Experimental and Theoretical Studies of the Factors Affecting the Cycloplatination of the Chiral Ferrocenylaldimine (SC)-[(η5-C5H5)Fe{(η5-C5H4)–C(H)=N–CH(Me)(C6H5)}

Concepción López,Carme Calvis,Marta Pujol,Ramón Bosque,Eila Sevilla,Ramon Messeguer,Mercè Font-Bardía,Jonathan Simó

doi:10.3390/inorganics2040620

Concepción López, Carme Calvis + Show 6 more

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https://doi.org/10.3390/inorganics2040620

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Journal: Inorganics	Publication Date: Nov 6, 2014
Citations: 70	License type: CC BY 4.0

Affiliation: University of Barcelona, Leitat Technological Center

Abstract

The study of the reactivity of the enantiopure ferrocenyl Schiff base (SC)-[FcCH=N–CH(Me)(C6H5)] (1) (Fc = (η5-C5H5)Fe(η5-C5H4)) with cis-[PtCl2(dmso)2] under different experimental conditions is reported. Four different types of chiral Pt(II) have been isolated and characterized. One of them is the enantiomerically pure trans-(SC)-[Pt{κ1-N[FcCH=N–CH(Me)(C6H5)]}Cl2(dmso)] (2a) in which the imine acts as a neutral N-donor ligand; while the other three are the cycloplatinated complexes: [Pt{κ2-C,N [(C6H4)–N=CHFc]}Cl(dmso)] (7a) and the two diastereomers {(Sp,SC) and (Rp,SC)} of [Pt{κ2-C,N[(η5-C5H3)–CH=N–{CH(Me)(C6H5)}]Fe(η5-C5H5)}Cl(dmso)] (8a and 9a, respectively). Isomers 7a-9a, differ in the nature of the metallated carbon atom [CPh (in 7a) or CFc (in 8a and 9a)] or the planar chirality of the 1,2-disubstituted ferrocenyl unit (8a and 9a). Reactions of 7a–9a with PPh3 gave [Pt{κ2-C,N[(C6H4)–N=CHFc]}Cl(PPh3)] (in 7b) and the diastereomers (Sp,SC) and (Rp,SC) of [Pt{κ2-C,N[(η5-C5H3)–CH=N–{CH(Me)(C6H5)}] Fe(η5-C5H5)}Cl(PPh3)] (8b and 9b, respectively). Comparative studies of the electrochemical properties and cytotoxic activities on MCF7 and MDA-MB231 breast cancer cell lines of 2a and cycloplatinated complexes 7b-9b are also reported. Theoretical studies based on DFT calculations have also been carried out in order to rationalize the results obtained from the cycloplatination of 1, the stability of the Pt(II) complexes and their electrochemical properties.

Highlights

Cyclometallated platinum (II) complexes containing bidentate (C,N)− or terdentate ((C,N,E)q,(N,C,E)q, (E = N, S or O and q = −1 or −2) or (C,N,C')2−) ligands are nowadays one of the most attractive type of organoplatinum compounds [1,2,3,4,5,6,7,8,9,10]
All the results presented here reveal that despite it is well-known that ferrocene derivatives are more prone to undergo electrophilic attacks than their phenyl analogues [34,35,58,61], for 1, that has different types of σ(C−H) bonds susceptible to metallate, the formation of the platinacycle 7a with a σ[Pt−C(phenyl)] is achieved under milder experimental conditions than those required to isolate the 8a and 9a with a σ[Pt−C(ferrocenyl)] bond
The results presented in this work reveal that the enantiopure imine 1 is a valuable ligand to achieve different types of chiral heterodimetallic complexes containing Pt(II) and Fe(II)

Summary

Introduction

(N,C,E)q, (E = N, S or O and q = −1 or −2) or (C,N,C')2−) ligands are nowadays one of the most attractive type of organoplatinum compounds [1,2,3,4,5,6,7,8,9,10] This is mainly due to their physical, chemical, photo-physical and electrochemical properties, or the reactivity of their ground and excited states that make them extremely useful in a wide range of fields [1,2,3,4,5,6,7,8,9,10]. For illustrative purposes recent examples of platinacycles with bidentate (CPh, N)− ligands showing greater cytotoxic activity than cisplatin are shown in Figure 1 [29,32,33]

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Conclusion