Iridium-complexes

We choose this reaction system as a model to test the basis set and methodology because the system is similar to the Ir dehydrogenation system but is smaller and relatively well understood. In the following, we will discuss the impact of methods, basis set and phosphine substituents. 

The next step, the oxidative addition of alkane to form the Ir(V) intermediate is quite sensitive to the methods and presents a challenging problem to determine which method gives the most accurate answer. The calculated activation (AE ) and reaction (AE°) energies show 

The Calculated Energies (kcal/mol) for the Reaction Based on the Geometries Optimized at B3LYP/BS1 

Four basis sets were examined BSl and BS3 are based on the Couty-Hall modification of the Hay and Wadt ECP, and BS2 and BS4 are based on the Stuttgart ECP. Two basis sets, BSl and BS2, are used to optimize the geometries of species in the OA reaction, [CpIr(PH3)(CH3)]++ CH4 [CpIr(PH3)(H)(CH3)2]+, at the B3LYP level, while the other basis sets, BS3 and BS4, are used only to calculate energies at the previously optimized B3LYP/BS1 geometries. BSl is double-zeta with polarization functions on every atom except the metal atom. BS2 is triple-zeta with polarization on metal and double-zeta correlation consistent basis set (with polarization functions) on other atoms. BS3 is similar to BSl but is triple-zeta with polarization on the metal. BS4 is similar to BS2 but is triple-zeta with polarization on the C and H that are involved in the reaction. The basis set details are described in the Computational Details section at the end of this chapter. 

The optimized geometries for the a-bond species 1, the transition state 2, and the intermediate product 3 from BSl at B3LYP level are shown in Fig. 2. The calculated geometries from BS2 are similar to those from BSl and the calculated bond lengths are listed in parenthesis in 

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By a suitable choice of conditions (metal hydrides or metal/ammonia) ketones at the 1-, 2-, 4-, 6-, 7-, 11-, 12- and 20-positions in 5a-H steroids can be reduced to give each of the possible epimeric alcohols in reasonable yield. Hov/ever, the 3- and 17-ketones are normally reduced to give predominantly their -(equatorial) alcohols. Use of an iridium complex as catalyst leads to a high yield of 3a-alcohol, but the 17a-ol still remains elusive by direct reduction. 

The rhodium and iridium complexes of dibenzothiophene (L) reveal an interesting case of linkage isomerism (91IC5046). Thus, the ti S) coordinated species [MCp LCb] on thermolysis with silver tetrafluoroborate afford the Ti -coordinated dicationic species. 

Reaction of the cyclopentadienyl rhodium and iridium tris(acetone) complexes with indole leads to the species 118 (M = Rh, Ir) [77JCS(D)1654 79JCS(D)1531]. None of these compounds deprotonates easily in acetone, but the iridium complex loses a proton in reaction with bases (Na2C03 in water, r-BuOK in acetone) to form the ri -indolyl complex 119. This reaction is easily reversed in the presence of small amounts of trifluoroacetic acid. 

In the rhodium and iridium complexes, the C-coordination, carbene function, and cyclometallated cases prevail. Benzothiazole-2-thione was studied extensively as a ligand and various situations of the exocyclic S-monodentate coordination as well as N,S-combinations in the di-, tri-, and tetranuclear species were discovered. 

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