No abstract

New tricyclic hexacoordinated phosphoranes 1-6 with internal NfP coordination containing ring sizes varying from five to eight membered have been synthesized by oxidative addition of a quinone or a diol to a cyclic phosphite.

The zwitterionic monocyclic λ5 Si-monofluorosilicates 3a−c were synthesized by reaction of the zwitterionic λ5 Si-trifluorosilicates 1a−c with 1 molar equiv of (Z)-Me3SiO(Ph)CNN(H)SiMe3 (2). The zwitterionic monocyclic λ5 Si-difluorosilicate 8 and the zwitterionic spirocyclic λ5 Si-silicate 9 (isolated as the isomer 9-I) were prepared in an analogous manner, starting from the zwitterionic λ5 Si-tetrafluorosilicate 7 and using 1 (→ 8) or 2 (→ 9) molar equiv of 2. Single-crystal X-ray diffraction studies showed that the Si-coordination polyhedra of 1a, 3a, 8, 9-I·CHCl3, and 9-I·CH3CN are distorted trigonal bipyramids. The axial positions are occupied by two fluorine atoms (1a), one fluorine atom and one oxygen atom (3a, 8), or two oxygen atoms (9-I·CHCl3, 9-I·CH3CN). These results are in agreement with the NMR data obtained for these compounds in solution. The chiral monocyclic compounds (3a−c and 8) undergo two distinct rate processes, inversion of absolute configuration of the chiral λ5 Si-silicate skeleton (enantiomerization) and a novel “ammonium-nitrogen inversion”, measured by variable-temperature and selective inversion recovery NMR experiments (activation barrier for “ammonium-nitrogen inversion”:  3a−c, 17.0 ± 0.3 kcal mol-1; 8, 20.8 ± 0.3 kcal mol-1; activation barrier for inversion of absolute configuration at the silicon atom:  3c, 20.7 ± 0.3 kcal mol-1; 8, 11.7 ± 0.3 kcal mol-1). In the spirocyclic λ5 Si-silicate 9-I only one of these processes, the “ammonium-nitrogen inversion” (ΔG ⧧ = 20.8 ± 0.3 kcal mol-1), could be observed, while inversion of absolute configuration at the silicon atom could not be detected by NMR spectroscopy. Furthermore, no interconversion of diastereomers 9-I ⇄ 9-II was observed.

Aminophosphoranes 2 and 4-9 with a cyclohexylamino substituent and ring sizes varying from five to eight have been synthesized by oxidative addition reactions of cyclic aminophosphites with diols or 1,2-diketones. The reactivities of these phosphoranes are compared with those of the corresponding cyclic aminophosphites. The difference in hydrolytic pathways between amino- and analogous phenoxyphosphoranes is discussed. X-ray structures of two sets of compounds, (a) (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O) (1) and (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O)(1,2-O(2)C(6)Cl(4)) (2) and (b) (C(6)H(11)NH)P{O-(t-Bu)(2)C(6)H(2))(2)CH(2)} (3) and (C(6)H(11)NH)P{(O-(t-Bu)(2)C(6)H(2))(2)CH(2)}(1,2-O(2)C(6)H(4)).(1)/(2)Et(2)O (4.(1)/(2)Et(2)O) have been determined and geometrical parameters compared between the P(III) and the corresponding P(V) compounds. In 1, the six-membered ring has a chair conformation with the amino group axial; in 2, the six-membered ring is located apical-equatorial in a trigonal bipyramidal geometry and has a boat conformation. The eight-membered ring has a boat-chair conformation in 3, whereas the same ring has a tub conformation in 4.

The zwitterionic spirocyclic λ5 Si-silicate (morpholiniomethyl)bis[salicylato(2−)-O 1,O 2]silicate (5) was synthesized by reaction of trimethoxy(morpholinomethyl)silane and dimethoxy(morpholinomethyl)phenylsilane, respectively, with salicylic acid (molar ratio 1:2) in acetonitrile at room temperature. Bis[salicylato(2−)-O 1,O 2][(2,2,6,6-tetramethylpiperidinio)methyl]silicate (6) was obtained analogously, starting from trimethoxy[(2,2,6,6-tetramethylpiperidino)methyl]silane. Compound 5 was isolated as a crystalline product consisting of enantiomorphic crystals, each containing exclusively zwitterions with the same absolute configuration. Crystallization of this product from acetonitrile yielded the crystalline solvate 5·CH3CN (crystals containing a 1:1 mixture of enantiomers with opposite absolute configuration). Compounds 5 (Δ-enantiomer), 5·CH3CN (racemate), and 6 (racemate) were structurally characterized by single-crystal X-ray diffraction. The spirocyclic frameworks of 5 and 6 are built up by two six-membered SiO2C3 ring systems. The zwitterions in the crystal of 5, 5·CH3CN, and 6 contain a pentacoordinate (formally negatively charged) silicon atom (SiO4C skeleton) and a tetracoordinate (formally positively charged) nitrogen atom. The coordination polyhedra around the silicon atoms are distorted trigonal bipyramids, the axial positions being occupied by the carboxylate oxygen atoms. Solid-state MAS NMR studies revealed the following isotropic 29Si chemical shifts:  δ −120.6 (5), −123.1 (5·CH3CN), −120.4 (6). The zwitterion 6 exists also in solution (CDCl3; 1H, 13C, and 29Si NMR studies).