Binuclear iron(III) compounds with bidentate bases

Summary Binuclear iron(III) derivatives, Fe₂Cl(anth)₅, Fe₂Cl(salH)₅, Fe₂Cl(acac)₅ and Fe₂Cl(quin)₅ · quinH have been prepared by reacting Fe₂Cl(OH)₂(AcO)₃ · 2AcOH with anthranilic acid (anthH), salicylic acid (salH₂), acetylacetone (acacH) and 8-hydroxyquinoline (quinH), respectively. These compounds have been characterised by molecular weight, conductance, i.r. spectral, magnetic susceptibility and Mössbauer measurements.     

Some compounds of iron(III) with bidentate bases

Summary The iron(III) compound, FeCl(OH)(MeCO₂) · MeCO₂H · 0.5 H₂O, (1), interacts with the sample bidentate ligand, 2,2-bipyridyl (bipy), to form an aduct, Fe₂Cl₂(OH)₂(MeCO₂)₂ · (bipy). By the loss of protons, anthranilic (anthH) and salicylic (salH₂) acids behave as uninegative charged ligands to give FeCl(anth)₂ · H₂O and FcCl(salH)₂ · H₂O, respectively. The former decomposes on heatingin vacuo to form Fe₂O(anth)₄ while the latter yields Fe₂O(sal)₂. Acetylacetone (acacH) and 8-hydroxyquinoline (quinH) give FeCl(acac)₂ and FeCl(quin)₂ · (quinH). The latter desolvates at 140°/10^–4 torr to form FeCl(quin)₂. l.r. spectra, thermal decomposition, molar conductance and magnetic susceptibility studies at room temperature have been used to characterize these compounds.     

Chiral and diastereoisomeric rhodium(I) coordination compounds with carvone as bidentate ligand

The chiral dienone p-mentha-6,8-dien-2-one (carvone) coordinates readily with rhodium(I) to form complexes of pronounced stability. Novel diastereoisomeric planar coordination compounds of rhodium(I) containing two chiral bidentate ligands have been prepared for the first time. The synthesis of the compounds is simple, and the yields are high.     

Molecular Mechanics Study of Cyclic and Unsymmetrical Diborane(4) Compounds

The results of a theoretical study on the structure of some diborane(4) compounds are presented in order to analyze the ralative stabilities of the 1,1- and 1,2-isomers. Using the molecular mechanics method, characteristic distances and angles have been calculated and compared with available experimental data. In order to rationalize the results, different energy components are discussed in a comparative fashion. A fairly satisfactory agreement between the theoretical and experimental data have been found. Some possible extensions are pointed out to complement this kind of analysis.     

Isolation and Characterization of Crystalline,Neutral Diborane(4) Radicals

Diaryldihalodiboranes(4) were reacted with bis(amidinato)‐ and bis(guanidinato)silylenes to generate the first neutral diborane‐centered radicals. These formally non‐aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid‐state structure determination, high‐resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4‐benzoquinone led to ring‐opening and B?O bond formation.     

Boranediyl- and Diborane(4)-1,2-diyl-Bridged Platinum A-Frame Complexes

Diplatinum A-frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)-bridged Pt⁰₂ complex. While structurally analogous to well-known μ-borylene complexes, in which delocalized dative three-center-two-electron M-B-M bonding prevails, theoretical investigations into the nature of Pt−B bonding in these A-frame complexes show them to be rare dimetalla(di)boranes displaying two electron-sharing Pt−B σ-bonds. This is experimentally reflected in the low kinetic stability of these compounds, which are prone to loss of the (di)boron bridgehead unit.     

Diborane(4) Azides: Surprisingly Stable Sources of Transient Iminoboranes

Herein we describe the first examples of isolable electron‐precise diboranes(4) that bear azide moieties: the acyclic 1,2‐diazido‐1,2‐bis(dimethylamino)diborane(4) and the cyclic 1,4‐diaryl‐2,3‐diazido‐1,4‐diaza‐2,3‐diborinines (aryl=mesityl, 2,6‐xylyl, 4‐tolyl). The reported examples are not only stable enough to be observed and isolated (putative transient diborane(4) azides previously reported by our group spontaneously decompose even below room temperature), but some of them are even robust enough to undergo controlled pyrolysis without explosive decomposition at temperatures well above 100 °C. In two cases, the controlled pyrolysis allows the isolation of complex diazaboretidines, which are the apparent dimerization products of endocyclic boryl‐iminoboranes.     

