Norbornadiene

About: Norbornadiene is a research topic. Over the lifetime, 2389 publications have been published within this topic receiving 38603 citations.

Tetracarbonyl diazaphosphole complexes of group 6b metals: the role of steric effects

Abstract: Thermal substitution reactions of [M(CO)5L1c] with cis diazaphosphole derivatives (L1= 3,4-dihydro-2,3,4,5-tetraphenyl-2H-1,2,3-diazaphosphole, L1c and L1t denote cis and trans L1 respectively) have yielded a mixture of cis and trans(2 : 3 ratio) tetracarbonyl complexes in which the ligands are bonded through the phosphorus atom. In contrast the reactions of [M(CO)5L1t] with the bulkier trans diazaphosphole isomers (L1t or L2t, L2= 5-benzyl-3,4-dihydro-2,3,4-triphenyl-2H-1,2,3-diazaphosphole) have only afforded the trans disubstituted tetracarbonyl [M(CO)4(Lt)2]. On the other hand, L1t and L2t have reacted with [M(CO)5L1c] affording the mixed-phosphine derivatives trans-[M(CO)4L1cLt](Lt= L1t or L2t). The norbornadiene complex [Mo(CO)4(nbd)] produced only cis-[Mo(CO)4(L1c)2] when treated with L1c in cyclohexane at room temperature, whereas with L1t no tetracarbonyl complexes (cis or trans) have been observed. In addition it has been found that cis(or trans)-[Mo(CO)4(L1c)2] thermally interconverts by a dissociative pathway to the trans(or cis)-[Mo(CO)4-(L1c)2] to give an equilibrium composition (cis : trans= 2 : 3) whereas trans-[Mo(CO)4(Lt)2] did not isomerize. All these different stereochemical results are tentatively explained by invoking fluxional or rigid five-co-ordinate intermediates in which only steric factors play a decisive role in determining the geometry and then the products distribution. The nature of the complexes has been established essentially by i.r. and 1H n.m.r. spectra. An X-ray study on cis-[Mo(CO)4(L1c)2] is also reported.

Preparation and thermal decarbonylation of some sterically compressed 5,6-endo-disubstituted norborn-2-en-7-ones

Abstract: Reaction of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene with norbornadiene and benzo-norbornadiene gave adducts having the endo-exo-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethano-naphthalene and endo-exo-1,4,4a,9,9a,l0-hexahydro-1,4:9,l0-dimethanoanthracene skeletons, respectively. These adducts were dechlorinated to give acetals, which were hydrolysed to give the corresponding ketones. The initial adducts, and the derived acetals and ketones, are all sterically compressed as a result of crowding of the C2-C3 etheno bridge against a methano hydrogen atom syn to that bridge. This steric compression manifests itself in a marked deshielding of the relevant methano proton in the N.M.R. spectra of these compounds, and in an increased rate of thermal decarbonylation of the ketones. The location of the deuterium atom in benzonorbornadiene[7-anti-D] (12) has been established chemically by observing an intramolecular deuterium transfer during photochemical half-cage formation from the adduct of (12) and 1,2,3,4-tetrachloro-5,5- dimethoxycyclopentadiene.

Low-Energy Pathway for Pauson—Khand Reactions: Synthesis and Reactivity of Dicobalt Hexacarbonyl Complexes of Chiral Ynamines.

Abstract: A family of dicobalt hexacarbonyl complexes of 1-(dialkylamino)-2-(trimethysilyl)acetylenes (3a−f) derived both from achiral and chiral amines [a, morpholine; b, (S)-2-methoxymethylpyrrolidine; c, (2R,5R)-2,5-bis(methoxymethyl)pyrrolidine; d, (±)-trans-2,5-bis(benzyloxymethyl)pyrrolidine; e, (2R,5R)-2,5-dimethylpyrrolidine; f, (S)-(α-methylbenzyl)benzylamine] has been prepared by a one-stage process from dichloroacetylene. The methanolysis at room temperature of these complexes (MeOH/K2CO3) induces the selective cleavage of the carbon−silicon bond, leading to the thermally unstable terminal ynamine complexes 12a−f. The Pauson−Khand reaction of 12a−f with strained olefins (norbornadiene and norbornene) takes place at unprecedentedly low temperatures (−35 °C) in the absence of chemical promoters. Diastereoselectivities of up to 94:6 are recorded in these reactions with the ynamine complexes derived from C2 symmetrical chiral auxiliaries (12c,d). The high reactivity depicted by terminal ynamines in the Pauso...