Metal olefin complexes that are ubiquitous intermediates in catalysis are investigated by a detailed analysis of their 13C‐NMR chemical shift tensors. This analysis allows evidencing specific electronic features, namely the olefin‐to‐metal σ‐donation and the metal‐to‐olefin π‐backdonation as proposed in the Dewar?Chatt?Duncanson model. Apart from these interactions, the chemical shift tensor analysis reveals an additional ligand‐to‐metal π‐donation of the olefin σ(C=C) orbital in systems with suitably oriented vacant d‐orbitals. This interaction which is not accounted for in the Dewar?Chatt?Duncanson model explains the reactivity of this type of metal olefin complexes towards oxidative cyclization (olefin insertion) and protonolysis. 相似文献
The catalytic activities of titanium alkoxides and alkali metal alkoxides for hydrosilylation of unfunctionalized olefins have been studied. Titanium(IV) alkoxides showed excellent catalytic activity, while alkali metal alkoxides have low catalytic activity for the hydrosilylation of olefins. However, by using titanocene dichloride as an additive, alkali metal alkoxides showed also excellent catalytic property for hydrosilylation. In comparison with titanium alkoxides, no α-adduct was obtained by using alkali metal alkoxides/Cp2TiCl2 as catalysts. 相似文献
Polycarbonate/polyethylene random block copolymers (RBCs) have been produced using olefin metathesis catalysis in a process termed segment interchange metathesis. An olefin metathesis catalyst tolerant of polar functionality was added to reagent polycarbonate and polyethylene polymers which contained internal unsaturated carbon–carbon bonds. Subsequent metathesis occurred, segmenting the reagent polymers, resulting in RBCs. The block copolymers self-assembled into microphase structures which persisted into the melt state as determined by small angle X-ray scattering (SAXS).
An exceptionally efficient ruthenium-based catalyst for olefin oxidation has been designed by exploiting N,N′-bis(pyridylidene)oxalamide (bisPYA) as a donor-flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson-type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state-of-the-art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h−1 and turnover numbers of several millions. 相似文献