Homobimetallic Complexes Research Articles

Homobimetallic Ruthenium(II) Complexes Catalysed Selective Transfer Hydrogenation of Aldehydes in Water.

Herein we report chemoselective transfer hydrogenation (TH) of aldehydes in aqueous medium using a series of homobimetallic Ru(II) catalysts. Two homobimetallic complexes (Ru1 and Ru3) and one monometallic complex (Ru2) have been employed in the catalytic reduction of aldehydes. Bimetallic complex [(p-cymene)2(RuCl)2L3] (Ru3) is obtained from the reaction of Schiff base ligand 2,2'-((1E,1'E)-((3,3',5,5'-tetraisopropyl-[1,1'-biphenyl]-4,4'diyl)bis(azaneylylidene))bis(methaneylylidene))bis(4-bromophenol) (H2L3) and characterized by various spectroscopic and analytical techniques. The use of formic acid/formate buffer as the hydride source and a catalyst loading of 0.01 mol% of Ru1 or Ru3 resulted in the conversion of various aldehydes to the corresponding alcohols in good to excellent yield. This method is very efficient for selective reduction of aldehydes in the presence of other reducible functional groups. A loading of 0.0001 mol% of Ru1 catalyst is sufficient to achieve a turnover frequency (TOF) of 5.5× 105 h-1. Furthermore, the catalyst can been recycled and reused for six consecutives cycles without sacrificing the efficiency. A comparison of results obtained between bimetallic and monometallic complexes offers valuable insights into the distinct reactivity patterns of the bimetallic complexes, presumably originating from a cooperative effect. We have explored the mechanistic pathway using DFT methods.

Visible-Light-Driven CO2 Reduction with Homobimetallic Complexes. Cooperativity between Metals and Activation of Different Pathways.

Visible-light-driven reduction of CO2 to both CO and formate (HCOO-) was achieved in acetonitrile solutions using a homobimetallic Cu bisquaterpyridine complex. In the presence of a weak acid (water) as coreactant, the reaction rate was enhanced, and a total of ca. 766 TON (turnover number) was reached for the CO2 reduction, with 60% selectivity for formate and 28% selectivity for CO, using Ru(phen)32+ as a sensitizer and amines as sacrificial electron donors. Mechanistic studies revealed that with the help of cooperativity between two Cu centers, a bridging hydride is generated in the presence of a proton source (water) and further reacts with CO2 to give HCOO-. A second product, CO, was also produced in a parallel competitive pathway upon direct coordination of CO2 to the reduced complex. Mechanistic studies further allowed comparison of the observed reactivity to the monometallic Cu quaterpyridine complex, which only produced CO, and to the related homobimetallic Co bisquaterpyridine complex, that has been previously shown to generate formate following a mechanism not involving the formation of an intermediate hydride species.

Four-Membered Bimetallic Carbon Complex [(MCp*)2(μ-NPh)(μ-C)] (M = Fe, Ru, Os) - An Ambiphilic Carbene with Lone Pair and σ-Hole Reactivity.

Singlet carbenes are extensively studied compounds capable of electrophilic, nucleophilic or ambiphillic behaviour. The ambiphilic reactivity of singlet carbenes have been conventionally observed in orthogonal planes. Here, we report a detailed bonding and reactivity study of a homobimetallic carbon complex [(MCp*)2(μ-NPh)(μ-C)] (1M, M = Fe, Ru, Os) that shows ambiphilicity in the same direction. The structure of this complex can be considered as two fused three-membered M-C-M and M-N-M rings. The bonding analysis suggests that these 17VE homobimetallic complexes have one formal M-M bond with a bridging carbene centre featuring a high lying spn-hybridised lone pair. Accordingly, the carbene centre shows high proton affinity and act as a good 2e- donor to Lewis acids and transition metal fragment. Apart from the transition metal non-bonding electrons, the π-framework of M-C-M and M-N-M arms can be best described as 3c-2e- bonds. The two transition metals in the four-membered skeleton generate many low-lying, virtual orbitals. These low-lying virtual orbitals induces electron excitation from the spn-hybrid orbital in presence of H- and other 2e- donor ligands such as PMe3, NHC and CO. Hence, the spn-hybrid lone pair orbital shows σ-hole reactivity in presence of Lewis bases.

