Isomerization urea complex

Following the linkage isomerization, a slow subsequent (noncatalytic) transformation of the urea complex 40a (but not of the dmu analogue 40b) leads to [(dien)Pt(NH3)], CO2, and urea (95). An intermediate assigned to [(dien)... 

Coordinated cyanamide does not add OH" to form the N-bound urea complex since it de-protonates 5.2) to ve the unreactive [Co(NCNH)(NH3)5p ion, but in acid it readily loses NH to form N-coordinated cyanate (equation 27). The analogous dimethylcyanamide complex cannot deprotonate and adds OH" to form urea (Scheme 21), but this does not proceed further to coordinated carbamic add and NHMCj in a process analogous to that suggested for the function of Ni in the metalloenzyme jack bean urease (which catalyzes the convemioo of urea to these products), nor does it lose NHMc2 to form the cyanato complex as suggested by Balahura and Jordan for the similar urea derivatives (equation 28). Alternatively, in acid solution the protonated urea rapidly isomerizes to the O-coordinated complex (r,/2 a 40 s, 25 °C Scheme 21). This isomer undergoes OH -catalyzed hydrolysis at the metal rather than at acyl carbon, so the function of the metalloenzyme has not been duplicated in this system. A similar property is found for 0-bound urea (equation 29). ... 

The photodecomposition of alkanones included within urea complexes has been reported by Casal et al. Urea, when crystallized in the hexagonal lattice, possesses long channels of approximately 5 A diameter into which guest molecules are incorporated. For 5-nonanone the possible reactions which may occur are shown in Scheme 6.15. In solution photodecomposition occurs principally via the Norrish Type n reaction, leading to 2-hexanone, propylene, and two isomeric cyclobutanols. The crystalline hexagonal urea complex gave, on the other hand, essentially only one cyclobutanol isomer — the cis. The formation of the cis isomer requires less stringent rotational requirements and is, therefore, the preferred product in the constrained channel environment. 

---