Phosphine and phosphonite complexes of Mn(III), Co(III) and Rh(III) porphyrins.

Abstract

This work is aimed at elucidating the structures and spectroscopic properties of phosphine and b phosphonite complexes of Mn(III), Co(III) and Rh(III) porphyrins, a class of coordination compounds that has been little reported on in the literature to date. In this work, a range of novel bis(phosphine) and bis(phosphonite) complexes of the three aforementioned metals have been synthesized, crystalized and analysed by means of X-ray structure determination, 1H NMR, 13C NMR, 31P NMR as well as electronic and IR spectroscopy. [Mn(TPP)(PPh3)2](SbF6) crystallizes in the monoclinic space group P21/c and displays an extraordinarily long Mn-P bond length of 3.088(2) A. Moderate ruffling of the porphyrin ligand is observed. This complex is paramagnetic with fast proton relaxation times, and thus did not yield any useful 1H NMR data. In an attempt to crystallize [Mn(TPP){P(OPh)3}2](SbF6), a complex bearing an O-donor contamination product, [Mn(TPP){(O)PH(OPh)2} ](SbF6), was isolated and its solid state structure determined by X-ray diffraction methods. The structure of this complex has been included in this work as it displays interesting structural features and is the very first phosphonate complex of a metalloporphyrin. This compound crystallizes in the monoclinic space group P21/n and shows a significantly saddled conformation. The axial Mn-O bond length measures 2.122(3) A. The Mn-Nporph bond lengths are 1.998(6) and 2.002(3) A for the bis(phosphine) and phosphonate complexes, respectively. Since the diethyl phosphonate complex was an unintended reaction product, no further characterisation of it was undertaken. [Co(TPP)(depp)2](SbF6), where depp = diethylphenylphosphine, crystallizes in the monoclinic space group P21/c. This complex displays inversion symmetry at the metal center and the porphyrin core is effectively planar. However, [Co(TPP)(edpp)2](SbF6), where edpp = ethyldiphenylphosphine, crystallizes in the· monoclinic space group P21/n and shows a significantly ruffled conformation of the porphyrin core and displays no inversion symmetry. [Co(TPP)(deppt)2](SbF6), where deppt = diethylphenylphosphonite, also crystallizes in the monoclinic space group P21/n, but displays inversion symmetry through the central cobalt ion. As a result, this complex does not display any significant conformational deviations of the porphyrin core from planarity. The axial Co-P bond lengths are significantly shorter than that of . the equivalentbond in the manganese bis(triphenylphosphine) complex at 2.312(1) A, 2.323(10) A and 2.258(2) A for [Co(TPP)(depp)2](SbF6), [Co(TPP)(edpp)2](SbF6) and [Co(TPP)(deppt)2](SbF6), respectively. The Co-Nporph bond lengths average to 1.980(3) A, 1.972(7) A and 1.980(4) A for these three complexes, respectively. I03Rh NMR measurements of three rhodium bis(phosphine)/bis(phosphonite) porphyrins have been performed by the indirect probing of the rhodium metal center by means of the phosphorus nucleus of the coordinated axial ligand. The resulting I03Rh NMR shifts for [Rh(TPP)(edpp)2](SbF6), [Rh(TPP)(edppt)2](SbF6), where edppt = ethyldiphenylphosphonite, and [Rh(TPP)(deppt)2](SbF6) are 2558, 2413 and 2365 ppm, respectively. [Rh(TPP)(edpP)2](SbF6) crystallizes in the monoclinic space group P21/n and shows moderate ruffling of the porphyrin core. The axial Rh-P bond length is 2.401(2) A. [Rh(TPP)(edppt)2](SbF6) and [Rh(TPP)(deppt)2](SbF6) both crystallize in the monoclinic space group P21/c. The porphyrin core of [Rh(TPP)(edppt)2](SbF6) displays a moderate degree of ruffling, as observed in [Rh(TPP)(edpp)2](SbF6), yet the axial Rh-P bond length is substantially shorter at 2.361(9) A. [Rh(TPP)(deppt)2](SbF6) exhibits the shortest Rh-P bond length of the three complexes at 2.332(2) A. The porphyrin core is mostly planar. The Rh-Nporph distances average 2.034(1) A for the S4-ruffled complexes and 2.044(3) A for the planar complex, the shorter distance in the ruffled derivatives being consistent with a distortion-induced compression of the Rh(III) ion.