Alkyl- und Arylkomplexe des Iridiums und Rhodiums. XIX. Reaktion von Carbonsäuren mit ausgewählten Organoverbindungen von Ir(I) und Rh(I): Bildung von Arylhydrido-, Carboxylatohydrido- und Carboxylato-Derivaten

Alkyl and Aryl Complexes of Iridium and Rhodium. XIX. Reaction of Carboxylic Acids with Selected Organo Compounds of Ir(I) and Rh(I): Formation of Arylhydrido, Carboxylatohydrido, and Carboxylato Derivatives cis-Arylhydridoiridium(III) complexes IrH(Ar)(O₂CR)(CO)(PPh₃)₂ (R = Me: Ar = C₆H₅, 4-MeC₆H₄; R = Et: Ar = 4-MeC₆H₄, 2,4-Me₂C₆H₃) could be prepared by oxidative addition of carboxylic acids to aryliridium(I) compounds Ir(Ar)(CO)(PPh₃)₂. Reaction of aliphatic carboxylic acids with alkyliridium(I) derivatives Ir(Alk)(CO)(PPh₃)₂ and Ir(Alk)[PhP(CH₂CH₂CH₂PPh₂)₂] (Alk = CH₂CMe₃, CH₂SiMe₃) lead to dicarboxylatoiridium(III) hydrides IrH(O₂CR)₂(CO)(PPh₃)₂ (R = Me, Et, i-Pr) and IrH(O₂CR)₂[PhP(CH₂CH₂CH₂PPh₂)₂] (R = Me, Et). Ir(4-MeC₆H₄CO₂)(CO)(PPh₃)₂ was obtained from Ir(CH₂SiMe₃)(CO)(PPh₃)₂ and 4-MeC₆H₄CO₂H. Interaction of organorhodium complexes Rh(R′)(CO)(PPh₃)₂ (R′ = CH₂SiMe₃, 4-MeC₆H₄) and Rh(R′)[PhP(CH₂CH₂CH₂PPh₂)₂] (R′ = CH₂CMe₃, 4-MeC₆H₄) with aliphatic and aromatic carboxylic acids yielded carboxylatorhodium(I) compounds Rh(O₂CR)(CO)(PPh₃)₂ (R = Me, t-Bu, 4-MeC₆H₄) and Rh(O₂CR)[PhP(CH₂CH₂CH₂PPh₂)₂] (R = Me, 4-MeC₆H₄).     

Alkyl- und arylkomplexe des iridiums und rhodiums: XXI. Chelatphosphan-stabilisiertepentakoordinierte organoiridium(I)-komplexe Ir(R)(CO)( chel-P33)

Novel five-coordinate organoiridium(I) complexes of the type Ir(R)(CO)(chel-P₃) (chel-P₃=PhP(CH₂CH₂CH₂PPh₂)₂: R = CH₂CMe₃, CH₂SiMe₃; chel-P₃ = MeP-(CH₂CH₂CH₂PPh₂)₂: R = CH₂SiMe₃; chel-P₃PhP(CH₂CH₂PPh₂)₂; R = CH₂SiMe₃, 4-MeC₆H₄) have been prepared from Ir(R)(CO)(PPh₃)₂ and the respective triphosphine. According to ³¹P NMR, these compounds are stereochemically rigid at normal temperatures. The reaction of Rh(R)(CO)(PPh₃)₂, where R = CH₂CMe₃ or 2-MeC₆H₄, with PhP(CH₂CH₂CH₂PPh₂)₂ yielded the four-coordinate derivatives Rh(CH₂CMe₃)[PhP(CH₂CH₂CH₂PPh₂)₂] and Rh(2-MeC₆H₄)[PhP(CH₂CH₂CH₂PPh₂)₂]), which arealready known from the literature.     

Synthesis and structures of complexes Os3(μ-H)2(CO)7(μ-RC5H3N){μ3-Ph2PCH2P(C6H4)Ph} (R = H, Me) with ortho-metalated pyridine ligands. The revised structure of the triosmium cluster ”Os3(μ-H)2(CO)7(μ-C6H4){μ3-Ph2PCH2P(C6H4)Ph}”

The structure of the previously synthesized triosmium cluster was revised. The structure Os₃(μ-H)₂(CO)₇(μ-C₆H₄){μ₃-Ph₂PCH₂P(C₆H₄)Ph} suggested earlier was not confirmed. The cluster has the composition Os₃(μ-H)₂(CO)₇(μ-C₅H₄N){μ₃-Ph₂PCH₂P(C₆H₄)Ph} and contains the ortho-metalated pyridine ligand. The X-ray diffraction study of the complex Os₃(μ-H)₂(CO)₇(μ-MeC₅H₃N){μ₃-Ph₂PCH₂P(C₆H₄)Ph} containing the ortho-metalated 4-methylpyridine ligand made it possible to distinguish between the C and N atoms of the pyridine ligands in the resulting triosmium clusters.     

