Coordination Chemistry of N-Heterocyclic Stannylenes: A Combined Synthetic and Mössbauer Spectroscopy Study

The N-heterocyclic stannylenes (NHSns), [(Dipp)N(CH2)nN(Dipp)Sn] (Dipp = 2,6- iPr2C6H3; n = 2, 1; n = 3, 5) and [(tBu)N(CHMe)2N(tBu)Sn] (10) are competent ligands toward a variety of transition metal centers, as seen in the complexes [W(CO)5·1] (2), [(OC)4Fe(μ-1)2Fe(CO)4] (3), [(OC)4Fe(μ-1)Fe(CO)4] (4), [Fe(CO)4·5]n (6, n = 1 or 2), [(OC)4Fe(μ-5)Fe(CO)4] (7), [Ph3PPt(μ-1)2PtPPh3] (8), [Fe(CO)4·10] (11), and [(η5-C5H5)(OC)2Mn·10] (12). X-ray crystallographic studies show that the NHSns are structurally largely unperturbed binding to the metal, but in contrast to the parent NHCs, NHSns often adopt a bridging position across dinuclear metal units. The balance between terminal and bridging positions for the stannylene is evidently closely balanced as shown by the observation of both monomers and dimers for 6 in the solid state and in solution. 119Sn and 57Fe Mössbauer spectroscopy of the complexes shows the tin atoms in such complexes to be consistent with electron deficient Sn(II) centers.