Coordination chemistry of higher oxidation states. Part 21. Platinum-195 NMR studies of platinum(II) and platinum(IV) complexes of bi- and multi-dentate phosphorus,arsenic and sulphur ligands

195-Platinum NMR spectra are reported for a series of complexes of bidentate ligands [Pt(LL)X₄] (X=Cl, Br; LL=diphosphine, diarsine, dithioether, diselenoether), [Pt(Me₂PCH₂CH₂PMe₂)₂X₂]X₂, [Pt(o-C₆H₄(AsMe₂)₂)₂X₂]X₂, and for the Pt(II) analogues. The trends in chemical shifts δ(Pt) and ¹J(PtP), ¹J(PtSe) coupling constants are discussed, and used to establish the nature of the solution species obtained by oxidation of Pt(II) complexes of some multidentate phosphorus and arsenic ligands. The [Pt(LL)I₄] materials are shown to exist as [Pt^II(LL)I₂] in dimethylsulphoxide solution, but [Pt(o-C₆H₄(AsMe₂)₂)₂I₂]²⁺ is a genuine Pt(IV) iodo-complex.     

Isokinetic Relationship in the Oxidation of Cuprous Stellacyanin by Cobalt(III) Complexes

Rate parameters have been obtained for the oxidation of cuprous stellacyanin by cobalt(III) ions of the form cis(N)-[CoN₂O₄]^?, including cis(N)-[Co(NTA)(gly)]^?, cis(N)-[Co(IDA)₂]^?, [Co(en)(ox)₂]^?(μ 0.5 M(phosphate), pH 7.0), and Co(EDTA)^?(μ 0.1 M(NaCl), pH 7.2, 0.001 M phosphate). An excellent isokinetic correlation between the activation parameters ΔH^≠ and ΔS^≠ exists for the reactions of aminopolycarboxylatocobalt(III) ions with reduced stellacyanin (β = 300 ± 12 K; correlation coefficient = 0.995). It is concluded that enthalpy-entropy compensation in these reactions may be understood in terms of differing orientations preferred by the various oxidants in forming precursor complexes with the reduced blue protein. While ΔH^≠ and ΔS^≠ values for electron transfer from stellacyanin to cis(N)-[CoN₂O₄]^? ions vary over ranges of 10.7 kcal/mol and 34 cal/mol-deg, respectively, room temperature rate constants are relatively constant (3.6–34.5 M^?1 sec^?1), as expected from Marcus theory for outer sphere electron transfer.     

Dinuclear complexes with a μ-cyano ligand. Part X. Synthesis and characterization of several derivatives of cis-diaquaamminecobalt(III) complexes. Influence of pH

Six new dinuclear complexes, derived from cis-[Co(H₂O)₂(NH₃)₄]³⁺, cis-[Co(H₂O)₂(en)₂]³⁺ and [M(CN)₄^2? (M = Ni, Pd, Pt) were prepared and characterized by means of chemical analysis, electronic and IR measurements. The influence of the pH on the rate of the reaction was studied for the two derivatives of [Pd(CN)₄]^2?, showing that the best conditions to obtain the dinuclear compounds are at pH near 6, where the predominant species are cis-[Co(OH)(H₂O)(amine)₂]²⁺. The [Pt(CN)₄]^2? derivatives show PtPt interactions both in the solid state and in solution.     

Transition metal nitrosyls as nitrosylation agents. IV. 51V NMR characteristics of dinitrosyl and carbonylmononitrosyl vanadium complexes