Komplexchemie polyfunktioneller liganden : XXXVII. Darstellungsmethoden für hydrido-kobalt(I)-komplexe des 1,1,1-tris(diphenylphosphinomethyl)äthans

[Co(CO)₂(R₂PCH₂)₃CCH₃][Co(CO)₄] (R  C₆H₅) reacts with NaBH₄, depending on the reaction conditions, to give CoH(CO)₂(R₂PCH₂)₂C(CH₃)CH₂PR₂ · BH₃ and CoH(CO)(R₂PCH₂)₃CCH₃. The hydride CoH(CO)(R₂PCH₂)₃CCH₃ is also formed by the reaction of [Co(CO)₂(R₂PCH₂)₃CCH₃][Co(CO)₄] with LiOH, NaOH and NaNH₂. The reaction with LiOH primarily gives (acetone)₃-LiCo(CO)(R₂PCH₂)₃CCH₃, which is also formed by reduction of [Co(CO)₂(R₂PCH₂)₂C(CH₃)CH₂PR₂]₂ with lithium in THF/acetone solution. In liquid ammonia [Co(CO)₂(R₂PCH₂)₃CCH₃][Co(CO)₄] at 20°C yields Co(CONH₂)(CO)(R₂PCH₂)₃CCH₃. This compound reacts in the same solvent at 60°C to yield the hydride CoH(CO)(R₂PCH₂)₃CCH₃. CH₃I and HClO₄ react with CoH(CO)(R₂PCH₂)₃CCH₃ yielding CoI(R₂PCH₂)₃CCH₃ and the unstable [Co(H)₂(CO)(R₂PCH₂)₃CCH₃]ClO₄, respectively. The deutero complex CoD(CO)(R₂PCH₂)₃CCH₃ was also synthesized. The new compounds were characterized, as much as possible, by their IR, ¹H NMR and ³¹P NMR data.     

Alkyl- und aryl-komplexe des iridiums und rhodiums: X. Chelatphosphin-stabilisierte rhodiumorganyle Rh(R)[PhP(CH2CH2CH2PPh2)2]: synthese,NMR-spektroskopischer cis,trans-einfluss und molekülstruktur von Rh(2-MeC6H4)[PhP(CH2CH2CH2PPh2)2]

The organorhodium(I) complexes Rh(R)[PhP(CH₂CH₂CH₂PPh₂)₂] (R  CH₂CMe₃, CH₂SiMe₃; 2-MeC₆H₄, 4-MeC₆H₄, 2,4-Me₂C₆H₃, 2,4,6-Me₃C₆H₂; C₂Ph) have been prepared and characterized by ³¹P and ¹H NMR spectroscopy and an X-ray structure determination of the tolyl derivative Rh(2-MeC₆H₄)-[PhP(CH₂CH₂CH₂PPh₂)₂].For these compounds, the relative ³¹P coordination shifts Δ(PPh₂) > Δ(PPh) distinctly reflect the electron-releasing properties of the organoligands σ-bonded trans to PPh. As expected, coupling between the ¹⁰³Rh nucleus and phenylphosphino P atoms is weak and varies only little as the strong trans influence groups R are changed. In contrast to this insensitivity of ¹J(Rh-PPh) to R, Rh-P coupling within the Ph₂P-Rh-PPh₂ moieties shows considerable dependence upon the nature of the C-donor producing the cis influence series sp³-C <sp²-C < sp-C.The ortho-tolyl complex crystallizes from toluene as 1/1 solvate Rh(2-MeC₆H₄)[PhP(CH₂CH₂CH₂PPh₂)₂] · C₇H₈. Crystals are orthorhombic, space group Pbc2₁, with a 1017.9(7), b 1974.3(14), c 2177.6(11) pm, and Z = 4. The structure has been refined to R = 0.079 for 2249 unique data with F₀ > 3σ(F₀). Metal-phosphorus distances are 225.7(5) and 229.6(6) pm for Rh-PPh₂ and 227.3(6) pm for Rh-PPh.     

