Two-coordinate group 14 element(II) hydrides as reagents for the facile, and sometimes reversible, hydrogermylation/hydrostannylation of unactivated alkenes and alkynes

Reactions of the solution stable, two-coordinate hydrido-tetrylenes, : E(H)(L-dagger) (E = Ge or Sn; L-dagger = -N(Ar-dagger)(SiPr3i); Ar-dagger = C6H2{C(H)Ph-2}(2)Pr-i-2,6,4), with a variety of unactivated cyclic and acyclic alkenes, and one internal alkyne, lead to the rapid and regiospecific hydrometallation of the unsaturated substrate at ambient temperature. The products of the reactions, [L-dagger E(C2H4R)] (E = Ge or Sn, R = H, Ph or Bu-t), [(LE)-E-dagger{CH(CH2)(3)(CH2)(n)}] (E = Ge, n = 1, 2 or 3; E = Sn, n = 1) and [(LE)-E-dagger{C(Ph)]=C(H)(Me)}], include the first structurally characterised examples of two-coordinate amido/alkyl germylenes and stannylenes. The cycloalkene hydrometallation reactions are cleanly reversible under ambient conditions, a process which computational and experimental van't Hoff analyses suggest proceeds via beta-hydride elimination from the metal coordinated cycloalkyl ligand. Similarly, the reactions of : Ge(H)(L-dagger) with 1,5-cyclooctadiene and 2-methyl-2-butene, both likely proceed via beta-hydride elimination processes, leading to the clean isomerisation of the alkene involved, and its subsequent hydrogermylation, to give [(LGe)-Ge-dagger(2-cyclooctenyl)] and [(LGe)-Ge-dagger{C2H4C(H)Me-2}], respectively. Reactions of [(LGeEt)-Ge-dagger] and [(LGe)-Ge-dagger(C5H9)] with the protic reagents, HCl, NH3 and EtOH, lead to oxidative addition to the germanium(II) centre, and formation of the stable chiral germanium(IV) complexes, [(LGe)-Ge-dagger(C5H9)(H) Cl] and [(LGe)-Ge-dagger(Et)(H)R] (R = NH2 or OEt). In contrast, related reactions between [(LSnEt)-Sn-dagger] and (BuOH)-O-t or TEMPOH (TEMP = 2,2,6,6-tetramethylpiperidinyl) proceed via ethane elimination, affording the tin(II) products, [(LSnR)-Sn-dagger] (R = OBut or OTEMP). In addition, the oxidation of [(LGe)-Ge-dagger(C6H11)] and [(LSn)-Sn-dagger(C2H4But)] with O-2 yields the oxo-bridged metal(IV) dimers, [{L-dagger(C6H11) Ge(m-O)}(2)] and [{L-dagger((BuC2H4)-C-t) Sn(m-O)}(2)], respectively.