Solution Conformational Features of the Unsymmetrical Metalla Crown Ether cis-Mo(CO)₄{2-(2,2‘-O₂C₁₂H₈)PO(CH₂CH₂O)₂- 2-C₂₀H₁₂-2‘-OP(2,2‘-O₂C₁₂H₈)} from 2D NMR Spectroscopy and Molecular Modeling

Abstract

A new unsymmetrical metalla crown ether, cis-Mo(CO)4{2-(2,2‘-O2C12H8)PO(CH2CH2O)2-2-C20H12-2‘-OP(2,2‘-O2C12H8)}, has been designed for solution conformation studies. The complex was prepared by the reaction of the α,ω-bis(phosphorus donor) polyether ligand 2-(2,2‘-O2C12H8)PO(CH2CH2O)2-2-C20H12-2‘-OP(2,2‘-O2C12H8) with Mo(CO)4(nbd). Separate 1H NMR resonances were observed for six of the eight methylene protons of the metalla crown ether, indicating that the motion of the metalla crown ether ring was restricted. The 1H, 13C, and 31P NMR chemical shifts of the metalla crown ether were completely assigned using a combination of 13C DEPT, 1H−1H COSY, 13C{1H} HETCOR, 31P{1H} HETCOR, 1H{13C} HMBC, and 1H−1H NOESY NMR experiments. The solution conformation was analyzed using 1H−1H vicinal coupling constants and 1H−1H NOESY NMR experiments. The vicinal 1H−1H coupling constants for the ethylene protons indicated that both ethylenes were gauche. The 1H−1H NOESY NMR experiments showed a number of close contacts between aromatic protons. Good qualitative agreement was observed between the H−H distances obtained from molecular modeling studies and the intensities of the direct 1H−1H NOEs of the aromatic protons. The structure of the metalla crown ether from the molecular modeling studies also explained the unusual shieldings and deshieldings of certain aromatic protons in the molecule.

Metallacrown ethers with a symmetric bis(phosphite) ligand derived from 1,2-bis-(2-hydroxyethoxy)benzene: Synthesis, characterization and hydroformylation of styrene

“…The 31 P{ 1 H} NMR resonance is a singlet. The chemical shift of the 31 P { 1 H} NMR resonance is close to those of other phosphite and bis(phosphite) ligands [2,32,33] derived from the 2,2 0 -biphenylylenephosphochloridite ester. The 1 H NMR spectrum of the ligand exhibits two resonances in the 4.09e4.30 ppm region, indicating that the protons attached to each methylene carbon are chemically equivalent.…”

Nucleophilic Displacement Reactions of cis-Bis((2,2‘-biphenylylene)phosphochloridite ester)tetracarbonylmolybdenum(0). The First Example of an Unusual Hydrolysis Reaction Yielding Unsymmetrically Substituted Products

“…A number of ligands containing [1,3,2]dioxaphosphepin groups ( Figure ) derived from bis(aryl)diols such as 2,2‘-biphenol are currently used in asymmetric catalysis. Such ligands include symmetrical bis([1,3,2]dioxaphosphepin) ligands, − asymmetrical bidentate phosphine−[1,3,2]dioxaphosphepin ligands, , and monodentate [1,3,2]dioxaphosphepin ligands . The axially chiral diaryl backbone in the [1,3,2]dioxaphosphepin groups should result in C 2 symmetry at the phosphorus; however, recent studies of ligands containing [1,3,2]dioxaphosphepin groups derived from 2,2‘-biphenol suggested that there is a low-energy pathway to inversion of the biphenyl group, even when the ligand is coordinated to an inert metal center .…”

Comparative Study of Novel Phosphordiamidite and Phosphite Ligands Used in Alkene Hydroformylation; Synthesis, Characterization, Metalation, and Catalytic Evaluation

“…These torsion angles are within the typical ranges observed for [Mo(CO) (6– n ) {P(X)(2,2′‐O 2 C 12 H 8 )} n ] complexes (O–P–O–C = |46.5 ± 7.1|°, P–O–C–C = |75.1 ± 3.9|°, ). Because the biphenyl groups of the [1,3,2]‐dioxaphosphepin rings racemize in solution, their complexes often crystallize in centrosymmetric space groups with both enantiomers in the same crystal as do 6 ( P 2 1 / c ) and 7 ( P 2 1 / n ) , , , . However, enantiomers can also segregate upon crystallization into a noncentrosymmetric space groups as does 3 , …”