Conformational and isomeric preferences of six-membered inorganic heterocycles [EtNP(E)(OR)]3 (E = Lone Pair, O, S, or Se): a synthetic, spectroscopic, structural, and computational study.
A silicophosphonate bearing four hydroxyl groups, [RSi(OH){OP(O)(H)(OH)}](2)O (2; R = (2,6-(i)Pr(2)C(6)H(3))N(SiMe(3))), has been isolated from the reaction between RSi(OH)(3) and [EtNPCl](3). In contrast, the reaction between the sodium salt of substituted phenols and [EtNPCl](3) yields [EtNP(OAr)](3) [Ar = -C(6)H(3)(i)Pr(2)-2,6 (3), -C(6)H(2)Me(3)-2,4,6 (4), -C(6)H(3)Me(2)-2,6 (5), -C(10)H(7)-1 (6), and -C(6)H(4)(t)Bu-4 (7)]. The cis isomers 3a-7a preferentially crystallize out from the cis/trans isomeric mixture. Single-crystal X-ray diffraction studies carried out for 3a, 4a, and 5a reveal that the P(3)N(3) ring adopts a flattened-chair conformation with the aryloxy substituent on all three phosphorus atoms occupying the axial position. Oxidation of the cis isomers 3 and 5 by H(2)O(2), sulfur, and selenium yields the trichalcogenides [EtNP(E)(OC(6)H(3)(i)Pr(2)-2,6)](3) (E = O (8), S (10), Se (12)) and [EtNP(E)(OC(6)H(3)Me(2)-2,6)](3) (E = O (9), S (11), Se (13)). The reaction leading to the formation of the triselenide 12 also produces small quantities of the diselenide [Et(3)N(3)P(3)(OR)(3)Se(2)] (R = -C(6)H(3)(i)Pr(2)-2,6) (14). The P(3)N(3) ring in these lambda(5)-phosphazanes is highly distorted and resembles more of a twist-boat conformation. The DFT calculations on model systems [HNP(S)(OMe)](3) (15) and [HNP(Se)(OMe)](3) (16) indicate five low-lying unique conformers A-E. The chair conformer with a triaxial-OMe group is identified as the lowest-energy conformer in both cases.
Murugavel
Ramaswamy
R
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India.
Prabusankar
Ganesan
G
Sharma
Ashish
A
Sunoj
Raghavan B
RB
Butcher
Ray J
RJ