Dinickel O Compounds

Specific active site stmctural features of urease are the bimetalhc arrangement with a Ni Ni distance of 3.5-3.7 A and nonsymmetric N/O-rich coordination environment, the bridging carbamate (often modeled by a bridging carboxylate), and the presence of a hydrolytically active Ni-bound hydroxide or water. Relevant dinickel complexes that emulate at least part of these features are introduced in this chapter. Of course, the ability to bind urea is a prerequisite for urease-like activity, and different urea-binding modes were observed in synthetic model compounds. Those model complexes and artificial systems that mediate the decomposition of urea are discussed in Section III. 

When complex lb, containing a ( j,-aquo)bis( j,-carboxylato) core, was reacted with 1 equiv of trimethylsilyl triflate, followed by the addition of urea, complex 50 could be isolated in 55% yield (Scheme 10) (110). A mononuclear species [Ni(OAc)(urea)2(tmeda)](OTf) was produced as a minor side product in this reaction. Complex 50 represented the first example of a synthetic compound with urea coordinated to a dinickel(II) site. The urea molecule binds in its most common mode, namely, through its carbonyl O, to one of the Ni(II) ions (Fig. 8). 

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