Synthesis, photophysics, and optical limiting of platinum(II) 4'-tolylterpyridyl arylacetylide complexes

A series of 4'-tolylterpyridyl platinum(II) complexes with different arylacetylide ligands, namely, phenylacetylide, 4-bromophenylacetylide, 4-nitrophenylacetylide, 4-methoxyphenylacetylide, 4-dimethylaminophenylacetylide, 1-naphthylacetylide, and 3-quinolinylacetylide, were synthesized. Their photophysical properties, such as electronic absorption spectra, emission characteristics at room temperature and 77 K, and transient difference absorption spectra, have been investigated. All of these complexes exhibit a metal-to-ligand charge-transfer (1MLCT) transition at ca. 420-430 nm in their electronic absorption spectra. For ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, an additional solvatochromic charge-transfer band appears at ca. 460-540 nm. This band is sensitive to the para substituents on the phenylacetylide ligand and is tentatively assigned to a metal- or/and acetylide-to-terpyridyl charge-transfer transition (i.e., a 1MLCT or/and 1LLCT transition). All of the complexes exhibit room-temperature phosphorescence. The emission can be attributed to a 3MLCT state except for ttpy-C6H4NO2-4, for which the emission likely originates from an intraligand 3pi,pi* state involving the nitrophenylacetylide ligand. For ttpy-C6H4OCH3-4, ttpy-C6H4N(CH3)2-4, and ttpy-Np, there probably is more than one low-energy state in close energy proximity, resulting in multiple exponential decays. In addition, the triplet transient absorption difference spectra of ttpy-Ph, ttpy-C6H4Br-4, ttpy-C6H4NO2-4, and ttpy-Quin exhibit moderately intense, broad absorption bands in the visible region and extending into the near-IR region, which likely originate from the same excited state that emits or from a state that is in equilibrium with the emitting state. It appears that the electron-rich arylacetylide ligands, especially 4-methoxyphenylacetylide and 4-dimethylaminophenylacetylide, cause a decrease of the emission efficiency and disappearance of the transient absorption. In contrast, the complexes that exhibit positive absorption bands in the visible spectral region of the triplet transient difference absorption spectra show substantial optical limiting for nanosecond laser pulses at 532 nm.     

Photophysics and nonlinear absorption of cyclometalated 4,6-diphenyl-2,2'-bipyridyl platinum(II) complexes with different acetylide ligands

The photophysical properties of a series of 4,6-diphenyl-2,2'-bipyridyl platinum(II) complexes bearing different σ-alkynyl ancillary ligands (1a-1k) were systematically investigated. All complexes exhibit strong (1)π,π* absorption bands in the UV region; and broad, structureless charge-transfer band(s) in the visible region, which systematically red-shift(s) when the electron-donating ability of the para substituent on the phenylacetylide ligand increases. All complexes are emissive in solution at room temperature. When excited at the charge-transfer absorption band, the complexes exhibit long-lived orange emission (λ(max): 555-601 nm), which is attributed to a triplet metal-to-ligand charge transfer/intraligand charge transfer emission ((3)MLCT/(3)ILCT). Most of these complexes exhibit broad triplet transient difference absorption in the visible to the near-IR region, with a lifetime comparable to those measured from the decay of the (3)MLCT/(3)ILCT emission. The reverse saturable absorption (RSA) of these complexes were demonstrated at 532 nm using nanosecond laser pulses. The degree of RSA follows this trend: 1k ≈ 1a > 1c > 1f ≈ 1i > 1h ≈ 1b > 1e > 1d > 1g, which is mainly determined by the ratio of the triplet excited-state absorption cross section to that of the ground-state and the triplet excited-state quantum yield.     

Structural, photophysical, and nonlinear absorption properties of trans-di-arylalkynyl platinum(II) complexes with phenyl and thiophenyl groups

