Complexation of the (η5-Cp)Ru+ and (η5-Cp*)Ru+ Arenophiles on Alkynylnaphthalene: Solvent Effect on the Regioselectivity and the Haptotropic Rearrangement

Abstract

The reactions of [Cp*Ru(NCMe)3](PF6) and 1,4-R-C6H4-C≡C-SiMe3 (R = Me, C≡C-SiMe3; Cp* = η5-C5Me5) in CH2Cl2 provided the complexes [Cp*Ru(η6-4-MeC6H4-C≡C-SiMe3)](PF6) (1) and [Cp*Ru(η6-1,4-C6H4(C≡C-SiMe3)2](PF6) (2) in 65% yield. A similar reaction using 1-(trimethylsilylethynyl)naphthalene provided the complexes [Cp*Ru(η6-C10H7(C≡C-SiMe3))](PF6), bearing the Cp*Ru+ arenophile on the monosubstituted (3A) or unsubstituted (3B) fused ring, in 86% yield. The 3A/3B kinetic ratio is 43/57, while the 3A/3B thermodynamic ratio is 27/73. The bis(alkynylnaphthalene) complexes [Cp*Ru(η6-1,4-C10H6(C≡C-SiMe3)2)](PF6) were also obtained in good yields with 4A/4B kinetic ratios ranging from 80/20 to 16/84 depending on the concentration of a labile ligand able to temporarily replace one acetonitrile ligand on [Cp*Ru(NCMe)3](PF6). In the absence of such a ligand the reaction did not take place. Isomer 4A can be quantitatively converted to the thermodynamic regioisomer 4B. The kinetic products were obtained in less than 4 h at temperatures ranging from −17 to 20 °C, while the isomerization is much slower. The thermodynamic equilibrium is reached after several days at 20 °C in a good coordinating solvent such as acetone. The bis(alkynylnaphthalene) was also reacted with [CpRu(NCMe)3](PF6) (Cp = η5-C5H5). The corresponding complexes 5A,B were isolated with an overall yield of 87% and 5A/5B kinetic ratios ranging from 5/95 to 20/80, while the thermodynamic ratio was 45/55. The experimental data analyzed with the support of theoretical calculations allowed us to propose a mechanism for the reactions of complexation and isomerization.