Reactivity of Schiff base rhenium(V) complexes with dimethylphenylphosphine

Summary The ReOX₂L(PPh₃) complexes (X = Cl or Br and L =N-methylsalicylideneiminate,N-phenylsalicylideneiminate, halfN,N-ethylenebis(salicylideneiminate) or 8-hydroxyquinolinate) react with dimethylphenylphosphine (PMe₂Ph) to give ReOX₂L(PMe₂Ph) initially by displacement of the phosphine ligand and then the ReX₂L(PMe₂Ph)₂ complexes with reduction of rhenium(V) to rhenium(III). The complexes were characterized by elemental analysis, magnetic susceptibility measurements and i.r. and¹H n.m.r. spectra.     

Substitutions of organopalladium(II) species with benzimidazole derivatives

The [Pd(cod)(cotl)]ClO₄ complex (cod = cycloocta-1,5-diene; cotl = cyclooctenyl, C₁₈H₁₃ ^–) undergoes substitutions with new Schiff base ligands containing benzimidazole L [L = 2-(2-N-n-propylidenephenyl)benzimidazole (L¹); 2-(2-N-i-propylidenephenyl)benzimidazole (L²); 2-(2-N-n-butylidenephenyl)benzimidazole (L³); 2-(2-N-i-butylidenephenyl)benzimidazole (L⁴)]. Facile displacement of cod by L occurs to produce complexes of the type [Pd(cotl)L]ClO₄· nMe₂CO (n= 0; L = L¹, L² or L³; n= 2, L = L⁴). Dihalobridge complexes of the type [Pd(cotl)X]₂(X = Cl or Br) undergo halogen-bridge cleavage with L¹–L⁴ to give mononuclear complexes of the type Pd(cotl)LX · nH₂O (n= 2, X = Cl, L = L¹; n= 0, X = Br, L = L¹; n= 0, X = Cl, L = L²; n= 0, X = Cl or Br, L = L³; n= 0, X = Cl, L = L⁴; n= 2, X = Br, L = L⁴) and a binuclear complex [Pd(cotl)Br]₂L². The complexes were characterised by physical properties, i.r., ¹H- and ¹³C-n.m.r. spectral techniques and by mass spectra. Probable structures have been proposed.     

Synthesis and spectroscopic studies of substituted molybdenum carbonyls ofN,N′-ethylenebis(1,2-dimethylpyrazole-3-carboxaldeneimine) and monodentate tertiary phosphines

Summary Improved preparations ofcis-[LMo(CO)₄],cis-[L₂Mo(CO)₂], and [LMo(CO)₃P] where L=N, N-ethylenebis(1, 2-dimethylpyrazole-3-carboxaldeneimine) and P=P(p-MeOC₆H₄)₃, P(p-MeC₆H₄)₃, P(p-ClC₆H₄)₃ or P(o-MeC₆H₄)₃ are reported. The compounds were characterized by elemental analysis and i.r., electronic and³¹P n.m.r. spectra. The (CO) values for the nonphosphine complexes indicate Mo(4d)–L(^*) back-bonding. Furthermore, L exists in two different configurations in the [{LMo(CO)₄}₂] and the monomeric derivatives. Electronic spectral data are discussed in terms of the effect of the -acceptor tendency of the Mo(4d)–L(^*) back bonding.³¹P n.m.r. and i.r. data of the phosphine-containing compounds indicate that the more electron-withdrawing substituents on the phosphines gave larger³¹P coordination chemical shifts and larger CO frequencies.     

The reactions of [MI2(CO)3(NCMe)2] (M=Mo or W) with one equivalent of L(L-phosphorus,arsenic and antimony donor ligands) to afford [MI2(CO)3(NCMe)L] and [M(μ-I)I(CO)3L]2

Summary The complexes [MI₂(CO)₃(NCMe)₂] (M=Mo or W) react with one molar equivalent of L in CH₂Cl₂ at room temperature initially to afford the mononuclear sevencoordinate complexes [MI₂(CO)₃(NCMe)L] which have been isolated for L-PPh₃, AsPh₃, SbPh₃, PPh₂Cy or P(OPh₃)₃. Many of these complexes dimerise to give the iodide bridged compounds [{M(–I)I(CO)₃L}₂]via displacement of acetonitrile. When L=PPhCy₂, PCy₃, PEt₃ or P(OMe)₃ only the dimeric complexes have been isolated. The ease of dimerisation of the mononuclear complexes [MI₂(CO)₃(NCMe)L] is discussed in terms of the electronic and steric effects of the ligands, L. Low temperature¹³C n.m.r. spectroscopy of the mononuclear [Wl₂(CO)₃(NCMe)(EPh₃)](E=P or As) complexes are interpreted as suggesting the likely stereochemistry of these seven-coordinate complexes.     

