Arylmercury(II) compounds involving intramolecular coordination via 2-Me2NCH2- and chiral (S)-2-Me2NCHMe-ring substituents

Arylmercury compounds of the type Ar₂Hg and ArHgX (X = Cl, OAc) have been synthesized and characterized by ¹H and ¹³C NMR spectroscopy; the Ar group was either 2-Me₂NCH₂C₆H₄ or (S)-2-Me₂NCH(Me)C₆H₄, both of which contain N-donor ligands. The observation of anisochronous NMe resonances in (S)-2-Me₂NCH(Me)C₆H₄HgX (X = Cl, OAc) at low temperature indicates that in solution the mercury centre is three-coordinate as a result of stable intramolecular HgN coordination     

Simultaneous 2-O-deacetylation and 4-amination of peracetylated Neu5Ac: application to the synthesis of (4→4)-piperazine derivatives linked sialic acid dimers

A simultaneous stereoselective 2-O-deacetylation and 4-amination reaction of peracetylated Neu5Ac 1 has been established with cyclic secondary amines, such as 1-N-Boc-piperazine. Four C₂-symmetric and two asymmetric sialic acid dimers with (4→4)-piperazine derivatives linked were synthesized. They may serve as precursors of unnatural polysialic acids.     

Reactions of [η:σ-Me2C(C5H4)(C2B10H10)]Ru(COD) with Lewis bases: Synthesis, structure, and electrochemistry of ruthenium amine, nitrile, carbene, phosphite and phosphine complexes

Treatment of [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(COD) (1) with phosphites, phosphines, amines or N-heterocyclic carbene in THF afforded the COD displacement complexes [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[P(OEt)₃]₂ (2), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[PPh₂(OEt)]₂ (3), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[NH₂CH₂CH₂Prⁱ]₂ (4), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NH₂Prⁿ)₂ (5), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru (η²-NH₂CH₂CH₂NH₂) (6), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[η²-NH(CH₃)CH₂CH₂NH(CH₃)] (7) or [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru[NHC]₂ (8, NHC = 1,3,4,5-tetramethylimidazol-2-yilidene), respectively. Ruthenium-amine complexes were much more labile than 1. Upon exposure to moisture, 5 was converted into [{η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)}Ru(μ-H₂O)]₂ (9). Reactions of 5 with PR₃ (R = PPh₃, Cy), TMEDA (TMEDA = N,N,N′,N′-tetramethylethylenediamine) and CH₃CN afforded the corresponding amine replacement products[η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NH₂Prⁿ)(PPh₃) (10), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NH₂Prⁿ)(PCy₃) (11), [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(TMEDA) (12) and [η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NCCH₃)₂ (13). These results indicated that the steric factor dominated these substitution reactions. The electrochemical studies showed that the electron richness of the Ru atom decreased in the order L₂Ru(NHC)₂ > L₂Ru(amine)₂ > L₂Ru(NCMe)₂ > L₂Ru(P)₂. All of these complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 2, 3, 5-10, 12 and 13 were further confirmed by single-crystal X-ray analyses.     

Arene complexes of transition metals in reactions with nucleophilic reagents: XXX. Reaction of π-halomesitylene [Tetramethyl(ethyl)cyclopentadienyl]rhodium(II) complexes with anions derived from CH acids

Reactions of fluoro-and chloromesitylene π-complexes [(η⁶-1-Hlg-2,4,6-Me₃C₆H₂)(η⁵-C₅EtMe₄)Rh]-(BF₄)₂ (Hlg = F, Cl) with diethyl malonate anion in THF or acetone-d ₆ at 20°C initially (within the first 5–30 min) involve nucleophile addition at unsubstituted carbon atom in the arene ligand with formation of π-cyclohexadienyl complexes {[η⁵-1-(EtOCO)₂CH-1-H-3-Hlg-2,4,6-Me₃C₆H₂](η⁵-C₅EtMe₄)Rh}(BF₄). The subsequent replacement of the halogen atom yields {[η⁶-1-(EtOCO)₂CH-2,4,6-Me₃C₆H₂](η⁵-C₅EtMe₄)Rh}(BF₄)₂, where the arene ligand is readily withdrawn from π-coordination by the action of chloride ion or the solvent. Dimethyl mesitylmalonate was isolated in 76% yield. Likewise, the reactions with anions derived from malononitrile and ethyl cyanoacetate gave 25–38% of the corresponding derivatives 1-R-2,4,6-Me₃C₆H₂ where R = (NC)₂CH or EtOCO(NC)CH.     