The action of [Co(X)(NO)₂]₂ (X = Cl, Br, L) on [V(H)(CO)_6?nL_n] (L = 1/ndi- and tritertiary phosphine; n = 2, 3) in thf yields [V(CO)_5?n(NO)L₂] and [V(NO)₂(thf)₄]X as the two main products. Thf is easilty replaced by other ligands L′, leading to the complexes cis-[V(NO)₂(thf)_4?nL′_n]X, where n = 1 to 4. In the case of L′= CNR (R = Cy, iPr, tBu), the species [VX(NO)₂L′₃] are formed. The presence of X in the first coordination sphere is established by the normal halogen dependence (Cl < Br < I) of ⁵¹V shielding.δ(⁵¹V) values have been obtained for the two series of complexes and compared with δ of other nitrosylvanadium species, including [VX(NO)L′₄]X. for [V(NO)₂L′₄]br, ⁵¹V shielding increases in the sequence {O} < {S} < NR₃ < NCMe < AsEt₃ < SbEt₃ < PEt₂Ph < P(OMe)₃ < CNR, reflecting a general increase of shielding as the polarizability of the ligand function increases and its electronegativity decreases. Superimposed effects arising from electronic influences (PEtPh₂) < PMe₃ < P(OMe)₃ and steric conditions (chelate-4 ring < 7 ring < 6 ring < 5 ring) are also discussed. Steric factors are especially pronounced in the [V(CO)₃(NO)Ph₂P(CH₂)_mPPh₃] series (m = 1–4). The thermo-labile parent compound, [V(CO)₅NO], has been characterized by its δ(⁵¹V) = ?1489 ppm at 245 K.     

Reactions of the cationic monobut-2-yne complex [WI(CO)(NCMe)(dppm)(η2-MeC2Me)][BF4] {dppm = Ph2P(CH2)PPh2} with carbon monoxide and tButylisonitrile

The compound [WI(CO)(NCMe)(dppm)(η²-MeC₂Me)][BF₄] reacts with carbon monoxide and ^tbutylisonitrile in CH₂Cl₂ at room temperature to give the substituted products [WI(CO)₂(dppm)(η²-MeC₂Me)][BF₄] (1) and [WI(CO)(CN^tBu)(dppm)(η²-MeC₂Me)][BF₄] (2) in good yield. The new complexes were fully characterised by elemental analysis, infrared, ¹H and ¹³C NMR spectroscopy. ¹³C NMR spectroscopy suggests that the but-2-yne ligand is donating four electrons to the tungsten in these complexes.     

Coordination chemistry of higher oxidation states. Part 15. Cobalt(III) complexes of bi- and multi-dentate phenylphosphines

Six-coordinate cobalt(III) complex trans-[Co{o-C₆H₄(PPh₂)₂}₂X₂]ClO₄, fac-[Co{PhP(CH₂CH₂PPh₂)₂}X₃],cis-[Co{P(CH₂CH₂PPh₂)₃}X₂]ClO₄ and cis-β-[Co{-CH₂P(Ph)CH₂CH₂PPh₂}₂X₂]PF₆ (X = Cl, Br) have been prepared by halogen oxidation of the Co(II) analogues, and characterised by IR, electronic and ³¹P NMR spectroscopy. The failure to obtain complexes with X = I, and with some related ligands is discussed, and the rather low stability of the above complexes is rationalised in terms of steric crowding at the metal centre.     

Synthesis and spectroscopic properties of CpRuCl(R-DAB(4e)) and CpRuCo(CO)3(R-DAB(6e)). Part XVII. X-ray structure determination of CpRuCo(CO)3(t-Bu-DAB(6e))

