On the transition state of the thermal propene elimination from allylphosphines

✍ Scribed by Edgar Ocando-Mavarez; Gonzalo Martin; Leonardo Rodriguez; Wasdin Muñoz

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 208 KB
• Volume: 8
• Category: Article
• ISSN: 1042-7163
• DOI: 10.1002/(sici)1098-1071(1997)8:2<97::aid-hc1>3.0.co;2-#

✦ Synopsis

Diallyltetramethylpiperidinophosphine 1, diallyldiisopropylaminophosphine 2, and diallylmesitylphosphine 3 were pyrolyzed in a stirred flow reactor over the temperature range 400-450ЊC, using toluene as carrier gas, producing, in all cases, mixtures of phosphorus-containing products. The pyrolysis of 1 produced 1-tetramethylpiperidino-1-phosphabutadiene, in addition to a mixture of phosphines and polyphosphines. Compound 2 produced the azadiphosphole 4, the phosphinine 5, allylphosphine, and diisopropylaminophosphine as major phosphorated products. The pyrolysis of 3 produced a mixture of phosphines and polyphosphines. The complex mixture generated by the three diallylphosphines indicates the formation of free radicals during their pyrolyses. AM1 calculations on the transition state of an expected retroenetype propene elimination reaction showed that, due to the phosphaalkene character of the transition state, the structure of the latter is very rigid and sensitive to steric effects. Steric hindrance of the substituents on the phosphorus atom compels the molecule to distort the half-chair transition structure, causing a rise on the activation energy to values in the range of a homolytic P-C bond dissociation energy.