Roy J. Doyle

Synthesis, resolution and reactions of (±)-(2-aminophenyl)methylphenylphosphine. Crystal and molecular structure of (R*,R*, S*, R*)-(±)-(1,3-bis{[2-(methylphenylphosphino)phenyl]amino}propane)nickel(II) perchlorate

Asymmetric bidentate (±)-(2-aminophenyl)methylphenylphosphine has been prepared in 80% yield from (2-aminophenyl)diphenylphosphine via the secondary phosphine (±)-(2-aminophenyl)phenylphosphine. The chiral tertiary phosphine has been resolved by the method of metal complexation via the separation by fractional crystallisation of a pair of internally diastereomeric palladium(II) complexes containing the racemic ligand and (S)-[1-(1-ethyl)naphthyl]dimethylamine. The optically pure antipodes of the phosphine have α± 160°(589 nm, CH2Cl2). A number of square-planar bis(bidentate ligand) complexes of bivalent nickel, palladium and platinum containing the various forms of the ligand have been prepared and their solution behaviour studied by 1H and 31P-{1H} NMR spectroscopy. Monodeprotonation of the co-ordinated amino groups in the complexes has also been achieved by reaction with anhydrous sodium carbonate in acetone. The palladium(II) and platinum(II) complexes form cis diastereomers exclusively, whereas trans diastereomers were observed for the nickel(II) analogues. Furthermore, most of the complexes are kinetically labile. Reaction of (±)-(2-aminophenyl)methylphenylphosphine with n-butyllithium and N,N,N′,N′-tetramethylethylenediamine in tetrahydrofuran followed by the addition of 1,3-bis(p-tolylsulfonyloxy)propane gave the quadridentate ligand (R*,R*)- and (R*,S*)-1,3-bis{[2-(methylphenylphosphino)phenyl]amino}propane. The (R*,R*) and (R*,S*) forms of the quadridentate ligand have been separated by complexation to nickel(II). The structure of the nickel(II) complex containing the (R*,R*) form of the quadridentate ligand, viz. (R*,R*,S*,R*)-(1,3-bis{[2-(methylphenylphosphino)phenyl]amino}propane)nickel(II) perchlorate, has been determined by X-ray crystallography.

Chiral Birch reduced tertiary phosphines: precursors to asymmetric 1,2-cyclohexenebis(tertiary phosphines)

The first examples of an optically active Birch reduced tertiary phosphine, viz. (R(P))-(cyclohexa-2,5-dienyl)(3-pentyl)phenylphosphine, and successful hydrophosphination of the related racemic ligand (±)-(cyclohexa-2,5-dienyl)(2-propyl)phenylphosphine with PHPh(2) in the presence of KOBu(t) in thf to give a 1,2-cyclohexenebis(tertiary phosphine), viz. (±)-1,2-C(6)H(8)(PPh(2))(PPhPr(i)), are described; as confirmed by crystal structure determinations of [SP-4-4-(S(P),S)]-chloro[(cyclohexa-2,5-dienyl)(3-pentyl)phenylphosphine][2-{1-(dimethylamino)ethyl}phenyl-C,N]palladium(II) and [SP-4-3-(±)]-dimethyl[(1-diphenylphosphino)(2-isopropylphenylphosphino)cyclohexene]platinum(II).

Synthesis, resolution and reactions of (±)-1-(dimethylarsino)-2-(methylphenylphosphino)benzene. Crystal and molecular structure of [(S), (S)]-(+)589-{2-[1-(dimethylamino)ethyl]phenyl-C1,N}[1-(dimethylarsino)-2-(methylphenylphosphino)benzene-As,P]palladium(II) hexafluorophosphate

Asymmetric bidentate (±)-1-(dimethylarsino)-2-(methylphenylphosphino)benzene has been prepared by the reaction of sodium dimethylarsenide with (±)-1-chloro-2-(methylphenylphosphino)benzene in tetrahydrofuran. Its resolution has been achieved by the separation by fractional crystallisation of a pair of internally diastereomeric palladium(II) complexes containing the racemic ligand and orthometallated (S)-dimethyl(1-phenylethyl)amine. The optically pure antipodes have α±32°(589 nm, dichloromethane). The absolute configuration of the R enantiomer of the ligand has been assigned by a crystal-structure determination of the least-soluble diastereomeric complex [(S),(S)]-(+)589-{2-[1-(dimethylamino)ethyl]phenyl-C1, N}[1-(dimethylarsino)-2-(methylphenylphosphino)benzene-As,P]palladium(II) hexafluorophosphate. Chemoselective cleavage of the dimethylarsino moiety of the free benzene derivative occurs in the presence of lithium metal in tetrahydrofuran.