High-Throughput Approach for Facile Access to Hetero-Dinuclear Synergistic Metal Complex for H2O2 Activation and Its Implications.

Hetero-dinuclear synergic catalysis is a promising approach for improving catalytic performance. However, employing it is challenging because the design principles for the metal complex are still not well understood. Further, these complexes have a broader set of possibilities than mononuclear or homometallic systems, increasing the time and effort required to understand them. In this study, we explored a high-throughput approach to obtain a new hetero-dinuclear synergistic metal complex for H2O2 activation. From the 1152 combinations of metal complex candidates obtained by changing three variables (metal ions, unsymmetrical dinucleating ligands, and pH), the lead complex (L3-(Ni, Co)), which has the highest peroxidase activity, was derived using colorimetric parallel analysis. A series of control experiments revealed that L3 plays a crucial role in the formation of active L3-(Ni, Co) complexes, Co2+ acts as a catalytic center, and Ni2+ serves as an assistant catalytic site within L3-(Ni, Co). In addition, the catalytic efficiency of L3-(Ni, Co), which was 125 times that of the homo-bimetallic complex (L3-(Co, Co)), revealed clear hetero-bimetallic synergism in the buffer. The ultraviolet-visible study and electron paramagnetic resonance-based spin-trap experiment provided mechanistic insight into H2O2 activation by the intermediate, which was found to be induced by the reaction of L3-(Ni, Co) and H2O2. Moreover, the intermediate could act as a donor of the hydroperoxyl radical (•OOH) in the buffer. Furthermore, L3-(Ni, Co) demonstrated potential for application as a signal transducer for H2O2 in an enzyme-coupled cascade assay that can be used for the colorimetric detection of glucose.

Homoleptic and heteroleptic ketodiiminate zinc complexes for the ROP of cyclic l-lactide.

Homo- and heteroleptic ketodiiminate zinc complexes L12Zn2 (1, L1 = [Me2NC2H4NC(Me)CH]2CO), L2(ZnCp)2 (2, L2 = [Me2NC3H6NC(Me)CH]2CO, Cp = C5H5) and L2HZnCp* (3, Cp* = C5Me5) were synthesized and characterized by 1H and 13C NMR and IR spectroscopy as well as by elemental analysis and single crystal X-ray diffraction (sc-XRD, 2, 3). The catalytical activity of heteroleptic complexes 2 and 3 were tested in the ring-opening polymerization (ROP) of l-lactide. Homobimetallic complex 2 showed the highest activity and selectivity for the synthesis of cyclic polylactide (cPLLA; TOF = 17 460 h-1) at 100 °C in toluene solution, while linear polymers are formed with mononuclear complex 3.

Coordination of cage compounds by Cu(I) nacnac compounds

The nacnac Cu(I) compound [L1Cu(MeCN)] (L1 = [{N(C6H3Me2-2,6)C(Me)}2CH]−) was reacted with E4 (P4, As4 and AsP3) yielding the homobimetallic complexes [(L1Cu)2(η2:2-E4)] (E4 = P4 (1a), As4 (1b), AsP3 (1c)) and the mononuclear complexes [L1Cu(η2-E4)] (E4 = P4 (2a), As4 (2b), AsP3 (2c)), revealing neutral, intact side-on coordinated E4 units. Furthermore, the reaction of [L1Cu(MeCN)] with Sered and E4S3 (E = P, As) afforded [(LCu)2(μ,η2:2Se2)] (L1 = 3a, L3 = 3b) and [(L3Cu)2(E4S3)] (E = P (4), As (5)). They represent rare examples of complexes of group 11 metals with polypnictogen, chalcogen and mixed E15/Q16 compounds.

Macrocycle-Induced Modulation of Internuclear Interactions in Homobimetallic Complexes.

