CHC CH Research Articles

σ 3,λ 4-Phosphandiyl-Komplexe: 1,3-Dipolare cycloaddition von Diazomethan an eine Phosphor-Metall-Mehrfachbindung

The reaction of (2,4,6- tBu 3C 6H 2O(HCCCH 2)PMoCp(CO) 2 ( I) (2,4,6- tBu 3C 6H 2O  R) with CH 2N 2 ( II) gives, via a 1,3-dipolar cycloaddition, the expected compound (R)(HCCCH 2) PNN CH 2M oCp(CO) 2 ( III), that contains a five-membered cycle of Mo, P, N and C; III can be isolated at low temperature in high yields. When solutions of III are warmed to 25°C, dinitrogen elimination takes place and the three-membered cycle of (R)(CHCCH 2) PCH 2M oCp(CO) 2 ( IV) is formed. Whereas I reacts with II to form III, no reaction takes place when {(R)[(η 2-HCCCH 2)Co 2(CO) 6]}PMoCp(CO) 2 ( VII) is treated with II. However, the expected product, {(R)[(η 2-CHCCH 2)Co 2(CO) 6]} PCH 2M oCp(CO) 2 ( VI), can be synthesized by the reaction of IV with Co 2(CO) 8 V. All new compounds have been identified by elemental analysis and IR, MS, 1H, 31P and 13C NMR spectroscopy.

Solution Conformation of the Tetrasaccharide Glycoside Xylβ1-(Manα1-3)2Manβ1-4Glcβ1R from the Mollu-Series Glycosphingolipids

The conformation of Xylβ1-(Manα1-3)2Manβ1-4Glcβ1-OCH 2CH(N 3)CH(OH) CHCHC 13H 27 tetrasaccharide glycoside in Me 2SO- d 6 was investigated with use of a distance mapping procedure based on rotating-frame NOE and hydrogen bond constraints, and Molecular Mechanics calculations. The Manα1-3Manβ linkage was found to be well defined in a single conformation, whereas some flexibility could he assumed for the remaining two glycosidic linkages. Similar conclusions, though based on a smaller number of constraints, were drawn for the title compound anchored in mixed D 2O/dodecylphosphocholine- d 38 micelles.

Hydride-phosphoniodithiocarboxylate/ phosphonium-betaine isomerism in Cy 3PCS 2 complexes of ruthenium

Reaction of Cy 3PCS 2 (Cy = cyclohexyl) with the hydrido complexes [RuClH(CA)(PPh 3) 3] (A  O, S), [RuH(CO)(NCMe) 2(PPh 3) 2] +, and [RuH(OClO 3)(CO)(CN tBu)(PPh 3) 2] leads to the complex cations [RuH(CA)(PPh 3) 2(η 2-S 2CPCy 3)] +, [Ru(η 2-S 2CHPCy 3)(CO) (PPh 3) 2] +, [RuH(η 1-S 2CPCy 3)(CO)(CN tBu)(PPh 3) 2] +. The σ-vinyl complex [Ru(CHCHC 6H 4Me-4)Cl(CO)(PPh 3) 2] reacts with Cy 3PCS 2 to give the cationic complex [Ru(CHCHC 6H 4Me-4) (CO)(PPh 3) 2(η 2-S 2CPCy 3)] +, but this complex is not formed by hydroruthenation of HCCC 6H 4Me-4 by [RuH(CO)(PPh 3) 2(η 2-S 2CPCy 3)] +. The inter-relationships between the above complexes are discussed.

Reaction of C 5Me 5(CO) 2Re(HCCCH 3)with Ph 3C +PF 6− produces the η 3-allyl complex C 5Me 5(CO) 2 Re[η 3-Ph 2CC(Ph)CHCH 3] +PF 6−

The reaction of C 5Me 5(CO)2Re(HCCCH 3) ( 3) with Ph 3C 0+PF 6 − led to an unusual rearrangement and the formation of the π-allyl complex C 5Me 5(CO) 2Re[η 3-Ph 2CC(Ph)CHCH 3] +PF 6 − ( 4). This transformation, involves addition of trityl to the η 3-allyl system, a migration resulting in attachment of methyl and hydrogen to the same carbon, and a phenyl migration.