Optical power limiting and luminescence properties of two Pt(II) complexes with thiophenyl and phenyl groups in the ligands, trans-Pt(P(n-Bu)3)2(C[triple bond]C-Ar)2, where Ar = -C4H2S-C[triple bond]C-p-C6H4-n-C5H11 (1) and -p-C6H4-C[triple bond]C-C4H3S (2), have been investigated. The fluorescence lifetimes were found to be on the sub-nanosecond time scale, and the quantum yields were low, in accord with fast intersystem crossing from the excited singlet to triplet manifold. The phosphorescence lifetimes of 1 and 2 were shorter than that of a Pt(II) complex having two phenyl groups in the ligands. In order to elucidate the C-Pt bonding nature in the ground state, the 13C NMR chemical shift of the carbon directly bonded to Pt, the coupling constants 1JPtC, 2JPtC, and 1JPtP, and IR nuC[triple bond]C wavenumbers were obtained for 1, 2, and three other trans-diarylalkynyl Pt(II) complexes. X-ray diffraction data of 1 and 2 and density functional theory calculated geometries of models of 1, 2, and trans-Pt(P(n-Bu)3)2(C[triple bond]C-p-C6H4-C[triple bond]C-C6H5)2 (3) show that 1 preferably exists in a different conformation from that of 2 and 3. The variations in photophysical, NMR, and IR data can be rationalized by differences in geometry and pi-backbonding from Pt to the alkynyl ligand.     

Tuning the electronic structures of platinum(II) complexes with a cyclometalating aryldiamine ligand

Triflate salts of four platinum(II) pyridyl complexes with a mer-coordinating tridentate pincer ligand, pip(2)NCN(-) (pip(2)NCNH = 1,3-bis(piperidylmethyl)benzene), are reported: Pt(pip(2)NCN)(L)(+) (2, L = pyridine; 3, L = 4-phenylpyridine; 5, L = 2,6-pyridinedimethanol) and [(Pt(pip(2)NCN))(2)(micro-4,4'-bipyridine)](2+) (4). The complexes have been fully characterized by (1)H NMR spectroscopy, elemental analysis, and X-ray crystallography. Compound 2(CF(3)SO(3)(-)): triclinic, P1, a = 9.7518(6) A, b = 12.0132(8) A, c = 12.6718(9) A, alpha = 114.190(2) degrees, beta = 100.745(3) degrees, gamma = 103.545(2) degrees, V = 1247.95(14) A(3), Z = 2. Compound 3(CF(3)SO(3)(-)): monoclinic, P2(1)/c, a = 15.550(2) A, b = 9.7386(11) A, c = 18.965(3) A, beta = 92.559(7) degrees, V = 2869.1(6) A(3), Z = 4. Compound 4(CF(3)SO(3)(-))(2).1/2(CH(3))(2)CO: monoclinic, I2/a, a = 21.3316(5) A, b = 9.6526(2) A, c = 26.1800(6) A, beta = 96.4930(10) degrees, V = 5356.0(2) A(3), Z = 4. Compound 5(CF(3)SO(3)(-)).3/2CHCl(3): monoclinic, P2(1)/n, a = 17.1236(10) A, b = 9.3591(5) A, c = 21.3189(11) A, beta = 96.11(3) degrees, V = 3397.2(3) A(3), Z = 4. The accumulated data indicate that the phenyl group of pip(2)NCN(-) labilizes the trans pyridyl ligand. The electronic structures were investigated using cyclic voltammetry, as well as UV-visible absorption and emission spectroscopies. Red emission from 2 in rigid media originates from a lowest triplet ligand field excited state, whereas yellow-green emissions from 3 and 4 originate from a lowest pyridyl ligand-centered triplet pi-pi state, indicating that substitution of the pyridyl ligand results in a dramatic change in the orbital character of the emissive state.     

Organoplumbio complexes of platinum(II)

The complex [Pt(C₂H₄)(PPh₃)₂] reacts with Pb₂Ph₆ to give cis-[PtPh(Pb₂Ph₅)(PPh₃)₂]; this decomposes in solution to cis-[PtPh(PbPh₃)(PPh₃)₂], which may also be obtained from the ethylene complex and PbPh₄. Lead compounds PbPhMe₃ and PbPh₃Br also give products of insertion into PbPh bonds, but PbMe₃Cl gives cis- and trans-[PtCl(PbMe₃)(PPh₃)₂]. The complex trans-[Pt(PbPh₃)₂(PEt₃)₂] reacts with 1,2-bis(diphenylphosphino)ethane (DPPE) to give [Pt(PbPh₃)₂(DPPE)] which readily decomposes in dichloromethane in presence of PEt₃ to give [Pt(PbPh₃)(PEt₃)(DPPE)]Cl and [PtPh(PEt₃)(DPPE)]Cl. The complex trans-[PtCl(PbPh₃)(PEt₃)₂] was detected in the products of reactions between trans-[PtCl₂(PEt₃)₂] and trans-[Pt(PbPh₃)₂(PEt₃)₂] or less than 2 moles of LiPbPh₃; it was not detected in the mixture after treatment of trans -[Pt(PbPh₃)₂(PEt₃)₂] with HCl. In contrast to an earlier report, we were unable to detect lead-containing complexes in the products of the reaction between trans-[PtHCl(PPh₃)₂] and Ph₃PbNO₃. The complexes and their decomposition products were identified by ^pre31P-{¹H} NMR spectroscopy.     

