Synthesis and reactivity of cyclic and acyclic phosphonous and phosphonodithious esters
Description
New tri-valent cyclic dioxa and dithiabisphospholanes (1) have been synthesized from methylenebis(dichlorophosphine) or methyliminobis(dichlorophosphine) with ethyleneglycol, 1,2-ethanedithiol, pyrocatechol, 2,3-dihydroxynaphthalene, and diethyl-2,3-dimercaptosuccinate in the presence of DABCO (1,4-diazabicyclo (2,2,2) octane). Also tri-valent cyclic and acyclic phenylphosphonodithioite esters (2) have been synthesized from the reaction of phenyldichlorophosphine with diethyl-2,3-dimercaptosuccinate or ethyl-3-mercaptopropanoate in the presence of triethylamine. In addition, their penta-valent oxides (3) and sulfides (4) have also been prepared by oxidation or by refluxing with sulfur of cyclic and acyclic compounds (2), respectively. X-ray crystallographic analysis of methylenebis(1,3,2-dithiaphospholane)(pcps) (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)shows a bischelate 5-membered ring structure. Since the P-O and P-S bonds of the ring system in the diphosphines (1) are easily cleaved under a hydrolytic condition, producing phosphinic acid and corresponding diol or dithiol. When RuCl$\sb2$(PPh$\sb3)\sb3$ reacts with 2 equivalents of pcps, or (methylimino)bis(1,3,2-dithiaphospholane)(pnps), two structurally different products are produced. One product, trans-RuCl$\sb2$(pcps)$\sb2$ has a structure which contains two P, S-bonded chelate 5-membered rings. The other product, trans-RuCl$\sb2$(pnps)$\sb2$ has two P, P-bonded chelate 4-membered rings. Treating PT(II) complex either cis-PtCl$\sb2$(COD (COD = cyclooctadiene) or cis-PtCl$\sb2$(PhCN)$\sb2)$ with pcps or pnps results in the monochelated products, cis-PtCl$\sb2$(pcps) or cis-PtCl$\sb2$(pnps). Both complexes contain P, P-bonded 4-membered ring structure. The hydrolytic cleavage of the P-S bond in the cyclic and acyclic phenylphos phonodithioite (2) produce phenylphosphinic acid and corresponding thiol. Comparative hydrolysis rate data indicates that except for the cyclic phenyl phosphonodithioite (2$\sp\prime),$ $\rm C\sb6H\sb5\overline{P(SCH(CO\sb2CH\sb2CH\sb3)CH(CO\sb2CH\sb 2CH\sb3)S}),$ and S-ethylpropionatephenylphosphonothioate, $\rm C\sb6H\sb5PH(O)(SCH\sb2CH\sb2CO\sb2CH\sb2CH\sb3),$ the acyclic phenylphosphonodithioite (2$\sp{\prime\prime}),$ the oxides (3) and the sulfides (4) do not undergo significant hydrolytic cleavage of the P-S bond in 5% aqueous acetone at 50$\sp\circ$C. The increased hydrolysis rate of $\rm C\sb6H\sb5PH(O)(SCH\sb2CH\sb2CO\sb2CH\sb2CH\sb3)$ is possibly due to hydrogen bonding between water and the PH(O) functionality. The hydrolysis of the cyclic phenylphosphono dithioite (2$\sp\prime),$ $\rm C\sb6H\sb5\overline{P(SCH(CO\sb2CH\sb2CH\sb3)CH(CO\sb2CH\sb 2CH\sb3)S}),$ in aqueous aceto nitrile follows a rate law that is first order in the concentration of $\rm C\sb6H\sb5\overline{P(SCH(CO\sb2CH\sb2CH\sb3)CH(CO\sb2CH\sb 2CH\sb3)S}),$ and independent of the concentration of water. The values of E$\sb{\rm a},$ $\Delta{\rm H}\sp\ddagger$ and $\Delta{\rm S}\sp\ddagger$ are 10.4 Kcal mol$\sp{-1},$ 9.6 k cal mol$\sp{-1}$ and $-$45 cal mol$\sp{-1}$ respectively. The isotope effect for D$\sb2$O as compared to H$\sb2$O is 2.5. A mechanism is proposed whereby a pre-equilibrium is established between the phosphonodithioite and water, with subsequent proton transfer from water to the trivalent phosphorus occurring in a subsequent step. The slow step involves hydrolytic cleavage of the first P-S bond to form $\rm C\sb6H\sb5P(SCH(CO\sb2CH\sb2CH\sb3)CH(CO\sb2CH\sb 2CH\sb3)SH).$ The compound 2-nitro-5-thiocyanatobenzoic acid is used to provide supporting evidence for the formation of such intermediate thiol