Diphosphan-tetraphenylnickelacyclopentadien

Reaction of 1,2-bis(diorganophosphino)ethanenickel dibromide (I) with 1,2,3,4-tetraphenyl-1,4-dilithiumbutadiene (II) at ?30°C yields diphosphannickelacyclopentadiene (III) which at elevated temperatures isomerizes to diphosphanecyclobutadienenickel(0) (IV). The thermodynamic and kinetic parameters of the rearrangement were determined. The structural and conformational analyses of III were carried out by means of ¹³C NMR, ³¹P NMR and Raman spectroscopy. The reactions of III and IV with CH₃COOH, CO, RCCR and RNCNR have been axamined and the observed reactivities III ? IV are discussed.     

Understanding the Initial Decomposition Pathways of the n‐Alkane/Nitroalkane Binary Mixture

Addition of nitroalkanes into n‐alkanes can lower the activation barriers of free‐radical production and accelerate the decomposition of n‐alkanes at relatively low temperatures. Four initial decomposition mechanisms of the n‐butane/nitroethane binary mixture were proposed for the promoting effect and considered theoretically at the B3LYP, BB1K, BMK, MPW1K, and M06‐2X levels with MG3S basis set. Energetics above was compared to high‐level CBS‐QB3 and G4 calculations. Calculated results confirm the feasibility of the four initial decomposition pathways: (I) the C? NO₂ bond rupture of nitroethane to produce ethyl and ·NO₂, (II) HONO elimination from nitroethane followed by decomposition to ·OH and ·NO, (III) rearrangement of nitroethane to ethyl nitrite which further dissociates into CH₃CH₂O· and ·NO, and (IV) direct hydrogen‐abstraction of nitroethane with n‐butane.     

An ESR study of PMMA mechanoradicals and of their interaction with oxygen

Analysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicals? CH₂? C(CH₃)(COOCH₃) (I) and CH₂? C(CH₃)(COOCH₃)? CH₂ (II) produced by the breaking of the polymer chain, and secondary radicals ? CH₂? C(CH₃)(COOCH₃)? CH? C(CH₃)? (COOCH₃)? CH₂? (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA).     

Insect pheromones and their analogues. XVIII. Regiospecific synthesis of (±)-15,19-dimethyltritriacontane — A component of the pheromone of Stomoxys calcitrans

(±)-15,19-Dimethyltritriacontane (II) — a component of the pheromone of the stable fly — has been obtained by a five-stage synthesis from dimethylcyclooctadiene (I). The coupling of 1,1-dimethoxy-4-methyl-8-oxonon-4Z-ene [the product of the ozonolysis of (I)] with n-C₁₃H₂₇CH=PPh₃ (THF; ?30°, 2 h; 25°, 15 h; Ar) gave 1,1-dimethoxy-4,8-dimethyldocosa-4Z,8Z(E)-diene (III). The hydrolysis of (III) (TsOH·Py, H₂O-Ac, boiling, 4 h) gave the corresponding aldehyde (IV). The condensation of (IV) with n-C₁₀H₂₁CH=PPh₃ (THF; ?60° to ?30°C, 2 h, 25°C, 15 h) led to 15,19-dimethyltritriaconta-11Z(E),15Z,19Z(E)-triene (V), the exhaustive hydrogenation of which (ethanol, H₂, 5% Pd/C, 25°C) gave (II). The substance, the yield in %, and R_f values are given, respectively: (II), 95, 0.92; (III), 29, 0.74; (IV), 80, 0.72; (V) 50, 0.8. The IR and PMR spectra of compounds (II)–(V) and the mass spectra of (II) and (III) are given.     

Structure,thermal stability and decomposition of bis-allyl-zinc compounds

The structure, thermal stability and decomposition of solutions of diallylzinc (I), bis(2-methylallyl)zinc (II), bis(3-methylallyl)zinc (III) and bis(3,3-dimethylallyl)zinc (IV) in deuterated solvents, have been investigated by¹H NMR and by kinetic measurements at temperatures between ?125 and +180°C. At room temperature I, II, III and IV are dynamic systems and are best described as being rapidly equilibrating mixtures of all isomeric σ-allyl forms; the NMR spectra are averages weighted according to the relative concentrations of the respective forms. I displays a¹H NMR spectrum of a static σ-allyl system only below ?125°C and II only below ?115°C. At temperatures above 100°C the thermal decomposition of I–IV results in coupling of the allyl groups, decomposition via radicals being the major process. The coupled products exhibit CIDNP, in which the multiplet polarisations confirm a decomposition via randomly diffusing allyl radicals. In the allyl radicals CH₂CR¹CR²R³ an alternating spin density was proved experimentally. The thermal stability decreases in the order I > II > III > IV.     

