Subtle Differences Between Zr and Hf in Early/Late Heterobimetallic Complexes with Cobalt

Added Complexity!-Mechanistic Aspects of Heterobimetallic Complexes for Application in Homogeneous Catalysis

Inspired by multimetallic assemblies and their role in enzyme catalysis, chemists have developed a plethora of heterobimetallic complexes for application in homogeneous catalysis. Starting with small heterobimetallic complexes with σ-donating and π-accepting ligands, such as N-heterocyclic carbene and carbonyl ligands, more and more complex systems have been developed over the past two decades. These systems can show a significant increase in catalytic activity compared with their monometallic counterparts. This increase can be attributed to new reaction pathways enabled by the presence of a second metal center in the active catalyst. This review focuses on mechanistic aspects of heterobimetallic complexes in homogeneous catalysis. Depending on the type of interaction of the second metal with the substrates, heterobimetallic complexes can be subdivided into four classes. Each of these classes is illustrated with multiple examples, showcasing the versatility of both, the types of interactions possible, and the reactions accessible.

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.

Techniques in the synthesis of organometallic compounds of Hafnium

Hafnium is a transition metal and it is the 45th most abundant transition element present on the earth. Hafnium has been successfully alloyed with several metals including titanium, iron, and niobium. Hafnium complexes are less active olefin polymerization catalysts. In the current review synthesis of hafnium complexes involving bonding through different linkages like “carbon, nitrogen, oxygen, carbon and oxygen, nitrogen and cobalt nitrogen and oxygen, nitrogen and phosphorus, nitrogen and sulfur, phosphorus and carbon, phosphorus and oxygen, sulfur carbon and oxygen, carbon–nitrogen and oxygen, carbon–nitrogen and phosphorus, carbon–nitrogen oxygen, sulfur and phosphorus, carbon–oxygen phosphorus and nitrogen”. The commonly used solvents for the synthesis of Hafnium complexes are tetrahydrofuran, n-hexane, and toluene, etc. These complexes were mostly reported at different temperatures ranges from −35 to 110 °C with continuous stirring, according to the nature of ligands. An overview of techniques in the synthesis of Hafnium complexes through various routes has been compiled.

Paramagnetic Metal-Metal Bonded Heterometallic Complexes

Significant progress has been made in the past 10-15 years on the design, synthesis, and properties of multimetallic coordination complexes with heterometallic metal-metal bonds that are paramagnetic. Several general classes have been explored including heterobimetallic compounds, heterotrimetallic compounds of either linear or triangular geometry, discrete molecular compounds containing a linear array of more than three metal atoms, and coordination polymers with a heterometallic metal-metal bonded backbone. We focus in this Review on the synthetic methods employed to access these compounds, their structural features, magnetic properties, and electronic structure. Regarding the metal-metal bond distances, we make use of the formal shortness ratio (FSR) for comparison of bond distances between a broad range of metal atoms of different sizes. The magnetic properties of these compounds can be described using an extension of the Goodenough-Kanamori rules to cases where two magnetic ions interact via a third metal atom. In describing the electronic structure, we focus on the ability (or not) of electrons to be delocalized across heterometallic bonds, allowing for rationalizations and predictions of single-molecule conductance measurements in paramagnetic heterometallic molecular wires.

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

The synthesis of a full series of group 4/nickel complexes supported by a 2-(diphenylphosphino)pyrrolide (NP) ligand is reported. Treatment of the homoleptic, 8-coordinate M(NP)4 monometallic precursors with Ni(COD)2 (COD = 1,5-cyclooctadiene) yielded the heterobimetallic complexes (κ(2)-NP)M(μ2-NP)3Ni (M = Ti, Zr, Hf). Although X-ray crystallographic analysis reveals similarly short metal-metal distances in all three complexes, quantum chemical calculations indicate that ZrNi () and HfNi () contain only single Ni → M dative bonds while TiNi () has an additional Ti-Ni π-bond. All three complexes have quasireversible reductions by cyclic voltammetry, and 1-electron chemical reduction of by Na(Hg) yields the anion, [Na][(κ(2)-NP)Ti(μ2-NP)3Ni] (). X-ray and computational analysis indicate that the 1-electron reduction of completely breaks the metal-metal bond, yielding a formally Ti(III)-Ni(0) complex. Ti-Ni bonding can also be disrupted by coordination of CO, wherein Ni → CO backbonding effectively outcompetes Ni → Ti dative bonding.

Through-space Förster-type energy transfer in isostructural zirconium and hafnium-based metal–organic layers

Identical energy transfer rates in isostructural Zr and Hf metal–organic layers revealed dominant through-space energy transfer over the through-bond one.

Bimetallic rare-earth/platinum complexes ligated by phosphinoamides

The heterometallic early-late 5d/4f binuclear phosphinoamido Ln/Pt(0) complexes [(Ph₂PNHPh)Pt{μ-(Ph₂PNPh)}₃Ln(μ-Cl)Li(THF)₃] (Ln = Y, Lu) and [(Ph₂PNHPh)Pt{μ-(Ph₂PNPh)}₃Ln{η²-(Ph₂PNPh)}][Li(THF)₄] (Ln = Y, Lu) are reported.

Allylic amination reactivity of Ni, Pd, and Pt heterobimetallic and monometallic complexes

Transition metal heterobimetallic complexes with dative metal–metal interactions have the potential for novel fast reactivity.

Bi- and trimetallic rare-earth–palladium complexes ligated by phosphinoamides

Heterometallic early–late 4d/4f bi- and trinuclear phosphinoamido Ln–Pd(0) complexes [(Ph₂PNHPh)Pd{μ-(Ph₂PNPh)}₃Ln(μ-Cl)Li(THF)₃] (Ln = Y, Lu) and [Li(THF)₄][{(Ph₂PNHPh)Pd}₂{μ-(Ph₂PNPh)}₄Ln] (Ln = Y, Lu) are described.