Isocyanates other multiple bonds

Isocyanate formation through multiple bond metathesis of C02 with carbodiimide has been also demonstrated [112]. This transformation can be promoted by titanium isopropoxide, at 383 K, in THF as solvent. It is worth noting that the reverse process, which opens an entry into carbodiimide synthesis, is a well-known process that is catalyzed by several other systems, including trialkylphosphine oxides [113] or vanadium-oxo or -imido complexes [114]. 

Electron-poor multiple bonds in acetylene dicarboxylates42 137 149), ketenes 150 152> isocyanates, isothiocyanates, carbodiimides 138-153) and arynes42) add metallated ynamines to give adducts that still carry the ynamine moiety. This behaviour contrast with that of other ynamines which mostly undergo various cycloadditions but it must be stressed that even here cycloadducts may be formed as by-products. 

This behaviour correponds to the observation that other unsaturated hydrocarbons, e.g. alkynes, allenes or 1,3-butadienes, which readily undergo transition metal catalyzed cyclooligomerizations, do also incorporate CX multiple bonds in such cycloadditions only with difficulty in most cases 207 208). Besides the well known cobalt-catalyzed pyridin synthesis from alkynes and nitriles98 cocyclooligomerizations have been achieved with alkynes on one side and isocyanates 209), carbodiimides210) and carbondioxide 211) on the other side as well as with 1,3-butadienes and aldehydes 212), carbondioxide213 and 2-aza- or 2,3-diaza- 1,3-butadiene214. ... 

Across carbon multiple bonds The reaction of acetylenes with phenylcarbonyl isocyanate affords the expected [2+2] cycloadduct 56 . However, the assigned structure is in doubt because MNDO results suggest that it is impossible to prepare the unsaturated )8-lactams by [2+2] cycloaddition of acetylenes with acyl isocyanates . In other acetylene reactions with isocyanates the [2+2] cycloadducts are only postulated as intermediates. 

Triazine and Other Heterocyclic Ring Formation. Several types of reactions can be used to form heterocyclic rings in which multiple C-N bonds contribute high thermal stability. When these are used to cross-link heat-stable oligomers, the resulting thermoset polymers may have high thermal stability and other useful properties. These include cyanate/cyanurate, isocyanate/isocyanurate, hexaazatriphenylene trianhydride, and phtha-lonitrile/phthalocyanine. 

Their multiple use-forms (e.g., in in situ-XQ-acting, neat, liquid systems solutions aqueous dispersions films webs powders) and other valuable attributes (e.g., adhesion to a variety of substrates vibration-damping bonds " gasoline, oil, and solvent resistance etc.) continue to make polyurethane- and isocyanate-based adhesives the materials of choice in many adhesive applications. 

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