Four Crystalline Forms of (Tetrahydrothiophene)trichloridogold(III): Polymorphism and Reversible Low‐temperature Phase Transitions

The title compound (tht)AuCl₃, previously known to crystallize at –95 °C in space group C2 with Z = 4 (form I ), converts reversibly to form II (P2₁/n, Z = 8) at ca. –150 °C; the b axis doubles and the centering is lost. A few crystals of a rarer form III (Pna2₁, Z = 4) were also investigated; these transform reversibly to form IV (P2₁/c, Z = 4) at ca. –160 °C. In all forms, stacks of molecules are formed, with short Au ··· Cl contacts within the stacks. For forms I and II , adjacent stacks are connected by C–H ··· Cl interactions; more striking for forms III / IV are short Cl ··· Cl contacts between the stacks. Detailed physico‐chemical studies of the relationships between the various phases proved to be impossible, largely because form III could not be obtained reproducibly in significant quantities.     

Insect pheromones and their analogs

A four-stage asymmetric synthesis of (+)-disparlure [(7R,8S)-(+)-cis-methyl-7,8-epoxyoctadecane (V)] has been effected from 8-methylnon-2Z-en-l-ol (I), obtained by the carboalumination of acetylene with tris(5-methylhexyl)aluminum using the Sharpless reaction. The asymmetric epoxidation of (I), (Ar, mol. sieve A, (+)-DET, (iOPr)₄Ti, t-BuOOH, ?15°C, 20 h; H₂O, 1 h, NaOH, ?7°C, 30 min) gave 8-methyl-2S,3R-epoxynonan-l-ol (II), which was oxidized (kieselguhr-CrO₃-Py, 0°C, 2 h; 25°C, 2 h) to 8-methyl-2S,3R-epoxynonan-l-al (III). The coupling of (III) with n-C₈H₁₇CH=PPh₃ (?78°C, 1 h; 25°C, 15 h) gave 2-methyl-7R,8S-epoxyoctadec-9Z-ene (IV), the hydrogenation (H₂/5% Pd-C, 25°C, 5 days) of which led to (V) in admixture with an isomerization product. Compound (V) was isolated by HPLC. Substance, yield, [α] _D ²⁵ : (II), 73, ?2.75°; (III), 80, [80.8°; (IV), 50, +37.25°; (V), 50, +0.8°. The IR and PMR spectra of (II–IV), the¹³C NMR spectra of (II) and (III), and the mass spectrum of (IV) are given.     

ESR.-Studies of Nonalternant Radicals Structurally Related to Phenalenyl

The radical anion and the radical cation of azuleno[1,2,3-cd]phenalene (III) have been investigated by ESR. spectroscopy, along with the radical anion of 2-phenylazulene (IV). Also studied has been the neutral radical obtained by one-electron reduction of cyclohepta[cd]phenalenium-cation (VI^⊕). Assignment of the proton coupling constants for the radical ions III. ·?, III ·⊕ and IV·⊕, and the radical VI · is supported by comparison with the ESR. spectra of specifically deuteriated derivatives III-d₅ ·?, III-d₅ ·⊕, IV-d₂ ·? and VI-d₁′. The experimental results are in full accord with qualitative topological arguments and predictions of HMO models. Whereas the radical anion III ·? exhibits α-spin distribution similar to that of IV ·?the corresponding radical cation III ·⊕ and the neutral radical VI · are related in this respect to phenalenyl (V·). It is noteworthy that oxidation of III by conc. H₂SO₄ yields a paramagnetic species (IIIa ·⊕) which has a similar – but not an identical – structure as the radical cation III ·⊕ produced from III with AlCl₃ in CH₃NO₂.     

