Formation of a complex with a carbide bridge between two iron atoms from the reaction of (tetraphenylporphyrin)iron(II) with carbon tetraiodide

A Lead-μ2-Tetrylide Complex with Osmium(IV) Terminal Components

A bare lead atom is a σ-donor ligand capable of linearly bonding and stabilizing two units of a classical polyhydride complex, with a high-valent metal center. As a proof of concept, we have prepared and characterized the μ2-tetrylide complex (PiPr3)2H4Os═Pb═OsH4(PiPr3)2 in the reaction of OsH6(PiPr3)2 with Pb{N(SiMe3)2}2. Although the Pb-Os bonds exhibit electrostatic interaction, the main orbital interactions result from two dative σ bonds from the lead atom to the osmium centers. The latter also provide much weaker π-backdonations.

Organometallic Allene [(μ-C)(Fe(CO)4 )2 ]: Bridging Carbon Showing Transformation from Classical Electron-Sharing Bonding to Double σ-Donor and Double π-Acceptor Ligation

Allenes (R2 C=C=CR2 ) have been traditionally perceived to feature localized orthogonal π-bonds between the carbon centres. We have carried out quantum-mechanical studies of the organometallic allenes envisioned by the isolobal replacement of the terminal CH2 groups by the d8 Fe(CO)4 fragment. Our studies have identified two organometallic allenes viz. D2d symmetric [(μ-C)(Fe(CO)4 )2 ] (2) and D3 symmetric [(μ-C)(Fe(CO)4 )2 ] (3) with trigonal bipyramidal coordination at the Fe atoms. Compound 2 features the bridging carbon atom in an equatorial position with respect to the ligands on the TM centre, while 3 features the central carbon atom in an axial position. The bis-pseudoallylic anionic delocalisation proposed in the C2-C1-C3 spine of organic allene is retained in the organometallic allene 2, and is transformed to a typical three-centre bis-allylic anionic delocalisation in the organometallic allene 3. The topological analysis of electron density also indicates a bis-allylic anionic type delocalisation in the organometallic allenes. The quantitative bonding analysis using the EDA-NOCV method suggests a transition from classical electron-sharing bonding between the central carbon atom and the terminal groups in 1 to donor-acceptor bonding in 3. Meanwhile, both electron-sharing and donor-acceptor bonding models are found to be probable heuristic bonding representations in the organometallic allene 2.

Partial Deoxygenative CO Homocoupling by a Diiron Complex

One route to address climate change is converting carbon dioxide to synthetic carbon-neutral fuels. Whereas carbon dioxide to CO conversion has precedent in homo- and heterogeneous catalysis, deoxygenative coupling of CO to products with C-C bonds-as in liquid fuels-remains challenging. Here, we report coupling of two CO molecules by a diiron complex. Reduction of Fe2 (CO)2 L (2), where L2- is a bis(β-diketiminate) cyclophane, gives [K(THF)5 ][Fe2 (CO)2 L] (3), which undergoes silylation to Fe2 (CO)(COSiMe3 )L (4). Subsequent C-OSiMe3 bond cleavage and C=C bond formation occurs upon reduction of 4, yielding Fe2 (μ-CCO)L. CO derived ligands in this series mediate weak exchange interactions with the ketenylidene affording the smallest J value, with changes to local metal ion spin states and coupling schemes (ferro- vs. antiferromagnetism) based on DFT calculations, Mössbauer and EPR spectroscopy. Finally, reaction of 5 with KEt3 BH or methanol releases the C2 O2- ligand with retention of the diiron core.

