Contrasting reactivities of silicon and germanium complexes supported by an N-heterocyclic guanidine ligand.

We report the synthesis of an acyclic two-coordinate germylene supported by two bulky and electron donating N-heterocyclic guanidine [IPr═N](-) ligands (IPr = [(HCNDipp)2C:]; Dipp = [2,6-(i)Pr2C6H3]), and its reactivity with molecular hydrogen to form IPr═NH, which presumably proceeds via the unstable intermediate [H2Ge(N═IPr)2]. Our attempts to isolate the corresponding silylene [:Si(N═IPr)2] led to an unexpected ligand activation/rearrangement process involving N-C(aryl) bond cleavage within the N-heterocyclic guanidine ligand; this transformation was also studied by computational methods.