Anionic complexes of some transition metals containing mixedβ-diketonato and alkylxanthato ligands

Summary Eleven complexes of the type K[M(acac)(Rxan)₂] and K[M(TTA)₂(Rxan)], where M=Co^II or Ni^II, acac=acetylacetonate, TTA=thenoyltrifluoroacetonate, and Rxan=alkylxanthate, R=methyl-, ethyl-, propyl-, butyl-, or cyclohexyl-, have been prepared. The magnetic and spectral data indicate that the complexes are octa-hedral and that the xanthate group is attached in a bidentate fashion to the metal ions. The conductivity data are commensurate with the ionic character in the complexes. T.g.a. were made for some of the complexes.Presented at the XXVI International Conference on Coordination Chemistry in Porto, Portugal, 28 August–2 September 1988.     

Unusual reactivity of methylene group adjacent to pyridine-2-carboxamido moiety in iron(III) and cobalt(III) complexes

The Fe(III) and Co(III) complexes of the ligand N-(2-picolyl)picolinamide (pmpH; H represents the dissociable amide hydrogen), namely, [Fe(pmp)(2)]BF(4) (1) and [Co(pmp)(2)]ClO(4) (2), have been synthesized and structurally characterized. The [bond]CH(2)[bond] moiety of pmp(-) in [M(pmp)(2)](+) (M = Fe, Co) is very reactive and is readily converted to carbonyl (C[double bond]O) group upon exposure to dioxygen. Such conversion results in [M(bpca)(2)]ClO(4) complexes (M = Fe (3), Co (5); bpcaH = bis(2-pyridylcarbonyl)amine) which have been characterized by spectroscopy and X-ray diffraction. The structure of 5 is reported here for the first time. The reactivity of the [bond]CH(2)[bond] moiety of pmp(-) has so far precluded the isolation of 1 although other metal complexes of pmp(-) have been reported years ago. The CH(2) --> C[double bond]O transformation arises from the tendency of the coordinated pmp(-) ligand to achieve further conjugation in the ligand framework and provides a better way to synthesize the metal complexes of bpcaH ligand. Reaction of 3 with NaH affords Fe(II) complex [Fe(bpca)(2)] (4) without any reduction of the ligand frame.     

Mössbauer and other spectral studies of iron(II) complexes with amide-containing ligands

Summary Iron(II) complexes of the type [FeL₂X₂] (L=bidentate ligand, X=H₂O, Cl, or SCN) and [FeL₂] (L=tridentate ligand) with polydentate ligands derived from 2-(acetylamino)benzoic acid, 2-(benzoylamino)benzoic acid,2-[2-aminobenzoylamino]benzoic acid, 2-[amino-carbonyl]benzoic acid, 2-[(phenylamino)carbonyl]-benzoic acid, 2-[aminobenzoyl]benzoic acid and 2-aminobenzanilide have been synthesized and characterized by elemental analyses, conductivity, magnetic susceptibility and i.r., electronic, n.m.r., and Mossbauer spectral studies. The different modes of ligand chelation and the stereochemistry around the metal ion are discussed. The small range of isomer shift values for iron(II) complexes confirms the similar geometry for all the complexes.     

Titanium and zirconium complexes of preorganized tripodal triaryloxide ligands

Tri(2-oxy-3,5-di-tert-butylphenyl)methane, [O3]3- has been used to prepare titanium and zirconium complexes of the general formula [O3]MX (M = Ti, X = NEt2, Cl, CH2Ph; M = Zr, X = CH2Ph). The tripodal [O3] ligand in titanium complexes adopt the syn- and the anti-conformation, while the syn complex of zirconium undergoes facile C-H activation to give a 5-carbametalatrane [O3C]Zr(THF)3.     

