Voltammetric behaviour of rhenium(I) complexes with phosphine and carbon monoxide ligands in acetonitrile solvent

Summary The anodic and cathodic behaviour of the complexesmer-[ReCl(CO)₃(PMe₂Ph)₂],fac[ReCl(CO)₃(PMe₂Ph)₂],mer-[ReCl(CO)₃(PPh₃)₂], and [ReCl(CO)₂(PMe₂Ph)₃] in acetonitrile solvent were studied using platinum and mercury electrodes. Cyclic voltammetry and controlled potential coulometry were the main electroanalytical techniques employed. The nature of the electrolysis products and of the electrode oxidation and reduction processes were investigated. In particular, [ReCl(CO)(MeCN)₂(PMe₂Ph)₃][ClO₄]₂, [ReCl₃(CO)₂(PMe₂Ph)₂], and a not completely defined rhenium(-I) complex were electrochemically synthesized and characterized by means of i.r. and¹H n.m.r. spectroscopy, and by elemental analysis.     

Coordination chemistry of H-spirophosphorane ligands towards pentacarbonylchlororhenium(I) – synthesis,structure and catalytic activity of complexes

Synthesis of a group of carbonyl rhenium coordination compounds with hydrospirophosphorane ligands was carried out and described. Different symmetrical HP(OCH₂CH₂NH)₂ L1 , HP(OCH₂CMe₂NH)₂ L2 , HP(OC₆H₄NH)₂ L3 , and unsymmetrical ligands HP (OCMe₂CMe₂O)(OC₆H₄NH) L4 were found to coordinate to the rhenium center as bidentate P,N donor ligands yielding fac-[ReCl (CO)₃ Ln ], where n = 1 – 4. Furthermore, monodentate coordination was also observed in some cases, as was clearly presented in the case of [ReCl(CO)₂( L4- κ²P,N)( L4- κP)] complex. All of the complexes were characterized using optical spectroscopy. Single-crystalX-ray diffraction was also performed in the case of fac-[ReCl(CO)₃ L3 ], fac-[ReCl(CO)₃ L4 ], [Re(CO)₂( L2 )₂]Cl and [ReCl (CO)₂( L4- κ²P,N)( L4- κP)] samples. Complexes [ReCl(CO)₃ L3 ] and [ReCl (CO)₃ L4 ], both bearing rings of conjugated double bonds within hydrospirophosphorane ligands, exhibited luminescence. Catalytic properties of rhenium complexes were assessed using the representative fac-[ReCl (CO)₃ L2 ] complex in the dimerization reaction of terminal alkynes. An efficient and selective procedure for synthesis of the E - enynes was developed. Coupling of (2-chlorophenyl)acetylene was mediated by [ReCl (CO)₃ L2 ]/TBAF system with a 100% conversion rate. Different substituents within aromatic alkynes were tolerated and the resulting products were dependent on the nature of the substituents.     

Reactions oftrans-[Mo(CNMe)2(PMe2Ph)4] andmer-[W(CNMe)3(PMe2Ph)3] complexes with methanol and with mineral acids to give amines,ammonia and hydrocarbons

Summary Treatment oftrans-[Mo(CNMe)₂(PMe₂Ph)₄] andme-[W(CNMe)₃(PMe₂Ph)₃] with sulphuric or hydrochloric acids in methanol or ethanol, or in methanol alone, under irradiation, gives methylamine, ammonia and hydrocarbons (mainly methane). The complex [W₂(CNMe)₄(-CNHMe)₂(PMe₂Ph)₄]²⁺ cation has been obtained by the treatment ofmer-[W(CNMe)₃(PMe₂Ph₃] with H₂SO₄ or [Et₂OH][BF₄] and gives methylamine, ammonia and methane on further acid treatment.     

