Terminal Carbonyl Ligands Research Articles

Selective synthesis and crystal structures of manganese(I) complexes with a bi- or tridentate terpyridine ligand.

The crystal structures of two manganese(I) complexes with a different coordination mode of the supporting ligand are reported: fac-bromido-tricarbon-yl(4'-phenyl-2,2':6',2''-terpyridine-κ2 N,N')manganese(I), [MnBr(C21H15N3)(CO)3], I, and cis-bromido-dicarbon-yl(4'-phenyl-2,2':6',2''-terpyridine-κ3 N,N',N'')manganese(I), [MnBr(C21H15N3)(CO)2], II. In both complexes, the manganese(I) atom is coordinated by terminal carbonyl ligands, a bromide ion, and a 4'-phenyl-2,2':6',2''-terpyridine ligand within a distorted octa-hedral environment. In I, the metal ion is facially coordinated by three carbonyl ligands and the terpyridine ligand binds in a bidentate fashion. The non-coordinating nitro-gen atom in the terpyridine ligand is positioned on the side opposite to the bromido ligand. In II, the metal ion is coordinated by two carbonyl ligands in a cis configuration and the terpyridine ligand binds in a tridentate fashion; notably, one carbonyl and the trans bromido ligand are mutually disordered over two positions. In I, the complex mol-ecules are linked by C-H⋯Br hydrogen bonds. In II, aromatic π-π contacts are present, as well as pairs of C-H⋯Br and C-H⋯O hydrogen bonds.

Synthesis, characterization, and electrochemistry of diiron ethane-1,2-dithiolate complexes with monosubstituted ethyldiphenylphosphine or dicyclohexylphenylphosphine

In this contribution, two diiron ethane-1,2-dithiolate complexes with one ethyldiphenylphosphine or dicyclohexylphenylphosphine ligand have been synthesized and characterized as mimics for the active site of [FeFe]-hydrogenases. Treatment of complex [Fe2(CO)6(μ-SCH2CH2S)] (1) with ethyldiphenylphosphine or dicyclohexylphenylphosphine and Me3NO · 2 H2O as decarbonylating agent gave complexes [Fe2(CO)5(Ph2PCH2CH3)(μ-SCH2CH2S)] (2) and [Fe2(CO)5{PhP(C6H11)2}(μ-SCH2CH2S)] (3) in 93% and 86% yields, respectively. Complexes 2 and 3 were characterized by elemental analysis, IR, and NMR spectroscopy. X-ray crystallographic studies confirmed the molecular structures of complexes 2 and 3, indicating that they contain a butterfly diiron ethane-1,2-dithiolate cluster with five terminal carbonyl ligands and an apically-coordinated phosphine ligand. Additionally, the electrochemical properties of these complexes were investigated by cyclic voltammetry, suggesting that they can be regarded as electrocatalysts for the reduction of protons to H2 in the presence of HOAc. A possible mechanism for the proton reduction was proposed.

Solvent mediated complete trans-to-cis isomerization of [Ru(polypyridine)(CO)2Cl2] complexes

Trans(Cl)-[Ru(polypyridine)(CO)2Cl2] complexes were completely isomerized to the corresponding cis(Cl)-isomers in the absence of a superacid or a reducing agent. X-ray crystallography was used to determine the molecular structures of the prepared cis-isomers. Spectroscopic, structural, and computational studies indicated that the isomerization occurs via an ethoxycarbonyl intermediate ({Ru–C(O)OC2H5}+), which is formed by the reaction of the solvent ethanol with a terminal carbonyl ligand. The electronic effects of the bidentate ligand in the complex were found to exert significant influence on isomerization. The mechanistic studies and the isomerization results will enable efficient syntheses of novel ruthenium complexes.

Spectroscopic and theoretical investigation of the [Fe2(bdt)(CO)6] hydrogenase mimic and some catalyst intermediates.

In [Fe-Fe] hydrogenase mimic systems the ene-1,2-dithiolene ligands play an important role in the stabilisation of the redox-active metal center. This is demonstrated by the benzenedithiolene (bdt) analogue, featuring six terminal carbonyl ligands connected to a di-iron metal center, i.e. [Fe2(bdt)(CO)6]. Here we present a combined experimental and theoretical study that elucidates key intermediates [Fe2(bdt)(CO)6]1- and [Fe2(bdt)(μ-CO)(CO)5]2- in the electrocatalytic production of dihydrogen. A DFT study shows that [Fe2(bdt)(CO)6]1- is the kinetic product after the first one electron reduction, while the previously proposed bridging intermediate species [Fe2(bdt)(μ-CO)(CO)5]1- is kinetically inaccessible. The doubly reduced species [Fe2(bdt)(μ-CO)(CO)5]2- was for the first time structurally characterized using EXAFS. XANES analysis confirms the existence of reduced iron zero species and confirms the distorted geometry that was suggested by the DFT calculations. Combining IR, UV-vis and XAS spectroscopic results with TD-DFT and FEFF calculations enabled us to assign the key-intermediate [Fe2(bdt)(CO)6]2-. This study emphasizes the strengths of combining computational chemistry with advanced spectroscopy techniques.