The seven-coordinate hydrido-tantalum complexes [Ta(H)(CO)6−n(oligophos)]: preparation and dynamics

The hydrido complexes cis-[HTa(CO)₄P₂] (P₂  Ph₂PCH₂CH₂PPh₂), HTa-(CO)₃P_m (P_m  P₃: PhP(CH₂CH₂PPh₂)₂, P₄: [Ph₂PCH₂CH₂PPhCH₂]₂, PP₃: P(CH₂CH₂PPh₂)₃) have been obtained from the photo-chemically produced complexes [Et₄N][Ta(CO)₄P_m] by ion-exchange chromatography on silica gel. The anionic and neutral complexes have been characterized by IR and ³¹P and ¹H NMR spectroscopy. The temperature-dependent ¹H(hydride)-³¹P NMR coupling patterns are interpreted in terms of a hydride-capped octahedral structure with restricted migration of the H⁻ ligand between the octahedral faces.     

Tertiary phosphine induced migratory carbonyl insertion in cyclopentadienyl complexes of iron(II)

Cyclopentadienyldicarbonylmethyliron, [CpFe(CO)₂Me] (1), undergoes migratory carbonyl insertion under the influence of isosteric phosphine ligands P(4-FC₆H₄)₃ and P(4-MeC₆H₄)₃. The products of the reaction, [CpFe(CO)(COMe)P(4-FC₆H₄)₃] (2a) and [CpFe(CO)(COMe)P(4-MeC₆H₄)₃] (2b), were characterised by X-ray crystallography. In both structures, the iron atom adopts a pseudo octahedral coordination geometry. Fe-P bond distances are the same at 2.1932(8) Å in 2a and 2b, respectively. Thus, contrary to what was expected, X-ray data could not be used to quantitatively differentiate between the two phosphine ligands in 2a and 2b. Therefore, additional spectroscopic techniques such as IR and NMR were employed. Similarly, the Fe-C bond lengths of the carbonyl (Fe-CO) and acetyl (Fe-COMe) are 1.748(3) and 1.955(3) in 2a, and 1.744(3) and 1.951(3) Å in 2b, respectively.The migratory carbonyl insertion was studied by NMR, IR, and UV-vis spectroscopies to determine the mechanism and the rate law. Results from NMR spectroscopy show that the formation of the product is accompanied by oxidation of the corresponding phosphine ligand. An increase in the reactivity of migratory carbonyl insertion for P(4-MeC₆H₄)₃ was observed when the solvent was changed from CH₂Cl₂ to MeCN. The kinetic data showed that P(4-MeC₆H₄)₃ reacts faster than P(4-FC₆H₄)₃.     

Synthesis and characterization of diiron ethanedithiolate complexes with monosubstituted phosphine ligands

Reactions of (μ-edt)Fe₂(CO)₆ (edt = SCH₂CH₂S) (1) with the monophosphine ligands Ph₂PCH₂Ph, Ph₂PC₆H₁₁, Ph₂PCH₂CH₂CH₃, or P(2-C₄H₃O)₃ in the presence of Me₃NO?2H₂O afforded (μ-edt)Fe₂(CO)₅L [L = Ph₂PCH₂Ph, 2; Ph₂PC₆H₁₁, 3; Ph₂PCH₂CH₂CH₃, 4; P(2-C₄H₃O)₃, 5] in 70–88% yields. Complexes 2–5 were characterized by spectroscopy and single crystal X-ray diffraction analysis. The phosphorus of 2–5 is in an apical position of the distorted octahedral geometry of iron.     

A crystallographic and DFT study on Vaska-type trans-[Rh(CO)Cl(PR3)2] complexes containing flexible ligands: The molecular structure of trans-[Rh(CO)Cl{P(OC6H5)3}2]

An investigation into the effect of the flexibility of substituents on the disorder of the Cl-Rh-CO moiety in Vaska-type trans-[Rh(CO)Cl(PR₃)₂] complexes is presented. The influence of the packing of the complexes with PR₃ = P(CH₂C₆H₅)₃, P(OC₆H₅)₃, P(O-2-MeC₆H₄)₃ and P(O-2,6-Me₂C₆H₃)₃ was evaluated by comparing the X-ray structures with the results of DFT calculations on these complexes. Reasonable agreement between the calculated and molecular structures was found. A good agreement, however, was found between the calculated and crystallographic structures when comparing the coordination polyhedron around the Rh atom. The main difference between the calculated and solid state structures appeared to be in the orientation of the phenyl groups of the P-donor ligands.     

