Zur reaktion von metall-koordiniertem kohlenmonoxid mit yliden : VII. Trimethylphosphoranylidenmethyl(trimethylsiloxy)carben-komplexe von chrom,molybdän und wolfram: aufbau einer metallvinyl-einheit durch c(carbanion)c(carben)-π-wechselwirkung und photochemische e/z-isomerisierung

The treatment of the hexacarbonylmetal compounds M(CO)₆ (M = Cr. Mo, W) with two equivalents Me₃PCH₂ yields the phosphonium acylmetalphosphorus ylides Me₄P[(CO)₅MC(O)CHPMe₃] 1a–1c. Their reaction with Me₃SiOSO₂CF₃ leads via O-silylation to formation of the neutral “siloxy(ylidecarbene) complexes” (CO)₅MC(OSiMe₃)CHPMe₃2a–2c, which are protonated by HX (X = Cl, CF₃SO₃) to give the thermolabile carbene complexes [(CO)₅MC(OSiMe₃)H₂CPMe₃]X, 3a, 3b. ¹H, ¹³C NMR and IR data suggest, that delocalization of the ylidic charge to the carbene carbon generates a metal-coordinated vinyl group in the case of 2a–2c. In addition this fact is proved by the X-ray analysis of 2c, for which a C(ylide)C(carbene) bond distance of 133 pm is found. 2a–2c are obtained as pure E-isomers but can be converted to the Z-isomers 2a′–2c′ upon photolysis.     

Addition conjuguee de derives lithies de dithianne-1,3 aux aldehydes αβ ethyleniques

In order to synthesize γ carbonyl aldehydes which are interesting precursors in organic synthesis, we examine the action of masked acylanions, the lithiated derivatives from 1,3 dithiane 1a and 2-phenyl-1,3- dithiane on selected unsaturated aldehydes: crotonaldehyde 2, cinnamaldehyde 3 3-methyl butenal 4 and methacrolein 5. In THF 1a leads with the four aldehydes to allylic alcohols. However 1b gives products resulting both from CC and CO additions. Using THF-HMPA, we show that CC addition is generally enhanced. Furthermore, in all cases examined CC and CO addition take place under kinetic control: the regioselectivity observed can be interpreted by repulsive interactions due to the substrate and the reagent structure as well as lithium-carbonyl compound interactions.     

A study of gaseous 3-membered ring oxonium and sulphonium ions

The 1-methyl-1-thionia cyclopropane 3 and 1-phenyl-1-thionia cyclopropane 4 ions are stable, with lifetimes greater than 10^?5 sec, and can be identified from their collisional activation spectra. Their metastable counterparts (lifetime window 10^?6–10^?5 sec) have undergone ring opening to the isomeric structures CH₃S⁺CHCH₃9 and C₆H₅S⁺CHCH₃11 prior to decomposition. The 1-methyl-1-oxonia cyclopropane 1 and 1-phenyl-1-oxonia cyclopropane 2 ions could not be generated: instead acyclic structures CH₃O⁺CHCH₃5 and C₆H₅O⁺CHCH₃7 were found for both metastable and long living species. Loss of a phenoxy radical from C₆H₅OCH₂CH₂OCH₃ is shown to be preceded by a reciprocal hydrogen transfer and is not due to a SN_i-type reaction.     

Ein neuer koordinationstyp bei acyclischen phosphaalkenen: F3CPC(F)NMe2 als (η1-μ2) 4e-donator

The chromium complex Cr(CO)₅[F₃CPC(F)NMe₂] (2) in chloroform solution is slowly transformed at room temperature to give the binuclear system [(CO)₅Cr]₂[F₃CPC(F)NMe₂] (3) besides the C-amino substituted phosphaalkene F₃CPC(F)NMe₂ (1). The yield of this process amounts to 21% within 6 months. The X-ray diffraction analysis of 3 reveals a so far unknown coordination mode of acyclic phosphaalkenes: 1 operates as (η¹-μ₂) 4e donor.     

