MeC CMe Research Articles

Investigations on non-classical silylium ions leading to a cyclobutenyl cation.

Instead of yielding the desired non-classical silylium ions, the reactions of different alkenes/alkynes with several [Me3Si]+ sources mostly led to oligomerization, or - in the presence of Me3SiH - hydrosilylation of the alkenes/alkynes. Yet, from the reaction of 2-butyne with ion-like Me3Si-F-Al(ORF)3 (RF = C(CF3)3) the salt of the silylated tetramethyl cyclobutenyl cation [Me4C4-SiMe3]+[al-f-al]- 1 ([al-f-al]- = [(RFO)3Al-F-Al(ORF)3]-) was obtained in good yield (NMR, scXRD, Raman, and IR). All the experimental and calculated evidence suggest a mechanism in which 1 was formed via a non-classical silylium ion as an intermediate. The removal of the [Me3Si]+ moiety from the cation in 1 was investigated as a means to provide free tetramethyl cyclobutadiene (CBD). However, the addition of [NMe4]F, in order to release Me3SiF and form CBD, led to the unexpected deprotonation of the cation. The addition of 4-dimethylaminopyridine to remove the [Me3Si]+ cation as a Lewis acid/base adduct, led to an adduct with the four-membered ring in the direct neighborhood of the Me3Si group. By the addition of Et2O to a solution of 1, the [F-Al(ORF)3]- anion (and Et2O-Al(ORF)3) was generated from the [al-f-al]- counterion. Subsequently, the [F-Al(ORF)3]- anion abstracted the [Me3Si]+ moiety from [Me4C4-SiMe3]+, probably releasing CBD. However, due to the immediate reaction of CBD with [Me4C4-SiMe3]+ and subsequent oligomerization, it was not possible to use CBD in follow-up chemistry.

Structure and bonding in a cyclobutyl tris(pyrazolyl)boratoniobium complex and the variation in agostic behaviour with ring size in the series TpMe2NbCl(c-CnH2n − 1)(MeCCMe), n = 3–6

The synthesis and characterisation of the cyclobutyl complex Tp(Me2)NbCl(c-C4H7)(MeC[triple bond]CMe) completes the family of cycloalkyl complexes Tp(Me2)NbCl(c-C(n)H(2n-1)), n = 3-6. The properties of the cyclobutyl complex are qualitatively similar to those of its cyclopentyl and cyclohexyl analogues, and dramatically different from those of the cyclopropyl derivative. Most conspicuously, the cyclobutyl system has an alpha-C-H agostic interaction in the dominant isomer, with no evidence for the alpha-C-C agostic character found for the smaller ring. C-C agostic character therefore seems to be unique to the cyclopropyl complex, where the acute C-C-C angles destabilise the C-C bonding orbitals.

EPR and NMR spectroscopic studies of [MoL2(MeC identical to CMe)Cp]z (L = P-donor ligand, z = 0 and 1): fluxionality in a metal-alkyne redox pair.

Variable temperature NMR and EPR spectroscopic studies provide rates and activation parameters for alkyne rotation and oscillation, respectively, in the fluxional redox pair [Mo(P(OMe)3)2(MeC identical to CMe)Cp][BF4] (diamagnetic) and [Mo(P(OMe)3)2(MeC identical to CMe)Cp] (paramagnetic).

Carbon–carbon coupling reactions of but-2-yne on a triruthenium framework: synthesis and molecular structure of Ru 3(CO) 7[NS(O)MePh](HCMeCMeCMeCMeCO) and Ru 3(CO) 8(CMeCMeCMeCMe)

The cluster HRu 3(CO) 9[NS(O)MePh] ( 1) reacts with two equivalents of MeCCMe in tetrahydrofuran at 60°C to give the dienonyl derivative Ru 3(CO) 7[NS(O)MePh](HCMeCMeCMeCMeCO) ( 2), along with an isomer mixture of Ru 3(CO) 8[NS(O)MePh](HCMeCMe) ( 3). At 100°C, the same reaction gives rise to the formation of the diendiyl cluster Ru 3(CO) 8(CMeCMeCMeCMe) ( 4). The single-crystal structure analyses reveal for 2 a closed Ru 3 skeleton and for 4 an open Ru 3 framework.

