Novel Coordination in the First Tellurium Porphyrin Complex: Synthesis and Crystal Structure of [Te(ttp)Cl2]

Abstract

Despite the wealth of fundamental and applied research on porphyrin complexes of the metallic elements, non-metal porphyrin complexes have been much less extensively studied. [1] Porphyrin complexes of the groups 13 ± 15 elements are well-established, but as yet no porphyrin complex of any group 16 element is known. Gouterman and co-workers reported UV/Vis spectral changes on reaction of free-base porphyrins with TeCl 4 and SeCl 4 , but no well-characterized species were isolated. [2] As part of our continuing studies of main group porphyrin complexes, [3] we have investigated the synthesis, characterization, and molecular structure analysis of the first tellurium porphyrin complex.The reaction between tellurium(iv) chloride and one equivalent of the dilithium meso-tetra-p-tolylporphyrin salt, Li 2 (ttp), in refluxing hexane yielded a dark green solid of [Te(ttp)Cl 2 ] (72 % yield). [Te(ttp)Cl 2 ] is moisture sensitive in solution and decomposes on exposure to air within seconds. However, it is stable in the solid state for weeks at ambient temperature in the dark in an inert atmosphere.The molecular structure of [Te(ttp)Cl 2 ] [4] is presented in Figure 1. The two molecules are related by a crystallographic inversion center. The tellurium coordination sphere is best described as a square pyramid in which the atoms Cl(1), Cl(2), N(1), and N(3) form the square base of the pyramid and are coplanar to within 0.024 ä. The angles at the Te center from the apical atom to the basal atoms range from 78.27(10) to 89.73(8)8. Three of the porphyrin nitrogen atoms occupy one triangular face of the square pyramid, with the apical TeÀN(2) bond length significantly shorter than those of the basal TeÀN(1) and TeÀN(3) bonds. Five-coordinate Te IV complexes are typically square pyramidal with a short bond to the apical atom. Comparable examples with a TeCl 2 N 3 coordination sphere are difficult to find, but several closely related TeCl 3 N 2 complexes show basal TeÀCl bond lengths in the range 2.370 ± 2.563 ä, basal TeÀN bond lengths in the range 2.185 ± 2.352 ä, and apical TeÀN bond lengths in the range 1.996 ± 2.096 ä. [5] The basal TeÀCl, basal TeÀN, and apical TeÀN bond lengths observed for [Te(ttp)Cl 2 ] are consistent with these. Figure 1. ORTEP plot of [Te(ttp)Cl 2 ]. The meso-tolyl groups and hydrogen atoms are omitted for clarity. Thermal ellipsoids are at the 30 % probability level. Selected bond lengths [ä] and angles [8]: Te-N(1) 2.The fourth porphyrin nitrogen atom (N(4)), and a chlorine atom from the symmetry-related molecule (Cl(2A)), are found on the open square face of [Te(ttp)Cl 2 ] at much longer TeÀN and TeÀCl distances. The TeÀN(4) separation (2.598(3) ä) considerably exceeds the sum (2.11 ä) of the covalent radii of tellurium and nitrogen atoms but is within the sum of the van der Waals radii (3.61 ä). Similarly, the long TeÀCl(2A) distance is within the sum of the van der Waals radii of Te and Cl atoms (3.81 ä). [6] The remarkable aspect of the structure of [Te(ttp)Cl 2 ] is the fact that it adopts five-c...

Chemistry inside a Porphyrin Skeleton: Platinacyclopentadiene from Tellurophene

“…The deformation of platinaporphyrin skeleton leads to a close proximityo ft he nitrogen N22 andt ellurium atom (2.409-2.460 (DFT,T able S3);2 .407(8) for 5-MeI (X-ray)), slightly longer than at ypical TeÀN(sp 2 )b ond length (1.989-2.365 ), [28] however much shorter than the sum of van der Waals radii (3.61 ), [30] and shorter than a" long TeÀNi nteraction" (2.598(3) )i nt he tellurium tetraphenylporphyrin complex. [31] Thus, although Lewis structures of 5 or 5-XY do not require drawingo fs uch ab ond, the distance indicates the presence of significant interatomic interactions.…”

Bismuth and Lead Hanging‐Carboxylate Porphyrins: An Unexpected Homobimetallic Lead(II) Complex

“…So far, this specific configuration has only been reported for monovalent metals such as Re, Tc,14 and Tl 15. A tridentate porphyrin bonding mode was also reported for tellurium in the mononuclear monometallic Te IV bis‐chloro complex of meso ‐tetra‐ p ‐tolylporphyrin 16. The crystal structure of 2 Pb 2 is the first example of such an arrangement for a bivalent metal.…”