Insertion d'une phosphine acétylénique dans un complexe μ-alkylidénique du tungstène suivie de la rupture d'une liaison CP

The diphosphinoalkyne Ph₂PCCPPh₂ (2) reacts with the μ-alkylidene complex (CO)₉W₂[CHCHC(CH₃)₂] (1) to give, upon insertion of the alkyne into one of the CW bonds of the bridging carbene followed by rupture of a CP bond, a phosphido complex (CO)₈W₂[C(PPh₂)CCHCHC(CH₃)₂] PPh₂ (3). An unexpected long-range ¹H³¹P coupling, through five bonds, is observed in complex 3.     

Electronic effect of η5-cyclopentadienyl and η3-allyl ligands on the nature of the metal—olefin bond: Reversal of the relative olefin affinity of palladium(II) and platinum(II) ions

The barrier to olefin rotation in [Pt(η³-CH₂CMeCH₂)(olefin)(PPh₃)]PF₆ (3) (olefin = CH₂CH₂, E-MeCHCHMe) has been found to be extremely low compared to those in the other known, 4-coordinate olefin complexes of Pt^II. This can be ascribed to the smaller steric congestion around the olefin in 3. The corresponding barrier in [Pt(η⁵-C₅H₅)(CH₂CH₂)(PPh₃]ClO₄ (2), possessing likewise small steric congestion, was substantially higher than that in 3 (olefin = CH₂CH₂). The ¹³C and ³¹P NMR measurements have revealed much larger J(Pt-C(olefin)) in 2 than that in 3 (olefin = CH₂CH₂), while J(Pt-P) are comparable in these two. Stability constant data suggested that Pd^II ion in the Pd(η⁵-C₅H₅)(PPh₃)⁺ moiety is a better π-donor to olefins than Pt^II ion in the Pt(η³-CH₂CMeCH₂)(PPh₃)⁺ moiety, a reversal of the normal trend in the relative olefin affinity of these metal ions. The above spectral and stability features have been related to the electronic effect of the Cp ligand in enhancing the π back-bond interaction in one particular orientation of the CC bond.     

Selenirene as an intermediate in the pyrolysis of 1,2,3-selenadiazole. Microwave spectra of 13C labelled selenoketene

Microwave Spectra of ¹³CH₂¹²C^80,78Se and ¹²CH₂¹³C^80,78Se (selenoketene) are recorded. B 5-¹³C-1,2,3-selenadiazole all four species are formed. The ¹³C scrambling may take place via a three-membered ring, selenirene, but as expected its microwave spectrum was not observed.     

Ethylenic compounds reactivity: bromination—XLI: Relative reactivities of R1CMeCH2 and R1CHCMe2 series as a criterion for distinguishing between bridged and acyclic transition states. Degree of symmetry of the bromonium ion-like transition state

Reactivities of homogeneous series of ethylenic compounds R¹CHCH₂1, trans R¹CHCHMe 2, R¹MeCCH₂3 and R¹CHCMe₂4 have been measured in methanol at 25°C (R¹ Me, Et, n-Pr, -CH₂C₆H₅-CH₂OCOCH₃, -CH₂Cl). The criterion developed to decide between a bridged and a carbonium ion-like transition state is based on an internal comparison of the series and avoids resorting to external structural scales. Even in the case of alkenes 3 and 4 which are very dissymmetric with respect to polarity, the sensitivity to polar effects remains constant and the transition state behaves like a symmetric entity; only a slight secondary effect, attributed to hyperconjugation, is detectable.     