Transition Metal Carbide Complexes

Carbide complexes remain a rare class of molecules. Their paucity does not reflect exceptional instability but is rather due to the generally narrow scope of synthetic procedures for constructing carbide complexes. The preparation of carbide complexes typically revolves around generating L_nM-CE_x fragments, followed by cleavage of the C-E bonds of the coordinated carbon-based ligands (the alternative being direct C atom transfer). Prime examples involve deoxygenation of carbonyl ligands and deprotonation of methyl ligands, but several other p-block fragments can be cleaved off to afford carbide ligands. This Review outlines synthetic strategies toward terminal carbide complexes, bridging carbide complexes, as well as carbide-carbonyl cluster complexes. It then surveys the reactivity of carbide complexes, covering stoichiometric reactions where the carbide ligands act as C₁ reagents, engage in cross-coupling reactions, and enact Fischer-Tropsch-like chemistry; in addition, we discuss carbide complexes in the context of catalysis. Finally, we examine spectroscopic features of carbide complexes, which helps to establish the presence of the carbide functionality and address its electronic structure.

Chromium carbides and cyclopropenylidenes

Carbon tetrabromide can be reduced with CrBr2 in THF to form a dinuclear carbido complex, [CrBr2(thf)2)][CrBr2(thf)3](μ-C), along with formation of [CrBr3(thf)3]. An X-ray diffraction (XRD) study of the pyridine adduct displayed a dinuclear structure bridged by a carbido ligand between 5- and 6-coordinate chromium centers. The carbido complex reacted with two equivalents of aldehydes to form α,β-unsaturated ketones. Treatment of the carbido complex with alkenes resulted in a formal double-cyclopropanation of alkenes by the carbido moiety to afford spiropentanes. Isotope labeling studies using a 13C-enriched carbido complex, [CrBr2(thf)2)][CrBr2(thf)3](μ-13C), identified that the quaternary carbon in the spiropentane framework was delivered by carbide transfer from the carbido complex. Terminal and internal alkynes also reacted with the carbido complex to form cyclopropenylidene complexes. A solid-state structure of the diethylcyclopropenylidene complex, prepared from 3-hexyne, showed a mononuclear cyclopropenylidene chromium(iii) structure.

Construction of an iminoketenylidene

The new isonitrile-μ-carbido complexes [WPt(μ-C)Br(CNR)(PPh₃)(CO)₂(Tp*)] (R = C₆H₂Me₃-2,4,6, C₆H₃Me₂-2,6; Tp* = hydrotris(dimethylpyrazolyl)borate) rearrange irreversibly in polar solvents to provide the first examples of iminoketenylidene (CCNR) complexes.

Benzyne addition to a metal-carbon multiple bond

The linear μ-carbido complex [Rh2(μ-C)Cl2(dppm)2] (dppm = bis(diphenylphosphino)methane) reacts with a benzyne equivalent (Me3SiC6H4OTf-2/F-) to afford [Rh2(μ-CC6H4)(μ-Cl)(C6H5)Cl2(μ-dppm)2], in which the benzyne moiety adds across one of the two metal-carbon double bonds.

Mixed-Valent Diiron μ-Carbyne, μ-Hydride Complexes: Implications for Nitrogenase

Binding of N₂ by the FeMo-cofactor of nitrogenase is believed to occur after transfer of 4 e^- and 4 H⁺ equivalents to the active site. Although pulse EPR studies indicate the presence of two Fe-(μ-H)-Fe moieties, the structural and electronic features of this mixed valent intermediate remain poorly understood. Toward an improved understanding of this bioorganometallic cluster, we report herein that diiron μ-carbyne complex (P₆ArC)Fe₂(μ-H) can be oxidized and reduced, allowing for the first time spectral characterization of two EPR-active Fe(μ-C)(μ-H)Fe model complexes linked by a 2 e^- transfer which bear some resemblance to a pair of E_n and E_n+2 states of nitrogenase. Both species populate S = 1/2 states at low temperatures, and the influence of valence (de)localization on the spectroscopic signature of the μ-hydride ligand was evaluated by pulse EPR studies. Compared to analogous data for the {Fe₂(μ-H)}₂ state of FeMoco (E₄(4H)), the data and analysis presented herein suggest that the hydride ligands in E₄(4H) bridge isovalent (most probably Fe^III) metal centers. Although electron transfer involves metal-localized orbitals, investigations of [(P₆ArC)Fe₂(μ-H)]⁺¹ and [(P₆ArC)Fe₂(μ-H)]^-1 by pulse EPR revealed that redox chemistry induces significant changes in Fe-C covalency (-50% upon 2 e^- reduction), a conclusion further supported by X-ray absorption spectroscopy, ⁵⁷Fe Mössbauer studies, and DFT calculations. Combined, our studies demonstrate that changes in covalency buffer against the accumulation of excess charge density on the metals by partially redistributing it to the bridging carbon, thereby facilitating multielectron transformations.

