Iridium complexes nitrogen ligands

Coordination Compounds. A large number of iridium complexes with nitrogen ligands have been isolated, particularly where Ir is in the +3 oxidation state. Examples of ammine complexes include [Ir(NH3)6]3+ [24669-15-6], [IrCl(NH3)]2+ [295894)9-1], and trans-[Ir(03SCF3)2(en)2]+ [90065-94 4]. Compounds of IV-heterocyclic ligands include trans- [IrCl4(py)2] [24952-67-8], [Ir(bipy)3]3+ [16788-86-6], and an unusual C-metalated bipyridine complex, [Ir(bipy)2(C3,N-bipy)]2+ [87137-18-6]. Isolation of this latter complex produced some confusion regarding the chemical and physical properties of Pi(bipy)3]3+ (167). 

Iridium complexes having oxygen ligands are not nearly as extensive as those having nitrogen. Examples include acetylacetonates [Ir(P(C(5H5)3)2 (acac)H2] [64625-61-2], aqua complexes Ir(OH2)6]3+ [61003-29-0], nitrato complexes [Ir(0N02)(NH3),J2 [42482 42-8], and peroxides IrCl(P(C6I fy)3)2(02-/-(>/ I I9)2(CO) [81624-11-5]. Unlike rhodium, very few Ir(II) carboxylate-bridged dimers have been claimed and [Ir,2(OOCCI I3)4 has not been reported. Some Ir(T) complexes exhibit reversible oxidative addition of 02 to form Ir(III) complexes. That chemistry has been reviewed (172). 

Examples of palladium- and rhodium-catalyzed hydroaminations of alkynes are shown in Equations 16.90-16.92 and Table 16.9. The reaction in Equation 16.90 is one of many examples of intramolecular hydroaminations to form indoles that are catalyzed by palladium complexes. The reaction in Equation 16.91 shows earlier versions of this transformation to form pyrroles by the intramolecular hydroamination of amino-substituted propargyl alcohols. More recently, intramolecular hydroaminations of alkynes catalyzed by complexes of rhodium and iridium containing nitrogen donor ligands have been reported, and intermolecular hydroaminations of terminal alkynes at room temperature catalyzed by the combination of a cationic rhodium precursor and tricyclohexylphosphine are known. The latter reaction forms the Markovnikov addition product, as shown in Equation 16.92 and Table 16.9. These reactions catalyzed by rhodium and iridium complexes are presumed to occur by nucleophilic attack on a coordinated alkyne. 

In contrast, iridium complexes of phosphoramidite ligands catalyze the enantiose-lective formation of the branched allyUc substitution products with high enantiomeric excess. Takeuchi and Helmchen " - - - reported that iridium complexes, hke rhodium complexes, generate the chiral, branched product from reactions of mono-substituted aUylic acetates and carbonates with carbon and nitrogen nucleophiles (Equations 20.45-20.47). 

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