Übergangsmetall—methylen-komplexe: LXI. Übergangsmetall—vinyliden-komplexe: Neuartige synthese aus diazoalken-vorstufen

The diazoolefines of composition N₂CCR₂ (R/R = CH₃/CH₃ and(-CH₂-)₅) are suitable precursors of the corresponding vinylidene ligands CCR₂. Thus, treatment of the RhRh complex [(η⁵-C₅Me₅)Rh(μ-CO)]₂ (1) with the N-nitrosourethanes 2a and 2b, resp., in the presence of lithium t-butoxide yields the otherwise inaccessible μ-vinylidene complexes (μ-CCR₂)[(η⁵-C₅Me₅)Rh(CO)]₂ (R = CH₃ (3a), R,R = (-CH₂-)₅ (3b)). The analogous cobalt compound (μ-CCMe₂)[(η⁵-C₅Me₅)Co(CO)]₂ (5a) is obtained similarly. This procedure extends the well-documented diazoalkane method for the synthesis of μ-alkylidene complexes to the less stable diazoalkenes. A single-crystal X-ray diffraction study of the dimethylvinylidene derivative 3a shows the CMe₂ ligand to adopt an almost symmetrically metal-bridging position (d(RhC) 197.8(1) and 204.3(1) pm), with a rhodium-rhodium single bond completing a three-membered Rh₂C-metallacycle (d(RhRh) 268.4(0) pm) analogous with cyclopropane.     

Synthesis and X-ray structure of two isomeric aminocarbene complexes of tungsten containing a free carbon-carbon double bond

The reaction of allylamine with (CO)₅WC(OCH₂CH₃)CH₃ gives two isomeric aminocarbene complexes (CO)₅WC(NHCH₂CHCH₂)CH₃ 2E and 2Z. Refluxing of a solution of this mixture in benzene gives the complexes (CO)₄WC(η²NHCH₂CHCH₂)CH₂ (3) and 2E, which have been separated. 2E was fully characterized by X-ray diffraction. Crystals of 2E are monoclinic, space group P2₁/n with Z = 4, a 7.188(3), b 14.312(2), c 12.530(2) Å and β 91.06(3)°.The same mixture when treated with lithium diisopropylamide (LDA) followed by allyl bromide gives a mixture of (CO)₅WC(N(CH₂CHCH₂)₂)CH₃ (4) and 2Z. These complexes were separated, and 2Z fully characterized by X-ray diffraction. Crystals of 2Z are monoclinic, space group P2₁/c, with Z = 4, a 6.593(5), b 14.584(3), c 13.323(1) Å and β 95.13(4)°.     

Amidinoethylation—a new reaction—IV : The amidinoethylation of alcohols: a facile synthesis of 3-alkoxy-N,N'-substituted-propanamidines

The amidinoethylation of alcohols takes place by the addition of sodium alkoxides 2 (R¹ = Me, Et) to the CC double bond of a variety of N,N'-substituted-propenamidines 1 (Method A). This illustrates the activation of the CC double bond by the conjugated amidine function and provides a new class of Michael acceptors for alcohols. However, this activation is poorer than with other nucleophiles or Michael acceptors. The amidinoethylation makes available 3-alkoxy-N,N'-substituted-amidines not easily accessible by other classical methods. However, it is demonstrated that the general N,N'-substituted-amidine synthesis via the nitrilium salts can also apply to nitrile compounds having an alkoxygroup present on the molecule (method B). Since the cyanoethylation of alcohols (4) is a very fast and facile reaction the method B is the preferred strategy for the synthesis of 3-alkoxy-N,N'-substituted-propanamidines 3.     

Preparation of siloxycarbenemanganese complexes including a chelated siloxycarbene-alkene complex

Reaction of Li{(η⁵-C₅H₄Me)Mn(CO)₂]C(O)Ph]} with one equivalent of RSiMe₂Cl yields (η⁵-C₅H₄Me)Mn(CO)₂[C(Ph)(OSiMe₂R)] for R  CH₃, CHCH₂, and CH₂CHCH₂ (1a–c, respectively). Low temperature photolysis of the vinyl derivative, 1b, results in formation of a chelated manganese siloxycarbene-alkene complex, (η⁵-C₅H₄Me)MN(CO)[C(Ph)(η²-OSiMe₂CHCH₂)]. (2). Photolysis of the allyl derivative, 1c, under similar conditions leads to uncharacterized decomposition products. Infrared, ¹H, ¹³C, and ²⁹Si NMR data are reported for these new siloxycarbenemanganese derivatives.     

