Alkali Metal Complexes of Silyl‐Substituted ansa‐(Tris)allyl Ligands: Metal‐, Co‐Ligand‐ and Substituent‐Dependent Stereochemistry

Abstract

The structures of alkali metal complexes of silyl-substituted ansa-tris (allyl) [endo,exo] stereochemistries. The trisodium complex [L 2 Na{Na-(tmeda)} 2 ] 2 (6) consists of a hexa(allylsodium) macrocycle that aggregates as a result of cation-π interactions between the phenyl substituents and the sodium cations. An attempt to prepare the tripotassium complex of L 1 resulted in the formation of the bimetallic potassium/lithium complex

Side‐Arm Effect of a Methyl α‐d‐Glucopyranoside Based Lariat Ether Catalysts in Asymmetric Syntheses

“…Another Michael reaction, the conjugate addition of diethyl acetamidomalonate (19) to βnitrostyrene (18), was carried out in a 4:1 mixture of ether-tetrahydrofuran (THF) as the solvent in the presence of Na 2 CO 3 (used in twofold excess) employing 15 mol% of the crown ether (Scheme 6) [18]. The enantioselectivities were determined by chiral HPLC analysis.…”

“…Unsubstituted 2a induced an enantioselectivity (ee) of 61% and 53%. It is known that the π -electron system of the allyl group may establish a donor bond with certain metal cations, such as sodium cation [19]. The substituents without heteroatoms, as in lariat ethers 2b-d, in general, decreased the extent of asymmetric induction (25-58% ee), except the allyl substituent, as in 2c, that resulted in an ee of 79% in the addition reaction of 2-nitropropane (16).…”

A tetrameric allyl complex of sodium, and computational modeling of the 23Na–allyl chemical shift

“…The monomeric Na(1-PhC 3 H 4 )(pmdta), in contrast, displays Na-C distances of 2.791(9) Å, 2.577(7) Å, and 2.676(3) Å [25], and although allyl ligand appears to be g 3 -bound, the C-C bonds are strongly localized (1.31 Å and 1.47 Å), raising some ambiguity about the rand p-nature of the sodium-allyl bond. A mix of bonding arrangements exists in the trimetallic MeSi{(C 3 H 3 SiMe 3 )Na(tmeda)} 3 ; for example, the D C-C bond lengths range from a very delocalized 0.027 Å to a more localized 0.080 Å, and Na-C distances range from 2.55(2) to 3.193(7) Å, with a possible longer contact at 3.38 Å; both g 3 -and g 2 -allyl coordination modes are present [26]. The sterically congested [PhSi{(C 3 H 3 SiMe 3 )Na} 3 (tmeda) 2 ] 2 also displays a large Na-C range, from 2.549(4) Å up to 3.472(6) Å [26].…”

“…A mix of bonding arrangements exists in the trimetallic MeSi{(C 3 H 3 SiMe 3 )Na(tmeda)} 3 ; for example, the D C-C bond lengths range from a very delocalized 0.027 Å to a more localized 0.080 Å, and Na-C distances range from 2.55(2) to 3.193(7) Å, with a possible longer contact at 3.38 Å; both g 3 -and g 2 -allyl coordination modes are present [26]. The sterically congested [PhSi{(C 3 H 3 SiMe 3 )Na} 3 (tmeda) 2 ] 2 also displays a large Na-C range, from 2.549(4) Å up to 3.472(6) Å [26]. It appears that highly symmetric Na-C bonding has not yet been crystallographically identified in sodium allyl complexes; the low charge/large size of the Na + evidently makes interaction with the allyl anion one that is readily distorted by crystal packing forces and intramolecular crowding.…”

“…Until recently, only a single complex displaying Na-allyl interactions had been structurally authenticated, the monomeric Na(1-PhC 3 H 4 )(pmdta) [25]. Trimetallic and hexametallic aggregates are now known [26]; these are derived from tris(allyl) ligands that facilitate the formation of polymetallic species.…”