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.     

Cyclometallated Pt(II) and Pd(II) complexes with a trithiacrown ligand

We report the synthesis and full characterization for a series of cyclometallated complexes of Pt(II) and Pd(II) incorporating the fluxional trithiacrown ligand 1,4,7-trithiacyclononane ([9]aneS3). Reaction of [M(C insertion mark N)(micro-Cl)]2 (M = Pt(II), Pd(II); C insertion mark N = 2-phenylpyridinate (ppy) or 7,8-benzoquinolinate (bzq)) with [9]aneS3 followed by metathesis with NH4PF6 yields [M(C insertion mark N)([9]aneS3)](PF6). The complexes [M(C insertion mark P)([9]aneS3)](PF6) (M = Pt(II), Pd(II); Cinsertion markP = [CH2C6H4P(o-tolyl)2-C,P]-) were synthesized from their respective [Pt(C insertion mark P)(micro-Cl)]2 or [Pd(C insertion mark P)(micro-O2CCH3)]2 (C insertion mark P) starting materials. All five new complexes have been fully characterized by multinuclear NMR, IR and UV-Vis spectroscopies in addition to elemental analysis, cyclic voltammetry, and single-crystal structural determinations. As expected, the coordinated [9]aneS3 ligand shows fluxional behavior in its NMR spectra, resulting in a single 13C NMR resonance despite the asymmetric coordination environment of the cyclometallating ligand. Electrochemical studies reveal irreversible one-electron metal-centered oxidations for all Pt(II) complexes, but unusual two-electron reversible oxidations for the Pd(II) complexes of ppy and bzq. The X-ray crystal structures of each complex indicate an axial M-S interaction formed by the endodentate conformation of the [9]aneS3 ligand. The structure of [Pd(bzq)([9]aneS3)](PF6) exhibits disorder in the [9]aneS3 conformation indicating a rare exodentate conformation as the major contributor in the solid-state structure. DFT calculations on [Pt([9]aneS3)(ppy)](PF6) and [Pd([9]aneS3)(ppy)](PF6) indicate the HOMO for both complexes is primarily dz2 in character with a significant contribution from the phenyl ring of the ppy ligand and p orbital of the axial sulfur donor. In contrast, the calculated LUMO is primarily ppy pi* in character for [Pt([9]aneS3)(ppy)](PF6), but dx2-y2 in character for [Pd([9]aneS3)(ppy)](PF6).     

(p-Cymene)thioglycollatoruthenium(II) dimer; a complex with an ambi-basic S,O-donor ligand

The title compound was prepared from the (p-cymene)ruthenium chloride dimer and thioglycollic acid. The structure is a centrosymmetric dimer bridged by the soft-base S atoms, with the hard-base O atoms of the carboxylate group chelating to form a five-membered twisted-ring. The coordination of the ruthenium atoms is completed by a η⁶-p-cymene ligand, giving an 18-electron count. The Ru–S bonds are essentially equal at 2.396(1) Å.     

Pt(II) complexes in activation of saturated hydrocarbons

The rate constants of deuterium exchange for cyclohexane in CH₃COOD/D₂O have been measured in the presence of 12 complexes of Pt(II) with various ligands (Cl, H₂O, NH₃, Br, NO₂, py, DMSO, PPh₃, etc.). The change in the rate constant is shown to follow the reverse series of the trans-effect of Pt(II) ligands. The rate constant of the interaction of PtCl₂S_n (S is H₂O, CH₃COOH, n=1, 2) with cyclohexane in CH₃COOD/D₂O (11), k, equals 2.5×10⁸ exp (–18200/RT) 1 mol^–1 sec^–1 (at 354–385 K). The ratio of rate constants for PtCl₂S₂, PtCl₃S^– and PtCl ₄ ^2– is 10060.5 at 100°C.

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CH₃COOD–D₂O 12- Pt(II) (Cl, H₂O, NH₃, Br, NO₂, , DMCO, PPh₃ .). , Pt(II). PtCl₂S_n (S–H₂O, CH₃COOH, n=1,2) 11 CH₃COOD–D₂O k=2,5·10⁸ exp(–18200/RT). ^{–1 –1} (354–385°). 100°C PtCl₂S₂, PtCl₃S^– PtCl ₄ ^2– 10060,5.

