Ruthenium complexes bearing bulky pentasubstituted cyclopentadienyl ligands and evaluation of [Ru(η5-C5Me4R)(MeCN)3][PF6] precatalysts in nucleophilic allylic substitution reactions

[Ru(eta(5)-C5Me4R)(MeCN)(3)][PF6] (R = CH(2)tBu, iPr, tBu, and CF3; 2-5) complexes were synthesized in two steps starting from the appropriate cyclopentadienes and RuCl3 center dot 3H(2)O. The fully substituted ruthenocenes [Ru(C5Me5)(C5Me4R*)], [Ru(C5Me5)(C(5)nPr(4)R*)] {R* = (lR,5S)-6,6-dimethylbicyclo[3.1.1]hept-2-en-2-yl} and [Ru(C5Me5)(C(5)nPr(5))] were obtained by treating [Ru(C5Me5)Cl](4) with the corresponding cyclopentadienyllithiurn salts. Complexes 2-5 were evaluated as catalyst precursors for nucleophilic allylic substitution reactions, and the results were compared to those obtained with the [Ru(C5Me5)(MeCN)(3)][PF6] (1) precatalyst. The etherification of p-methoxyphenol with the typical aliphatic chlorohexene allylic substrate shows that the introduction of the bulky tert-butyl and trifluoromethyl groups into the tetramethylcyclopentadienyl ring results in a valuable enhancement in regioselectivity in favour of the branched allyl aryl ether. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).