Relevant articles and documents
Enhanced Electrophilicity of Heterobimetallic Bi-Rh Paddlewheel Carbene Complexes: A Combined Experimental, Spectroscopic, and Computational Study
Collins, Lee R. Van Gastel, Maurice Neese, Frank Fürstner, Alois
Dirhodium paddlewheel complexes are indispensable tools in modern organometallic catalysis for the controlled decomposition of diazo-compounds. Tuning the reactivity of the thus-formed transient carbenes remains an active and dynamic field of research. Herein, we present our findings that the distal metal center plays an as yet underappreciated role in modulating this reactivity. Replacement of one rhodium atom in the bimetallic core for bismuth results in the formation of a significantly more electrophilic carbene complex. Bismuth-rhodium catalysts thereby facilitate previously unknown modes of reactivity for α-diazoester compounds, including the cyclopropanation of alkenes as electron deficient as trichloroethylene. While dirhodium paddlewheel complexes remain the catalysts of choice for many carbene-mediated transformations, their bismuth-rhodium analogues exhibit complementary reactivity and show great potential for small molecule and solvent activation chemistry. DFT calculations highlight the importance of metal-metal bonding interactions in controlling carbene electrophilicity. The paucity of these interactions between the 4d orbitals of rhodium and the 6p orbitals of bismuth results in weaker π-back-bonding interactions for bismuth-rhodium carbene complexes compared to dirhodium carbene complexes. This leads to weakening of the rhodium-carbene bond and to a more carbene-centered LUMO, accounting for the observed enhancement in bismuth-rhodium carbene electrophilicity. These findings are supported by a detailed spectroscopic study of the "donor-donor" carbene complexes Rh2(esp)2C(p-MeOPh)2 (19) and BiRh(esp)2C(p-MeOPh)2 (20), employing a combination of UV-vis and resonance Raman spectroscopy. The results reveal that carbene chemoselectivity in MRh(L)4 catalysis can be modulated to a previously unrecognized extent by the distal metalloligand.
Microwave synthesis of chloroacetic acid with acetic anhydride catalyzing chlorination of acetic acid
Wang, Li-Sheng Song, Guo-Qiang Meng, Ying Li, Shou-Gao Li, Fu-Xiang
In this paper, the chloroacetic acid has been synthesized with the acetic anhydride catalyzing chlorination of acetic acid by microwave irradiation. The volume fraction of acetic anhydride in acetic acid, reaction time, microwave power and reaction temperature have been investigated in the self-designed experimental device. The results showed that the optimum conditions were the volume fraction of acetic anhydride in acetic acid of 20 %, reaction time of 3.5 h, microwave power of 300 W, reaction temperature of 95 °C, the yield of chloroacetic acid was 94.31 % and the selectivity was 93.01 %. Compared with ordinary heating, the selectivity and the reaction rate of using microwave irradiation were apparently improved.
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