Synthesis, Structure, and Coordination Chemistry of the Bicyclic π-Acid Phosphatri(3-methylindolyl)methane

Reaction of tri(3-methylindolyl)methane ( 1 ) with PCl 3 in the presence of triethylamine produces the bicyclic π-acid phosphatri(3-methylindolyl)methane ( 2 ). The unconstrained analogue tri( N -3-methylindolyl)phosphine ( 3 ) was synthesized by reaction of lithium 3-methylindolide with PCl 3 . Both 2 and 3 are stable to hydrolysis, alcoholysis, and aerial oxidation. Reactions of 2 with t BuOOH, S 8, or Se powder under forcing conditions produce the chalcogenide derivatives 2 O ( 4 ), 2 S ( 5 ), and 2 Se ( 6 ), respectively. Tri( N -3-methylindolyl)phosphine selenide ( 7 ) and Se P( N -pyrrolyl) 3 ( 8 ) were synthesized by reaction of Se powder with 3 and P( N -pyrrolyl) 3, respectively. The reaction of 2 with Rh(acac)(CO) 2 (acac = acetylacetonate) under forcing conditions yields Rh(acac)(CO)( 2 ) ( 9 ), whereas Rh(acac)(CO)( 3 ) ( 10) was synthesized by reaction of 3 with Rh(acac)(CO) 2 under mild conditions. Spectroscopic data for 6 − 10 were used to assess the electronic properties of 2 and 3 . Reduced σ-basicity of 2 and 3 is indicated by lack of their reactivity with methyl iodide. Furthermore, comparison of the 1 J P - Se values of 6 − 8 shows the parent phosphines to be slightly stronger σ-bases than P(OPh) 3, but much weaker than triaminophosphines. In addition, comparison of the ν CO data of 9 and 10 with those of known Rh(acac)(CO)(PR 3 ) complexes shows 2 is a stronger π-acid than P( N -pyrrolyl) 3 and P(OPh) 3, while 3 has π-acceptor properties similar to P(OPh) 3 . The molecular structures of compounds 2, 4, and 9 were determined by X-ray crystallography.