Carbones and Carbon Atom as Ligands in Transition Metal Complexes

This review summarizes experimental and theoretical studies of transition metal complexes with two types of novel metal-carbon bonds. One type features complexes with carbones CL₂ as ligands, where the carbon(0) atom has two electron lone pairs which engage in double (σ and π) donation to the metal atom [M]⇇CL₂. The second part of this review reports complexes which have a neutral carbon atom C as ligand. Carbido complexes with naked carbon atoms may be considered as endpoint of the series [M]-CR₃ → [M]-CR₂ → [M]-CR → [M]-C. This review includes some work on uranium and cerium complexes, but it does not present a complete coverage of actinide and lanthanide complexes with carbone or carbide ligands.

Heterobimetallic μ2-carbido complexes of platinum and tungsten

The tungsten–platinum μ-carbido complex [WPt(μ-C)Br(CO)₂(PPh₃)₂(Tp*)] (Tp* = hydrotris(dimethylpyrazol-1-yl)borate) undergoes facile substitution of both bromide and phosphine ligands to afford a diverse library of μ-carbido complexes.

A heterobimetallic cumulenic μ-carbido complex

Cleavage of a selenocarbonyl ligand in [W(CSe)(NO)(CO)(Tp*)] by [Re(THF)(CO)₂(Cp)] provides heterobimetallic cumulenic μ-carbido and μ-selenido complexes.

Dimetalla-heterocyclic carbenes: the interconversion of chalcocarbonyl and carbido ligands

Different classes of dirhodium μ-carbido complexes cleave CS₂ to afford mono- and bi-nuclear CS complexes, the CSe analogues of which are also described.

Carbyne decorated porphyrins

Porphyrins peripherally decorated with four transition-metal carbynes substituents are obtained in one step via a Pd⁰/Au^I transmetallation shuttle beginning with a stannyl carbyne.

Halogenation of A-frame μ-carbido complexes: a diamagnetic rhodium(ii) carbido complex

Chlorination of the new μ-carbido [Rh₂(μ-C)Cl₂(μ-dppf)₂] (dppf = 1,1′-bis(diphenylphosphino)ferrocene) affords the dirhodium(ii) complex [Rh₂(μ-C)Cl₄(μ-dppf)₂] the carbido bridge of which can only be adequately described by delocalised bonding.

From Ylides to Doubly Yldiide-Bridged Iron(II) High Spin Dimers via Self-Protolysis

A synthetic strategy for the preparation of novel doubly yldiide bridged iron(II) high spin dimers ([(μ2-C)FeL]2, L = N(SiMe3)2, Mesityl) has been developed. This includes the synthesis of ylide-iron(II) monomers [(Ylide)FeL2] via adduct formation. Subsequent self-protolysis at elevated temperatures by in situ deprotonation of the ylide ligands results in a dimerization reaction forming the desired bridging μ2-C yldiide ligands in [(μ2-C)FeL]2. The comprehensive structural and electronic analysis of dimers [(μ2-C)FeL]2, including NMR, Mössbauer, and X-ray spectroscopy, as well as X-ray crystallography, SQUID, and DFT calculations, confirm their high-spin FeII configurations. Interestingly, the Fe2C2 cores display very acute Fe-C-Fe angles (averaged: 78.6(2)°) resulting in short Fe···Fe distances (averaged: 2.588(2) Å). A remarkably strong antiferromagnetic coupling between the Fe centers has been identified. Strongly polarized Fe-C bonds are observed where the negative charge is mostly centered at the μ2-C yldiide ligands.