Metal-proton interactions in palladium(II) and rhodium(I) complexes ofortho-alkylanilines

Summary Reaction of 1 equivalent ofo-alkylaniline with Pd(OAc)₂ gave the acetate bridged complexes [Pd(OAc)₂L]₂. The^*H n.m.r. spectra showed downfield shifts for theo-benzylic protons indicating an above-plane geometry involving a significant interaction with the metal orbitals. Similar interactions were found for Pd(OAc)₂L₂ and Pd(OAc)₂L(L) (L= differento-alkylaniline; t-butylpyridineetc.) prepared from the dimer and for Rh(CO)₂Cl(L) complexes. Theo-benzylic carbons of the palladium complexes did not show downfield shifts in the¹³C n.m.r. spectra.     

N-Phthaloylglycinate ternary complexes with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) metal ions and aromatic mono,bi and tridentate amines

Complexes of N-phthaloylglycinate (N-phthgly) and Co^II, Ni^II, Cu^II, Zn^II and Cd^II containing imidazole (imi), N-methylimidazole (mimi), 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen), and tridentate amines such as 2,2,2-terpyridine (terpy) and 2,4,6-(2-pyridyl)s-triazine (tptz), were prepared and characterized by conventional methods, i.r. spectra and by thermogravimetric analysis. For imi and mimi ternary complexes, the general formula [M(imi/mimi)₂(N-phthgly)₂]·nH₂O, where M = Co^II, Ni^II, Cu^II and Zn^II applies. For Cd^II ternary complexes with imi, [Cd(imi)₃(N-phthgly)₂]·2H₂O applies. For the bi and tridentate ligands, ternary complexes of the formula [M(L)(N-phthgly)₂]·nH₂O were obtained, where M = Co^II, Ni^II, Cu^II and Zn^II; L = bipy, phen, tptz and terpy. In all complexes, N-phthgly acts as a monodentate ligand, coordinating metal ions through the carboxylate oxygen, except for the ternary complexes of Co^II, Ni^II and Cu^II with mimi and Cu^II and Zn^II with imi, where the N-phthgly acts as a bidentate ligand, coordinating the metal ions through both carboxylate oxygen atoms.     

Insertions of phenylacetylene with chelated bis(triphenylphosphine) - ruthenium(II)hydridocarbonyl complexes

Summary Phenylacetylene reacts stoichiometrically or in excess with the Ru—H bond of RuH(CO)(PPh₃)₂(L) (LH = 2-hydroxypyridine, 2-hydroxy-6-methylpyridine, acetylacetone, benzoylacetone, 2-hydroxyacetophenone, 2-hydroxypropiophenone, 2-hydroxybenzophenone and 4-methoxy-2-hydroxybenzophenone) in boiling benzene to give -vinylic or -vinylalkynyl complexes of the type Ru(CO)-(PPh₃)₂(L)(CH CHPh) and Ru(CO)(PPh₃)₂(L){C-(C CPh) CHPh} in good yield. The vinylic complex can also be obtained by reacting the sodio derivative of the chelating ligand with the 16e^– unsaturated complex, [Ru(CO)Cl(CH CHPh)(PPh₃)₂], in CH₂Cl₂/MeOH mixture at ambient temperature. These complexes have been characterized by elemental analyses, and i.r., ¹H, ¹³C and ³¹P n.m.r. spectroscopy.N.C.L Communication No. 5404.     

Ruthenium(II) carbonyl complexes containing tridentate Schiff bases

New ruthenium(II) complexes, [Ru(CO)(B)(LL)(PPh₃)] (where, LL = tridentate Schiff bases; B = PPh₃, pyridine, piperidine or morpholine) have been prepared by reacting [RuHCl(CO)(PPh₃)₃] or [RuHCl(CO)(PPh₃)₂(B)] with Schiff bases containing donor groups (O, N, X) viz., salicylaldehyde thiosemicarbazone (X = S), salicylaldehyde semicarbazone (X = O), o-hydroxyacetophenone thiosemicarbazone (X = S) and o-hydroxyacetophenone semicarbazone (X = O). The new complexes were characterised by elemental analysis, spectral (i.r., ¹H- and ³¹P-n.m.r.), data.     

