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 {κP,κC,κP-2,6-(i-Pr2PO)2C6H3}­Ni­(OSiMe3) (1-OSiMe3) reacts with 2,4,6-Me3-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 {κP,κC,κP-(i-Pr2POCH2)2CH}­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-N3 or 2-N3 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 Ni–OSiMe3 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-N3 proved
to be much more reactive than 1-N3. The analogous reactions with the trifluoromethyl derivatives are
much more complicated and appear to convert PhCH2Br to
Me-PhCF3 and PhBr to PhF.