In chemistry, a sigma complex or σ-complex usually refers to a family of coordination complexes where one or more ligands interact with the metal using the bonding electrons in a sigma bond. Transition metal silane complexes are often especially stable sigma complexes.

With a slight reorganization of electrons and geometry, an L-type σ ligand can become two X-type ligands. Why, then, are σ complexes stable? How can we control the ratio of σ complex to X 2 complex in a given situation? How does complexation of a σ bond change the ligand’s properties? We’ll address these questions and more in this post.

Step 2: Benzene pi electrons form a sigma bond with the Strong Electrophile to create the "sigma complex", a resonance stabilized, charged intermediate. Step 3: Deprotonation of the sigma complex to reform the aromatic ring. The generic mechanism shared by …

2015年10月12日 · What is a sigma complex? According to Wikipedia, "sigma complex" refers to an arenium ion. The suffix "-ium" denotes a positively charged ion. So, it is correct to call the resonance structures in the below picture depictions of a sigma complex? It's distinctly anionic rather than cationic.

For Electrophilic Aromatic Substitution (EAS) reactions, the rate determining step is the formation of a positively charged sigma complex. In future reactions, the intermediate may have a negative charge.

In chemistry, a sigma complex or σ-complex usually refers to a family of coordination complexes where one or more ligands interact with the metal using the bonding electrons in a sigma bond. Dihydrogen complexes are examples.

A σ-complex, also known as a sigma complex, is an intermediate species formed during electrophilic addition reactions to conjugated dienes. It is characterized by the formation of a three-membered ring structure that stabilizes the allylic carbocation, a key step in the mechanism of these reactions.

For historic reasons this complex is also called a Wheland intermediate, after American chemist George Willard Wheland (1907–1976). [2] They are also called sigma complexes. [3] The smallest arenium ion is the benzenium ion (C 6 H + 7), which is protonated benzene.

In step 1 the π electrons of benzene attack the electrophile which takes two electrons of the six-electron aromatic system. This forms a σ bond between one carbon atom of the benzene ring and the electrophile. Because of the new sigma bond formed, this …

The first thing to realize about \(\sigma\) complexes is that they are highly sensitive to steric bulk. Any old \(\sigma\) bond won’t do; hydrogen at one end of the binding bond or the other (or both) is necessary. The best studied \(\sigma\) complexes involve …