The tautomerization and ring closure in the Claisen rearrangement: A DFT study

Elementary processes of the aromatic Claisen rearrangement were investigated by DFT calculations. First, rearrangements of four substrates Ph—O—CH₂—CHCH₂ [A], Ph—O—CH₂—CHCH(OMe) [B], Ph—O—CH₂—CHCH₂····BF₃ [C], and Ph—O—CH—CHCH(OMe)····BF₃ [D] were examined. In these systems, the tautomerization is initiated by the intermolecular proton transfer involving the transient ion‐pair intermediate. An ignition‐propagation chain‐reaction mechanism in the tautomerization was suggested. For [A], the (ortho‐allyl phenol → α‐methyl‐dihydrobenzofuran (α‐methyl‐cumarane)) process was found to be ready and the product of the Claisen rearrangement seems to be the cumarane rather than the phenol. In [D] (activated both by the terminal methoxy group and by the BF₃ catalyst), not the [3,3]‐sigmatropic shift but the tautomerization is the rate determining step. Second, the parent system, Ph—O—CH₂—CHCH₂, was investigated with (H₂O) _n (n = 2, 4, 6, and 10) systematically. The tautomerization takes place by the proton transfer via the water dimer or trimer. Except n = 2, similar changes of Gibbs free energies were obtained from the ether substrate to the cumarane.     

Dibenz [b,f]-1, 4-oxazepin-11 (10 H)-one und Dibenz [b,e]-1, 4-oxazepin-11 (5 H)-one. 12. Mitteilung über siebengliedrige Heterocyclen

The syntheses of dibenzo [b, f]-1, 4-oxazepin-11 (10 H)-ones (I) with electron-attracting substituents in position 2 by ring closure of the sodium salts of 2-halogeno-2′-hydroxy-benzanilides (II) are described. The reaction of II (R = SO₂·N(CH₃)₂) in N-methylpyrrolidone also led, by SMILES rearrangement, to the isomeric minor product dibenzo [b, e]-1, 4-oxazepin-11 (5 H)-one (III; R = SO₂·N(CH₃)₂), whose constitution was proven by synthesis from VI. In the case of II (R = SO₂·CH₃), the 5-methylsulfonyl-2-(2-hydroxyanilino)-benzoic acid (VI; R = SO₂·CH₃) was obtained directly after hydrolysis. The lactam I (R = NO₂) was rearranged to the corresponding acid VI by heating with dilute caustic soda.     

5-Aza(Oxa,Thia)-2,8-dithia-1-stanna(II)-bicyclo[3.3.01,5]octane Intramolekular basenstabilisierte Stannylene

5-Aza(oxa, thia)-2, 8-dithia-1-stanna(II)-bicyclo[3.3.0^1,5]octanes — Intramolecular Stabilized Stannylenes By the reaction of tin(II) butoxide with mercaptanes of the general type E(CH₂? CH₂SH)₂ (E ? N-t-Bu, NMe, O, S) at temperatures up to 50°C the 5-aza(oxa, thia)-2, 8-dithia-1-stanna(II)-bicyclo[3.3.0^1,5]octanes I—IV are obtained in high yields. The compounds are monomeric in solution. Contrary at higher reaction temperatures (80°C) the spiro-compounds of the type [E(CH₂CH₂S)₂]₂Sn ( V—VIII ) are formed. Some typical stannylene reactions of I—IV with BF₃, Cr(CO)₆, Br₂, and PhS? SPh show the high reactivity of the compounds. Their structure is investigated by ¹H, ¹³C, and ¹¹⁹Sn n.m.r., i.r., and Mössbauer spectroscopy.     

