A study of cis-trans isomerisation of the bis-chelated complexes of platinum (II) and palladium (II) with N,N-dialkyl-N'aroyl(acyl)thiourea ligands

Hanekom, Dirk C. (2006-04)

Thesis (MSc) -- University of Stellenbosch, 2006.

Thesis

ENGLISH ABSTRACT: The N,N-diakyl-N'-aroyl(acyl)thiourea ligands coordinate to platinum(ll) and palladium(ll) in solution to form stable chelated cis-[M(L-S,O)z] (M = Pt, Pd) complexes. Variation of solvent, mode of synthesis, starting material and the groups attached to the carbonyl moeity had no effect on the isomer distribution. The molecular structure of cis-bis(N, N-dialkyl-N'-3,4,5-trimethoxybenzoylthioureato )- platinum(ll), cis-bis(N,N-dialkyl-N'-3,5-dimethoxybenzoylthioureato)platinum(ll), cisbis(N,N-dialkyl-N'-3,4,5-trimethoxybenzoylthioureato)palladium(ll) and cis-bis(N,Ndialkyl-N'-3,5-dimethoxybenzoylthioureato)palladium(ll) were determined and verified as cis geometries. However, these cis-[M(L-S,O)z] [M = Pt, Pd] complexes have been shown to undergo a photo-induced cis-[M(L-S,O)z] to trans-[M(L-S,O)z] isomerisation with no such isomerisation observed in the absence of light. This process was followed and studied by Reversed Phase High Performance Liquid Chromatography. No thermal isomerisation reaction could be identified in the dark even when these solutions where heated to 80°C for 100 hours. Thereafter the addition of an excess of free ligand, to this heated solution, also had no effect on the cis-trans isomer distribution. Irradiation and subsequent isomerisation of these complex solutions was studied in acetonitrile using yellow, blue, red and white light. No isomerisation took place with light of wavelenghts higher than 600nm. As with white light, when blue light (radiation cut-off - 300nm) and yellow light was used (radiation cut-off - 480nm) isomerisation did occur. In an experiment where yellow light was used for irradiation, it was shown that the intensity of the light passing through the solution (i.e. the 'flux of photons) has a direct effect on the steady-state cis-trans ratio of the molecules in solution. When solutions of cis complexes were irradiated with white light to their respective steady-state cis-trans ratios, and then kept in the dark, the trans complex reverts to the cis complex again. This trans-cis isomerisation reaction was found to be thermally controlled; relative steady-state equilibruim constant (Ke = [trans]/[cis]) values for cis-bis(N,N-dialkyl-N'-3,4,5-trimethoxybenzoylthioureato)palladium(ll) in acetonitrile were determined at 0°C, 20°C and 40°C (no light) respectively. The addition of electron donating methoxy groups to the benzoyl moeity did not lead to higher Ke-values, but the bulky camphanoyl moeity present in cis-bis(N,N-diethylN'-camphanoylthioureato)platinum(ll) led to a higher Ke-value than any of the bis(N,N-dialkyl-N'-3,4,5-trimethoxybenzoylthioureato)platinum(ll), bis(N,N-dialkyl-N'- 3,5-dimethoxybenzoylthioureato)platinum(ll) and bis(N,N-dialkyl-N'-4-monomethoxybenzoylthioureato)platinum(ll) complexes. The cis-trans steady-state and Ke-values for cis-bis(N,N-diethyl-N'-pivaloylthioureato)platinum(ll) in acetonitrile were also determined. A solvent study revealed that the trans-isomer, having a zero dipole moment by virtue of it's planar symmetrical structure, was not necessarily favoured by more nonpolar solvents such as 1,4-dioxane and THF - as have previously been shown for similar monodentate complexes. A ligand exhange reaction between two chelated complexes, cis-bis(N,N-dialkyl-N'- 3,4,5-trimethoxybenzoylthioureato)platinum(ll) and cis-bis(N,N-dialkyl-N'-naphthoylthioureato)platinum(ll), was observed in acetonitrile in both the light and in the dark. In the presence of light both ligand exhange and isomerisation (also of the "mixed" complex) occurred, while in the dark only ligand exchange occurred with no evidence of isomerisation. Prelimary 195Pt NMR experiments have proved to be very promising and 195Pt peaks for all the cis- and trans-[Pt(L-S,0)2] isomers have been assigned after white light irradiation of the CDCl3 solutions directly in the NMR tube.