Synthesis and some reactions of n5-pentamethylcyclopentadienylnickel complexes

Reaction of Me₅C₅Li and Ni(CO)₄ gave [(n⁵-Me₅C₅)Ni(CO)]₂ ($\text{I}$) in 40 % yield. Reaction of $\text{I}$ with iodine followed by addition of a tertiary phosphine or reaction of (PPh₃)₂NiX₂ with Me₅C₅Li or Me₅C₅SnBu₃ gave (n⁵-Me₅C₅)Ni(L)X ($\text{II}$) (L = tertiary phosphine, X = halogen). Treatment of $\text{II}$ with RLi (R = Me, PhCC) afforded (n⁵-Me₅C₅)Ni(L)R ($\text{III}$). The spectroscopic properties and the reactivities of n⁵-pentamethylcyclopentadienylnickel complexes indicate that the n⁵-Me₅C₅ ligand is more electron-donating and a sterically more bulky than the n⁵-C₅H₅ ligand.     

New protocol for allylic substitution with aryl and alkenyl copper reagents derived from organolithiums

Substitution of allylic picolinoates with copper reagents derived from sp²-carbon-lithiums and CuBr·Me₂S was established to furnish anti S_N2′ products with almost perfect regioselectivity and chirality transfer. The preparations of organolithiums such as lithium-halogen exchange and ortho lithiation were coupled to the substitution to install various sp²-carbon groups, which include Ph, 2,6-Me₂C₆H₃, 4-Me-2,6-(MOMO)C₆H₂, and cis and trans 1-heptenyl groups.     

Reaction of [η 5:σ-Me2C(C5H4)(C2B10H10)]Ru(NCCH3)2 with internal alkynes: Synthesis and structural characterization of ruthenium-cyclobutadiene and ruthenacyclopentatriene complexes

Reaction of [η ⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(NCCH₃)₂ (1) with R¹C≡CR¹(R¹ = Et, Ph) in toluene at 80°C yielded organoruthenium cyclobutadiene complexes [η ⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)]Ru(η ⁴-C₄R ₄ ¹ ) in >80% yield. Treatment of 1 with diynes R₂C≡C(CH₂)₃C≡CR² (R² = Me, Et) in toluene at room temperature yielded ruthenacyclopentatrienes [η ⁵:σ-Me₂C (C₅H₄)(C₂B₁₀H₁₀)]Ru[=C₂(R²)₂C₂(CH₂)₃] in >85% yield. These new complexes were fully characterized by various spectroscopic techniques, elemental analyses and single-crystal X-ray diffraction studies. The possible reaction mechanism was proposed.     

Synthesis of neutral and cationic monocyclopentadienyl alkyl niobium and tantalum complexes

Compound [NbCp′Me₄] (Cp′ = η⁵-C₅H₄SiMe₃, 1) reacted with several ROH compounds (R = tBu, SiiPr₃, 2,6-Me₂C₆H₃) to give the derivatives [NbCp′Me₃(OR)] (R = tBu 2a, SiiPr₃2b, 2,6-Me₂C₆H₃2c). The diaryloxo tantalum compound [TaCp^∗Me₂(OR)₂] (Cp^∗ = η⁵-C₅Me₅, R = 2,6-Me₂C₆H₃3) was obtained by reaction of [TaCp^∗Cl₂Me₂] with 2 equiv of LiOR (R = 2,6-Me₂C₆H₃). Abstraction of one methyl group from these neutral compounds 1-3 with the Lewis acids E(C₆F₅)₃ (E = B, Al) gave the ionic derivatives [NbCp′Me₂X][MeE(C₆F₅)₃] (X = Me 4-E. X = OR; R = SiiPr₃5b-E, 2,6-Me₂C₆H₃5c-E. E = B, Al) and [TaCp^∗Me(OR)₂][MeE(C₆F₅)₃] (R = 2,6-Me₂C₆H₃6-E; E = B, Al). Polymerization of MMA with the aryloxoniobium compound 2c and Al(C₆F₅)₃ gave syndiotactic PMMA in a low yield, whereas the tetramethylniobium compound 1 and the diaryloxotantalum derivative 3 were inactive.     

