Combined NMR and DFT Study on the Complexation Behavior of Lappert's Tin(II) Amide

The complexation chemistry of the stannylene Sn{N[Si(CH3)(3)](2)}(2), first reported by Lappert in the 1970s, was investigated by Sn-119 NMR chemical shift measurements. To this end, experimental NMR data and theoretical density functional theory (DFT) calculations were combined to get an insight into the interaction between the stannylene and various solvent molecules with sigma- and/or pi-coordinating power. Small variations in the measured Sn-119 chemical shifts revealed a donor-acceptor interaction with the solvent molecules. In comparison to the noncoordinating solvent cyclohexane taken as a reference, a weak coordination was observed with aromatic solvent molecules (benzene and toluene) and a much stronger coordination with the sigma-donors THF and pyridine. Pyridine was confirmed to be the strongest donor, as evidenced by its large upfield chemical shift Delta delta(Sn-119) of 635 ppm. The experimental chemical shifts were reproduced by DFT (NMR) calculations, demonstrating similar trends in the interaction strength with the sigma- and pi-donors. The stannylene Sn{N[Si(CH3)(3)](2)}(2) showed the ability to react with Fe(CO)(5) and Fe-2(CO)(9) in the molar ratio 1/1 to provide L2SnFe(CO)(4) complexes. With a molar excess of Fe-2(CO)(9), L2Sn[Fe(CO)(4)](2) was generated irreversibly. Upon prolonged UV irradiation in the presence of W(CO)(6), in the molar ratio 1/1, a mixture of L2SnW(CO)(5) and two (L2Sn)(2)W(CO)(4) complexes was generated.