CpRuCl(PPh₃)₂ reacted with excess R-DAB in refluxing toluene to give CpRuCl(R-DAB(4e)) (1a: R = i-Pr; 1b: R = t-Bu; 1c: R = neo-Pent; 1d: R =p-Tol). ¹H NMR and ¹³C NMR spectroscopic data indicated that in these complexes the R-DAB ligand is bonded in a chelating 4e coordination mode.Reaction of 1a and 1b with one equivalent of [Co(CO)₄]⁻ afforded CpRuCo(CO)₃(R-DAB(6e)) (2a: R = i-Pr; 2b: R = t-Bu). The structure of 2b was determined by a single crystal X-ray structure determination. Crystals of 2b are monoclinic, space group P2₁/n, with four molecules in a unit cell of dimensions: a = 16.812(4), b = 12.233(3), c = 9.938(3) Å and β = 105.47(3)°. The structure was solved via the heavy atom method and refined to R = 0.060 and R_w = 0.065 for the 3706 observed reflections. The molecule contains a RuCo bond of 2.660(3) Å and a cyclopentadienyl group that is η⁵-coordinated to ruthenium [RuC(cyclopentadienyl) = 2.208(3) Å (mean)]. Two carbonyls are terminally coordinated to cobalt (CoC(1) = 1.746(7) and CoC(2) = 1.715(6) Å) while the third is slightly asymmetrically bridging the RuCo bond (RuC(3) = 2.025(6) and CoC(3) = 1.912(6) Å). The RuC(3)O(3) and CoC(3)O(3) angles are 138.4(5)° and 136.5(5)°, respectively. The t-Bu-DAB ligand is in the bridging 6e coordination mode: σ-N coordinated to Ru (RuN(2) = 2.125(4) Å), μ₂-N′ bridging the RuCo bond and η²-CN coordinated to Co (RuN(1) = 2.113(5), CoN(1) = 1.941(4) and CoC(4) = 2.084(5) Å). The η²-CN′ bonded imine group has a bond length of 1.394(7) Å indicating substantial π-backbonding from Co into the anti-bonding orbital of this CN bond.¹H NMR spectroscopy indicated that 2a and 2b are fluxional on the NMR time scale. The fluxionality of 6e bonded R-DAB ligands is rarely observed and may be explained by the reversible interchange of the σ-N and η²-CN′ coordinated imine parts of the R-DAB ligand.     

Inner sphere oxidation of L-ascorbic acid by Ru(III) ion and its complexes in aqueous acidic medium

The kinetics of electron transfer from L-ascorbic acid [H₂A] to oxidants, dichlorotetraaquoruthenium(III) [RuCl₂(H₂O)₄]⁺, iminodiacetatoruthenium(III) [Ru(III)IMDA]⁺ and ethylenediaminetetraacetatoruthenate(III) [Ru(III)EDTA]⁻ exhibit a first order dependence both on L-ascorbic acid and oxidants and inverse first order dependence on hydrogen ion concentration. Kinetic, spectroscopic and thermodynamic parameters are reported for the formation of intermediate Ru(III) (1:1) and Ru(III)chelateascorbate (1:1:1) complexes during the oxidation of L-ascorbic acid. The results are interpreted in terms of a mechanism involving a rate-determining inner sphere one electron transfer from L-ascorbic acid to the oxidants used in the present investigation, followed by a subsequent and kinetically rapid transfer of the second electron of ascorbic acid to another molecule of the oxidant. A detailed discussion of the kinetic data, temperature and ionic strength dependence of the oxidation reactions is presented.     

New nickel complexes with an S4 coordination sphere; synthesis, characterization and reactivity towards nickel and iron compounds

Three new nickel complexes have been synthesized with the ligands Hbss (4-mercapto-2-thia-1-butylbenzene) and Hbsms (2-(benzylsulfanyl)-2-methyl-1-propanethiol). [Ni(bss)₂] is a mononuclear complex with an S₄ coordination environment. [Ni₃(bss)₄](BF₄)₂ and [Ni₃(bsms)₄](BF₄)₂ are linear trinuclear complexes that can be synthesized either directly from the ligands Hbss and Hbsms in a reaction with Ni(BF₄)₂, or via the mononuclear complexes [Ni(bss)₂] and [Ni(bsms)₂] in a reaction with Ni(BF₄)₂. These reactions have been monitored with ligand field spectroscopy. Crystals suitable for X-ray diffraction were obtained for [Ni₃(bss)₄](BF₄)₂. The complex crystallizes in the space group P2₁/c. The nickel centers are in a square-planar environment; two peripheral nickel centers with an S₂S₂^′ (S=thiolato; S^′=thioether) coordination environment and the central nickel ion with an S₄ coordination environment.The mononuclear nickel complexes [Ni(bss)₂] and [Ni(bsms)₂] were reacted with FeCl₂, resulting in the hetero-tetranuclear nickel-iron complexes [Ni(bss)₂FeCl₂]₂ and [Ni(bsms)₂FeCl₂]₂. All complexes were characterized by analytical and spectroscopic methods.     