Cyclopentadienyleisen-komplexe mit P(OR)3-liganden; Synthese und spektroskopische charakterisierung

Reactions of reactive cyclopentadienyliron complexes C₅H₅Fe(CO)₂I, [C₅H₅Fe(CO)₂THF]BF₄, [C₅H₅Fe(CO)((CH₃)₂S)₂]BF₄ and [C₅H₅Fe(p-(CH₃)₂C₆H₄)]PF₆ with P(OR)₃ as ligands (R = CH₃, C₂H₅, i-C₃H₇ and C₆H₅) lead to the formation of the complex compounds C₅H₅Fe(CO)_2?n(P(OR)₃)_nI and [C₅H₅Fe(CO)_3?n(P(OR)₃)_n]X (n = 1, 2 and n = 1–3, X = BF₄, PF₆). Spectroscopic investigations (IR, ¹H, ¹³C and ³¹P NMR) indicate an increase of electron density on the central metal with increasing substitution of CO groups by P(OR)₃ ligands. The stability of the compounds increase in the same way.     

Studies of lambert's reaction: The formation of [Mn2(CO)8(μ-AsR2)2] complexes from tertiary arsines and [Mn2(CO)10] at high temperatures

Although very bulky ligands e.g.(o-MeC₆H₄)₃E or (μ-C₁₀H₇)₃E (E = P or As) are inert, the normal photochemical or thermal reaction of tertiary phosphines or arsines, L, with [Mn₂(CO)₁₀] is CO substitution with the formation of [Mn₂(CO)₈(L)₂] derivatives (I). At elevated temperatures some triarylarsines, R₃As, undergo Lambert's reaction with ligand fragmentation to give [Mn₂(CO)₈(μ-AsR₂)₂] complexes (II) (R = Ph, p-MeOC₆H₄, p-FC₆H₄, or p-CIC₆H₄) even though, in the absence of [Mn₂(CO)₁₀] R₃As are stable under the same conditions. Exceptional behaviour is exhibited by (p-Me₂NC₆H₄)_3- As which forms a product of type I; by some HN(C₆H₄)₂AsR which give a product of type II as a result of loss of the non-aryl groups R = PhCH₂, cyclo-C₆H₁₁, or MeO; and by Ph(α-C₁₀H₇₂P which is the only phosphine to form a product of type II, albeit in trace amounts only. The thermal decomposition of a n-butanol solution of [Mn₂(CO)₈(AsPh₃)₂] in a sealed tube gives C₆H₆ and [Mn₂(CO)₈(α-AsPh₂)₂], whilst in an open system in the presence of various tertiary phosphines, L, [Mn(H)(CO)₃(L)₂] are obtained. It is suggested that Lambert's reaction is a thermal fragmentation of [Mn(CO)₄(AsR₃]^* radicals, the first to be recognised. They lose the radical R^* which abstracts hydrogen from the solvent. The resulting [Mn(CO)₄(AsR₂)] moiety dimerises to [Mn₂(CO)_8-(α-AsR₂)₂]. the reaction is facilitated by the stability of the departing radical (e.g. PhCH₂ or MeO) and, as the crowding about As is relieved, by its size (e.g. Ph, cyclo-C₆H₁₁, o-MeC₆H₄, or α-C₁₀H₇). In general, phosphine-substituted radicals [Mn(CO)₄(PR)₃]^* do not undergo this decomposition, probably because the PC bonds are much stronger than AsC.     

The preparation and X-ray crystal and molecular structure of (α,1,2-η-6-methylbenzyl) bis(triphenylphosphine)rhodium(I)

Reaction of [RhCl(PPh₃)₃] with [o-MeC₆H₄CH₂MgBr] affords high yields of the non-fluxional complex, [Rh(CH₂C₆H₄Me)(PPh₃)₂] which has been shown crystallographically to contain a 1-3-η-benzyl group bound through the phenyl carbon atom that is not substituted with the methyl group. Crystals of this compound are triclinic, space group P$\text{1}$, with a = 10.561(6). b = 17.705(3), c = 10.934(4) Å, α = 80.69(3), β = 116.86(4), γ = 102.30(4)° and Z = 2. The structure was solved via the heavy-atom method and refined to R = 0.032 using 5379 diffractometer data with I > 1.56(I). Attempts to prepare π-bonded xylylene complexes from this compound by reaction with base have been unsuccessful, but protonation followed by recrystallisation from acetone gives [Rh{(CH₃)₂CO}₂(PPh₃)₂]BF₄.     