Halogenation of A-frame μ-carbido complexes: synthesis of μ2-halocarbynes

The new A-frame μ₂-carbido complexes [Rh₂(μ₂-C)X₂(μ₂-dppm)₂] (X = Cl, Br; dppm = Ph₂PCH₂PPh₂) react with PhICl₂ or [pyH][Br₃] to provide rare examples of μ₂-halocarbyne complexes [Rh₂(μ-CX)(μ-X)X₄(μ-dppm)₂] (X = Cl, Br).

Tungsten–platinum μ-carbido and μ-methylidyne complexes

The lithiocarbyne [W]CLi ([W] = W(CO)₂(Tp*); Tp* = tris(dimethylpyrazolyl)borate) with divalent platinum complexes afford access to μ-carbido, μ-methylidyne and carbyne-based metallo-ligand complexes.

Platinum(ii) as an assembly point for carbide and nitride ligands

The sequential treatment of (Cy₃P)₂Cl₂RuC with [PtCl₂(C₂H₄)]₂ and (dbm)₂CrN affords a platinum(ii) center coordinated by both carbide and nitride ligands.

Confluence of disparate carbido chemistries: [WRuAu2(μ-C)2Cl2(CO)2(PCy3)2(Tp*)]

The reaction of [Ru(CAuCl)Cl₂(PCy₃)₂] with [W(CSnⁿBu₃)(CO)₂(Tp*)] (obtained from [W(CBr)(CO)₂(Tp*)], ⁿBuLi and ClSnⁿBu₃) affords the heterotetrametallic bis(carbido) complex [WRuAu₂(μ-C)₂Cl₃(CO)₂(PCy₃)₂(Tp*)] in which the two distinct μ-carbido ligands adopt linear and T-shaped geometry at carbon.

Cofacial porphyrin dimers assembled from N-heterocyclic carbene–metal bonds

Cofacial porphyrin dimers assembled from eight metal–carbene bonds were synthesized by using porphyrins with four imidazolium groups as precursors.

Simple generation of a dirhodium μ-carbido complex via thiocarbonyl reduction

The reaction of [RhCl(CS)(PPh₃)₂] with excess catecholborane affords the cumulenic carbido complex [Rh₂(μ-C)Cl₂(PPh₃)₄] which undergoes phosphine and halide substitution to afford a range of complexes in which the RhCRh spine remains intact.

Synthons for carbide complex chemistry

Harnessing lability, the miniaturized ligand sphere in a [RuC–Pt] complex establishes a straightforward building-block approach to carbide complexes.

Insight into the Iron-Molybdenum Cofactor of Nitrogenase from Synthetic Iron Complexes with Sulfur, Carbon, and Hydride Ligands

Nitrogenase enzymes are used by microorganisms for converting atmospheric N2 to ammonia, which provides an essential source of N atoms for higher organisms. The active site of the molybdenum-dependent nitrogenase is the unique carbide-containing iron-sulfur cluster called the iron-molybdenum cofactor (FeMoco). On the FeMoco, N2 binding is suggested to occur at one or more iron atoms, but the structures of the catalytic intermediates are not clear. In order to establish the feasibility of different potential mechanistic steps during biological N2 reduction, chemists have prepared iron complexes that mimic various structural aspects of the iron sites in the FeMoco. This reductionist approach gives mechanistic insight, and also uncovers fundamental principles that could be used more broadly for small-molecule activation. Here, we discuss recent results and highlight directions for future research. In one direction, synthetic iron complexes have now been shown to bind N2, break the N-N triple bond, and produce ammonia catalytically. Carbon- and sulfur-based donors have been incorporated into the ligand spheres of Fe-N2 complexes to show how these atoms may influence the structure and reactivity of the FeMoco. Hydrides have been incorporated into synthetic systems, which can bind N2, reduce some nitrogenase substrates, and/or reductively eliminate H2 to generate reduced iron centers. Though some carbide-containing iron clusters are known, none yet have sulfide bridges or high-spin iron atoms like the FeMoco.

