Molecular design ultimately furnishes improvements in performance over time, and this has been the case for Rh-and Irbased molecular catalysts currently used in transfer hydrogenation (TH) reactions for fine chemical synthesis. In this report, we describe a molecular pincer ligand Al catalyst for TH, (I 2 P 2À )Al(THF)Cl (I 2 P = diiminopyridine; THF = tetrahydrofuran). The mechanism for TH is initiated by two successive Al-ligand cooperative bond activations of the OÀ H bonds in two molecules of isopropanol ( i PrOH) to afford six-coordinate (H 2 I 2 P)Al(O i Pr) 2 Cl. Stoichiometric chemical reactions and kinetic experiments suggest an ordered transition state, supported by polar solvents, for concerted hydride transfer from i PrO À to substrate. Metal-ligand cooperative hydrogen bonding in a cyclic transition state is a likely support for the concerted hydride transfer event. The available data does not support involvement of an intermediate Al-hydride in the TH. Proof-ofprinciple reactions including the conversion of isopropanol and benzophenone to acetone and diphenylmethanol with 90 % conversion in 1 h are described. The analogous hydride compound, (I 2 P 2À )Al(THF)H, also cleaves the OÀ H bond in i PrOH to afford (HI 2 P À )Al(O i Pr)H and (HI 2 P À )Al(O i Pr) 2 , but no activity for catalytic TH was observed.

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