A crystallographic and mechanistic investigation of rhenium(I) tricarbonyl complexes for model drug design

Abstract

English: Four new complexes of the type fac-[Re(L,L'-Bid)(CO)3(L)] (L,L'-Bid = monoanionic N,O bidentate Schiff-base ligands: 5Me-SalH-iProp = 2-(isopropylimino)methyl-5-methylphenol, 5Me-SalH-CyPent = 2-(cyclopentylimino)methyl-5-methylphenol and 5Me-SalH-Hist = 2-(2-imidazol-4-yl)ethyliminomethyl-5-methylphenol; L = pyridine or imidazole ligand) and a polymorphic form of a complex previously reported were synthesized during this study. The ligands were consciously selected due to their varying steric and electronic character afforded by the substituent bonded to the nitrogen imine donor atom. The complexes obtained were characterized by single crystal X-ray diffraction as well as other spectroscopic techniques (IR, NMR, UV-Vis) and included the following: fac-[Re(5Me-Sal-iProp)(CO)3(Pyridine)], fac-[Re(5Me-Sal-CyPent)(CO)3(Pyridine)], fac-[Re(5Me-Sal-CyPent)(CO)3(Imidazole)], fac-[Re(κO-5Me-Sal-CyPent)(CO)3(Pyridine)(Br)] and fac-[Re(5Me-Sal-Hist)(CO)3].MeOH. The new crystal structures reported all crystallize in the same crystal system (monoclinic), same space group (P21/c) and contain the same number of molecules in the unit cell (Z = 4). Two of the complexes, fac-[Re(5Me-Sal-CyPent)(CO)3(Pyridine)] and fac-[Re(5Me-Sal-CyPent)(CO)3(Imidazole)] were found to be iso-structural. The different substituents on the nitrogen imine donor atom do not affect the bond distances significantly. However, the bond distance of the imidazole ligand coordinated to the sixth position is significantly shorter than that of the coordinated pyridine ligand. Thus, imidazole coordinates more strongly to the metal center than pyridine. Multiple reactions were observed for the reaction between the fac-[Re(CO)3]+ core and N,O bidentate ligands, therefore the preliminary formation kinetics was studied with more simple and symmetric ethylene amine type ligands. The preliminary formation reactions between the fac-[Re(CO)3]+ core and ethylene amine type ligands, ethylenediamine and diethylenetriamine were performed at 25 °C. Two separate reaction were identified, a rapid first reaction, followed by a slower second reaction. The second reaction was investigated during this study. The second reaction followed pseudo first-order conditions with equilibrium rate constant, K2 of 27(8) M-1s-1 for the reaction with ethylenediamine and 31(1) M-1s-1 for the reaction with diethylenetriamine at 25 oC. The second order rate constant, k2 for the reaction between the fac-[Re(CO)3]+ core and ethylenediamine as well as diethylenetriamine was found to be 0.00826(4) M-1s-1 and 0.00715(3) M-1s-1 respectively. The reaction with ethylenediamine is faster than that with diethylenetriamine, which can be attributed to the simple, symmetrical nature of ethylenediamine ligand as opposed to the large steric demand of diethylenetriamine ligand.

Afrikaans: Vier nuwe komplekse van die tipe fac-[Re(L,L'-Bid)(CO)3(L)] (L,L'-Bid = monoanioniese N,O bidentate Schiff-basis ligande: 5Me-SalH-iProp = 2-(isopropielimino)metiel-5-metielfenol, 5Me-SalH-CyPent = 2-(siklopentielimino)metiel-5-metielfenol en 5Me-SalH-Hist = 2-(2-imidasool-4-iel)etieliminometiel-5-metielfenol; L = piridien of imidasool ligand), en `n polimorfiese vorm van `n voorheen gerapporteerde kompleks is tydens hierdie studie vervaardig. Die ligande is bewustelik gekies as gevolg van hulle veranderlike steriese en elektroniese karakters wat veroorsaak word deur die substituent wat aan die imien se stikstof skenkeratoom gebind is. Die vervaardigde komplekse is deur X-straal diffraksie asook ander spektroskopiese metodes (IR, KMR, UV-Sig) gekarakteriseer en sluit die volgende in: fac-[Re(5Me-Sal-iProp)(CO)3(piridien)], fac-[Re(5Me-Sal-CyPent)(CO)3(piridien)], fac-[Re(5Me-Sal-CyPent)(CO)3(imidasool)], fac-[Re(κO-5Me-Sal-CyPent)(CO)3(piridien)(Br)] en fac-[Re(5Me-Sal-Hist)(CO)3].MeOH. Die nuwe gerapporteerde kristalstrukture kristalliseer almal in dieselfde kristalstelsel (monoklinies) en ruimtegroep (P21/c) en bevat dieselfde getal molekule in die eenheidsel (Z = 4). Daar is vasgestel dat twee van die komplekse, fac-[Re(5Me-Sal-CyPent)(CO)3(piridien)] en fac-[Re(5Me-Sal-CyPent)(CO)3(imidasool)], iso-struktureel is. Die verskillende substituente op die stikstof imien skenkeratoom het nie `n beduidende invloed op die bindingsafstande nie. Die bindingsafstand van die imidasool ligand wat aan die sesde posisie gekoördineer is is egter beduidend korter as dié van die gekoördineerde piridien ligand. Imidasool koördineer dus sterker aan die metaalsenter as piridien. Veelvoudige reaksies is waargeneem vir die reaksie tussen die fac-[Re(CO)3]+ kern en N,O bidentate ligande, daarom is voorlopige vormingskinetika met meer eenvoudige en simmetriese etileenamien-tipe ligande bestudeer. Die voorlopige vormingsreaksies tussen die fac-[Re(CO)3]+ kern en etileenamine-tipe ligande, etileendiamien en dietileentriamien is uitgevoer teen 25 °C. Twee afsonderlike reaksies is geïdentifiseer; `n vinnige eerste reaksie gevolg deur `n stadiger tweede reaksie. Die tweede reaksie is tydens hierdie studie ondersoek. Die tweede reaksie volg pseudo eerste-orde toestande met `n ewewigstempokonstante, K2, van 27(8) M-1s-1 vir die reaksie met etileendiamien en 31(1) M-1s-1 vir die reaksie met dietileentriamien teen 25 oC. Die tweede orde tempokonstante, k2, vir die reaksie tussen die fac-[Re(CO)3]+ kern en etileendiamien asook dietileentriamien is bepaal as onderskeidelik 0.00826(4) M-1s-1 en 0.00715(3) M-1s-1. Die reaksie met etileendiamien is vinniger as die reaksie met dietileentriamien, wat toegeskryf kan word aan die eenvoudige, simmetriese natuur van etileendiamien in kontras met die groot steriese aanvraag van die dietileentriamien ligand.