Cumulated double bond systems as ligands : X. N-sulfinylaniline complexes of rhodium(I) and iridium(I) of the type [MCl(PR3)2L] in which L is coordinated via the π-NS and via the sulfur atom respectively; crystal and molecular structure of [RhCl(P-i-Pr3)2(4-MeC6H4NSO)]; determination of the 1J(103Rh15N) by 15N NMR spectroscopy

Each of the compounds [MCl(Pr₃)₂(ArylNSO)] (M = Rh^I, Ir^I; R = i-Pr, Cy: Aryl = C₆H₅, 4-MeC₆H₄, 4-ClC₆H₄, 2,4,6-Me₃C₆H₂ appears to exist as two isomers both in the solid state and in solution. The molecular and single crystal structure of one of the isomers of [RhCl(P-i-Pr)₃)₂(4-Me₆H₄NSO)] shows that the N-sulfinylaniline ligand is in the cis-configuration and coordinated to the rhodium atom via the sulfur-atom. The ligand lies in a plane which includes the rhodium atom and is in agreement with the Rh-S distance of 2.10 Å. IR results of the compounds (solid and solutions), ²¹P NMR data and ¹⁵N NMR of a ¹⁵N labelled compound, which yielded a ¹⁰³Rh¹⁵N coupling constant of 15.5 Hz, show that in the second isomer the N-sulfinylaniline ligand is probably bonded to the metal atom via the π-NS bond.The ratio of the metal-π-NS bonded isomer and the metal-S bonded isomer decreases in the order Aryl = 4-ClC₆H₄ > C₆H₅ > 4-MeC₆H₄; R = i-Pr > Cy and M = Rh > Ir. The interconversion of the two isomers is intramolecular and becomes observable on the ³¹P NMR time scale at about 40° C for M = Rh.In the case of [Ir(P-i-Pr₃)₂(4-MeC₆H₄NSO)], cyclometallation of the sul- finylaniline is observed via the ortho-carbon atom, whereas cyclometallation via P-i-Pr₃ is observed when the ortho-positions are blocked by methyl groups, e.g. when L = 2,4,6-Me₃C₆H₂NSO.     

Group IB organometallic chemistry: XXXIII. ArAuPPh3, ArAu(CNR), (ArAu)n and Ar4Cu2Au2 compounds in which the aryl group contains 2-MeO, 2,6-(MeO)2, 2-Me2N, 2-Me2NCH2 and (S)- or (R)-2-Me2NCHMe substituents as potential ligands