Acetylene, methylacetylene and ethylacetylene polymerization on H-ZSM5: a spectroscopic study

Acetylene, methylacetylene and ethylacetylene interact with the Bronsted acid sites of H-ZSM5 with the formation of hydrogen-bonded (precursor) species characterized by well defined IR properties. These precursors are then protonated to give intensely coloured carbocationic species. The speed of protonation is in the order: C2H5—CCH > CH3—CCH > HCCH. Insertion of the monomer into the first protonation product, leads to an oligomeric species with carbocationic character. The IR and UV–VIS spectra of the carbocationic species are discussed in detail and found to correspond to those of analogous species generated in the homogeneous phase. The π-delocalization of the positive charge on the backbone is responsible for the peculiar and intense spectroscopic manifestations both in the IR and UV–VIS. The positive charge in the carbocationic species can be captured by bases (NH3, pyridine) and subtracted to π-delocalization. This is accompanied by the disappearance of the spectroscopic manifestations associated with the positive charge and by the appearance of new absorptions associated with neutral oligomeric chains. The process can be fully reversed.The dimensions and shape of the oligomers are discussed in terms of the steric constraints imposed by the zeolitic framework, by means of computer graphics and molecular mechanics modelling.

An energy-resolved study of the fragmentation of some siloxide ions

The reaction of O − with substituted trimethylsilanes, RSi(CH 3) 3, under chemical ionization (CI) conditions produces [M − H] −, [M − 2H] − , R(CH 3) 3SiO − and (CH 3) 3SiO −. The ratio of the R(CH 3) 2SiO − to (CH 3) 3SiO − products is much greater under O − Cl conditions than under OH − CI conditions, consistent with different mechanisms for fragmentation of the transitory pentacoordinate intermediates formed by attack of O − and OH − at silicon. The collision-induced fragmentation reactions of R(CH 3) 2SiO − (R  C 6H 5, HCC, CH 3CC, HCCCH 2, c-C 5H 5, CH 2CH and CH 2CHCH 2) have been studied as a function of collision energy over the range from 5 to 50eV on a laboratory scale using N 2 collision gas. The dominant fragmentation reactions involve formation of RH + CH 3Si(O)CH 2 − and formation of R − + CH 3Si(O)CH 3, with the latter generally increasing in importance with increasing collision energy. The results are consistent with fragmentation occurring through the intermediacy of an R −/CH 3Si(O)CH 3 ion/dipole complex. When R  CH 2CH and CH 2CHCH 2, elimination of CH 4 from R(CH 3) 2SiO − is observed as well as elimination of [R  H]. The results for the R(CH 3) 2SiO − ions are compared with those for their carbon analogues, R(CH 3) 2CO −.

A stereoselective synthesis of 1-phenyl-1-buten-3-yne and some 1-heteroaryl analogues.

Z-Enynes, RCHCHCCH (R= phenyl, 2-furyl, 2- and 3-thienyl and 3-pyridyl) can be obtained in ∼ 40% overall yields and with a stereoselectivity of > 95% by Pd/Cu-catalyzed cross-coupling of the readily available enyne sulfide HCCCHCHSC 2H 5 with RBr and RI, reduction of the products with activated zinc powder in ethanol and elimination of ethanethiol from the reduction products RCHCHCHCHSC 2H 5 with an excess of sodamide in liquid ammonia. In the case of the 2-pyridyl-substituted substrate the E-enyne HCCCHCH-2-pyridyl is isolated.

Ab initio study of the structures and thermodynamic properties of some gem-disubstituted propyl radicals: The effects of ethyl groups on the stabilization energies of these disubstituted radicals

The equilibrium structures and vibrational frequencies of some disubstituted propyl radicals, especially CH 3CH 2C(OH) 2, CH 3CH 2C(NH 2) 2, CH 3CH 2C(CHO) 2, CH 3CH 2C(OH)-(CHO) and CH 3CH 2C(NH 2)(CHO), were studied by ab initio molecular orbital methods. Geometries were optimized at the unrestricted Hartree-Fock (UHF) level of theory for open-shell species, using the 6–31G and 6–31G ∗∗ basis sets. The enthalpies of formation of these radicals were estimated by using the concept of the isodesmic reaction. These data were used to calculate the thermodynamic stabilization energies of these compounds which influence the methyl addition radical reactions to olefins.

