Synthesis, structure, and coordination chemistry of the bicyclic π-acid phosphatri(3-methylindolyl)methane

Reaction of tri(3-methylindolyl)methane (1) with PCl3 in the presence of triethylamine produces the bicyclic pi -acid phosphatri(3-methylindolyl)methane (2). The unconstrained analogue tri(N-3-methylindolyl)phosphine (3) was synthesized by reaction of lithium 3-methylindolide with PCl3. Both 2 and 3 are stable to hydrolysis, alcoholysis, and aerial oxidation. Reactions of 2 with (BuOOH)-Bu-t, 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 sigma -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 sigma -bases than P(OPh)(3), but much weaker than triaminophosphines. In addition, comparison of the v(Co) data of 9 and 10 with those of known Rh(acac)(CO)(PR3) complexes shows 2 is a stronger pi -acid than P(N-pyrrolyl)(3) and P(OPh)(3), while 3 has pi -acceptor properties similar to P(OPh)(3). The molecular structures of compounds 2, 4, and 9 were determined by X-ray crystallography.