A series of alkylammonium-imidazolium chloride salts [RImH(CH 2) n NMe 2 ]Cl•HCl (R = Me, t-Bu, Mes, n = 2, 3) have been prepared by alkylation of 1-substituted imidazole compounds with the corresponding chloro-alkyl-dimethylamine hydrochloride. These salts are precursors for the synthesis of a library of rhodium (I) complexes containing amino-alkyl functionalized N-heterocyclic carbene (NHC) ligands with hemilabile character by varying the substituent on the heterocyclic ring and the length of the linker with the dimethylamino moiety. The monodeprotonation of alkylammoniumimidazolium salts with NaH in the presence of [{Rh(µ-Cl)(cod)} 2 ] gave the amino-imidazolium salts [RImH(CH 2) n NMe 2 ][RhCl 2 (cod)]. Further deprotonation with NaH under non anhydrous conditions gave the neutral complexes [RhCl(cod)(RIm(CH 2) n NMe 2)] in good yields. The abstraction of the chloro ligand by silver salts rendered the cationic complexes [Rh(cod)(κ 2 C,N-RIm(CH 2) 3 NMe 2)][BF 4 ] (R = Me, Mes) by coordination of the NMe 2 fragment of the sidearm of the functionalized NHC ligands. The catalytic activity of the rhodium complexes in the hydrosilylation of terminal alkynes using HSiMe 2 Ph has been investigated with Ph-C≡CH, t-Bu-C≡CH, n-Bu-C≡CH, and Et 3 Si-C≡CH as substrates. Higher activities were achieved using neutral complexes having small substituents at the heterocyclic ring (R = Me). Excellent selectivities in the β-(Z)-vinylsilane isomer were found in the hydrosilylation of 1hexyne and predominantly the β-(E) and α-bis(silyl)alkene isomers were obtained in the hydrosilylation of triethylsilylacetylene.

Oxidized multiwall carbon nanotubes (CNT) were covalently modified with appropriate hydroxylending imidazolium salts using their carboxylic acid groups. Characterization of the imidazoliummodified samples through typical solid characterization techniques, such as TGA or XPS, allows for the determination of 16 wt.% in CNT-1 and 31 wt.% in CNT-2 as the amount of the imidazolic fragments in the carbon nanotubes. The imidazolium-functionalized materials were used to prepare nanohybrid materials containing iridium N-heterocyclic carbene (NHC) type organometallic complexes with efficiencies as high as 95 %. The nanotube-supported iridium-NHC materials were active in the heterogeneous iridium-catalyzed hydrogen-transfer reduction of cyclohexanone to cyclohexanol with 2-propanol/KOH as hydrogen source. The iridium hybrid materials are more efficient than related homogeneous catalysts based on acetoxy-functionalized Ir-NHC complexes with initial TOFs up to 5550 h -1 . A good recyclability of the catalysts, without any loss of activity, and stability on air was observed.

A series of neutral and cationic rhodium and iridium(I) complexes based on hemilabile O-donor-and N-donor-functionalized NHC ligands having methoxy, dimethylamino, and pyridine as donor functions have been synthesized. The hemilabile fragment is coordinated to the iridium center in the cationic complexes [Ir(cod] has been determined by X-ray diffraction. The iridium complexes are efficient precatalysts for the transfer hydrogenation of cyclohexanone in 2-propanol/KOH. A comparative study has shown that cationic complexes are more efficient than the neutral and also that complexes having O-functionalized NHC ligands provide much more active systems than the corresponding N-functionalized ligands with TOFs up to 4600 h À1 . The complexes [Ir(NCCH 3 )(cod)(MeImR)] + (R = 2-methoxyethyl and 2-methoxybenzyl) have been successfully applied to the reduction of several unsaturated substrates as ketones, aldehydes, α,β-unsaturated ketones, and imines. The investigation of the reaction mechanism by NMR and MS has allowed the identification of relevant alkoxo intermediates [Ir(OR)(cod)(MeImR)] and the unsaturated hydride species [IrH(cod)(MeImR)]. The β-H elimination in the alkoxo complex [Ir(OiPr)(cod)(MeIm(2-methoxybenzyl))] leading to hydrido species has been studied by DFT calculations. An interaction between the β-H on the alkoxo ligand and the oxygen atom of the methoxy fragment of the NHC ligand, which results in a net destabilization of the alkoxo intermediate by a free energy of +1.0 kcal/mol, has been identified. This destabilization facilitates the β-H elimination step in the catalytic process and could explain the positive effect of the methoxy group of the functionalized NHC ligands on the catalytic activity.

