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

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 = C₆H₄^tBu-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 = C₆H₄^tBu-4), [Pt₄(μ-OCOCH₃)₄(μ-OCOC₆H₂ⁱPr₃-2,4,6)₃]₂-{μ-(ArN)₂C(C₆H₄)₂C(NAr)₂} (15: Ar = C₆H₄^tBu-4), and [Pt₄(μ-OCOCH₃)₄(μ-OCOC₅H₄FeCp)₃]₂-{μ-(ArN)₂C(C₆H₄)₂C(NAr)₂} (16: Ar = C₆H₄^tBu-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.