Synthesis and characterisation of mixed ligand Pt(II) and Pt(IV) oxadiazoline complexes

The nitrile ligands in trans-[PtX2(PhCN)2] (X = Cl, Br, I) undergo sequential 1,3 dipolar cycloadditions with nitrones R1R2C=N+(Me)-O(-) (R1 = H, R2 = Ph; R1 = CO2Et, R2 = CH2CO2Et) to selectively form the Delta4-1,2,4-oxadiazoline complexes trans-[PtX2(PhCN) (N=C(Ph)-O-N(Me)-CR1R2)] or trans-[PtX2(N=C(Ph)-O-N(Me)-CR1R2)2] in high yields. The reactivity of the mixed ligand complexes trans-[PtX2(PhCN)(N=C(Ph)-O-N(Me)-CR1R2)] towards oxidation and ligand substitution was studied in more detail. Oxidation with Cl2 or Br2 provides the Pt(IV) species trans-[PtX2Y2(PhCN)(N=C(Ph)-O-N(Me)-CH(Ph))] (X, Y = Cl, Br). The mixed halide complex (X = Cl, Y = Br) undergoes halide scrambling in solution to form trans-[PtX(4-n)Yn(PhCN)(N=C(Ph)-O-N(Me)-CH(Ph))] as a statistical mixture. Ligand substitution in trans-[PtCl2(PhCN)(N=C(Ph)-O-N(Me)-CR1R2)] allows for selective replacement of the coordinated nitrile by nitrogen heterocycles such as pyridine, DMAP or 1-benzyl-2-methylimidazole to produce mixed ligand Pt(II) complexes of the type trans- [PtX2(heterocycle)(N=C(Ph)-O-N(Me)-CR1R2)]. All compounds were characterised by elemental analysis, mass spectrometry, IR and 1H, 13C and 195Pt NMR spectroscopy. Single-crystal X-ray structural analysis of (R,S)-trans-[PtBr2(N=C(Ph)-O-N(Me)-CH(Ph))2] and trans-[PtCl2(C5H5N)(N=C(Ph)-O-N(Me)-CH(Ph))] confirms the molecular structure and the trans configuration of the heterocycles relative to each other.     

Preparation, properties and structures of the first series of organometallic Pt(II) and Pt(IV) complexes with stibine co-ligands

The planar Pt(II) monomers [PtMe2(L-L)] and [(PtMe2)2(L'-L')2] dimers (L-L = R2Sb(CH2)3SbR2, o-C6H4(CH2SbMe2)2; L'-L' = R2SbCH2SbR2; R = Me or Ph) are obtained in good yield via reaction of [PtMe2(SMe2)2] with L-L or L'-L' in benzene. The Pt(iv) stibines, [PtMe3(L-L)I] (L-L = R2Sb(CH2)3SbR2, o-C6H4(CH2SbMe2)2 or 2 x SbPh3, SbMePh2 or SbMe2Ph) are obtained by treatment of [PtMe3I] with L-L in chloroform. These represent the first series of stable Pt(IV) stibine complexes. All of the products have been characterised by 1H, 13C{1H}, 195Pt NMR spectroscopy, electrospray mass spectrometry and analysis. Crystal structure determinations on [PtMe3{R2Sb(CH2)3SbR2}I], [PtMe3{o-C6H4(CH2SbMe2)2}I] and [PtMe3(SbPh3)2I] confirm the distorted octahedral environment at Pt, with fac Me groups and mutually cis Sb donor atoms. The Sb-Pt-Sb angle in the seven-membered chelate ring of the o-C6H4(CH2SbMe2)2 complex is ca. 96 degrees , compared to <90 degrees in the complexes with six-membered chelates. The C1-distibines R2SbCH2SbR2 afford only the dinuclear [(PtMe3)2(mu-R2SbCH2SbR2)(mu-I)2] in which the stibine ligand and two I atoms bridge two Pt atoms giving an edge sharing bioctahedral geometry which has been confirmed by a crystal structure analysis. The Pt(II) species undergo oxidative addition with MeI to give the corresponding Pt(IV) species, while the Pt(IV) species reductively eliminate ethane upon thermolysis.     