The synthesis and structural characterization by ¹H NMR and ¹⁹⁷Au Mössbauer spectroscopy as well as by chiral labelling of the built-in ligands of three different types of arylgold(I) compounds is described.¹⁹⁷Au Mössbauer data revealed that the benzyl- and arylgold(I) triphenylphosphine complexes which bear potential coordinating substituents at an ortho position still contain linearly coordinated Au^I with 2c-2e gold(I)carbon bonds. The observation of isochronous NME resonances in (S)-2-Me₂NCH(Me)C₆H₄AuPPh₃ confirms that no additional intramolecular AuN coordination occurs in solution. Preliminary results of an X-ray diffraction study of 2,6-(MeO)₂C₆H₃AuPPh₃ are reported (R = 0.040, PAuC₁ angle 172.6°. Unsymmetrical AuC₁C₂ and AuC₁C₆ angles of 126.4 and 117.4°, respectively).Pure, uncomplexed arylgold(I) compounds have been isolated from the reaction of diarylgoldlithium compounds (arylaurates) with trimethyltin bromide. (S)-2-Me₂NCHMeC₆H₄Au has a dimeric structure which most likely consists of two monomeric units associated by intermolecular AuN coordination thus forming a ten-membered chelate ring. The structure of insoluble 2-Me₂NCH₂C₆H₄Au and 2-Me₂NC₆H₄Au are less clear. The former compound probably has a structure similar to (S)-2-Me₂NCHMeC₆H₄Au (IS/QS values for two-coordinate Au^I centers). However, the strongly deviating IS and QS values of 2-Me₂NC₆H₄Au indicate that a polynuclear structure for this compound similar to that proposed for 2-Me₂NC₆H₄Cu cannot be excluded (a polymeric structure containing 2-Me₂NC₆H₄ groups which span three Au atoms by 3c-2e Au₂C bonds and AuN coordination).The mixed Au/Cu cluster (2-Me₂NCH₂C₆H₄)₄Au₂Cu₂ is accessible via the $\text{1}\text{2}$ reaction of (2-Me₂NCH₂C₆H₄)₄Au₂Li₂ with CuI. Molecular weight and ¹H NMR studies point to a tetranuclear structure in solution, while mass spectrometry shows fragment ions with m/e corresponding to (2-Me₂NCH₂C₆H₄)₃Au₂Cu₂⁺, (2-Me₂NCH₂C₆H₄)₃Cu₂Au⁺, (2-Me₂NCH₂C₆H₄)₂CuAu₂⁺ and of (2-Me₂NCH₂C₆H₄)₂Au⁺.     

o-Phenylene-bridged Cp/amido titanium and zirconium complexes and their polymerization reactivity

o-Phenylene-bridged trimethylcyclopentadienyl/amido titanium complexes [(η⁵-2,3,5-Me₃C₅H)C₆H₄NR-κN]TiCl₂ (18, R = CH₃; 19, R = CH₂CH₃; 20, R = CH₂C(CH₃)₃; 21, R = CH₂(C₆H₁₁)) and zirconium complexes {[(η⁵-2,3,5-Me₃C₅H)C₆H₄NR-κN]ZrCl-μCl}₂ (22, R = CH₃; 23, R = CH₂CH₃; 24, R = CH₂C(CH₃)₃; 25, R = CH₂(C₆H₁₁); 26, R = C₆H₁₁; 27, R = CH(CH₂CH₃)₂) are prepared via a key step of the Suzuki-coupling reaction between 2-dihydroxyboryl-3-methyl-2-cyclopenten-1-one (2) and the corresponding bromoaniline compounds. The molecular structures of titanium complexes 18 and 19 and dinuclear zirconium complexes 24 and 26 were confirmed by X-ray crystallography. The Cp(centroid)-Ti-N and Cp(centroid)-Zr-N angles are smaller, respectively, than those observed for the Me₂Si-bridged complex [Me₂Si(η⁵-Me₄C₅)(N^tBu)]TiCl₂ and its Zr-analogue, indicating that the o-phenylene-bridged complexes are more constrained than the Me₂Si-bridged complex. Titanium complex 19 exhibits comparable activity and comonomer incorporation to the CGC ([Me₂Si(η⁵-Me₄C₅)(N^tBu)]TiCl₂) in ethylene/1-octene copolymerization. Complex 19 produces a higher molecular-weight polymer than CGC.     

Aspects of transmetallation reactions of 2-Me2NCH2C6H4- and 2,6-(Me2NCH2)C6H3-Metal (Pd,Pt, Hg,Tl) complexes with metal carboxylates and low-valent metal (Pd,Pt) complexes