Reactivity of dirhenium and triruthenium carbonyls toward a biphosphole ligand: M–M, P–P and C–H bonds cleavage

The reaction of [Re2(CO)8(CH3CN)2] with bis(2-thienyl)biphosphole in refluxing n-octane affords the complex [Re(CO)3(η5-PC16H14S2)] (1) where cleavage of the Re–Re and P–P bonds occurs; its molecular structure confirms the formation of a rhenium mononuclear compound with a η5-coordinated phospholyl unit and three carbonyl groups oriented in a tripod. On the other hand, bis(2-thienyl)biphosphole reacts with [Ru3(CO)12] in refluxing cyclohexane to affording two new compounds [Ru3(CO)9(μ:η1:η5-PC16H13S2)] (2) and [Ru4(CO)13(μ:η1-PC16H14S2)2] (3). Spectroscopic data and theoretical studies of 2 suggest the formation of an open Ru3 cluster with two metal–metal bonds bridged by a (η1:η5-PC16H13S2) unit and a C-H bond activation of one of the thienyl substituents. X-ray structure of 3 reveals a novel tetranuclear ruthenium cluster containing 13 terminal carbonyl ligands and two phospholyl units coordinated as μ-phosphide.

Ruthenium complexes bearing a tridentate polypyridyl ligand with non-coordinating donor atoms: Construction of a specific coordination environment involving noncovalent interactions

We have prepared carbonyl (CO) ruthenium complexes which contained the tridentate polypyridyl type ligand (2,6-di(1,8-naphthyridin-2-yl)pyridine; dnp) with non-coordinating nitrogen atoms, for the development of specific reactions using noncovalent interactions. Similar to the aqua precursors that display intramolecular hydrogen bonds between the aqua and dnp ligands, a noncovalent interaction is formed between the terminal carbonyl ligand and non-coordinating nitrogen atoms of dnp; its strength depends on the identity of the axial ligand (triphenylphosphine or pyridine). Additionally, we investigated the reactivity of dnp-containing complexes bearing carbonyl ligands in both the equatorial and axial positions. As a result, it is suggested that the noncovalent interaction between dnp and CO ligands in positions equatorial to the dnp ligand is relatively strong, because the axial carbonyl ligand dissociates preferentially in ligand substitution reactions using organic solvents. Furthermore, in the ligand substitution reaction with a nitrile derivative, the coordination space constructed by the {Ru-dnp}2+ unit enables regulation of not only the ligand substitution reaction rate but also the identity of the donor atom. The present complex also leads to activation and cleavage of inert CCl and CBr bonds.

Potent in vitro antiproliferative properties for a triplatinum cluster toward triple negative breast cancer cells

The trinuclear platinum cluster [Pt3(μ-PBut2)3(CO)3]CF3SO3 (I) was designed featuring the presence of a nearly equilateral platinum triangle bridged by three di-tert-butylphosphide ligands; in addition, each platinum center bears a terminal carbonyl ligand. This triplatinum cluster was initially developed in view of applications in the field of cluster-containing innovative materials. Yet, due to the large success of platinum complexes in cancer treatment, we also decided to explore its cytotoxic and anticancer properties. Accordingly, the solubility profile of this compound in several solvents was preliminarily investigated, revealing a conspicuous solubility in DMSO and DMSO/buffer mixtures; this makes the biological testing of I amenable. UV–Vis measurements showed that the triplatinum cluster is stable for several hours under a variety of conditions, within aqueous environments. No measurable reactivity was observed for I toward two typical model proteins, i.e. lysozyme and cytochrome c. On the contrary, a significant reactivity was evidenced when reacting I with small sulfur-containing ligands. In particular, a pronounced reactivity with reduced glutathione and cysteine emerged from ESI-MS experiments, proving complete formation of I-GSH and I-Cys derivatives, with the loss of a single carbonyl ligand. Starting from these encouraging results, the cytotoxic potential of I was assayed in vitro against a panel of representative cancer cell lines, and potent cytotoxic properties were disclosed. Of particular interest is the finding that the triplatinum species manifests potent antiproliferative properties toward Triple Negative Breast Cancer Cells, often refractory to most anticancer drugs. Owing to the reported encouraging results, a more extensive biological and pharmacological evaluation of this Pt cluster is now warranted to better elucidate its mode of action.

