Iridium Dionate Complexes

In what may be a mechanistically different process, mono-, di-, and even trisubstituted benzylamines, as well as anilines, were found to be deuterated in ortho positions from deuterium gas by use of the catalyst precursor cyclooctadienyliridium 1,1,1,5,5,5-hexa-fluoropentane-2,4-dionate ((cod)Ir(hfpd)). This neutral complex, with an anionic 0,0 -bidentate ligand, was the most active of three related ones tested. This class of complex had been discovered in screening for catalysis of substrate labeling from a isotope 

So far, the only published use of (cod)Ir(hfpd) in tritium labeling has been a tracer experiment with a model compound, but the method should work generally with tritium gas. It remains to be seen how broad the applicability will be to complex substrates. The utility of this catalyst class appears to be largely complementary to that of the iridium phosphine class, mainly because of its apparently general ability to label benzylamines and anilines and its activity in DMF and DMA solvents. Nitro groups tend to be reduced. But as with iridium phosphine complexes, (cod)Ir(hlipd) tends to reduce double bonds but 

The regioselectivity of the labeling of aminobenzoic acids and aminoacetophenones by (cod)Ir(hfpd) from deuterium gas - adjacent to the amino functions - is complementary to the locations labeled - adjacent to the carbonyl-containing function - when is the isotope source, reinforcing the probability that different reaction mechanisms are at work under different conditions (Section 3.4.3). 

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Figure 3.33 Exchange labeling of aristolochic acids from tritiated water catalyzed by an iridium dionate complex...

To date, the only soluble catalysts reported to have significant activity in mediating exchange between atmospheric (isotopic) hydrogen and substrates in solution are organometallic complexes of iridium. They can be considered as consisting of three classes iridium phosphine complexes, iridium dionate complexes, and iridium cyclopentadiene complexes. 

The iridium(III) complex [Ir(H)3(AsPh3)2(p-MeC6H4NC)] (99) is known to react with HX (or pseudohalides) to yield substitution products [lr(H)2(X)(AsPh3)(p-MeC6H4NC)i (X = Cl, Br, I, Nj). With carboxylic acids or pentane-2,4-dione, complex (99) yields the chelated complexes [Ir(L2)(AsPh3)(p-MeC6H4NC)] (L2 = carboxylate or pentane-2,4-dionate) in which Ir is reportedly reduced to 11. Reactions (52>-(60) reveal the utility of complex (99) in synthesizing complexes with iridium in various oxidation states. ... 

The latter procedure (involving isolation of the organoiridium-substrate complex) is not practical for use in the tritiation of most substrates, but the former may be if deactivation of the complex by polar functional groups is avoided. The regioselectivity that these iridium cyclopentadienide complexes display is largely complementary to those of iridium phosphines and iridium dionates therefore cyclopentadienide complexes could be valuable additions to the repertory. Unfortunately the air-sensitivity of these complexes and their immediate precursors is a hindrance to their use. Further development of this class would be highly desirable. 

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