A study has been made of reactions involving organometallic compounds containing ortho-Me₂NCH₂ substituted aryl ligands. The single step syntheses of the new compounds [(2-Me₂NCH₂C₆H₄)₂TlCl], [ [{(S)-2-Me₂NCH(Me)C₆H₄}₂TlCl], [{(S)-2-Me₂NCH(Me)C₆H₄}TlCl₂], [{2,6-(Me₂NCH₂)₂C₆H₃}TlClBr] and [{2,6-(Me₂NCH₂)₂C₆H₃}HgCl] are described. Stable internal NTl coordination at low temperatures has been established for the C-chiral thallium compounds. Reactions of the other Tl and Hg compounds and of [(2-Me₂NCH₂C₆H₄)₂Hg] with Pd(O₂CMe)₂, and also of the reverse reaction of cis-[(2-Me₂NCH₂C₆H₄)₂Pd] with Hg(O₂CR)₂ or Tl(O₂CR)₃, gave transmetallation of one organo ligand and led to a single mono-organopalladium compound and corresponding by-products. Reaction of cis-[(₂-Me₂NCH₂C₆H₄)₂Pd] with Pd(O₂CR)₂ gave the dimeric compound [{(2-Me₂NCH₂C₆H₄)Pd(O₂CR)}₂]. cis-[(2-Me₂NCH₂C₆H₄)₂Pt] did not react with Pd(O₂CMe)₂, while reaction of trans-[(2-Me₂NCH₂C₆H₄)₂Pt] or cis-[(2-Me₂NC₆H₄CH₂)₂Pt] with Pd(O₂CMe)₂ resulted in decomposition. Upon heating, trans-[(2-Me₂NCH₂C₆H₄)₂Pt] was isomerized to cis-isomer. A redox reaction between [(2-Me₂NCH₂C₆H₄)₂Hg] and [Pt(COD)₂] (COD  1,5-cyclo-octadiene) and [Pd₂(DBA)₃] (DBA  dibenzylideneacetone) gave the cis-isomers of [(2-Me₂NCH₂C₆H₄)₂M] (M  Pd, Pt).The results are discussed in terms of influence of internal coordination of the CH₂NMe₂ group. It is concluded that although internal coordination of the CH₂NMe₂ ligand can stabilize metal—carbon bonds it cannot prevent cleavage of such bonds by electrophiles. In this respect, there is no difference in the behaviour of Hg(O₂CR)₂ and Tl(O₂CR)₃. The reactions are influenced by the metal—nitrogen bond strength, which follows the order PtN > PdN > HgN, TlN. The reactivity of Pt compounds is greatly influenced by their structure and type of ligand. It is proposed that cleavege of PdC bonds occurs mainly by a mechanism involving direct electrophilic attack at the carbon centre.     

The carbon-13 chemical shifts and the analysis of the relaxation times T1 and long range 13C−1H coupling constants of quinoline and of 1-(X-quinolyl)ethyl acetate derivatives

The ¹³C chemical shifts and the ¹³C−¹H coupling constants of quinoline (1-(X-quinolyl)ethyl acetate derivatives (where X=−CH(OAc)CH₃ substituted at positions 2,4,5–8) are reported. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift of 4.5 and 4.8 ppm was observed at C-4 and C-5, arising from the peri interaction of 5- and 4-ethyl acetate substituents respectively. A vicinal (peri) ³J CCCH coupling constant of approximately 5 Hz is observed between both C₅−H₄ and C₄−H₅. Carbon-13 relaxation times (T₁) and nuclear Overhauser enhancements (η) have been measured for quinoline and its derivatives, and the contributions of dipolar, T₁^DD, and spin rotation, T₁^SR, relaxation have been determined. Intramolecular dipole-dipole interactions are found to provide by far the most important spin-lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Non-protonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution to T₁, and can form the basis for spectral assignments, as in 1-phenylethyl acetate. Long-range ¹³C−¹H coupling constants were observed both between ring carbons and between ring carbons with ring side-chain hydrogens. These results have been used for the structure determination of the title compounds.     

Sulfides,sulfones, and sulfoxides of the furan-2(5H)-one series. synthesis and structure

A number of 4- and 5-R-sulfanylfuran-2(5H)-one derivatives were synthesized, and their oxidation with various reagents was studied. The corresponding sulfones were obtained using hydrogen peroxide in acetic acid. 4-R-sulfanyl derivatives were selectively oxidized to sulfoxides with m-chloroperoxybenzoic acid. The molecular and crystal structures of some new sulfones and sulfoxides were determined by X-ray analysis.     