The preparation and molecular structure oftrans-[MoCl2(PMe2Ph)4]

Summary The compoundtrans-[MoCl₂(PMe₂Ph)₄] has been prepared by the reduction of MoCl₅ (by Mg) or of [MoCl₃(PMe₂Ph)₃] (by LiBuⁿ) in the presence of PMe₂Ph in tetrahydrofuran (THF). It has _eff=2.84 B.M. and crystallises in space group P1 witha=11.591(3),b=12.931(3),c=12.703(3) Å, = 95.28(2), =105.97(2), =103.54(2)°. Refinement of the structure gave R=0.036. The Mo-Cl and Mo-P distances average 2.443(6) and 2.534(8) Å, respectively.Low-valent phosphine complexes of the Group VI metals continue to attract much attention because of their involvement in studies of the catalytic activation of dinitrogen⁽¹⁾, dihydrogen(^{2, 3}), alkenes and alkynes(⁴). As a by-product during our studies of dinitrogen(¹) and hydride(²) complexes of molybdenum and tungsten, we obtainedtrans-[MoCl_2- (PMe₂Ph)₄] as yellow, paramagnetic crystals (_eff= 2.84 B.M.). We first obtained the compound during the attempted synthesis ofcis-[Mo(N₂)₂(PMe₂Ph)₄] by reduction of MoCl₅ with Mg in the presence of PMe₂Ph (see Experimental). Upon identification of the compound we found that it could be readily synthesised by treatment of [MoCl₃(PMe₂Ph)₃]⁽⁵⁾ with LiBuⁿ in THF in the presence of PMe₂Ph (experimental).The complex was shown to have thetrans structure by x-ray analysis (Figure). Analogues oftrans-[MoCl₂(PMe₂Ph)₄] have been prepared, namely [CrCl₂(Me₂PCH₂CH₂PMe₂)₂]⁽⁶⁾,trans- [MoCl₂(PMe₃)₄]⁽⁷⁾, [WCl₂(PMe₂Ph)₄]⁽⁸⁾ and [WCl₂(PMe₃)₄]⁽⁴⁾, of which onlytrans-[MoCl₂(PMe₃)₄] has been examined by X-rays⁽⁷⁾. Its principal structural parametersi.e. d(Mo-Cl)= 2.420(6), d(Mo-P)_av=2.496(3) Å⁽⁶⁾ are close to those found here fortrans-[MoCl₂(PMe₂Ph)₄].     

Preparation of poly(p-chlorostyrene)-supported phenyl(dipyridyl)nickel chloride

The complexes [ReCl(N₂)(PMe₂Ph)jtJ. Amer. Chem. Soc.4₃] and [ReCl(N₂)(PMe₂Ph)₃(pyridine)] react with organic acid halides, RCOCl, to form acylazo- and aroylazo-complexes, [ReCl₂(N₂COR)(PMe₂Ph)₃], for which X-ray diffraction studies confirm the formation of the NC bond; the osmium complex [OsCl₂(N₂)(PEt₂Ph)₃] does not undergo analogous reactions.     

A cyclometallated iridium(III) dimethylphenylphosphine complex

[Ir(cod)Cl]₂ (cod = 1,5-cyclooctadiene) reacts with PMe₂Ph in CH₃CN to give the red cation [Ir(PMe₂Ph)₄]⁺. This complex in CH₃CN reacts with H₂ to give cis-[IrH₂(PMe₂Ph)₄]⁺, but on reflux for 6 h in the absence of H₂, it gives the first example of a cyclometallated PMe₂Ph complex fac-[IrH(PMe₂C₆H₄)(PMe₂Ph)₃]⁺, as shown by PMR spectroscopy and preliminary X-ray crystallographic data.     

t-Butyl isocyanide complexes of rhenium(I), chromium(O), tungsten(O,I) and platinum(II); X-ray crystal structures of bis(t-butylisocyanide)- tris(trimethylphosphine)chlororhenium(I) and tris(t-butylisocyanide)bis(trimethyl- phosphine)chlororhenium(I)