Structural comparisons between methylated and unmethylated nitrophenyl lophines

The lophine derivative 2‐(2‐nitrophenyl)‐4,5‐diphenyl‐1H‐imidazole, C₂₁H₁₅N₃O₂, (I), crystallized from ethanol as a solvent‐free crystal and from acetonitrile as the monosolvate, C₂₁H₁₅N₃O₂·C₂H₃N, (II). Crystallization of 2‐(4‐nitrophenyl)‐4,5‐diphenyl‐1H‐imidazole from methanol yielded the methanol monosolvate, C₂₁H₁₅N₃O₂·CH₄O, (III). Three lophine derivatives of methylated imidazole, namely, 1‐methyl‐2‐(2‐nitrophenyl)‐4,5‐diphenyl‐1H‐imidazole methanol solvate, C₂₂H₁₇N₃O₂·CH₄O, (IV), 1‐methyl‐2‐(3‐nitrophenyl)‐4,5‐diphenyl‐1H‐imidazole, C₂₂H₁₇N₃O₂, (V), and 1‐methyl‐2‐(4‐nitrophenyl)‐4,5‐diphenyl‐1H‐imidazole, C₂₂H₁₇N₃O₂, (VI), were recrystallized from methanol, acetonitrile and ethanol, respectively, but only (IV) produced a solvate. Compounds (III) and (IV) each crystallize with two independent molecules in the asymmetric unit. Five imidazole molecules in the six crystals differ in their molecular conformations by rotation of the aromatic rings with respect to the central imidazole ring. In the absence of a methyl group on the imidazole [compounds (I)–(III)], the rotation angles are not strongly affected by the position of the nitro group [44.8 (2) and 45.5 (1)° in (I) and (II), respectively, and 15.7 (2) and 31.5 (1)° in the two molecules of (III)]. However, the rotation angle is strongly affected by the presence of a methyl group on the imidazole [compounds (IV)–(VI)], and the position of the nitro group (ortho, meta or para) on a neighbouring benzene ring; values of the rotation angle range from 26.0 (1) [in (VI)] to 85.2 (1)° [in (IV)]. This group repulsion also affects the outer N—C—N bond angle. The packing of the molecules in (I), (II) and (III) is determined by hydrogen bonding. In (I) and (II), molecules form extended chains through N—H...N hydrogen bonds [with an N...N distance of 2.944 (5) Å in (I) and 2.920 (3) Å in (II)], while in (III) the chain is formed with a methanol solvent molecule as the mediator between two imidazole rings, with O...N distances of 2.788 (4)–2.819 (4) Å. In the absence of the imidazole N—H H‐atom donor, the packing of molecules (IV)–(VI) is determined by weaker intermolecular interactions. The methanol solvent molecule in (IV) is hydrogen bonded to imidazole [O...N = 2.823 (4) Å] but has no effect on the packing of molecules in the unit cell.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XL. Über Lithium-alkenylmanganate(II)

Contributions to the Chemistry of Transition Metal Alkyl Compounds. XL. About Lithium Alkenylmanganates(II) MnCl₂ reacts with vinyl, 2,2-dimethylvinyl, allyl, and methallyl lithium giving rise to alkenyl manganates(II). In a pure state the compounds Li₂[Mn(CH?CH₂)₄] · 1.5 diox, Li₂[Mn(CH?C(CH₃)₂)₄] · 1.5 diox, Li₂[Mn(CH₂? CH?CH₂)₄] · 2.5 diox and Li₃[Mn(CH₂? C(CH₃)?CH₂)₅] · 2 diox were isolated. The compounds were characterized by elementary analysis, EPR and IR spectra, magnetic moments, and reactions with iodine.     

Reaction of chlorine with platinum(IV) triamine containing N,N-dimethylethylenediamine. The crystal structure of [Pt{(CH3)2N(CH2)2NH2}PyCl3]Cl·H2O[Pt{(CH3)2N(CH2)2NCl}PyCl3], and [Pt{(CH3)2N(CH2)2NH2}PyCl4]