     

Ligand effects on the Pt(II) → Pt(0) reduction of dichlorobis(tertiary phosphine)platinum(II) complexes: Correlations between electrochemical data,spectroscopic data,and electronic ligand parameters

Cyclic voltammetry has been employed to study the diffusive, irreversible platinum(II) → platinum(0) reduction of three sets of structurally related complexes: cis-[PtCl₂P{p-C₆H₄X}₃)₂] (X = H, CH₃, Cl, F, OCH₃, N(CH₃)₂); cis-[PtCl₂(PPh₂R)₂] (R = CH₃, n-C₃H₇, n-C₅H₁₁, n-C₆H₁₃, n-C₁₂H₂₅) and cis-[PtCl₂(PR₃)₂] (R = CH₃, C₂H₅, CH₂ch₂CN). Relationships between the peak potentials for the Pt(II) → Pt(0) reduction and thermodynamic parameters which measure the electronic properties of the ligands are shown to exist for complexes of P{p-C₆H₄X}₃ ligands, implying a thermodynamic origin for the sensitivity of the peak potentials to structural change. Complexes of both P{p-C₆H₄X}₃ and PPh₂R ligands show correlations between peak potentials for reduction and the ³¹P{¹H} NMR spectroscopic parameter, ¹J(¹⁹⁵Pt, ³¹P). Correlations with values of δ(³¹P) exist in both cases, but a correlation with the coordination chemical shift, Δδ(³¹P), exists for complexes of PPh₂R, and not for complexes of P{C₆H₄X}₃. Complexes of PR₃ ligands show no correlation between the peak potentials measured for the Pt(II) → Pt(0) reduction and electronic or spectroscopic parameters, except possibly ¹J(¹⁹⁵Pt, ³¹P).     

Synthesis and ligand exchange reactions of P2Pd(II) and P2Pt(II) salicylaldimates

Reaction of (dppe)MCl(2)(dppe = 1,2-bis(diphenylphosphino)ethane) with 2-(N-phenyliminomethyl)phenol leads to air-stable (dppe)M(N,O) chelates (M = Pd, 1a; M = Pt, 1b). The N-4-methylphenyl derivative of 1a has been characterized by X-ray analysis. The N,O ligands are kinetically labile and exchange occurs in solution in the presence of other salicylaldimines. In the presence of anilines, a metal-mediated imine exchange process occurs. Hammett analysis reveals that the platinum complexes are sensitive to the electronics at N but not at O. Electron donating groups on the N-aryl ring stabilize the metal complex.     

Chelating or bridging Pd(II) and Pt(II) metalloligands from the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine. New heterometallic Pd(II)/Pt(II) and Pt(II)/Au(I) complexes

The reaction of two equivalents of the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine Ph2PNHC=NNCHS (2) with [PdCl2(NCPh)2] in the presence of NEt3 gives the neutral, P,N-chelated complex cis-[Pd(Ph2PN=CNN=CHS)2] ([Pd(2-H)2], 3b), which is analogous to the Pt(II) analogue cis-[Pt (Ph2PN=CNN=CHS)2] ([Pt(2-H)2], 3a) reported previously. These complexes function as chelating metalloligands when further coordinated to a metal through each of the CH-N atoms. In the resulting complexes, each endo-cyclic N donor of the thiadiazole rings is bonded to a different metal centre. Thus, the heterodinuclear palladium/platinum complexes cis-[Pt(Ph2PN=CNN=CHS)2PdCl2]([Pt(2-H)2·PdCl2], 4a) and cis-[Pd(Ph2PN=CNN=CHS)2PtCl2]([Pd(2-H)2·PtCl2], 4b) were obtained by reaction with [PdCl2(NCPh)2] and [PtCl2(NCPh)2], respectively. In contrast, reaction of 3a with [AuCl(tht)] occurred instead at the P-bound N atom, and afforded the platinum/digold complex cis-[Pt{Ph2PN(AuCl)=CNN=CHS}2] ([Pt(2-H)2(AuCl)2], 5). For comparison, reaction of 4a with HBF4 yielded cis-[Pt(Ph2PNH=CNN=CHS)2PdCl2](BF4)2([H24a](BF4)2, 6), in which the chelated PdCl2 moiety is retained. Complexes 3b, 4a·CH2Cl2, 4b·0.5C7H8, 5·4CHCl3 and 6 have been structurally characterized by X-ray diffraction.     