Novel oxorhenium and oxotechnetium complexes from an aminothiol[NS]/thiol[S] mixed-ligand system

The simultaneous action of a bidentate aminothiol ligand, LnH, (n = 1: (CH3CH2)2NCH2CH2SH and n = 2: C5H10NCH2CH2SH) and a monodentate thiol ligand, LH (LH: p-methoxythiophenol) on a suitable MO (M = Re, 99gTc) precursor results in the formation of complexes of the general formula [MO(Ln)(L)3] (1, 2 for Re and 5. 6 for 99gTc). In solution these complexes gradually transform to [MO(Ln)(L)2] complexes (3, 4 for Re and 7, 8 for 99gTc). The transformation is much faster for oxotechnetium than for oxorhenium complexes. Complexes 1-4, 7, and 8 have been isolated and fully characterized by elemental analysis and spectroscopic methods. Detailed NMR assignments were made for complexes 3, 4, 7, and 8. X-ray studies have demonstrated that the coordination geometry around rhenium in complex 1 is square pyramidal (tau = 0.06), with four sulfur atoms (one from the L1H ligand and three from three molecules of p-methoxythiophenol) in the basal plane and the oxo group in the apical position. The L1H ligand acts as a monodentate ligand with the nitrogen atom being protonated and hydrogen bonded to the oxo group. The four thiols are deprotonated during complexation resulting in a complex with an overall charge of zero. The coordination geometry around rhenium in complex 4 is trigonally distorted square pyramidal (tau = 0.41), while in the oxotechnetium complex 7 it is square pyramidal (tau = 0.16). In both complexes LnH acts as a bidentate ligand. The NS donor atom set of the bidentate ligand and the two sulfur atoms of the two monodentate thiols define the basal plane, while the oxygen atom occupies the apical position. At the technetium tracer level (99mTc), both types of complexes, [99mTcO(Ln)(L)3] and [99mTcO(Ln)(L)2], are formed as indicated by HPLC. At high ligand concentrations the major complex is [99mTcO(Ln)(L)3], while at low concentrations the predominant complex is [99mTcO(Ln)(L)2]. The complexes [99mTcO(Ln)(L)3] transform to the stable complexes [99mTcO(Ln)(L)2]. This transformation is much faster in the absence of ligands. The complexes [99mTcO(Ln)(L)2] are stable, neutral, and also the predominant product of the reaction when low concentrations of ligands are used, a fact that is very important from the radiopharmaceutical point of view.     

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).     

New rare earth metal complexes with nitrogen-rich ligands: 5,5'-bitetrazolate and 1,3-bis(tetrazol-5-yl)triazenate-on the borderline between coordination and the formation of salt-like compounds

From the two nitrogen-rich ligands BT(2-) (BT=5,5'-bitetrazole) and BTT(3-) (BTT=1,3-bis(1H-tetrazol-5-yl)triazene), a series of novel rare earth metal complexes were synthesised. For the BT ligand, a vast number of these complexes could be structurally characterised by single-crystal XRD, revealing structures ranging from discrete molecular aggregates to salt-like compounds. The isomorphous complexes [La2(BT)3]14 H2O (1) and [Ce2(BT)3]14 H2O (2) reveal discrete molecules in which one BT(2-) acts as a bridging ligand and two BT groups as chelating ligands. The complexes, [M(BT)(H2O)7]2[BT] x (x) H2O (3-5), (M=Nd (3), Sm (4), and Eu (5)), are also isomorphous and consist of [M(BT)(H2O)7]+ ions in which only one BT(2-) acts as a chelate ligand for each metal centre. [Tb(H2O)8]2[BT]3 x H2O (6) and [Er(H2O)8](2)[BT](3)x H2O (7) are salt-like compounds that do not exhibit any significant metal-nitrogen contacts. In the BTT-samarium compound 9, discrete molecules were found in which BTT(3-) acts as a tridentate ligand with three Sm--N bonds.     

