First Examples of Diazepanylidene Carbenes and Their Late-Transition-Metal Complexes

The synthesis of the novel seven-membered N-heterocyclic carbene (NHC) 1,3-dicyclohexyl-1,3-diazepan-2-ylidene ( 3 ) and its 5,6-dioxolane derivative 4 is reported and their coordination chemistry with Rh(I), Ir(I), and Pt(0) discussed. The M(cod)( 3 )Cl, where M = Rh and Ir, complexes display a high rotation barrier at room temperature about the M−C NHC bond, whereas for the M(CO) 2 ( 3 )Cl and Pt(nbe) 2 ( 3 ) complexes rapid rotation of the carbene ligand is observed at ambient temperature. The infrared ν(CO) values of the Rh(I) and Ir(I) derivatives M(CO) 2 ( 3 )Cl give a measure of the donor ability of the new carbene ligands. The crystal structures of the amidinium salts 3 ·HPF 6 and 4 ·HPF 6 together with those of M(cod)( 3 )Cl [M = Rh, Ir], Ir(cod)( 4 )Br, Ir(CO) 2 ( 3 )Cl, and Pt(nbe) 2 ( 3 ) are reported. Both the salts and the coordinated carbene ligands exhibit extremely large NCN angles; for the complexes the angles are in the range 115.5(3)° [Pt( 3 )] to 122(11)° [Ir( 4 )].