Übergangsmetall—methylen-komplexe: LIX. Ein neues darstellungsverfahren für vinyliden-komplexe

The diazo olefins N₂CCR₂ (R/R = CH₃/CH₃ and (CH₂)₅, respectively), generated in situ from the corresponding cyclic N-nitrosourethanes 2a, 2b, are suitable precursors for the corresponding vinylidene ligands 6CCR₂. Thus, treatment of the RhRh complex [(η⁵-C₅Me₅)Rh(μ-CO)]₂ (1) with 2a, 2b in the presence of lithium ethoxide yields the otherwise inaccessible μ-vinylidene complexes (μ-CCR₂)[(η⁵-C₅Me₅)Rh(CO)]₂ (3a, 3b). This procedure extends the well-documented diazoalkane method for synthesis of μ-alkylidene complexes to the less stable diazoalkenes*     

Factors controlling the regioselectivity of additions to α-enones—III: Reactions of 3-aryl α-enones with phosphorylated anions

Reaction of phosphonoester 2 and phosphononitrile 3 with chalcone and p-methoxychaleone in THF-t-BuOK at room temperature gives only the product resulting from CC double bond attack. The same reagents with benzalacetone lead to mixture of products resulting from CC double bond and carbonyl attack, though phosphine oxide 4 gives only the products of CC attack. Dypnone gives products of carbonyl attack with 3 and does not react with 2.These results are discussed in terms of perturbation theory: C₄ attack increases with delocalization of the reagent's negative charge and lowering of the α-enone LUMO level.     

Thermolysis of [tris(trimethylsilyl)methyl](diphenyl)fluorosilane. Isomerization of a sila-olefin intermediate

The compound (Me₃Si)₃CSiPh₂F loses Me₃SiF under reflux or on passage through a tube at 450°C to give three products, A, B, and C, in approximately 20/20/60 ratio. Products A and B, which are solids, were shown by X-ray crystallographic analysis to be the diastereoisomeric forms of 1-dimethylsila-2-trimethylsilyl-3-[(methyl)(phenyl)sila]indane. From its mass and ¹H NMR spectra, C (a liquid) was tentatively identified as 1,3-bis(dimethylsila)-2-[(dimethyl)(phenyl)silyl]indane. All three products are isomers of the sila-olefin (Me₃Si)₂CSiPh₂, and it is suggested that the latter is first formed by loss of Me₃SiF from (MeSi)₃CSiPh₂F, and the equilibrium (Me₃Si)₂CSiPh₂ ? (Me₃Si)(Ph₂MeSi)CSiMe₂ ? (Me₃Si)(PhMe₂Si)CSiMePh ? (Me₂PhSi)₂CSiMe₂ is then rapidly established; internal cyclizations involving addition of aryl CH bonds across SiC bonds then occur to give the observed products. Consistent with this is the observation that a mixture of silicon alkoxides, thought to be (Me₃Si)₂CHSiPh₂OMe and its isomers (which would be formed by addition of methanol across the SiC bonds of the four sila-olefins) is produced when methanol is passed through the hot tube with the (Me₃Si)₃CSiPh₂F.Full structural details are given for compounds A and B. Some features of interest are: (a) the conformation of the 5-membered ring is different in the two diastereoisomers; (b) the exocyclic SiCSiMe₃ bond angles, of ca. 120° are unusually large; and (c) there is a little distortion of the fused benzene ring, which is attributed to the effect of silicon substituents on the hybridization of carbon atoms to which they are attached.     

Acetolysis of the trifluoromethanesulphonates of syn-12-hydroxyaldrin and syn-12-hydroxyisodrin and their dihydro derivatives : Reduction in neighbouring double bond participation effected by chlorine substituents