Extending the coordination chemistry of cobalt with the metalloligand [Pt2(μ-S)2(PPh3)4]: Synthesis of the first cobalt(III) derivatives

The coordination chemistry of the metalloligand [Pt₂(μ-S)₂(PPh₃)₄] towards cobalt(II) and cobalt(III) centres has been explored using an electrospray ionisation mass spectrometry (ESI MS)-directed methodology. Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with CoCl₂·6H₂O in methanol gave a green-yellow suspension of the known adduct [Pt₂(μ-S)₂(PPh₃)₄CoCl₂], and the CoBr₂ adduct could be similarly prepared. When in situ-generated [Pt₂(μ-S)₂(PPh₃)₄CoCl₂] is reacted with 8-hydroxyquinoline (HQ) and base, the initial product is the cobalt(II) adduct [Pt₂(μ-S)₂(PPh₃)₄CoQ]⁺, which is then converted in air to the cobalt(III) adduct [Pt₂(μ-S)₂(PPh₃)₄CoQ₂]⁺, isolated as its hexafluorophosphate salt. The corresponding picolinate (Pic) derivative [Pt₂(μ-S)₂(PPh₃)₄Co(Pic)₂]⁺ was similarly prepared, however reaction of [Pt₂(μ-S)₂(PPh₃)₄], CoCl₂·6H₂O and 8-(tosylamino)quinoline (HTQ) produced only the cobalt(II) adduct [Pt₂(μ-S)₂(PPh₃)₄CoTQ]⁺. Reactions of [Pt₂(μ-S)₂(PPh₃)₄], CoCl₂·6H₂O and dithiocarbamates gave cobalt(III) complexes [Pt₂(μ-S)₂(PPh₃)₄Co(S₂CNR₂)₂]⁺ [R = Et or R₂ = (CH₂)₄], and proceeded much more rapidly, consistent with the known ability of the dithiocarbamate ligand to stabilize cobalt in higher oxidation states. A study of the fragmentation of cobalt(III) adducts by positive-ion ESI mass spectrometry indicated that [Pt₂(μ-S)₂(PPh₃)₄CoQ₂]⁺ fragments to form the radical cation [Pt₂(μ-S)₂(PPh₃)₄]⁺, which could also be generated by ESI MS analysis of [Pt₂(μ-S)₂(PPh₃)₄] in methanol-NaOH solution. In contrast, the corresponding indium(III) derivative [Pt₂(μ-S)₂(PPh₃)₄InQ₂]⁺, and the cobalt(III) dithiocarbamate [Pt₂(μ-S)₂(PPh₃)₄Co(S₂CN(CH₂)₄)₂]⁺ are much more reluctant to fragment under analogous conditions, and the differences are discussed in terms of cobalt(III) redox chemistry.     

Catalytic effect of cis-diammineplatinum α-pyrrolidone tan adsorbed on a platinum electrode in electrochemical oxidation of water into molecular oxygen