Mechanistic studies of ethylene hydrophenylation catalyzed by bipyridyl Pt(II) complexes

Cationic platinum(II) complexes [((t)bpy)Pt(Ph)(L)](+) [(t)bpy =4,4'-di-tert-butyl-2,2'-bipyridyl; L = THF, NC(5)F(5), or NCMe] catalyze the hydrophenylation of ethylene to generate ethylbenzene and isomers of diethylbenzene. Using ethylene as the limiting reagent, an 89% yield of alkyl arene products is achieved after 4 h at 120 °C. Catalyst efficiency for ethylene hydrophenylation is diminished only slightly under aerobic conditions. Mechanistic studies support a reaction pathway that involves ethylene coordination to Pt(II), insertion of ethylene into the Pt-phenyl bond, and subsequent metal-mediated benzene C-H activation. Studies of stoichiometric benzene (C(6)H(6) or C(6)D(6)) C-H/C-D activation by [((t)bpy)Pt(Ph-d(n))(THF)](+) (n = 0 or 5) indicate a k(H)/k(D) = 1.4(1), while comparative rates of ethylene hydrophenylation using C(6)H(6) and C(6)D(6) reveal k(H)/k(D) = 1.8(4) for the overall catalytic reaction. DFT calculations suggest that the transition state for benzene C-H activation is the highest energy species along the catalytic cycle. In CD(2)Cl(2), [((t)bpy)Pt(Ph)(THF)][BAr'(4)] [Ar' = 3,5-bis(trifluoromethyl)phenyl] reacts with ethylene to generate [((t)bpy)Pt(CH(2)CH(2)Ph)(η(2)-C(2)H(4))][BAr'(4)] with k(obs) = 1.05(4) × 10(-3) s(-1) (23 °C, [C(2)H(4)] = 0.10(1) M). In the catalytic hydrophenylation of ethylene, substantial amounts of diethylbenzenes are produced, and experimental studies suggest that the selectivity for the monoalkylated arene is diminished due to a second aromatic C-H activation competing with ethylbenzene dissociation.     

Phosphorescent platinum(II) complexes derived from multifunctional chromophores: synthesis, structures, photophysics, and electroluminescence

The synthesis and structural, photophysical, electrochemical, and electroluminescent properties of a novel class of trifunctional Pt(II) cyclometalated complexes are reported in which the hole-transporting triarylamine, electron-transporting oxadiazole, and electroluminescent metal components are integrated into a single molecule. These neutral metal chelates display good thermal stability (>250 degrees C under N2) and morphological stability. All of them exhibit intense ligand-centered fluorescence and phosphorescence in fluid solutions at room temperature, but the emission spectra become largely dominated by triplet emission bands in CH2Cl2 glass at 77 K. Substituents with different electronic properties were introduced into the bipolar cyclometalating ligands to fine-tune the absorption and emissive characteristics of the compounds, and the results were correlated with theoretical calculations using density functional theory. A comparison of the photophysics and electrochemistry of our multifunctional systems to those only derived from each of the constituent components was also made and discussed. These Pt complexes can be vacuum-sublimed and applied as emissive dopants for the fabrication of vapor-deposited electrophosphorescent organic light-emitting devices (OLEDs), which generally exhibit good device performance with efficiencies up to 3.6%, 11.0 cd A-1, and 5.8 lm W-1. While the electroluminescence energy resembles that recorded in fluid solutions for these Pt emitters, these monochromatic OLEDs can emit tunable colors by varying the aryl ring substituents and the level of doping. Saliently, single dopant white-light electroluminescence, triggered by the simultaneous fluorescence/phosphorescence emission of the metal complexes and a variation of applied driving voltages, has also been realized based on some of these multifunctional complexes with peak electrophosphorescence efficiencies of 6.8 cd A-1 and 2.6%.     

