Properties of Carbene Complexes

Reactive organic fragments can be stabilized by coordination to a metal center, and many stable complexes of carbenes have been prepared. Several types of carbene complexes 

Many examples of vinylidene complexes have been isolated, and the two tautomers of alk5me and vinylidene complexes shown in Equations 2.10a and 2.10b are sitnilar in stability. As shown by these two equations, either can be more stable, depending on the number and identity of the ligands on the metal fragment. Wiylidene complexes have also been invoked as intermediates in both stoichiometric and catalytic reactions. Vinyhdenes are typically electrophilic at the carbene carbon CJ and nucleophilic at the metal and C. The HI NMR chemical shift of the carbene carbon typically lies downfield, between 250 and 380 ppm, while the NMR chemical shift of the P-carbon typically lies between 87 and 143 ppm. 

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Table 5.6. EPR Parameters and Magnetic Properties of Carbene Complexes of Chromium(I) and Iron(I) ...

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