Cyclic voltammograms of cis-diammineplatinum α-pyrrolidone-blue and -tan, [Pt₄(NH₃)₈(C₄H₆NO)₄]ⁿ⁺ (n = 5 and 6, respectively) show for either complex only one redox peak at 0.53 V (average potential of the anodic and cathodic peak potentials). Coulometry and UVVis spectra of bulk- electrolyzed solution indicated that the redox peak corresponds to the reaction [Pt₄(NH₃)₈(C₄H₆NO)₄]⁸⁺ + 4e ⇄ 2[Pt₂(NH₃)₄(C₄H₆NO)₂]²⁺. When cyclic voltammetry is carried out in a solution of [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ or a platinum electrode adsorbed with [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ is used in the presence of oxidizing agent in the solution, O₂ gas generates from the electrode surface with large catalytic cathodic current at potentials below ca. 0.8 V. The O₂ gas was confirmed to generate from water by GC-MS analysis. This abnormal O₂ generation phenomenon is explained with cyclic reactions of chemical surface oxide formation on the electrode by the oxidizing agent and electrochemical reduction of the surface oxide. Oxygen gas generates from the reaction of [Pt₄(NH₃)₈(C₄H₆NO)₄]⁸⁺ or [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ with OH⁻ produced in the course of the electrochemical reduction of the electrode surface oxide. The ability of [Pt₄(NH₃)₈(C₄H₆NO)₄]⁸⁺ and [Pt₄(NH₃)₈(C₄H₆NO)₄]⁶⁺ to oxidize OH⁻ into O₂ has been reported previously.     

Synthesis and coordination chemistry of a diphospha-tetrathia macrocycle, 1,10-diphenyl-1,10-diphospha-4,7,13,16-tetrathiacyclooctadecane

Reaction of 1,2-dichloroethane with PhP(CH₂CH₂SH)₂ and caesium carbonate affords 1,10-diphenyl-1,10-diphospha-4,7,13,16-tetrathiacyclooctadecane (18P2S4) in high yield (ca. 90%). 18P2S4 slowly decomposes in solution to afford insoluble PhP(S)(CH₂CH₂SCH₂CH₂SCH₂CH₂)₂P(S)Ph which was characterised by single crystal X-ray diffraction. Reaction of 18P2S4 with [Ni(H₂O)₆](BF₄)₂ or Fe(BF₄)₂ affords [M(18P2S4)](BF₄)₂ (M = Ni or Fe). The structure of [Ni(18P2S4)]²⁺ is a tetragonally distorted octahedron in which there are two short Ni-S bonds [2.2152(6) Å] and two long Ni-S bonds [2.9268(6) Å]. For comparison the structure of [Ni(9PS2)₂]²⁺ was determined and found to a have a similar, but less marked distortion, in which the difference between the long and short bonds is ca. 0.5 Å. In contrast the structure of [Fe(18P2S4)]²⁺ is octahedral with approximately equal Fe-S bonds. The electrospray mass spectra of the cations [M(9PS2)₂]²⁺ and [M(18P2S4)]²⁺ (M = Ni or Fe) all display ethene loss from the ligands as has been previously observed with trithiacyclononane complexes. The results of P-C and C-S bond rupture were also observed in the reaction of ruthenium(III) triflate with 9PS2 which unexpectedly afforded crystals containing [Ru₂(S)₂(18P2S4)₂], in which the two ruthenium centres are bridged by two sulfides and the two 18P2S4 ligands coordinated only through the phosphine centres. Also present in the crystals was one equivalent of tetrathiacycloundecane (12S4).     

Reactivity of [PdCl(μ-med)]2 with monodentate or bidentate ligands. Structure of the dinuclear complexes [Pd(μ-med)(PPh3)]2(BF4)2 and [Pd(μ-med)(bpy)]2(BF4)2. [Hmed=N-(2-mercaptoethyl)-3,5-dimethylpyrazole]

