Polymetallic complexes linked to a single-frame ligand: cooperative effects in catalysis

Direct oxide transfer from an η2-keto ligand to generate a cobalt PCcarbeneP(O) pincer complex

We report the direct carbonyl cleavage in a κ³-P′,(η²-C,O),P′′ ligand by a monomeric cobalt centre through metal–ligand cooperativity.

Hydrogenolysis of carbon–carbon σ-bonds using water catalysed by semi-rigid diiridium(iii) porphyrins

Semi-rigid diiridium(iii) porphyrins alkyls with m-xylyl and p-xylyl diether linkers were synthesized. They were found to be catalysts for the carbon–carbon σ-bond hydrogenolysis of [2.2]paracyclophane in neutral conditions using water as the hydrogen source.

Highly Active Dinuclear Titanium(IV) Complexes for the Catalytic Formation of a Carbon-Heteroatom Bond

A series of mononuclear titanium(IV) complexes with the general composition κ³-[R{NHPh₂P(X)}₂Ti(NMe₂)₂] [R = C₆H₄, X = Se (3b); R = trans-C₆H₁₀, X = S (4a), Se (4b)] and [{κ²-N(PPh₂Se)₂}₂Ti(NMe₂)₂] (6b) and two dinuclear titanium(IV) complexes, [C₆H₄{(NPh₂PS)(N)}Ti(NMe₂)]₂ (3c) and [{κ²-N(PPh₂Se)}Ti(NMe₂)₂]₂ (6c), are reported. Dinuclear titanium(IV) complex 6c acts as an efficient catalyst for the chemoselective addition of an E-H bond (E = N, O, S, P, C) to heterocumulenes under mild conditions. The catalytic addition of aliphatic and aromatic amines, alcohol, thiol, phosphine oxide, and acetylene to the carbodiimides afforded the corresponding hydroelemented products in high yield at mild conditions with a broader substrate scope. The catalytic efficiency of the dinuclear complex depends on the cooperative effect of the Ti^IV ions, the systematic variation of the intermetallic distance, and the ligand's steric properties of the complex, which enhances the reaction rate. Most interestingly, this is the first example of catalytic insertion of various E-H bonds into the carbodiimides using a single-site catalyst because only the titanium-mediated insertion of E-H into a C═N unsaturated bond is reported to date. The amine and alcohol insertion reaction with the carbodiimides showed first-order kinetics with respect to the titanium(IV) catalyst as well as substrates. A most plausible mechanism for hydroelementation reaction is also proposed, based on the spectroscopic data of the controlled reaction, a time-course study, and the Hammett plot.

En Route to Bis-Carbene Analogues of the Heavier Group 13 Elements: Consideration of Bridging Group and Metal(I) Source

With the aim of exploring the effect of steric constraints imposed on the metal-metal interaction of bis-carbene analogues of thallium by the linking scaffold, seven dinuclear thallium diyls with a series of rigid, semirigid, and flexible bridging scaffolds were synthesized. The solid-state molecular structures were determined for four of these compounds by single-crystal XRD and compared with the results of DFT calculations, which were performed for all substances. These compounds serve as models to investigate the metal-metal distance in the absence of co-coordinated molecules (additional ligands, solvent molecules). In addition, the effect of the metal(I) precursor, and more specifically the counterion, on the synthetic access to bis-carbene analogues of indium and thallium was investigated. For indium, only InI yields the desired dinuclear indium diyl. With InBr no reaction was observed, and using InCl gave rise to a mononuclear indium(III) compound. For thallium, both TlI and TlBr allow access to the related bis-carbene analogue, although the yield with the latter is significantly lower. In contrast, no reactions were observed with TlCl and TlBF₄ .

Synthesis, characterization and olefin polymerization behaviors of phenylene-bridged bis-β-carbonylenamine binuclear titanium complexes

Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-β-carbonylenamine [O⁻NS^R] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (Ti²L₁–Ti²L₅) were synthesized and characterized by ¹H NMR, ¹³C NMR, FTIR and elemental analysis. The molecular structure of ligand L₂ (R = ⁿPr) and its corresponding Ti complex Ti²L₂ were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from β-carbonylenamine to β-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 10⁶ g mol (Ti)⁻¹ h⁻¹ atm⁻¹) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL₆ was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex Ti²L₅ bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-β-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.