The Platinum(II) diamine with N,N-dimethylethylenediamine (N,N-dimeEn) [Pt{(CH₃)₂N(CH₂)₂NH₂}Cl₂] (I) was synthesized. The reaction of the diamine with pyridine gave Pt(II) tetramine [Pt{(CH₃)₂N(CH₂)₂NH₂}Py₂]Cl₂ (II), which was oxidized with chlorine to give Pt(IV) triamine Pt{[(CH₃)₂N(CH₂)₂}PyCl₃]Cl · H₂O (III). The reaction of III with chlorine (chloroamidation) yielded chloroimide [Pt{(CH₃)₂N(CH₂)₂NCl}PyCl₃] (IV). The IR spectra of complexes I–IV and UV/Vis spectra of III and IV were studied. X-Ray diffraction analysis was performed for III (monoclinic crystals, space group P2₁/c, a = 7.7437(6), b = 8.1100(7), c = 28.52992(2) Å, β = 93.7280(10)°, Z = 4, R _hkl = 0.0420) and IV (orthorhombic crystals, space group Pna2₁, a = 15.7825(12), b = 7.4447(6), c = 12.3099(6) Å, Z = 4, R _hkl = 0.0539). During oxidation of Pt(II) tetramine with chlorine, the pyridine molecule is removed from the cis position relative to the (CH₃)₂N group (trans position relative to the NH₂ group) of N,N-dimethylethylenediamine. The reaction of chloroimide complex IV with concentrated HCl (dechloroamidation) at 20°C afforded the initial complex III; that at 100°C, gave triamine III together with Pt(IV) diamine [Pt(N,N-dimeEn)Cl₄] (V) (monoclinic crystals, space group P2₁/n, a = 7.1278(5), b = 11.5384(8), c = 12.7501(9) Å, β = 93.23(10)°, Z = 4, R _hkl = 0.0239).     

Synthesis and Thermal Study of Magnesium Complexes with 8-hydroxyquinolinate Derivatives

Magnesium ion was reacted with 5,7-dibromo-, 5,7-dichloro-, 7-iodo-and 5-chloro-7-iodo-8-hydroxyquinoline, in acetone/ammonium hydroxide medium under constant stirring to obtain (I) Mg[(C₉H₄ONBr₂)₂]·2H₂O; (II) Mg[(C₉H₄ONCl₂)₂]·3H₂O; (III) Mg[(C₉H₅ONI)₂]·2H₂O and (IV)Mg[(C₉H₄ONICl)₂]·2.5H₂O complexes. The compounds were characterized by elemental analysis, IR spectra, ICP, TG-DTA and DSC. Through thermal decomposition residues were obtained and characterized, by X-ray diffractometry, as a mixture of hexagonal MgBr₂ and cubic MgO to the (I) compound at 850°C; cubic MgO to the (II), (III) and (IV) compounds at750, 800 and 700°C, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Syntheses and structures of three macrocyclic supramolecular complexes and one ZnII‐containing coordination polymer generated from a semi‐rigid multidentate N‐containing ligand

Semirigid organic ligands can adopt different conformations to construct coordination polymers with more diverse structures when compared to those constructed from rigid ligands. A new asymmetric semirigid organic ligand, 4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine ( L ), has been prepared and used to synthesize three bimetallic macrocyclic complexes and one coordination polymer, namely, bis(μ‐4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine)bis[dichloridozinc(II)] dichloromethane disolvate, [Zn₂Cl₄(C₁₂H₁₀N₆)₂]·2CH₂Cl₂, ( I ), the analogous chloroform monosolvate, [Zn₂Cl₄(C₁₂H₁₀N₆)₂]·CHCl₃, ( II ), bis(μ‐4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine)bis[diiodidozinc(II)] dichloromethane disolvate, [Zn₂I₄(C₁₂H₁₀N₆)₂]·2CH₂Cl₂, ( III ), and catena‐poly[[[diiodidozinc(II)]‐μ‐4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine] chloroform monosolvate], {[ZnI₂(C₁₂H₁₀N₆)]·CHCl₃}_n, ( IV ), by solution reaction with ZnX₂ (X = Cl and I) in a CH₂Cl₂/CH₃OH or CHCl₃/CH₃OH mixed solvent system at room temperature. Complex ( I ) is isomorphic with complex ( III ) and has a bimetallic ring possessing similar coordination environments for both of the Zn^II cations. Although complex ( II ) also contains a bimetallic ring, the two Zn^II cations have different coordination environments. Under the influence of the I^? anion and guest CHCl₃ molecule, complex ( IV ) displays a significantly different structure with respect to complexes ( I )–( III ). C—H…Cl and C—H…N hydrogen bonds, and π–π stacking or C—Cl…π interactions exist in complexes ( I )–( IV ), and these weak interactions play an important role in the three‐dimensional structures of ( I )–( IV ) in the solid state. In addition, the fluorescence properties of L and complexes ( I )–( IV ) were investigated.     

