13.6.5: Carbon Wires- Polyyne and Polyene Bridges

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Organic molecules with conjugated \(\pi\) systems are known to have interesting optical and electronic properties. When ligands with conjugated \(\pi\) systems are used to bridge two metal centers, the two metals can behave in a cooperative way because the electronic state of one metal ion is conjugated to the other. The most intensely investigated complexes are bimetallic metal complexes (two metal ions) that are bridged by long carbon chains with alternating single and double bonds. Some examples are given below. (This topic is reviewed in Aguirre-Etcheverry D. O’Hare, Chem. Rev., 2010, 110, 4839, doi: 10.1021/cr9003852)

Polyene

Polyenes are organic molecules with alternating double and single bonds. In other words, they contain a series of consecutive \(\ce{(-C= C-)_{n)}\) with \(n >1\). Aromatic and cyclic polyenes were discussed in a previous section. One of the longest ligands reported as of 2010 was a \(\ce{Ru-(CH)14-Ru}\) complex (shown in Figure \(\PageIndex{1}\)).

Source: Aguirre-Etcheverry D. O’Hare, Chem. Rev., 2010, 110, 4839, doi: 10.1021/cr9003852

Polyyne ligands

Polyynes are organic molecules with alternating single and double bonds. In other words, they contain a series of consecutive \(\ce{(-C \bond{#} C-)_n}\) with \(n >1\).

Organometallic polyynes capped with metal complexes are well characterized. As of the mid-2010s, the most intense research had concerned rhenium (ReC_nRe, n=6-20), ruthenium (RuRuC_nRuRu, n = 8–20), iron (FeC₁₂CFe), platinum (PtC_nPt, n = 16–28), palladium (ArC_nPd, n = 6–10), and cobalt (Co₃C_nCo₃, n = 14–26) complexes (Figure \(\PageIndex{1}\)).

Figure \(\PageIndex{1}\): Examples of known polyyne organometallic complexes. (Pigulski, Organometallic polyynes, CC BY-SA 4.0)

Source: https://en.Wikipedia.org/wiki/Polyyne