A synthetic route has been developed for a series of 3d homobimetallic complexes of Mn, Fe, Co, Ni, and Cu using three different pyridyldiimine and pyridyldialdimine macrocyclic ligands with ring sizes of 18, 20, and 22 atoms. Crystallographic analyses indicate that while the distances between the metals can be modulated by the size of the macrocycle pocket, the flexibility in the alkyl linkers used to construct the macrocycles enables the ligand to adjust the orientation of the PD(A)I fragments in response to the geometry of the [M2(μ-Cl)2]2+ core, particularly with respect to Jahn-Teller distortions. Analyses by UV-vis spectroscopy and SQUID magnetometry revealed deviations in the properties [M2(μ-Cl)2]2+-containing complexes bound by standard mononucleating ligands, highlighting the ability of macrocycles to use ring size to control the magnetic interactions of pseudo-octahedral, high-spin metal centers.

Structure and stability of Eu3+ complexes derivatives from non-steroidal anti-inflammatory drug ibuprofen through a DFT study

This work presents a study based on density functional theory (DFT) calculations of electronic structural, thermodynamic, and spectroscopic parameters of Eu3+ ibuprofenate complexes containing the ancillary bipyridine ligands 4,4′-dimethyl-2,2′-bipyridine (4,4′-dmbpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′-dmbpy) or 6,6′-dimethyl-2,2′-bipyridine (6,6′-dmbpy). Formation reactions of these Eu3+ complexes as a function of the –CH3 groups position in the ancillary ligands were analyzed. Our DFT results obtained at B3LYP/MWB52/6-31G(d,p) level demonstrated that in equilibrium of ethanol solution, through a DFT study with molar fraction × = 0.05, the [Eu(Ibf)3(H2O)2] monometallic complex is thermodynamically more stable than the [Eu2(Ibf)6(6,6′-dmbpy)2] homobimetallic complex. The [Eu(Ibf)3(H2O)2] complex had a Gibbs free energy of formation about 19.2 kcal mol−1 less than the homobimetallic complex containing the 6,6′-dmbpy ligand. In addition, the [Eu2(Ibf)6(6,6′-dmbpy)2] complex is electronically less stable among the homobimetallic complexes investigated. These results were justified by increasing the distance between Eu3+ ions, low concentration of electronic density and by the QTAIM analysis performed in the coordination region of the bipyridine ligands in the optimized geometry of homobimetallic complex. In addition, the simulated IR spectra for the Eu3+ complexes studied showed a good agreement with previous experimental results. This work provides important DFT results for the modeling of photoluminescent lanthanide compounds with ancillary bipyridine ligands.

Hetero- and Homobimetallic Complexes Bridged by a Bis(NHC) Ligand: Synthesis via Selective Sequential Metalation and Catalytic Applications in Tandem Organic Transformations

A (bis)azolium salt [L1-H2]Br2 (5), synthesized following multistep procedures, was realized to be a suitable platform for accessing the bis(NHC) ligand supported heterobimetallic IrIII-M (M = PdII...

A new homobimetallic cobalt(II) complex based on the tetradentate 3,5-bis(2-pyridyl)-1H-1,2,4-triazole ligand: Synthesis, crystal structure, Hirshfeld analysis, spectroscopic characterization, magnetic properties and antimicrobial activities

A novel homobimetallic cobalt(II) complex, [Co2(bpt)2(H2O)4](NO3)2·2H2O (bpt = 3,5-bis(2-pyridyl)-1,2,4-triazolate), has been synthesized and characterized by single crystal X-ray diffraction, Hirshfeld surface analysis, as well as UV–Visible and FTIR techniques. The crystal structure determination shows that the dinuclear complex crystallizes in the triclinic crystal system with the P1- space group. The (N′,N1,N2,N″)2 double bridging coordination mode is realised with a distorted octahedral N4O2-coordinated cobalt centre. The structure cohesion is ensured by different intermolecular hydrogen bonds, π–π stacking interactions and intermolecular lone-pair···π interactions. The structure consists of [Co2(bpt)2]2+ dimeric units with a cobalt-cobalt distance of 4.170(2) Å. Magnetic measurements carried out on the homobimetallic complex indicate a relatively weak antiferromagnetic interaction between the two cobalt centres. This complex exhibited antimicrobial activity against several strains of the fungal phytopathogens Verticillium dahliae and Fusarium oxysporum fsp. melonis, as well as against the phytopathogenic bacteria Agrobacterium tumefaciens, suggesting its use in crop protection.