Reactions of the rhenium allyl hydrido complex Cp*Re( η3-C 3H 5)(CO)(H) with the electrophiles CF 3CO 2H, CF 3SO 3H, NOBF 4, [ p-N 2C 6H 4OMe][BF 4] and [Ph 3C][BF 4

The rhenium hydrido allyl complex Cp*Re( η 3-C 3H 5)(CO)(H) ( 1) reacted with NOBF 4 or [ p-N 2C 6H 4OMe][BF 4] at −78°C to give [Cp*Re( η 2-C 3H 6)(CO)(NO)][BF 4] ( 2) or [Cp*Re( η 2-C 3H 6)(CO)(N 2C 6H 4OMe)][BF 4] ( 3), respectively. In these reactions addition of the electrophile is accompanied by transfer of the hydride ligand to the allyl group to form the propene ligand. Complex 1 reacted with [Ph 3C][BF 4] in CH 3CN at −78°C to abstract the hydride ligand and form the allyl acetonitrile complex [Cp*Re( η 3-C 3H 5)(CO)(CH 3CN)][BF 4] ( 4). Complex 1 reacted with CF 3CO 2H or CF 3SO 3H to form the hydrido propene complexes Cp*Re( η 2-C 3H 6)(H)(CO)(CF 3CO 2) (5) or Cp*Re( η 2-C 3H 6)(H)(CO)(CF 3SO 3) ( 6). Studies with CF 3CO 2D demonstrated that both Cp*Re( η 2-C 3H 6)(D)(CO)(CF 3CO 2) and Cp*Re( η 2-C 3H 5D)(H)(CO)(CF 3CO 2) are formed. This is consistent with a mechanism in which D + attacks the metal followed by transfer of either D or H to the allyl group. Complex 1 was found not to react with C 2H 4, hexene, cyclohexene, MeCCMe, PhCCMe, CH 3CN or PMe 3.

Synthesis, characterisation and reactivity of the first heptamethylindenyl-molybdenum complexes: crystal structures of [Mo(CO)( η2-MeCCMe) 2( η5-C 9Me 7)]BF 4 and MO(CO) 2( η3-C 3H 5)( η5-C 9Me 7)

The synthesis and characterisation of the first ( η 5-heptamethylindenyl)molybdenum complexes are reported. Reaction of Li[C 9Me 7] with Mo(CO) 6 in refluxing THF readily forms Li[Mo(CO) 3( η 5-C 9Me 7)]. which is shown to be a useful precursor in the formation of (carbonyl)(η 5-heptamethylindenyl)molybdenum complexes. The compounds [MoI(CO) 3( η 5-C 9Me 7] 3, [Mo(Me)(CO) 3( η 5-C 9Me 7)] 4 and [Mo(CO) 2( η 3-C 3H 5)( η 5-C 9Me 7)] 5 have been prepared from this intermediate and characterised Treatment of 3 with AgBF 4 and MeCCMe affords [Mo(CO)(MeCCMe) 2( η 5-C 9Me 7)]BF 4 6a; for this and the indenyl analogue, a new route to carbonylbis(alkyne)-molybdenum derivatives is demonstrated. Reaction of 3 with TIPF 6 in MeCN forms the complex [Mo(MeCN) 2(CO) 2( η 5-C 9Me 7)]PF 6 7. Protonation of 5 in the presence of MeCCMe, or reaction of 7 with the same acetylene, also yields 6 with appropriate counter anions. Single crystal X-ray diffraction studies of compounds 5 and 6a are reported.

Reactions of dinuclear and polynuclear complexes XVI. Chemistry of hydrido-, thiolato-bridged complexes [Mo 2Cp 2(μ-H)(μ-SR)(CO) 4] (R  Me, Ph): Reactivity and electrochemical behaviour; crystal structure of [Mo 2Cp 2(μ-SPh) { μ- σ : η2-C(CH 3)  CHCH 3}(CO) 2

Photolysis of [Cp 2Mo 2(μ-H)(μ-ER)(CO) 4] (ER  SMe ( 1) or SPh ( 2)) with MeCCMe gives the μ-vinyl complex [Cp 2Mo 2{ μ- σ : η 2-C(CH 3)CHCH 3}( μ-ER)(CO) 2] (ER  SMe ( 5) or SPh ( 6)) as the major product. Partial oxidation of 5 leads to the oxo compounds [Cp 2Mo 2(O) { μ- σ : η 2-C(CH 3)CHCH 3}( μ-SR)(CO] with a low yield. Compound 6 has been structurally characterized by X-ray diffraction. The structure contains μ- σ : η 2-C(CH 3)CHCH 3 bridging an MoMo double bond whose length is 2.644(1) Å. Chemical deprotonation of [Cp 2Mo 2(μ-H)(μ-ER)(CO) 4] ( 1 or 2) affords the anionic complex [Cp 2Mo 2(μ-ER)(CO) 4] − (R  SMe ( 8) and SPh ( 9)), which is also obtainable by electrochemical reduction. The fluxional behaviour of 8 and 9 and the mechanism of reduction of 1–4 (ER  S tBu( 3) or SePh( 4)) are described.

