View source for Sn1CB mechanism

The '''S<sub>N</sub>1CB (conjugate base) mechanism''' describes the pathway by which many metal [[amine]] [[Coordination chemistry|complexes]] undergo substitution, that is [[ligand exchange]]. Typically, the reaction entails reaction of a polyamino metal halide with aqueous [[Base (chemistry)|base]] to give the corresponding polyamine metal hydroxide:<ref>G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.</ref>
:[Co(NH<sub>3</sub>)<sub>5</sub>Cl]<sup>2+</sup>  +  OH<sup>-</sup>  →  [Co(NH<sub>3</sub>)<sub>5</sub>OH]<sup>2+</sup>  +  Cl<sup>-</sup>
The [[rate law]] for the reaction is:
:rate = ''k''([Co(NH<sub>3</sub>)<sub>5</sub>Cl]<sup>+</sup>)([OH<sup>-</sup>])
The rate law is deceptive: hydroxide serves not as a nucleophile but as a base to deprotonate the coordinated ammonia.  Simultaneously with deprotonation, the halide dissociates.  Water binds to the [[18 electron rule|coordinatively unsaturated]] complex followed by proton transfer to give the hydroxy complex.  The conjugate base resulting from deprotonation of the amine is rarely observed.<ref>Clark, C. R. and Buckingham, D. A., "Alkaline hydrolysis of [Co(cyclen)(O<sub>2</sub>CO)]<sup>+</sup> and direct observation of deprotonated S<sub>N</sub>1CB intermediates", Inorganica Chimica Acta, 1997, 254, 339-343.</ref>

==References==
<references/>

[[Category:Substitution reactions]]
[[Category:Coordination chemistry]]
[[Category:Reaction mechanisms]]
[[Category:2Fix]]