Doubly Bonded Derivatives of Si and Ge: Cycloaddition Reactions and Polymer Chemistry

(Di)tetrelenes are a fundamental class of unsaturated Group 14 compounds and play a central role in the synthesis of functional Group 14 compounds. The objective of this research was to investigate the various aspects of group 14 (di)tetrelenes (R2M=ER2, M = Si, Ge, and E = C, Si, Ge) reactivity. The addition of a series of nitrone and nitro compounds to the group 14 (di)tetrelenes Mes2Si=SiMes2, Mes2Ge=GeMes2 and Mes2Ge=CH(CH2-t-Bu), was examined. In general, the addition of the 1,3-dipolar nitrogen oxides to the (di)tetrelene gave 5-membered ring adducts via a formal [3+2] cycloaddition where the (di)tetrelene acts as the 2p component and the nitro/nitrone act as the 4p component. In some cases, the ring underwent rearrengment or cleavage to give secondary products. Reactivity of (di)tetrelenes toward R2HP=O derivatives, where R = Ph, OPh, OCH3, and R3P:,where R = OCH3,to tetramesityldigermene 1.2 and/or the germene 1.1 is reported in an effort to give a broader understanding of the chemistry of the addition of phosphine oxides to (di)tetrelenes. In general, a 1,2-adduct is formed which appears to be derived from the isomeric hydroxyphosphines. Notably, the phosphine oxides are reduced during the course of the reaction. A comparison to the analogous chemistry of alkenes and surface digermenes is made. A variety of alkyllithium (R = Me, Bu, t-Bu) reagents and potassium tert-butoxide were added to the highly reactive silene Mes2Si=CHCH2t-Bu and the germene Mes2Ge=CHCH2t-Bu, in diethyl ether. 1,2-Addition products were obtained regioselectively and in good yield after treatment with a weak acid with no evidence for any rearrangement products and no polymerization was observed. The reactivity of the silene and germene toward organometallic reagents is compared to previous studies of analogous silenes and germenes. The characterization of polysilenes and polygermenes derived from the anionic polymerization of silenes and germenes, respectively, is reported. The molecular weight of the polygermene was determined by static light scattering (SLS) in THF which showed that Mw to be 41500 g mol-1. The Mw determined by SLS was compared to the data obtained by GPC. Characterization of polysilene and polygermene by ESI-MS revealed the presence of oligomers (n \u3c 10) of the polytetrelenes. The mass spectral data also reveal the presence of R-Ge and C-H end groups, consistent with a chain growth mechanism where the R group is derived from the anionic initiator. NMR spectroscopic analysis of the polysilene provided further evidence of a chain growth mechanism for the anionic polymerization of the silene without rearrangement during the polymerization