PM3 study of phosphines and phosphine chalcogenides. Conformational and configurational properties of tri-o-tolyl phosphine and its chalcogenides

An investigation employing the PM3 semiempirical self-consistent field mole cular orbital method to calculate structure optimization and pyramidal phos phorus atom inversion barriers for phosphines and phosphine chalcogenides 1 -16 has been undertaken. The calculated structural parameters (for 1-12) an d inversion barriers (for 13-16) are in good agreement with experimental re sult,,,. The conformational interconversion pathway,,, for tri-o-tolylphosp hine (9), tri-o-tolylphosphine oxide (10), tri-o-tolylphosphine sulfide (11 ) and tri-o-tolylphosphine selenide (12) were investigated in detail. For c ompounds 9-12, four rotamers are possible with respect to the position of t he methyl groups. In the most stable geometry of 9, two of the methyl group s are close to the phosphorus lone pair, In 10, the methyl groups assume th e paddle conformation, having all methyl groups close to the oxygen atom. I n 11, the most stable rotamer is similar to that in 9. In the most stable r otamer of 12, all methyl groups are far from the selenium atom.