Treatment of the ligand N-(2-mercaptoethyl)-3,5-dimethylpyrazole with [Pd(CH₃COO)₂]₃ and reaction of [PdCl(μ-med)]₂ with pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ produced the following complexes: [Pd(CH₃COO)(μ-med)]₂, [Pd(μ-med)(py)]₂(BF₄)₂ and [Pd(μ-med)(PPh₃)]₂(BF₄)₂. Similar reactions carried out with 2,2^′-bipyridine (bpy) or 1,3-bis(diphenylphosphino)propane (dppp) produced [Pd(μ-med)(bpy)]_x(BF₄)_x (x=1 or 2) and [Pd(μ-med)(dppp)]_x(BF₄)_x (x=1 or 2). Treatment of [Pd(μ-med)(bpy)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced [Pd₃Cl₂(μ-med)₂(bpy)₂](BF₄)₂. Treatment of [Pd(μ-med)(dppp)]_x(BF₄)_x with [PdCl₂(CH₃CN)₂] produced a mixture of [Pd(μ-Cl)(dppp)]₂(BF₄)₂ and [Pd(μ-med)₂(dppp)]²⁺. X-ray crystal structures of [Pd(μ-med)(PPh₃)]₂(BF₄)₂ · 2CH₃CN and [Pd(μ-med)(bpy)]₂(BF₄)₂ · 0.5CH₃OH are presented.     

Ni(II), Pd(II), and Pt(II) complexes of two new ditertiary phosphines, 1-diphenylphosphino-2-bis(m- or p-fluorophenyl) phosphinoethane

New complexes of the type cis-[MX₂(PP′)] (M= Ni, Pd and Pt; X=Cl, Br, I or NCS and PP′=(m- FC₆H₄)₂PCH₂CH₂PPh₂ or (p-FC₆H₄)₂PCH₂CH₂PPh₂) have been synthesized and characterized on the basis of ³¹P{¹H}NMR¹H NMR, IR and UV spectroscopy, elemental analysis and magnetic susceptibility measurements. All these complexes are found to be low spin, diamagnetic and square planar. ³¹P{¹H} spectra of these complexes exhibit extraordinarily large downfield coordination chemical shifts, J(³¹P³¹P′) and J(¹⁹⁵pt³¹P) couplings are discussed. Ring contribution (ΔR) values for palladium and platinum complexes are calculated from ³¹P NMR data.     

Transition-metal(II) thiocyanate coordination compounds containing 4-allyl-1,2,4-triazole. Structure and magnetic properties.

The synthesis and characterisation of a series of dinuclear and polynuclear coordination compounds with 4-allyl-1,2,4-triazole are described. Dinuclear compounds were obtained for Mn(II) and Fe(II) with composition [M₂(Altrz)₅(NCS)₄], and for Co(II) and Ni(II) with composition [M₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂. The crystal structure of [Co₂(Altrz)₄(H₂O)(NCS)₄](H₂O)₂ was solved at room temperature. It crystallizes in the monoclinic space group P2₁/n. The lattice constants are a = 18.033(3) Å, b = 13.611(2) Å, c = 15.619(3) Å, β = 92.04(2)° Z = 4. One cobalt ion has an octahedrally arranged donor set of ligands consisting of three vicinal nitrogens of 1,2-bridging triazoles (CoN = 2.14–2.15 Å), one terminal triazole nitrogen (CoN = 2.12 Å) and two N-bonded NCS anions (CON = 2.08 Å). The other Co(II) ion has the same geometry, but the terminal triazole ligand is replaced by H₂O (CoO = 2.15 Å). The crystal structure is stabilised by hydrogen bonding through H₂O molecules, S-atoms of the NCS anions and the lone-pair electron of the monodentate triazole. The magnetic exchange in the Mn, Co and Ni compounds is antiferromagnetic with J-values of ?0.4 cm^?1, ?10.9 cm^?1 and ?8.7 cm^?1 respectively. The Co compound was interpreted in terms of an Ising model. For [Zn₂(Altrz)₅(NCS)₂]∞[Zn(NCS)₄], [Cu₂(Altrz)₃(NCS)₄]∞ and [Cd₂(Altrz)₃(NCS)₄]∞ chain structures are proposed. In the Cu compound thiocyanates appear to be present, bridging via the nitrogen atom, as deduced from the IR spectrum.     

