fac-[Re(CO)(3)L](+) complexes with N-CH(2)-CH(2)-X-CH(2)-CH(2)-N tridentate ligands. synthetic, X-ray crystallographic, and NMR spectroscopic investigations.
Polyamine ligands (L) have excellent binding characteristics for the formation of fac-99mTc(CO)3-based radiopharmaceuticals. Normally, these L are elaborated so as to leave pendant groups designed to impart useful biodistribution characteristics to the fac-[99mTc(CO)3L] imaging agent. Our goal is to lay a foundation for understanding the features of the bound elaborated ligands by using the fac-[Re(CO)3L]-analogue approach with the minimal prototypical ligands, diethylenetriamine (dien) or simple dien-related derivatives. Treatment of the fac-[Re(CO)3(H2O)3]+ cation with such triamine (NNN) ligands afforded fac-[Re(CO)3L]+ complexes. Ligand variations included having a central amine thioether donor, thus allowing X-ray crystallographic and NMR spectroscopic comparisons of fac-[Re(CO)3L]+ complexes with NNN and NSN ligands. fac-[Re(CO)3L]+ complexes with two terminal exo-NH groups exhibit unusually far upfield exo-NH NMR signals in DMSO-d6. Upon the addition of Cl-, these exo-NH signals move downfield, while the signals of any endo-NH or central NH groups move very little. This behavior is attributed to the formation of 1:1 ion pairs having selective Cl- hydrogen bonding to both exo-NH groups. Base addition to a DMSO-d6 solution of meso-exo-[Re(CO)3(N,N',N''-Me3dien)]PF6 led to isomerization of only one NHMe group, producing the chiral isomer. The meso isomer did not form. The [Re(CO)3(N,N,N',N'',N''-pentamethyldiethylenetriamine)]triflate.[Re(CO)3(mu3-OH)]4.3.35H2O crystal, the first structure with a fac-[Re(CO)3L] complex cocrystallized with this well-known cluster, provided parameters for a bulky NNN ligand and also reveals CO-CO interlocking intermolecular interactions that could stabilize the crystal.
Christoforou
Anna Maria
AM
Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA.
Marzilli
Patricia A
PA
Fronczek
Frank R
FR
Marzilli
Luigi G
LG
D002248:Carbon Monoxide / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry; D018360:Crystallography, X-Ray; D007477:Ions / Q000737:chemistry; D007536:Isomerism; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*; D012997:Solvents
D007477:Ions; D008024:Ligands; D009930:Organic Chemicals; D012997:Solvents; D002713:Chlorine; D012211:Rhenium; D002248:Carbon Monoxide