Delivering carbide ligands to sulfide-rich clusters

The propensity of the terminal ruthenium carbide Ru(C)Cl₂(PCy₃)₂ (RuC) to form carbide bridges to electron-rich transition metals enables synthetic routes to metal clusters with coexisting carbide and sulfide ligands.

Carbide complexes as π-acceptor ligands

A terminal carbide complex binds as a π-acceptor towards electron-rich metal centers, mirroring CO, and provides the first homoleptic, carbide-ligated complex.

The π-accepting character of a terminal carbide complex acting as a ligand is demonstrated experimentally and corroborates earlier theoretical predictions. As a result, coordination of a terminal ruthenium carbide complex to electron-rich metal centres is shown to provide a facile and versatile route to carbide-bridged heterometallic complexes. Synthesis, reactivity, spectroscopic and structural characterization are reported for heterobimetallic systems with auxiliary metals from groups 9–11: Rh(i), Ir(i), Pd(ii), Pt(ii), Ag(i), and Au(i) coordinated by [Ru(C)Cl₂(PCy₃)₂] (RuC). This encompasses the first example of a homoleptic carbide-ligated transition metal complex: [{(Cy₃P)₂Cl₂RuC}₂Au]⁺. Kinetics of substitution on Pt(ii) by RuC ranks the carbide complex as having intermediate nucleophilicity. The ¹³C-NMR signals from the carbide ligands are significantly more shielded in the bridged heterobimetallic complexes than in the parent terminal carbide complex. Structurally, RuC forms very shorts bonds to the heterometals, which supports the notion of the multiple bonded complex acting as a π-backbonding ligand. Reactions are reported where RuC displaces CO coordinated to Rh(i) and Ir(i). A strong trans influence exerted by RuC indicates it to be a stronger σ-donor than CO. The geometries around the carbide bridges resemble those in complexes of electron-rich metals with carbonyl or bridging nitride-complex-derived ligands, which establishes a link to other strong π-acceptor ligands.