Carbon‐iodide bond activation by cyclometalated Pt (II) complexes bearing tricyclohexylphosphine ligand: A comparative kinetic study and theoretical elucidation

Cyclometalated Pt (II) complexes [PtMe(C^N)(L)], in which C^N = deprotonated 2,2′‐bipyridine N‐oxide (Obpy), 1 , deprotonated 2‐phenylpyridine (ppy), 2 , deprotonated benzo [h] quinolone (bzq), 3 , and L = tricyclohexylphosphine (PCy₃) were prepared and fully characterized. By treatment of 1–3 with excess MeI, the thermodynamically favored Pt (IV) complexes cis‐[PtMe₂I(C^N)(PCy₃)] (C^N = Obpy, 1a ; ppy, 2a ; and bzq, 3a ) were obtained as the major products in which the incoming methyl and iodine groups adopted cis positions relative to each other. All the complexes were characterized by means of NMR spectroscopy while the absolute configuration of 1a was further determined by X‐ray crystal structure analysis. The reaction of methyl iodide with 1–3 were kinetically explored using UV–vis spectroscopy. On the basis of the kinetic data together with the time‐resolved NMR investigation, it was established that the oxidative addition reaction occurred through the classical S_N2 attack of Pt (II) center on the MeI reagent. Moreover, comparative kinetic studies demonstrated that the electronic and steric nature of either the cyclometalating ligands or the phosphine ligand influence the rate of reaction. Surprisingly, by extending the oxidative addition reaction time, very stable iodine‐bridged Pt (IV)‐Pt (IV) complexes [Pt₂Me₄(C^N)₂(μ‐I)₂] (C^N = Obpy, 1b ; ppy, 2b ; and bzq, 3b ) were obtained and isolated. In order to find a reasonable explanation for the observation, a DFT (density functional theory) computational analysis was undertaken and it was found that the results were consistent with the experimental findings.     

Pt(II) uptake by dendrimer outer pockets: 1. Solventless ligand exchange reaction

Density functional theory is used to elucidate molecular-level details of the complexation of Pt(II) metal compounds with PAMAM dendrimers. Particular attention is given to the ligand exchange reaction (LER). Binding of Pt(II) complexes to one dendrimer atom site (monodentate binding) is found to be thermodynamically feasible. Tertiary amine nitrogen (N3) is found to be the most favorable binding site in agreement with previous experimental work. Comparing the binding of Pt(II) species to atom sites in simple molecules with those to similar sites in dendrimer outer pockets allowed us to assess the impact of dendrimer branches on the binding. The impact of branches is manifested in more complex reaction profiles for complexation of Pt(II) species, because of the numerous ways in which a single molecule could be hosted by an outer dendrimer pocket. It is found that branches slightly improve the binding strength to all sites, particularly to N3. However, they could also be responsible for the increase of the activation energy for direct LER of PtCl(4)(2-) and PtCl(3)(H(2)O)- at the N3 site. Considering the thermodynamics of both complexation steps, namely noncovalent binding (NCB) and LER, it is found that to have a PtCl(3)(-) moiety bound to N3, as a result of NCB + LER operating on PtCl(4)(2-), is more likely than to have any other ion hosted in the outer pockets. However, the activation energy for direct LER of PtCl(4)(2-) at the N3 site is found to be the largest among all Pt(II) metal complexes and even larger than the barrier to its own aquation yielding PtCl(3)(H(2)O)(-).     

Complexing of Pd(II) and Pt(II) by dithiooxamide immobilized on SiO2

It is shown that dithiooxamide immobilized on SiO₂ can bind Pd(II) and Pt(II) from aqueous chloride solutions by complexing. Values have been derived for the effective Pd(II) and Pt(II) sorption constants for dithiooxamide immobilized on SiO₂, which represent stronger binding of Pd(II) than Pt(II). L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 6, pp. 366–370, November–December, 1998.     

Catalytic dioxygen activation by Co(II) complexes employing a coordinatively versatile ligand scaffold

The ligand bis(2-isobutyrylamidophenyl)amine has been prepared and used to stabilize both mononuclear and dinuclear cobalt(II) complexes. The nuclearity of the cobalt product is regulated by the deprotonation state of the ligand. Both complexes catalytically oxidize triphenylphosphine to triphenylphosphine oxide in the presence of O(2).     