Phenyl-bridged bis-β-carbonylenamine binuclear titanium complexes were synthesized, characterized and used to catalyze ethylene (co)polymerization with extremely high activity.

A Redox-Switchable Germylene and its Ligating Properties in Selected Transition Metal Complexes

The synthesis, structure, and full characterization of a redox-switchable germylene based on a [3]ferrocenophane ligand arrangement, [Fc(NMes)₂ Ge] (4), is presented. The mesityl (Mes)-substituted title compound is readily available from Fc(NHMes)₂ (2) and Ge{N(SiMe₃ )₂ }₂ , or from the dilithiated, highly air- and moisture-sensitive compound Fc(NLiMes)₂ ⋅3 Et₂ O (3) and GeCl₂ . Cyclic voltammetry studies are provided for 4, confirming the above-mentioned view of a redox-switchable germylene metalloligand. Although several 1:1 Rh^I and Ir^I complexes of 4 (5-7) are cleanly formed in solution, all attempts to isolate them in pure form failed due to stability problems. However, crystalline solids of [Mo(κ¹ Ge-4)₂ (CO)₄ ] (8) and [W(κ¹ Ge-4)₂ (CO)₄ ] (9) were isolated and fully characterized by common spectroscopic techniques (8 by X-ray diffraction). DFT calculations were performed on a series of model compounds to elucidate a conceivable interplay between the metal atoms in neutral and cationic bimetallic complexes of the type [Rh(κ¹ E-qE)(CO)₂ Cl]^0/+ (qE=[Fc(NPh)₂ E] with E=C, Si, Ge). The bonding characteristics of the coordinated Fc-based metalloligands (qE/qE⁺ ) are strongly affected upon in silico oxidation of the calculated complexes. The calculated Tolman electronic parameter (TEP) significantly increases by approximately 20 cm^-1 (E=C) to 25 cm^-1 (E=Si, Ge) upon oxidation. The change in the ligand-donating abilities upon oxidation can mainly be attributed to Coulombic effects, whereas an orbital-based interaction appears to have only a minor influence.

Palladium complexes of ferrocene-based phosphine ligands as redox-switchable catalysts in Buchwald–Hartwig cross-coupling reactions

Redox-switchable catalysis: Palladium(ii) complexes of two differently substituted [1]phosphaferrocenophanes FcPR (R = Mes, biaryl) and of diphenylferrocenyl phosphine Ph₂PFc were applied in redox-switchable Buchwald–Hartwig cross-coupling reactions.

Insight into Oxide-Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe⋅THF with [Cp*₂ Zr(Me)OH] gave [(TBBP)Al(THF)-O-Zr(Me)Cp*₂ ] (TBBP=3,3',5,5'-tetra-tBu-2,2'-biphenolato). Reaction of [DIPPnacnacAl(Me)-O-Zr(Me)Cp₂ ] with [PhMe₂ NH]⁺ [B(C₆ F₅ )₄ ]^- gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)-O-Zr(THF)Cp₂ ]⁺ [B(C₆ F₅ )₄ ]^- (DIPPnacnac=HC[(Me)C=N(2,6-iPr₂ -C₆ H₃ )]₂ ). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40-47 kcal mol^-1 ) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six-membered-ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal-Me-C angle that prevents synchronized bond-breaking and making. A more-likely pathway is dissociation of the Al-O-Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ ZrMe]⁺ .

Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity

Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di- and monozinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the dizinc catalysts significantly out-perform the monozinc analogs. Further, for the best dizinc catalyst, the ligand conformation controls activity: the catalyst with "folded" ligand conformation shows turnover frequency (TOF) values up to 60 000 h(-1) (0.1 mol % loading, 298 K, [LA]=1 m), whilst that with a "planar" conformation is much slower, under similar conditions (TOF=30 h(-1) ). Dizinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol % whilst conserving high activity (TOF=12 500 h(-1) ).

