Hydrogen-Bonded Di(hydroperoxy)alkane Adducts of the Type Cy₃P=O·(HOO)₂CHR (R = Alkyl)

Five representatives of a novel type of di(hydroperoxy)alkane adducts of phosphine oxides have been synthesized and fully characterized, including their solubility in organic solvents. The phosphine oxide Cy₃PO (1) has been used in combination with the corresponding aldehydes to create the adducts Cy₃PO·(HOO)₂CHCH₃ (2), Cy₃PO·(HOO)₂CHCH₂CH₃ (3), Cy₃PO·(HOO)₂CH(CH₂)₂CH₃ (4), Cy₃PO·(HOO)₂CH(CH₂)₃CH₃ (5), and Cy₃PO·(HOO)₂CH(CH₂)₇CH₃ (6). All adducts crystallize easily and contain the peroxide and phosphine oxide hydrogen-bonded in 1:1 ratios. The single crystal X-ray structures of 2-6 and their unique features are discussed. The ³¹P NMR spectra of the adducts 2-6 show downfield-shifted signals as compared to Cy₃PO. In the IR spectra, the ν(P=O) wavenumbers of the adducts have smaller values than the neat phosphine oxide. All spectroscopic results of 2-6 show that the P=O bond is weakened by hydrogen-bonding to the di(hydroperoxy)alkane moieties. Adduct 6 selectively oxidizes PPh₃ to OPPh₃ within minutes, and nonanal is reformed in the process. The easy synthesis, handling, and administration of these stable, solid, and soluble peroxides with well-defined composition will have a positive impact on synthetic chemistry.