A metal-mediated boron-centred isomerisation reaction via C-H activation.

A heterocyclic manganese complex (4) derived from a carbonyl-borylene coupling reaction undergoes isomerisation, during which the former borylene moiety migrates to the cyclopentadienyl ligand and inserts into a C-H bond. This reaction and a computational study of its mechanism are discussed.

Photochemical dihydrogen production using an analogue of the active site of [NiFe] hydrogenase.

Photoproduction of dihydrogen (H2) by a low molecular weight analogue of the active site of [NiFe] hydrogenase has been investigated by reduction of the [NiFe2] cluster, 1, by a photosensitier PS (PS = [ReCl(CO)3(bpy)] or [Ru(bpy)3][PF6]2). Reductive quenching of the (3)MLCT excited state of the photosensitizer by NEt3 or N(CH2CH2OH)3 (TEOA) generates PS(•-), and subsequent intermolecular electron transfer to 1 produces the reduced anionic form of 1. Time-resolved infrared spectroscopy (TRIR) has been used to probe the intermediates throughout the reduction of 1 and subsequent photocatalytic H2 production from [HTEOA][BF4], which was monitored by gas chromatography. Two structural isomers of the reduced form of 1 (1a(•-) and 1b(•-)) were detected by Fourier transform infrared spectroscopy (FTIR) in both CH3CN and DMF (dimethylformamide), while only 1a(•-) was detected in CH2Cl2. Structures for these intermediates are proposed from the results of density functional theory calculations and FTIR spectroscopy. 1a(•-) is assigned to a similar structure to 1 with six terminal carbonyl ligands, while calculations suggest that in 1b(•-) two of the carbonyl groups bridge the Fe centers, consistent with the peak observed at 1714 cm(-1) in the FTIR spectrum for 1b(•-) in CH3CN, assigned to a ν(CO) stretching vibration. Formation of 1a(•-) and 1b(•-) and production of H2 was studied in CH3CN, DMF, and CH2Cl2. Although the more catalytically active species (1a(•-) or 1b(•-)) could not be determined, photocatalysis was observed only in CH3CN and DMF.

Bridging Rhodium–Iron Borataaminocarbyne Complexes Formed by Intramolecular Isonitrile–Borane Coordination

Reaction of [(TXPB)Rh(μ-CO)2Fe(CO)Cp] (1; TXPB = 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene) with both aryl and alkyl isonitriles formed [(TXPB)Rh(μ-CO)(μ-CNR)Fe(CO)Cp] (R = C6H4Cl-p (2), Xyl (3), nBu (4); Xyl = 2,6-dimethylphenyl), in which the CNRBR3 unit is best described as a borataaminocarbyne ligand with single bonds between carbon and nitrogen and between nitrogen and boron. The carbon atom of the borataaminocarbyne ligand is doubly bound to iron and singly bound to rhodium. For comparison, borane-free [(TXPH)Rh(μ-CO)2Fe(CO)Cp] (5; TXPH = 2,7-di-tert-butyl-4-diphenylphosphino-9,9-dimethylthioxanthene) was prepared from [(TXPH)RhCl(CO)] and K[CpFe(CO)2], and reaction of 5 with either 1 or 2 equiv of CNC6H4Cl-p afforded [(TXPH)Rh(CO)(μ-CNC6H4Cl-p)2Fe(CO)Cp] (6), which contains two μ-isonitrile ligands and two terminal carbonyl ligands: one bound to iron and the other to rhodium. The C–N stretching frequency for 6 is 124 cm–1 higher than that for the TXPB CNC6H4Cl-p complex 2, and the Rh–(μ-CNR) and Fe–(μ-CNR) distances are notably longer than those in 2, and the C–N distance is shorter.