Mo(CO)2(PPh3)2(O3SCF3)2: Ein neuer Vorläufer einer dikationischen, metallorganischen Lewis‐Säure mit drei freien Koordinationsstellen

AbstractOrganometallic Lewis Acids, LIV. — Mo(CO)2(PPh3)2(O3SCF3)2: A New Precursor for an Organometallic Dicationic Lewis Acid with Three Accessible Coordination SitesThe reaction of Mo(CO)2(PPh3)2Br2 (1) with AgO3SCF3 gives the bis(triflate) complex Mo(CO)2(PPh3)2(O3SCF3)2 (3) which can be considered as a precursor for the 12‐e− system “Mo‐(CO)2(PPh3)2+2”. According to the spectroscopic data one of the two coordinated CF3SO−3 anions is acting as a chelate ligand. Treatment of 3 and of the in situ generated W(CO)2(PPh3)2(O3SCF3)2 (4) with H2O affords the dinuclear hydroxo‐bridged complexes [M2(μ‐OH)3(CO)4(PPh3)4][CF3SO3] (5: M = Mo; 6: M = W). Acetonitrile replaces the CF3SO−3 ligands in 3 and 4 to afford the cationic complexes [M(CO)2(PPh3)2(NCMe)3][CF3SO3]2 (7: M = Mo; 8: M = W). The reaction of 3 with an excess of 2‐butyne and 1‐phenyl‐1‐propyne leads to the monoalkyne complexes Mo(CO)(MeCCR)(PPh3)2(O3SCF3)2 (9: R = Me; 10: R = Ph) in moderate yield. In contrast, the bisalkyne complexes [M(CO)(MeCCMe)2(PPh3)2(O3SCF3)][CF3SO3] (11: M = Mo; 12: M = W) are formed in high yield when a CH2Cl2 solution of 2‐butyne is added to 1 and 2 in the presence of AgO3SCF3. At room temperature, 11 and 12 are highly fluxional in solution, while 9 and 10 are stereochemically rigid. Treatment of 11 with acetonitrile yields [Mo(CO)(MeCCMe)2(PPh3)2(NCMe)][CF3SO3]2 (13). Compounds 3–13 (except 4) are characterized by IR, 1H‐, 13C‐, 19F‐, and 31P‐NMR spectrescopy.

Matrix-isolation studies of alkyne complexes in the photochemical reactions of Mo(CO) 6 with alkynes

Photolysis of a low-temperature matrix X (X  Ar or CH 4) doped with molybdenum hexacarbonyl and an alkyne RCCR′ (HCCH, MeCCH, or MeCCMe) leads to the formation of the corresponding alkyne complex of molybdenum pentacarbonyl, [( η 2-RCCR′)Mo(CO) 5], in addition to [X … Mo(CO) 5] and CO; the products have been detected and characterised by their IR and UV-vis absorption spectra. The species [( η 2-RCCR′)Mo(CO) 5], unlike [X … Mo(CO) 5], is stable with respect to irradiation in the green region of the visible spectrum, and a scheme has been devised for the photochemical interconversion of the three species [Mo(CO) 6], [( η 2-RCCR′)Mo(CO) 5] and [X … Mo(CO) 5] in a mixed matrix composed of RCCR′ and X molecules. An η 2-alkyne complex of the type [(RCCH)Mo(CO) 5] (R  H or Me) undergoes rearrangement to give what is believed to be a vinylidene complex [R(H)CCMo(CO) 5]. Continued irradiation at λ = 313 nm causes the various pentacarbonyl complexes to lose CO with the formation of tetracarbonyl species. More significantly, irradiation at λ = 369 nm also results in photoejection of CO; this favours the formation of a product believed, on the evidence of its IR spectrum and of experiments with C 2D 2 and 12C 13CH 2, to be [( η 2-RCCR′)Mo(CO) 4] (R,R′ = H,H or Me,Me) in which the alkyne is acting formally as a 4e ligand. The IR spectra serve notice of further changes on prolonged photolysis under these conditions. The results are discussed in relation to intermediates in the catalytic polymerization of 1-alkynes.

