The ruthenocenylmethylium cation: Isolation and structures of eta(5)-cyclopentadienyl-eta(6)-fulvene-ruthenium(II) salts

Salts of the ruthenocenylmethylium. cation, I, can be synthesized from the reaction of ruthenocenylmethanol with either Bronsted or Lewis acids. The X -ray crystal structures of the tetrakis 3,5-bis(trifluoromethyl)phenyl}bora te and trifluoromethanesulfonate salts of 1(+) reveal that the methylium ca rbon is bound to the ruthenium with Ru-C bond lengths in the range 2.251(9) -2.40(1) Angstrom and confirm the description of the cation structure as et a (5)-cyclopentadienyl-eta (6) eta (5)-fulvene-ruthenium(II). The UV-vis sp ectrum of 1(+) shows a d-d transition at an energy similar to those of ruth enocene and the eta (5)-cyclopentadienyl-eta (6)-benzeneruthenium(II) catio n, but with increased absorptivity. Cyclic voltammetry indicates 5 that 1() is reduced at considerably less negative potential than its isomer, the e ta (5)-cyclopentadienyl-eta (6)-benzeneruthenium(II) cation. Chemical reduc tion with sodium amalgam in tetrahydrofuran leads to the formation of methy lruthenocene, 1,2-bis(ruthenocenyl)ethane, and bis(ruthenocenylmethyl)ether . Reaction of 1+ with triphenylphosphine affords the (ruthenocenylmethyl)tr iphenylphosphonium cation; the crystal structure of the dichloromethane sol vate of its tetrafluoroborate salt has been determined. Density functional calculations closely reproduce the crystallographically determined geometry of 1(+) and allow rationalization of some characteristics of its structure , spectroscopy, and reactivity. The calculations suggest that the ferroceny lmethylium cation, 3(+), has a geometry similar to 1+ with similar orbital structure, albeit with considerably more d-character to the occupied fronti er orbitals.