Stable Cationic and Neutral Ruthenabenzenes

Reversible protonation of the purple ruthenabenzofuran (or tethered ruthenacyclohexadiene) Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CO)(PPh3)2 (1) with HBF4·OEt2 gives the structurally characterized stable cationic tethered ruthenabenzene [Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)](CO)(PPh3)2][(BF4)2H] (2), while the thermal reaction of 1 with HCl forms the stable neutral tethered ruthenabenzene Ru[C5H2(CO2Me-2)(CO2Me-4)(CH2CO2Me-5)]Cl(PPh3)2 (3) as the major product. The cyclopentadienyl complex Ru(η5-C5H2(CH2CO2Me-1)(CO2Me-2)(CO2Me-4)Cl(CO)(PPh3) (4), which is formed in this reaction as a minor product, can be separated from 3 by chromatography. Treatment of the ruthenabenzene 3 with CNR (R = p-tolyl) gives the purple ruthenabenzofuran (or tethered ruthenacyclohexadiene) complex Ru[C5H2(CO2Me-2)(CO2Me-4)(CHCO2Me-5)](CNR)(PPh3)2 (5), which is the isocyanide analogue of 1.