POCOP-Ligated Nickel Siloxide Complexes: Syntheses, Characterization, and Reactivities

This report describes the reactivities of POCOP-type pincer complexes of nickel bearing a trimethylsiloxide ligand. The complex {kappa(P),kappa(C),kappa(P)-2,6-(i-Pr2PO)(2)C6H3}Ni(OSiMe3) (1-OSiMe3) reacts with 2,4,6-Me-3-C6H2OH (MesOH) to give the stable derivative 1-OMes, whereas the corresponding tert-butoxide derivative could not be prepared. Reaction of 1-OSiMe3 and its aliphatic analogue {kappa(P),kappa(C),kappa(P)-(i-Pr2POCH2)(2)CH}Ni(OSiMe3) (2-OSiMe3) with Ph3SiOH led to facile formation of the corresponding protonolysis products 1-OSiPh3 and 2-OSiPh3. Treating 1-OSiMe3 or 2-OSiMe3 with Me3SiN3 gave the azide derivatives 1-N-3 or 2-N-3 in high isolated yields, whereas the analogous reactions with Me3SiCF3 gave 2-CF3 but not 1-CF3. These observations allow us to compare the reactivities of the NiOSiMe3 moiety as a function of pincer ligand backbone. All new complexes have been characterized fully. The reaction of the azide derivatives with benzyl bromide led to the formation of benzyl azide and the corresponding bromo derivatives; 2-N-3 proved to be much more reactive than 1-N-3. The analogous reactions with the trifluoromethyl derivatives are much more complicated and appear to convert PhCH2Br to Me-PhCF3 and PhBr to PhF.