The syntheses of the 2,9‐dimesityl‐1,10‐phenanthroline (
In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+and Ga3+ion sites catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+is similar to Ni2+, while Ga3+forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250 °C where oligomerization is catalytically relevant. This work illuminates new chemistry for main group metal catalysts with potential for development of new oligomerization processes.
more » « less- NSF-PAR ID:
- 10222393
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract dmesp ) metal complexes, [Cu(dmesp)(MeCN)]PF6(1 ), [Cu(dmesp)2]PF6(2 ), Fe(dmesp)Cl2(3 ), Co(dmesp)Cl2(4 ), Ni(dmesp)Cl2(5 ), Zn(dmesp)Cl2(6 ), Pd(dmesp)MeCl (7 ), Cu(dmesp)Cl (8 ), and Pd(dmesp)2Cl2(9 ), in good to high yields are described. These complexes were characterized by1H and13C NMR spectroscopy, HR–MS (ESI and/or APPI), and elemental analysis (CHN). The solid‐state structures of complexes1 –8 were determined by single‐crystal X‐ray analysis and their photophysical properties were also characterized. To demonstrate the versatility of this new platform, complexes3 –5 ,8 , and9 were employed in the catalytic oligomerization of ethylene using modified methyl aluminoxane (MMAO) as the cocatalyst, where Co(II) and Ni(II) complexes (4 and5 , respectively) were found to exhibit moderate selectivity for catalytic dimerization of ethylene to butenes over tri‐ or tetramerization. Complex8 is an effective catalyst of both the commonly encountered “click” reaction and amine arylation chemistries. Complexes6 and9 were found to be excellent catalysts for Friedel‐Crafts alkylation and Suzuki‐Miyaura coupling, respectively. -
null (Ed.)Conspectus By using transition metal catalysts, chemists have altered the “logic of chemical synthesis” by enabling the functionalization of carbon–hydrogen bonds, which have traditionally been considered inert. Within this framework, our laboratory has been fascinated by the potential for aldehyde C–H bond activation. Our approach focused on generating acyl-metal-hydrides by oxidative addition of the formyl C–H bond, which is an elementary step first validated by Tsuji in 1965. In this Account, we review our efforts to overcome limitations in hydroacylation. Initial studies resulted in new variants of hydroacylation and ultimately spurred the development of related transformations (e.g., carboacylation, cycloisomerization, and transfer hydroformylation). Sakai and co-workers demonstrated the first hydroacylation of olefins when they reported that 4-pentenals cyclized to cyclopentanones, using stoichiometric amounts of Wilkinson’s catalyst. This discovery sparked significant interest in hydroacylation, especially for the enantioselective and catalytic construction of cyclopentanones. Our research focused on expanding the asymmetric variants to access medium-sized rings (e.g., seven- and eight-membered rings). In addition, we achieved selective intermolecular couplings by incorporating directing groups onto the olefin partner. Along the way, we identified Rh and Co catalysts that transform dienyl aldehydes into a variety of unique carbocycles, such as cyclopentanones, bicyclic ketones, cyclohexenyl aldehydes, and cyclobutanones. Building on the insights gained from olefin hydroacylation, we demonstrated the first highly enantioselective hydroacylation of carbonyls. For example, we demonstrated that ketoaldehydes can cyclize to form lactones with high regio- and enantioselectivity. Following these reports, we reported the first intermolecular example that occurs with high stereocontrol. Ketoamides undergo intermolecular carbonyl hydroacylation to furnish α-acyloxyamides that contain a depsipeptide linkage. Finally, we describe how the key acyl-metal-hydride species can be diverted to achieve a C–C bond-cleaving process. Transfer hydroformylation enables the preparation of olefins from aldehydes by a dehomologation mechanism. Release of ring strain in the olefin acceptor offers a driving force for the isodesmic transfer of CO and H2. Mechanistic studies suggest that the counterion serves as a proton-shuttle to enable transfer hydroformylation. Collectively, our studies showcase how transition metal catalysis can transform a common functional group, in this case aldehydes, into structurally distinct motifs. Fine-tuning the coordination sphere of an acyl-metal-hydride species can promote C–C and C–O bond-forming reactions, as well as C–C bond-cleaving processes.more » « less
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Abstract Vanadium‐based catalysts have shown activity and selectivity in ring‐opening metathesis polymerization of strained cyclic olefins comparable to those of Ru, Mo, and W catalysts. However, the application of V alkylidenes in routine organic synthesis is limited. Here, we present the first example of ring‐closing olefin metathesis catalyzed by well‐defined V chloride alkylidene phosphine complexes. The developed catalysts exhibit tolerance to various functional groups, such as an ether, an ester, a tertiary amide, a tertiary amine, and a sulfonamide. The size and electron‐donating properties of the imido group and the phosphine play a crucial role in the stability of active intermediates. Reactions with ethylene and olefins suggest that both β‐hydride elimination of the metallacyclobutene and bimolecular decomposition are responsible for catalyst degradation.
