De Novo design in organometallic chemistry: stabilizing iridium(V)
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abstract
Modern density functional theory (DFT) calculations are well suited for designing and testing alternative ligand schemes for transition-metal organometallic complexes. DFT methods have been applied to a variety of ligand systems and substrates (alkanes and silane) for the reaction (x-L)LIrIIIR+RH (x-L)LIrVRRH (x-L = CpR, Tp, and carborane; L = PR3, CR3-, SiR3-, and SnR3-; R = CH3, H; R = Aryl, CR3, and H) with the goal of finding ligand-substrate combinations that will stabilize the Ir(V) species. This species is of particular interest, as it is the putative intermediate in the C-H bond activation by Ir(III) complexes. Among the donor ligands examined were various multihapto ligands (x-L), alternative phosphines, anionic silanes (SiR3-) and stannanes (SnR3-), and chelating ligands. Cationic Ir(V) intermediates produced by oxidative addition of an alkane are not easily stabilized when compared with their Ir(III) counterparts. Replacing the phosphine donor ligands with more covalent inorganic ligands, specifically silyl and stannyl ligands (AR3), produces neutral Ir(V) complexes that are more stable than the Ir(III) reactants but would be subject to alkane elimination except at very low temperatures. Reacting the unsaturated 16 e- species [CpIrIIIPR3LR3]+ (where R = H, CH3 and L = C, Si) with the appropriate amount of silane (HSiR3) might also afford Ir(V) complexes [CpIrVPR3LR3SiR3 H]+ that are stable enough to be observed spectroscopically, and in some instances, possibly isolated. 2003 Elsevier Science B.V. All rights reserved.