Half-way coordination state of a butadienyl group on ruthenium. η 3-Allylic bonding with η 1-character or vice versa

The butadienyl complexes formed by the reaction of trans-(R 1)CHCHCCR 2 (R 1, R 2  SiMe 3, tBu, Me, Et) with RuCl(CO)H(PPh 3) 3 exhibit unique structures: instead of taking the 18-electron configuration of the metal by conventional η 3-coordination of the butadienyl ligand, they shift significantly to the 16-electron η 1-coordination state.

Polyazolyl chelate chemistry: IV. Dihydrobis(benzotriazolyl)borato complexes of ruthenium(II)

The reactions of the salt K[H 2B(bta) 2] (bta = benzotriazol-1-yl) with the compounds [RuCIR(CO)-(PPh 3) n ] ( n = 3, R = H; n = 2, R = C 6H 4Me-4, CHCHC 6H 4Me-4, CHCHC 4H 9, C(CCHPh) give high yields of the chelate complexes [RuR(CO)(PPh 3) 2{η 2-H 2B(bta) 2}]. The hydrido complex can also be made by similar treatment of the salt [RuH(NCMe) 2(CO)(PPh 3) 2]BF 4, and gives the chloro-derivative [RuCl(CO)(PPh 3) 2{η 2-H 2B(bta) 2}] upon treatment with N-chlorosuccinimide.

Propargyl complexes of ruthenium

The first ruthenium-propargyl complexes CpL 2RuCH 2 C=CPh (LCO ( 1) and PPh 3 ( 2)) were synthesized by reaction of [Cp(CO) 2Ru] − with PhCCCH 2Cl or PhCCCH 2OS(O) 2C 6H 4Me- p and of Cp(PPh 3) 2RuCl with PhC CCH 2MgCl, respectively. In contrast, treatment of [Cp(CO) 2Ru] − with HCCCH 2Cl affords the ruthenium-η 1-allenyl complex Cp(CO) 2RuCHCCH 2 ( 3). Complex 1 is protonated by HBF 4·OEt 2 to ( syn-Cp(CO) 2Ru(η 2CH CCHPh)]BF 4 ( 4a), which isomerizes within 2 h in acetone solution at room temperature to [ anti-Cp(CO) 2Ru(η 2-CH 2 CCHPh)]BF 4 ( 4b). Compound 4b reacts with Pt(PPh 3) 2(C 2H 4) to give the ruthenium-substituted platinum (II)-η 3allyl complex [(η-CH 2C(Ru(CO) 2Cp)CHPh)Pt(PPh 3) 2]BF 4 as the anti isomer quantitatively. Compound 1 undergoes facile [3 + 2] cycloaddition reactions with tetracyanoethylene (TCNE) and p-toluenesulfonyl isocyanate (TSI); the latter reaction in CH 2 Cl 2 solution at 25°C proceeds slightly more rapidly (1.3 times) than the corresponding reaction of Cp(CO) 2FeCH 2 CCPh. With Co2(CO) 8, 1 yields the trinuclear (CO) 3Co(μ-η 2-PhCCCH 2 Ru(CO) 2Cp)Co(CO) 3, which undergoes very slow cleavage of the RuCH 2 bond with CF 3CO 2H, and replacement of CO (at Co) with PPh 3. The foregoing reactions are compared and contrasted with the corresponding reactions of Cp(CO) 2FeCH 2CCPh. Where a comparison has been made, 2 was found to react faster than 1; however, its chemistry tends to be complicated by the lower stability of products and a facile PPh 3-Co ligand exchange. With TSI and CO 2 (CO) 8, the products are analogous to those of 1 but with Fe 2(CO) 9 Cp(CO)PPh 3)RuCH 2CCPh and Fe(CO) 4PPh 3 are obtained instead of heteronuclear metal complexes.

Synthesis and characterization of 5-cyano-6-methyl-2,2'- bipyridine metal-complex dyes

New 1:1 5-cyano-6-methyl-2,2'-bipyridine-metal (Co, Ni, Cu, and Zn) complex dyes have been synthesized in good yields. The metals do not significantly affect the wavelength of maximum absorption of the complexes; substituents at the 4-position showed remarkable bathochromic shifts in the following order: CHCHC 6H 4NMe 2(p)>C 6H 4NMe 2(p)>C 6H 5, ferrocenyl.

