Polymerization of phenylacetylene by novel Rh (I)-, Ir (I)- and Ru (IV) 1,3-R2-3,4,5,6-tetrahydropyrimidin-2-ylidenes (R = mesityl, 2-propyl): Influence of structure on activity and polymer structure

The preparation of novel Rh (I) and Ir (I) complexes, i.e. [Rh(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD)]+[PF6]− (1), Rh(CF3SO3)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (2) and Ir(CF3CO2)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (3) (COD = 1,5-cyclooctadiene), is described. Compounds 1 and 3 were structurally characterized by X-ray diffraction. In 1, the N-heterocyclic carbene acts as a bidentate ligand with the carbene coordinating to the Rh(I) center and an arene group acting as a homoazallyl ligand. The catalytic activity of complexes 1–3 in the polymerization of phenylacetylene was studied and compared to that of RhCl(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (4), Rh(CF3COO)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (5), [Rh(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD)]+[BF4]− (6), IrCl(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (7), IrCl(1,3-diisopropyl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) (8), IrBr(1,3-di-2-propylimidazolin-2-ylidene)(COD) (9), RuCl2(PCy3)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(double bond; length as m-dashCH–C6H5) (10), RuCl2(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(double bond; length as m-dashCH-2-(2-PrO)-5-NO2-C6H3) (11), Ru(CO2CF3)2(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(double bond; length as m-dashCH-2-(2-PrO)-5-NO2-C6H3) (12). Compounds 1–6 were active in the polymerization of phenylacetylene. cis-Poly(phenylacetylene) (PPA) was obtained with the rhodium-based catalysts 1, 2, 4–6, trans-PPA was obtained with the Ir-based catalysts 3 and 8. In addition, compounds 1 and 6 were found to produce highly stereoregular PPA with a cis-content of 100% in the presence of water. Finally, the Ru-based metathesis initiator 12 allowed for the synthesis of trans-PPA, representing the first example of a ruthenium complex being active in the polymerization of a terminal alkyne.