Tetranuclear [Cu-Ln]2 single molecule magnets: synthesis, structural and magnetic studies

A trianionic ligand H3L (2-hydroxy-N-(2-[[(2-hydroxyphenyl)methylene]amino]-2-methylpropyl)benzamide) with an inner N2O2 coordination site and an oxygen atom coming from an amide function not involved in this site yields monoanionic LCu- complexes that react with Ln(hfa)3 x 2H2O (hfa = hexafluoroacetylacetonato ligand) to give dinuclear Cu-Ln complexes that self-assemble into tetranuclear species, as demonstrated by the structural determination of the [LCuDy(hfa)2(dmf)2]2 complex. High-spin species are then isolated for two ferromagnetic interactions are active in the [Cu-Gd]2 entities, through the double phenoxo bridge (J = 3.2 cm(-1)) and through the single amide bridge (j = 0.54 cm(-1)). These interactions are still present in the [Cu-Tb]2 and [Cu-Dy]2 complexes which behave as single molecule magnets (SMMs), due to the introduction of anisotropic Ln ions in place of Gd ions.     

Palladium and platinum dihalide complexes with dl-selenomethionine

Palladium and platinum dihalides react with dl-selenomethionine (sem), yielding the complexes [M(sem)X2](M=Pd,X=Cl or Br;M=Pt,X=Cl) and, in the presence of N,N-dimethylformamide (dmf), the species [M(sem)X2]·dmf (M=Pd, X=I; M=Pt, X=Cl, Br or I). The complexes were characterized by i.r. and proton n.m.r. spectroscopy and by thermogravimetric analysis, and their properties were compared with those of the dl-methionine analogues [M(Met)Cl2] and [Pt(Met)Cl2]·dmf. On the basis of n.m.r. data in deuteriated dimethyl sulfoxide, the platinum complexes undergo ligand rearrangement to form [Pt(sem)2]2+ moieties whereas the solvent does not seem to interact with the palladium coordination sphere, which contains the chelated N, Se ligand.     

Synthesis and characterisation of second-generation metallodithiolene complexes of the type [Tp*ME(dithiolene)](M=Mo, W; E=O, S) and a novel 'organoscorpionate' complex of tungsten

Paramagnetic, chalcogenido-M(v) dithiolene complexes, [Tp*ME{S2C2(CO2Me)2}][M=Mo, E=O, S; M=W, E=O, S; Tp*=hydrotris(3,5-dimethylpyrazol-1-yl)borate] are generated in the reactions of dimethyl acetylenedicarboxylate (DMAC) and the sulfur-rich complexes NEt4[Tp*MoS(S4)] and NEt4[Tp*WS3]; the oxo complexes result from hydrolysis of the initial sulfido products. As well, a novel 'organoscorpionate' complex, [W{S2C2(CO2Me)2}{SC2(CO2Me)2-Tp*}], has been isolated from the reactions of NEt4[Tp*WS3] with excess DMAC. Complexes , and have been isolated and characterised by microanalytical, mass spectrometric, spectroscopic and (for and) X-ray crystallographic techniques. Complexes and have been partially characterised by mass spectrometry and IR and EPR spectroscopy. Six-coordinate, distorted-octahedral contains a terminal sulfido ligand (W=S=2.108(3)A), a bidentate dithiolene ligand (S-Cav=1.758 A, C=C=1.332(10)A) and a fac-tridentate Tp* ligand. Seven-coordinate contains a planar, bidentate dithiolene ligand (S-Cav=1.746 A, C=C=1.359(5)A) and a novel pentadentate 'organoscorpionate' ligand formed by the melding of DMAC, sulfido and trispyrazolylborate units. The latter is coordinated through two pyrazolyl N atoms (kappa2-N,N') and a tridentate kappa3-S,C,C' unit appended to N-beta of the third (uncoordinated) pyrazolyl group. The second-generation [Tp*ME(dithiolene)] complexes represent a refinement on first-generation [Tp*ME(arene-1,2-dithiolate)] complexes and their synthesis affords an opportunity to compare and contrast the electronic structures of true vs. pseudo-dithiolene ligands in otherwise analogous complexes.     

