Recent advances in the synthesis and application of tris(pyridyl) ligands containing metallic and semimetallic p-block bridgeheads

Highly Adaptive Nature of Group 15 Tris(quinolyl) Ligands─Studies with Coinage Metals

“…Tripodal, facially coordinating tris(pyridyl) ligands have farreaching applications in coordination, organometallic catalysis, and supramolecular chemistry. 1,2 The selection of the bridgehead atom and the position of the N-donor atoms in the pyridyl rings have a fundamental impact on the behavior and coordination properties of this family of ligands. 3,4 Classically, studies have focused on tris(2-pyridyl) ligands containing nonmetallic bridgehead atoms, E(2-py) 3 (e.g., E = CR, COR, CH, N, P, P�O; 2-py = 2-pyridyl).…”

“…Tripodal, facially coordinating tris (pyridyl) ligands have far-reaching applications in coordination, organometallic catalysis, and supramolecular chemistry. , The selection of the bridgehead atom and the position of the N-donor atoms in the pyridyl rings have a fundamental impact on the behavior and coordination properties of this family of ligands. , Classically, studies have focused on tris (2-pyridyl) ligands containing nonmetallic bridgehead atoms, E­(2-py) 3 (e.g., E = CR, COR, CH, N, P, PO; 2-py = 2-pyridyl) . 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. ,− Recent studies have explored the coordination chemistry of tris (2-pyridyl) ligands based on Sb and Bi, which coordinate metals (e.g., Cu + , Ag + , Li + ) through the three pyridyl arms in an N , N , N -chelate coordination mode, which is typical of the tris (2-pyridyl) family (intramolecular coordination, Figure a). , In addition, changing the position of the pyridyl N-donor atom from the 2- to the 3-position with respect to the bridgehead atom/group significantly changes the coordination behavior of the ligands, permitting the coordination of multiple metal centers. , The coordination of the tris (3-pyridyl) and tris (4-pyridyl) ligands to Cu and Ag salts gives extended structures involving a combination of N-donor and bridgehead-donor bonding (intermolecular coordination, Figure b). , …”

“…■ RESULTS AND DISCUSSION Ligand Synthesis. The synthesis of both the new trisquinolyl antimony and bismuth ligands [E(2-Me-8-qy) 3 ] [E = Sb (1), Bi (2)] is similar to that of the previously reported Al(III) counterpart [EtAl(2-Me-8-qy) 3 ] −23 and is achieved via the lithium-halogen exchange of 8-bromo-2-methylquinoline with n BuLi at −78 °C in THF followed by a 3:1 reaction with ECl 3 (Scheme 1). Previous work on the unsubstituted 2pyridyl group 15 counterparts indicated that these ligands can decompose through reductive elimination of the 2-pyridyl rings, a problem that appears to be suppressed using substitution of the ring units at the 6-position (i.e., adjacent to the donor-N atom), possibly providing electronic stabilization.…”

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 …”

Synthesis of tris(3-pyridyl)aluminate ligand and its unexpected stability against hydrolysis: revealing cooperativity effects in heterobimetallic pyridyl aluminates

“…[2][3][4][5][6][7][8][9][10][11][12] Recently, the use of more metallic elements in the tris(2pyridyl) framework bridgehead to introduce new reactivity and properties has become a focus of interest in this area. 4,[13][14][15][16][17][18][19][20][21][22] This strategy parallels the use of different main group element bridgeheads, which has emerged as a strategy to modulate the reactivity and structure for a large variety of ligands. 21,[23][24][25][26] Metallic tris(2-pyridyl)aluminates 27 represent one of the few anionic members of the tris(2-pyridyl) family (Fig.…”