Synthesis and reactivity of unsymmetrical difluoro Pt(IV) complexes

Difluoro Pt(IV) complexes (P-P)Pt(Ar)₂F₂ were prepared and characterized. One of the fluoro ligands can be selectively removed from the Pt coordination sphere giving the cationic product with the phosphine ligand trans to the empty coordination site.     

α-氨基酸乙酯卤根合铂(II)的合成和构型研究

Sixteen new halogenoethylaminoacidato Pt(II) complexes were synthesized and characterized, of which eightiodo complexes (PtA2I2) (A = DL-a-AlaOEt, L-a-alaOEt, DL-a-PheOEt, L-a-PheOEt, DI-A-AspOEt, L-a-AspOEt, DL-a-SerOEt and L-a-Lys OEt), four chloro compounds (PtA2Cl2)(A = DL-a-PheOEt, DL-a-AspOEt, L-a-Asp OEt) and (DL-a-PheHOEt)2(PtCl4) were obtained by reaction of K2 (PtX4)(X = I^-, Cl^-) with the corresponding ethylaminoacidates in water. The other chlorethylaminoacidato Pt(II) complexes (PtA2Cl2) (A = DL-a-AlaOEt, L-a-AlaOEt, L-a-PheOEt, DL-a-Ser OEt) were synthesized in acetone by exchange reaction of the corresponding iodo complexes with AgCl in order to avoid hydrolysis of the ethyl aminoacidates. Molar conductivity determination showed that all the Pt(II) complexes obtained were neutral molecules with the exception of (DL-a-PheHOEt)2(PtCl4) which existed as an anion. As shown by diole moment determination and modified thiourea reaction, iodo complexes 1-7 and some of the chloro complexes (PtA2Cl2) (A = DL-a-alaOEt, D-a-AlaOEt, DL-a-SerOEt) were of cis-configuration and the other chloro complexes were of trans-configuration.     

Synthesis, crystal structures, and properties of oxovanadium(IV)-lanthanide(III) heteronuclear complexes

A new series of oxovanadium(IV)-lanthanide(III) heteronuclear complexes [Yb(H2O)8]2[(VO)2(TTHA)](3)21 H2O (1), {[Ho(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)} 8.5 H2O (2), {[Gd(H2O)7(VO)2(TTHA)][(VO)2(TTHA)](0.5)}8.5 H2O (3), {[Eu(H2O)7][(VO)2(TTHA)](1.5)} 10.5 H2O (4), and [Pr2(H2O)6(SO4)2][(VO)2(TTHA)] (5) (H6TTHA=triethylenetetraaminehexaacetic acid) were prepared by using the bulky flexible organic acid H(6)TTHA as structure-directing agent. X-ray crystallographic studies reveal that they contain the same [(VO)2(TTHA)]2- unit as building block, but the Ln3+ ion lies in different coordination environments. Although the lanthanide ions always exhibit similar chemical behavior, the structures of the complexes are not homologous. Compound 1 is composed of a [Yb(H2O)8]3+ ion and a [(VO)2(TTHA)]2- ion. Compounds 2 and 3 are isomorphous; both contain a trinuclear [Ln(H2O)7(VO)2(TTHA)]+ (Ln=Ho for 2 and Gd for 3) ion and a [(VO)2(TTHA)]2- ion. Compound 4 is an extended one-dimensional chain, in which each Eu3+ ion links two [(VO)2(TTHA)]2- ions. For 5, the structure is further assembled into a three-dimensional network with an interesting framework topology comprising V2Pr2 and V4Pr2 heterometallic lattices. Moreover, 4 and 5 are the first oxovanadium(IV)-lanthanide(III) coordination polymers and thus enlarge the realm of 3d-4f complexes. The IR, UV/Vis, and EPR spectra and the magnetic properties of the heterometallic complexes were studied. Notably, 2 shows unusual ferromagnetic interactions between the VO2+ and Ho3+ ions.     

Reaction of sterically hindered arylmercury compounds with Pt(IV), Pt(II), and Pd(II) chloride complexes

Conclusion Heating of a solution of the PtCl₆ ^2– ion and an arylmercury compound containing a substituent in the ortho position to mercury leads to the formation of a diaryl (in the case of -naphthylmercury) or arene (in the case of the mesityl or pentamethylphenyl mercury derivatives).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2374–2376, October, 1986.The authors express their gratitude to A. E. Shilov and A. K. Yatsimirskii for a useful discussion of these results.     

