Substituent effect on low coordination phosphorus chemistry

It has been shown by means of computational chemistry that the successful synthesis of some of the most remarkable phosphorus containing molecules in the last decades (e.g., 1,3,5-triphosphinine or 1,3-isodiphosphinine) was greatly facilitated by the presence of the bulky tBu group. This substituent is needed to stabilize tBuCP, which is used to be the starting material in many reactions. In a six-membered ring the repulsion of the neighboring tBu substituents brings a destabilization of about 22–25 kcal/mol for each tBu unit, this amount of energy is comparable to the aromatic stabilization in benzene. The minimization of this steric repulsion between neighboring tBu moieties in the possible isomers plays a crucial role in determining the stability of the product. The effect of the steric repulsion on the kinetics of the cycloaddition reaction between tBuCP and diazomethane has also been shown to be important, accounting for the observed regioselectivity in the reaction.