The thermally generated 16-electron fragment [(triphos)RhH] reacts with benzo[b]thiophene (BT) by C-S bond scission to ultimately yield the 2-vinylthiophenolate complex (triphos)Rh[q3-S(C6H4)CH=CH2] (l), which is an efficient catalyst precursor for the hydrogenation of BT into 2-ethylthiophenol (ETSH) and, to a lesser extent, into 2,3-dihydrobenzo[b]thiophene (DHBT) at 160 "C and 30 atm H2 [triphos = MeC(CH2PPh2)3]. The mechanism of this unusual catalytic transformation has been established by high pressure NMR spectroscopic (HPNMR) studies combined with the isolation and characterization of key species related to the catalysis. Under catalytic conditions 1 was shown by HPNMR to be completely transformed into (~~~~~os)R~(H)~[o-S(C~H~)CZH~] (2) and [(q2-triphos)-Rh@-o-S(C&&2H5}]2 (3); removal of H2 in the presence of ETSH leads to the quantitative formation of (triphos)-R~H [ o -S ( C~H~) C~H~]~ (4), which is also the terminal state of the catalytic system in all experiments carried out in a high pressure reactor under various reaction conditions. The dimer 3 was prepared in a pure form by reaction of (triphos)RhH3 with 1 equiv of ETSH in THF and reacted with excess ETSH to produce 4, with H2 to give 2, and with CO to yield (~~~~~os)R~H(CO)[O-S(C~H~)C~H~] (6). Conversely, 3 could be obtained by thermally induced reduction elimination of H2 from 2 even under 30 atm of H2 or of ETSH from 4. The formation of the dihydride 2 from the vinylthiophenolate derivative 1 under H2 (> 15 atm) was also observed by HPNMR; this reaction was mimicked by the stepwise addition of Hf to yield [(triphos)Rh{q4-S(C6H4)CH(CH3)}]BF4 (7). Reaction of the latter complex with H-produces (triphos)RhH[v2-S(C&)CH(CH3)] (8), which converts to the dimer 3 by reductive coupling of the terminal hydride ligand with the metalated alkyl substituent in the thioligand, via the unsaturated fragment [(triphos)Rh{o-s(C6&)c2H5}].In the mechanistic picture proposed, the catalytically active species for both reactions is [(triphos)RhH] generated from 2 by the rate-determining reductive elimination of ETSH. The hydrogenation of BT to ETSH occurs after the substrate has been C-S inserted, although hydrogenation to DHBT also takes place as a minor, parallel path. Then 7'-S and q2-2,3-BT isomers probably exist in equilibrium, but the 7'4 intermediate prevails over the q2-2,3 isomer for steric reasons, thus determining the chemoselectivity of the reaction. The chemistry herein described provides further insight into the mechanistic aspects of HDS reactions on solid catalysts.

A series of cationic complexes [Rh(diene){Ph 2 P(CH 2 ) n Z}] [BF 4 ] (diene = 1,5-cyclooctadiene (cod), tetrafluorobenzobarralene (tfb) or 2,5-norbonadiene (nbd)) containing functionalized phosphine ligands of the type Ph 2 P(CH 2 ) n Z (n = 2, or 3; Z = OMe, NMe 2 , SMe) have been prepared and characterized. These complexes have shown a great catalytic activity for phenylacetylene (PA) polymerization. Catalyst screening and optimization have determined the superior performance of complexes containing a P,N-functionalyzed phosphine ligand, [Rh(diene){Ph 2 P(CH 2 ) 3 NMe 2 }][BF 4 ] (diene = cod 5, tfb 6, nbd 7), and tetrahydrofuran as solvent. The influence of the diene ligand and the effect of temperature, PA to rhodium molar ratio, addition of water or a co-catalyst, DMAP (4-(dimethylamino)pyridine), have been studied. Diene ligands strongly influence the catalytic activity and complexes 6 and 7 are far more active than 5. Both complexes gave polyphenylacetylene (PPA) with very high number-average molecular weights (M n ) of 970 000 (6) and 1 420 000 (7). The addition of DMAP resulted in a dramatic drop in the PPA molecular weight, 106 000 (6) and 233 000 (7,). The PPA obtained with the system 6/DMAP showed a narrow molecular weight distribution (M w /M n = 1.20) and incremental monomer addition experiments have demonstrated the quasi-living nature of the polymerization reaction under these conditions. The PPA obtained with these catalytic systems has been characterized by 1 H and 13 C{ 1 H} NMR spectroscopy and shows a cis-transoidal configuration with a high level of steroregularity (cis content superior to 99%). TGA, DSC, and IR analysis have revealed a thermal cis↔trans

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The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for CC bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3 )(cod)(MeIm(2- methoxybenzyl))][BF4 ] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0 ) of 1283 h(-1) , and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new CC bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde.