Iridium hydrides in carbon-carbon coupling, carbon-hydrogen activation, double insertion, and intramolecular oxygen transfer reactions

Different types of stoichiometric reactions between iridium hydrides and unsaturated molecules such as alkenes and alkynes are discussed in this dissertation.; Chapter 2 shows that unactivated alkenes can formally insert into an iridium alkyl hydride to afford an iridium carbene dihydride. Mechanistic studies show that alkenes insert into the Ir-H bond, followed by a rather rare C(sp3)-C(sp3 ) reductive elimination and double C-H activation to eventually lead to the carbene dihydride complex. Alkynes also insert into the Ir-H bond to give vinyls, followed by a rare C(sp3)-C( sp2) reductive elimination and C-H activation to give eta 3-allyl iridium hydrides.; Chapter 3 deals with the synthesis of various iridium hydrides from the C-H activation of acetophenone and both cyclic and acyclic alpha,beta-unsaturated ketones or esters using an iridium dihydride. In the case of acyclic alpha,beta-unsaturated ketones or esters, the beta-C-H bond is activated to afford iridafuran hydrides as cyclometalation products. For cyclopentenone, a cyclic alpha,beta-unsaturated ketone, the C-H activation affords a hydroxycyclopentadienyl hydride. The activation of the ortho C-H bonds in acetophenone affords orthometalated products structurally related to the iridafuran hydrides. Different mechanisms are proposed in each case.; Chapter 4 shows the regio- and stereochemistry of the insertion of various electronically and sterically different alkynes into an iridafuran hydride obtained by the work reported in Chapter 3. For relatively electron rich alkynes, double insertion occurs with two independent alkyne to vinylidene rearrangements to afford eta2-butadienyls. Mechanistic studies show that the first alkyne to vinylidene rearrangement is intraligand. For the second alkyne insertion, a C-H agostic intermediate was isolated. Electron-poor alkynes also undergo double insertion, but a rare case of reversible alkyne C-H oxidative addition is involved preceding insertion. Insertion of highly polarized alkynes [R1C≡CC(O)R2] occurs only once and involves no vinylidene intermediates even when R1 = H. The regio- and stereochemistry in this case is mainly controlled by the steric hindrance of the R1 group.; In Chapter 5, we continue to investigate the formal insertion of the functionalized o-RC≡C(C6H4)NO 2 (R = H or alkyl) into two iridium hydrides, where the ortho nitro group plays a direct role because intramolecular O-transfer of the nitro group into the C≡C bond of o-RC≡C(C 6H4)NO2 is observed. For the terminal alkyne with R = H, iridium(III) nitroso complexes were isolated. For terminal alkynes with R = Me or nPr, iridium hydride anthranil complexes were obtained as a result of O-transfer with a different regiochemistry. Mechanisms for these transformations, including a previously unknown step of O-transfer from the nitro to the RC≡C bond, are proposed.