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

We report the elusive metallic anion [EtAl(3-py)₃]^- (3-py = 3-pyridyl) (1), the first member of the anionic tris(3-pyridyl) family. Unexpectedly, the lithium complex 1Li shows substantial protic stability against water and alcohols, unlike related tris(2-pyridyl)aluminate analogues. This stability appears to be related to the inability of the [EtAl(3-py)₃]^- anion to chelate Li⁺, which precludes a decomposition pathway involving Li/Al cooperativity.

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

In this work, we report the transfer of alkyl bis- and tris(pyrazolyl)aluminates metalloligands to an electron-rich organotransition metal center. The 16-electron heterobimetallic complexes of rhodium [Rh(COD){Al(Ph₂pz)₂Me₂}] (3) and [Rh(COD){Al(Ph₂pz)₃Me}] (4) were obtained by metathesis reaction of the sodium bis- (1) and tris(pyrazolyl)aluminate (2) with [RhCl(COD)]₂. For 3, ¹H and ¹³C NMR in solution along with DFT calculations are consistent with a κ²-coordination mode of the bis(pyrazolyl)aluminate to a square-planar Rh(I) center. The X-ray structure of 4 shows a similar κ²-coordination mode of the tris(pyrazolyl)aluminate to Rh(I) with a pendant pyrazolyl moiety. The attempted synthesis of aluminate-rhodium complexes with R = CF₃, ^tBu on the pyrazolate ring afforded [Rh(R₂pz)(COD)]₂ and [R₂pzAlMe₂]₂. Complexes 3 and 4 were investigated as homogeneous catalysts in the polymerization of phenylacetylene (PA). Both complexes showed enhanced catalytic activity compared to analogous rhodium poly(pyrazolyl)borates. Optimized gas-phase DFT geometries of 3, 4, [Rh(COD){B(Ph₂pz)₂Me₂}], and [Rh(COD){B(Ph₂pz)₃Me}] were used to compare bite angles, while DFT geometries of 3-CO, 4-CO, [Rh(CO)₂{B(Ph₂pz)₂Me₂}], and [Rh(CO)₂{B(Ph₂pz)₃Me}] were employed to probe the electronic situation of the rhodium center through IR CO stretching modes. The wider bite angles and the less electron-rich rhodium center of the poly(pyrazolyl)aluminates compared with their borate analogues could be implicated in the better performance of the active catalytic species during polymerization of PA.

Coordination chemistry of the bench-stable tris-2-pyridyl pnictogen ligands [E(6-Me-2-py)3] (E = As, As[double bond, length as m-dash]O, Sb)

Tripodal ligands with main group bridghead units are well established in coordination chemistry and single-site organometallic catalysis. Although a large number of tris(2-pyridyl) main group ligands [E(2-py)₃] (E = main group element, 2-py = 2-pyridyl) spanning across the whole p-block are now synthetically acessible, only limited work has been done on the coordination chemistry on the tris(2-pyridyl) group 15 ligands for the heavier elements (As, Sb). In the current study we investigate the coordination chemistry of the ligand family E(6-Me-2-py)₃ (E = As, Sb) and of the As(v) ligand O[double bond, length as m-dash]As(6-Me-2-py)₃. The air- and mositure-stability of all of these main group ligands makes them especially attractive in future catalytic applications.