Redox Communication between Two Diarylamido/Bis(phosphine) (PNP)M Moieties Bridged by Ynediyl Linkers (M = Ni, Pd, Pt).

A series of binuclear homo- and heterobimetallic complexes of the general type (PNP)M-[linker]-M(PNP) have been prepared (M = Ni, Pd, Pt; PNP = a diarylamido/bis(phosphine) pincer ligand; -[linker]- = -C≡C-, -C≡CC≡C-, -C≡CC6H4C≡C-). Each (PNP)M site can be oxidized by one electron, and this work reports the investigation of the mixed-valence behavior in terms of the communication between the two redox sites and the degree of the delocalization in the monooxidized cation. The compounds were evaluated using cyclic voltammetry, UV-vis-NIR and EPR spectroscopy, X-ray crystallography, and DFT calculations. The complex with the longest examined linker, (PNP)Ni-C≡CC6H4C≡C-Ni(PNP) (9Ni), exhibited no discernible communication between the redox sites. The homobimetallic complexes (PNP)M-C≡CC≡C-M(PNP) (6M) displayed a lower degree of communication in comparison to the -C≡C- linker analogues (PNP)M-C≡C-M(PNP) (3M). Within each of these two subsets, the relative degree of communication and delocalization was determined to be Pd < Ni ≤ Pt. On the Robin-Day scale, compounds 6M can be assigned class I for M = Pd and class II for M = Ni, Pt. Complex 3Pd also falls into class II, while 3Ni and 3Pt may be viewed as borderline class II/III cases. It is likely that the communication in the Ni systems has the advantage of the smaller size of Ni, resulting in a greater physical proximity of the redox sites, while the 5d metal Pt possesses the greatest ability for orbital interaction with the -C≡C- linker.

Solvent Effect on the Regulation of Urea Hydrolysis Reactions by Copper Complexes

Abiotic allosterism is most commonly observed in hetero-bimetallic supramolecular complexes and less frequently in homo-bimetallic complexes. The use of hemilabile ligands with high synthetic complexity enables the catalytic center by the addition or removal of allosteric effectors and simplicity is unusually seen in these systems. Here we describe a simpler approach to achieve kinetic regulation by the use of dimeric Schiff base copper complexes connected by a chlorido ligand bridge. The chlorido ligand acts as a weak link between monomers, generating homo-bimetallic self-aggregating supramolecular complexes that generate monomeric species in different reaction rates depending on the solvent and on the radical moiety of the ligand. The ligand exchange was observed by electron paramagnetic resonance (EPR) and conductivity measurements, indicating that complexes with ligands bearing methoxyl (CuIIL2) and ethoxyl (CuIIL5) radicals were more prone to form dimeric complexes in comparison to ligands bearing hydrogen (CuIIL1), methyl (CuIIL3), or t-butyl (CuIIL4) radicals. The equilibrium between dimer and monomer afforded different reactivities of the complexes in acetonitrile/water and methanol/water mixtures toward urea hydrolysis as a model reaction. It was evident that the dimeric species were inactive and that by increasing the water concentration in the reaction medium, the dimeric structures dissociated to form the active monomeric structures. This behavior was more pronounced when methanol/water mixtures were employed due to a slower displacement of the chlorido bridge in this medium than in the acetonitrile/water mixtures, enabling the reaction kinetics to be evaluated. This effect was attributed to the preferential solvation shell by the organic solvents and in essence, an upregulation behavior was observed due to the intrinsic nature of the complexes to form dimeric structures in solution that could be dismantled in the presence of water, indicating their possible use as water-sensors in organic solvents.