An iron(II) dihydrogen hydrido complex containing the tripodal tetraphosphine ligand P(CH2CH2PMe2)3

The dihydrogen hydrido complex [FeH(H2)(PP3)]+ 1 (PP3 = P(CH2CH2PMe2)3 2) was formed by the protonation of the dihydrido complex FeH2(PP3) 3 with methanol or ethanol. The observation of H-D coupling in partially deuterated isotopomers of 1 and measurement of T1 relaxation times for the hydrido and dihydrogen resonances of 1 confirmed the presence of the eta2-dihydrogen ligand. Complex 1 shows dynamic NMR behaviour in both the 31P and 1H NMR spectra with facile exchange between the protons in the eta2-dihydrogen ligand and the eta1-hydrido ligand. The dihydrogen ligand of 1 is easily displaced by both anionic and neutral ligands to afford the corresponding hydrido complexes [FeHX(PP3)]+ (X = CO 11, X = PPh3 12) or FeHX(PP3)(X = Cl 13, X = Br 14, X = I 15, X = N3 16). Small quantities of the alkoxy hydrido complexes FeH(OR)(PP3)(R = Me 4; R = Et 5) are observed in methanol and ethanol solutions containing 1. In methanol solution, FeH(OMe)(PP3) 4 reacts to form the carbonyl hydrido complex [FeH(CO)(PP3)]+ 11 and isotopic labelling confirms that the carbonyl ligand of 11 is derived from the methanol solvent. The mechanism of methanol oxidation presumably proceeds through beta-hydride elimination from FeH(OMe)(PP3) to produce formaldehyde as an intermediate which is further dehydrogenated to form the carbonyl ligand. [FeH(H2)(PP3)]+ 1 and FeHCl(PP3) 13 react rapidly with paraformaldehyde to also form [FeH(CO)(PP3)]+ 11. Complex 11 also decarbonylates acetaldehyde to afford the methyl carbonyl complex [FeMe(CO)(PP3)]+ 17. The structure of 17 was confirmed by X-ray crystallography.     

Encapsulation of nickel(II) and copper(II) by a tetraazamacrocyclic ligand

A tetraazamacrocyclic ligand, L, containing six non-equivalent benzene rings, derived from the condensation of benzil with 1,2- diaminobenzene, has been isolated and its complexes [MLCl₂] (M = Ni²⁺ and Cu²⁺) prepared and characterized by elemental analysis, i.r., u.v.–vis., e.p.r. spectral studies, magnetic moments, redox potentials and conductivity measurements. The complexes have axially elongated octahedral geometries with two axial chlorines, and adopt the trans-configuration. These studies also indicate the covalent nature and the high-spin octahedral structure for these complexes. A cyclic voltammetric investigation reveals that the complexes exhibit a single one-electron redox couple, as anticipated for a copper(II) complex (Cu²⁺/Cu⁺) and a single two-electron redox couple for a nickel(II) complex (Ni²⁺/Ni⁰). The electrochemical processes are considered quasi-reversible. Antimicrobial activities of the ligand and the complexes have been tested against Bacillus megaterium and Candida tropicallis.     

Co(III), Ni(II), and Cu(II) complexes of bidentate N,O-donor Schiff base ligand derived from 4-methoxy-2-nitroaniline and salicylaldehyde

Asymmetric bidentate Schiff base ligand (HL) and its cobalt(III), nickel(II), and copper(II) complexes have been synthesized (where L = 2-[(4-methoxy-2-nitrophenyl)iminomethyl]phenol). The ligand and its metal complexes have been characterized by elemental analyses (CHN) and FTIR spectroscopy. Thermogravimetric analyses of the compounds reveal their thermal stabilities along with their thermal decomposition pattern. In addition, the complexes have been used for the preparation of corresponding metal oxide nanoparticles by controlled aerobic thermal decomposed at 500 °C. The FTIR pattern of the obtained solids receals the formation of the metal oxides nanoparticles.     

Ruthenium(II) and ruthenium(III) complexes derived from O,O-donor ligands

The new [Ru¹¹(PPh₃)₂L₂] complexes [L=monoanion of tropolone, benzoylacetone, or 3-hydroxy-2-pyridinone (hypy)], [RuH(PPh₃)₃L′][HL′=maltol, dibenzoylmethane or 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdmhypy)] and [Ru^IIIX₂(EPh₃)₂L″] complexes (X=Cl, Br; E=As or P; L″=hypy, dmhypy) have been prepared, and characterized by spectroscopic techniques. Their redox behaviour was studied by cyclic voltammetry. Most of the complexes were found to be effective catalysts for the oxidation ofp-methoxybenzyl alcohol to the corresponding aldehyde in the presence ofN-methylmorpholine-N-oxide as co-oxidant.     

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.