The reduction of ReCl₄(THF)₂ in the presence of excess t-butylisocyanide by sodium amalgam produces pentakis(t-butylisocyanide)chlororhenium(I), which has been converted to the corresponding methyl and ethyl derivatives. The reaction of pentakis(trimethylphosphine)chlororhenium(I) with Bu^tNC gives partially substituted complexes, ReCl(CNBu^t)₂(PMe₃)3 and ReCl(CNBu^t)₃(PMe₃)₂. The structures of both compounds have been determined by X-ray methods. Octahedral ReCl(CNBu^t)₂(PMe₃)₃ has trans isocyanide groups with one linear [C---N---C = 175(1)°] and one slightly bent [C---N---C = 159(1)°]. The Re---C bond lengths are equal within experimental error [2.004(7), 2.003(7)Å]. In the octahedral ReCl(CNBu^t)₃(PMe₃)₂, for which the structure is not well defined, due to disorder, the unique isocyanide trans to chlorine is considerably bent at the nitrogen atom [C--- ---C = 141(6)°] and appears to show the shortest Re---C bond length, 1.94(5) vs 2.02(5)Å for the other two isocyanides which are mutually trans. Protonation of these two isocyanide complexes with fluoroboric acid gives, respectively, the salts [ReCl(CNBu^t)CNHBu^t(PMe₃)₃]BF₄ and [ReCl(CNBu^t)₂CNHBu^t(PMe₃)₂]BF₄, whose configurations have been determined by NMR spectroscopy. The reduction by sodium amalgam of Cr₂(CO₂Me)₄ in tetrahydrofuran in presence of Bu^tNC gives a high yield of Cr(CNBu^t)₆ while similar reduction of the dimeric tungsten(II) complex of the anion (mhp) of 2-methyl-6- hydroxypyridine gives W(CNBu^t)₆. Interaction of W₂(mhp)₄ in methanol-ether with Bu^tNC gives a tungsten(I) complex W₂(η-mhp)₂(Bu^tNC)₄, which may be an intermediate in the reductive cleavage reaction. Interaction of cis-PtMe₂(PMe₃)₂ with Bu^tNC leads only to replacement of one PMe₃ group to give the complex cis-PtMe₂(PMe₃)(CNBu^t).     

A luminescent rhenium(I) complex of 2,7-dimethyl-1,8-naphthyridine: synthesis,spectroscopy and X-ray crystal structure

2,7-Dimethyl-1,8-naphthyridine (L¹) reacts with pentacarbonylchlororhenium in toluene or chloroform to give the target complex fac-{ReCl(CO)₃(L¹)}. X-ray crystallographic data were obtained for fac-{ReCl(CO)₃(L¹)}. The structural and ¹H NMR data suggest that the ligand coordinates to the rhenium in a bidentate fashion in both solid and solution states. The complex was also found to be luminescent in both solution and solid states. The fluxionality of the ligand in solution causes ligand-centred emission to be observed in solution, whereas only ³MLCT emission was observed in the solid state. Although the complex was air-stable, the lability of L¹ was studied in ¹H NMR experiments where CD₃OD induced complete ligand dissociation over the course of 24 h, and also in reaction of fac-{ReCl(CO)₃(L¹)} with one equivalent of 2,2′-bipyridine in chloroform which resulted in quantitative ligand exchange. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The optical sensor fac-tri­carbonyl­chloro­(di-2-pyridyl­methanone p-nitro­phenyl­hydrazone)­rhenium(I) di­methyl sulfoxide solvate

The first metal complex of di-2-pyridyl­methanone p-nitro­phenyl­hydrazone (dpknph), i.e. the title compound, fac-[ReCl(C₁₇H₁₃N₅O₂)(CO)₃]·C₂H₆OS, crystallizes as well separated pseudo-tetrahedral DMSO (DMSO is di­methyl sul­foxide) and pseudo-octahedral fac-[ReCl(dpknph)(CO)₃] moieties. Two N atoms from dpknph, three C atoms from the carbonyl groups and one chloride ion occupy the coordination sphere around rhenium. The coordinated dpknph ligand forms a six-membered ring in a boat conformation, with the pyridine rings in a butterfly formation. The p-nitro­phenyl­hydrazone moiety is planar, with all C and N atoms in sp²-hybridized forms. The mol­ecules pack as stacks of interlocked fac-[ReCl(dpknph)(CO)₃]·DMSO units via a network of non-covalent bonds that include solute–solute, solvent–solute and π–π interactions.     

