Ruthenium Complexes with Vinyl, Styryl, and Vinylpyrenyl Ligands:  A Case of Non-innocence in Organometallic Chemistry

Abstract

We herein describe a systematic account of mononuclear ruthenium vinyl complexes L-{Ru}-CH=CH-R where the phosphine ligands at the (PR'3)2Ru(CO)Cl={Ru} moiety, the coordination number at the metal (L = 4-ethylisonicotinate or a vacant coordination site) and the substituent R (R = nbutyl, phenyl, 1-pyrenyl) have been varied. Structures of the enynyl complex Ru(CO)Cl(PPh3)2(eta1:eta2-nBuHC=CHCCnBu), which results from the coupling of the hexenyl ligand of complex 1a with another molecule of 1-hexyne, of the hexenyl complexes (nBuCH=CH)Ru(CO)Cl(PiPr3)2 (1c) and (nBuCH=CH)Ru(CO)Cl(PPh3)2(NC5H4COOEt-4) (1b), and of the pyrenyl complexes (1-Pyr-CH=CH)Ru(CO)Cl(PiPr3)2 (3c) and (1-Pyr-CH=CH)Ru(CO)Cl(PPh3)3 (3a-P) have been established by X-ray crystallography. All vinyl complexes undergo a one-electron oxidation at fairly low potentials and a second oxidation at more positive potentials. Anodic half-wave or peak potentials show a progressive shift to lower values as pi-conjugation within the vinyl ligand increases. Carbonyl band shifts of the metal-bonded CO ligand upon monooxidation are significantly smaller than is expected of a metal-centered oxidation process and are further diminished as the vinyl CH=CH entity is incorporated into a more extended pi-system. ESR spectra of the electrogenerated radical cations display negligible g-value anisotropies and small deviations of the average g-value from that of the free electron. The vinyl ligands thus strongly contribute to or even dominate the anodic oxidation processes. This renders them a class of truly "non-innocent" ligands in organometallic ruthenium chemistry. Experimental findings are fully supported by quantum chemical calculations: The contribution of the vinyl ligand to the HOMO increases from 46% (Ru-vinyl delocalized) to 84% (vinyl dominated) as R changes from nbutyl to 1-pyrenyl.

Polynuclear carbon-rich organometallic complexes: clarification of the role of the bridging ligand in the redox properties

“…44 In these species, the vinyl ligands contribute more strongly to, or even dominate, the anodic oxidation processes, and experimental findings are fully supported by quantum chemical calculations. For example, a small deviation of <g> from g e and small Dg (< 0.05) values are usually observed at 77 K. It was also found that extending the conjugation within the vinyl ligand gradually modifies the nature of the frontier orbitals and thus the anodic redox processes from fully delocalised across the metal-vinyl entity to ligand dominated with smaller, yet still detectable, metal contribution.…”

Syntheses, structures and redox properties of tris(pyrazolyl)borate-capped ruthenium vinyl complexes

“…Plots of the HOMO, LUMO and LUMO+1 for 4b´ which are representative of the key molecular orbitals across the series are given in Figure 7, whilst orbital energies and composition of selected important frontier orbitals are summarised in (Ar = Ph, Py) have been computed by Winter and his team [18]. Thus, in each case, the HOMO is predominately comprised of a Ru-CH=CH-Ar -type system and can be termed a "metal-ligand" (ML) orbital ( Figure 7, Table 7).…”

“…It has now been firmly established that ruthenium alkynyl complexes Ru(CCR)(PP)Cp´ (P = phosphine, PP = bis(phosphine); Cp´ = Cp, Cp*) [13][14][15] and Ru(X)(CCR´´)(PP) 2 made progressively lower and lower in energy (e.g. 1-naphthyl, 9-anthryl, ethynylphenyl) [18][19][20], and when incorporated into bridging ligands spanning two strongly electron-donating ruthenium fragments [21][22][23][24][25][26][27][28]. 6 The complexes Ru(CH=CHR´´)(Cl)(CO)(PR 3 ) 2 L, which are readily prepared by insertion of an alkyne into the Ru-H bond in RuHCl(CO)(PR 3 ) n (n = 2, 3) [29] offer an entry point to a wide range of vinyl complexes through facile substitution reactions of the supporting phosphine and chloride ligands by a wide range of neutral and anionic mono and bidentate ligands (Scheme 1) [30,31].…”

“…The five-coordinate species are convenient precursors to a range of derivatives through ligand substitution reactions [37][38][39][40][41][42][43][44], giving considerable scope to tune the metal-ligand coordination sphere. [18] and Ru(CH=CHR)(Cl)(CO)(PMe 3 ) 3 [28,46].…”

Multimetallic Alkenyl Complexes Bearing Macrocyclic Dithiocarbamate Ligands

“…Ruthenium (and to a lesser extent osmium) alkenyl complexes 7 4c,i,5,15i,s,18 The facile generation of the alkenyl complexes themselves from insertion of both terminal and internal alkynes into the Ru-H bond allows for the introduction of alkenyl substituents known for their electrochemical (ferrocene) 4c or photophysical (pyrene) 19,20 properties, for example. This route has been exploited by Winter and co-workers to join ruthenium alkenyl centers within a conjugated system.…”