P–C Bond Cleavage Induced Ni(II) Complexes Bearing Rare-Earth-Metal-Based Metalloligand and Reactivities toward Isonitrile, Nitrile, and Epoxide

Synthesis and characterization of homometallic cobalt complexes with metal-metal interactions

Complexes featuring metal-metal bonds play crucial roles in catalysis and small molecule activation due to the synergistic effects between the metals. Here, we report a series of homometallic cobalt complexes with metal-metal interactions that have been successfully stabilized by a multidentate ligand platform. Theoretical studies on metal-metal interactions in these cobalt complexes are discussed.

Flexible interactions of the rare-earth elements Y, La, and Lu with phosphorus in metallacyclohexane rings

A geometrically flexible bifunctional (bis)aminophosphine ligand was synthesized in a three-component, one-pot Kabachnik-Fields reaction using tert butylphosphine, paraformaldehyde, and 3,5-dimethyl aniline. The product, bis((3,5-dimethylphenyl)aminomethyl) tert butylphosphine (ArBiAMP t Bu), containing two secondary amines and a tertiary phosphine, was isolated in good yields. Deprotonation of both N-H groups with (trimethylsilyl)methylpotassium (K-CH2SiMe3), followed by salt metathesis with LaI3, YI3, and LuI3 generated the corresponding MI(ArBiAMP t Bu)(thf)3 complexes (M = Y (1), La (2), and Lu (3)) in good yields. A sterically encumbered indene, 1,3-diisopropyl-4,7-dimethyl-1H-indene, iPrMeInd, was deprotonated in situ and installed via salt-metathesis to generate the organometallic series of η5-indenide complexes, M(ArBiAMP t Bu)(η5-iPrMeInd)(thf) (M = Y (4), La (5), and Lu (6)). 1H, 31P, 13C, and 89Y NMR experiments, IR spectroscopy, and single crystal X-ray diffraction (SC-XRD), were used to characterize these complexes. The Y-P coupling constant was found to be variable depending on the modifiable coordination environment of the metal center, indicating potential as both a spectroscopic handle as well as providing insight into the influence of additional ligands on the metal center.

Rare-Earth Metalloligands for LowValent Cobalt Complexes: Fine Electronic Tuning via Co→RE Dative Interactions

Rare-earth metalloligand supported low-valent cobalt complexes were synthesized by utilizing a small-sized heptadentate phosphinomethylamine LsNH3 and a large-sized arene-anchored hexadentate phosphinomethylamine LlArH3 ligand precursors. The RE(III)-Co(-I)-N2 (RE = Sc, Lu, Y, Gd, La) complexes containing rare-earth metals including the smallest Sc and largest La were characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, electrochemistry, and computational studies. The Co(-I)→RE(III) dative interactions were all polarized with major contributions from the 3dz2 orbital of the cobalt center, which was slightly affected by the identity of rare-earth metalloligands. The IR spectroscopic data and redox potentials obtained from cyclic voltammetry revealed that the electronic property of the Co(-I) center was finely tuned by the rare-earth metalloligand, which was revealed by variation of the ligand systems containing LsN, LmN, and LlAr. Unlike the direct alteration of the electronic property of metal center via an ancillary ligand, such a series of rare-earth metalloligand represents a smooth strategy to tune the electronic property of transition metals.

A scandium metalloligand supported Ni(0) complex with a heterobimetallocycle: versatile reactivity with unsaturated bonds

A N2-bridged tetranuclear Sc(III)-Ni(0) complex featuring a Ni → Sc interaction and a 4-membered [Sc-N-C-Ni] ring was synthesized and characterized. Bimetallic reactivity was demonstrated via reactions with a series of unsaturated compounds containing NC, CN, CC, CO and NN bonds.

Heterometallic Clusters with Cerium-Transition-Metal Bonding Supported by Nitrogen-Phosphorus Ligands

Ligands are known to play a crucial role in the construction of complexes with metal-metal bonds. Compared with metal-metal bonds involving d-block transition metals, knowledge of the metal-metal bonds involving f-block rare-earth metals still lags far behind. Herein, we report a series of complexes with cerium-transition-metal bonds, which are supported by two kinds of nitrogen-phosphorus ligands N[CH2CH2NHPiPr2]3 (VI) and PyNHCH2PPh2 (VII). The reactions of zerovalent group 10 metal precursors, Pd(PPh3)4 and Pt(PPh3)4, with the cerium complex supported by VI generate heterometallic clusters [N{CH2CH2NPiPr2}3Ce(μ-M)]2 (M = Pd, 2 and M = Pt, 3) featuring four Ce-M bonds; meanwhile, the bimetallic species [(PyNCH2PPh2)3Ce-M] (M = Ni, 5; M = Pd, 6; and M = Pt, 7) with a single Ce-M bond were isolated from the reactions of the cerium precursor 4 supported by VII with Ni(COD)2, Pd(PPh3)4, or Pt(PPh3)4, respectively. These complexes represent the first example of species with an RE-M bond between Ce and group 10 metals, and 2 and 3 contain the largest number of RE-M donor/acceptor interactions ever to have been observed in a molecule.