Synthesis and spectroscopy of diethyl (pyridinylmethyl)phosphates and their palladium (II) complexes: X-ray crystal structures of Pd(II) complexes

The synthesis of diethyl (pyridin-2-, -3-, -4-ylmethyl)phosphate (2-pmOpe, 3-pmOpe, 4-pmOpe) ligands and their palladium (II) complexes of general formula trans-[PdCl₂L₂] (L = 2-pmOpe, 3-pmOpe,4-pmOpe) has been described. Pyridine phosphate derivatives were synthesized via the condensation of phosphorochloridic acid diethyl ester with an appropriate pyridinylmethanol in the presence of triethylamine. The compounds have been identified and characterized by IR, far-IR, ¹H NMR, ³¹P NMR, ³¹P CP-MAS NMR and elemental analyses. The crystal and molecular structures of palladium (II) complexes, i.e., [PdCl₂(2-pmOpe)₂] and [PdCl₂(4-pmOpe)₂] determined by the X-ray diffraction method, are presented. In both structures, Pd(II) ions are four-coordinated by two chlorine atoms and two pyridine nitrogen atoms. The geometry of complexes is square-planar and adopt a trans configuration, which is consistent with preparation method.     

Mono- and bis-cobalt complexes with carbonyl, nitrosyl, and monocarbollide ligands

Reaction of [Co(CO)₃(NO)] with [2-NMe₃-closo-2-CB₁₀H₁₀] in refluxing CH₂Cl₂ affords the mono- and di-cobalt complexes [1-NMe₃-2-CO-2-NO-closo-2,1-CoCB₁₀H₁₀] (3) and [2,7-{Co(CO)(NO)}-7-(μ-H)-1-NMe₃-2-CO-2-NO-closo-2,1-CoCB₁₀H₉] (4), respectively, of which 4 contains formally both Co(I) and Co(-I) centers. Compound 4 reacts with CO to give 3, or with donor ligands L in the presence of Me₃NO to afford simple substituted species, [1-NMe₃-2-L-2-NO-closo-2,1-CoCB₁₀H₁₀] (compounds 5; L = PEt₃, PPh₃, CNBu^t).     

Synthesis and characterization of cobalamines with anionic and neutral phosphorous donor ligands

In dimethyl formamide as solvent aquacobalamine reacts with the triorganyl phosphites 3–7 to give the corresponding (diorganylphosphito-P)cobalamines, their new β-axial ligands [P(O)(OR)₂]⁻ (3a–7a) being formed by partial hydrolysis. In methanol, however, additional methanolysis normally leads to (dimethylphosphito-P)cobalamine with the axial ligand [P(O)-(OMe)₂]⁻ (2a). Exceptions are P(OCH₂CH₂NMe₂)₃ (4) giving a complex with the only partially methanolized chiral ligand [P(O)(OCH₂CH₂NMe₂)- (OMe)]⁻ (4b), too, and the bicyclic phosphite 5 which is also coordinated in the unchanged, nonhydrolyzed form. All complexes are characterized by elementary analysis, electrophoresis, UVVis and ¹H, ³¹P NMR spectra. The chirality of the cobalamine moiety causes diatropism of the two organyl groups in the prochiral ligands [P(O)(OR)₂]⁻ which is well seen in the NMR spectra of the complexes with the methyl and phenyl derivatives 2a and 6a, whereas the spectra with ligands 3a and (in part) 4a are not resolved well enough to distinguish the two forms. With the chiral ligand 4b two diastereomers are obtained in different yields; this asymmetric induction is indicated by the intensities of the respective signals in the NMR spectra.     