Acetolysis rates of the trifluoromethanesulphonates of two geometric isomers of hexachlorotetracyclo[6.2.1.1^3,6.O^2,7]dodeca-4,9-dien-12-ol (6, 8; syn-12-hydroxyaldrin, syn-12-hydroxy-isodrin) and of two geometric isomers of hexachlorotetracyclo[6.2.1.1^3,6.O^2,7dodec-9-en-12-ol (7,9; syn-12-hydroxy-4, 5-dihydroaldrin, syn-12-hydroxy-4,5-hydroisodrin) have been determined. The results show that neighbouring double bond participation by a —ClCCCl— grouping that is juxtaposed to an incipient secondary carbenium ion (> CH·OSO₂CF₃ is negligible compared with that seen in the non-chlorinated prototypes containing an analogously-situated —CHCH— grouping (e.g.4). The products of acctolysis of 8 and 9 were acetates of the original carbocyclic ring system, but the acctolysis of 6 at 64° yielded, as the sole rearranged product, a hexachloropentacyclo[7.2.1.O^2,8.O^3,5.O⁴]dodecen-6-yl acetatc10. The major products of acetolysis at 64° of 7 were a mixture of two isomeric hexachlorotetracyclol[6.3.1.O^2,9.O^3,7]dodecen-11-yl acetates(17,18) and a hexachloropentacyclo[6.4.0.O^2,10.O^3,7.O^9,11 dodec-4-ene 15; these were each formed via an initial bridging reaction and subsequent rearrangement steps. The factors that dictate the nature of products formed from each compound are discussed, and probable pathways to each are delineated.     

Semiempirical calculations of ground state properties and rotational barriers in conjugated ethylenes

Ground state properties of methyl-2-carbomethoxy-3-dimethylaminoacrylate 4, and methyl-2-carbomethoxy-3-(1-aziridino) acrylate 5 were calculated by semiempirical methods and found to be in good agreement with the experiment. Barriers to rotation about the CC double bond and the C-N single bond were also calculated, allowing for structure relaxation in the transition state. A comparison of the calculated and experimental barriers to rotation shows good agreement for the rotation about the C-N bond and poor agreement for the rotation about the CC bond. This discrepancy is explained in terms of solvent stabilization of the polar transition state.     

Ligandgesteuerte Ringkontraktion von Nickela-fünf- in Vierringkomplexe—neuartige startsysteme für die präparative chemie

Nickela-compounds with a five-membered ring, 4, are formed on Ni⁰ from CO₂ and alkenes in the presence of the heterodifunctional ligand (cyclo-C₆H₁₁)₂PCH₂CH₂-2-pyridyl (2). A ring contraction occurs on addition of a promoteor, such as BeCl₂, or on heating. The greater reactivity of the nickela-complex with a four-membered ring, 6, can be used in the former reactions with CO₂, CO or CH₂CH₂. Such a sequence of reactions can be employed for the catalytic reaction of ethene with acrylic anilide on a (C₆H₁₁)₃P/Ni⁰ system.     

Mechanistic study of the aldol condensation occurring in the alkaline solution of 3-hydroxy 2-oxo propranoate (β hydroxypyruvate)

With 3-bromo-2-oxopropanoate (β bromopyruvate) and its ethyl ester, the ionisation of the gemdiol of the hydrated form BrCH₂-C(OH)₂-COOR 1 initiates the elimination of bromide anion yielding 3-hydroxy-2-oxopropanoate 2 (β-hydroxypyruvate). The mechanism of the reaction was investigated essentially by polarography in aqueous solution.In neutral (and acid) media, the polarographic behaviour of 2 resembled that of other α-ketoacids: reduction at the mercury electrode yielded glycerate.In alkaline media, there was evidence of the carbanion enolate ^-O—CHC(OH)—COO^-. 3'. The overall rate constant was determined according to a kinetic law of the typer:v = k.¦2¦.¦OH^-¦; found k = 1,56 min^-1 in NaOH 0.5 N at 25°.In the pH range 10.5 to 11.5,3' existed in minor amounts and initiated a slow aldol condensation with the tautomer 3-oxo-2-hydroxypropanoate 4 (tartronate Semialdehyde) according to a kinetic law of the type v = k?.¦2¦².¦OH^-¦found k? = 211.mol^-1 min ^-1 at 25° , at pH 11.0.The aldol product was isolated as a sodium sail and its structure established by ¹³C NMR.