Dinitrogen Complexes of Cobalt(-I) Supported by Rare-Earth Metal-Based Metalloligands

Sequential reactions of heptadentate phosphinoamine LH₃ with rare-earth metal tris-alkyl precursor (Me₃SiCH₂)₃Ln(THF)₂ (Ln = Sc, Lu, Yb, Y, Gd) and a low-valent cobalt complex (Ph₃P)₃CoI afforded rare-earth metal-supported cobalt iodide complexes. Reduction of these iodide complexes under N₂ allowed the isolation of the first series of dinitrogen complexes of Co(-I) featuring dative Co(-I) → Ln (Ln = Sc, Lu, Yb, Y, Gd) bonding interactions. These compounds were characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, electrochemistry, and computational studies. The correlation of N-N vibrational frequencies with the pK_a of [Ln(H₂O)₆]³⁺ showed that strongest activation of N₂ was achieved with the least Lewis acidic Gd(III) ion. Interestingly, these Ln-Co-N₂ complexes catalyzed silylation of N₂ in the presence of KC₈ and Me₃SiCl with turnover numbers (TONs) up to 16, where the lutetium-supported Co(-I) complex showed the highest activity within the series. The role of the Lewis acidic Ln(III) was crucial to achieve catalytic turnovers and tunable reactivity toward N₂ functionalization.

Recent advances in heterometallic clusters with f-block metal-metal bonds: synthesis, reactivity and applications

Due to the heterometallic synergistic effects from different metals, heterometallic clusters are of great importance in small-molecule activation and catalysis. For example, both biological nitrogen fixation and photosynthetic splitting of water into oxygen are thought to involve multimetallic catalytic sites with d-block transition metals. Benefitting from the larger coordination numbers of f-block metals (rare-earth metals and actinide elements), heterometallic clusters containing f-block metal-metal bonds have long attracted the interest of both experimental and theoretical chemists. Therefore, a series of effective strategies or platforms have been developed in recent years for the construction of heterometallic clusters with f-block metal-metal bonds. More importantly, synergistic effects between f-block metals and transition metals have been observed in small-molecule activation and catalysis. This tutorial review highlights the recent advances in the construction of heterometallic molecular clusters with f-block metal-metal bonds and also their reactivities and applications. It is hoped that this tutorial review will persuade chemists to develop more efficient strategies to construct clusters with f-block metal-metal bonds and also further expand their applications with heterometallic synergistic effects.

The Backbone of Success of P,N-Hybrid Ligands: Some Recent Developments

Organophosphorus ligands are an invaluable family of compounds that continue to underpin important roles in disciplines such as coordination chemistry and catalysis. Their success can routinely be traced back to facile tuneability thus enabling a high degree of control over, for example, electronic and steric properties. Diphosphines, phosphorus compounds bearing two separated PIII donor atoms, are also highly valued and impart their own unique features, for example excellent chelating properties upon metal complexation. In many classical ligands of this type, the backbone connectivity has been based on all carbon spacers only but there is growing interest in embedding other donor atoms such as additional nitrogen (-NH-, -NR-) sites. This review will collate some important examples of ligands in this field, illustrate their role as ligands in coordination chemistry and highlight some of their reactivities and applications. It will be shown that incorporation of a nitrogen-based group can impart unusual reactivities and important catalytic applications.

Phosphinoamido Ligand Supported Heterobimetallic Rare-Earth Metal-Palladium Complexes: Versatile Structures and Redox Reactivities

Heterobimetallic Ln(III)-Pd(0) complexes (Ln = Y, Sm, Gd, Yb) featuring tetranuclear structures with COD as bridges were obtained via the metallation of tris(phosphinoamido) rare-earth metal complexes [Ph2PNAd]3Ln (Ad = admantyl)...

Three-Coordinate Pd(0) with Rare-Earth Metalloligands: Synergetic CO Activation and Double P-C Bond Cleavage-Formation Reactions

Metalation of β-diketiminato rare-earth metal complexes L^nacnacLn(PhNCH₂PPh₂)₂ (Ln = Y, Yb, Lu) with (COD)Pd(CH₂SiMe₃)₂ afforded three-coordinate Pd(0) complexes supported by two sterically less bulky phosphines and a Pd → Ln dative interaction. The Pd(0) center is prone to ligation with isonitrile and CO; in the latter case, the insertion of a second CO with the Y-N bond was assisted via a precoordination of CO on the Pd(0) center, which led to the formation of an anionic Pd(0) carbamoyl. The reaction of the Pd-Y complex with iodobenzene showed a remarkable double P-C bond cleavage-formation pathway within the heterobimetallic Pd-Y core to afford (Ph₃P)₂PdI(Ph), imine PhNCH₂, and a β-diketiminato yttrium diiodide. In the related reaction of L^nacnacY(PhNCH₂PPh₂)₂ with (Ph₃P)₂PdI(Ph), the P-C bond cleavage following with a N-C bond formation was observed. Computational studies revealed a synergetic bimetallic mechanism for these reactions.