Controlling Regiochemistry in the Syntheses of Boraindanes from Diborane(4) Starting Materials

The reaction of tert‐butylisonitrile (tBuNC) with 1,2‐dihalo‐1,2‐diduryldiborane leads initially to the formation of the mono‐base adduct of the symmetrical diborane(4), which then undergoes an intramolecular cyclization resulting in the formation of a 1‐boraindane. This result is in contrast to a previously reported cyclization of a mono‐isonitrile adduct of an unsymmetrical 1,1‐pinacol‐2,2‐diaryldiborane(4), which results in the formation of a 1‐boraindane. This latter result is herein confirmed by the reaction of 1,1‐difluoro‐2,2‐dimesityldiborane(4) with tBuNC, which yielded the 2‐boraindane compound. The mechanism of the former reaction has been computationally elucidated, and the differences between this route and the pathway to 1‐boraindanes is discussed. These reactions further the understanding of the chemistry of the increasingly popular mono‐base adducts of diborane(4), demonstrate the versatility of isonitriles in comparison to standard two‐electron donors, and elucidate selective routes to boron‐containing polycyclics, such as those being proposed as analogues for conventional organic pharmaceuticals.     

Dirhodium formamidinate compounds with bidentate nitrogen chelating ligands

The reactions of [Rh(2)(DTolF)(2)(CH(3)CN)(6)][BF(4)](2) (1) (DTolF = N,N'-di-p-tolylformamidinate) with 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) proceed with substitution of CH(3)CN molecules to give products with the N-N ligands chelating in an equatorial-equatorial (eq-eq) fashion. Compound 1 reacts with 1 equiv of bpy to yield a mixture of [Rh(2)(DTolF)(2)(bpy)(CH(3)CN)(3)][BF(4)](2).(CH(3))(2)CO (2a) and [Rh(2)(DTolF)(2)(bpy)(CH(3)CN)(4)][BF(4)](2) (2b). Compound 2a crystallizes in the monoclinic space group P2(1)/n with a = 13.5856(2) A, b = 18.0402(2) A, c = 21.4791(3) A; alpha = 90 degrees, beta = 101.044(1) degrees, gamma = 90 degrees; V = 5167.27(12) A(3), Z = 4, R = 0.0531, and R(w) = 0.0948. Compound 2b crystallizes in the monoclinic space group P2(1)/n with a = 10.9339(2) A, b = 24.4858(1) A, c = 19.4874(3) A; alpha = 90 degrees, beta = 94.329(1) degrees, gamma = 90 degrees; V = 5202.38(13) A(3), Z = 4, R = 0.0459, and R(w) = 0.1140. The reaction of compound 1 with 2 equiv of bpy affords [Rh(2)(DTolF)(2)(bpy)(2)(CH(3)CN)][BF(4)](2) (3) which crystallizes in the monoclinic space group P2(1)/a with a = 19.4534(4) A, b = 13.8298(3) A, c = 19.8218(5) A; alpha = 90 degrees, beta = 109.189(1) degrees, gamma = 90 degrees; V = 5036.5(2) A(3), Z = 4, R = 0.0589, and R(w) = 0.0860. Compound 1 reacts with 1 equiv of phen to form [Rh(2)(DTolF)(2)(phen)(CH(3)CN)(3)][BF(4)](2).2C(2)H(5)OC(2)H(5) (4) which crystallizes in the triclinic space group P1macro with a = 12.6346(2) A, b = 13.5872(2) A, c = 19.0597(3) A; alpha = 71.948(1) degrees, beta = 73.631(1) degrees, gamma = 71.380(1) degrees; V = 2886.70(8) A(3), Z = 2, R = 0.0445, and R(w) = 0.1207. A notable feature of the cations in 2a, 3, and 4 is the presence of only one axial (ax) CH(3)CN ligand, a fact that can be attributed to the steric effect of the formamidinate bridging ligands. Compounds 2a, 2b, 3, and 4 were fully characterized by X-ray crystallography and (1)H NMR spectroscopy, whereas [Rh(2)(DTolF)(2)(phen)(2)(CH(3)CN)(2)][BF(4)](2) (5) was characterized by (1)H NMR spectroscopy.     

Diborane(4)-metal bonding: between hydrogen bridges and frustrated oxidative addition

The metal complexes [M{HB(hpp)}(2)(CO)(4)] (M = Cr, Mo or W) and [M(cod){HB(hpp)}(2)Cl] (M = Rh or Ir) of the doubly-base stabilized diborane(4) ligand [HB(hpp)](2) were fully characterized and their bonding nature was investigated in detail. While bonding in the group 6 complexes predominantly occurs through the hydrogen atoms, the metal-ligand interaction in the group 9 complexes can be regarded as an early stage oxidative addition of the boron-boron bond leading to diboryl compounds.     

