Norbornadienes isomerisation

The intermolecular Pauson-Khand reaction of the resulting S/P-cobalt complexes with norbornadiene was studied under thermal and A -oxide activation conditions. Thus, heating the diastereomerically pure complex (R = Ph, R = Cy) with ten equivalents of norbornadiene at 50 °C in toluene afforded the corresponding exo-cyclopentenone in a quantitative yield and with an enantio-selectivity of 99% ee. Under similar conditions, the analogous trimethylsilyl complex (R = TMS, R = Cy) afforded the expected product in a high yield but with a lower enantioselectivity of 57% ee. In order to increase this enantio-selectivity, these authors performed this reaction at room temperature in dichloromethane as the solvent and in the presence of NMO, which allowed an enantioselectivity of 97% ee to be reached. These authors assumed that the thermal activation promoted the isomerisation of the S/P ligand leading to a nonstereoselective process. 

The ligand ap reacts with (norbornadiene) M (CO) 4 (M = Cr, Mo, W) (vide infra), to give complexes (phosphine) M (CO)4. The phosphine is not coordinated as ap but as ortho-cis-propenyl-phenyldiphenylphosphine (pp) the production of this species is discussed below. There is no evidence that this isomerisation takes place on coordination to platinum (II) or palladium(II). The chelate complex PtBr2 (pp) was prepared by Interrante (20) and shown by its spectral properties to be distinct from PtBr2 (ap). 

It was also discovered that the exo-isomer was formed exclusively in the reaction (except in cases involving norbornadiene where the formed exoisomer underwent irreversible isomerisation to the entfo-isomer, catalysed by dicobalt octacarbonyl) and noted when the products are derived from unsymmetrical acetylenes (MeC=CH or PhC=CH) only a single position isomer is isolated... it is readily shown that the single substituent always occurs on the carbon atom adjacent to the carbonyl group , 3... 

Ni(COD)2/DPEphos was demonstrated to catalyse polyfluoroaiylcyanation of norbornene and norbornadiene in the presence of BPhs (Scheme 14.47). Ni(COD)2/PMc2Ph catalyses the reaction of 1,2-dienes with ethyl cyano-formate affording kinetically favoured p-cyano-a-methylenealkanoates regioselectively without the requirement of a Lewis-acid additive. In this reaction, thermodynamically favoured a-cyanomethyl-a,p-unsaturated carb-oxylates were also obtained as byproducts (Scheme 14.47), which are formed via isomerisation of p-cyano-a-methylenealkanoates at high temperatures under the nickel catalysis. ... 

Low molecular weight Schiff base complexes of many metals are well known and in the case of aromatic ligands these tend to have high thermal stability. Polymeric Schiff bases likewise have been well reported, and although many of these have the Schiff base appended as a substituent on a vinyl polymer backbone, others have the Schiff base residue as part of the mainchain. The latter continue to complex metals very well [140, 141] and one early paper reports the use of a Mn(II) polymeric complex in the aerobic oxidation of cumene at 30-100°C [142]. Indeed there is an implication in the paper that the polymer complex is stable to 200°C when complexed O2 tends to be liberated. Wohrle s group have also studied polymeric Schiff bases extensively, again mostly with pendant groups. However, they have reported a mainchain poly Schiff base [143], its complexation with Co(II), Ni(II) and Cu(II), and use of the supported complexes as catalysts in quadricyclane isomerisation to norbornadiene. 

Cycloocta-1,3-diene merely rearranges to the 1,5-isomer, norbornadiene is polymerised, and no reaction occurs with 2,5-dimethylhexa-2,4-diene. Disubstituted alkenes, RCH=CHR, afford isomerised terminal 1 1 adducts. Similarly, terminal alkenes RCH CH2 gave RCH2CH2SiX2 (X = Ph, OEt) or a mixture of... 

Valence isomerisations of some norbornadienes have been photosensitised using N-methylcarbazole and evidence presented supports the view that single... 

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