The Doubly Base‐Stabilized Diborane(4) [HB(μ‐hpp)] 2 (hpp = 1,3,4,6,7,8‐hexahydro‐2 H ‐pyrimido[1,2‐ a ]pyrimidinate): Synthesis by Catalytic Dehydrogenation and Reactions with S 8 and Disulfides

In this work we report on new experiments on the catalytic dehydrogenation of [H 2 B(μ‐hpp)] 2 leading to the doubly base‐stabilized diborane(4) [HB(μ‐hpp)] 2 featuring two hpp bridges (hpp = 1,3,4,6,7,8‐hexahydro‐2 H ‐pyrimido[1,2‐ a ]pyrimidinate) under mild conditions. Several dehydrogenation (pre)catalysts were tested. The best one turned out to be Ru 3 (CO) 12 , allowing quantitative dehydrogenation already at 60 °C. Subsequently we subjected [HB(μ‐hpp)] 2 to reactions with S 8 and disulfides (Ph 2 S 2 and Bn 2 S 2 , Bn = benzyl). Reaction with S 8 leads to oxidative insertion of one sulfur atom into the B–B bond and formation of [HB(μ‐hpp)] 2 (μ‐S). In the case of disulfides, substitution reactions leading to the doubly base‐stabilized diborane(4) species [RSB(μ‐hpp)] 2 and HB(μ‐hpp) 2 BSR (R = Ph or Bn) compete with sulfuration again leading to [HB(μ‐hpp)] 2 (μ‐S).