Cycloaddition of Alkenes and Alkynes to the P‐centered Singlet Biradical [P(μ‐NTer)]2.

The reaction of biradical [P(μ‐NTer)]2 (1, Ter = 2,6‐bis(2,4,6‐trimethylphenyl)phenyl) towards different alkenes (R = 2,3‐dimethyl–butadiene, 2,5‐dimethyl‐2,4‐hexadiene, 1,7‐octadiene, 1,4‐cyclohexadiene) and alkynes (R = 1,4‐diphenyl‐1,3‐butadiyne) was studied experimentally. Although these olefins can react in different ways, only [2+2] cycloaddition products (1R) were observed. The reaction with 2,3‐dimethylbutadiene also led to the [2+2] product (1dmb). Thermal treatment of 1dmb above 140 °C resulted in the recovery of biradical 1 upon homolytic bond cleavage of the two P–C bonds and the release of 2,3‐dimethylbutadiene. In contrast to this reaction, all other [2+2] additions products (1R, R = 1,7‐octadiene, 1,4‐cyclohexadiene, 1,4‐diphenyl‐1,3‐butadiyne) began to decompose at temperatures between 200 °C and 300 °C. Only unidentified products were obtained but no temperature‐controlled equilibrium reactions were observed. Computations were carried out to shed light into the formal [2+2] as well as the possible [4+2] addition reaction. [ABSTRACT FROM AUTHOR]