Butyllithium-induced dimerization of pent-3-en-1-yne and related additions

The enynes HCCCHCHCH 2R (R  H, Me, OMe, NMe 2 SMe), are converted into dimers by treatment with slightly more than two equivalent of butyllithium. The Zconfiguration predominates in the dimers obtained after aqueous workup. The lithiated enynes (R  H, Me, SMe) and acetylenic compounds LiCCCH 2R (R  SMe, C 6H 5) add in an analogous way to the double bond of LiCCCHCH 2.

Acetylen-Komplexe von Di(η 5-cyclopentadienyl)molybdän: Synthesen und Protonierung. Struktur von [Cp 2MoH{η 2-C 2(SiMe 3) 2}]PF 6

Cp 2MoH 2 reacts with methyl acrylate in the presence of acetylenes (L = C 2H 2, C 2Me 2, HCC tBu, HCCSiMe 3, C 2(SiMe 3) 2, HCCCH 2OMe, HCCCH 2NMe 2) to form acetylene complexes Cp 2Mo(L) 5. Protonation takes place with CF 3CO 2H at −80°C to give short-lived cations [Cp 2MoH(L) + ( 8) (L = C 2Me 2, HCCSiMe 3, C 2(SiMe 3) 2). The structure of [Cp 2MoH{η 2-C 2(SiMe 3) 2}]PF 6( 9) was determined by an X-ray diffraction study.

Some chiral alkyne-cobalt complexes

The trimethyl phosphite substituted pentacarbonylpropargyldicobalt cation, [(CHCCH 2) Co 2(CO) 5L] + [L = P(OMe) 3], is significantly more stable than its phosphine analogues (L = PPh 3, PBu 3), and has been converted to a series of ethers. (CHCCH 2OR)Co 2(CO) 5L. Reaction of the (cholesteryl propargyl ether)hexacarbonyldicobalt complex with trimethyl phosphite proceeds without stereoselectivity, and the product suffers metal-carbon rather than oxygen-carbon cleavage on treatment with acid.

Hydrogen bonding between vinylacetylene and HF: the role of steric effects in the geometry of vinylacetylene…HX complexes

The rotational spectrum of a hydrogen-bonded dimer between vinylacetylene (H 2CCHCCH) and HF has been obtained with a pulsed-nozzle Fourier-transform microwave spectrometer. Analysis of the derived spectroscopic constants shows that the HF molecule attaches preferentially to the triple bond in vinylacetylene, in a T-type configuration close to the CC bisector, at a perpendicular distance R CC…F of 3.072 Å. The r o structure of the dimer is planar and a limit of 9° is placed on the equilibrium departure from planarity by consideration of the average r * structure. This is in contrast to an out-of-plane angle of 34° in vinylacetylene…HCl; the difference is rationalised in terms of changes in steric interaction between vinylacetylene and the HX proton donor.

Selectivity in the propargylation of polyfunctional amines by (propargylium)-Co 2(CO) 6+ and -(C 5H 5) 2Mo 2(CO) 4+

[(HCCCH 2)Co 2(CO) 6]BF 4 ( 1) [(HCCCH 2)Mo 2(C 5H 5) 2(CO) 4]BF 4 ( 2) react with primary and secondary amines in CH 2Cl 2 solution. In the case of primary amines, the products of mono and dialkylation are obtained. The more stable (less reactive) molybdenum complexes can be employed to alkylate amines in a protic, two-phase medium. The results are interpreted mechanistically and shown to dependent on the thermodynamic stability of the metal-stabilized carbocation.