Naphthyl-(2-pyridylmethylene)amine complexes of silver(I) and ruthenium(II): synthesis,spectral studies and electrochemical behaviour

Pyridine-2-carboxaldehyde reacts with /-naphthylamine to give /-naphthyl-(2-pyridylmethylene)amine [-L (1), -L (2)]. L belongs to the unsymmetric diimine (—N=C—C=N—) family which can form five–membered chelate rings with metal ions. {donor centers are abbreviated as N[N(Py)] and N [N(nap)]} [Ag(L)₂]⁺ complexes were prepared and characterized by spectroscopic data. The reaction between L and RuCl₃ in boiling EtOH yielded green and blue–green compounds of composition RuCl₂(L)₂. I.r., u.v.–vis. and ¹H-n.m.r. data determined the stereochemistry of the complexes as trans-cis-cis (green) and cis-trans-cis (blue–green) according to the sequence of the coordination pair of Cl, N [N(Py)] and N [N(nap)]. Upon treatment of Ag(L)₂ ⁺ with Ru(bpy)₂Cl₂ in alcoholic suspension the ternary complexes, [Ru(bpy)₂(L)](ClO₄)₂, were isolated and characterized by spectroscopic data. [Ru(bpy)(L)₂](ClO₄)₂ complexes were synthesized similarly from ctc-Ru(L)₂Cl₂ and 2,2-bipyridine (bpy) in the presence of AgNO₃ and NaClO₄. These complexes show well-defined m.l.c.t transitions in the visible region. The sterochemistry of the complexes was established by ¹H-n.m.r. data. Cyclic voltammetry shows a high potential Ru^III/Ru^II couple and follows the order: [Ru(bpy)(L)₂]²⁺ > [Ru(bpy)₂(L)]²⁺ > Ru(-L)₂Cl₂ > Ru(-L)₂Cl₂.     

Copper (II)-thiolate complexes with novel tripodal- and tetrapodal-like benzimidazoles

Summary The tripodal copper(II) thiolate complexes Cu(L1)(Cl)-2H₂O and Cu(L1)(mim)(Cl) [H(L1) = N-(2-mercaptoethyl)-N,N-bis (pyrid-2-ylmethyl)amine and mim = N-methylimidazole] have been isolated. Both contain monomeric copper(II) and display two ligand field bands and axial cryogenic e.p.r. spectra, suggesting a squarebased geometry. A copper(II) thiolate complex Cu(L2)(Cl)-H₂O [H(L2) = N-(2-mercaptoethyl)-N,N,N-tris(benzimidazol-2-ylmethyl)-1,2-ethanediamine] with a CuN₅S chromophore has been also isolated. It exhibits only one ligand field band and an axial cryogenic e.p.r. spectrum, consistent with a distorted tetragonal coordination geometry. All the thiolates display intense S^– Cu^II charge transfer bands in the u.v. region, suggesting equatorial thiolate coordination. All of the complexes exhibit irreversible electrochemical behaviour.     

Carbonyl cationic rhodium(I) and iridium(I) complexes with sulphur donor and triphenylphosphine ligands

Summary The reaction of previously reported Rh^I and Ir^I cationic complexes towards carbon monoxide and triphenylphosphine has been studied. Carbonyl rhodium(I) mixed complexes of the formulae [Rh(CO)L₂(PPh₃)]ClO₄, (L=tetrahydrothiophene(tht), trimethylene sulfide(tms), SMe₂, or SEt₂), [(CO)(PPh₃)Rh{-(L-L)}₂Rh(PPh₃)(CO)](ClO₄)₂ (L-L= 2,2,7,7-tetramethyl-3,6-dithiaoctane (tmdto), (MeS)₂(CH₂)₃ (dth), or 1,4-dithiacyclohexane (dt), [Rh(CO)L(PPh₃)₂]ClO₄ (L= tht, tms, SMe₂, or SEt₂), and carbonyl iridium(I) complexes of the formulae [Ir(CO)₂(COD)(PPh₃)]ClO₄, [Ir(CO)(COD)(PPh₃)₂]ClO₄, [(CO)(COD)(PPh₃) Ir{-(L-L)} Ir(PPh₃)(COD)(CO)](ClO₄)₂ (L-L = tmdto or dt), [(CO)₂ (PPh₃)Ir(-tmdto)Ir(PPh₃)(CO)₂](ClO₄)₂, [(CO)₂(PPh₃) Ir(-dt)₂Ir(PPh₃)(CO)₂](ClO₄)₂, were prepared by different synthetic methods.     