Palladium Chemistry Related to Benzyl Bromide Carbonylation: Mechanistic Studies

 Palladium(II) complexes of the general formula PdCl₂ (PR₃)₂ with PR₃ = { P(OPh)₃}, P(O-4-MeC₆H₄)₃, P(O-2-MeC₆H₄)₃, and PPh₂(OBu) were reduced by NEt₃ in chloroform or benzene to Pd(0) complexes Pd(PR₃)₄ and Pd(PR₃)_x(NEt₃) _4−x . The same reaction performed in the presence of air gave CH₃CHO or CH₃CH₂CHO when NPr₃ was used instead of NEt₃. Pd(P(OPh)₃)₄ reacted with benzyl bromide affording the oxidative addition product cis-PdBr(CH₂Ph)(P(OPh)₃)₂. The reaction of PdCl₂(P(OPh)₃)₂ with benzyl bromide was observed only in the presence of NEt₃, and a dimeric complex of [PdBr(CH₂Ph)(P(OPh)₃)]₂ was identified as the reaction product. Both benzyl complexes reacted fast with CO (1 atm) to form acyl complexes exhibiting ν(CO) bands at 1709 and 1650 cm⁻¹.     

Alkylidenverbrückte diphosphane und dichlalkogenodiphosphorane als liganden in kationischen cyclopentadienyleisencarbonyl-komplexen

Oxidative cleavage of the FeFe bond in [C₅H₅Fe(CO)₂]₂ in the presence of alkylide-bridged diphosphanes LL (LL = (C₆H₅)₂P(CH₂)_n(P(C₆H₅)₂; n = 1–3), (C₆H₅)₂PCH₂As(C₆H₅)₂ and dichalcogenodiphosphoranes (X)LL(X) ((X)LL(X) = (C₆H₅)₂P(X)(CH₂)_n(X)P(C₆H₅)₂; X  O, S, Se; n = 1–3) yields the complexes [C₅H₅Fe(CO)₂L′]BF₄ (L′ = LL, (X)LL(X); X  S, Se) in high yield. the complexes react with Ni(CO)₄ under photochemical conditions to form [C₅H₅Fe(CO)₂(μ-L′)Ni(CO)₃]BF₄ in quantitative yield, and lose a CO group under irradiation (λ_max > 300 nm) to form the chelate compounds [C₅H₅Fe(CO)L′]BF₄, which are isolable for L′  LL (P,As ligand) and (X)LL(X) (X = S, Se). Some substitution reactions with phosphanes are described.     

Palladium Chemistry Related to Benzyl Bromide Carbonylation: Mechanistic Studies

Summary.  Palladium(II) complexes of the general formula PdCl₂ (PR₃)₂ with PR₃ = { P(OPh)₃}, P(O-4-MeC₆H₄)₃, P(O-2-MeC₆H₄)₃, and PPh₂(OBu) were reduced by NEt₃ in chloroform or benzene to Pd(0) complexes Pd(PR₃)₄ and Pd(PR₃)_x(NEt₃) _4−x . The same reaction performed in the presence of air gave CH₃CHO or CH₃CH₂CHO when NPr₃ was used instead of NEt₃. Pd(P(OPh)₃)₄ reacted with benzyl bromide affording the oxidative addition product cis-PdBr(CH₂Ph)(P(OPh)₃)₂. The reaction of PdCl₂(P(OPh)₃)₂ with benzyl bromide was observed only in the presence of NEt₃, and a dimeric complex of [PdBr(CH₂Ph)(P(OPh)₃)]₂ was identified as the reaction product. Both benzyl complexes reacted fast with CO (1 atm) to form acyl complexes exhibiting ν(CO) bands at 1709 and 1650 cm⁻¹.     

