes formed through metal—carbon σ bonds: cis- and trans-monohydrido derivatives

New neutral platinum(II) monohydridocarborane complexes of general formula cis- and trans-L₂PtH(σ-carb), where L = (C₂H₅)₃P, (C₆H₅)₃P, (C₆H₅)₂(CH₃)P, (C₆H₅)(CH₃)₂P and carb = 2-R-1,2- or 7-R-1,7-B₁₀C₂H₁₀^? (R = H, CH₃, C₆H₅), have been prepared. The configurations of the complexes obtained have been assigned by ¹H NMR spectroscopy. The _cis-monohydridocarborane complexes here reported are the first examples of neutral _cis-monohydrido derivates of platinum(II) containing platinum—carbon σ bonds. ¹H NMR chemical shifts and coupling constants of the prepared complexes are also reported, and used in a tentative evaluation of the _trans-influence of the carbonage ligands.     

Reactivity of a functionalized trisamido ligand with Zr(NMe2)4 and GaMe3

NMR study of the reactivity of multifunctional ligand cis,cis-C₆H₉(NHCH₂C₆H₄-o-PPh₂)₃ (1) with GaMe₃ and Zr(NMe₂)₄ was carried out, yielding [cis,cis-(κ^N-NHCH₂C₆H₄-o-PPh₂)(κ^N-NCH₂C₆H₄-o-PPh₂)₂C₆H₉]GaMe (2) and [cis,cis-(NCH₂C₆H₄-o-PPh₂)₃C₆H₉]Ga₂Me₃ (3), and [cis,cis-(NCH₂C₆H₄-o-PPh₂)₃C₆H₉]Zr(NMe₂) (4), respectively. The spectral properties of 2 and 3 are very similar to that observed for the equivalent aluminum species already reported, but form at a much slower rate which allows for the observation of a GaMe₃⋅1 adduct. Species 4 undergoes coordination/displacement of one of the phosphine arms, which was observed using both NMR spectroscopy and DFT analyses.     

The reaction of π-cyclopentadienyldicarbonylcobalt with silyl-substituted acetylenes

The reaction of (π-C₅H₅)Co(CO)₂ with PhCCSiMe₂R (R = Me, SiMe₃) gave two isomeric cyclobutadiene complexes, cis- and trans-(π-C₅H₅)Co[Ph₂C₄(SiMe₂R)₂], in almost quantitative yields. However, the reaction with RMe₂SiCCSiMe₂R (R = Me, Ph) led to the formation of new dinuclear cobalt complexes. For example, with bis(trimethylsilyl)acetylene, (π-C₅H₅)₂Co(CO)[(Me₃Si)₂C₂] was obtained quantitatively. The latter was further converted to (π-C₅H₅)Co(Ph₄C₄) and (πC₅H₅)Co[cis-Ph₂C₄(Me₃Si)₂] by treatment with PhCCPh. The physical properties and spectroscopic characteristics of these new compounds are described.     

Insertion of isocyanides into the palladium-(2-pyridyl) bond

The reaction of the pyridyl-bridged binuclear complex [PdBr(μ-2-C₅H₄N)(PPh₃)]₂ with isocyynides CNR (R  p-C₆H₄OMe, Me, C₆H₁₁) yields the complex $\text{PdBr}${(&2.dbnd;NR)C(&2.dbnd;NR) (2-C₅H₄N)}(PPh₃)] containing a C,N-chelated 1,2-bis(imino)-2-(2-pyridyl)ethyl group, which results from successive insertions of two isocyanides molecules into the palladium2-pyridyl bond. The mononuclear compound trans-[PdBr(2-C₅H₄N)(PMePh₂)₂] readily reacts with various CNR ligands (R  p-C₆H₄OMe, Me, C₆H₁₁, CMe₃) to give the imino(2-pyridyl)methylpalladium(II) derivatives, trans-[Pdbr{C(=NR)(2-C₅H₄N)} (PMePh₂)₂].     