Photosensitized generation of singlet oxygen from ruthenium(II) and osmium(II) bipyridyl complexes

Photophysical properties for a number ruthenium(II) and osmium(II) bipyridyl complexes are reported in dilute acetonitrile solution. The lifetimes of the excited metal to ligand charge transfer states (MLCT) of the osmium complexes are shorter than for the ruthenium complexes. Rate constants, kq, for quenching of the lowest excited metal to ligand charge transfer states by molecular oxygen are found to be in the range (1.1-7.7) x 10(9) dm3 mol(-1) s(-1). Efficiencies of singlet oxygen production, fDeltaT, following oxygen quenching of the lowest excited states of these ruthenium and osmium complexes are in the range of 0.10-0.72, lower values being associated with those compounds having lower oxidation potentials. The rate constants for quenching of the excited MLCT states, kq, are found to be generally higher for osmium complexes than for ruthenium complexes. Overall quenching rate constants, kq were found to give an inverse correlation with the energy of the excited state being quenched, and also to correlate with the oxidation potentials of the complexes. However, when the contribution of quenching due exclusively to energy transfer to produce singlet oxygen, kq1, is considered, its dependence on the energy of the excited states is more complex. Rate constants for quenching due to energy dissipation of the excited MLCT states without energy transfer, kq3, were found to show a clear correlation with the oxidation potential of the complexes. Factors affecting both the mechanism of oxygen quenching of the excited states and the efficiency of singlet oxygen generation following this quenching are discussed. These factors include the oxidation potential, the energy of the lowest excited state of the complexes and spin-orbit coupling constant of the central metal.     

Tuning of spin transition in radical-containing iron(III) complexes by remote ligand substituents

Two new iron(III) complexes, Fe(III)(LF*)3 (1) and FeIII(L(t-Bu*))3 (2), of remote substituted o-aminophenol-based ligands are reported; complexes 1 and 2 contain three O,N-coordinated o-iminobenzosemiquinonate(1-) radical anions with ferric centers in high-spin and low-spin configurations. The crystal structures of 1 and 2 were determined by X-ray diffraction at 100 and 293 K, and the electronic structures were established by various physical methods including M?ssbauer (4-290 K) and variable-temperature (2-290 K) susceptibility measurements. Electrochemical measurements (cyclic and square-wave voltammetry) indicate primarily ligand-centered redox processes. Complex 1, with the more electron-withdrawing fluoro substituents, retains the high-spin character of the ferric ion throughout the temperature range studied (2-290 K) and exhibits, as expected, strong antiferromagnetic coupling operating between three radicals (SR = 1/2) and the high-spin Fe(III) center (SFe = 5/2) yielding an St = 1 as the ground state. In contrast, the occurrence of a thermally induced spin crossover process (SFe = 5/2 <--> SFe = 1/2) is observed for complex 2 FeIII(L(t-Bu*))3, in which more electron donating tert-butyl substituents in the ligand are present. A rationale for the control of the electronic state of ferric ions in 2 together with spin-coupling schemes for 1 and 2 are provided.     

Nonlinear optical and two-photon absorption properties of octupolar tris(bipyridyl)metal complexes

The linear (absorption and emission) and nonlinear optical (NLO) properties of a series of D(3) [(Fe(II), Ru(II), Ni(II), Cu(II), Zn(II)] octupolar metal complexes featuring the 4,4'-bis[(dibutylamino)styryl]-2,2'-bipyridine ligand are reported. Zinc(II), nickel(II), and copper(II) complexes exhibit similar absorption spectra in the visible region (lambda(ILCT) = 474-476 nm) which are assigned to intraligand charge-transfer (ILCT) bands. The quadratic and cubic NLO properties are strongly influenced by the nature of the metallic center. Harmonic light scattering studies at lambda = 1.91 microm reveal that these chromophores display large first hyperpolarizabilities beta(1.91) in the range of (211-340) x 10(-30) esu; replacing the Zn(II) metal ion by Ni(II) or Cu(II) results in a decrease of the static beta(0) coefficient by a factor of 1.5-1.6. Z-scan measurements at 765 and 965 nm reveal relatively large two-photon absorption cross-sections [650 < sigma(2) < 2200 GM], showing that both beta and sigma(2) values can be tuned by simple modification of the metal ion.     

Switchable thiophene coordination in Ru(II) bipyridyl phosphinoterthiophene complexes

Switching between P,S- and P,C coordination modes of 3'-phosphinoterthiophene to Ru(II) results in substantial differences in the electronic spectra and cyclic voltammetry of these complexes.     