Synthesis and Spectral Properties of Ni(II), Pd(II), Pt(II), and Pt(IV) Tetraphenyltetrabenzoporphyrinates

Complexation reactions of 5,10,15,20-tetraphenyltetrabenzoporphyrin and transmetallation of its cadmium complex with nickel(II) acetate, Ni(II), Pd(II), and Pt(II) chlorides in dimethylformamide and phenol have been studied. The corresponding Ni(II), Pd(II), and Pt(II) porphyrinates have been synthesized. Pt^IVBr₂ porphyrinate has been obtained by the treatment of Pt(II) 5,10,15,20-tetraphenyltetrabenzoporphyrinate with bromine in chloroform. The obtained compounds have been characterized by elemental analysis, electronic absorption and ¹H NMR spectroscopy and mass spectrometry.     

Reduction of (imine)Pt(IV) to (imine)Pt(II) complexes with carbonyl-stabilized phosphorus ylides

A novel method is reported for generation of the difficult-to-obtain (imine)Pt(II) compounds that involves reduction of the corresponding readily available Pt(IV)-based imines by carbonyl-stabilized phosphorus ylides, Ph3P=CHCO2R, in nonaqueous media. The reaction between neutral (imino)Pt(IV) compounds [PtCl4[NH=C(Me)ON=CR1R2]2] [R1R2 = Me2, (CH2)4, (CH2)5, (Me)C(Me)=NOH], [PtCl4[NH=C(Me)ONR2]2] (R = Me, Et, CH2Ph), (R1 = H; R2 = Ph or C6H4Me; R3 = Me) as well as anionic-type platinum(IV) complexes (Ph3PCH2Ph)[PtCl5[NH=C(Me)ON=CR2]] [R2 = Me2, (CH2)4, (CH2)5] and 1 equiv of Ph3P=CHCO2R (R = Me, Et) proceeds under mild conditions (ca. 4 h, room temperature) to give selectively the platinum(II) products (in good to excellent isolated yields) without further reduction of the platinum center. All thus prepared compounds (excluding previously described Delta4-1,2,4-oxadiazoline complexes) were characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C[1H], 31P[1H] and 195Pt NMR spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2[NH=C(Me)ON=CMe2]2] [crystal system tetragonal, space group P4(2)/n (No. 86), a = b = 10.5050(10) A, c = 15.916(3) A] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna2(1) (No. 33), a = 19.661(7) A, b = 12.486(4) A, c = 10.149(3) A]. The reaction is also extended to a variety of other Pt(II)/Pt(IV) couples, and the ylides Ph3P=CHCO2R are introduced as mild and selective reducing agents of wide applicability for the conversion of Pt(IV) to Pt(II) species in nonaqueous media, a route that is especially useful in the case of compounds that cannot be prepared directly from Pt(II) precursors, and for the generation of systematic series of Pt(II)/Pt(IV) complexes for biological studies.     

Nitrile-amidine coupling at Pt(IV) and Pt(II) centers. An easy entry to imidoylamidine complexes