Perfect Spin Filtering in Homobimetallic Ni Complex with High Tolerance to Structural Changes.

In the theory of ligand fields, depending on the nature and field strength of the surrounding ligands, the central metal ion may exhibit different electronic configurations, low spin (LS) or high spin (HS). Realizing stable spin polarization is one of the main challenges in the field of molecular spintronic devices because of spin switching triggered by an external stimulus. Here, an asymmetric homobimetallic complex has been investigated using the nonequilibrium Green's function and spin density functional theory. Our calculations indicate that the homobimetallic complex can achieve negative differential resistance, rectification effect, and perfect spin filtering transport on the level of an individual molecule. Strikingly, when the molecule is stretched by 0.45 Å, the HS state is still the most stable because of the weak magnetic Ni-Ni interaction. Although its conductivity decreases by 30%, the efficiency of spin filtering remains 100%. These obtained theoretical findings suggest that the homobimetallic complexes hold great potential in molecular spintronics.

Synthesis and properties of a heterobimetallic iron-manganese complex and its comparison with homobimetallic analogues

Heterobimetallic cofactors containing one manganese and one iron ion have recently been found within the di-metal carboxylate protein family. Herein we report the synthesis and characterization of three binuclear metal complexes with Fe-Fe, Mn-Mn, and Fe-Mn metal composition. All three complexes use the same ligand framework, the BPMP ligand (HBPMP = 2,6-bis[(bis (-2-pyridylmethyl)amine) methyl]-4-methylphenol)) with two additional acetate ligands bridging the two metals. In terms of stability towards metal exchange, the Fe-Mn is more stable than the Mn-Mn complex but less stable than the Fe-Fe complex. Cyclic voltammetry shows that the Fe-Mn complex behaves markedly different than the homobimetallic complexes. The Fe-Mn complex also shows higher reactivity with O2 than both the Fe-Fe and the Mn-Mn counterparts.

Study of energy transfer mechanism in the EuIII and GdIII homobimetallic complexes containing the anti-inflammatory drug naproxen and N,N-donors ligands

Abstract In this work, we present the synthesis, solid state characterization and complete photoluminescence study of new important homobimetallic lanthanide complexes containing the non-steroidal anti-inflammatory drug (NSAID) naproxen. The analytical and spectroscopic techniques reveals the formation of eight compounds of general formula [Ln2(nap)6(H2O)4] (Eu 1 and Gd 2), [Ln2(nap)6(bpy)2] (Eu 3 and Gd 4), [Ln2(nap)6(4,4'-dmbpy)2] (Eu 5 and Gd 6) and [Ln2(nap)6(phen)2] (Eu 7 and Gd 8), where: nap = naproxen ligand, bpy =2,2'-bipyridine, 4,4'-dmbpy = 4,4'-dimethyl-2,2'-bipyridine and phen = 1,10-phenanthroline. Using the RM1 model, the molecular structures of the EuIII complexes were calculated, with your optimized ground state geometries used to obtain all details involved in the energy transfer process. From the respective GdIII complexes were obtained the lowest ligand triplet states, proving that the photoluminescence in the EuIII naproxen complexes is proposed to be a ligand sensitized luminescence process. On the other hand, the position of the triplet states also explains the non-effective energy transfer in the TbIII naproxen complexes. The presence of N,N-donors ligands (bpy, 4,4'-dmbpy and phen) results in an 3–4-fold increase in the quantum efficiency when compared with the EuIII complex without nitrogen ligands. The high values of emission quantum efficiency (η ~ 70 - 98%) show the EuIII complexes can be potential candidates as emitters in biologic assays.