Phosphine carbonyl-technetium(I) and -technetium(III) complexes

Treatment of trans-[TcX₄L₂] (X Cl, Br and L PPH₃, PMe₂Ph) with carbon monoxide (1 atm) in boiling ethyleneglycol methyl ether, gives trans-[TcX-(CO)₃L₂]. Under these conditions the mer-[TcX₃(PMe₂Ph)₃] (X Cl, Br) gives a mixture of the trans-[TcX(CO)₃(PMe₂Ph)₂] and cis-[TcX(CO)₂(PMe₂Ph)₃] complexes, but when added free dimethylphenylphosphine is present only the second product is obtained. Carbon monoxide reacts with mer-[TcCl₃(PMe₂Ph)₃] in refluxing ethanol to give [TcCl₃(CO)(PMe₂Ph)₃] a C_{3 v} seven-coordinate technetium(III) complex.The stereochemistry of the complexes was determined from their IR and¹H NMR spectra.     

Preparation of Ru(CO)3(PMe3)MeI and its acetyl derivatives

[Ru(CO)₄PMe₃] reacts with MeI to give fac-[Ru(CO)₃(PMe₃)(Me)I]. The latter reacts with PMe₃ to give a mixture of the three isomers of cis-bis(trimethylphosphine)-cis-dicarbonyl acetyl iodide [Ru(CO)₂(PMe₃)₂(COMe)I]. Decarbonylation of the mixture gives only the trans-bis(trimethylphosphine)-cis-dicarbonyl methyl iodide complex [Ru(CO)₂(PMe₃)₂MeI], which was also prepared by oxidative addition of MeI to [Ru(CO)₃(PMe₃)₂].     

Hydrido-silyl complexes,Part VIII. Photochemical reaction of [Fe(CO)3H(PR′3)SiR3] with silanes,HSiR3: Influence of PR′3 and SiR3 on formation and structures of bis-silyl complexes [Fe(CO)3(PR′3)(SiR3)2]

Summary Upon u.v. irradiation of [Fe(CO)₄(PR ₃ )] with HSiR₃ (HSiR₃ = HSiMePh₂, PR₃ = PPh₃; HSiR₃ = HSiMe₂Cl, PR₃ = PPh₃ or PMe₂Ph; HSiR₃ = HSiMeCl₂, PR₃ = PPh₃, PMePh₂, PMe₂Ph or PMe₃; HSiR₃ = HSiCl₃, PR₃ = PPh₃, PMePh₂, PMe₂Ph, PMe₃ or PBu ₃ ⁿ ) the corresponding hydridosilyl complexes [Fe(CO)₃H(PR₃)SiR₃] are formed. The complexes have themer configuration with acis disposition of the hydride and the silyl ligands. Prolonged irradiation with an excess of silane results in the formation of bis-silyl complexes [Fe(CO)₃(PR₃)(SiR₃)₂], if electron density at the metal is not too high. Thus, [Fe(CO)₃H(PPh₃)SiMePh₂] and [Fe(CO)₃-H(PMe₂Ph)SiMe₂Cl] can be obtained but not the corresponding bis-silyl complexes. Most bis-silyl complexes are obtained asmer-isomers with acis-arrangement of the silyl ligands. Only for [Fe(CO)₃(PR₃)(SiCl₃)₂] with small phosphine ligands (PR₃ = PMe₃ or PMe₂Ph) is thefac-isomer formed.Part VII of this series, ref. (1).     

