Ca[(Ph₂PO)₂N]₂·nTHF, an α-hydroperoxidation promoter of coordinated THF molecules

Abstract

Ca[(Ph 2 PO) 2 N] 2 ×nTHF (2) was obtained by direct synthesis from tetraphenylimidodiphosphinic acid and Ca8 in THF. X-ray quality single crystals of Ca 2 [(Ph 2 PO) 2 N] 4 ×H 2 O (3) and Ca[(Ph 2 PO) 2 N] 2 ×2C 4 H 8 O 3 (4) were obtained upon crystallization of 2 under different conditions. The solid-state structure of 3 reveals a Ca 2 O 3 core in which the two hexacoordinated calcium metals are linked together by three m-oxygen atoms from three independent tetraphenylimidodiphosphinate ligands. Compound 4 is a monomeric octahedral complex bearing two tetraphenylimidodiphosphinate ligands in the equatorial plane and two ahydroperoxidated THF molecules, formed in situ, in the axial positions. Compound 4 represents the first example of a metal center exhibiting this type of hydroperoxidation behavior.

Oxidative Degradation of Ethers Promoted by Strontium and Barium Tetraphenylimidodiphosphinates

“…Recently, we have reported on a calcium tetraphenylimidodiphosphinate complex containing coordinated α-hydroperoxytetrahydrofuran molecules formed by in situ oxidation of the solvating THF . Because hydroperoxides are known intermediates in the oxidative ring opening of THF, we decided to study the oxidation abilities of tetraphenylimidodiphosphinate complexes based on the heavier alkaline-earth metals, strontium and barium, toward cyclic and acyclic ethers.…”

Spontaneous Stereoselective Oxidation of Crystalline Avermectin B1a to Its C-8a-(S)-Hydroperoxide

“…Thus, the X-ray crystallography results definitively confirmed the structure of 1 as containing a hydroperoxide group (−OOH) attached stereospecifically to C-8a from the β-face. Similar stereoselectivity has been observed in the transformation of morphine samples, where prolonged storage yielded small amounts of 10α-hydroxymorphine, as well as in the oxidation of tetraphenylimido­diphosphinic acid at the α position of the tetrahydrofuran residue upon crystallization of this compound as a calcium salt . At first glance such selective oxidation of avermectin B 1a at C-8a seems surprising.…”

“…Similar stereoselectivity has been observed in the transformation of morphine samples, where prolonged storage yielded small amounts of 10α-hydroxymorphine, 17 as well as in the oxidation of tetraphenylimidodiphosphinic acid at the α position of the tetrahydrofuran residue upon crystallization of this compound as a calcium salt. 18 At first glance such selective oxidation of avermectin B 1a at C-8a seems surprising. However, inspection of the structure reveals that the C-8a hydrogen atoms are uniquely activated toward radical abstraction since they are allylic, located at the α position relative to an oxygen atom and relatively exposed.…”