TRANS-DIFLUOROSILICON(IV) COMPLEXES OF TETRA-P-TOLYLPORPHYRIN AND TETRAKIS(P-(TRIFLUOROMETHYL)PHENYL)PORPHYRIN - CRYSTAL-STRUCTURES AND UNPRECEDENTED REACTIVITY IN HEXACOORDINATE DIFLUOROSILANES

Single-crystal X-ray structures have been determined for the difluoro( porphyrinato)silicon(IV) complexes trans-(Por)SiF2 (Por = the dianions of tetra-p-tolyporphyrin (TTP) and tetrakis(p-(trifluoromethyl)phenyl )porphyrin). Crystallographic data for (TTP)SiF2 . Et(2)O: monoclinic, space group C2/c, a = 30.228(4) Angstrom, b = 9.913(4) Angstrom, c = 15.474(5) Angstrom, alpha = gamma = 90 degrees, beta = 114.58(3)degree s, V = 4217(2) Angstrom(3), Z = 4, R1 = 0.0588. Crystallographic data for (TTFP)SiF2: monoclinic, space group C2/c, a = 31.557(2) Angstrom, b = 9.546(1) Angstrom, c = 15.941(1) Angstrom, alpha = gamma = 90 degr ees, beta = 115.83(1)degrees, V = 4322.4(8) Angstrom(3), Z = 4, R1 = 0 .0489. In both structures, the silicon lies in a slightly distorted oc tahedral geometry (average distances: Si-F 1.642 Angstrom and Si-N 1.9 19 Angstrom) with the fluorides in a trans configuration, and the porp hyrin is in a ruf nonplanar form. The trans-(Por)SiF2 structures were compared to the structures of related hexacoordinate cis-difluorosilan es and other group 14 metalloporphyrins. (TTP)SiF2 readily reacts with excess MeMgBr or LiPh to give (TTP)SiMe(2) or (TTP)SiPh(2), respectiv ely, in contrast to related hexacoordinate cis-difluorosilanes which d o not react with strong nucleophiles. The enhanced reactivity of (TTP) -SiF2 may be a combination of a trans-effect, even though the structur al parameters for cis and trans Si-F bonds and Si-N bonds are essentia lly the same, and a single-electron transfer process involving the por phyrin ligand.