Seven-coordinate complexes of molybdenum(II) and tungsten(II). Preparation and spectral properties of [MI2(CO)3LL′] {M=Mo or W; L=PPh3, AsPh3 or SbPh3; L′=SC(NH2)2, SC(NMe2)2 or SC(NH2)Me}

Summary The seven-coordinate complexes [MI₂(CO)₃(NCMe)₂] (M=Mo or W) react either in acetone or methanol with one equivalent of L (L=PPh₃, AsPh₃ or SbPh₃) to give [MI₂(CO)₃(NCMe)L], which when reactedin situ with one equivalent of L {L=SC(NH₂)₂, SC(NMe₂)₂ or SC(NH₂)Me} affords good yields of the new mixed complexes [MI₂(CO)₃LL]via successive displacement of acetonitrile ligands.     

New synthesis and low temperature13C n.m.r. spectra of some anionic seven-coordinate complexes of molybdenum(II) and tungsten(II) of the type [NBu 4 n ][MI2X(CO)3L]

Summary The bisacetonitrile complexes [MI₂(CO)₃(NCMe)₂] react with an equimolar amount of L in CH₂Cl₂ at room temperature to give [MI₂(CO)₃(NCMe)L] which when mixedin situ with an equimolar amount of [NBu ₄ ⁿ ]X affords the anionic seven-coordinate compounds [NBu ₄ ⁿ ][MI₂X(CO)₃L][M=Mo or W,X=I, L=PPh₃ (for M=W only), AsPh₃ or SbPh₃ (for M=Mo only); M=Mo and W, X=Br₃ or Br₂I, L=PPh₃, AsPh₃ or SbPh₃]. These reactions are likely to occurvia the stepwise dissociative displacement of two acetonitrile ligands. Low-temperature (–70° C, CD₂Cl₂)¹³C n.m.r. spectra (CO resonances) are reported for several of the complexes in order to infer the likely stereochemistry of these compounds.     

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.     

Antibacterial activity of ruthenium(II) carbonyl complexes containing tetradentate Schiff bases

Several new hexa-coordinated ruthenium(II) complexes of the type [Ru(CO)(LL)(B)] (where, LL = anthacac, anthdibm, 2-amtpacac or 2-amtpdibm; B = PPh₃ or py or pip or morph) have been prepared by reacting [RuHCl(CO)(PPh₃)₃] or [RuHCl(CO)(PPh₃)₂(B)] with tetradentate Schiff bases such as bis(anthranilic acid)acetylacetimine (H₂-anthacac), bis(anthranilic acid) dibenzoylmethimine (H₂-anthdibm), bis(2-aminothiophenol) acetylacetimine (H₂-2-amptacac) or bis(2-aminothiophenol) dibenzoylmethimine (H₂-2-amtpdibm). The complexes have been characterised by elemental analyses and spectral (i.r., electronic spectra, ¹H- and ³¹P-n.m.r.) data. An octahedral structure has been tentatively proposed for the complexes, which were also tested for their antibacterial properties.     

Synthesis,reactivity and x-ray crystal structures of mixed thiazolato- or carboxylato- carbonyl(phosphine) rhenium(I) complexes

Summary The compound [Re(CO)₃(PPh₃)₂Cl] reacts with the lithium salt of thiazole derivatives (L¹H = 2-amino-benzothiazole, L²H = 2–N-methyl-aminothiazole, L³H = 2–N-phenylaminothiazole, L⁴H = 2–N-(4-methoxyphenyl)aminothiazole, L⁵H = 2–N(4-nitrophenyl)aminothiazole) to give [Re(CO)₂-(PPh₃)₂(L)]. The compounds have been characterized by elemental analysis, i.r. and¹H n.m.r. spectra. At room temperature [Re(CO)₂(PPh₃)(L²)] reacts with L⁶H (L⁶H = diphenylacetic acid), to give the carboxylato complex [Re(CO)₂ .The crystal structures of [Re(CO)₂(PPh₃)₂(L²)] (2) and [Re(CO)₂(PPh₃)₂(L⁶)] (6) were determined by x-ray crystallography. [Re(CO)₂(PPh₃)₂(L²)] crystallizes in the monoclinic space group P2₁/m witha = 9.16(1),b= 24.82(2),c =9.12(1) Å, and = 115.81(4)°; D_c = 1.56 g cm^–3for Z = 2.The structure was refined to a final R of 6.4%. The molecules have C_s symmetry. The rhenium atom is six-coordinate with approximately octahedral geometry. The anionic ligand is chelating through the nitrogen atoms and is strictly planar allowing delocalization of the -electron density. [Re(CO)₂(PPh₃)₂(L⁶)] (6) crystallizes in the monoclinic space group P2₁/n witha = 22.203(5),b = 18.651(5),c =10.653(3) Å, = 91.08(3)°, Dc = 1.47 g cm^–3 for Z = 4. The structure was refined to a final R of 4.7%. The complex is monomeric and the rhenium atom is distorted octahedral with two mutuallytrans PPh₃ ligands, twocis CO ligands and one chelating Ph₂CHCO ₂ ^– ion.     

