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Luminescent Rhenium(I)-Dipyrrinato Complexes

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journal contribution
posted on 02.01.2012, 00:00 by Tracey M. McLean, Janice L. Moody, Mark R. Waterland, Shane G. Telfer
The first Re­(I)-dipyrrinato complexes are reported. Complexes with the general formulas fac-[ReL(CO)3Cl], fac-[ReL(CO)3PR3], and [ReL(CO)2(PR3)­(PR′3)] have been prepared, where L is one of a series of meso-aryl dipyrrinato ligands. Access to these complexes proceeds via the reaction of [Re­(CO)5Cl] with the dipyrrin (LH) to produce fac-[ReL(CO)3Cl]. A subsequent reaction with PR3 (R = phenyl, butyl) leads to displacement of the chloride ligand to generate fac-[ReL(CO)3PR3], and further reaction with PR′3 leads to the displacement of the CO ligand trans to the first PR3 ligand to give trans­(P), cis­(C)-[ReL(CO)2(PR3)­(PR′3)]. The structures of the complexes were determined in the solid state by X-ray crystallography and in solution by 1H NMR spectroscopy. Electronic absorption spectroscopy reveals a prominent band in the visible region at relatively low energy (472–491 nm) for all complexes, which is assigned as a π–π* transition of the dipyrrin chromophore. Weak emission (λex = 485 nm, quantum yields <0.01) was observed for [ReL(CO)3Cl] and [ReL(CO)3PR3] complexes, but no emission was generally evident from the [ReL(CO)2(PR3)­(PR′3)] complexes. On the basis of the large Stokes shift (∼6000 cm–1), the emission is ascribed to phosphorescence from a triplet excited state. The emission intensity is sensitive to dissolved oxygen and methyl viologen; a Stern–Volmer plot in the latter case gave a straight line. Photochemical ligand substitution reactions of [ReL(CO)3PR3] were induced by excitation with a 355 nm laser in acetonitrile. [ReL(CO)2(PR3)­(CH3CN)] is formed as a putative intermediate, which reacts thermally with added PR′3 to produce [ReL(CO)2(PR3)­(PR′3)] complexes.