μ-Carbido Diporphyrinates and Diphthalocyaninates of Iron and Ruthenium

μ-Carbido diporphyrinates and diphthalocyaninates of general formula [{ Mp 2−}2(μ- C )] ( p 2− = tpp ( M = Fe ), oep ( Fe ), pc ( Fe , Ru ); H 2 tpp : 21H,23H-5,10,15,20-tetraphenylporphine; H 2 oep : 21H,23H-2,3,4,8,12,13,17,18-octaethylporphine; H 2 pc : 29H,31H-phthalocyanine) of formally Fe IV and Ru IV are prepared by a new and improved ‘one-pot’ synthesis. The corresponding chloro complexes of the tervalent metal ions react successively with potassium hydroxide in boiling 2-propanol and then with trichloromethane. Potassium hydroxide is proven to be a very versatile and powerful reductant in tetrapyrrolic chemistry. As evidenced from electron spin resonance and UV vis spectral measurements, the precursor is reduced primarily to an ate-complex of type [ M I p 2−]− of a formally monovalent metal ion. This active species is assumed to react with trichloromethane via a dichlorocarbene complex of type [ M II( CCl 2) p 2−] to yield the actual -carbido complex. [{ Feoep 2−}2(μ- C )] is crystallographically characterized. It is monoclinic, space group C12/c1 (15), with a = 18.279(3) Å, b = 15.005(2) Å, c = 23.392(7) Å, β = 107.12(2)°, Z = 4, R1 = 0.0773. The iron atom is displaced by 0.192(3) Å out of the centre ( Ct ) of the ( N p )4 plane toward the (μ- C ) atom. Average d ( Fe - N p ) is 1.986(5) Å; d ( Fe -(μ- C )) is 1.6638(9) Å. The Fe - C - Fe skeleton is linear (179.5(3)°). The two slightly waving porphyrinato cores are in a staggered conformation, the ( N p - Fe - Fe ″- N p ″) torsion angle being 21.0(3)°. Solutions of each μ-carbido complex in pyridine/dichloromethane show four distinct quasi-reversible redox processes in their differential-pulse voltammograms and these are assigned to the successive one-electron reduction and oxidation of the macrocyclic ligands. 13 C CP MAS NMR spectra indicate effective four-fold symmetry within the series of the μ-carbido complexes with isotropic shifts occurring at similar fields to those of the corresponding macrocyclic complex of a closed-shell metal ion. Resonances of the bridging carbon atom are not detected. A characteristic increase of line broadening within the series tpp 2− > oep 2− > pc 2− may be due to Fermi contact interactions with the strongly coupled low-spin M IV centres. The magnetic susceptibility studies show that the complexes all display non-zero μ values at 295 K increasing from pc 2− to tpp 2−. Mössbauer spectra confirm the low-spin Fe IV oxidation state for the iron centres. Isomer shift, δ, and quadrupole splitting, ΔE Q , for [{ Fepc 2−}2(μ- C )] and [{ Fetpp 2−}2(μ- C )] are identical to those previously reported. Data for [{ Feoep 2−}2(μ- C )] are essentially the same as for the pc and tpp complex. Thus the order of δ is tpp ≈ oep > pc whilst that of Δ E Q is pc >> oep > tpp . Small impurity lines are observed which help explain the magnetic data. UV vis/NIR spectra of the μ-carbido complexes show the characteristic π-π* transitions. These are shifted with respect to the corresponding mononuclear complexes to higher energy because of excitonic interactions. Vibrational spectra are discussed in detail ν as ( M - C - M ) (in cm−1) is at 937 ( M = Fe ; tpp ) < 976 ( Fe / oep ) < 997 ( Fe / pc ) < 1050 ( Ru / pc ), ν s ( M - C - M ) (in cm−1 at 433 ( Fe / tpp ) < 460 ( Fe / oep ) < 477 ( Fe / pc ). Hence, valence force constants increase significantly in the order tpp < oep < pc . ν s ( Fe - C - Fe ) of [{ Fepc 2−}2(μ- C )] is selectively resonance Raman enhanced. As evidenced from the excitation profile a C → Fe charge transfer, not detected in the vis spectrum, is assumed to be present at 22 000 > ν > 25 000 cm −1.

