Synthesis of 1,3-azaphosphol-2-ones. Crystal and molecular structures of [SP-4-2]-dichlorobis(3-phenyl-1,3-dihydrobenzo[1,3]azaphosphol-2-one-P)palladium(II) and its chloro(methyl)platinum(II) analogue

Reaction of secondary phosphine (±)-(2-aminophenyl)phenylphosphine, (±)-app, with PCl₅ in toluene gives the hydrochloride salt of the expected chlorophosphine (±)-(2-aminophenyl)chlorophenylphosphine, (±)-acpp.HCl, however, this is not the case with triphosgene. Rather the first example of a 1,3-azaphosphol-2-one is isolated, viz. (±)-3-phenyl-1,3-dihydrobenzo[1,3]azaphosphol-2-one, (±)-pbap. The hydrochloride salt (±)-acpp.HCl readily reacts with excess vinyl-, 2-methylphenyl- or 2-methoxyphenyl magnesium bromide to give the corresponding tertiary phosphines (±)-(2-H₂NC₆H₄)PPhR (where R = CHCH₂, 2-C₆H₄Me or 2-C₆H₄OMe). Hydrophosphination of the vinyl substituted tertiary phosphine with (±)-app in the presence of KOBu^t provides a synthetic route to the elusive P₂N₂ quadridentate ligand (R_P*,R_P*)- and (R_P*,S_P*)-(CH₂)₂(PPhC₆H₄NH₂-2)₂, albeit in low yield. The azaphospholone (±)-pbap can be readily deprotonated with KOBu^t in thf and subsequently alkylated with methyl iodide or benzyl bromide to give the analogous N-methyl or N-benzyl derivatives. Alkylation with 1,3-dibromopropane gives the bis(azaphospholone) (R_P*,R_P*)- and (R_P*,S_P*)-1,3-bis[1-{3-phenyl-1,3-dihydrobenzo[1,3]azaphosphol-2-one}]propane. The latter and the N-methyl substituted azaphospholone can also be synthesised by the reaction of the corresponding secondary phosphine, viz. (R_P*,R_P*)- and (R_P*,S_P*)-(CH₂)₃(NHC₆H₄PHPh-2)₂ and (±)-(2-methylaminophenyl)phenylphosphine, with triphosgene. All three azaphospholones react with [PtClMe(1,5-cyclooctadiene)] in thf to give complexes of the type cis-[PtClMeL₂] in which ligand L is coordinated via the P atom of the azaphospholones. The ligand (±)-pbap has also been complexed to palladium(II) via the reaction with Li₂[PdCl₄] in methanol to give cis-[PdCl₂{(±)-pbap}₂]. The structures of cis-[PtClMe{(±)-pbap}₂] and cis-[PdCl₂{(±)-pbap}₂] have been confirmed by X-ray analysis.