Tin(II) Hydrides as Intermediates in Rearrangements of Tin(II) Alkyl Derivatives

Reactions of the Sn(II) hydrides [ArSn(mu-H)](2), (1) (At. = Ar-iPr4 (1a), Arinr6 Ar-iP4 = C6H3-2,6-(C6H3-2,6)-Pr-i(2))(2), Ar-iPr6 = C6H3-2,6-(C6H2-2,4,6-Pr-i(3))(2)) with norbornene (NB) or norbornadiene (NBD) readily generate the bicyclic alkyl-/alkenyl-substituted stannylenes, ArSn(norbornyl) (2a or 2b) and ArSn(norbornenyl) (3a or 3b), respectively. Heating a toluene solution of 3a or 3b at reflux afforded the rearranged species ArSn(3-tricydo[2.2.1.0(2,6)]heptane) (4a or 4b), in which the norbornenyl ligand is transformed into a nortricyclyl group. H-1 NMR studies of the reactions of 4a or 4b with tert-butylethylene indicated the existence of an apparently unique reversible beta-hydride elimination from the bicyclic substituted aryl/alkyl stannylenes 2a or 2b and 3a or 3b. Mechanistic studies indicated that the transformation of 3a or 3b into 4a or 4b occurs via a beta-hydride elimination of la or lb to regenerate NBD. Kinetic studies showed that the conversion of 3a or 3b to 4a or 4b is first order. The rate constant k for the conversion of 3a into 3b was determined to be 3.33 X 10(-5) min(-1), with an activation energy E-a of 16.4 +/- 0.7 kcal mol(-1).