Completely stereoselective synthesis of a chiral quadridentate ligand with As2NP donor atoms. Crystal and molecular structure of [OC-6,35-(R*,S*)]-(±)-dichloro{1-[(2-dimethylarsinophenyl)methylarsino]-2-[(2-aminophenyl)methylphosphino]benzene-As, As′,N,P}cobalt(III) chloride dihydrate

Reaction of (±)-(2-aminophenyl)(2-chlorophenyl)methylphosphine with sodium (2-dimethylarsinophenyl)methylarsenide is completely stereoselective giving (R*, S*)-1-[(2-dimethylarsinophenyl)methylarsino]-2-[(2-aminophenyl)methylphosphino]benzene, (R*,S*)-1; as confirmed by a crystal structure determination of cis-[CoCl2{(R*,S*)-1}]Cl·2H2O.

Stereoselective synthesis of chiral multidentate ligands withAs2NP or As4P donor atoms

The asymmetric bidentate ligand (±)-(2-aminophenyl)(2-chlorophenyl)methylphosphine has been prepared via chemoselective cleavage of the phenyl group from (±)-(2-aminophenyl)methylphenylphosphine using lithium in tetrahydrofuran (thf), to give (2-aminophenyl)methylphosphine upon hydrolysis, followed by deprotonation of the secondary phosphine with sodium in thf and subsequent reaction with 1,2-dichlorobenzene. The chlorophenyl-substituted tertiary phosphine has been resolved by the method of metal complexation. The absolute configuration of the R enantiomer of the ligand has been assigned by a crystal structure determination of the diastereomeric palladium(II) complex [(S P ),(R)]-[(2-aminophenyl)(2- chlorophenyl)methylphosphine-N,P]{1-[1- (dimethylamino)ethyl]naphthyl-C 2 ,N} palladium(II) hexafluorophosphate. Reaction of (±)-(2-aminophenyl)(2-chlorophenyl)methylphosphine with an equimolar quantity of sodium (2-dimethylarsinophenyl)methylarsenide in thf at -20 ± 5 °C gave a 1:1 diastereomeric mixture of the chiral pentadentate ligands (R As *,R As *,S P *)-(±)- and (R As *,S As *,S P *)-(±)-{2-[(2-dimethylarsinophenyl) methylarsinophenyl}{2-[(2-dimethylarsinophenyl) methylarsinoamino]phenyl}methylphosphine. The chiral quadridentate ligand (R As *,S P *)-(±)-1-[(2- aminophenyl)methylphosphino]-2-[(2-dimethylarsinophenyl)methylarsino] benzene can be isolated, however, when the coupling reaction is performed at 50 ± 5 °C. The chiral multidentate ligands have been isolated by complexation to cobalt(III) and the structures of the three complexes determined by X-ray analyses. It is clear from the structural data that the quadridentate ligand has formed a single dichlorocobalt(III) complex with cis-α stereochemistry and in which the stereogenic arsenic and phosphorus atoms of the ligand have opposite relative configurations. Two other complexes have also been isolated from the coupling reaction: trans-dichlorobis[1,2-phenylenebis(dimethylarsine)]cobalt( III) chloride and bis[(2-aminophenyl)methylphenylphosphine]dichlorocobalt(III) chloride. The latter is isolated as an isomeric mixture. The formation of asymmetric bidentate (±)-(2-aminophenyl)methylphenylphosphine is believed to result from reduction of the chloro group in the tertiary phosphine precursor by the sodium arsenide reagent. Metal-assisted methylation of a (2-dimethylarsinophenyl)methylarsino moiety by methanol is postulated to account for the formation of 1,2-phenylenebis(dimethylarsine) in the reaction. Optically active analogues of the three multidentate ligands have also been synthesized by reaction of (R)-(2-aminophenyl)(2-chlorophenyl)methylphosphine with sodium (2-dimethylarsinophenyl)methylarsenide in thf and similarly isolated by complexation to cobalt(III).

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 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.

Completely stereoselective synthesis of a chiral tetra(tertiary phosphine). Crystal and molecular structure of [OC-6-22-(R*,R*)]-(±)-dichloro{1,2-bis[(2-dimethylphosphinophenyl)methylphosphino]benzene-P,P′,P′′,P′′′}cobalt(III) hexafluorophosphate

Reaction of (±)-(2-chlorophenyl)(2-dimethylphosphinophenyl)methylphosphine with sodium (2-dimethylphosphinophenyl)methylphosphide is completely stereoselective giving (R*,R*)-1,2-bis[(2-dimethylphosphinophenyl)methylphosphino]benzene, (R*,R*)-1; as confirmed by a crystal structure determination of cis-α-[CoCl2{(R*,R*)-1}]PF6.