C₇and C₉Carbon-Rich Bridges in Diruthenium Systems:  Synthesis, Spectroscopic, and Theoretical Investigations of Different Oxidation States

Abstract

Two methodologies of C-C bond formation to achieve organometallic complexes with 7 or 9 conjugated carbon atoms are described. A C7 annelated trans-[Cl(dppe)2Ru=C=C=C-CH=C(CH2)-C[triple bond]C-Ru(dppe)2Cl][X] (X = PF6, OTf) complex is obtained from the diyne trans-[Cl(dppe)2Ru-(C[triple bond]C)2-R] (R = H, SiMe3) in the presence of [FeCp2][PF6] or HOTf, and C7 or C9 complexes trans-[Cl(dppe)2Ru-(C[triple bond]C)n-C(CH3)=C(R1)-C(R2)=C=C=Ru(dppe)2Cl][X] (n = 1, 2; R1 = Me, Ph, R2 = H, Me; X = BF4, OTf) are formed in the presence of a polyyne trans-[Cl(dppe)2Ru-(C[triple bond]C)n-R] (n = 2, 3; R = H, SiMe3) with a ruthenium allenylidene trans-[Cl(dppe)2Ru=C=C=C(CH2R1)R2][X]. These reactions proceed under mild conditions and involve cumulenic intermediates [M+]=(C=)nCHR (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 angstroms 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 C7 complexes toward protonation and deprotonation led to original bis(acetylides), vinylidene-allenylidene, or carbyne-vinylidene species such as trans-[Cl(dppe)2Ru[triple bond]C-CH=C(CH3)-CH=C(CH3)-HC=C=Ru(dppe)2Cl][BF4]3.

Charge localization on a redox-active single-molecule junction and its influence on coherent electron transport

“…We chose this particular system because it was used in previous conductance measurements 22,23 as a monomer of chains -albeit with different anchor groups -where it was found that depending on the chain length either coherent transport or electron hopping is observed 22 . In addition spectroscopic and quantum chemical studies on similar Ru complexes [24][25][26][27][28] suggest that this molecular species offers the possibility to easily link two carbon-rich chains to each other for the formation of reversible redox systems [29][30][31] with distinct optical transition properties 32,33 , thereby serving as a starting point for the investigation of chains with multiple redox active centers 27 . In contrast to Ref.…”

Synthesis, characterization, and substituent effects of mononuclear ruthenium complexes [RuCl(CO)(PMe3)3(CHCH-C6H4-R-p)] (R=H, CH3, OCH3, NO2, NH2, NMe2)

“…Highly unsaturated, rigid -(C"C) n -and -(C@C) n -bridges offer an extended p-system and have been recognized as being particularly efficient in mediating electronic transfer [5][6][7][8][9][10]. In this context, a vast number of mono-and bimetallic complexes with polyynediyl or polyacetylene bridges have been extensively studied [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26].…”

Long-distance electronic interaction in a molecular wire consisting of a ferrocenyl–ethynyl unit bridging two [(η5-C5H5)(dppe)M] metal centers

“…Furthermore, the decreasing of the DE 1/2 value from 0.53 V in n = 2, 0.38 V in n = 3 to 0.28 V in n = 4 indicates that the magnitude of Re 2+ -Re 2+ interaction is decreased significantly on the number of C"C moiety. Furthermore, complexes with an odd numbered carbon linear or cyclic bridge has been recently found to promote very efficient electronic communication between two [RuCl(dppe) 2 ] + metal centers [25].…”