Acceptorless, intramolecular, alkyl dehydrogenation in the solid-state in a rhodium phosphine complex; reversible uptake of three equivalents of H(2) per molecule

Addition of H(2) to the phosphine alkene ligated complex [Rh(dppe)(PCyp(2)Cyp')][BAr(4)(F)] 1 (Cyp = cyclo-C(5)H(9); Cyp' = cyclo-C(5)H(7), Ar(F) = 3,5-(CF(3))(2)C(6)H(3)) in the solid state results in hydrogenation of the alkene and uptake of two further equivalents of H(2) to afford the dihydride-dihydrogen complex [Rh(dppe)(PCyp(3))(H)(2)(eta(2)-H(2))][BAr(4)(F)] 2. Placing 2 under a vacuum or argon results in sequential loss of H2 and dehydrogenation of one of the cyclopentyl rings to reform 1. The hydrogenation-dehydrogenation cycle has been repeated 5 times without apparent degradation and has been followed by solid-state (31)P{(1)H} NMR spectroscopy. Intermediates on this process have been trapped using acetonitrile to give stable complexes that have been characterised in solution. We have previously shown that this hydrogenation-dehydrogenation process also happens in the solution-state; and evidence is presented that shows that, apart from a subtle difference, the same overall transformation occurs in the solid-state.