Unique stepwise substitution reaction of a mono(guanidinate)tetraplatinum complex with amidines, giving mono(amidinate)tetraplatinum complexes through mixed-ligand intermediate complexes?

Dalton Transactions Pub Date: 2012-11-28 DOI: 10.1039/C2DT32136J

Abstract

A mono(guanidinate)tetraplatinum complex [Pt4(μ-OCOCH3)7(μ-(TolN)2CNiPr2)] (5: Tol = C6H4Me-4) was prepared by treating [Pt4(μ-OCOCH3)8] (1) with excess amounts of N,N′-bis(p-tolyl)-N′′-diisopropylguanidine (4a). A substitution reaction of the guanidinate moiety of 5 with N,N′-bis(aryl)formamidine (10: aryl = C6H4Me-4, C6H4COMe-4, and C6H4OMe-4) via mixed-ligand intermediates, trans-[Pt4(μ-OCOCH3)6(μ-(TolN)2CNiPr2)(μ-ArNCHNAr)] (11: Tol = C6H4Me-4; Ar = C6H4Me-4, C6H4COMe-4, and C6H4OMe-4), as a stepwise substitution mechanism, afforded the corresponding mono(amidinate)tetraplatinum complexes [Pt4(μ-OCOCH3)7(μ-ArNCHNAr)] (2a: Ar = C6H4Me-4; 2b: Ar = C6H4COMe-4; 2c: Ar = C6H4OMe-4) along with trans-bis(amidinate)tetraplatinum complexes trans-[Pt4(μ-OCOCH3)6(μ-ArNCHNAr)2] (3a: Ar = C6H4Me-4; 3b: Ar = C6H4COMe-4; 3c: Ar = C6H4OMe-4) as minor products. A Pt4 dimer complex [Pt4(μ-OCOCH3)7]2-{μ-(ArN)2C(C6H4)2C(NAr)2} (13: Ar = C6H4tBu-4) was selectively obtained upon treatment of 5 with a bis(amidine) linker ligand, N4,N4,N4′,N4′-tetrakis(p-(tert-butyl)phenyl)-[1,1′-biphenyl]-4,4′-dicarboxamidine (12). All in-plane acetates of the two Pt4 cores in 13 were fully substituted by 2,6-dimethylbenzoic acid, 2,4,6-triisopropylbenzoic acid, and ferrocenecarboxylic acid while maintaining its dimer structure to give the corresponding derivatives [Pt4(μ-OCOCH3)4(μ-OCOC6H3Me2-2,6)3]2-{μ-(ArN)2C(C6H4)2C(NAr)2} (14: Ar = C6H4tBu-4), [Pt4(μ-OCOCH3)4(μ-OCOC6H2iPr3-2,4,6)3]2-{μ-(ArN)2C(C6H4)2C(NAr)2} (15: Ar = C6H4tBu-4), and [Pt4(μ-OCOCH3)4(μ-OCOC5H4FeCp)3]2-{μ-(ArN)2C(C6H4)2C(NAr)2} (16: Ar = C6H4tBu-4). The electrochemistry of the four Pt4 dimer complexes 13–16 displayed a one-electron process attributed to Pt49+/Pt48+, and another one-electron process due to Fe3+/Fe2+ was observed for the hexaferrocenyl derivative 16.

Graphical abstract: Unique stepwise substitution reaction of a mono(guanidinate)tetraplatinum complex with amidines, giving mono(amidinate)tetraplatinum complexes through mixed-ligand intermediate complexes
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