Synthesis, structures and properties of platinum(ii) complexes of oligothiophene-functionalized ferrocenylacetylene

Abstract

A series of rigid-rod alkynylferrocenyl precursors with oligothiophene (from thiophene to terthiophene) linkage units in the backbone, [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mBr] 2a–2c, [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCSiMe3] 3a–3c and [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCH] 4a–4c (m = 1–3), have been prepared in moderate to good yields. The ferrocenylacetylene complexes 4a–4c can be used to form a range of stable platinum(II) alkynyl and bis(alkynyl) compounds trans-[(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCPt(PEt3)2Ph] 5a–5c and trans-[(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)mCCPt(PBu3)2CC(C4H2S)mCC(η5-C5H4)Fe(η5-C5H5)] 6a–6c (m = 1–3). All these new compounds have been fully characterized by analytical and spectroscopic methods and the molecular structures of the bithienyl-linked complexes [(η5-C5H5)Fe(η5-C5H4)CC(C4H2S)2CC(η5-C5H4)Fe(η5-C5H5)], 2b, 4b, 5b and 6b have been established by X-ray crystallography. Structural analysis of 6b confirms its rigid-rod structural motif, featuring coplanar bithienyl rings and a trans arrangement of the two bithiophene groups. An iron–iron through-space distance of ca. 32 A is observed in 6b. Although there is no significant metallocene–metallocene interaction through the alkynyl–platinum–oligothiophene bridge, a slight negative shift of the ferrocene–ferrocenium redox potential in the platinum-containing species indicates some degree of electron delocalization into the platinum segment, in line with the results from theoretical studies. Oxidation of the thiophene units is facilitated by the presence of the platinum centre and increased conjugation in the chain.