Preparation and properties of palladium(II) and rhodium(I) complexes containing bidentate phosphine sulphide and selenide ligands

Summary The synthesis and properties of cationic complexes of general formula [ML₂{CH₂(Ph₂PE)₂}]BF₄, where M = Pd^II and Rh^II, L₂ = ³-MeC₃H₄, {P(O)(OR)₂}₂H (R = Me, Et), COD, (CO)₂, (CO)PPh₃ and E = S, Se are described. The methylene proton of the coordinated phosphine sulphide or selenide ligands react with strong bases as BuLi in n-hexane or NaH in THF, to give neutral complexes of the type [ML₂{CH(Ph₂PE)₂}], where M = Pd^II, Rh^I; L₂ = ³-MeC₃H₄, COD and E = S, Se. The complexes have been characterized by elemental analyses, molar conductivities, i.r., ¹H n.m.r. and ³¹P{¹H} n.m.r. spectroscopy.     

4,4′-Bipyridine complexes of molybdenum(II) and tungsten(II)

Treatment of [MI₂(CO)₃(NCMe)₂] with two equivalents of 4,4-bipyridine (4,4-bipy) in CH₂Cl₂ at room temperature gave the MeCN displaced products, [MI₂(CO)₃(4,4-bipy-N)₂] (1) and (2). Equimolar amounts of [MI₂(CO)₃(NCMe)₂] and L (L = PPh₃, AsPh₃ or SbPh₃) react to give [MI₂(CO)₃(NCMe)L], which when reacted in situ with 4,4-bipy yield the new complexes, [MI₂(CO)₃(4,4-bipy-N)L] (3)–(8). Reaction of equimolar quantities of [WI₂(CO)(NCMe)( ²-RC₂R)₂] (R = Me or Ph) and 4,4-bipy gave the new bis(alkyne) complexes, [WI₂(CO)(4,4-bipy-N)( ²-RC₂R)₂] (9) and (10). Treatment of [MI₂(CO)₃(NCMe)₂] with two equivalents of (9) or (10) in CH₂Cl₂ at room temperature affords the bimetallic complexes, [MI₂(CO)₃{WI₂(CO)(4,4-bipy-N,N)( ²-RC₂R)₂}₂] (11)–(14). Equimolar quantities of [MI₂(CO)₃(NCMe)(PPh₃)] (prepared in situ) and (9) or (10), react to give the 4,4-bipy-bridged complexes, [MI₂(CO)₃{WI₂(CO)(4,4-bipy-N,N)( ²-RC₂R)₂}(PPh₃)] (15)–(18). All the new complexes, (1)–(18) were characterised by elemental analysis (C, H and N), i.r. and ¹H-n.m.r. spectroscopy.     

Energetics of the oxidative addition of I2 to [Ir(Μ-L)(CO)2]2 (L=S t Bu, 3,5-Me2pz,7-aza) complexes. X-ray structures of Ir(Μ-S t Bu)(I)(CO)2]2 and [Ir(Μ-3,5-Me2pz)(I)(CO)2]2

