Structure and bonding of group 4-nickel heterobimetallics supported by 2-(diphenylphosphino)pyrrolide ligands

Heterometallic bond activation enabled by unsymmetrical ligand scaffolds: bridging the opposites

Heterobi- and multimetallic complexes providing close proximity between several metal centers serve as active species in artificial and enzymatic catalysis, and in model systems, showing unique modes of metal-metal cooperative bond activation. Through the rational design of well-defined, unsymmetrical ligand scaffolds, we create a convenient approach to support the assembly of heterometallic species in a well-defined and site-specific manner, preventing them from scrambling and dissociation. In this perspective, we will outline general strategies for the design of unsymmetrical ligands to support heterobi- and multimetallic complexes that show reactivity in various types of heterometallic cooperative bond activation.

Construction of modular Pd/Cu multimetallic chains via ligand- and anion-controlled metal-metal interactions

The presence of Pd⋯Cu and Pd⋯Pd interactions as well as the order of metal atoms in a chain held by a modular polynucleating ligand is controlled by the coordinating ability of the anions, leading to selective formation of bi- and tetranuclear Pd/Cu and Pd₄ chains. Metal-metal cooperative reactivity in these complexes was tested in Ar-O bond formation and alkyne activation.

H2 and carbon-heteroatom bond activation mediated by polarized heterobimetallic complexes

The field of heterobimetallic chemistry has rapidly expanded over the last decade. In addition to their interesting structural features, heterobimetallic structures have been found to facilitate a range of stoichiometric bond activations and catalytic processes. The accompanying review summarizes advances in this area since January of 2010. The review encompasses well-characterized heterobimetallic complexes, with a particular focus on mechanistic details surrounding their reactivity applications.

Computational prediction on the catalytic activity of heterobimetallic complex featuring MM' triple bond in acetylene cyclotrimerization: Mechanistic study

A detailed reaction mechanism of acetylene cyclotrimerization catalyzed by V(ⁱ PrNPMe₂ )₃ Fe-PMe₃ (denote as CAT), a heterobimetallic complex featuring V-Fe triple bond, was computationally investigated using density functional theory. The calculated results show that the first acetylene firstly attaches to the V atom of CAT to get a four-membered ring structure through [2 + 2] cycloaddition reaction. For the second acetylene addition, there are two cyclotrimerization mechanisms, outer sphere mechanism and inner mechanism. The inner sphere reaction pathway is the main reaction pathway. By replacing the V with Nb and Ta, Fe with Ru and Os, a series of new catalysts are screened computationally. The calculated results show that, all of the nine heterobimetallic complexes show high activity at mild condition. The energy barrier of the rate determining step is related to the natural population analysis (NPA) charge of M' and the Wiberg bond index (WBI) of M-M' bond. The more negative NPA charge of M' and the smaller WBI of M-M' bond, the lower energy barrier is.

Metal-metal cooperative bond activation by heterobimetallic alkyl, aryl, and acetylide PtII/CuI complexes

We report the selective formation of heterobimetallic Pt^II/Cu^I complexes that demonstrate how facile bond activation processes can be achieved by altering the reactivity of common organoplatinum compounds through their interaction with another metal center. The interaction of the Cu center with the Pt center and with a Pt-bound alkyl group increases the stability of PtMe₂ towards undesired rollover cyclometalation. The presence of the Cu^I center also enables facile transmetalation from an electron-deficient tetraarylborate [B(Ar^F)₄]⁻ anion and mild C–H bond cleavage of a terminal alkyne, which was not observed in the absence of an electrophilic Cu center. The DFT study indicates that the Cu center acts as a binding site for the alkyne substrate, while activating its terminal C–H bond.

The selective formation of heterobimetallic Pt^II/Cu^I complexes demonstrates how facile bond activation processes can be achieved by altering the reactivity of common organoplatinum compounds through their interaction with another metal center.