μ-Carbido Diporphyrinates and Diphthalocyaninates of Iron and Ruthenium

μ-Carbido diporphyrinates and diphthalocyaninates of general formula [{ Mp 2−}2(μ- C )] ( p 2− = tpp ( M = Fe ), oep ( Fe ), pc ( Fe , Ru ); H 2 tpp : 21H,23H-5,10,15,20-tetraphenylporphine; H 2 oep : 21H,23H-2,3,4,8,12,13,17,18-octaethylporphine; H 2 pc : 29H,31H-phthalocyanine) of formally Fe IV and Ru IV are prepared by a new and improved ‘one-pot’ synthesis. The corresponding chloro complexes of the tervalent metal ions react successively with potassium hydroxide in boiling 2-propanol and then with trichloromethane. Potassium hydroxide is proven to be a very versatile and powerful reductant in tetrapyrrolic chemistry. As evidenced from electron spin resonance and UV vis spectral measurements, the precursor is reduced primarily to an ate-complex of type [ M I p 2−]− of a formally monovalent metal ion. This active species is assumed to react with trichloromethane via a dichlorocarbene complex of type [ M II( CCl 2) p 2−] to yield the actual -carbido complex. [{ Feoep 2−}2(μ- C )] is crystallographically characterized. It is monoclinic, space group C12/c1 (15), with a = 18.279(3) Å, b = 15.005(2) Å, c = 23.392(7) Å, β = 107.12(2)°, Z = 4, R1 = 0.0773. The iron atom is displaced by 0.192(3) Å out of the centre ( Ct ) of the ( N p )4 plane toward the (μ- C ) atom. Average d ( Fe - N p ) is 1.986(5) Å; d ( Fe -(μ- C )) is 1.6638(9) Å. The Fe - C - Fe skeleton is linear (179.5(3)°). The two slightly waving porphyrinato cores are in a staggered conformation, the ( N p - Fe - Fe ″- N p ″) torsion angle being 21.0(3)°. Solutions of each μ-carbido complex in pyridine/dichloromethane show four distinct quasi-reversible redox processes in their differential-pulse voltammograms and these are assigned to the successive one-electron reduction and oxidation of the macrocyclic ligands. 13 C CP MAS NMR spectra indicate effective four-fold symmetry within the series of the μ-carbido complexes with isotropic shifts occurring at similar fields to those of the corresponding macrocyclic complex of a closed-shell metal ion. Resonances of the bridging carbon atom are not detected. A characteristic increase of line broadening within the series tpp 2− > oep 2− > pc 2− may be due to Fermi contact interactions with the strongly coupled low-spin M IV centres. The magnetic susceptibility studies show that the complexes all display non-zero μ values at 295 K increasing from pc 2− to tpp 2−. Mössbauer spectra confirm the low-spin Fe IV oxidation state for the iron centres. Isomer shift, δ, and quadrupole splitting, ΔE Q , for [{ Fepc 2−}2(μ- C )] and [{ Fetpp 2−}2(μ- C )] are identical to those previously reported. Data for [{ Feoep 2−}2(μ- C )] are essentially the same as for the pc and tpp complex. Thus the order of δ is tpp ≈ oep > pc whilst that of Δ E Q is pc >> oep > tpp . Small impurity lines are observed which help explain the magnetic data. UV vis/NIR spectra of the μ-carbido complexes show the characteristic π-π* transitions. These are shifted with respect to the corresponding mononuclear complexes to higher energy because of excitonic interactions. Vibrational spectra are discussed in detail ν as ( M - C - M ) (in cm−1) is at 937 ( M = Fe ; tpp ) < 976 ( Fe / oep ) < 997 ( Fe / pc ) < 1050 ( Ru / pc ), ν s ( M - C - M ) (in cm−1 at 433 ( Fe / tpp ) < 460 ( Fe / oep ) < 477 ( Fe / pc ). Hence, valence force constants increase significantly in the order tpp < oep < pc . ν s ( Fe - C - Fe ) of [{ Fepc 2−}2(μ- C )] is selectively resonance Raman enhanced. As evidenced from the excitation profile a C → Fe charge transfer, not detected in the vis spectrum, is assumed to be present at 22 000 > ν > 25 000 cm −1.

Diphthalocyanine metal complexes and their analogues

The present overview deals with ditetrapyrrolic macrocycles, mainly diphthalocyanine systems, of the following three classes: (a) sandwich-type molecules (I); (b) metal-metal bonded systems (II); (c) single-atom bridged dimers (III). The available information focuses on the structural and electronic features, redox properties and partial oxidation. Practical applications, e.g. electrochromic devices, molecular metals, liquid crystals, non-linear optics, etc., make these classes of complexes particularly attractive and promising materials. The bonding mechanism and the structural, magnetic, conductive and optical properties of these systems are elucidated by density functional calculations.

Iodine doping of substituted μ-carbido iron diphthalocyanines

Hemi and amphi-substituted μ-carbido iron diphthalocyanine having general formula (t- bu ) 4PcFe-C-FePc and (t- bu ) 4PcFe-C-FePc (t- bu )4 have been oxidized with I2. The oxidized compounds have been characterized and their physicochemical properties have been studied; the results obtained lead to assign them the formula [(t- Bu ) 4PcFe-C-FePc ] (I5)0.66 and [[(t- Bu ) 4PcFe ]2 C ]] (I5)0.66 respectively. The conduction properties, related to the role played by the pushing groups inserted in the peripheral macrocycles, are discussed. Moreover, an effective purification method for improving the yield and purity of iron tetra-tert-butyl phthalocyanine is described, the difficulty being able to obtain this precursor with a high purity grade.