Size discrimination in the coordination chemistry of an isoindoline pincer ligand with CdII and ZnII

The reactions of Cd2+ and Zn2+ with the pyridine-arm isoindoline ligand 4'-MeLH = 1,3-bis[2-(4-methylpyridyl)imino]isoindoline produced the series of octahedrally coordinated complexes M(4'-MeL)2, [M(4'-MeLH)2]2+, and [M(4'-MeL)(4'-MeLH)]+. The complexes M(4'-MeL)2 resulted from reactions of the respective metal perchlorates with deprotonated ligand, whereas the complexes [M(4'-MeLH)2](ClO4)2 resulted from reactions with ligand in the absence of added base. The mixed-ligand complexes [M(4'-MeL)(4'-MeLH)]+ were generated in solution by reactions of equimolar quantities of M(4'-MeL)2 and [M(4'-MeLH)2]2+. Whereas [Cd(4'-MeL)(4'-MeLH)]+ is stable in solution, [Zn(4'-MeL)(4'-MeLH)]+ converts to and establishes equilibrium with the tetrahedrally coordinated, trinuclear complex [Zn3(4'-MeL)4]2+. The complexes Cd(4'-MeL)2 (1), Zn(4'-MeL)2 (2), and [Cd(4'-MeL)(4'-MeLH)]ClO4 (5) were characterized by single-crystal X-ray diffraction, with the latter complex being shown to contain 4'-MeLH coordinated as a protonated iminium zwitterionic ligand. The [M(4'-MeLH)2]2+ and [M(4'-MeL)(4'-MeLH)]+ complexes are tautomeric in solution because of the shuttling of the iminium protons between imine N atoms. The rate of prototropic tautomerism in [Cd(4'-MeLH)2]+ was followed by 1H NMR spectroscopy. Over the temperature range 276-312 K, a linear Eyring plot with the activation parameters DeltaG++ = 16.0 +/- 0.1 kcal/mol, DeltaH++ = 2.9 +/- 0.1 kcal/mol, and DeltaS++ = -44.0 +/- 0.3 cal/mol.K was obtained.     

Rhenium(V) oxo complexes with acetylacetone derived Schiff bases: structure and catalytic epoxidation

Substitution reactions of rhenium(V) oxo precursors [ReOCl3(PPh3)2] or [NBu4][ReOCl4] with the bidentate acetylacetone-derived ketoamine ligands APOH = 4-anilino-3-penten-2-one, DPOH = 4-[2,6-dimethylanilino]-3-penten-2-one, and MTPOH = 4-[2-(methylthio)anilino]-3-penten-2-one gave the complexes [ReO(APO)Cl2(PPh3)] (1), [ReO(DPO)Cl2(PPh3)] (2), and [NBu4][ReOLCl3] (3, L = APO; 4, L = DPO; 5, L = MTPO), respectively. All complexes exhibit only one ketoamino chelate, independent of the amount of ligand added to the rhenium precursors. The complexes were characterized by 1H and 13C NMR spectroscopy. X-ray crystal structures of the complexes 1, 2, 4, and 5, including that of MTPOH, were determined, revealing the trans position of the two oxygen atoms and the trans-Cl,Cl conformation in 1 and 2, in contrast to most other rhenium complexes of this type where the cis-Cl,Cl conformation is observed. Coordination of the potentially tridentate ligand MTPOH in 5 is bidentate with a dangling thioether substituent. Compound 2 shows catalytic activity in the oxidation of cis-cyclooctene with tert-butylhydroperoxide.     

