Zwitterionic base-stabilized digermadistannacyclobutadiene and tetragermacyclobutadiene

The syntheses of a zwitterionic base-stabilized digermadistannacyclobutadiene and tetragermacyclobutadiene supported by amidinates and low-valent germanium amidinate substituents are described. The reaction of the amidinate Ge^I dimer, [LGe:]₂ (1, L=PhC(NtBu)₂), with two equivalents of the amidinate tin(II) chloride, [LSnCl] (2), and KC₈ in tetrahydrofuran (THF) at room temperature afforded a mixture of the zwitterionic base-stabilized digermadistannacyclobutadiene, [L₂Ge₂Sn₂L ₂] (3; L=LGe:), and the bis(amidinate) tin(II) compound, [L ₂Sn:] (4). Compound 3 can also be prepared by the reaction of 1 with [L^ArSnCl] (5, L^Ar=tBuC(NAr)₂, Ar=2,6-iPr ₂C₆H₃) in THF at room temperature. Moreover, the reaction of 1 with the "onio-substituent transfer" reagent [4-NMe₂-C₅H₄NSiMe₃]OTf (8) in THF and 4-(N,N-dimethylamino)pyridine (DMAP) at room temperature afforded a mixture of the zwitterionic base-stabilized tetragermacyclobutadiene, [L ₄Ge₆] (9), the amidinium triflate, [PhC(NHtBu) ₂]OTf (10), and Me₃SiSiMe₃ (11). X-ray structural data and theoretical studies show conclusively that compounds 3 and 9 have a planar and rhombic charge-separated structure. They are also nonaromatic.