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−CNHC 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·HPF6 and 4·HPF6 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)].