Ligand localized triplet excited states in platinum(II) bipyridyl and terpyridyl peryleneacetylides

An investigation of the photophysics of two complexes, [Pt((t)Bu3tpy)(C triple bond C-perylene)]BF4 (1) and Pt((t)Bu2bpy)(C triple bond C-perylene)2 (2), where (t)Bu3tpy is 4,4',4'-tri( tert-butyl)-2,2':6',2'-terpyridine, (t)Bu2bpy is 4,4'-di( tert-butyl)-2,2'-bipyridine, and C triple bond C-perylene is 3-ethynylperylene, reveals that they both exhibit perylene-centered ligand localized excited triplet states ((3)IL) upon excitation with visible light. These complexes do not display any significant photoluminescence at room temperature but readily sensitize (1)O2 in aerated CH2Cl2 solutions, as evidenced by its characteristic emission near 1270 nm. The transient absorption difference spectra were compared to bi- and tridentate phosphine peryleneacetylides intended to model the (3)IL peryleneacetylide excited states in addition to the related phenylacetylide-bearing polyimine analogues, with the latter model being the respective triplet charge-transfer ((3)CT) excited states. The transient difference spectra of the two title compounds display excited-state absorptions largely attributable to perylene localized (3)IL states yet exhibit somewhat attenuated excited-state lifetimes relative to those of the phosphine model chromophores. The abbreviated lifetimes in 1 and 2 may suggest the involvement of the energetically proximate (3)CT triplet state exerting an influence on excited-state decay, and the effect appears to be stronger in 1 relative to 2, consistent with the energies of their respective (3)CT states.     

Organometallic formate complexes of platinum(II)

The compounds trans-[Pt(OCHO)R(PPh₃)₂] (R = C₆Cl₅; 2,3,4,6-C₆HCl₄; 2,3,4,5-C₆HCl₄; 2,5-C₆H₃Cl₂) have been prepared by treatment of [PtIR(PPh₃)₂] with AgClO₄ followed by reaction with NaOCHO in methanol. The cis isomers have been obtained by the direct reaction of HCO₂H with compounds containing PtHg bonds. For these and the analogous compounds containing C₆F₅ ligands, the dependence of J(³¹P¹⁹⁵Pt) on R has been studied, and the effects of cis-R shown to be in the opposite direction from those of trans-R ligands.     

Cationic pentafluorophenyl complexes of platinum(II)

The complex [O₃ClOPt(C₆F₅)(PEt₃)₂] which we have prepared for the first time, is used as a precursor of a series of cationic complexes [LPt(C₆F₅)(PEt₃)₂]ClO₄ (L = PEt₃, AsPh₃, H₂O, CO, OPPh₃, SPPh₃, HNPr₂, py), which are easily obtained by adding L to the perchlorato complex.     

Luminescence of ortho-metallated platinum(II) complexes

The absorption spectra, emission spectra, and emission lifetimes of Pt(Phpy)₂, Pt(Thpy)₂, and Pt(Bhq)₂ complexes (Phpy⁻, Thpy⁻, and Bhq⁻ are the ortho C-deprotonated forms of 2-phenylpyridine, 2-(2-thienyl)-pyridine, and benzo(h)quinoline) have been studied and compared with those of the C-protonated neutral ligands. For all complexes examined the low-energy absorption bands in the near UV and visible region are assigned to metal-to-ligand charge-transfer transitions. The strong and structured luminescence emissions observed in the 500–600 nm region (lifetime in the microsecond range at 77 K) are assigned to metal-to-ligand charge-transfer excited states.     

Carbamoyl and alkoxycarbonyl complexes of palladium(II) and platinum(II)

Carbamoyl and alkoxycarbonyl complexes of palladium(II) and platinum(II) of the type M(pnp)(CONHR)Cl (pnp = 2,6-bis(diphenylphosphinomethyl)pyridine; M Pd, R  C₆H₅, p-CH₃C₆H₄, p-CH₃OC₆H₄, C₆H₁₁, t-Bu; M  Pt, R  C₆H₅), Pd(pnp)[CON(Pr)₂]Cl (Pr = propyl), M(pnp)(COOR)Cl (M  Pd, R  C₆H₅, CH₃; M  Pt, R  CH₃), Pd(pnp)(COOCH₃)₂ result from reaction of M(pnp)Cl₂ with carbon monoxide and amines or alkoxides at room temperature and atmospheric pressure.The carbamoyl complexes react with bases to give urethane or diphenylurea depending upon the experimental conditions.     

