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.

The synthesis and characterization of optically active phosphinooxazoline chloride complexes (S M and R M )-[(η 6 -p-MeC 6 H 4 iPr)MCl(PN)]A (M ) Ru, Os; PN ) phosphinooxazoline ligand; A ) counteranion) and the derived aqua complexes (R M and S M )-[(η 6 -p-MeC 6 H 4 iPr)M(PN)(H 2 O)](A) 2 are reported. The OPOF 2 -containing compounds (R M and S M )-[(η 6 -p-MeC 6 H 4 iPr)M(OPOF 2 )(PNiPr)][PF 6 ] (M ) Ru, Os; PNiPr ) (4S)-2-(2-diphenylphosphinophenyl)-4-isopropyl-1,3-oxazoline) have been also prepared and characterized. The molecular structures of (S M )-[(η 6 -p-MeC 6 H 4 iPr)MCl( PNiPrand that of the OPOF 2 -containing compounds (R Ru and S Ru )-[(η 6 -p-MeC 6 H 4 iPr)Ru(OPOF 2 )(PNiPr)][PF 6 ] have been determined by X-ray diffractometric methods. Dichloromethane solutions of the aqua complexes [(η 6p-MeC 6 H 4 iPr)M(PN)(H 2 O)][SbF 6 ] 2 are active catalysts for the Diels-Alder reaction between methacrolein and cyclopentadiene. The reaction occurs rapidly at room temperature with good exo:endo selectivity (from 85:15 to 96:4) and moderate enantioselectivity (up to 47%). The intermediate Lewis acid-dienophile compound (R Ru and S Ru )-[(η 6 -p-MeC 6 H 4 iPr)Ru(PNInd)(methacrolein)][SbF 6 ] 2 was isolated, and the molecular structure of the S epimer was determined by diffractometric means. The osmium complexes (S Os and R Os )-[(η 6 -p-MeC 6 H 4 iPr)Os(PN)(H 2 O)][A] 2 (PN ) PNiPr, A ) SbF 6 , BF 4 ; PN ) PNInd, A ) SbF 6 ) evolve to the phenyl-containing compounds (S Os and R Os )-[(η 6 -p-MeC 6 H 4 iPr)OsPh(PN′)][SbF 6 ] (PN′ ) (4S)-2-(2-hydroxyphenylphosphinophenyl)-4-isopropyl-1,3-oxazoline (PNOHiPr), PN′ ) (3aS,8aR)-2-(2-hydroxyphenylphosphinophenyl)-3a,8a-dihydroindane[1,2d]oxazole] (PNOHInd)) and (S Os and R Os )-[(η 6 -p-MeC 6 H 4 iPr)OsPh(PNFiPr)][BF 4 ] (PNFiPr ) (4S)-2-(2-fluorophenylphosphinophenyl)-4-isopropyl-1,3-oxazoline), respectively, in which the phosphinooxazoline ligand incorporates a hydroxy or fluoro functionality. On the basis of spectroscopic and crystallographic observations, a common pathway for these reactions is proposed.

Ruthenium complexes of formula [(η6‐arene)Ru(LL*)(H2O)][SbF6]2 (arene = C6H6, p‐MeC6H4iPr, C6Me6; LL* = bidentate chelate chiral ligand with PN, PP or NN donor atoms) have been tested as catalyst precursors for the asymmetric 1,3‐dipolar cycloaddition of nitrones to methacrolein. The reaction occurs quantitatively with perfect endo selectivity and moderate enantioselectivity (up to 74 % ee). The ruthenium aqua complexes can be prepared from the corresponding chlorides, [(η6‐arene)RuCl(LL*)][SbF6]. Dipolarophile intermediates [(η6‐arene)Ru(PNiPr)(methacrolein)][SbF6]2 {PNiPr = (4S)‐2‐(2‐diphenylphosphanylphenyl)‐4‐isopropyl‐1,3‐oxazoline} as well as nitrone‐containing complexes [(p‐MeC6H4iPr)Ru(PNiPr)(nitrone)][SbF6]2 (nitrone = N‐benzylidenephenylamine N‐oxide, N‐benzylidenemethylamine N‐oxide, 3,4‐dihydroisoquinoline N‐oxide) have been also isolated and characterised. The crystal structures of the chlorides (RRu)‐[(η6‐C6Me6)RuCl(PNiPr)][SbF6], (RRu)‐[(η6‐C6H6)RuCl(PNInd)][SbF6] {PNInd = (3aR,8aS)‐2‐[2‐(diphenylphosphanyl)phenyl]‐3a,8a‐dihydroindane[1,2‐d]oxazole} and those of the aqua solvates (RRu)‐[(η6‐arene)Ru(PNiPr)(H2O)][SbF6]2 (arene = C6H6, C6Me6) were determined by X‐ray diffraction methods. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Novel PNP ligands bearing N-triptycene backbone was developed and evaluated for selective ethylene oligomerization. Upon activation with MMAO-3A, the pre-catalyst mixture containing Cr(acac)3/ligand efficiently promotes ethylene tetramerization with remarkably high...

A variety of [M(L) 2 (L') 2 {κC,C'-bis(NHC)}]BF 4 complexes (M = Rh or Ir; L = CH 3 CN or wingtip group; L' = I -or CF 3 COO -; NHC = N-heterocyclic carbene) have been tested as precatalysts for the transfer hydrogenation of ketones and imines. The conversions and TOF's obtained are closely related to the nature of the ligand system and metal centre, more strongly coordinating wingtip groups yielding more active and recyclable catalysts. Theoretical calculations at the DFT level support a classic stepwise metal-hydride pathway against the concerted Meerwein-PonndorfVerley (MPV) mechanism. The calculated catalytic cycle involves a series of ligand rearrangements due to the high trans effect of the carbene and hydrido ligands, which are more stable when situated in mutual cis positions. The reaction profiles obtained for the complexes featuring an iodide or a trifluoroacetate in one of the apical positions agree well with the relative activity observed for both catalysts.