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

Abstract

The complexes {Cp*(PP)Ru}2(μ-C≡CC≡C) (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(C≡CH)(PP)Cp* (3a/b), oxidative coupling ([FeCp 2][PF6]) to the bis(vinylidenes) [{Ru(PP)Cp*} 2{μ-(=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 E° values than found for the Ru(PPh3)2Cp 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(1) [1.931(2) Å] and C-C distances [1.248-1.338(3) Å] are intermediate between those found in 5b and the dication [5b]2+. The short Ru-C [1.857(5) Å] and experimentally equal C-C distances [1.269-1.280(6) Å] in [5b] [PF6]2 confirm the anticipated dicarbene-cumulene structure for the Ru=C=C=C=C=Ru bridge.