fac-Re(CO)3L complexes containing tridentate monoanionic ligands (L-) with a seldom-studied sulfonamido group as one terminal ligating group.
To achieve a net-neutral coordination unit in radiopharmaceuticals with a fac-M(CO)3+ core (M = Tc, Re), facially coordinated monoanionic tridentate ligands are needed. New neutral fac-Re(CO)3L complexes were obtained by treating fac-[Re(CO)3(H2O)3]+ with unsymmetrical tridentate NNN donor ligands (LH) based primarily on a diethylenetriamine (dien) moiety with an aromatic group linked to a terminal nitrogen through a sulfonamide. LHs contain 2,4,6-trimethylbenzenesulfonyl (tmbSO2) and 5-(dimethylamino)naphthalene-1-sulfonyl (DNS) groups. X-ray crystallographic and NMR analyses confirm that in both the solid and the solution states all L- in fac-Re(CO)3L complexes are bound in a tridentate fashion with one donor being nitrogen from a deprotonated sulfonamido group. Another fundamental property that is important in radiopharmaceuticals is shape, which in turn depends on ring pucker. For L- = tmbSO2-dien-, tmbSO2-N'-Medien-, and tmbSO2-N,N-Me2dien-, the two chelate rings have a different pucker chirality, as is commonly found for a broad range of metal complexes. However, for fac-Re(CO)3(DNS-dien), both chelate rings have the same pucker chirality because the sulfonamido ring has an unusual pucker for the absolute configuration at Re; a finding that is attributable to intramolecular and intermolecular hydrogen bonds from the sulfonamido oxygens to the NH2 groups. Averaging of tmb NMR signals, even at -90 degrees C for Re(CO)3(tmbSO2-N,N-Me2dien), indicates rapid dynamic motion in the complexes with this group. However, examination of the structures suggests that free rotation about the S-C(tmb) bond is not possible but that concerted coupled rotations about the N-S and the S-C bonds can explain the NMR data.
Christoforou
Anna Maria
AM
Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA.
Fronczek
Frank R
FR
Marzilli
Patricia A
PA
Marzilli
Luigi G
LG
D000838:Anions; D018360:Crystallography, X-Ray; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D019275:Radiopharmaceuticals / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*; D013449:Sulfonamides / Q000737:chemistry*; D013667:Technetium / Q000737:chemistry*
D000838:Anions; D008024:Ligands; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D013449:Sulfonamides; D012211:Rhenium; D013667:Technetium