Zwitterionic nickel(II) complexes: Synthesis, characterization, decomposition, and stoichiometric and catalytic reactivities

Abstract

Zwitterionic nickel(II) compounds with a borate-containing anionic bidentate phosphine ligand (PBP -) have been synthesized and some of them crystallographically characterized. The methyl complex, (PBP -)Ni + CH 3 (NCCH 3 ), reacts with H 2 to form an 12-membered macrocycle containing three Ni nuclei and reacts with carbon monoxide (CO) to afford the acetyl complex (PBP -)Ni + COCH 3 (CO). The square planar acetyl complex is stable in solution under one atmosphere of CO but undergoes irreversible decomposition under high CO pressure at room temperature. X-Ray crystallographic characterization of a decomposition product revealed fragmentation of the anionic borate under high pressure. (PBP -)Ni + COCH 3 (CO) is an active catalyst for ethylene-CO copolymerization, but its productivity is low likely due to its instability under high CO pressure.

Zwitterionic Cobalt(I)–NHC Complexes with Tetraphenylborate Ligation: Synthesis, Characterization, and Reactivity

“…Along with the exploration of the zwitterionic precious metal complexes, there are also great interests in their 3d metal analogs, − particularly the cobalt complexes. As the first structurally well-defined 3d metal complex featuring an π-coordinated tetraphenylborate anion, [(PMe 3 ) 2 Co­((η 6 -C 6 H 5 )­BPh 3 )] ( B ) was obtained from the reaction of (PMe 3 ) 3 CoBr with NaBPh 4 .…”

Electrostatic vs. inductive effects in phosphine ligand donor properties and reactivity

“…77 Indeed, cationic and anionic moieties have previously been incorporated into phosphines, frequently leading to distinct properties or reactivity in comparison to neutral analogues. [78][79][80][81][82][83] Phosphine borate ligands specically have been prepared through the incorporation of triaryl-and triuoroborate and carborane functional groups, and have shown enhanced reactivity in polymerization, [84][85][86][87][88][89][90][91][92][93] cross coupling, [94][95][96] and hydrofunctionalization 97,98 reactions. These anionic phosphines are uniformly considered to be stronger donors than their neutral isostructural analogues.…”

Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers

“…[21] Thep revious zwitterionic Ni II catalysts suffered from insufficient stability under CO and were inactive for the COP of cyclic ethers.W ith our newly developed ligands that feature ortho-methoxy auxiliaries to stabilize the coordination, we demonstrate here the validity of the zwitterionic design principle of Ni II catalysts for the COP of cyclic ethers. [21] Thep revious zwitterionic Ni II catalysts suffered from insufficient stability under CO and were inactive for the COP of cyclic ethers.W ith our newly developed ligands that feature ortho-methoxy auxiliaries to stabilize the coordination, we demonstrate here the validity of the zwitterionic design principle of Ni II catalysts for the COP of cyclic ethers.…”