SUBSTITUENT EFFECTS ON THE SPECTROSCOPIC PROPERTIES AND REACTIVITY OFHEXACOORDINATE SILICON(IV) PORPHYRIN COMPLEXES

A general high-yield synthetic route to the hexacoordinate silicon por phyrin dichloride complexes trans-(For)SiCl2 {For = the dianions of oc taethylporphyrin (OEP), tetraphenylporphyrin (TPP), and tetrakis(p-(tr ifluoromethyl)phenyl)porphyrin (TTFP)} is reported. Reacting (Por)SiCl 2 with SbF3 and AgOTf produces the corresponding difluoro trans-(Por)S iF2 and bis(triflato) trans-(Por)Si(OTf)(2) complexes, respectively. T he spectroscopic properties (H-1, F-19, and Si-29 NMR and visible) of these hexacoordinate silicon compounds are surprisingly insensitive to the electron-donating ability of the porphyrin or the nature of the a xial substituents. The nature of the porphyrin and the axial substitue nt do play a role in the reactivity of these silicon complexes. The st rong SI-F bond makes the difluorides stable to hydrolysis and methanol ysis. The dichlorides, on the other hand, do undergo hydrolysis and me thanolysis, the extent of which is determined by the electronics of th e porphyrin ring. The strong electron-donating ability of OEP stabiliz es (OEP)SiCl2 with respect to hydrolysis and methanolysis. (TTFP)SiCl2 , containing the least electron-donating porphyrin, reacts with MeOH t o give a mixture of (TTFP)Si(OMe)CI and (TTFP)Si(OMe)(2), whereas (TTP )SiCl2 (TTP = the dianion of tetra-p-tolylporphyrin) reacts with MeOH to give only the monomethoxy derivative. The triflate groups on (OEP)S i(OTf)(2) are more labile than those in the corresponding tetraarylpor phyrin complexes and can be displaced by THF to give the cationic spec ies [(OEP)Si(OTf)(THE)]OTf or [(OEP)Si(THF)(2)](OTf)(2).