Treatment of trans-[PtCl4(RCN)2] (R = Me, Et, Ph, NEt2) with 2 equiv of the amidine PhC(=NH)NHPh in a suspension of MeCN (R = Me), CHCl3 (R = Et, Ph), or in CHCl3 solution (R = NEt2) results in the formation of the imidoylamidine complexes trans-[PtCl4{NH=C(R)N=C(Ph)NHPh}2] (1-4) isolated in good yields (66-84%). The reaction of soluble complexes 3 and 4 with 2 equiv of Ph3P=CHCO2Me in CH2Cl2 (40 degrees C, 5 h) leads to dehydrochlorination resulting in a chelate ring closure to furnish the platinum(IV) chelates [PtCl2{NH=C(R)NC(Ph)=NPh}2] (R = Ph, 5; R = NEt2, 6), accordingly, and the phosphonium salt [Ph3PCH2CO2Me]Cl. Treatment of 5 with 3 equiv of Ph3P=CHCO2Me at 50 degrees C for 5 d resulted in only a 30% conversion to the corresponding Pt(II) complex [Pt{NH=C(NEt2)NC(Ph)=NPh}2] (15). The reduction can be achieved within several minutes, when Ph2PCH2CH2PPh2 in CDCl3 is used. When the platinum(II) complex trans-[PtCl2(RCN)2] is reacted with 2 equiv of the amidine, the imidoylamidinato complexes [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) and [PhC(=NH)NHPh] x HCl (7) are formed. The reaction of trans-[PtCl2(RCN)2] with 4 equiv of the amidine under a prolonged reaction time or treatment of [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) with 2 more equiv of the amidine yields the complex bearing two chelate rings [Pt{NH=C(R)NC(Ph)=NHPh}2] (12-15). The treatment of cis-[PtCl2(RCN)2] (R = Me, Et) with the amidine gives ca. 50-60% yield of [PtCl2{NH=C(R)NHC(Ph)=NHPh}] (16 and 17). All of the platinum compounds were characterized by elemental analyses; FAB mass spectrometry; IR spectroscopy; 1H, 13C{1H}, and 195Pt NMR spectroscopies, and four of them (4, 6, 8, and 15) were also characterized by X-ray crystallography. The coupling of the Pt-bound nitriles and the amidine is metal-mediated insofar as RCN and PhC(=NH)NHPh do not react in the absence of the metal centers in conditions more drastic than those of the observed reactions. The nitrile-amidine coupling reported in this work constitutes a route to the synthesis of imidoylamidine complexes, some of them exhibiting luminescent properties.     

Synthesis, structure and magnetic properties of the first Mn(II)-Gd(III) heteronuclear complex

The synthesis and crystal structure of a novel pentanuclear Mn(II)-Gd(III) complex is reported; the magnetic measurement conclusively demonstrated anti-ferromagnetic behaviour between Mn(II) and Gd(III) for this complex.     

Synthesis and structures of the first cationic perfluoroaryllanthanoid(II) complexes

Tetraphenylborate salts of solvated pentafluorophenyllanthanoid(II) cations [Ln(C(6)F(5))(thf)(n)](+) (Ln=Eu, n=6 (1); Ln=Yb, n=5 (2)) were readily synthesized in high yield by reactions of ytterbium or europium with HgPh(C(6)F(5)) and Me(3)NHBPh(4) in THF. The structures of 1.THF and 2 confirmed the existence of well-separated ions and both 1 and 2 show notable thermal stability at room temperature. The cation in 2 was also observed in the remarkable mixed-valent complex [Yb(II)(C(6)F(5))(thf)(5)][Yb(III)(C(6)F(5))(2)[N(SiMe(3))(2)](2)] (3), fortuitously isolated in low yield from a reaction of ytterbium metal, HgPh(C(6)F(5)), and HN(SiMe(3))(2) in THF, and which additionally has an unusual bis(pentafluorophenyl)bis[bis(trimethylsilyl)amido)]ytterbate(III) anion. (171)Yb-(19)F coupling has been observed in the low-temperature (171)Yb NMR spectra of 2 and [Yb(C(6)F(5))(2)(thf)(4)].     

Synthesis and solid-state structural characterisation of Pt(II,IV) bromide complexes containing bidentate organothiomethylpyridine heteroleptic ligands

A convenient synthetic method for the preparation of organothiomethylpyridine ligands 2-(RSCH₂)C₅H₄N (R = Ph (L¹), Me (L²)), 2-MeS–6-Me-C₅H₃N (L³), and 2-MeS–4-Me-C₅H₃N (L⁴) via the initial lithiation of substituted 2-picolines followed by the nucleophilic reaction with a diorganyldisulfide is described. The complexes [PtBr₂L] (L = L¹–L⁴) have been prepared in good to high yields as yellow solids with low solubility in organic solvents. The solid state structures of the complexes have been determined, showing the spatial arrangement of the complexes to depend significantly upon varying substituents within the ligand. The complexes undergo oxidation by bromine to form the tetravalent complexes [PtBr₄(L)] (L = L¹–L⁴). The solid state structures of [PtBr₄(L²)] and [PtBr₄(L₄)] have been determined, and shown to be monomeric with the ligand chelating the platinum centre.     