Comparative reactivity study of cyclopentadienyl and fulvalene molybdenum complexes

The reactions of cis-1,1′-[η⁵:η⁵-(C₅H₃CO₂Me)₂]Mo₂(CO)₆ (1), in the presence of 1 equiv. of Me₃NO, and [(η⁵-C₅H₄CO₂Me)Mo(CO)₃]₂ (2) with dppe produce CO labilization and formation of the dinuclear zwitterions trans-1,1′-[η⁵:η⁵-(C₅H₃CO₂Me)₂]Mo₂(CO)₅(dppe) (3) and disproportionation species [(η⁵-C₅H₄CO₂Me)Mo(CO)₂(dppe)]⁺ [(η⁵-C₅H₄CO₂Me)Mo(CO)₃]⁻ (4), respectively. Using the same method, the reactions of trans-1,1′-[η⁵:η⁵-(C₅H₃CO₂Me)₂]Mo₂(CO)₆I₂ and (η⁵-C₅H₄CO₂Me)Mo(CO)₃I with PPh₃ in the presence of 1 and 2 equiv. of Me₃NO yield trans-1,1′-[η⁵:η⁵-(C₅H₃CO₂Me)₂]Mo₂(CO)₄(PPh₃)₂I₂ (5) and (η⁵-C₅H₄CO₂Me)Mo(CO)₂(PPh₃)I (6). The reactions of the several anionic carbonyl species {trans-1,1′-[η⁵:η⁵-(C₅H₃CO₂Me)₂]Mo₂(CO)₆}²⁻, [(η⁵:η⁵-C₁₀H₈)W₂(CO)₆]²⁻ and [(η⁵-C₅H₄CO₂Me)Mo(CO)₃]⁻ with S₂Ph₂ give rise to the thiolate–fulvalene complexes cis-1,1′-[η⁵:η⁵-(C₅H₃CO₂Me)₂]Mo₂(CO)₄(μ-SPh)₂ (7) and (η⁵:η⁵-C₁₀H₈)W₂(CO)₆(SPh)₂ (8) and the thiolate-bridged dimer [(η⁵-C₅H₄CO₂Me)Mo(CO)(μ-SPh)]₂ (9). Treatment of 6 with 1 equiv. of HCCCCH and with (η⁵-C₅H₅)Mo(CO)(dppe)(CCCCH), in the presence of CuI at room temperature, afford the cyclopentadiene complexes (η⁵-C₅H₄CO₂Me)Mo(CO)₂(PPh₃)(CCCCH) (10) and (η⁵-C₅H₄CO₂Me)(PPh₃)(CO)₂Mo(CCCC)Mo(CO)(dppe)(η⁵-C₅H₅) (11), respectively. The reaction of (η⁵-C₅H₅)Mo(CO)(dppe)(CCCCH) with Co₂(CO)₈ yields [Co₂{μ-HC₂CC[Mo(CO)(dppe)(η⁵-C₅H₅)]}(CO)₆] (12). All the new compounds have been characterized by analytical and spectroscopic methods.     

Syntheses and structural characterizations of novel mono- and dinuclear iridium hydrido complexes with polydentate nitrogen donor ligands

New five mono- and dinuclear Ir hydrido complexes with polydentate nitrogen ligands, [Ir(H)₂(PPh₃)₂(tptz)]PF₆ (1), [Ir₂(H)₄(PPh₃)₄(tptz)](PF₆)₂ · 2H₂O (2 · 2H₂O), [Ir(H)₂(PPh₃)₂(tppz)]BF₄ (3), [Ir₂(H)₄(PPh₃)₄(tppz)](BF₄)₂ (4) and [Ir₂(H)₄(PPh₃)₄(bted)](BF₄)₂ · 6CHCl₃ (5 · 6CHCl₃), were systematically prepared by the reactions of the precursor Ir hydrido complex [Ir(H)₂(PPh₃)₂(Me₂CO)₂]X (X=PF₆ and BF₄) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 1,4-bis(2,2^′:6^′,2″-terpyridine-4^′-yl)benzene (bted), and their structures and properties were characterized in the solid state and in solution. Each of the Ir hydrido complexes with polydentate nitrogen ligands crystallographically described a unique coordination mode. Their ¹H NMR spectra demonstrated unusual ¹H NMR chemical shifts of pyridyl rings that are likely induced by the ring current effect of neighboring ligands.