Oxidation reactions of the phosphinidene oxide ligand

The (H-DBU)+ salt of the anionic phosphinidene oxide complex [MoCp(CO)2{P(O)R*}]- (1) (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene; R* = 2,4,6-C6H2tBu3) 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 1 with [FeCp2]BF4 gives the dimer [Mo2Cp2(CO)4{P(O)R*}2], and reaction with bromine gives the phosphinous acid complex [MoBrCp{P(OH)(CH2CMe2C6H2tBu2}(CO)2], the latter arising from an unprecedented C-H bond addition to the oxide P=O moiety. In contrast, reaction of 1 with p-benzoquinone occurs at the P site to give the P,O-bound phosphonite complex [MoCp{kappa2-OP(OC6H4OH)R*}(CO)2]. Finally, oxygen or sulfur atoms are added to the Mo=P bond by reaction of 1 with Me2CO2 and S8 to give the novel dioxophosphorane or thiooxophosphorane complexes [MoCp(CO)2{kappa2-EP(O)R*}]- (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 (Me3O)BF4) to give the isomers [MoCp{kappa2-(MeS)P(O)R*}(CO)2] and [MoCp{kappa2-SP(OMe)R*}(CO)2], both having novel organophosphorus ligands.