摘要:

IntroductionIt is well known that transition metals mediate cycloaddition reaction of alkynes in organic synthesis reactions. The results range from the formation of small rings such as cyclopropenes to furans and benzene to larger rings such as cyclooctatetraenes.1Most of the transition metal complexes utilized in reactions of this type are mononuclear, with the exception of the Pauson–Khand reaction which employs [Co2(CO)8] as a catalyst.2–4However, there is an appealing analogy between the nature of the interactions between unsaturated organic ligands on a cluster and those of organic molecules on a catalytic metal surface,5,6fuelling the field of cluster–polyyne study. Unfortunately, for most cluster-catalysed reactions, there is little direct evidence for the participation of cluster intermediates.The chemistry of alkynes when coordinated to transition metal carbonyl clusters is well documented,7–16along with analogous reactions involving polyynes. Both alkynes and polyynes display a wide range of coordination modes when coordinated to polynuclear carbonyl clusters, and their reactivity is characterised by transition-metal mediated carbon–carbon bond formation and cyclisations of unsaturated hydrocarbons.11–16Recently, the reactions of 1,3-conjugated diynes with ruthenium and osmium clusters have attracted considerable interest because of the unusual transformations that these molecules undergo when they are attached to the cluster core. For the osmium systems, observed chemistry includes intramolecular rearrangement or cyclisation of the ligand under mild conditions17–23and carbon–carbon bond rupture in thermolysis reactions,24and related results are observed for ruthenium cluster systems.25The result of the ligand rearrangement generally depends essentially on the nature of the terminal substituents of the diyne.The activated cluster [Os3(CO)10(MeCN)2] typically reacts with diynes (RC&z.tbd;C–C&z.tbd;CR′) to form 48-electron clusters [Os3(μ3-η2-RC2C&z.tbd;CR′)(μ-CO)(CO)9] in which the diyne is coordinated by one alkyne unit, with the possibility of two isomers in instances where the substituent on the diyne is inequivalent.18,22,26,27The reaction can also lead to the formation of linear 50-electron clusters [Os3(μ3-η4-RC2C2R)] (R = Fc [ferrocenyl], 2-C4H3S)27–29in which both alkyne units are coordinated. Upon reacting [Os3(CO)10(MeCN)2] with (MeC&z.tbd;C–C&z.tbd;CMe) further metallocyclic products incorporating two diynes and CO incorporating one or two Os3units are also obtained.20Reactions involving [Os3(CO)10(MeCN)2] have also been reported for 1,8-bis(ferrocenyl)-octatetrayne30to give Os3(CO)10(μ3-η2-Fc–C2–C&z.tbd;C–C&z.tbd;C–C&z.tbd;C–Fc), Os3(CO)10(μ3-η2-Fc–C&z.tbd;C–C2–C&z.tbd;C–C&z.tbd;C–Fc), and Os6(CO)20(μ6-η4-Fc–C&z.tbd;C–C2–C&z.tbd;C–C2–Fc).The diyne ligands in the cluster of the type [Os3(μ3-η2-RC2C&z.tbd;CR′)(μ-CO)(CO)9] may be cleaved on heating to form the acetylide cluster [Os3(μ-η1-C2R)(μ3-η2-C2R)(CO)9]22,26,28or alternatively the cluster can be reacted with water to form ethynyl complexes [Os3(μ3-η3-RC3CHR)(μ-H/μ-OH)(CO)9] (R = Fc, Me, Ph).20,31The cluster [Os3(μ3-η2-RC2C&z.tbd;CR′)(μ-CO)(CO)9] (R = H) can also undergo CO loss and transform to the hydrido acetylide complex [Os3(μ-H)(μ3-η2-C2C&z.tbd;CR′)(CO)9]. The free alkyne group in [Os3(μ3-η2-RC2C&z.tbd;CR′)(μ-CO)(CO)9] (R = H,18R′ = SiMe3,18R = R′ = Me20) can be coordinated to a Co2(CO)8moiety to give clusters of the type [Os3(μ3-η2-||-RCC)(μ2-η2-CCR′)(μ-CO)(CO)9(Co2(CO)6)].Hydrido clusters exhibit different reactivity with diynes as hydrogen is usually transferred from the cluster to the diyne. For example, [Os4(μ-H)4(CO)12] can react with RC&z.tbd;C–C&z.tbd;CR′ (R = R′ = Fc) to give an ethynyl cluster [Os4(μ-H)3(μ-η2-FcCCHC&z.tbd;CFc)(CO)11], with the diyne being hydrogenated at the second carbon atom.32Reactions of diynes with [Os3(μ-H)2(CO)10] are thought to proceedviaan abstraction of a hydrogen atom attached to the β-carbon atom of the diyne which leads to the formation of a bond between the β-carbon atom and the third carbon of the –C2–C2– diyne group.22,23The result of the ligand rearrangement generally depends essentially on the nature of the terminal substituents of the diyne. This process, accompanied by the elimination of H2O, leads to the formation of a cyclic product incorporating a furan ring in the case of HOH2CC&z.tbd;C–C&z.tbd;CCH2OH.17The [HOs3(CO)10(η1:η1-OC4H2CCH3] has been shown to undergo an aldol condensation reaction with aromatic aldehydes.33Similar cyclisation products have also been observed in the reaction of [Os3(μ-H)2(CO)10] with substituted diynes RC&z.tbd;C–C&z.tbd;CR′ (R = Ph, R′ = CH2NHPh; R = Ph, R′ = CH2NHCH2Ph; R = R′ = CH2NHPh and R = R′ = Ph).24,34Reactions involving [Os3(μ-H)2(CO)10] and Me3SiC&z.tbd;C–C&z.tbd;CSiMe3do not result in cyclisation products due to the 1,2-shift of the SiMe3stabilising the ethynyl ligand.19Similarly, a 1,2-shift of one of the ferrocenyl groups along the butadiyne chain has been suggested to account for the products of the reaction of FcC2C2Fc with [Os3(μ-H)(CO)10(μ-η2-NC5H4)].28More recently, the reaction of 1,8-bis-(ferrocenyl)-octatetrayne with [Os3(μ-H)2(CO)10] has been shown to yield products involvingtrans-hydrogenation and cyclisations with the incorporation of CO.21In this paper, we extend these studies to the reactions of 1,4-dipyridylbuta-1,3-diyne with the activated clusters [Os3(μ-H)2(CO)10] and [Os3(CO)10(MeCN)2].

ISSN:1144-0546    

DOI:10.1039/b412578a

出版商:RSC    

年代:2004

数据来源: RSC