On the nuclearity of tricarbonylrhenium(I) complexes with N,O,O-donating Schiff bases derived from amino acids

The reaction of [ReBr(CO)5] with AgOOCCH3 followed with N-(2-hydroxynaphtalidene)-β-alanine (bala2hnH2); NEt4[ReBr3(CO)3] with the potassium salt of N-(2-hydroxynaphtalidene)-(d,l)-β-phenylalanine (bphala2hnH2), or with N-(5-bromine-2-hydroxysalicylidene)-(d,l)-β-phenylalanine (bphalabrsalH2) gave the complexes [fac-{Re(bala2hnH)(CO)3}2] (1), (H3O)[Re(fac-bphala2hn)(CO)3]·CHCl3·H2O (2), K[fac-Re(bphala2hn)(CO)3]·⅓CHCl3·2H2O (3) and K[fac-Re(bphalabrsal)(CO)3]·2H2O (4), respectively. Single crystal X-ray crystallography showed that the neutral dinuclear complex 1 is centrosymmetric with each rhenium(I) atom having an octahedral coordination geometry comprising of three terminal carbonyl ligands, in a fac configuration, and both ligands bala2hnH are bridging and chelating the two rhenium(I) centers. In the anionic mononuclear complexes 2 and 3, bphala2hn2– acts as a N,O,O tridentate ligand to the fac-{Re(CO)3}+ fragment giving rise an octahedral geometry around the rhenium(I) atom.

Unprecedented Tris-Phosphido-Bridged Triangular Clusters with 42 Valence Electrons. Chemical, Electrochemical and Computational Studies of their Formation and Stability

This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBu(t)2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e(-). The new species were obtained by an apparent bielectronic oxidation of the 44e(-) monohalides Pt3(μ-PBu(t)2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e(-) analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(μ-PBu(t)2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e(-) intermediate [Pt3(μ-PBu(t)2)3(CO)2I](+) was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt3(μ-PBu(t)2)3I3, the transient 44e(-) species [Pt3(μ-PBu(t)2)3(CO)3](+) is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e(-) intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e(-) associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e(-) phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.

ChemInform Abstract: Supramolecular Self‐Assembly of Transition Metal Carbonyl Molecules Through M—CO(Lone Pair)...π(Arene) Interactions

AbstractReview: 124 refs.

Reversible P–C Coupling Reactions at the Unsaturated Dimolybdenum Carbyne Complex [Mo2(η5-C5H5)2(CPh)(μ-PCy2)(μ-SPh)(CO)]+

The title complex was formed instantaneously by reacting [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] with [FeCp2]BF4 in the presence of diphenyl disulfide, but it could not be isolated as a pure material. It most likely displays bridging phosphide and thiolate ligands and essentially terminal carbonyl (Mo–C = 1.987 A) and carbyne (Mo–C = 1.820 A) ligands, according to density functional theory calculations. In solution this complex released CO spontaneously to yield the 30-electron complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)]BF4 (Mo–Mo = 2.4772(6) A), and attempts to crystallize it at low temperature yielded instead the electron-precise aquo derivative [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-SPh)(CO)(OH2)]BF4 (Mo–Mo = 2.7820(4) A). The addition of CO induced the coupling between the carbyne and phosphide ligands, to yield the tricarbonyl phosphinocarbene complex [Mo2Cp2(μ-η1:η1,κ1-CPhPCy2)(μ-SPh)(CO)3]BF4 (Mo–Mo = 2.928(1) A). This coupling process was reversible, since the latter complex could be decarbonylated stepwise by thermal methods...

μ-(3,4,5,6,7-η:1,9,10,11,12)-5,11-Di-tert-butyl-2,2,8,8-tetra-methyl-2,8-disila-tricyclo-[7.3.0.0(3,7)]dodeca-tetra-enedi-yl]bis-[dicarbonyl-ruthenium(I)

The title compound, [Ru2(C22H34Si2)(CO)4], contains two RuI atoms linked by a bridging (η5-tBuC5H2)2(SiMe2)2 ligand (tBu is a tert-butyl and Me is a methyl group) with an Ru—Ru bond length of 2.8401 (7) Å. The dihedral angle between the planes of the cyclo­penta­dienyl rings of the ligand is 123.13 (19)°. The four terminal carbonyl ligands are bound in a symmetrical and staggered array. In the crystal, mol­ecules are linked via pairs of C—H⋯O hydrogen bonds, forming inversion dimers.

μ-Bis(diphenylarsino)methane-1:2κ2As:As]decacarbonyl-1κ3C,2κ3C,3κ4C-triangulo-triosmium(0)

The title compound, [Os3(C25H22As2)(CO)10], contains a triangle of singly bonded Os atoms; both arsine ligands are equatorial with respect to the Os3 triangle. Each arsine-substituted Os atom bears one equatorial and two axial terminal carbonyl ligands, whereas the unsubstituted Os atom bears two equatorial and two axial terminal carbonyl ligands. The dihedral angles between the two benzene rings in the diphenyl­arsino groups are 67.42 (16) and 61.99 (16)°. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds into zigzag chains propagating along [010].

