M-Terphenyl

Discovery The earliest known synthesis of meta-terphenyl was completed in 1866 by Pierre Eugène Marcellin Berthelot by heating benzene to high temperatures leading to a mixture of hydrocarbons including a mixture of meta-terphenyl and para-terphenyl. Reactivity By the 1930s, focus had shifted to experimenting with the reactivity of meta-terphenyl and its potential use as a ligand. The first verified modified version of meta-terphenyl was created in 1932 by Arthur Wardner and Alexander Lowy and led to the creation of nitro-substituted meta-terphenyls as well as amino-meta-terphenyls from the oxidation of the nitro-substituted compounds. Walter and Kathryn Cook halogenated meta-terphenyl with chlorine and bromine with further applications such as use in as Grignard reaction, the first such suggestion for meta-terphenyl as a ligand for a main group element. They later confirmed their results using the Stepanow Method. This trend continued with C.K. Breadsher and I. Swerlick publishing a review of all known reactions that meta-terphenyl could undergo. G. R. Ames also wrote an article detailing not only reactions of meta-terphenyls, but also covering all the different experimental methods to obtain meta-terphenyl known at the time. Early synthetic methods During this time, the method of producing meta-terphenyl had remained the same. While people did experiment with other ways to obtain the compound, for the most part the method of heating benzene in a glass tube remained the primary method. In 1948, however, G. Woods and Irwin Tucker put forth an alternative method. Instead of heating benzene, they found that a combination of dihydroresocinol and two equivalents of phenyllithium would create unsymmetrical meta-terphenyl molecules. This was significant as the previous method required the separation of meta-terphenyl from other compounds and this novel synthesis allowed meta-terphenyls to be the major product and much more easily isolatable. This method would remain the most popular form of making meta-terphenyls until the end of the 20th century. It was during this time that it was discovered that meta-terphenyls occurred in nature. In 1975, Karl-Werner Glombitza, Hans-Willi Rauwald, and Gert Eckhardt isolated two meta-terphenyls from the algae Fugus vesiculosus. More naturally occurring meta-terphenyls have been isolated since then and have shown promising applications in the field of biochemistry. ==Synthesis==

Hart Method As the demand for meta-terphenyl and its derivatives grew through the latter half of the 20th century, it became necessary to increase the yield of reactions producing meta-terphenyls as well as have the ability to uniquely create symmetric and unsymmetric meta-terphenyls to investigate their reactivity as well utilize their increased steric control. Such a method was discovered by Akbar Saednya and Harold Hart in 1986. Using an excess of Grignard reagent that had a phenyl group attached, meta-terphenyl was able to be made quickly, in one step, with a relatively high yield. Saednya and Hart continued their work and provided two alternate paths to create meta-terphenyls in 1996. One involved using a halogenated benzene and three equivalents of the phenyl group attached to the benzene. The second involved a dichloro-substituted benzene and butyl lithium followed by two equivalents of the Grignard reagents mentioned above. This led to increased yields of larger terphenyl compounds, however as the size of the substituents has been hypothesized to have a limit due to the increased steric hindrance of the molecule. Other approaches m-Terphenyl compounds can be prepared by reacting anionic diphenyl derivatives with functional ketones in a solution of potassium hydroxide and DMF in an ultrasound bath, a bulky meta-terphenyl molecule can be obtained. The yields are not high but the procedure ccan be completed within an hour. Additionally, meta-terphenyl synthesis has begun to become more focused. As opposed to general routes to produce common meta-terphenyl compounds, the shift has been to improve certain derivatives to accomplish particular goals. Examples of this include a method to produce a very sterically hindered meta-terphenyl with the purpose of forming phosphorus-phosphorus double bonds and a heavily fluorinated meta-terphenyl being produced to help stabilize silylium compounds. Additionally, reaction to add other bulky substituents to the center phenyl group has been shown to discourage rotation of the outer phenyl groups in hopes of stabilizing boron and silicon radicals and bonded complexes. ==Derivatives==

Organometallics Their large size can help to sterically force a certain reaction, however they are mainly used to stabilize compounds that would be unstable otherwise. Additionally, meta-terphenyl ligands were used to stabilize phosphorus-phosphorus double bonds. This was proven multiple times with a variety of different meta-terphenyl compounds being used to confirm the result and led to the confirmation of the appropriate length of a phosphorus-phosphorus double bond. Organomagnesium compounds have been prepared using meta-terphenyl ligands. Organoiron, chromium, and manganese derivatives are also known. M-terphenyls have also been quite helpful in getting preliminary structures of divalent lithium and sodium, although both molecules had substantial stabilization from the electron-rich meta-terphenyl group. M-terphenyls have also helped, along with the electronic support of sodium ions, to stabilize the first gallium-gallium triple bond, although this is contested due to the high coordination of the sodium atoms in the complex. == References ==