1,1′-Disubstituierte Titanocen-dithiolen-Chelate des Typs (η5-Me3EC5H4)2Ti(S2C2R2) (E = C,Si, Ge)

1,1′-Disubstituted Titanocene Dithiolene Chelates of Type (η⁵-Me₃EC₅H₄)₂Ti(S₂C₂R₂) (E = C, Si, Ge) Reaction of the titanocene dichlorides (η⁵-Me₃EC₅H₄)₂TiCl₂ (E = C, 1a ; E = Si, 1b ; E = Ge, 1c ) with the 1,2-dithiolates (NaS)₂C₂H₂, (NaS)₂C₂(CN)₂ or (LiS)₂C₆H₃Me-4 gave the new titanocene dithiolene chelates (η⁵-Me₃EC₅H₄)₂Ti(S₂C₂H₂) ( 2a–c ), (η⁵-Me₃EC₅H₄)₂Ti[S₂C₂(CN)₂] ( 3a–c ) and (η⁵-Me₃EC₅H₄)₂Ti(S₂C₆H₃Me-4) ( 4a–c ). These have been characterized by ¹H NMR, IR, and mass spectroscopy, and have been compared with the unsubstituted η⁵-C₅H₅ analogues 2d, 3d and 4d . Activation energies for the chelate ring inversion in solution of 2a–c, 3a–d and 4a–c have been estimated by temperature-dependent ¹H NMR spectroscopy.     

H-, C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

Using ¹H- and ¹³C-NMR spectroscopies, cationic intermediates formed by activation of L₂ZrCl₂ with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L₂ are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R)₂ZrCl₂ (R=Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, Me₅, n-Bu, t-Bu), rac-ethanediyl(Ind)₂ZrCl₂, rac-Me₂Si(Ind)₂ZrCl₂, rac-Me₂Si(1-Ind-2-Me)₂ZrCl₂, rac-ethanediyl(1-Ind-4,5,6,7-H₄)₂ZrCl₂, (Ind-2-Me)₂ZrCl₂, Me₂C(Cp)(Flu)ZrCl₂, Me₂C(Cp-3-Me)(Flu)ZrCl₂ and Me₂Si(Flu)₂ZrCl₂. Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R)₂ZrCl₂/MAO (R=H, Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, Me₅, n-Bu, t-Bu) and rac-Me₂Si(Ind)₂ZrCl₂ were established. The catalysts (Cp-R)₂ZrCl₂/AlMe₃/CPh₃⁺B(C₆F₅)₄⁻ (R=Me, 1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄, n-Bu, t-Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R)₂ZrMe⁺←Me⁻-Al≡MAO (IV) with different [Me-MAO]⁻ counteranions have been identified in the (Cp-R)₂ZrCl₂/MAO (R=n-Bu, t-Bu) systems at low Al/Zr ratios (50-200). At Al/Zr ratios of 500-1000, the complex [L₂Zr(μ-Me)₂AlMe₂]⁺[Me-MAO]⁻ (III) dominates in all MAO-based reaction systems studied. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr=200-1000) for the systems (Cp-R)₂ZrCl₂/MAO (R=H, Me, n-Bu, t-Bu), while it is virtually constant in the same range of Al/Zr ratios for the catalytic systems (Cp-R)₂ZrCl₂/MAO (R=1,2-Me₂, 1,2,3-Me₃, 1,2,4-Me₃, Me₄) and rac-Me₂Si(Ind)₂ZrCl₂/MAO. The data obtained are interpreted on assumption that complex III is the main precursor of the active centers of polymerization in MAO-based systems.     

(η2-Me4C5H)Me2Si(η5-Me4C5)Ge+ GeCl3−:: Alkene coordination at divalent germanium

The compound (η²-Me₄C₅H)Me₂Si(η⁵-Me₄C₅)Ge⁺GeCl₃⁻ is the first example of alkene coordination at a main group element substantiated by X-ray crystallography. The complex was prepared from monometalated dimethylsilanediylbis(2,3,4,5-tetramethylcyclopenta-2,4-diene) and germanium dichloride-dioxane. The intramolecular interaction between the diene and the central germanium atom suggests that main group elements can coordinate with ordinary unsaturated hydrocarbons.     