Protonation studies of reduced ruthenium(II) complexes with polypyridyl ligands

The pKa values associated with protonation of the one-electron reduced forms of series of [L'2Ru(II)L]2+ complexes [L' = bidentate polypyridyl ligand; L = bidentate polypyridyl ligand with additional uncoordinated N atoms in the aromatic ring system: e.g., dpp = 2,3-bis(2-pyridyl)pyrazine, bpz = 2,2'-bipyrazine] were assessed using pulse radiolysis techniques by the measurement of spectral variations as a function of pH. A linear correlation was observed between pKa and E (RuL'2L2+/+) for complexes in which the protonatable ligand was at the same time the site of reduction. In complexes where one or more of the nonprotonatable ligands (L') had very low pi* energy levels [e.g. (CF3)4bpy], reduction occurs on a nonprotonatable ligand and a dramatic decrease in the pKa values was observed for the reduced species. In complexes where the energies of the protonatable and nonprotonatable ligands were comparable, the protonation behavior was consistent with some orbital mixing/ delocalization of the electronic charge.     

Spectroscopic characterization of chromium(III), manganese(II) and nickel(II) complexes with a nitrogen donor tetradentate, 12-membered azamacrocyclic ligand

The complexes of Cr(III), Mn(II) and Ni(II) were synthesized with macrocyclic ligand i.e. 5,11-dimethyl-6,12-diethyl-dione-1,2,4,7,9,10-hexazacyclododeca -1,4,6,10-tetraene. The ligand (L) was prepared by [2+2] condensation reaction of 2,3-pentanedione and semicarbazide hydrochloride. These complexes were found to have the general composition [Cr(L)X(2)]X and [M(L)X(2)] (where M=Mn(II) and Ni(II); X=Cl(-), NO(3)(-), (1/2)SO(4)(2-), NCS(-) and L=ligand [N(6)]). The ligand and its transition metal complexes were characterized by the elemental analysis, molar conductance, magnetic susceptibility, mass, IR, electronic and EPR spectral studies. On the basis of IR, electronic and EPR spectral studies, an octahedral geometry has been assigned for these complexes except sulphato complexes which are of five coordinated geometry.     

Coinage metal complexes of tris(pyrazolyl)methanide [C(3,5-Me2pz)3]-: kappa3-coordination vs. backbone functionalisation

Tris(pyrazolyl)methanides, [C(3,5-R2pz)3]-, contain an unassociated tetrahedral carbanionic centre in the bridgehead position. In addition to nitrogen donor centres for transition metal coordination, an accessible reactive site for further manipulations is available in the backbone of the ligand. The coordination variability of the ambidental C-/N ligand [C(3,5-Me2pz)3]- was elucidated by investigating its coinage metal complexes. Two principle coordination modes were found for complexes of general formula [LMPR3] (with M = Cu(I), Ag(I), Au(I); L =[C(3,5-Me2pz)3]-; R = Ph, OMe). While for Cu(I) (2,3) and Ag(I) (4) complexes the anionic ligand acts as a face-capping, six electron N3-donor, gold(I) (5) is coordinated by the bridging carbanion yielding a two coordinate Au(I) complex comprising a covalent Au-C bond. The complexes featuring the kappa3-coordinated N3-donor ligand were investigated by 31P CP (MAS) NMR in the solid state.     

Solid state and solution structures of rhodium and iridium poly(pyrazolyl)borate diene complexes