Synthesis and characterisation of sterically bulky lithium amidinate and bis-amidinate complexes

The synthesis and characterisation of the amidines, (tript)C(NR)(NHR), R = Prⁱ or cyclohexyl (Cy), tript = triptycenyl, and lithium amidinate complexes, [Li(THF)₂{(tript)C(NR)₂}] bearing the bulky triptycenyl substituent on the amidine or amidinate backbone carbon is described. NMR spectroscopic studies have shown these to exist solely as their Z-syn isomeric forms in solution due to the steric effect of the triptycenyl moiety. The X-ray crystal structures of two examples confirm this is also the case in the solid state. A new bis-amidine ligand, 1,4-{(PrⁱHN)(PrⁱN)C}₂{2,3,5,6-C₆(p-C₆H₄Bu^t)₄}, and the corresponding lithium bis-amidinate complex, [1,4-{Li(THF)₂(PrⁱN)₂C}₂{2,3,5,6-C₆(p-C₆H₄Bu^t)₄}], which incorporate a sterically bulky tetraarylphenylene spacer unit have also been prepared. In solution, the amidine undergoes facile inter-conversion between its E-syn:E-syn and Z-syn:E-syn isomers. The bis-amidinate complex has been structurally characterised and shown to chelate both of its lithium centres.     

Polyfluoroorganotrifluoroborates and -difluoroboranes: interesting materials in fluoroorgano and fluoroorgano-element chemistry

The aimed introduction of the polyfluoroorgano groups (4-C₅F₄N), C₆F₁₃C₂H₄, and C₂F₅ into methoxy group-containing boron electrophiles is reported. The new compounds obtained after transformations K[(4-C₅F₄N)BF₃], (4-C₅F₄N)BF₂, K[C₆F₁₃C₂H₄BF₃], C₆F₁₃C₂H₄BF₂, K[(C₂F₅)₂B(OMe)₂], and K[(C₂F₅)₂BF₂] were isolated and characterised. Additionally some of their precursors as there are Li(4-C₅F₄N), Li[(4-C₅F₄N)B(OMe)₃], (4-C₅F₄N)B(OH)₂ and the by-products Li[(4-C₅F₄N)₂B(OMe)₂], (4-C₅F₄N)₂BOH, and K[(4-C₅F₄N)₂BF₂] are described. The usefulness of polyfluoroorganodifluoroboranes for introducing polyfluoroorgano groups into hypervalent FEF bonds is demonstrated by the synthesis of [C₆F₅(4-C₅F₄N)I][BF₄] and [p-FC₆H₄(trans-CF₃CFCF)I][BF₄].     

Studies of lambert's reaction: The formation of [Mn2(CO)8(μ-AsR2)2] complexes from tertiary arsines and [Mn2(CO)10] at high temperatures

Although very bulky ligands e.g.(o-MeC₆H₄)₃E or (μ-C₁₀H₇)₃E (E = P or As) are inert, the normal photochemical or thermal reaction of tertiary phosphines or arsines, L, with [Mn₂(CO)₁₀] is CO substitution with the formation of [Mn₂(CO)₈(L)₂] derivatives (I). At elevated temperatures some triarylarsines, R₃As, undergo Lambert's reaction with ligand fragmentation to give [Mn₂(CO)₈(μ-AsR₂)₂] complexes (II) (R = Ph, p-MeOC₆H₄, p-FC₆H₄, or p-CIC₆H₄) even though, in the absence of [Mn₂(CO)₁₀] R₃As are stable under the same conditions. Exceptional behaviour is exhibited by (p-Me₂NC₆H₄)_3- As which forms a product of type I; by some HN(C₆H₄)₂AsR which give a product of type II as a result of loss of the non-aryl groups R = PhCH₂, cyclo-C₆H₁₁, or MeO; and by Ph(α-C₁₀H₇₂P which is the only phosphine to form a product of type II, albeit in trace amounts only. The thermal decomposition of a n-butanol solution of [Mn₂(CO)₈(AsPh₃)₂] in a sealed tube gives C₆H₆ and [Mn₂(CO)₈(α-AsPh₂)₂], whilst in an open system in the presence of various tertiary phosphines, L, [Mn(H)(CO)₃(L)₂] are obtained. It is suggested that Lambert's reaction is a thermal fragmentation of [Mn(CO)₄(AsR₃]^* radicals, the first to be recognised. They lose the radical R^* which abstracts hydrogen from the solvent. The resulting [Mn(CO)₄(AsR₂)] moiety dimerises to [Mn₂(CO)_8-(α-AsR₂)₂]. the reaction is facilitated by the stability of the departing radical (e.g. PhCH₂ or MeO) and, as the crowding about As is relieved, by its size (e.g. Ph, cyclo-C₆H₁₁, o-MeC₆H₄, or α-C₁₀H₇). In general, phosphine-substituted radicals [Mn(CO)₄(PR)₃]^* do not undergo this decomposition, probably because the PC bonds are much stronger than AsC.