Vinyliden-Übergangsmetallkomplexe XXVI. Synthese und struktur kationischer Carbonyl-, Alken-, Vinyliden-, Alkinyl- und Alkin-Rhodiumkomplexe mit der Baueinheit trans-[Rh(P iPr 3) 2

The complex trans-[Rh(CO)(NH 3)(PiPr 3) 2]PF 6 ( 2) was prepared from [(η 3-C 3H 5)Rh(P iPr 3) 2] ( 1), NH 4PF 6 and CO or from 1 and NH 4PF 6 in presence of an excess of methanol. With an excess of CO, the dicarbonyl and tricarbonyl compounds trans-[Rh(CO) 2(P iPr 3) 2]PF 6 ( 3) and [Rh(CO) 3(P iPr 3) 2]PF 6 ( 4) were obtained. Displacement of one CO ligand in 3 by pyridine and acetone led to the formation of trans-[Rh(CO)(py)P iPr 3) 2]PF 6 ( 5a) and trans-[Rh(CO) (OCMe 2(P iPr 3) 2]PF 6 ( 6), respectively. Treatment of 1 with [pyH]BF 4 and pyridine gave trans-[Rh(py) 2(P iPr 3) 2]BF 4 (7); in presence of H 2 the dihydrido complex [RhH 2(py) 2(P iPr 3) 2]BF 4 ( 8) was formed. The reaction of 1 with NH 4PF 6 and ethylene produced trans [Rh(C 2H 4(NH 3(P iPr 3) 2]PF 6(9) whereas with methylvinylketone and acetophenone the octahedral hydridorhodium(III) complexes [RhH(η 2-CHCHC(O)CH 3 (NH 3(P iPr 3) 2]PF 6( 11) and [RhH(η2-C 6H 4C(O)CH 3(NH 3(P ipr 3) 2]PF 6 ( 13) were obtained. The synthesis of the cationic vinylidenerhodium(I) compounds trans-[Rh(CCHR)(py)(P iPr 3) 2]BF 4 ( 14–16) and trans-[Rh(CCHR)(NH 3)(P iPr 3) 2]PF6 ( 17–19) was achieved either on treatment of 1 with [pyH]BF 4 or NH 4PF 6 in presence of 1-alkynes or by ethylene displacement from 9 by HCCR. With tert-butylacetylene as substrate, the alkinyl(hydrido)rhodium(III) complex [RhH(CC tBu)(NH 3)(OCMe 2)(P iPr 3) 2]PF 6 ( 20) was isolated which in CH 2Cl 2 solution smoothly reacted to give 19 (R  tBu). The cationic but-2-yne compound trans-[Rh(MeCCMe)(NH 3)(P i Pr 3) 2]PF 6 ( 21) was prepared from 1, NH 4PF 6 and C 2Me 2. The molecular structures of 3 and 14 were determined by X-ray crystallography; in both cases the square-planar coordination around the metal and the trans disposition of the phosphine ligands was confirmed.

Synthese und struktur zweikerniger cyclopentadienyltricarbonylmangan-komplexe vom Typ (CO)3Mn[(η5-C5H4)-X-(η 5-C5H4)]Mn(CO)3

