New [Ir(CH 3 CN) 2 (I) 2 {κC,C′-bis(NHC)}]BF 4 complexes featuring bis-NHC ligands with a methylene bridge and different N substitution (−CH 2 CH 2 CH 2 CH 3 and −CH 2 CH 2 OPh) were synthesized. NMR studies and X-ray diffraction structures evidenced that the wingtip group −CH 2 CH 2 OPh presents a hemilabile behavior in solution, with the oxygen atom coordinating and dissociating at room temperature, which contrasts with the strong coordination of the ether functions in the complex [Ir-(I) 2 {κC,C′,O,O′-bis(NHC OMe )}]BF 4 (bis(NHC OMe ) = methylenebis(N,N′-bis(2-methoxyethyl)imidazol-2-ylidene)), previously reported by us. These complexes proved to be efficient catalysts for the hydrolysis and methanolysis of silanes, affording molecular hydrogen and silyl alcohols or silyl ethers as the main reaction products in excellent yields. The hydrogen generation rates were very much dependent on the nature of the hydrosilane and the coordination ability of the wingtip group. The latter also played a key role in the recyclability of the catalytic system.

The Ir(i) complexes [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 and [IrCl(cod)(κC-NHO(OMe))] (cod = 1,5-cyclooctadiene, NHO(PPh2) = 1,3-bis(2-(diphenylphosphanyl)ethyl)-2-methyleneimidazoline) and NHO(OMe) = 1,3-bis(2-(methoxyethyl)-2-methyleneimidazoline), both featuring an N-heterocyclic olefin ligand (NHO), have been tested in the transfer hydrogenation reaction; this representing the first example of the use of NHOs as ancillary ligands in catalysis. The pre-catalyst [Ir(cod)(κP,C,P'-NHO(PPh2))]PF6 has shown excellent activities in the transfer hydrogenation of aldehydes, ketones and imines using (i)PrOH as a hydrogen source, while [IrCl(cod)(κC-NHO(OMe))] decomposes throughout the reaction to give low yields of the hydrogenated product. Addition of one or two equivalents of a phosphine ligand to the latter avoids catalyst decomposition and significantly improves the reaction yields. The reaction mechanism has been investigated by means of stoichiometric studies and theoretical calculations. The formation of the active species ([Ir(κP,C,P'-NHO(PPh2))((i)PrO)]) has been proposed to occur via isopropoxide coordination and concomitant COD dissociation. Moreover, throughout the catalytic cycle the NHO moiety behaves as a hemilabile ligand, thus allowing the catalyst to adopt stable square planar geometries in the transition states, which reduces the energetic barrier of the process.

Tetramerization of ethylene by chromium catalysts stabilized with functionalized N -aryl phosphineamine ligands C 6 H 4 ( m -CF 3 )N(PPh 2 ) 2 ( 1 ), C 6 H 4 ( p -CF 3 )N(PPh 2 ) 2 ( 2 ), C 6 H 4 ( o -CF 3 )N=PPh 2 -PPh 2 ( 3 ), and C 6 H 3 (3,5-bis(CF 3 ))N(PPh 2 ) 2 ( 4 ) was evaluated. The parameter optimization includes temperature, co-catalyst, and solvent. Upon activation with MMAO-3A, the new catalyst system especially with m -functional PNP ligand ( 1 ) exhibited high 1-octene selectivity and productivity while giving minimum undesirable polyethylene and C 10 + olefin by-products. Using PhCl as a solvent at 75 °C led to a remarkable α-olefin (1-C 6 + 1-C 8 ) selectivity (>90 wt %) at a reaction rate of 2000 kg·g Cr –1 ·h –1 . Under identical conditions, analogous PNP ligands bearing −CH 3 , −Et, and −Cl functional moieties at the meta position of the N -phenyl ring displayed significantly lower reactivity. The catalyst with p -functional ligand ( 2 ) exhibited lower activity and comparable selectivities, while the Cr/PPN (with ligand 3 ) system gave no noticeable reactivity. The molecular structure of the precatalyst ( 1 -Cr), exhibiting a monomeric structural feature, was elucidated with the aid of single-crystal X-ray diffraction study.

Bimetallic catalysts have shown promise for improving polar comonomer incorporation by late transition metals, but such effects are underexplored using early transition metal catalysts. Herein, the copolymerization of ethylene and α-olefins bearing alcohol groups was performed using mono- and dizirconium bisamine bisphenolate catalysts in the presence of MAO and Al i Bu3. Under these conditions, catalyst activity was retained with comonomer incorporation trends mirroring those observed with unfunctionalized α-olefins, i.e., lower incorporation by bimetallic catalysts. Although incorporation levels are low, these data provide mechanistic insight for polar comonomer incorporation. These results are consistent with our earlier proposal that larger comonomers sterically clash with the distal metal center of the bimetallic catalysts, leading to lower incorporation. Additionally, a bimetallic mechanism for polar comonomer coordination and incorporation is not supported by the current data.