Regioselective anion generation and alkylation at carbon α to nitrogen in (CO)5WC[N(CH3)2]C6H4-p-CH3

Treatment of (CO)₅WC[N(CH₃)₂]C₆H₄-p-CH₃ (1) with lithium diisopropylamide (LDA) in THF at −78°C followed by quenching with D₂O leads to incorporation of deuterium into the (E)-N-methyl group only. Reaction of the anion of 1 with benzyl bromide at −78°C followed by quenching with water gave the E-isomer of (CO)₅WC[N(CH₃)CH₂CH₂C₆H₅]C₆H₄-p-CH₃ (2E, 26%) and recovered 1. When a mixture of the anion of 1 and benzyl bromide was warmed from −78°C to ambient temperature, a mixture of the E-isomer of the dibenzylated product (CO)₅WC[N(CH₃)CH(CH₂C₆H₅)₂]C₆H₄-p-CH was obtained. Reaction of the anion of 1 with allyl bromide gave (CO)₅WC[N(CH₃)CH₂CH₂CHCH₂]C₆H₄-p-CH₃ (5, 38%) and with methyl iodide gave a mixture of (CO)₅WC[N(CH₃)CH₂CH₃]C₆H₄-p-CH₃ (6, 7%) and (CO)₅W C[N(CH₃)CH(CH₃)₂]C₆H₄-p-CH₃ (7, 16%).     

A new and unusual isomerism in [Fe(CO)2 {P(OR)3}2 (SO2)] complexes (R = aryl)

[Fe(CO)₂ {P(OR)₃}₂ (SO₂)] complexes (R = aryl) exist in solution as equilibrium mixtures of two isomers; both have been shown by X-ray diffraction studies (where R = Ph or o-MeC₆H₄) to have planar coordination about SO₂ and trigonal bipyramidal coordination about Fe, but in one isomer (R = Ph) the equatorial plane is occupied by SO₂ and two CO ligands whilst in the other one (R = o-MeC₆H₄) it is occupied by the SO₂ and two P ligands.     

Metal Ions in Biological Systems,Volume 4. Metal Ions as Probes; : edited by Helmut Sigel,Marcel Dekker,New York, 1974, xii + 261 pages, $24.75.

Trends in ³¹P NMR coordination shifts for the complexes M(CO)₃BrL₂, [M(CO)₃L₂(NCMe)]⁺, MeC₅H₄Mn(CO)L₂ and [MeC₅H₄Mn(CO)₂]₂L₂ (M = Mn and Re;L₂ = Ph₂PCH₂PPh₂, Ph₂PCH₂CH₂PPh₂ and Ph₂PCH₂CH₂AsPh₂) are discussed.     

Organische Phosphorverbindungen XXXVIII. Darstellung und Eigenschaften von Tris-(dialkoxyphosphonyl-methyl)-, Tris-(alkoxyphosphinyl-methyl)-und Tris-(oxophosphoranyl-methyl)-phosphinsäureestern sowie der entsprechenden Säuren [1]

Tris-chloromethyl-phosphine oxide, (ClCH₂₎₃ P?O(I), is obtained by chlorination of (HOCH₂₎₃P?O with PCl₅ or (C₆H₅₎₃PCl₂, and also by oxidation of (CICH₂₎₃P?O and (ClCh₂₎₂(CH₃)P?O. High yields of tris-(dialkyloxyphosphonly-methyl)-phosphine oxides, [RO₂(O)PCH_2]2P?O (II) (R?CH₃, C₂H₅, iso-C₃H₇, n-C₄H₉, 2- ethyl-hexyl), tris (alkyloxyphosphinyl-methyl)-phosphine oxides, [R₂(O)PCH_2]3P?O(R = C₆H₅, CH₃) are obtained by heating tris-chloromethyl-phosphine oxides, [(RO) (R′) (O)PCH_2]3P?O (R = C₄H₉, R′? C₆H₅) and tris-(oxophosphoranyl-phosphine oxides with phosphites, phosphonites and phosphinites, respectively, at 170–180°C for several hours. Compounds II possess an extraordinarily high absorption capacity. Thus a warm. 2% solution of II (R = C₂H₅) in benzene solidifies completely on cooling so that no benzene can be poured off. Tris-dihydroxyphosphonyl-methyl)-phosphine oxide, [(HO)₂(O)PCH_2]3P?O, obtained by hydrolysis of II (R ? C₂H₅) with refluxing conc. HCl or by thermal decomposition of II (R ? iso-C₃H₇) at 190°, titrates in aqueous solution as a hexabasic acid with breaks at pH = 4,4 (three equivalents) and pH = 10,7 (three equivalents). It forms crystalline salts with amines, alkali and alkaline earth metals, and is an excellent chelating agent. The ¹H- and ^31?P-NMR. spectra of all the compounds prepared are discussed.