Oxidation Reactions of the Phosphinidene Oxide Ligand

The (H-DBU)<sup>+</sup> salt of the anionic phosphinidene oxide complex [MoCp(CO)<sub>2</sub>{P(O)R*}]<sup>-</sup> (<b>1</b>) (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene; R* = 2,4,6-C<sub>6</sub>H<sub>2</sub><i><sup>t</sup></i><sup></sup>Bu<sub>3</sub>) reacts with different oxidizing agents, displaying a multisite activity located at the Mo and P atoms or at the MoP bond. Thus, reaction of <b>1</b> with [FeCp<sub>2</sub>]BF<sub>4</sub> gives the dimer [Mo<sub>2</sub>Cp<sub>2</sub>(CO)<sub>4</sub>{P(O)R*}<sub>2</sub>], and reaction with bromine gives the phosphinous acid complex [MoBrCp{P(OH)(CH<sub>2</sub>CMe<sub>2</sub>C<sub>6</sub>H<sub>2</sub><i><sup>t</sup></i><sup></sup>Bu<sub>2</sub>}(CO)<sub>2</sub>], the latter arising from an unprecedented C−H bond addition to the oxide PO moiety. In contrast, reaction of <b>1</b> with <i>p</i>-benzoquinone occurs at the P site to give the <i>P</i>,<i>O</i>-bound phosphonite complex [MoCp{κ<sup>2</sup>-OP(OC<sub>6</sub>H<sub>4</sub>OH)R*}(CO)<sub>2</sub>]. Finally, oxygen or sulfur atoms are added to the MoP bond by reaction of <b>1</b> with Me<sub>2</sub>CO<sub>2</sub> and S<sub>8</sub> to give the novel dioxophosphorane or thiooxophosphorane complexes [MoCp(CO)<sub>2</sub>{κ<sup>2</sup>-EP(O)R*}]<sup>-</sup> (E = O, S). The thiooxophosphorane anion is a good nucleophile and is methylated at either the S or O positions depending on the electrophile used (MeI or (Me<sub>3</sub>O)BF<sub>4</sub>) to give the isomers [MoCp{κ<sup>2</sup>-(MeS)P(O)R*}(CO)<sub>2</sub>] and [MoCp{κ<sup>2</sup>-SP(OMe)R*}(CO)<sub>2</sub>], both having novel organophosphorus ligands.