The structures adopted by a range of poly(pyrazolyl)borate complexes [ML2Tp(x)] [M = Rh, Ir; L2 = diene; Tp(x) = Bp' {dihydrobis(3,5-dimethylpyrazolyl)borate}, Tp' {hydrotris(3,5-dimethylpyrazolyl)borate}, Tp {hydrotris(pyrazolyl)borate}, B(pz)4 {tetrakis(pyrazolyl)borate}] have been investigated. Low steric hindrance between ligands in [Rh(eta-nbd)Tp] (nbd = norbornadiene), [Rh(eta-cod)Tp] (cod = cycloocta-1,5-diene) and [Rh(eta-nbd)Tp'] results in K3 coordination of the pyrazolylborate but [M(eta-cod)Tp'] (M = Rh, Ir) are kappa2 coordinated with the free pyrazolyl ring positioned above and approximately parallel to the square plane about the metal. All but the most sterically hindered Tp(x) complexes undergo fast exchange of the coordinated and uncoordinated pyrazolyl rings on the NMR spectroscopic timescale. For [Rh(eta-cod){B(pz)4}], [Rh(eta-dmbd)Tp'] (dmbd = 2,3-dimethylbuta-1,3-diene) and [Rh(eta-cod)Tp(Ph)] {Tp(Ph) = hydrotris(3-phenylpyrazolyl)borate} the fluxional process is slowed at low temperatures so that inequivalent pyrazolyl rings are observed. The bonding modes of the Tp' ligand (but not of other pyrazolylborate ligands) can be determined by 11B NMR and IR spectroscopy. The 11B chemical shifts (for a series of Tp' complexes) show the general pattern, kappa3 < -7.5 ppm < kappa2 and the nu(BH) stretch kappa3 > 2500 cm(-1) > kappa2. The electrochemical behaviour of the pyrazolylborate complexes is related to the degree of structural change which occurs on electron transfer. One-electron oxidation of complexes with Tp', Tp and B(pz)4 ligands is generally reversible although that of [Ir(etacod)Tp] is only reversible at higher scan rates and that of [Ir(eta-cod){B(pz)4}] is irreversible. Of the complexes with the more sterically hindered Tp(Ph) ligand, only [Rh(eta-nbd)Tp(Ph)] shows any degree of reversible oxidation. The ESR spectra of a range of Rh(II) complexes show coupling to both 14N and 103Rh nuclei in most cases but what appears to be coupling to rhodium and one hydrogen atom, possibly a hydride ligand, for the oxidation product of [Rh(eta-nbd)Tp(Ph)].     

Electrochemical and phosphorescent properties of new mixed-ligand Ir(II) complexes coordinated with both terpyridine and various bipyridine derivatives.

Seven useful mixed-ligand complexes in the form of [Ir(terpy)(L)Cl]2+ were prepared and their spectroscopic and electrochemical properties were investigated. The ligands used were terpy = 2,2':6',2'-terpyridine, L = 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine, 4,4'-diphenyl-2,2'-bipyridine, 1,10-phenanthroline, 5-phenyl-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, 2,3-bis(2-pyridyl)pyrazine. Synthetic methods were developed by a sequential ligand-replacement which occurred in the reaction vessel using a microwave oven. All complexes showed that LUMOs are based on the pi-system contribution of the terpyridine ligand for [Ir(terpy)(bpy)Cl]2+, [Ir(terpy)(dmbpy)Cl]2+, [Ir(terpy)(dpbpy)Cl]2+, [Ir(terpy)(phen)Cl]2+, [Ir(terpy)(dpphen)Cl]2+ and [Ir(terpy)(phphen)Cl]2+. On the other hand, the LUMO in the [Ir(terpy)(bppz)Cl]2+ complex is localized on the pi-system of the bppz ligand, whereas the HOMOs in the iridium complexes are localized on the terpyridine ligand. It was found that Ir(terpy)(L)Cl emits in a fluid solution at room temperature. The ancillary ligands, such as terpy and bpy, have been explored to extend the lifetime of the triplet 3(pi-pi') excited states of Ir(III) terpyridine complexes. Ir(III) terpyridine units with an electron donor (dmbpy) or electron acceptor substituents (terpy, dpbpy, phphen, dpphen and bppz) are found to decrease the energy of the 3LC states for use as photosensitizer molecular components in supramolecular devices. The spectroscopic and electrochemical details are also reported herein.     

