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

A series of rigid-rod alkynylferrocenyl precursors with oligothiophene (fro m thiophene to terthiophene) linkage units in the backbone, [(eta (5)-C5H5) Fe(eta (5)-C5H4)C=C(C4H2S)(m)Br] 2a-2c, [(eta (5)-C5H5)Fe(eta (5)-C5H4)C=C( C4H2S)(m)C=CSiMe3] 3a-3c and [(eta (5)-C5H5)Fe(eta (5)-C5H4)C=C(C4H2S)(m) C =CH] 4a-4c (m = 1-3), have been prepared in moderate to good yields. The fe rrocenylacetylene complexes 4a-4c can be used to form a range of stable pla tinum(II) alkynyl and bis(alkynyl) compounds trans-[(eta (5)-C5H5)Fe(eta (5 )-C5H4)C=C(C4H2S)(m)C=CPt(PEt3)(2)Ph] 5a-5c and trans-[(eta (5)-C5H5)-Fe(et a (5)-C5H4)C=C( C4H2S)(m)C=CPt(PBu3)(2)C=C(C4H2S)(m)C=C(eta (5)-C5H4)Fe(eta (5)-C5H5)] 6a-6c (m = 1-3). All these new compounds have been fully charac terized by analytical and spectroscopic methods and the molecular structure s of the bithienyl-linked complexes [(eta (5)-C5H5)Fe(eta (5)-C5H4)C=C(C4H2 S)(2) C=C(eta (5)-C5H4)Fe(eta (5)-C5H5)], 2b, 4b, 5b and 6b have been estab lished by X-ray crystallography. Structural analysis of 6b con rms its rigi d-rod structural motif, featuring coplanar bithienyl rings and a trans arra ngement of the two bithiophene groups. An iron-iron through-space distance of ca. 32 Angstrom is observed in 6b. Although there is no significant meta llocene-metallocene interaction through the alkynyl-platinum-oligothiophene bridge, a slight negative shift of the ferrocene-ferrocenium redox potenti al in the platinum-containing species indicates some degree of electron del ocalization into the platinum segment, in line with the results from theore tical studies. Oxidation of the thiophene units is facilitated by the prese nce of the platinum centre and increased conjugation in the chain.