2138-72-9Relevant academic research and scientific papers
Strongly Polarized Iridiumδ--Aluminumδ+Pairs: Unconventional Reactivity Patterns including CO2Cooperative Reductive Cleavage
Escomel, Léon,Del Rosal, Iker,Maron, Laurent,Jeanneau, Erwann,Veyre, Laurent,Thieuleux, Chloé,Camp, Clément
, p. 4844 - 4856 (2021)
The iridium tetrahydride complex Cp*IrH4 reacts with a range of isobutylaluminum derivatives of general formula Al(iBu)x(OAr)3-x (x = 1, 2) to give the unusual iridium aluminum species [Cp*IrH3Al(iBu)(OAr)] (1) via a reductive elimination route. The Lewis acidity of the Al atom in complex 1 is confirmed by the coordination of pyridine, leading to the adduct [Cp*IrH3Al(iBu)(OAr)(Py)] (2). Spectroscopic, crystallographic, and computational data support the description of these heterobimetallic complexes 1 and 2 as featuring strongly polarized Al(III)δ+-Ir(III)δ- interactions. Reactivity studies demonstrate that the binding of a Lewis base to Al does not quench the reactivity of the Ir-Al motif and that both species 1 and 2 promote the cooperative reductive cleavage of a range of heteroallenes. Specifically, complex 2 promotes the decarbonylation of CO2 and AdNCO, leading to CO (trapped as Cp*IrH2(CO)) and the alkylaluminum oxo ([(iBu)(OAr)Al(Py)]2(μ-O) (3)) and ureate ({Al(OAr)(iBu)[κ2-(N,O)AdNC(O)NHAd]} (4)) species, respectively. The bridged amidinate species Cp*IrH2(μ-CyNC(H)NCy)Al(iBu)(OAr) (5) is formed in the reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.
γ-Agostic species as key intermediates in the vinyl addition polymerization of norbornene with cationic (allyl)Pd catalysts: Synthesis and mechanistic insights
Walter, Marc D.,Moorhouse, Rebecca A.,Urbin, Stephanie A.,White, Peter S.,Brookhart, Maurice
, p. 9055 - 9069 (2009)
Several cationic (allyl)Pd(II) complexes were synthesized and shown to be highly active for (2,3)-vinyl addition polymerization of norbornene (NB) to yield polymers with low molecular weight distributions (MWDs) ranging from 1.2-1.4. Despite the low MWDs,
Molybdenum and tungsten monoalkoxide pyrrolide (MAP) alkylidene complexes that contain a 2,6-dimesitylphenylimido ligand
Gerber, Laura C. H.,Schrock, Richard R.,Mueller, Peter
, p. 2373 - 2378 (2013)
Molybdenum and tungsten bispyrrolide alkylidene complexes that contain a 2,6-dimesitylphenylimido (NAr) ligand have been prepared, in which the pyrrolide is the parent pyrrolide or 2,5-dimethylpyrrolide. Monoalkoxide pyrrolide (MAP) complexes were prepared through addition of 1 equiv of an alcohol to the bispyrrolide complexes. MAP compounds that contain the parent pyrrolide (NC 4H4-) are pyridine adducts, while those that contain 2,5-dimethylpyrrolide are pyridine free. Molybdenum and tungsten MAP 2,5-dimethylpyrrolide complexes that contain O-t-Bu, OCMe(CF3) 2, or O-2,6-Me2C6H3 ligands were found to have approximately equal amounts of syn and anti alkylidene isomers, which allowed a study of the interconversion of the two employing 1H-1H EXSY methods. The Keq values ([syn]/[anti]) are all 2-3 orders of magnitude smaller than those observed for a large number of Mo bisalkoxide imido alkylidene complexes, as a consequence of the destabilization of the syn isomer by the sterically demanding NAr* ligand. The rates of interconversion of syn and anti isomers were found to be 1-2 orders of magnitude faster for W MAP complexes than for Mo MAP complexes.
Comparative reactivity of Zr- and Pd-alkyl complexes with carbon dioxide
Lau, Ka-Cheong,Petro, Benjamin J.,Bontemps, Sebastien,Jordan, Richard F.
, p. 6895 - 6898 (2013)
Structure/reactivity trends and DFT studies reveal mechanistic differences and parallels for the carboxylation of Zr and Pd alkyls. CO2 reacts with Cp2ZrMe(C6D5Cl)+ >10 4 faster than with Cp2ZrMe2, yielding monoacetate products in both cases. These reactions proceed by insertion mechanisms in which Zr- - -O interactions activate the CO2. In contrast, CO2 reacts readily with [(PO-iPr)PdMe 2]- (PO-iPr- = 2-P iPr2-4-Me-C6H3SO3 -) to yield [(PO-iPr)PdMe(OAc)]- but not with (PO-iPr)PdMe(L) species. Carboxylation of [(PO-iPr) PdMe2]- occurs by direct SE2 attack of CO 2 at the Pd-Metrans-to-P group, and the nucleophilicity of the Pd-Me group controls the reactivity. However, the SE2 process is accelerated by a Li+- OCO interaction when Li+ is present.
