Activation of the N–H bond of ethyl carbamate and urea by ruthenium hydride complexes. Unexpected loss of alcohol or ammonia to yield isocyanato complexes

Abstract

The complex [RuH₂(CO)(PPh₃)₃]1 reacted with ethyl carbamate (urethane), H₂NCO₂Et, or urea to yield the complex [RuH(NCO)(CO)(PPh₃)₃]2, which was spectroscopically characterised. The analogous reaction of [RuH₂(PPh₃)₄]3 gave a mixture of products in which [RuH(NCO)(C₆H₅Me)(PPh₃)₃]4 predominates. Treatment of this mixture with CO allowed the isolation of [RuH(NCO)(CO)₂(PPh₃)₂]5 the crystal structure of which was solved by X-ray diffraction. The reactions appear to proceed through the intermediate formation of a N-bonded carbamato or ureido complex, formed by elimination of H₂, followed by irreversible elimination of alcohol or ammonia. This synthesis of isocyanate complexes appears to be quite general. The reactivity of the complexes obtained with olefins has been investigated. Only isomerisation was observed, with no evidence for organic isocyanate formation.