The synthesis of various members of the family of title compounds (CO)3Mn[(η5-C5H4)-X-(η5-C5H4)] MnCO)3 has been achieved by a variety of methods: the mononuclear bridging groups X  S (1a) and X  Si(C6 H5)2 (1b) have been introduced by standard methods via (η5-C5H4Li)Mn(CO)3. The dicarbon bridging entities MeCCMe and MeC(OH)(OH)CMe have been formed by reductive coupling of the corresponding ring acetylated complexes. Reductive coupling of [η5-α-C5H3CH3(COCH3)]Mn(CO)3 (2a) under mild conditions with TiCl3/LiAlH4 leads to the corresponding vicinal diol (CO)3Mn[η5-C5H3(α-CH3)] C(OH)(CH3)C(OH)(CH3)[η5-C5H3(α-CH3)]Mn(CO)3 (3). Under less mild conditions the McMurry type reduction leads to the corresponding olefin (CO)3Mn[η5-C5H3(α-CH3)]C(CH3)C(CH3)[η5 -C5 H3(α-CH3)]Mn(CO)3 (4a). The olefin is obtained as a mixture of Z/E- and R/S-isomers; the corresponding four diastereomeric forms of 4a are separable by capillar gas chromatography. Using the same approach the β-isomer [η5-β-C5H3CH3(COCH3)]Mn(CO)3 (2b) yields a mixture of the four isomers of (CO)3Mn[η 5-C5H3(β-CH3)]C(CH3)C(CH3)[ η5-C5H3(β-CH3)]Mn(CO)3 (4b). In an analogous way (η5-C5H4-COCH3)Mn(CO)3 (5) is coupled to give the Z-(6a) and E-isomers (6b) of (CO)3 Mn[η5-C5H4]C(CH3)C(CH3)[η5-C5H4]Mn(CO)3. The isomers are easily separated by column chromatography. As a binuclear species closely related to the title compounds, {η5-C5H3CH3 [β-COCH2(η6-C6H5)Cr(CO)3]}Mn(CO)3 (8) is obtained by Cr(CO)3-complexation of {η5-C 5H3CH3[β-COCH2(C6H5)]}Mn(CO)3 (7). All the compounds have been characterised by the usual spectroscopic and analytical techniques. In addition the compounds 1a, 1b, 2a, the meso-form of 3, 3a, 6a, 6b and 8 have been characterised by X-ray analyses.

Umwandlung der Cluster Fe 3 (CO) 9 (μ 3 ‐η 2 ‐N 2 Et 2 ) und Fe 3 (CO) 9 (μ 3 ‐NEt) 2 zu organischen Produkten 1)

Conversion of the Clusters Fe3(CO)9(μ3-η2-N2Et2 and Fe3(CO)9(μ3-NEt)2 into Organic Products The azoalkane-bridged cluster Fe3(CO)9(μ3-η2-N2Et2) (1) and its thermal rearrangement product Fe3(CO)9(μ3-NEt)2 (2) are converted by standard routes into derivatives with one carbene ligand C(Ph)OEt (3, 4). Degradation (thermally or oxidatively) of these compounds produces the diaziridine (5) and/or the iminoester EtN = C(Ph)OEt (6). 4 and moist p-tolyl isocyanide form the indole derivative 8. 1 adds one or two equiv. of alkynes leading to the alkyne-bridged cluster 9 or the ferrole-type clusters 10. The clusters 10, resulting from HCCPh, exist as two isomers 10a and b which can be equilibrated and separated. An alternative route to 10 c (alkyne: MeCCMe) starts from Fe2(CO)6(C4Me4) by treating it with Fe2(CO)9 and N2Et2. Photolytic or oxidative degradation of the clusters 10 produces substituted furan 13, pyrrole 14, or dihydropyridazine 15. The crystal structures of the clusters 4, 9, 10a, and 10b have been determined.

Di(η 5-cyclopentadienyl)tantal-Chemie: Insertionen aktivierter Acetylene in die Tantal—Wasserstoff-Bindung der Tantalocen(acetylen)hydrido-Komplexe

The (acetylene)hydrido complexes Cp 2TaH(RCCR) (R = Me, Ph, Me 3Si, Bu t) react with activated acetylenes HCCX (X = Co 2Me, CN) to give α-insertion products Cp 2Ta(RCCR)[C(X)CH 2]. With dimethyl acetylenedicarboxylate (DMAC) stereospecific cis insertion affords the maleic ester derivatives Cp 2Ta(RCCR)[( E)-C(CO 2Me)CHCO 2Me] (R = Ph, Bu t). The structure of Cp 2Ta[C(CN)CH 2](MeCCMe) is that of a bent sandwich molecule with the 2-butyne lying in the pseudoequatorial plane and the alkenyl group in an almost perpendicular orientation (109.9°) to it.

