Se-Substituted Carbene Complexes

The development of the chemistry of carbene complexes of the Group 8a metals, Ru, Os, and Ir, parallels chemistry realized initially with transition metals from Groups 6 and 7. The pioneering studies of E. O. Fischer and co-workers have led to the characterization of many hundreds of carbene complexes in which the heteroatoms N, O, and S are bonded to the carbene carbon atoms. The first carbene ligands coordinated to Ru, Os, and Ir centers also contained substituents based on these heteroatoms, and in this section the preparation and properties of N-, O-, S-, and Se-substituted carbene complexes of these metals are detailed. 

The ruthenium formimidoyl complex 15 is converted to neutral and cationic compounds containing the secondary carbene ligands CHNHR and CHN(Me)R by protonation and methylation, respectively (41,42)  

The formimidoyl group in Ru(CH=NR) (7j1-02CMe) (CO) (CNR) (PPh3)2 is readily methylated by Mel, with iodide replacing both acetate and triphenylphosphine (43)  

The osmium formimidoyl 16 is reversibly protonated to a secondary carbene complex (44)  

Alkylation of an anionic acylmetallate is the second step in the classic Fischer synthesis of carbene complexes. The same type of reaction can be performed with stable neutral acyl complexes, producing cationic carbene compounds. Compound 17 has been prepared from a ruthenium acetyl complex by direct methylation and by protonation with subsequent methylenation (45)  

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Table I summarizes the range of N-, O-, S-, and Se-substituted carbene complexes of Ru, Os, and Ir that have been prepared to date. While not...

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