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.

Abstract

Reaction of secondary phosphine (+/-)-(2-aminophenyl)phenylphosphine, (+/-)-app, with PCl(5) 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-H(2)NC(6)H(4))PPhR (where R = CH=CH(2), 2-C(6)H(4)Me or 2-C(6)H(4)OMe). Hydrophosphination of the vinyl substituted tertiary phosphine with (+/-)-app in the presence of KOBu(t) provides a synthetic route to the elusive P(2)N(2) quadridentate ligand (R(P)*,R(P)*)- and (R(P)*,S(P)*)-(CH(2))(2)(PPhC(6)H(4)NH(2)-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)*)-(CH(2))(3)(NHC(6)H(4)PHPh-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-[PtClMeL(2)] 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 Li(2)[PdCl(4)] in methanol to give cis-[PdCl(2){(+/-)-pbap}(2)]. The structures of cis-[PtClMe{(+/-)-pbap}(2)] and cis-[PdCl(2){(+/-)-pbap}(2)] have been confirmed by X-ray analysis.