Reaktionen an μ3‐verbrückenden Alkin‐Liganden auf Heterometallclustern

Reactions of μ3‐Bridging Alkyne Ligands on Heterometallic ClustersThe metal‐exchange methods to obtain alkyne‐bridged heterometallic clusters from RuCo2(CO)9(μ3‐RCC') (2) were improved, and the new clusters RuCoMoCp(CO)8(PhCCPh) (3c), RuCoNiCp(CO)6(MeCCPh) (5b), RuMoNiCp2(CO)5‐(MeCCMe) (6a), and HFeRuMoCp(CO)8(MeCCMe) (7a) were obtained thereby. Some of the alkyne‐bridged clusters were found to react with additional alkyne. One alkyne unit was incorporated in the products RuCoNiCp(CO)6(RCC')2 (9), two alkyne units were incorporated in the products Ru‐Co2(CO)7(RCC')3 (8). In a side reaction, butyne was trimerized to hexamethylbenzene. Radical anions of the clusters FeCo2(CO)9(RCC') (1) were formed by reduction with cobaltocene. The reaction of these radical anions with alkylating reagents was accompanied by cluster fragmentation and CO insertion converting the former alkyne ligand by acylation into the new trisubstituted oxoalkenyl ligand in the products FeCo(CO)6(μ‐CRCR'‐CR″O) (11). The constitutions of the cluster types 7, 9 and 11 were confirmed by crystal‐structure determinations.

Further studies of the synthesis of 1-naphthols and 4-hydroxy-5,6-dimethylbenzothiophene by protonation of Cp(CO) 2WCTol and Cp(CO) 2WC(2-C 4H 3S) in the presence of alkynes and carbon monoxide

The previously reported (K.E. Garrett et al., J. Am. Chem. Soc., 111 (1989) 8383) preparation of a naphthol derivative by protonation of Cp(CO) 2WCTol in the presence of MeCCMe has been extended to a variety of other alkynes (EtCCEt, HCC nPr, HCC iPr, HCC tBu, MeCC nPr, MeCC iPr). Naphthols were produced in each case with the terminal alkynes giving complete regioselectivity for the isomer with the alkyne hydrogen substituent located adjacent to the hydroxy group of the naphthol. This is exactly opposite to the regiochemistry typically observed for Dötz-type benzannulation reactions using (CO) 5CrC(OR)R′ complexes. Also reported is the crystal structure of the thiophene-substituted carbyne complex Cp(CO) 2WC(2-C 4H 3S) and its reaction with MeCCMe to form 4-hydroxy-5,6-dimethylbenzothiophene.

Reaktivität von μ 3-carbincarbonyltrieisenclustern: CO-substitution, thermolyse zu μ 2-carbinkomplexen und addition von alkinen unter bildung von η 6-ferracyclopentadienonliganden

The carbyne cluster Fe 3(CO) 9(μ 3-PhC)(μ 2- tBuPOEt) ( 1) upon thermolysis at 80° C yields the μ 2-carbyne compound Fe 2(CO) 6(μ 2-PhC)(μ 2- tBuPOEt) ( 2) with the loss of one Fe(CO) 3 group. Two-electron donor ligands L (L = P(OMe) 3, P(O iPr) 3) allow the replacement of one carbonyl group in 1 to give 3. Cluster 1 reacts with PhCCPh to give compound 4a, which contains an η 6-1-tricarbonylferracyclopentadien-2-one ligand, which in turn is facially coordinated to a (μ 2- tBuPOEt)Fe 2(CO) 4 entity. The same framework-geometry is observed for 4b and 4c, which are the result of the reaction of 1 with MeCCMe. The diastereomers 4b and 4c differ in the sequence in which the alkyne and carbyne carbon atoms are linked in the ferracyclopentadienone ring. All compounds have been characterised by the usual spectroscopic and analytical methods as well as by X-ray diffraction studies.

Alkinkomplexe des η 5-Cyclopentadienylnickelmethyls und deren Thermolyse

Cp 2Ni reacts at −78°C with MeLi and RCCR to give thermolabile complexes of the type CpNiMe(η 2-RCCR) (R = Me ( 1), SiMe 3 ( 2)). 2-Butyne dissociates from 1 above −30°C and ethane is liberated to give (CpNi) 2(MeCCMe) ( 6) via (CpNiMe) 2(MeCCMe) ( 3), which is present in only small concentrations. 2 is more stable and reacts above 0°C to give both the known compounds (CpNi) 2(Me 3SiCCSiMe 3) ( 7) and the [bis(1,1-trimethylsilyl)-η 3-allyl]nickel compound 5 as a result of the addition of the MeNi bond to the CC bond of the coordinated alkyne in 2 followed by various rearrangements. The alkyne can be displaced from 1 and 2 in an equilibrium reaction with acetonitrile to give CpNiMe(MeCN) ( 4).