The fragmentation of some alkyl thio-phosphate esters by electron-impact

The mass spectra of the following compounds have been studied: and the fragmentation pathways established with the aid of accurate mass measurements, metastable transition and appearance potential determination. The mass spectra show that the sulphur-containing compounds (II to IV) give a stronger molecular ion that that of compound I. A further significant difference is the low intensity, in the mass spectra of II to IV, of the fragments relative to the processes that occur in I, probably because the electron removed upon ionisation belongs to the sulpher atom in compounds II to IV and to the oxygen in compound I. The isomeric compounds, (III and IV) show quite different mass spectra, The radicals containing only Phosphorus and oxygen have an ionisation potential close to 9 eV and the presence of sulphur considerably lowes this value. The measured ionisation potentials of compounds I to IV are respectively, 10·7₀, 9·5₅, 9·2₀ and 9·0₀eV. The heats of formation of compounds II and III have been estimated as ?176 and ?118 Kcal mole^?1, respectively.     

Lanthanide complexes with pyridine-2,6-dicarboxylic acid: synthesis,crystal structure,thermal and magnetic properties of [LnPDA)2(PDAH2)] · (DMAH2)2(DMAH0.5)2

Mild solvothermal synthesis, structures, thermal and magnetic properties of coordination complexes [Ln(PDA)₂(PDAH₂)] · (DMAH₂)₂(DMAH_0.5)₂(I–IV) (PDA = pyrdine-2,6-dicarboxylate anion, DMAH = dimethylamine, Ln = Ce, Nd, Sm, and Ho) are described. The DMAH molecules in I–IV, generated in situ from hydrolysis of N,N-dimethylformamide, are responsible to assemble three dimensional coordination polymers through N–H···O and C–H···O hydrogen bonds. Distorted tricapped trigonal prismatic LnO₆N₃ geometry having 14 triangular faces is attributed to mean deviation of dihedral angles while nitrogen shows fairly triangular faces having dihedral angle close to 60°C (CIF files CCDC nos. 872065 (I), 872070 (II), 872069 (III), and 872066 (IV)). Curie–Weiss law and the overall magnetic behavior are typical for the presence of antiferromagnetic exchange coupling interactions between lanthanide. Thermal decomposition analyses reveal removal of ammonia and resultant complexes showthermal stability. Complexes have been further characterized by using elemental analyzer and FT-IR spectroscopy.     

Redox reactions of peroxo terpyridine complexes of Cu(II), Zn(II), and Cu(II)?Zn(II): A pulse radiolysis study

The reactions of e_aq⁻, CH₂OH·, (CH₃)₂COH·, CO, OH· and N₃· radicals with peroxo terpyridine complexes of Cu(II), Zn(II), and Cu(II) Zn(II) in aqueous solution were investigated by pulse radiolysis. The primary products from the reduction and oxidation of the macrocyclic complexes were assigned a radical nature by comparing their optical spectra with those of Cu(I), Zn(I), and Cu(III) species. Such metal–ligand radical products undergo disproportionation that does not lead to the formation of Cu(0) or colloidal copper. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 92–98, 2000     

Ringöffnende acetylierung eines an kobalt koordinierten ringliganden vom divinylboran-typ

(C₅H₅)Co[2–6-η-(CH₃)₂Si(CHCH)₂BC₆H₅(III) is prepared photochemically from (C₅H₅)Co(CO)₂ and (CH₃)₂Si(CHCH)₂BC₆H₅ (II). Acetylation of the new complex III with CH₃COCl/AlCl₃ and subsequent hydrolysis effect ring-opening new complex III with CH₃COCl/AlCl₃ and subsequent hydrolysis effect ring-opening to give (C₅H₅)Co[(1,2-η-(cis-CH₃COCH)CH(η-CH₂CH)Si(CH₃)₂] (IV) which slowly isomerizes (ΔG^≠₂₉₆ 100 ± 2 kJ mol^?1) to the corresponding trans-isomer (V).Pure (CH₃)₂Si(CHCH)₂Sn(CH₃)₂ (I) can be obtained in preparative quantities via the new complex (CH₃)₂Si(CHCH)₂Sn(CH₃)₂ · 2 CuCl.