Heterobimetallic Complexes Bridged by Imidazol{[4,5-f][1,10]-phenanthrolin}-2-ylidene: Synthesis and Catalytic Activity in Tandem Reactions

A series of monometallic complexes obtained by metalation of the phenanthrolin donor in 1,3-dibutyl-1H-imidazol[4,5-f][1,10]phenanthrolin}ium hexafluorophospate 1 (M = Pd 2, Ru 3, Ir 4) have been prepared. Subsequently, the imidazolium moiety of complexes 2–4 was metalated with M′, leading to the heterobimetallic phenanthroline/NHC complexes (M/M′ = Pd/Rh 5, Pd/Ir 6, Pd/Ru 7, Ru/Pd 8, Ir/Pd 9) and the homobimetallic complex (M/M′ = Ir/Ir 10). The new complexes were characterized by elemental analysis, FTIR, UV–vis, and NMR spectroscopy. The molecular structures of the heterobimetallic complexes 5 and 6 were determined by X-ray diffraction studies. The catalytic activity of the heterobimetallic complexes 5–9 were tested in selected tandem reactions (dehalogenation/transfer hydrogenation and Suzuki–Miyaura coupling/transfer hydrogenation). It was found that the M/M′ heterobimetallic complexes display higher catalytic activities when compared to equimolar mixtures of the mononuclear complexes M and M′, thus ...

Ruthenium(ii) and palladium(ii) homo- and heterobimetallic complexes: synthesis, crystal structures, theoretical calculations and biological studies.

Four Ru-Pd heterobimetallic complexes, each one in two different coordination modes (NNSS and NS) having metals connected by a binucleating dialkyldithiooxamidate [N(R)SC-CS(R)N] [R = methyl, ethyl, n-butyl and isopropyl], were prepared by reacting the monochelate [(trinpropyl-phosphine)ClPd(HR2C2N2S2κ-S,S-Pd)] with [(η6-p-cymene)RuCl2]2. Furthermore, two palladium homobimetallic complexes having two (trinpropyl-phosphine)ClPd moieties joined by a diethyldithiooxamidate in both κ-N,S Pd, κ-N',S' Pd' and κ-N,N' Pd, κ-S,S' Pd' coordination modes were synthesized. For both kinds of complexes, homo- and heterobimetallic, at room temperature and in chloroform solution, the NNSS coordination mode (kinetic compounds) turns out to be unstable and therefore the resulting complexes rearrange into a thermodynamically more stable form (NS coordination mode). The crystal structures of [(trinpropyl-phosphine)ClPd]2[μ-(ethyl)2-DTO κ-N,S Pd, κ-N',S' Pd'] (2) and [(η6-p-cymene)ClRu][μ-(methyl)2-DTO κ-N,S Ru, κ-N,S Pd] [(trinpropyl-phosphine)ClPd] (1c) were determined by solid state X-ray crystallography. Moreover, the higher stability of the thermodynamic species in the heterobimetallic complexes (Ru-Pd) was evaluated by means of computational studies in accordance with the maximum hardness principle. All stable NS complexes (i.e.1c-4c, 2 and the previously reported homobimetallic Ru complex 3) were tested against two leukemia cell lines, namely the drug-sensitive CCRF-CEM cell line and its multidrug-resistant sub-cell line CEM/ADR5000 showing anti-proliferative activity in the low micromolar range (∼1-5 μM) and micromolar range (∼10-25 μM), respectively. In addition, these complexes efficaciously block at least two out of the three proteolytic activities of the tumor target 20S proteasome, with heterobimetallic complex 3c and homobimetallic complex 3 possessing the best inhibitory profile.

Catalytic effects of p-phenylene-bridged methylated binuclear ferrocenes on thermal decomposition of the main component of composite solid propellants

This contribution describes the catalytic activity of homobimetallic complexes derived from p-phenylene on the thermal decomposition of ammonium perchlorate (abbreviated as AP). The complexes, [CpFe-p-Ph-FeCp] (1), [Cp*Fe-p-Ph-FeCp*] (2), [CpFe-p-Ph’-FeCp] (3) and [Cp*Fe-p-Ph’-FeCp*] (4) (with p-Ph: p-Bis(3,4-dimethylcyclopentadienyl)benzene and p-Ph’: p-Bis(2,3,4,5-tetramethylcyclopentadienyl)benzene), were compared with the catalytic activity of the catocene (cat) complex previously reported. Furthermore, in order to clarify the mechanism of the bimetallic compounds, it was tested ferrocene (Fc), frequently used as burning rate (BR) catalyst on the thermal decomposition of AP. The synthetized compounds shown a shift on the peak temperature to lower values and an increase in the released heats during thermal decomposition of AP. The burning rate catalytic activity of the compounds on thermal decomposition of AP were examined by thermogravimetry and differential scanning calorimetry techniques. Theoretical calculations of these compounds were carried out to gain further understanding of these catalysts systems.