μ-Benzylidenbis(pentacarbonylwolfram)-Komplexe: Thermolyse und Reaktionen mit Alkinen

The μ-benzylidenebis(pentacarbonyltungsten) complexes, [(CO) 5W] 2[μ-C(C 6H 4R)H] (R  H (Ia), Me(Ib), OMe (Ic) reversibly lose one CO ligand to form (CO) 9W 2[C(C 6H 4R)H] (II), in solution at room temperature. The X-ray crystallography of IIc indicates tha he μ-C(C 6H 4R)H groups is η 1-bonded to the W(CO) 5 fragment and η 3-bonded to the W(CO) 4 fragment incorporating one C( ipso)C( ortho) bond of the aryl ring into the bridging system. Complexes I and Ii initiate he polymerization of terminal as well as internal alkynes. The reaction of IIc with butyne-2 is faster than that of Ic. Two complexes were isolated from the reaction mixture containing Ia and butyen-2 (ratio 1 9 , viz. the product of the formal insertion of MeCCMe into a Wμ-C bond of IIa, (CO) 5W[μ-η 1,η 3-C(Me)C(Me)C(Ph)H]W(CO) 4 (VIa), and the product of the substitution of two molecules of butyne-2 for four CO ligands in Ia, [(CO) 3(MeCCMe)W] 2[C(Ph)H] (VIIa).

Reactions of alkynes with mononuclear benzylidene complexes and with binuclear μ-benzylidene complexes of tungsten

Benzylidene(pentacarbonyl)tungsten complexes, (CO) 5WC(C 6H 4R- p)H (R=H, Me), react with (a) diethylaminopropyne, Et 2NCCMe, via the insertion of one CC bond into the WC bond to give (CO) 5WC(NEt 2)-C(Me)C(C 6H 4R- p)H and with (b) an excess of 2-butyne to give (CO) 5W-[MeCCMe] and different C(C 6H 4R- pH/MeCCMe coupling products. With both alkynes no polymerization occurs. In contrast, when t-BuCCH is employed in large excess, rapid polymerization is observed. A mechanism for the polymerization is proposed which involves the initial formation of a vinylidene complex. On thermolysis of the terminal benzylidene complexes in inert solvents benzylidene-bridged bis(pentacarbonyltungsten) complexes are formed which slowly lose one CO ligand. These binuclear complexes initiate the polymerization of 2-butyne. From the reaction mixture two different complexes can be isolated: (CO) 5W[μ-C(Me)C(Me)C(Ph)H]W(CO) 4 and (CO) 6-(MeCCMe) 2W 2[μ-C(Ph)H].

A study of the reaction between Mo 2(OCH 2CMe 3) 6(μ-η 1,η 2-NCNR 2) compounds (R = Me and Et) and 2-butyne

The compound Mo 2(ONp) 6(μ-η 1,η 2-NCNEt 2) reacts with MeCCMe (2 equiv.) in hydrocarbon solvents at ca 0°C to give Mo 2(ONP) 6(μ-C 4Me 4)(NCNEt 2), I, which is shown to be structurally related to the previously characterized compound Mo 2(ONp) 6(μ-C 4H 4)py obtained in the reaction between Mo 2(ONp) 6 and HCCH (2 equiv.) in the presence of pyridine (py = pyridine and Np = neopentyl). Compound I is unstable in hydrocarbon solutions at room temperature. It rapidly and reversibly loses NCNEt 2 and addition of py or PMe 3 leads to the compounds Mo 2(ONp) 6(μ-C 4Me 4)L, where L = py or PMe 3. Compound I also reacts by CC and NH bond formation to give Mo 2(ONp) 6(μ-C 4Me 3CH 2C(NEt 2)NH), II. A mechanism for the conversion of I to II is proposed to involve (i) initial dissociation of NCNEt 2, (ii) CH bond cleavage of a β-CMe group and (iii) insertion of the CN moiety into the MoH bond with CC bond formation. Rate studies show that the conversion of I to II is suppressed by the addition of excess py or PMe 3 supporting the view that initial dissociation of NCNEt 2 is required in a rapid pre-equilibrium step. The new compounds I and II have been characterized by elemental analyses, IR spectroscopy, 1H and 13C NMR spectroscopy and single crystal X-ray studies.