Complexation of the (η5-Cp)Ru+ and (η5-Cp*)Ru+ arenophiles on alkynylnaphthalene: solvent effect on the regioselectivity and the haptotropic rearrangement
Résumé
The reactions of [Cp*Ru(NCMe)3](PF6) and 1,4-R-C6H4C≡CSiMe3 (R = Me, C≡CSiMe3; Cp* = η5-C5Me5) in CH2Cl2 provided the complexes [Cp*Ru(η6-4-MeC6H4C≡CSiMe3)](PF6) (1) and [Cp*Ru[η6-1,4-C6H4(C≡CSiMe3)2]](PF6) (2) in 65% yield. A similar reaction using 1-(trimethylsilylethynyl)naphthalene provided the complexes [Cp*Ru(η6-C10H7C≡CSiMe3)](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 thermodn. ratio is 27/73. The bis(alkynylnaphthalene) complexes [Cp*Ru(η6-1,4-C10H6(C≡CSiMe3)2)](PF6) were also obtained in good yields with 4A/4B kinetic ratios ranging from 80/20 to 16/84 depending on the concn. 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 quant. converted to the thermodn. regioisomer 4B. The kinetic products were obtained in less than 4 h at temps. ranging from -17° to 20°, while the isomerization is much slower. The thermodn. equil. is reached after several days at 20° 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 thermodn. ratio was 45/55. The exptl. data analyzed with the support of theor. calcns. allowed us to propose a mechanism for the reactions of complexation and isomerization.