Reductive Cleavage of the CO Molecule by a Reactive Vicinal Frustrated PH/BH Lewis Pair
Sun, Qiu,Daniliuc, Constantin G.,Mück-Lichtenfeld, Christian,Bergander, Klaus,Kehr, Gerald,Erker, Gerhard
supporting information, p. 17260 - 17264 (2020/11/12)
A dimeric ethylene-bridged PH/BH system reduced carbon monoxide to the -CH2-O- state. In the presence of B(C6F5)3, the frustrated PH/BH Lewis pair reacted with carbon monoxide by reductive coupling of two CO molecules at the template. Removal of the B(C6F5)3 borane with pyridine liberated one equiv of carbon monoxide to give a cyclic five-membered P(=O)-CH2-B compound, the product of reductive cleavage of carbon monoxide. It reacted as a borylated Horner P(=O)CH2B carbon nucleophile with carbon dioxide to give a bicyclic product by P-CH2 attack on CO2 combined with internal P=O to boron coordination.
C-H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)-Oxo Complex
Chan, Ka Wing,Lam, Erwin,D'Anna, Vincenza,Allouche, Florian,Michel, Carine,Safonova, Olga V.,Sautet, Philippe,Copéret, Christophe
supporting information, p. 11395 - 11401 (2018/09/06)
In alkene metathesis, while group 6 (Mo or W) high-oxidation state alkylidenes are accepted to be key reaction intermediates for both homogeneous and heterogeneous catalysts, it has been proposed that low valent species in their +4 oxidation state can serve as precatalysts. However, the activation mechanism for these latter species - generating alkylidenes - is still an open question. Here, we report the syntheses of tungsten(IV)-oxo bisalkoxide molecular complexes stabilized by pyridine ligands, WO(OR)2py3 (R = CMe(CF3)2 (2a), R = Si(OtBu)3 (2b), and R = C(CF3)3 (2c); py = pyridine), and show that upon activation with B(C6F5)3 they display alkene metathesis activities comparable to W(VI)-oxo alkylidenes. The initiation mechanism is examined by kinetic, isotope labeling and computational studies. Experimental evidence reveals that the presence of an allylic CH group in the alkene reactant is crucial for initiating alkene metathesis. Deuterium labeling of the allylic C-H group shows a primary kinetic isotope effect on the rate of initiation. DFT calculations support the formation of an allyl hydride intermediate via activation of the allylic C-H bond and show that formation of the metallacyclobutane from the allyl "hydride" involves a proton transfer facilitated by the coordination of a Lewis acid (B(C6F5)3) and assisted by a Lewis base (pyridine). This proton transfer step is rate determining and yields the metathesis active species.
Dinuclear dicyclopentadienyl titanium complexes with bridging cyclopentadienylsiloxo ligands
Postigo, Lorena,Bellarosa, Luca,Sanchez-Nieves, Javier,Royo, Pascual,Lledos, Agusti,Mosquera, Marta E. G.
, p. 642 - 655 (2010/04/25)
Addition of 1 equiv of T1Cp to compound [(TiCl2) 2(μ-{(η5-C5Me4SiMeO) 2(μ-O)})] (A) at 80°C gave a mixture with different molar ratios of the two possible isomers of [(TiClCp)(TiCl 2)(μ-{(η5C5Me4SiMeO) 2(μ-O)})] (1). Reaction of compound A with 2 equiv of TlC p at 80°C afforded [(TiClCp)2(μ- {(η5-C5Me4SiMeO)2(μ-O)})] (2as) as the unique reaction product. Each Cp ligand of 2as is located in different positions anti and syn with respect to the Si-O-Si bridge. However, a mixture of two isomers of [(TiClCp)2(μ-{(η5-C 5Me4SiMeO)2(μ-O)})], 2as ( > 95% by NMR) and 2aa ( a mixture of the three possible isomers [(TiMeCp) 2(μ-{(η5-C5Me4SiMeO) 2(μ-O)})] (3as, 3aa, 3ss). The proportion of each was dependent on the reaction temperature. Isomer 2as reacted with Lewis acids E(C 6Fs)3 (E = B, Al) and with Li[B(C6F 5)4] to give the chloro-bridged dititanium compounds [(TiCp)2(μ-{(η5-C5Me4SiMeO) 2(μ-O)})μ-Cl)][Q] (Q = ClB(C6F5) 3, 4B; C1A1(C6F5)3, 4Al; Q = B(C6F5)4, 4C) as the unique reaction products. Addition of [Ph3C][B(CgF5)4] to the mixture of isomers in 3 gave a mixture of complexes [(TiCpMe)(TiCp)(μ- {(η5-C5Me4SiMeO)2(μ-O)})][Q] (5aC and 5sC; Q = B(C6F5)4), with the remaining methyl ligand located at anti or syn positions depending on the methyl group being abstracted. DFT studies were carried out to determine the stability of the isomers of 2 and 3, to determine which chlorine atom in compound 2as was more easily eliminated, and also to clarify the transformation of isomer 2as into the mixture of isomers 3as, 3aa, and 3ss during the alkylation reaction.