Conformational analysis—XXI : H NMR Conformational Study of Alkyl-Substituted 2-Oxo-1,3,2-Dioxathianes

2-Oxo-1,3,2-dioxathiane and all methyl- and several alkyl-substituted 2-oxo-1,3,2-dioxathianes were prepared for a ¹H NMR conformational study. The conformational energy of the axial SO group in CCl₄, - ΔG^θ_SO = 14.8±0.3kJ mol^?1, was determined by chemical equilibration of the epimeric cis-4,6-dimethyl derivatives and it was found to decrease with the increasing solvent polarity. The conformational equilibria of alkyl-substituted derivatives were solved and the proportions of the conformers estimated using ¹H NMR chemical shifts, vicinal coupling constants and in three cases also dipole moments. The configurational interactions in the C₄C₅C₆ moiety are close to the corresponding values of 1,3-dioxanes.     

Gallium tri-chloride derivatives of the sterically demanding pyridines 2,6-Ar2C6H3N (Ar = 2,4,6-Me3C6H2 or 2,4,6-Pr3C6H2)

The sterically demanding pyridines 2,6-Ar₂C₆H₃N [Ar = 2,4,6-Me₃C₆H₂ (1) or 2,4,6-Prⁱ₃C₆H₂ (2)] were prepared by a palladium catalysed Kumada C–C coupling reaction in high yield. Pyridine 1 reacted with one equivalent of GaCl₃ to afford the tetra-chloro gallate–pyridinium ion pair complex [GaCl₄]⁻[2,6-(2,4,6-Me₃C₆H₂)₂C₆H₃NH]⁺ (3). Contrastingly, pyridine 2 reacted with one equivalent of GaCl₃ to afford the anticipated donor-acceptor complex [GaCl₃{2,6-(2,4,6-Prⁱ₃C₆H₂)₂C₆H₃N}] (4). Complexes 1–4 have been characterised variously by single crystal X-ray diffraction, NMR, CHN, and mass spectrometry.     

Synthesis and reactivity of zirconium and hafnium complexes incorporating chelating diamido-N-heterocyclic-carbene ligands

Early transition metal complexes employing a diamido N-heterocyclic carbene (NHC) ligand set (denoted [NCN]) render the centrally disposed NHC moiety stable to dissociation. Aminolysis reactions with the mesityl-substituted ligand precursor (^Mes[NCN]H₂) and M(NMe₂)₄ (M = Zr, Hf) provide bis(amido)-NHC-metal complexes that can be further converted to chloro and alkyl derivatives. Activation of ^Mes[NCN]M(CH₃)₂ with [Ph₃C][B(C₆F₅)₄] yields {^Mes[NCN]MCH₃}{B(C₆F₅)₄}, which is surprisingly inactive for the polymerization of 1-hexene. The zirconium cation did, however, show moderate ability to catalytically polymerize ethylene. The hafnium dialkyls are thermally stable with the exception of the diethyl complex, ^Mes[NCN]Hf(CH₂CH₃)₂, which undergoes β-hydrogen transfer and subsequent C–H bond activation with an ortho-methyl substituent on the mesityl group. The hafnium dialkyl complexes also insert carbon monoxide and substituted isocyanides to yield η²-acyls and η²-iminoacyls, respectively. In some circumstances, further C–C bond coupling occurs to yield enediolates and eneamidolate metallocycles. The molecular structures of ^Mes[NCN]Hf(CH₂CHMe₂)₂, ^Mes[NCN]Hf(η²-(2,6-Me₂C₆H₃NCCH₃)(CH₃), ^Mes[NCN]Hf(η²-(2,6-Me₂C₆H₃NCCH₃)₂, ^Mes[NCN]Hf(OC(CH₃)C(CH₃)NXy), and [^Mes[NCN]Hf(OC(ⁱBu)C(ⁱBu)O)]₂ are included.