μ-Bis(di-o-tolylphosphanyl)methane-1:2κ2 P:P′]nonacarbonyl-1κ3 C,2κ3 C,3κ3 C-[tris(2-chloroethyl) phosphite-3κP]-triangulo-triruthenium(0)

In the title compound, [Ru3(C6H12Cl3O3P)(C29H30P2)(CO)9], the bis­(di-o-tolyl­phosphan­yl)methane ligand bridges one Ru—Ru bond and the monodentate phosphite ligand bonds to the third Ru atom. Both ligands are equatorial with respect to the Ru3 triangle. Each Ru atom bears one equatorial and two axial terminal carbonyl ligands. The dihedral angles between the two benzene rings in the diphenyl­phosphanyl groups are 79.52 (10) and 69.88 (10)°. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds into chains along [100].

μ-Bis(di-o-tolylphosphanyl)methane-1:2κ2 P:P′]nonacarbonyl-1κ3 C,2κ3 C,3κ3 C-(triphenyl phosphite-3κP)-triangulo-triruthenium(0) chloroform disolvate

In the title solvated triangulo-triruthenium compound, [Ru3(C18H15O3P)(C29H30P2)(CO)9]·2CHCl3, the bis­(di-o-tolyl­phosphan­yl)methane (dtpm) ligand bridges one of the Ru—Ru bonds and the monodentate phosphine ligand bonds to the third Ru atom. All the P atoms are equatorial with respect to the Ru3 triangle: each Ru atom also bears one equatorial and two axial terminal carbonyl ligands. The dihedral angles between the two benzene rings are 75.92 (10) and 78.95 (10)° for the two diphenyl­phosphanyl groups of the dtpm ligand. In the crystal, C—H⋯O hydrogen bonds link the mol­ecules into chains along [010].

μ-1,6-Bis(diphenyphosphanyl)hexane-1:2κ2P:P′]decacarbonyl-1κ3C,2κ3C,3κ4C-triangulo-triruthenium(0)

The title triangulo-triruthenium(0) compound, [Ru3(C30H32P2)(CO)10], contains a triangle of singly bonded Ru atoms. The phosphane-bridged Ru—Ru distance [2.9531 (2) Å] is significantly longer than the non-bridged Ru—Ru distances [2.8842 (2) and 2.8876 (2) Å] . The bis­(diphenyl­phosphan­yl)hexane ligand bridges the Ru—Ru bond. Each phosphane-substituted Ru atom bears one equatorial and two axial terminal carbonyl ligands, whereas the unsubstituted Ru atom bears two equatorial and two axial terminal carbonyl ligands. The dihedral angles between the benzene rings attached to each P atom are 72.75 (7) and 82.02 (7)°. The mol­ecular structure is stabilized by an intra­molecular C—H⋯O hydrogen bond involving a methyl­ene group of the phosphane ligand and an axial carbonyl O atom, which generates an S(6) ring motif. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds into layers parallel to (100).

Computational Chemical Analysis of [FeFe] Hydrogenase H-Cluster Analogues To Discern Catalytically Relevant Features of the Natural Diatomic Ligand Configuration

Density functional theoretical models of the electronic structure of several configurational isomers and analogues of the [2Fe](H) H-cluster in [FeFe] hydrogenase were analyzed to identify distinguishing features of the canonical cofactor structure potentially relevant to catalysis. Collective analysis of geometric changes over models of oxidized and reduced [2Fe] clusters highlighted movement of the bridging carbonyl and anticorrelation of the proximal and distal Fe-C(terminal) bonds as key explanatory factors for variance over the considered models. Charge and bond order analysis suggest that as the bridging carbonyl favors the distal iron upon reduction, bonding simultaneously becomes more ionic in nature, raising the possibility of simple electrostatic stabilization as a factor in charge accumulation prior to ultimate H(2) creation and release. Frontier orbital energies show cis and trans arrangements of cyanide on the Fe-Fe core to have distinctive energies from the other models, which may be important for redox poise. Altogether, few factors qualitatively distinguish the cis- from the trans-cyano configurations, which may in fact enhance catalytic robustness under conditions leading to exchange of the bridging and terminal carbonyl ligands. However, the naturally occurring trans configuration possesses two distinct donor-metal-acceptor S-Fe-C(O) interactions, which might play a role in enforcing a low-spin ground state for the hydridic mechanism of H(2) production.