Zirconium and hafnium (1-pyridinio)imido complexes: Functionalized terminal hydrazinediido analogues
Herrmann, Heike,Gehrmann, Thorsten,Wadepohl, Hubert,Gade, Lutz H.
, p. 6231 - 6241 (2009/03/11)
Reaction of the diamidozirconium complex [Zr(N2 TBSNpy)(NMe2)2] (1) (N 2TBSNpy = CH3C(C5H 4N)(CH2NSiMe2tBu)2) or the diamidohafnium complex [Hf(N2TBSNpy)(NMe 2)2] (2) with one molar equiv. of 1-aminopyridinium triflate in the presence of one equiv. of pyridine gave the corresponding (1-pyridinio)imido complexes [Zr(N2TBSN py)(N-NC5H5)(OTf)(py)] (3) and [Hf(N 2TBSNpy)(N-NC5H5)(OTf) (py)] (4). These were converted to the acetylide complexes [Zr(N 2TBSNpy)(N-NC5H5)(CCPh) (py)] (5) and [Hf(N2TBSNpy)(N-NC 5H5)(CCPh)(py)] (6) by reaction with lithium phenylacetylide and substitution of the triflato ligand. Upon reaction of 3 and 4 with one molar equivalent of R-NC (R = tBu, Cy, 2,6-xyl), N-N bond cleavage in the (1-pyridinio)imido unit took place and the respective carbodiimido complexes [M(N2TBSNpy](NCNR)(OTf)(py)] (7-12) were formed instantaneously. A similar type of reaction with CO gave the isocyanato complex [Zr(N2TBSNpy](NCO)(OTf)(py)] (13). Finally, the abstraction of the pyridine ligand in compounds 3 and 4 with B(C6F5)3 led to the formation of the triflato-bridged dinuclear complexes [Zr(N2TBSN py)(N-NC5H5)(OTf)]2 (14) and [Hf(N2TBSNpy)(N-NC5H 5)(OTf)]2 (15). The Royal Society of Chemistry 2008.
Ethylene polymerization by palladium alkyl complexes containing bis(aryl)phosphino-toluenesulfonate ligands
Vela, Javier,Lief, Graham R.,Shen, Zhongliang,Jordan, Richard F.
, p. 6624 - 6635 (2008/10/09)
The reaction of L′2PdR2 (L′ = pyridine (py), pyridazine; L′2 = cyclooctadiene, TMEDA) with 2-{(2OMe-Ph)2P}-4-Me-benzenesulfonic acid ([PO-OMe]H, [1a]H) or 2- {(2-Et-Ph)2P}-4-Me-benzenesulfonic acid ([PO-Et]H, [1b]H) yields [PO-OMe]Pd(R)(L) (L = py, R = CH2SiMe3 (2a), CH 2tBu (3a), CH2Ph (4a); R = Me, L = pyridazine (5a), py (6a), PPh3 (7a)) or [PO-Et]Pd(Me)(py) (6b). 2a and 6b have square-planar structures in which the alkyl group is cis to the phosphine and the [PO]Pd chelate rings are puckered. The reaction of 2a and 3a with B(C 6F5)3 yields {[PO-OMe]Pd(R)}2 (R = CH2SiMe3 (8a), CH2tBu (9a)). 8a is a sulfonate-bridged dimer in the solid state. 2a, 6a, and 6b polymerize ethylene to linear polyethylene that contains low levels of Me branches, one C=C unit per chain (mostly 1- or 2-olefins), and Mn in the range 6000 to 19 000. 6a is slightly more active but produces polymers with similar molecular weight and structure compared to 6b. 6a copolymerizes ethylene and hexene at low ethylene pressure (5 atm), but no α-olefin incorporation is observed at high pressure (30 atm). An ethylene polymerization mechanism is proposed, which involves insertion and chain transfer of [PO]Pd(R)(ethylene) species (II) and ethylene trapping and much slower chain-walking of the [PO]Pd(CH 2CH2R) species (III) formed by insertion of II.
