Half-Sandwich-Type Complexes with Non-Fischer-Type Carbene Ligands: Synthesis, Molecular Structure, Substitution, and C−C Coupling Reactions

Half-sandwich-type complexes with non-Fischer-type carbene ligands and rhodium, iridium, ruthenium, and osmium as the metal centers are accessible by two routes. While the rhodium and iridium η 5 -cyclopentadienyl and η 5 -indenyl compounds with Rh CRR‘ and Ir CRR‘ as the molecular fragments are prepared from starting materials that already contain the carbene ligand, the related ruthenium η 5 -cyclopentadienyl and η 5 -indenyl complexes as well as the corresponding osmium η 6 -arene derivatives are obtained from half-sandwich-type precursors which react with a diazoalkane to give the metal carbene. The reactions of the rhodium and iridium compounds [(η 5 -C 5 H 5 )M( CRR‘)(L)] (M = Rh, Ir) and [(η 5 -C 9 H 7 )Rh( CRR‘)(L)] with Lewis bases and acids result not only in ligand substitution, sometimes accompanied by C−C coupling, but also in migratory insertion of the CRR‘ unit into one of the C−H bonds of the cyclopentadienyl or indenyl ring. The ruthenium complexes [(η 5 -C 5 H 5 )RuCl( CRR‘)(L)] and [(η 5 -C 9 H 7 )RuCl( CRR‘)(L)] readily react with Grignard reagents and organolithium compounds by displacement of the chloride and subsequent C−C coupling to yield half-sandwich complexes with η 3 -allyl, η 3 -benzyl, and substituted olefins as ligands. The reactivity of the osmium arene carbenes [(η 6 -mes)OsX 2 ( CR 2 )] is highlighted by the observation that treatment of these complexes with water in acetone solution transforms the OsX 2 ( CR 2 ) fragment into an OsR 2 (CO) moiety.