AFRIKAANSE OPSOMMING: N,N-diakyl-N'-aroyl(acyl)thiourea ligande koordineer met platinum(ll) en palladium(ll) in oplossing om stabiele, bidentate cis-[M(L-S,0)2] (M = Pt, Pd) komplekse te vorm. Variasie in oplosmiddel, metode van sintese, uitgangsstof en die funksionele groepe geheg aan die karboniel groep het geen effek gehad op die cis-trans isomeer verdeling nie. Die molekulere struktuur van cis-bis(N,N-dialkyl-N'-3,4,5-trimethoxybenzoylthioureato)platinum(ll), cisbis(N,N-dialkyl-N'-3,5-dimethoxybenzoylthioureato)platinum(ll), cis-bis(N,Ndialkyl-N'-3,4,5-trimethoxybenzoylthioureato)palladium(ll) en cis-bis(N,Ndialkyl-N'-3,5-dimethoxybenzoylthioureato)palladium(ll) is bepaal - dit het bevestig dat die geometrie van die molekules wel cis was. Daar is egter gevind. dat hierdie cis-[M(L-S,0)2] [M = Pt, Pd] komplekse 'n foto-geinduseerde cis-[M(L-S,0)2] na trans-[M(L-S,0)2] isomerisasie ondergaan. Geen bewys van 'n soortgelyke proses kon gevind word in die afwesigheid van lig nie. Hierdie proses is gevolg en bestudeer deur gebruik te maak van Reversed Phase High Performance Liquid Chromatography. Selfs toe oplossings tot en met 80°C verhit was vir 'n periode van 100 uur, kon geen termies-geinduseerde isomerisasie reaksie ge-indentifiseer word nie. Die byvoeging van ligand tot die verwarmde oplossing het ook geen effek gehad op die cis-trans isomeer verdeling nie. Die effek wat bestraling met wit, geel, blou en rooi lig op oplossings van die komplekse het is bestudeer. Vir lig met golflengte hoer as 600nm is geen cistrans isomerisasie waargeneem nie. Soos gevind is met wit lig het isomerisasie plaasgevind met blou lig (bestralings afsnypunt - 300nm) en met geel lig (bestralings afsnypunt - 480nm). In 'n eksperiment waar geel lig gebruik is vir bestraling, is dit bewys dat die intensiteit van die lig wat deur die oplossing beweeg 'n direkte invloed het op die cis-trans verdeling van molekules in oplossing. In oplossings wat in die danker gelaat is, na bestraling met wit lig tot 'n cistrans isomeer verdeling, het die trans-kompleks terug ge-isomeriseer na die cis-kompleks. Dit is ook bevind dat hierdie trans-cis isomerisasie reaksie termies gekontrolleerd is. Ke = [trans]l[cis] waardes vir cis-bis(N,N-dialkyl-N'- 3,4,5-trimethoxybenzoylthioureato)palladium(ll) in asetonitriel is bepaal by 0°C, 20°C en 40°C (geen lig). Die byvoeging van elektron donerende metoksi groepe aan die benzoyl groep het nie gelei tot hoer K9 -waardes nie maar die bonkige camphanoyl groep in cis-bis(N,N-diethyl-N'-camphanoylthioureato)platinum(ll) lei tot 'n hoer Kewaarde as vir enige van die bis(N,N-dialkyl-N'-3,4,5-trimethoxybenzoylthioureato)platinum(ll), bis(N,N-dialkyl-N'-3,5-dimethoxybenzoylthioureato)- platinum(ll) en bis(N,N-dialkyl-N'-4-monomethoxybenzoylthioureato)- platinum(ll) komplekse. Die cis-trans bestendige-toestand K9 -waardes vir cisbis(N, N-diethyl-N'-pivaloylthioureato)platinum(ll) is ook bepaal. 'n Oplosmiddel studie het gewys dat die trans-isomeer (wat 'n dipool moment gelyk aan nul het as gevolg van sy planere, simmetriese struktuur) nie noodwendig - soos voorheen bewys is vir soortgelyke monodentate komplekse - bevoordeel word deur die meer nie-polere oplosmiddels soos 1,4-dioksaan en THF nie. 'n Uitruilings meganisme wat plaasvind in die teenwoordigheid en afwesigheid van lig is waargeneem tussen die twee bidentaat gekoordineerde komplekse cis-bis(N,N-dialkyl-N'-3,4,5-trimethoxybenzoylthioureato)platinum(ll) and cisbis(N, N-dialkyl-N' -naphthoylthioureato )platinum(! I). In die eksperiment waar lig wel teenwoordig was het uitruiling van ligande en isomerisasie (ook van die "gemengde kompleks") plaasgevind, terwyl slegs uitruiling in die donker eksperiment plaasgevind het. Preliminere 195Pt KMR eksperimente wat gedoen is blyk belowend; 195Pt pieke vir al die cis- en trans-[Pt(L-S,0)2] isomere is aangewys na direkte wit lig bestraling van CDCb oplossings in KMR buise.

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