Trinuclear platinum(II) 4,6-diphenyl-2,2'-bipyridyl complex with bis(diphenylphosphinomethyl)phenylphosphine auxiliary ligand: synthesis, structural characterization, and photophysics

A trinuclear cyclometalated Pt(II) 4,6-diphenyl-2,2'-bipyridyl complex with bis(diphenylphosphinomethyl)phenylphosphine bridging ligand ([4-Ph(C--N--N)Pt](3)dpmp) has been synthesized and characterized. It exhibits a broad electronic absorption band from 400 to 600 nm because of its intramolecular Pt...Pt interactions that have been revealed by X-ray crystal structure analysis. This complex shows strong red emission in acetonitrile at room temperature and 77 K. The electronic and emission spectra exhibit concentration and temperature dependence. With increased concentrations, the UV band of the absorption spectrum gradually decreases and broadens, accompanied by an increase of the (1)[dsigma*,pi*] band between 400 and 600 nm. For emission spectra, the 550 nm band that originates from the mononuclear platinum(II) component gradually decreases with increased concentrations, while the band at approximately 700 nm that corresponds to the (3)[dsigma*,pi*] state increases. In addition, the UV-vis and emission spectra exhibit temperature and viscosity-dependence. The concentration-, temperature-, and viscosity-dependent characteristics indicate a conformational change of the complex arising from the rotation along the oligophosphine axis. This complex exhibits broad, positive, and strong transient difference absorption bands from the near-UV to near-IR spectral region. However, because of the increased ground-state absorption in the visible region, the nonlinear transmission of this trinuclear platinum complex decreases.     

Palladium(II) and platinum(II) complexes of dithiocarbamates and L-methioninol

The [M(dithiocarbamato)(Mol)]Cl complexes [M = Pd or Pt; dithiocarbamato = DMDT (Me₂NCS^– ₂) or ESDT (EtO₂CCH₂MeNCS^– ₂); Mol = L-methioninol (L-2-amino-4-methylthio-1-butanol)] have been prepared by reacting methioninol with the appropriate [M(dithiocarbamato)Cl] _n complex in a 1:1 molar ratio in chlorinated hydrocarbons. By operating at a 1:2 molar ratio, the binuclear species [M₂(dithiocarbamato)₂(Mol)Cl₂] were obtained. The complexes were characterized by i.r., n.m.r. and electrospray ionisation (ESI) mass spectra and by t.g.a. The [M(dithiocarbamato)(Mol)]Cl species are ionic and contain S,N-chelated methioninol. The ligand forms an S,N bridge between two metal atoms in the binuclear species, whose formation is confirmed by the presence of the deprotonated molecular ion in the ESI negative ion mode.     

Palladium(II) and platinum(II) complexes with N-substituted methionines

Summary As an approach to systems containing methionine residues, 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one (HDh, dehydroacetic acid) was treated with L-methionine (MetH) or L-methionine methylester (MetM). By condensation at the acyl group and transfer of the phenolic hydrogen on the nitrogen atom, the related ligands DhMetH and DhMetM, were isolated, and form complexes of formula [MX₂(L)₂](M = Pd or Pt, L = DhMetM, X = Cl, Br or I; L = DhMetH, X = Cl or Br) and [MI₂(DhMetH)] with palladium and platinum dihalides. The reaction of the DhMetK carboxylate with MCl₂ in various media is discussed. Ligands and complexes were characterized by i.r. and n.m.r. (¹H and¹³C) spectroscopy and, in some cases, by thermogravimetric measurements. The ligands behave as monodentate sulphur donors, the 12 complexes showing atrans geometry except for [PtCl₂(DhMetH)₂], which is probably a mixture ofcis andtrans isomers.     

Some palladium(II) and platinum(II) lead bonded complexes

Complexes of the type M(PPh₃)₂(PbPh₃)₂ [M = Pd, (Ia) and Pt, (Ib)] have been prepared by oxidative addition of hexaphenyldilead to M(PPh₃)₄. The compound Pt(PPh₃)₂(PbPh₃)₂, (Ib), slowly decomposes in dichloromethane to give cis-Pt(PPh₃)₂(PbPh₃)Ph, (II). which can also be obtained by treating (Ib) with the stoichiometric amount of LiPh. Reaction of Pt(PPh₃)₄ with hexamethyldidead gives the complex Pt(PPh₃)₂(PbMe₃)Me directly.The MPb bonds are easily cleaved by bromine, iodine and hydrogen bromide. The X-ray structure of (II) has been determined using three-dimensional counter data and refined by the least-square method (R = 0.07). The crystals are monoclinic a = 22.501, b = 10.502, c = 24.120 Å, β = 113.43°, space group P2₁/c with Z = 4. The complex exhibits a cis configuration, with the coordination around the platinum atom essentially square-planar: the PtPb and PtC(phenyl)bond lengths are 2.698(1) and 2.055(3)Å, respectively.