Interaction of Rh(I) with meso-arylsapphyrins and -rubyrins: First structural characterization of bimetallic hetero-rubyrin complex

The ligational behavior of meso-arylsapphyrins and rubyrins toward Rh(I) is investigated. Sapphyrins form monometallic complexes with coordination of one imine and amine type nitrogens of the bipyrrole unit in an eta (2) fash ion. The Rh(I) coordination is completed by the presence of two ancillary c arbon monoxide ligands. Rubyrins form both monometallic and bimetallic comp lexes. Two types of bimetallic complexes have been isolated. In the first t ype, both rhodium atoms are projected above the mean rubyrin plane, while i n the second type, one rhodium atom is projected above and the other below the mean plane. Detailed H-1 and 2D NMR spectral analyses along with IR and UV-visible spectra of the complexes confirm the proposed binding modes for the rhodium complexes. Furthermore, the single-crystal X-ray analysis of o ne of the bimetallic complexes of rubyrin shows a bowl-shaped symmetric str ucture where both Rh(I) atoms are projected above the mean rubyrin plane at an angle of 71.73 degrees. The geometry around each rhodium center is appr oximately square planar [N1-Rh1-N2, 80.38(9)degrees; C15-Rh1-C16, 86.95(14) degrees; N1-Rh1-C15, 97.13(12)degrees; and N2-RH1-C16, 94.97(12)degrees]. T he observed distance of 4.313 Angstrom between the two rhodium centers reve als very little interaction between the two rhodium atoms. This type of met al binding is accompanied by a 180 degrees ring flip of the heterocyclic ri ng connecting the two bipyrrole units, In dioxarubyrin, where one of the py rrole rings of the bipyrrole unit is inverted, Rh(I) binds at the periphery to the pyrrole nitrogen, leaving the rubyrin cavity empty. The absence of one amino and one imino nitrogen on the dipyrromethene subunits in the sapp hyrins and rubyrins described here forces Rh(I) to bind to bipyrrole nitrog ens.