C7 and C9 carbon-rich bridges in diruthenium systems:: Synthesis, spectroscopic, and theoretical investigations of different oxidation states

Two methodologies of C-C bond formation to achieve organometallic complexes with 7 or 9 conjugated carbon atoms are described. A C-7 annelated trans-[CI(dppe)(2)Ru=C=C=C-CH=C(CH2)-C=CRu(dppe)(2)CI][X] (X = PF6, OTf) complex is obtained from the diyne trans-[Cl(dppe)(2)Ru-(C=C)(2)-R] (R H, SiMe3) in the presence of [FeCp2][PF6] or HOTf, and C7 or C9 complexes trans-[Cl(dppe)(2)Ru-(C=C)(n)-C(CH3)=C(R-1)-C(R-2)=C=C=Ru(dppe)(2)CI][X] (n = 1, 2; R, = Me, Ph, R-2 = H, Me; X = BF4, OTf) are formed in the presence of a polyyne trans-[CI(dppe)(2)Ru-(C equivalent to C)(n)-R] (n = 2, 3; R = H, SiMe3) with a ruthenium allenylidene trans-[CI(dPPe)(2)Ru=C=C=C(CH2R,)R-2][X]. These reactions proceed under mild conditions and involve cumulenic intermediates [M+]=(C=)(n)CHR (n = 3, 5), including a hexapentaenylidene. A combination of chemical, electrochemical, spectroscopic (UV-vis, IR, NIR, EPR), and theoretical (DFT) techniques is used to show the influence of the nature and conformation of the bridge on the properties of the complexes and to give a picture of the electron delocalization in the reduced and oxidized states. These studies demonstrate that the C7 bridging ligand spanning the metal centers by almost 12 A is implicated in both redox processes and serves as a molecular wire to convey the unpaired electron with no tendency for spin localization on one of the halves of the molecules. The reactivity of the C-7 complexes toward protonation and deprotonation led to original bis(acetyl ides), vinylidene-allenylidene, or carbynevinylidene species such as trans-[CI(dppe)(2)Ru=-C-CH=C(CH3)-CH=C(CH3)-HC=C=Ru(dppe)(2)Cl][BF4](3).