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(†)) (E = Ge or Sn; L(†) = –N(Ar(†))(SiPr(i)(3)); Ar(†) = C(6)H(2){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(†)E(C(2)H(4)R)] (E = Ge or Sn, R = H, Ph or Bu(t)), [L(†)E{CH(CH(2))(3)(CH(2))(n)}] (E = Ge, n = 1, 2 or 3; E = Sn, n = 1) and [L(†)E{C(Ph)[double bond, length as m-dash]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 β-hydride elimination from the metal coordinated cycloalkyl ligand. Similarly, the reactions of :Ge(H)(L(†)) with 1,5-cyclooctadiene and 2-methyl-2-butene, both likely proceed via β-hydride elimination processes, leading to the clean isomerisation of the alkene involved, and its subsequent hydrogermylation, to give [L(†)Ge(2-cyclooctenyl)] and [L(†)Ge{C(2)H(4)C(H)Me(2)}], respectively. Reactions of [L(†)GeEt] and [L(†)Ge(C(5)H(9))] with the protic reagents, HCl, NH(3) and EtOH, lead to oxidative addition to the germanium(ii) centre, and formation of the stable chiral germanium(iv) complexes, [L(†)Ge(C(5)H(9))(H)Cl] and [L(†)Ge(Et)(H)R] (R = NH(2) or OEt). In contrast, related reactions between [L(†)SnEt] and Bu(t)OH or TEMPOH (TEMP = 2,2,6,6-tetramethylpiperidinyl) proceed via ethane elimination, affording the tin(ii) products, [L(†)SnR] (R = OBu(t) or OTEMP). In addition, the oxidation of [L(†)Ge(C(6)H(11))] and [L(†)Sn(C(2)H(4)Bu(t))] with O(2) yields the oxo-bridged metal(iv) dimers, [{L(†)(C(6)H(11))Ge(μ-O)}(2)] and [{L(†)(Bu(t)C(2)H(4))Sn(μ-O)}(2)], respectively.