Benchtop-Stable Carbyl Iminopyridyl NiII Complexes for Olefin Polymerization

Design of catalysts for Ni-catalyzed olefin polymerization predominantly focuses on ligand design rather than the activation process when attempting to achieve a broader scope of polyolefin micro- and macrostructures. Air-stable alkyl-or aryl-functionalized NiII precatalysts were designed which eliminate the need of in situ alkylating processes and are activated solely by halide abstraction to generate the cationic complex for olefin polymerization. These complexes represent an emerging class of olefin polymerization catalysts, enabling the study of various cocatalysts forming either inner- or outer-sphere ion pairs. It is demonstrated that an organoboron cocatalyst activation produces a well-defined ion pair, which in contrast to ill-defined organoaluminum cocatalysts, can directly activate the complex by halide abstraction to yield comparatively higher molecular weight homo/copolymers. Under high ethylene pressure, broader branching densities and the gradual incorporation of short-chain branches were achieved, circumventing the need for elaborate ligand design and copolymerization with α-olefins. The underlying chain-walking mechanism and ion pair interactions were further elucidated by DFT calculations. A phenyl group on the bridging carbon functioned as a rotational barrier, producing higher molecular weight polymers compared to methyl-substituted analogs. Here, we provide a perspective to manipulate the iminopyridyl NiII system, leveraging ion pair interactions and ligand design to govern polyolefin molecular weights and microstructures.

Multifaceted role of silver salts as ligand scavengers and different behavior of nickel and palladium complexes: beyond halide abstraction

The reaction of [NiArBr(PPh₃)₂] with AgBF₄ brings about the abstraction of both the halide and phosphine from the nickel center by silver. When the reaction is carried out in CH₂Cl₂/toluene a mixture of the cationic aquo derivatives [NiAr(H₂O)(PPh₃)₂]BF₄ (2) and [NiAr(H₂O)₂(PPh₃)]BF₄ (3) is formed, along with AgBr and [Ag(PPh₃)_n]BF₄. When the same reaction is carried out in acetone as the solvent, it leads to the completely different complex [NiAr(κ²-O, O-MeC(O)CH₂C(OH)Me₂)(PPh₃)] (5), bearing a chelating ligand formed by the aldol self-condensation of acetone. Phosphine abstraction by silver is less favorable for the analogous palladium(II) complexes and only occurs if a large excess of AgBF₄ is used. Thus, silver salts can be safely used as halide scavengers for palladium derivatives. However, the generation of cationic Ni complexes from neutral precursors by halide extraction with a silver salt may produce naked species, different than those expected, and highly reactive in certain media.

Effect of Nature of Substituents on Coordination Properties of Mono- and Disubstituted Derivatives of Boron Cluster Anions [BnHn]2– (n = 10, 12) and Carboranes with exo-Polyhedral B–X Bonds (X = N, O, S, Hal)

This review systematizes data on the coordination ability of mono- and disubstituted derivatives of boron cluster anions and carboranes in complexation with transition metals. Boron clusters anions [BnHn]2–, monocarborane anions [CBnHn–1]–, and dicarboranes [C2BnHn–2] (with non-functionalized carbon atoms) (n = 10, 12) containing the B–X exo-polyhedral bonds (X = N, O, S, Hal) are discussed. Synthesis and structural features of complexes known to date are described. The effect of complexing metal and substituent attached to the boron cage on the composition and structures of the final complexes is analyzed. It has been established that substituted derivatives of boron cluster anions and carboranes can act as both ligands and counterions. A complexing agent can coordinate substituted derivatives of the boron cluster anions due to three-center two-electron 3c2e MHB bonds, by the substituent functional groups, or a mixed type of coordination can be realized, through the BH groups of the boron cage and the substituent. As for B-substituted carboranes, complexes with coordinated substituents or salts with non-coordinated carborane derivatives have been isolated; compounds with MHB bonding are not characteristic of carboranes.

Synthesis and characterization of α-diamine palladium complexes and insight into hybridization effects of nitrogen donor atoms on norbornene (co)polymerizations

Hybridization effects of nitrogen donor atoms showed that the α-diamine palladium catalyst more easily produced highly active Pd²⁺cations for norbornene (co)polymerization.

Deactivation of the coordinating ability of the iminophosphorane group by the effect of ortho-carborane

An electron-withdrawing carborane group deactivates the nitrogen donor atom of an iminophosphorane ligand, which is not observed for organic ligands.

Triflyloxy-substituted carboranes as useful weakly coordinating anions

New carborane anions carrying one or three triflyloxy substituents are described.

Well-defined phosphino-phenolate neutral nickel(ii) catalysts for efficient (co)polymerization of norbornene and ethylene

With B(C₆F₅)₃as a singular cocatalyst, a series of phosphino-phenolate neutral nickel catalysts were found to be highly efficient for norbornene (co)polymerization. High molecular weight (co)polymers with good solubility in common organic solvents were obtained.

M[P(1,2-O2C6H4)3] (M = K or Na) — Synthesis, characterization, and use in halide abstraction

Alkali metal salts of the tris(o-phenylenedioxy)phosphate anion, K[P(1,2-O2C6H4)3] (K[1]) and Na[P(1,2-O2C6H4)3] (Na[1]), were prepared by treating Et3NH[1] with KH or NaH, respectively. X-ray crystallographic analysis of K[1], crystallized in the presence of DMSO, revealed a dimeric structure of formulation K2(DMSO)6[1]2·C7H8. In contrast, the crystal structure of K[1] grown from MeCN consists of fascinating hexagonal macrocycles with formulation {K(MeCN)2[1]}6 with an outside diameter of about 25 Å and a very small hole (≤2.5 Å). Remarkably, these hexagonal macrocycles stack one upon the other with a spacing of about 9.4 Å. The salt, K[1], is an effective halide abstraction agent reacting with (dppp)PdCl2 (dppp = 1,3-bis(diphenylphosphino)propane) (1:1 ratio) or [(cod)RhCl]2 (2:1 ratio) to afford [(dppp)Pd(µ-Cl)]2[1]2 and (cod)Rh[1], respectively. The molecular structures of each complex were determined.