Stereoisomeric Pt(IV) complexes with threonine

Stereoisomeric Pt(IV) complexes with threonine (ThrH = HOCH(CH₃)CH(NH₂)COOH, ??-amino-??-hydroxybutyric acid) were obtained. In the complexes trans-[Pt(S-ThrH)₂Cl₄] and trans-[Pt(R-ThrH)(S-ThrH)Cl₄], the ThrH molecules act as monodentate ligands coordinated through the NH₂ group. In the complexes cis- and trans-[Pt(S-Thr)₂Cl₂] and trans-[Pt(R-Thr)(S-Thr)Cl₂], the deprotonated ligands are coordinated in a bidentate fashion through the NH₂ and COO^?-groups (R,S is the absolute configuration of the asymmetric carbon atom). All the complexes were identified using elemental analysis, IR spectroscopy, and ¹⁹⁵Pt, ¹³C, and ¹H NMR spectroscopy. The complexes trans-[Pt(S-ThrH)₂Cl₄] · 3H₂O and cis-[Pt(S-Thr)₂Cl₂] · 2H₂O were additionally characterized by X-ray diffraction.     

The first acetimino complexes of Rh(III). 4-imino-2-methylpentan-2-amino-Rh(III) complexes through metal-assisted intramolecular aldol-type condensation of two acetimino ligands

[Rh(Cp)Cl(mu-Cl)](2) (Cp = pentamethylcyclopentadienyl) reacts (i) with [Au(NH=CMe(2))(PPh(3))]ClO(4) (1:2) to give [Rh(Cp)(mu-Cl)(NH=CMe(2))](2)(ClO(4))(2) (1), which in turn reacts with PPh(3) (1:2) to give [Rh(Cp)Cl(NH=CMe(2))(PPh(3))]ClO(4) (2), and (ii) with [Ag(NH=CMe(2))(2)]ClO(4) (1:2 or 1:4) to give [Rh(Cp)Cl(NH=CMe(2))(2)]ClO(4) (3) or [Rh(Cp)(NH=CMe(2))(3)](ClO(4))(2).H(2)O (4.H(2)O), respectively. Complex 3 reacts (i) with XyNC (1:1, Xy = 2,6-dimethylphenyl) to give [Rh(Cp)Cl(NH=CMe(2))(CNXy)]ClO(4) (5), (ii) with Tl(acac) (1:1, acacH = acetylacetone) or with [Au(acac)(PPh(3))] (1:1) to give [Rh(Cp)(acac)(NH=CMe(2))]ClO(4) (6), (iii) with [Ag(NH=CMe(2))(2)]ClO(4) (1:1) to give 4, and (iv) with (PPN)Cl (1:1, PPN = Ph(3)P=N=PPh(3)) to give [Rh(Cp)Cl(imam)]Cl (7.Cl), which contains the imam ligand (N,N-NH=C(Me)CH(2)C(Me)(2)NH(2) = 4-imino-2-methylpentan-2-amino) that results from the intramolecular aldol-type condensation of the two acetimino ligands. The homologous perchlorate salt (7.ClO(4)) can be prepared from 7.Cl and AgClO(4) (1:1), by treating 3 with a catalytic amount of Ph(2)C=NH, in an atmosphere of CO, or by reacting 4with (PPN)Cl (1:1). The reactions of 7.ClO(4) with AgClO(4) and PTo(3) (1:1:1, To = C(6)H(4)Me-4) or XyNC (1:1:1) give [Rh(Cp)(imam)(PTo(3))](ClO(4))(2).H(2)O (8) or [Rh(Cp)(imam)(CNXy)](ClO(4))(2) (9), respectively. The crystal structures of 3 and 7.Cl have been determined.     

Complexes of Pt(II) and Pt(IV) with disubstituted purines

Mixed-ligand complexes of Pt(II) and Pt(IV) with 2,6-diaminopurine and 6-thioguanine were synthesized and characterised. The complexes were prepared in acidic and basic media. The binding of the ligands to the metal ion varies according to the pH of the medium. Thus, in the complexes of 6-thioguanine, the ligand acts as a monodentate ligand coordinating through the neutral C₆-SH group in the acidic medium and in the basic medium as a bidentate ligand binding to the metal ion through C₆S^? and N₇, forming a five-membered chelate ring. In an acidic medium 2,6-diaminopurine forms mononuclear complexes with Pt(II) and Pt(IV) binding through N₇. In a basic medium binuclear hydroxobridged complexes are formed with Pt(IV) and the ligand is monodentate, coordinating through N₇.     