Symmetric Ni(II) dithiocarbamates with bidentate phosphines ligands

Ni(II) mononuclear dithiocarbamate complexes with bidentate P,P ligands of composition [Ni(R₂dtc)(P,P)]X {R?=?pentyl (pe), benzyl (bz); dtc?=?S₂CN^?; P,P?=?1,2-bis(diphenylphosphino)ethane (dppe), 1,4-bis(diphenylphosphino)butane (dppb), 1,1′-bis(diphenylphosphino) ferrocene (dppf); X?=?ClO₄, Cl, Br, NCS} and binuclear complexes of composition [Ni₂(μ-dpph)(R₂dtc)₂]X₂ with a P,P-bridging ligand {P,P?=?1,6-bis(diphenylphosphino)hexane (dpph); X?=?Cl, Br, NCS} have been synthesized. The complexes have been characterized by elemental and thermal analysis, IR, electronic and ³¹P{¹H}-NMR spectroscopy, magnetochemical and conductivity measurements. Single crystal X-ray analysis of [Ni(pe₂dtc)(dppf)]ClO₄ confirmed a distorted square planar coordination in the NiS₂P₂ chromophore. For selected samples, the catalysis of graphite oxidation was studied.     

ChemInform Abstract: Identification of Diborane(4) with Bridging B—H—B Bonds.

Photolysis of B₂H₆ dispersed in solid neon with far‐UV light (120—220 nm) at 3 K leads to the formation of B₂H₄, which is characterized by IR spectroscopy and B3LYP quantum chemical computations.     

Neutral bidentate organophosphorus compounds as novel ionophores for potentiometric membrane sensors for barium(II)

Bis(diarylphosphine oxide) naphthalene compounds are used as novel ionophores in plasticized poly(vinyl chloride) matrix membrane sensors for barium ions. The most favorable sensor was 1,2-bis(diethylphenylphosphine oxide)naphthalene containing potassium tetrakis(4-chlorophenyl)borate as lipophilic salt and o-nitrophenyloctyl ether as plasticizer for ion-selective electrode membrane construction. The electrode showed excellent properties. It gave a linear response with a Nernstian slope of 30 mV per decade within the concentration range 10(-1)-10(-5) mol L(-1) BaCl2. The electrode exhibits a high selectivity towards Ba2+ with respect to Li+, Na+, K+, Rb+, Cs+, NH4+, Ag+, Mg2+, Ca2+, Sr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+, Al3+, La3+, and Ce3+ ions. The electrode response was stable over a wide pH range (3-11). The lifetime of the electrode was about 2 months. It was successfully applied to the determination of Ba2+ contents in some rocks.     

Synthesis, structure and isomerization of arylphosphoranes with anti-apicophilic bonding modes using a novel bidentate ligand with two C(2)F(5) groups

A series of anti-apicophilic pentacoordinate phosphoranes (with one chelating substituent in an O-equatorial, C-apical bonding mode at pentacoordinated phosphorus atom) bearing a para-substituted aryl group (-C(6)H(4)(p-X); X = H, CF(3), F, OMe) or a mesityl (2,4,6-trimethylphenyl) group were isolated using a novel bulky bidentate ligand with two C(2)F(5) groups. These phosphoranes were stable to isomerization at room temperature, and quantitatively converted into the corresponding more stable isomers (O-apical) at elevated temperatures in solution. On the basis of a kinetic study, the free energy of activation (DeltaG(double dagger)) of the stereomutation of the O-equatorial mesitylphosphorane to its O-apical isomer was higher than that of the CF(3) derivative by 2.6 kcal mol(-1), giving rise to a further example of the steric effect of the C(2)F(5) group to freeze the isomerization of the pentacoordinate phosphorus compounds. Kinetic measurements of the isomerization of the O-equatorial ortho-unsubstituted derivatives (-C(6)H(4)(p-X)) to the corresponding O-apical isomers suggested that the O-equatorial isomers were stabilized by the pi --> sigma*(P-O) interaction in the ground state.     

Unique Rearrangement of an Oxycarbyne Complex: Synthesis and Structure of Novel Diborane(4)yl Complexes

Nucleophilic attack of a carbonyl oxygen atom of the complexes K[(η⁵-C₅H₅)M(CO)₃] (M=Mo, W) on each boron center gave the oxycarbyne complexes 1 . These novel products undergo a unique type of rearrangement with quantitative formation of the diborane(4)yl complexes 2 . Complex 2 (M=Mo) is the first structurally characterized boryl complex with a Mo–B bond (see structure).     

Reactions of dichloro-bis(cyclopentadienyl)titanium(IV) with bidentate Schiff bases

A series of Cp₂Ti(SB)Cl complexes, whereSB is the anion of bidentate Schiff bases derived from salicylaldehyde and different primary aminesviz o-anisidine,m-anisidine,o-phenetidine,o-chloroaniline,m-chloroaniline,m-nitroaniline, α-naphthylamine and benzylamine, have been synthesised by the reaction of dichloro-bis(cyclopentadienyl) titanium(IV), Cp₂TiCl₂, and bidentate Schiff base (sbh) in a 1:1 molar ratio in refluxingthf in the presence of triethylamine. The new derivatives have been characterised on the basis of their elemental analyses, conductance measurements and spectral (IR,¹Hnmr and electronic) studies