Zirconoxycarbene complexes obtained by regioselective coupling of (isoprene)zirconocene with hexacarbonyltungsten and a ketone. Crystal structure of Cp 2[formula omitted]H 2

(η 4-Isoprene)zirconocene reacts with hexacarbonyltungsten to give the metallacyclic (π-allyl)zirconoxycarbene complex Cp 2 ZrOC[W(CO) 5]CH 2CHC(CH 3)C H 2 ( 14a), the structure of which has been determined by an X-ray diffraction study. Only one regioisomer is formed, that with the methyl substituent at the meso-position (C2) of the π-allyl-carbene ligand chain. Complex 14a undergoes insertion of one equivalent of acetone to give the nine-membered metallacyclic zirconoxycarbene complex Cp 2 ZrOC[W(CO) 5]CH 2CHC(CH 3)CH 2CR 1R 2O ( 18, R 1 = R 2 = CH 3), which has an E-configurated endocyclic CC double bond. The chiral metallacycle 18 undergoes a thermally induced intramolecular enantiomerization, the activation barrier for which has been determined by dynamic 1H NMR spectroscopy to be Δ G ent ≠ (280 K) = 14.3 ± 0.3 kcal/mol. With pinacolone, 14a forms an analogous nine-membered metallacyclic zirconoxycarbene complex (only one diastereoisomer observed under thermodynamic control), which undergoes a stereo-unselective base-induced α-alkylation reaction to yield a 55/45 mixture of diastereomeric C6-monomethylated carbene complexes.

An NMR spectroscopic and EHMO investigation of cationic mixed metal clusters: X-ray crystal structure of (1,7,7-trimethyl-μ 2-2-propynylnorbornene)-bis(cyclopentadienyl)tetracarbonyldimolybdenum

The reaction of (C 5H 5) 2Mo 2(CO) 4 with 2- endo-propynylborneol yields the tetrahedral cluster (R ★CCMe)Mo 2(CO) 4(C 5H 5) 2 ( 7), where R ★ is the 2-norbornenyl group. This chiral molecule crystallizes in the orthorhombic space group P2 12 12 1 with a 8.938(4), b 14.074(4), c 19.510(6) Å, V 2268(1) Å 3, D c 1.65 g cm −3, D m 1.64 g cm −3, for Z = 4, and R 1 = 0.0290 ( R 2 = 0.0276) for 4350 unique reflections ( R 1 = 0.0236, R 2 = 0.0245 for 3846 reflections with I > 2.5σ( I)). Protonation of 7 and of the related dicobalt cluster (2- endo-propynylborneol)Co 2(CO) 6 leads to metal stabilized cations which maintain their terpenoid skeletons and are stable towards carbocationic rearrangement. Protonation of the mixed metal clusters (C 5H 4Me)W(CO) 2Co(CO) 3(HCCCH 2OH), (C 5H 5)Mo(CO) 2Co(CO) 3(HCCCH 2OH), and (C 5H 5)Mo(CO) 2Co(CO) 3(HCCHEtOH) yields the corresponding cationic clusters [M-Co(CO) 3(HCCCR 2)] +. High field NMR spectroscopy reveals that the capping vinylidene moiety leands preferentially towards one vertex and the facile antarafacial migration which is observed in the homometallic complexes [M-M(HCCCH 2)] + (M = Co(CO) 3, (C 5H 5)Mo(CO) 2 or (C 5H 5)W(CO) 2) has a very high barrier in these mixed metal systems. Variable-temperature NMR studies on the mixed trimetallic cluster cation [(C 5H 5)Mo(CO) 2Co 2(CO) 6CC(CH 3) 2] + confirm that the carbocationic centre is better stabilized on the molybdenum vertex rather than by the tricarbonylcobalt fragment. These results are supplemented by EHMO calculations which demonstrate not only that the positive charge is better tolerated at the (C 5H 5)Mo(CO) 2 vertex but also that the transition state for antarafacial migration is strongly disfavored.

ORGANOGERMANIUM(IV) O,O,ALKYLENEDI-THIOPHOSPHATES

Abstract Tri- and di-organogermanium(IV) O,O-alkylenedithiophosphates R4-n ,Ge(S2PO2G)n (where R = Ph. Bu, Et. G =—C(CH3)2C(CH3)2[sbnd], [sbnd], CH2C(CH3)2CH2[sbnd], [sbnd]CH—CH3CH2C(CH3)2[sbnd], n= 1, 2) were synthesized by treatment of organogermanium(IV) chlorides with ammonium O,O-alkylenedithiophosphates in benzene. These are volatile, liquids except the phenyl ones which are solids. All of these are miscible in organic solvents and monomeric in refluxing benzene. Like dialkyldithiophosphate derivatives of organogermanium these cyclic ones also appear to be tetrahedral with the ligands behaving as unidentate ones.