Bimetallic Schiff base complexes for stereoselective polymerisation of racemic-lactide and copolymerisation of racemic-lactide with ε-caprolactone

Bimetallic Schiff-base complexes with different bridging parts and silyl-substituents were applied for stereoselective ROP ofrac-LA, and copolymerisation ofrac-LA/ε-CL.

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.

Manganese coordination chemistry of bis(imino)phenoxide derived [2 + 2] Schiff-base macrocyclic ligands

Products resulting from the reaction of MnCl₂ with [2 + 2] Schiff-base macrocycles have been structurally characterized, and were found to be poorly active for the ROP of ε-caprolactone.

Synthesis and structure of the first discrete dinuclear cationic aluminum complexes

The preparation of discrete mono- and dicationic dinuclear aluminum complexes from the parent charge neutral dinuclear precursors has been studied. The first crystal structure of a dicationic dialuminum complex is reported.

Facile high-yield synthesis of unsymmetric end-off compartmental double Schiff-base ligands: easy access to mononuclear precursor and unsymmetric dinuclear complexes

Novel approach to unsymmetric end-off compartmental ligands with a selective high-yield synthesis and access to unsymmetric dinuclear complexes.

Mono and dimetallic pyrene-imidazolylidene complexes of iridium(iii) for the deuteration of organic substrates and the C–C coupling of alcohols

Two pyrene-NHC complexes of Ir(iii) and one di-iridium(iii) complex with a pyrene-di-NHC ligand have been prepared and characterized. Their catalytic activity in the deuteration of organic substrates, and in the β-alkylation of secondary alcohols with primary alcohols is described.

Diamagnetic molybdenum nitride complexes supported by diligating tripodal triamido-phosphine ligands as precursors to paramagnetic phosphine donors

The reaction of the ligand precursors P[CH2NHAr(R)]3 () with (Me2N)3Mo[triple bond, length as m-dash]N generated the complexes P(CH2NAr(R))3Mo[triple bond, length as m-dash]N (), where Ar(R) = 3,5-(CH3)2C6H3 (), Ph (), and 3,5-(CF3)2C6H3 (), with (Me2N)3Mo[triple bond, length as m-dash]N generated the complexes P(CH2NAr(R))3Mo[triple bond, length as m-dash]N (). Complex was obtained in poor yield, due to the formation of P(CH2N-3,5-(CF3)2C6H3)2(CH2NH-3,5-(CF3)2C6H3)(NMe2H)(NMe2)Mo[triple bond, length as m-dash]N () as the major product. Reaction of with VMes3THF generated the paramagnetic complexes P(CH2NAr(R))3Mo(μ-N)V(Mes)3 (). The reaction of with Ni(acac)2 generated the Ni(0) complexes Ni[P(CH2NAr(R))3Mo[triple bond, length as m-dash]N]4 () in poor yield. These complexes were synthesized in higher yields from the reaction of with Ni(COD)2, where COD = 1,5-cyclooctadiene. Reaction of either with V(Mes)3THF or with Ni(COD)2 generated the paramagnetic nonanuclear complex Ni[P(CH2NAr(R))3Mo(μ-N)VMes3]4 ().

Facile tandem Suzuki coupling/transfer hydrogenation reaction with a bis-heteroscorpionate Pd-Ru complex

Design and synthesis of the bis(pyrazol-1-yl)methane based bis-heteroscorpionate Pd-Ru complex results in efficient tandem Suzuki coupling/transfer hydrogenation reaction with a broad range of substrate reactivity.

Time-resolved IR spectroscopy of a trinuclear palladium complex in solution

Time-resolved IR spectroscopic methods covering the femto- to microsecond range in combination with (TD-)DFT computations were used to investigate the electronically excited state structure of a trinuclear Pd complex.

Mono- and tetra-nuclear copper complexes bearing bis(imino)phenoxide derived ligands: catalytic evaluation for benzene oxidation and ROP of ε-caprolactone

Mono- and tetra-nuclear copper bis(imino)phenoxide complexes have been evaluated as catalysts for benzene oxidation and ROP of ε-caprolactone.