Syntheses, structures, and spectro-electrochemistry of {Cp*(PP)Ru}C CC C{Ru(PP)Cp*} (PP = dppm, dppe) and their mono- and dications

The complexes {Cp*(PP)Ru}(2)(mu-Cequivalent toCCequivalent toC) (PP = dppm 5a, dppe 5b) have been synthesized from RuCl(PP)Cp* (1a/b) via the corresponding vinylidenes [Ru(=C=CH2)(PP)Cp*](+) (2a/b), deprotonation (KOBut) to the ethynyls Ru(Cequivalent toCH)(PP)Cp* (3a/b), oxidative coupling ([FeCp2][PF6]) to the bis(vinylidenes) [{Ru(PP)Cp*}2{mu-(=C=CHCH=C=)}](2+) (4a/b), and deprotonation [dbu (4a), KOBut (4b)]. Electrochemistry of 5a/b revealed the expected sequence of four le redox steps, which occurred at significantly lower Edegrees values than found for the Ru(PPh3)(2)Cp analogue. Single-crystal X-ray structure determinations are reported for 1a/b, 2a/b, 3a/b, 4a/b, and 5a/b, together with the oxidized products [5b] [PF6](n) (n = 1, 2). In the monocation [5b] [PF6] the Ru-C(l) [1.931(2) Angstrom] and C-C distances [1.248-1.338(3) Angstrom] are intermediate between those found in 5b and the dication [5b](2+). The short Ru-C [1.857(5) Angstrom] and experimentally equal C-C distances [1.269-1.280(6) Angstrom] in [5b] [PF6](2) confirm the anticipated dicarbene-cumulene structure for the Ru=C=C=C=C=Ru bridge