A cross-coupling strategy for the synthesis of dimetallic assemblies containing mixed bipyridine-terpyridine bridging ligands: luminescence and energy transfer properties

Tris-bidentate complexes of the form [Ir(N[symbol: see text]C)2(N[symbol: see text]N)]+ and [Ru(N[symbol: see text]N)3]2+ incorporating a boronic acid substituent (N[symbol: see text]C=2-phenylpyridyl, N[symbol: see text]N=a 2,2'-bipyridyl ligand), are cross-coupled with bromo-substituted bis-terpyridyl ruthenium and iridium complexes to generate heterometallic assemblies comprising bpy-phi(n)-tpy bridges; they display efficient energy transfer from Ir(III) to Ru(II).     

Solid-state and solution properties of cationic lanthanide complexes of a new neutral heptadentate N4O3 tripodal ligand

The synthesis of the potentially heptadentate ligand tris[6-((2-N,N-diethylcarbamoyl)pyridyl)methyl]amine, tpaam, containing three pyridinecarboxamide arms connected to a central nitrogen is described. Lanthanide complexes of this ligand are prepared and characterized. The crystallographic structure of the complexes of three lanthanide ions (La, Nd, Lu) is determined. The lanthanide(III) complexes of tpaam crystallize as monomeric species (in the presence of chloride or iodide counterions) in which the ligand tpaam acts as a N4O3 donor. The crystal structures presented here show that the Ln[bond]O and Ln[bond]N(pyridyl) distances in the complexes of tpaam are similar to those found for the tpaa complexes (H(3)tpaa = alpha,alpha',alpha' '-nitrilotri(6-methyl-2-pyridinecarboxylic acid) despite the difference in charge. A lengthening of the Ln[bond]N(apical) distance is observed in the tpaam complexes compared to the tpa (tris[(2-pyridyl)methyl]amine) complexes which is more marked for larger lanthanides than for smaller ones. The solution structures of the tpaam complexes were analyzed across the 4f series and compared to the solution structures of the lanthanide complexes of the tetradentate ligand tpa. Proton NMR studies are in agreement with the presence of C(3)(v) symmetric solution species for both ligands. For the larger lanthanides, the cation moves away from the apical nitrogen compared to the position occupied in tpa complexes, whereas for the smaller lanthanides, the metal ion is located in a similar position for the two ligands. Quite surprisingly, the formation constant of the Eu(tpaam)Cl(3) complex in D(2)O at 298 K (log beta(110) = 2.34(4)) is very similar to the one reported for Eu(tpa)Cl(3) (log beta(110) = 2.49(4) at 298 K in D(2)O) indicating that the addition of three amide groups to the ligand tpa does not lead to any increase in stability of the lanthanide complexes of tpaam compared to those of tpa.     

Synthesis and coordination chemistry of an alkyne functionalised bis(pyrazolyl)methane ligand

The alkyne functionalised bidentate N-donor ligand (2-propargyloxyphenyl)bis(pyrazolyl)methane was prepared in high yield from the reaction of (2-hydroxyphenyl)bis(pyrazolyl)methane with propargyl bromide in the presence of base. A series of transition-metal complexes including [MCl2] (M=Cu, Co, Ni, Zn, Pt), [M2](NO3)2 (M=Cu, Co, Ni, Zn), [Ag]NO3 and [Pd(dppe)](OTf)2 were prepared and characterised by spectroscopic techniques. In addition, ligand as well as the Co(II) and Zn(II) complexes [CoCl2]2, [ZnCl2] were structurally characterized by single-crystal X-ray diffraction. The organometallic gold(I) and platinum(II) acetylide complexes [Pz2CH(C6H(4)-2-OCH2C[triple bond, length as m-dash]CAuPPh3)] and trans-[{Pz2CHC6H(4)-2-OCH2C[triple bond, length as m-dash]C}2Pt(PPh3)2] were prepared from and [AuCl(PPh3)] and trans-[PtCl2(PPh3)2], respectively. Treatment of these complexes with [Pd(OTf)2(dppe)] or [Cu(MeCN)4]PF6 results in formation of the cationic, mixed-metal complexes, which were isolated (Pt/Pd, Au/Pt) or detected by electrospray mass spectrometry (Au/Cu, Pt/Cu).