Synthesis and characterisation of the first carbene and diazabutadiene-indium(II) complexes

The reactions of IMes [:CN(Mes)C2H2N(Mes), Mes = mesityl] and DAB [(ArN=CH)2, Ar = C6H3Pri2-2,6] with indium(I) halides have afforded the first carbene and diazabutadiene indium(II) complexes, [In2Br4(IMes)2] and [In2Cl2(DAB.)2], both of which have been crystallographically characterised.     

Pnictogen-thiacrown complexes with Pt(II) and Pd(II)

Platinum(II) and palladium(II) complexes of the trithiacrown [9]aneS(3) containing a range of Group 15 donors are reviewed. These complexes have the general formula [M([9]aneS(3))(L(2))](n+) where L represents at least one Group 15 donor. Complexes involving pnictogens, with the exception of bismuth, are observed. The complexes generally have an elongated square pyramidal geometry with a long distance interaction to the third sulphur of the [9]aneS(3) which forms the apex of the square pyramid. This axial metal-sulphur distance is quite sensitive to the donor properties of L. Poorer donors such as Sb and As ligands show short axial distances whereas the better N donor ligands show longer distances. Pt(II) complexes of the formula [Pt([9]aneS(3))(EPh(3))(2)](2+) (E = P, As, Sb) show a considerable distortion towards a trigonal bipyramidal geometry due to intramolecular π-π interactions. Over seventy of these types of complexes have been crystallographically characterized and are discussed in this article. Other unique features of the complexes, including NMR spectroscopy, redox chemistry, and electronic spectroscopy, are also discussed.     

Synthesis and characterization of multimeric salicylaldimine thiosemicarbazones and their Pd(II) and Pt(II) complexes

A series of di- and trithiosemicarbazone ligands as well as their Pd(II) and Pt(II) 1,3,5-triaza-7-phosphaadamantane (PTA) complexes have been synthesised using templated reactions between various substituted salicylaldimine thiosemicarbazone ligands and metal precursors of the general formula cis-[M(PTA)₂Cl₂], where M = Pd or Pt. Characterization of these complexes was achieved using various analytical and spectroscopic techniques: elemental analysis, ESI-MS, FT-IR, and NMR (¹H, ¹³C{¹H} and ³¹P{¹H}) spectroscopy. The data revealed tridentate (O-N-S) coordination of the thiosemicarbazone moieties via the imine nitrogen, thiolato sulfur and phenolic oxygen to each metal center. In vitro biological evaluation of selected compounds was conducted against WHCO1 oesophageal cancer cells. Some of the multimeric compounds display some promising biological activity.     

Synthesis, structure and catalytic activity of thioether-phosphane complexes of Pd(II) and Pt(II)

New thioether-phosphanes 2-RSC6H4CH2PPh2(RS-PPh2: R = Me, tBu, Ph) and the corresponding complexes [PdCl2(MeS-PPh2)], [PdCl2(tBuS-PPh2)], [PdCl2(PhS-PPh2)], [PdClMe(MeS-PPh2)] and [PtMe2(MeS-PPh2)] have been prepared, characterized and the X-ray crystal structures of all complexes determined. Whilst Pd(II) complexes of RS-PPh2 show low activity for CO/ethene copolymerisation, the complexes [PdCl2(RS-PPh2)] have been found to be very efficient for the Heck arylation of n-butylacrylate with bromobenzene under aerobic conditions.     

Synthesis and structural features of 1,3,2,5-dioxaboraphosphorinane complexes with Pt(II) and Pd(II) salts

Complexes of composition L₂MCl₂ [M=Pt, R=H (I), Me (II), Ph (III)], and LMC1₂ [M=Pd, R=H (IV)] are prepared by reaction of 4,6-R₂-2,5-diphenyl-1,3,2,5-dioxaboraphosphorinanes (L) with MCl₂. Far-IR and³¹P NMR spectroscopy are used to demonstrate that I is cis whereas II and III are trans complexes in the solid. The conformational behavior of I is studied by³¹P and¹H NMR. The asymmetric form of I exhibits anomalous stability.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2309–2312, October, 1991.