The energetics of the oxidative additive of I₂ to [Ir(-L)(CO)₂]₂ [L =t-buthylthiolate (S ^t Bu), 3,5-dimethylpyrazolate (3,5-Me₂pz), and 7-azaindolate (7-aza)] complexes was investigated by using the results of reaction-solution calorimetric measurements, X-ray structure determinations, and extended Hückel (EH) molecular orbital calculations. The addition of 1 mol of iodine to 1 mol of [Ir(-L)(CO)₂]₂, in toluene, leads to [Ir(-L)(I)(CO)₂]₂, with the formation of two Ir-I bonds and one Ir-Ir bond. The following enthalpies of reaction were obtained for this process: –125.8±4.9 kJ mol^–1 (L = S ^t Bu), –152.0±3.8 kJ mol^–1 (L=3,5-Me₂pz), and –205.9±9.9 kJ mol^⊃ (L=7-aza). These results are consistent with a possible decrease of the strain associated with the formation of three-, four-, and five-membered rings, respectively, in the corresponding products, as suggested by the results of EH calculations. The calculations also indicate a slightly stronger Ir-Ir bond for L = 3,5-Me₂pz than for L= S ^t Bu despite the fact that the Ir-Ir bond lengths are identical for both complexes. The reaction of 1 mol of [Ir(-S ^t Bu)(CO)₂]₂ with 2 mol of iodine to yield [Ir(-S ^t Bu)(I)₂(CO)₂]₂ was also studied. In this process four Ir-I bonds are formed, and from the corresponding enthalpy of reaction (–186.4±2.7 kJ mol^–1) a solution phase Ir-I mean bond dissociation enthalpy in [Ir(-S ^t Bu)(I)₂(CO)₂]₂, , was derived. This value is lower than most values reported for octahedral mononuclear Ir¹¹¹ complexes. New large-scale syntheses of the [Ir(-L)(CO)₂]₂ complexes, with yields up to 90%, using [Ir(acac)(CO)₂] as starting material, are also reported. The X-ray structures of [Ir(-L)(I)(CO)₂]₂ (L=S^tBu and 3,5-Me₂pz) complexes have been determined. For L=S^tBu the crystals are monoclinic, space group P2_l/c,a=10.741(2) å,b= 11.282(3) å,c=18.308(3) å,=96.71(1), andZ=4. Crystals of the-3,5-Me₂pz derivative are monoclinic, space group P2_l/n,a=14.002(3) å,b= 10.686(1) å,c=15.627(3) å,=112.406(8), andZ=4. In both complexes the overall structure can be described as two square-planar pyramids, one around each iridium atom, with the iodine atoms in the apical positions, and the equatorial positions occupied by two CO groups and the two sulfur atoms of the S ^t Bu ligands, or two N atoms of the pyrazolyl ligands. In the case of L=S^tBu the pyramids share a common edge defined by the two bridging sulfur atoms and for L =3,5-Me₂pz they are connected through the two N-N bonds of the pyrazolyl ligands. The complexes exhibit short Ir-Ir single bonds of 2.638(1) å for L=S^tBu and 2.637(1) å for L=3,5-Me₂Pz. The oxidative addition of iodine to [Ir(-3,5-Me₂pz)(CO)₂]₂ results in a remarkable compression of 0.608 å in the Ir-Ir separation.     

Cyclic ligands with fixed co-ordination geometry. Part 6(1). Chalcogenanthrenes as bridging ligands in dinuclear complexes of rhenium(I) and platinum(IV)-X-ray crystal structure of di(μ-chloro) (μ-2, 3, 7, 8-tetramethoxyselenanthrene) hexamethyl diplatinum(IV)

Summary The chalcogenanthrenes Vn₂EE; 2, 3, 7, 8-tetramethoxythianthrene (E=E=S), 2, 3, 7, 8-tetramethoxydibenzothiaselenin (E=S, E=Se), and 2, 3, 7, 8-tetramethoxyselenanthrene (E=E=Se), react with [{ReBr(CO)₃(THF)}₂] and [{PtXMe₃}₄] (X=Cl or Br) to give the dinuclear complexes [(fac-L₃M)₂(-X)₂ (-Vn₂EE)] (M=Re, L=CO, X=Br; M=Pt, L=Me, X=Cl or Br) in which the chalcogenanthrenes reveal a hitherto unknown co-ordination mode as bridging ligands. Telluranthrene (Pn₂ Te₂), however, forms mononuclear complexes of compositionfac-[L₃MX(Pn₂Te₂)] (M=Re, L=CO, X=Br; M=Pt, L=Me, X=Br) with a chelating chalcogenanthrene ligand. Whereas the rhenium compounds are not stable enough in solution to be studied by i.r. spectroscopy, the platinum compounds can be well characterised by their¹H n.m.r. spectra. Furthermore, the results of a single-crystal structure determination of [Pt₂Cl₂Me₆(Vn₂Se₂)] are reported. The Pt–Se distance of 259 pm indicates a relatively weak interaction between the chalcogenanthrene and the remaining dinuclear fragment of the molecule.