Ligand-Enforced Switch of the Coordination Mode in Low-Valent Group 6 Carbonyl Complexes Containing Pyrimidine-Based Bisphosphines

The reaction of M(CO)6 (M = Cr, Mo, W) with N,N′-bis(diisopropylphosphine)-N,N′-dimethylpyrimidine-4,6-diamines (PymR-iPr) bearing R = Me, Ph, tBu substituents in the 2-position was investigated. The pyrimidine-based bisphosphine ligands with R = Me, Ph reacted with M(CO)6 to yield mononuclear and homobimetallic complexes of the types [M(κ2P,N-PymMe-iPr)(CO)4] and [M(CO)4-μ2-(κ2P,N-PymPh-iPr)M(CO)4], respectively. Heterobimetallic complexes of the type [M1(CO)4-μ2-(κ2P,N-PymMe-iPr)M2(CO)4] were obtained by reacting mononuclear complexes [M1(κ2P,N-PymMe-iPr)(CO)4] with 1 equiv of the respective M2(CO)6. Replacing these substituents by a bulky tBu group led to a switch in the coordination mode of the pyrimidine ligand. In the case of chromium, the complex [Cr(κ3P,CH,P-PymtBu-iPr)(CO)3] containing an η2-Caryl–H agostic bond was selectively formed and no C–H bond cleavage took place. However, in the case of molybdenum, the reaction led to the formation of an inseparable mixture of the agostic complex [Mo(κ3P,...

All That Glitters Is Not Gold: A Computational Study of Covalent vs Metallophilic Bonding in Bimetallic Complexes of d10 Metal Centers—A Tribute to Al Cotton on the Tenth Anniversary of His Passing

As the tenth year that follows the premature passing of the inorganic chemistry legend F. Albert (Al) Cotton comes to a close, we provide some soul food that we believe Al would have enjoyed as he looks down upon two generations of disciples, a grandchild and two great grandchildren, in his scientific family tree. This article also represents a new tradition by which the editors of Comments on Inorganic Chemistry wish to lead by example, whereby we start publishing original research content that nonetheless preserves the journal’s identity as a niche for “critical discussion of the current literature” of inorganic chemistry. Thus, we show novel demonstrations of a posteriori validation and a priori prediction of possible counterintuitive covalent M-M’ bonds—after and before synthesis, respectively—contrasted with non-covalent M···M interactions of the metallophilic type in bridge-dimeric systems of d10 metal centers. Mixing of (n + 1)s0/p0 orbitals with (n)d10 orbitals in the former heterobimetallics case—and lack thereof in the latter homobimetallics case—is hypothesized to be responsible for the presence or absence of covalency, respectively. However, we also demonstrate that the consequent d-s’ and/or d-p’ orbital mixing/hybridization can occur even in homobimetallic complexes that contain asymmetric bridging ligands (e.g., with -S^C- donor atoms that lead to orbital interactions between M-S and M-C fragments). Hence, the “control” metallophilic case for the hypothesized d10-d10 polar-covalent bonding herein is best manifest by M2(P^P)2 homobimetallics vis-à-vis M2(S^C)2 embodiments. Finally, we also offer a point/counterpoint commentary to the readers to contrast factors that argue for covalency vs metallophilicity and forewarn against exaggerating the extent of covalent bonding in such d10-d10 species. Thus, scrutinizing the various theoretical parameters has pointed to M-M’ and M-M partially bonded S^C-bridge dinuclear d10 complexes vis-à-vis the classic Cotton-type multiple metal-metal bond description in d0<n<10 species.