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)degrees, 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 degrees, 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 octahedral geometry (average distances : Si-F 1.642 Angstrom and Si-N 1.919 Angstrom) with the fluorides in a trans configuration, and the porphyrin is in a ruf nonplanar form. The trans-(Por)SiF2 structures were compared to the structures of related hexacoordinate cis-difluorosilanes and other group 14 metalloporphyrins. (TTP)SiF2 readily reacts with excess MeMgBr or LiPh to give (TTP)SiMe(2) or (TTP)SiPh(2), respectively, in contrast to related hexacoordinate cis-difluorosilanes which do not react with strong nucleophiles. The enhanced reactivity of (TTP)-SiF2 may be a combination of a trans-effect, even though the structural parameters for cis and trans Si-F bonds and Si-N bonds are essentially the same, and a single-electron transfer process involving the porphyrin ligand.