The Flexible Coordination Modes of Guanidine Ligands in Zn Alkyl and Halide Complexes: Chances for Catalysis

Due to their high basicity, guanidines are versatile ligand systems. In principal, they could use both their imino and amino nitrogen to establish a dative metal-N bond. However, generally only the imino N of a guanidine ligand is bound to a metal. Herein we present some examples in which both the imino and amino groups of guanidine ligands are directly engaged in the bonding to a metal ion. Under certain conditions the amino group could establish an additional link to a metal center acting as a hemilabile ligand. This result is likely to be of relevance for catalytic reactions, demonstrating the possibility to stabilize a vacancy at the metal (for instance generated by ligand dissociation).