The efficient copolymerization of acrylates with ethylene using Ni catalysts remains a challenge. Herein, we report two neutral Ni­(II) catalysts (POP-Ni-py (1) and PONap-Ni-py (2)) that exhibit high thermal stability and significantly higher incorporation of polar monomer (for 1) or improved resistance to tert-butylacrylate (tBA)-induced chain transfer (for 2), in comparison to previously reported catalysts. Nickel alkyl complexes generated after tBA insertion, POP-Ni-CCO­(py) (3) and PONap-Ni-CCO­(py) (4), were isolated and, for the first time, characterized by crystallography. Weakened lutidine vs pyridine coordination in 2-lut facilitated the isolation of a N-donor-free adduct after acrylate insertion PONap-Ni-CCO (5) which represents a novel example of a four-membered chelate relevant to acrylate polymerization catalysis. Experimental kinetic studies of six cases of monomer insertion with aforementioned nickel complexes indicate that pyridine dissociation and monomer coordination are fast relative to monomer migratory insertion and that monomer enchainment after tBA insertion is the rate limiting step of copolymerization. Further evaluation of monomer insertion using density functional theory studies identified a cis–trans isomerization via Berry-pseudorotation involving one of the pendant ether groups as the rate-limiting step for propagation, in the absence of a polar group at the chain end. The energy profiles for ethylene and tBA enchainments are in qualitative agreement with experimental measurements.

While P(4) is the stable molecular form of phosphorus, a recent study illustrated the possibility of P(2) generation for reactions in organic media under mild conditions. The heavier group 15 element arsenic can exist as As(4) molecules, but As(4) cannot be stored as a pure substance because it is both light-sensitive and reverts thermally to its stable, metallic gray form. Herein we report As(4) activation giving rise to a mu-As(2) diniobium complex, serving in turn as precursor to a terminal arsenide anion complex of niobium. Functionalization of the latter provides the new AsPNMes* ligand, which when complexed with tungsten pentacarbonyl elicits extrusion of the (AsP)W(CO)(5) molecule as a reactive intermediate. Trapping reactions of the latter with organic dienes are found to furnish double Diels-Alder adducts in which the AsP unit is embedded in a polycyclic organic framework. Thermal generation of (AsP)W(CO)(5) in the presence of the neutral terminal phosphide complex P identical withMo(N[(i)Pr]Ar)(3) leads to the cyclo-AsP(2) complex (OC)(5)W(cyclo-AsP(2))Mo(N[(i)Pr]Ar)(3). The (AsP)W(CO)(5) trapping products were crystallized and characterized by X-ray diffraction methods, and computational methods were applied for analysis of the As-As and As-P bonds in the complexes.

The synthesis and comprehensive characterization of a new series of N-heterocyclic phosphine, arsine, and stibine compounds is presented. The diamidochloropnictines ClPn(NR)2C10H6 (Pn = P, As, Sb) were prepared via the dehydrohalide coupling reactions of N,N‘-diisopropyl-1,8-diaminonaphthalene, ( i PrNH)2C10H6, or N,N‘-diphenyl-1,8-diaminonaphthalene, (PhNH)2C10H6, with the appropriate pnictogen trichloride. Reaction of these pnictines with appropriate halide abstraction agents yielded the corresponding phosphenium and arsenium salts. These planar pnictogenium cations {Pn(NR)2C10H6}+ (Pn = P, As; R = i Pr, Ph) display dicoordinate pnictogen centers that are stabilized by an electron-rich diamidonaphthalene framework and represent rare examples of six-membered N-heterocyclic pnictogenium cations possessing a π-conjugated carbon backbone. The related stibenium salts could not be prepared via this route; however, the reaction of the new heteroleptic triamidostibene, (Me2N)Sb( i PrN)2C10H6, with triflic acid does generate the base-stabilized stibenium cation, [Sb( i PrN)2C10H6·(Me2NH)]+. The phosphenium and arsenium salts exhibit different modes of packing in their solid-state structures depending upon the identity of the nitrogen substituents. The two phenyl substituted compounds display an interaction between the pnictogen center and the π-system of an adjacent naphthyl moiety. In contrast, the isopropyl substituted species undergo metastable dimerization through naphthyl π-stacking. These dimers are bound by strong dipole−dipole and dispersion interactions as revealed through computational studies.