Postfunctionalization of Tris(pyridyl) Aluminate Ligands: Chirality, Coordination, and Supramolecular Chemistry

Abstract

Postfunctionalization of the aluminate anion [EtAl(6-Me-2-py) ] (1) (2-py=2-pyridyl) with alkoxide ligands can be achieved by the selective reactions of the lithium salt 1 Li with alcohols in the appropriate stoichiometry. This method can be used to introduce 3- and 4-py functionality in the form of 3- and 4-alkoxymethylpyridyl groups, while maintaining the integrity of the aluminate framework, thereby giving entry to new supramolecular chemistry. Chirality can be introduced either by using a chiral alcohol as a reactant or by the stepwise reaction of 1 Li with two different nonchiral alcohols. The latter route has allowed the synthesis of a rare example of a chiral-at-aluminium aluminate.

Tris(2-pyridyl) Bismuthines: Coordination Chemistry, Reactivity, and Anion-Triggered Pyridyl Coupling

“…One further potential consequence of incorporating more electropositive (metallic and semimetallic) bridgehead atoms is an increase in the polarity of the bridgehead atom–C bonds to the pyridyl groups. In contrast to more robust tris (2-pyridyl) borate ligands, − tris (2-pyridyl)­aluminates [RAl­(2-py) 3 ] − (Figure c) react as bases with H 2 O, alcohols, or carboxylic acids in a controlled manner, providing an interesting route to new aluminates containing additional donor functionality. − This behavior has led to new applications as thermally stable pyridyl-transfer reagents as well as reagents for the rapid NMR spectroscopic determination of the enantiomeric excess ( ee ) of chiral alcohols. − …”

Cyclooctadiene Rh(I) Bis- and Tris(pyrazolyl)aluminate Complexes and Their Catalytic Activity on the Polymerization of Phenylacetylene

“…Other metal halides gave bimetallic pyrazolates [M 2 X 2 (Ph 2 pz) 2 (THF) 3 ] with M = Mg, X = Br; M = Co; X = Cl, whereas reactions with first row transition metal halides of Mn, Fe, Ni, and Cu produced intractable powders . These results highlight the difficulties of this chemistry and underpin the need for a better understanding of the factors that might lead to well-defined poly­(pyrazolyl)­aluminate metalloligands and complexes as it has been shown for the related tris­(pyridyl)­aluminates. − We surmised that a better performance of the poly­(pyrazolyl)­aluminate ligand system toward its transfer to a transition metal center could be achieved using alkyl groups on the aluminum atom instead of hydrogen to prevent hydride transfer, on the one hand, and, by using a more electron-rich low-valent organotransition metal center, potentially leading to more stable, less reactive complexes. Indeed, we report herein the preparation and full characterization of the new bis- and tris­(pyrazolyl)­aluminates [{Na­(THF) 2 }­{Al­(Ph 2 pz) 2 Me 2 }] ( 1 ) and [{Na­(THF)}­{Al­(Ph 2 pz) 3 ­Me}] ( 2 ) and the complexation of aluminates 1 and 2 to an electron-rich Rh­(I) center to afford [Rh­(COD)­{Al­(Ph 2 pz) 2 ­Me 2 }] ( 3 ) and [Rh­(COD)­{Al­(Ph 2 pz) 3 ­Me}] ( 4 ).…”

“…9 These results highlight the difficulties of this chemistry and underpin the need for a better understanding of the factors that might lead to well-defined poly(pyrazolyl)aluminate metalloligands and complexes as it has been shown for the related tris(pyridyl)aluminates. [10][11][12][13][14][15][16][17] We surmised that a better performance of the poly(pyrazolyl)aluminate ligand system towards its transfer to a transition metal center could be achieved using alkyl groups on the aluminum atom instead of hydrogen to prevent hydride transfer on the one hand and, on the other hand, by using a more electron rich low-valent organotransition metal center, potentially leading to more stable, less reactive complexes. Indeed, we report herein the preparation and full characterization of the The X-ray crystallographic studies of complexes 1 and 2 reveal mononuclear complexes.…”

Cation- and Anion-Mediated Supramolecular Assembly of Bismuth and Antimony Tris(3-pyridyl) Complexes

“…; 2-py = 2-pyridyl; Figure b) . However, incorporating heavier and more metallic main-group bridgehead atoms has been shown to provide an important tool for tuning the ligand character, enabling systematic modification of the bite angle, donor/acceptor properties, and reactivity. − A case in point is the series of Group 15 tris­(2-pyridyl) ligands E­(6-Me-2-py) 3 (6-Me-2-py = 6-methyl-2-pyridyl; E = As, Sb, Bi) for which changing the bridgehead can be used to provide incremental change in the σ-donor character and (thereby) the catalytic activity and behavior …”