Synthesis and Characterization of Tantalum-Based Early-Late Heterobimetallic Complexes Supported by 2-(diphenylphosphino)pyrrolide Ligands

The synthesis of the metalloligand Ta(κ²-NP)₃Cl₂ (NP = 2-diphenylphosphinopyrrolide) and its coordination chemistry with group 9 and 10 metals is reported. Treatment of Ta(κ²-NP)₃Cl₂ with group 9 and 10 metals resulted in clean formation of the heterobimetallic complexes Cl₂Ta(μ₂-NP)₃M (M = Ni (2), Pd (3)) or Cl₂Ta(μ₂-NP)₃MCl (M = Rh (4), Ir (5)). Each pair of complexes is isostructural and contains three phosphinopyrrolide ligands that bridge the metal centers. The d¹⁰ or d⁸ complexes are all diamagnetic and X-ray crystallographic analysis reveals similarly short metal-metal distances, ranging from 2.2979(5) Å to 2.4366(2) Å. Despite the similar bonding metrics in 2-5, treatment with an L type donor (2,6-dimethylphenylisocyanide (CNXylyl)) reveals 3 different coordination geometries in TaNi(CNXylyl) (6), TaPd(CNXylyl) (7), and TaIr(CNXylyl) (8). While complexes 6, 7, and 8 all bind the isocyanide at the late metal, ligand rearrangements are observed in the first row complex 6. Complex 7 binds the isocyanide in the axial position while equatorial binding is observed in 8. All isocyanide adducts maintain close metal-metal contacts in the solid state.

Ionic-caged heterometallic bismuth-platinum complex exhibiting electrocatalytic CO2 reduction

An air-stable heterometallic Bi-Pt complex with the formula [BiPt(SAc)5]n (1; SAc = thioacetate) was synthesized. The crystal structure, natural bond orbital (NBO) and local orbital locator (LOL) analyses, localized orbital bonding analysis (LOBA), and X-ray absorption fine structure (XAFS) measurements were used to confirm the existence of Bi-Pt bonding and an ionic cage of O atoms surrounding the Bi ion. From the cyclic voltammetry (CV) and controlled potential electrolysis (CPE) experiments, 1 in tetrahydrofuran reduced CO2 to CO, with a faradaic efficiency (FE) of 92% and a turnover frequency (TOF) of 8 s-1 after 30 min of CPE at -0.79 V vs. NHE. The proposed mechanism includes an energetically favored pathway via the ionic cage, which is supported by the results of DFT calculations and reflectance infrared spectroelectrochemistry data.

Selective Synthesis of a Series of Isostructural MII CuI Heterobimetallic Complexes Spontaneously Assembled by an Unsymmetrical Naphthyridine-Based Ligand

Metal-metal cooperation is integral to the function of many enzymes and materials, and model complexes hold enormous potential for providing insights into the capabilities of analogous multimetallic cores. However, the selective synthesis of heterobimetallic complexes still presents a significant challenge, especially for systems that hold the metals in close proximity and feature open or reactive coordination sites for both metals. To address this issue, a rigid, naphthyridine-based dinucleating ligand featuring distinct binding environments was synthesized. This ligand enables the selective synthesis of a series of M^II Cu^I bimetallic complexes (M=Mn, Fe, Co, Ni, Cu, Zn), in which each metal center exclusively occupies its preferred binding pocket, from simple chloride salts. The precision of this selectivity is evident from cyclic voltammetry, ESI-MS and anomalous X-ray diffraction measurements.

Acetonitrile Adduct [MoReCp(μ-H)(μ-PCy2)(CO)5(NCMe)]: A Surrogate of an Unsaturated Heterometallic Hydride Complex

The title compound was prepared upon irradiation of acetonitrile solutions of the readily available hexacarbonyl [MoReCp(μ-H)(μ-PCy₂)(CO)₆]. The acetonitrile ligand in this compound could be replaced easily by donor molecules or displaced upon two-electron reduction. In most cases, the substitution step was followed by additional processes such as insertion into the M-H bonds, E-H bond cleavage, H₂ elimination, and other transformations.

An Unsymmetric Ligand Framework for Noncoupled Homo- and Heterobimetallic Complexes

We introduce a new unsymmetric ligand, PDIpCy (PDI = pyridyldiimine; Cy = cyclam), that offers two distinct, noncoupled coordination sites. A series of homo- and heterobimetallic complexes, [Zn₂(PDIpCy)(THF)(OTf)₄] (1; THF = tetrahydrofuran and OTf = triflate), [Ni₂(PDIpCy)(THF)(OTf)₂](OTf)₂ (2), and [NiZn(PDIpCy)(THF)(OTf)₄] (3), are described. The one-electron-reduced compounds, [Zn₂(PDIpCy)(OTF)₃] (4), [Ni₂(PDIpCy)(OTf)](OTf)₂ (5), and [NiZn(PDIpCy)(OTf)₃] (6), were isolated, and their electronic structures were characterized. The reduced compounds are charge-separated species, with electron storage at either the PDI ligand (4) or at the PDI-bound metal ion (5 and 6).