Nitrosyls ancillary ligand

The Ancillary Ligand Function of Nitrosyl Ligands in Homogeneous Catalysis. 176... 

As an ancillary ligand, the linear nitrosyl is a strong n-acceptor, even stronger in this respect than CO. However, the ancillary NO has also specific influence on... 

Remarkably, mononitrosyl iron(—II) complexes displayed great potential in the activation of diazo compormds and carbene-transfer reactions [102]. Generally, the activation of diazo compound can be realized by electrophilic transition metal complexes. However, according to the concept of Umpoirmg [103], the electron-rich, nucleophilic iron(—II) compound 31 is expected to react with diazo compounds of electron-poor carbenes, such as ethyl diazoacetate (Scheme 42). At first the iron center would add the C=N bond of the diazo compound followed by release of N2 and formation of the electrophilic iron carbene moiety. The nitrosyl group in such transformations is assumed to support as an ancillary ligand the N2 release by pulling electron density to the iron center. 

In these rhenium nitrosyl complexes the nitrosyl ligand takes different functions (1) as an ancillary NO ligand mimicking isoelectronic metal carbonyls (2) as a frans-influence ligand to activate donor ligands for atom or group transfer reaction. 

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