Preparation of models and oligomers of metal alkynyls: NMR, GPC and X-ray structural characterization of building blocks for the construction of molecular devices

A systematic study has been carried out for the use of the palladium-based Extended One Pot (EOP) synthetic protocol toward the preparation of metal alkynyl oligomers of general formula [CCArCCM(L)m]n (M=Pt, Pd). Model compounds of type trans-M(PBu3)2(CCC6H5)2 have been prepared by the reaction of tributyltinethynylbenzene with trans-M(PBu3)2Cl2, in the absence of palladium catalysis, since the presence of catalytic Pd(PPh3)4 yields reaction mixtures containing starting material, product and intermediate complex trans-MCl(PBu3)2(CCC6H5). Palladium catalysis has been used for the formation of the bistinacetylide compounds Bu3SnCCArCCSnBu3 (Ar=C6H4; bis(2,5-n-octyloxy)C6H4). Subsequent coupling of these compounds with MCl2(PBu3)2 in the absence of palladium catalyst yields metal alkynyl oligomers. Comparison of 31P-NMR and gel permeation chromatography (GPC) analyses indicates that the GPC technique represents a reliable method to estimate polymer chain lengths for polymers bearing branched aromatic spacers, in spite of the rigid-rod shape of the polymer backbone. Single crystal X-ray determinations of model compounds demonstrate the essential role of side substituents in the aromatic ring to control the supramolecular order and, as a consequence, the optoelectronic properties of materials.