[M(CO)2(NO)], a new core in bioorganometallic chemistry: model complexes of [Re(CO)2(NO)] and [Tc(CO)2(NO)]

In this study selected bidentate (L²) and tridentate (L³) ligands were coordinated to the Re(I) or Tc(I) core [M(CO)₂(NO)]²⁺ resulting in complexes of the general formula fac-[MX(L²)(CO)₂(NO)] and fac-[M(L³)(CO)₂(NO)] (M = Re or Tc; X = Br or Cl). The complexes were obtained directly from the reaction of [M(CO)₂(NO)]²⁺ with the ligand or indirectly by first reacting the ligand with [M(CO)₃]⁺ and subsequent nitrosylation with [NO][BF₄] or [NO][HSO₄]. Most of the reactions were performed with cold rhenium on a macroscopic level before the conditions were adapted to the n.c.a. level with technetium (^99mTc). Chloride, bromide and nitrate were used as monodentate ligands, picolinic acid (PIC) as a bidentate ligand and histidine (HIS), iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) as tridentate ligands. We synthesised and describe the dinuclear complex [ReCl(μ-Cl)(CO)₂(NO)]₂ and the mononuclear complexes [NEt₄][ReCl₃(CO)₂(NO)], [NEt₄][ReBr₃(CO)₂(NO)], [ReBr(PIC)(CO)₂(NO)], [NMe₄][Re(NO₃)₃(CO)₂(NO)], [Re(HIS)(CO)₂(NO)][BF₄], [⁹⁹Tc(HIS)(CO)₂(NO)][BF₄], [^99mTc(IDA)(CO)₂ (NO)] and [^99mTc(NTA)(CO)₂(NO)]. The chemical and physical characteristics of the Re and Tc-dicarbonyl-nitrosyl complexes differ significantly from those of the corresponding tricarbonyl compounds.     

Synthesis of cationic carbonyl complexes of manganese(I) with bidentate ligands

Summary Bidentate ligands can readily replace acetone in thefac-[Mn(CO)₃(chel)(OCMe₂)]⁺ complexes or the perchlorate group fromfac-[Mn(CO)₃(chel)(OClO₃)] yieldingfac-[Mn(CO)₃(chel)(L-L)]⁺ or [{fac-Mn(CO)₃(chel)}₂(L-L)]²⁺ [chel = 1,10-phenanthroline (phen), 2,2-bipyridine (bipy), 1,2-bis(diphenylphosphine)ethane (dpe); L-L = bis(diphenylphosphine)methane (dpm), dpe, 1,4-bis(diphenylphosphine)butane (dpb), succinonitrile (suc), and glutaronitrile (glu)]. Some of these mononuclear complexes are precursors for binuclear complexes which are linked by bridging phosphines or nitriles.     

Diene and dienyl complexes of transition elements: VII. Carbonylchlorobis(dimethylphenylphosphine)-(η3-pentadienyl)ruthenium

The reaction between [{Ru(CO)Cl₂(PMe₂Ph)₂}₂] and SnBu₃(C₅H₇) in chloroform yields the η³-pentadienyl complex [Ru(CO)Cl(η³-C₅H₇)(PMe₂Ph)₂]. The ¹H NMR spectra are reported and discussed.     

Chelating and Tellurolate Ligand‐Transfer Studies of the Complex fac‐[Fe(CO)3(TePh)3]−: Crystal Structures of Heterodinuclear (CO)3Mn(μ‐TePh)3Fe(CO)3 and CpNi(TePh)(PPh3)

Complex fac‐[Fe(CO)₃(TePh)₃]^? was employed as a “metallo chelating” ligand to synthesize the neutral (CO)₃Mn(μ‐TePh)₃Fe(CO)₃ obtained in a one‐step synthesis by treating fac‐[Fe(CO)₃(TePh)₃]^? with fac‐[Mn‐(CO)₃(CH₃CN)₃]⁺. It seems reasonable to conclude that the d⁶ Fe(II) [(CO)₃Fe(TePh)₃]^? fragment is isolobal with the d⁶ Mn(I) [(CO)₃Mn(TePh)₃]^2? fragment in complex (CO)₃Mn(μ‐TePh)₃Fe(CO)₃. Addition of fac‐[Fe(CO)₃(TePh)₃]^? to the CpNi(I)(PPh₃) in THF resulted in formation of the neutral CpNi(TePh)(PPh₃) also obtained from reaction of CpNi(I)(PPh₃) and [Na][TePh] in MeOH. This investigation shows that fac‐[Fe(CO)₃(TePh)₃]^? serves as a tridentate metallo ligand and tellurolate ligand‐transfer reagent. The study also indicated that the fac‐[Fe(CO)₃(SePh)₃]^? may serve as a better tridentate metallo ligand and chalcogenolate ligand‐transfer reagent than fac‐[Fe(CO)₃(TePh)₃]^? in the syntheses of heterometallic chalcogenolate complexes.     

