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 (μ-C⋮CC⋮C) (PP = dppm 5a, dppe 5b ) have been synthesized from RuCl(PP)Cp* ( 1a / b ) via the corresponding vinylidenes [Ru( C CH 2 )(PP)Cp*] + ( 2a / b ), deprotonation (KOBu t ) to the ethynyls Ru(C⋮CH)(PP)Cp* ( 3a / b ), oxidative coupling ([FeCp 2 ][PF 6 ]) to the bis(vinylidenes) [{Ru(PP)Cp*} 2 {μ-( C CHCH C )}] 2+ ( 4a / b ), and deprotonation [dbu ( 4a ), KOBu t ( 4b )]. Electrochemistry of 5a/b revealed the expected sequence of four 1e redox steps, which occurred at significantly lower E ° values than found for the Ru(PPh 3 ) 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 ][PF 6 ] n ( n = 1, 2). In the monocation [ 5b ][PF 6 ] 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 ][PF 6 ] 2 confirm the anticipated dicarbene-cumulene structure for the Ru C C C C Ru bridge.