Modification of the acid-base properties of hydroxycarbonyl complexes of iridium(III) by substitution of carbon monoxide by a tertiary phosphine ligand

A dichloromethane solution of the cationic carbonyl complex [IrCl₂(CO)(PMe₂Ph)₃)][ClO₄] reacts with aqueous KOH to give [IrCl₂(CO₂H)(PMe₂Ph)₃] which has been characterised spectroscopically. This CO₂H compound is very much more basic and very much less acidic than [IrCl₂(CO₂H)(CO)(PMe₂Ph)₂). Tertiary amines will not deprotonate [IrCl₂(CO₂H)(PMe₂Ph)₃] while Li[N(SiMe₃)₂] leads to decarboxylation products trans, mer- and cis, mer-[IrHCl₂(PMe₂Ph)₃]. The mechanisms of these reactions are considered and the hydroxycarbonyl complex is compared with its formato isomer which decarboxylates much less readily.     

Ligand exchange reactions of fac -(dihapto-[60]fullerene) (dihapto-1,2- bis -(diphenylphosphino)ethane tricarbonyl chromium(0)

The complex fac-(η²-C₆₀)(η²-dppe)Cr(CO)₃ (dppe?=?1,2-bis(diphenylphosphino)ethane and C₆₀?=?[60]fullerene) reacts with piperidine (pip) to produce fac-(η²-C₆₀)(η¹-pip)₂Cr(CO)₃. The reactions are first order with respect to [?fac-(η²-C₆₀)(η²-dppe)Cr(CO)₃] under flooding conditions where [pip]???[?fac-(η²-C₆₀)(η²-dppe)Cr(CO)₃]. The pseudo-first order rate constant values (k _obsd) are [pip]-dependent. Curved (upward) plots of k _obsd versus [pip] and linear plots of k _obsd versus [pip]² indicate that the piperidine-assisted dppe displacement from fac-(η²-C₆₀) (η²-dppe)Cr(CO)₃ is second order with respect to [pip]. The proposed mechanism involves a [60]fullerene-stabilized intermediate.     

Intramolecular rearrangement of the bridging σ,π-acetylide ligand in the Os3H(CO)9(L)(μ-η2-CCPh) (L = CO,PMe2Ph) clusters and crystal structure of Os3H(CO)9(PMe2Ph)(μ-η2-CCPh)

Clusters Os₃H(Cl)(CO)₉(L) (L= CO, PMe₂Ph) react with lithium phenyl-acetylide to yield Os₃H(CO)₉(L)(μ-η²-CCPh),which has a bridging acetylide ligand. The Os₃H(CO)₁₀(μ-η²-CCPh) complex (II) is fluxional owing to rapid π → σ, σ → π interchange of acetylide ligand between the bridged osmium atoms, whereas the phosphine-substituted derivative, Os₃H(CO)₉(PM₂Ph)(μ-η²-CCPh) (III), is stereochemically rigid and exists at room temperature in two isomeric forms. These isomers have been isolated as solids and have been characterized by ¹H and ³¹P{¹H} NMR spectroscopy. According to the spectroscopic data, in the major (IIIa) and minor (IIIb) isomers the phosphine ligand is coordinated to the metal atom which is σ- or π-bonded to the bridging acetylide group, respectively. The isomerization of IIIb into IIIa occurs only at 80°C. The structure of IIIa has been confirmed by an X-ray diffraction study.