Palladium-meta-terarylphosphine catalyst for the Mizoroki-Heck reaction of (hetero)aryl bromides and functional olefins.

The evolutionary meta-terarylphosphine ligand architecture of Cy*Phine was recently shown to be a key feature that imposed outstanding performance in palladium-catalyzed copper-free Sonogashira applications. Herein, the Pd-Cy*Phine combination has similarly proven to be a powerful catalyst system for the Mizoroki-Heck reaction. Using high-throughput screening (HTS) methodology, DMF and NaHCO3 were rapidly identified as the most effective solvent and base pair for the cross-coupling catalysis of challenging and industrially valuable substrates including highly electron-rich heteroaryl bromides and unactivated olefins. Unprotected functional groups were well tolerated using low catalyst loadings, and the simple protocol produced excellent yields (up to 99%) with unprecedented substrate diversity. The Pd-Cy*Phine system broadly outperformed many state-of-the-art commercial alternatives, which demonstrated its potential as a next-generation cross-coupling catalyst.

Noninnocent behavior of ancillary ligands: apparent trans coupling of a saturated N-heterocyclic carbene unit with an ethyl ligand mediated by nickel.

Oxidative addition of the tridentate N-heterocyclic carbene (NHC) diphosphine ligand precursor ([PCP]H)PF(6) (1) {[PCP] = o-(i)Pr(2)PC(6)H(4)(NC(3)H(4)N)o-C(6)H(4)P(i)Pr(2)} to Ni(COD)(2) results in the formation of the nickel(II) hydride complex ([PCP]NiH)PF(6) (2). This hydride undergoes a rapid reaction with ethylene to generate a nickel(0) complex in which an ethyl group has been transferred to the carbene carbon of the original NHC-diphosphine ligand. If the first intermediate is the anticipated square-planar nickel(II) ethyl species, then the formation of the product would require a process that involves a trans C-C coupling of the NHC carbon and a presumed Ni-ethyl intermediate. Deuterium-labeling studies provide evidence for migratory insertion of the added ethylene into the Ni-H bond rather than into the Ni-carbene linkage; this is based on the observed deuterium scrambling, which requires reversible beta-elimination, alkene rotation, and hydride readdition. However, density functional theory studies suggest that a key intermediate is an agostic ethyl species that has the Ni-C bond cis to the NHC unit. A possible transition state containing two cis-disposed carbon moieties was also identified. Such a process represents a new pathway for catalyst deactivation involving NHC-based metal complexes.

Empirical and Computational Insights into N-Arylation Reactions Catalyzed by Palladium meta-Terarylphosphine Catalyst.

An in situ generated Pd-Cy*Phine catalyst has been successfully applied to the N-arylation of primary and secondary amines, and it exhibited high performance across multiple substrate classes. The performance induced by the meta-terarylphosphine motif of the Cy*Phine ligand for C-N cross-coupling displayed only subtle differences to that of its biarylphosphine congener XPhos. DFT studies demonstrated comparable reaction energetics in the catalytic cycle steps for both Pd-Cy*Phine and Pd-XPhos, which was consistent with previous findings. The computational investigation also indicated that a putative rate-determining step occurred after amine binding, which was likely to have annulled the expected benefits of having a meta-terarylphosphine ligand architecture.

[Au(CN)4]- as a supramolecular building block for heterobimetallic coordination polymers.

A series of the first coordination polymers using the [Au(CN)(4)](-) anion as a building block has been prepared. The planar tetracyanoaurate anion uses one, two, or four cyano groups to bridge to Ni(II) or Cu(II) centers and exhibits weak Au(III)-N(cyano) interactions between anions. Ni(en)(2)[Au(CN)(4)](2).H(2)O (1, en = ethylenediamine) is a molecular compound with the two [Au(CN)(4)](-) anions coordinating in a trans orientation to Ni(II) without further cyanide coordination. Cu(dien)[Au(CN)(4)](2) (2, dien = diethylenetriamine) forms a similar molecular complex; however, the dimensionality is increased through weak intermolecular Au-N(cyano) interactions of 3.002(14) A to form a 1-D zigzag chain. Cu(en)(2)[Au(CN)(4)](2) (3) also forms a molecular complex similar to 1, but with elongated axial bonds. The complex further aggregates through Au-N(cyano) interactions of 3.035(8) A to form a 2-D array. In [Cu(dmeda)(2)Au(CN)(4)][Au(CN)(4)] (4, dmeda = N,N-dimethylethylenediamine) one [Au(CN)(4)](-) anion coordinates via two cis-N(cyano) donors to the axial sites of two Cu(II) centers to form a 1-D zigzag chain of alternating [Cu(dmeda)(2)](2+) and [Au(CN)(2)](-) units; the other [Au(CN)(4)](-) anion forms a 1-D chain via Au-N(cyano) interactions. In [Cu(bipy)(H(2)O)(2)(Au(CN)(4))(0.5)][Au(CN)(4)](1.5) (5, bipy = 2,2'-bipyridine) one [Au(CN)(4)](-) anion uses all four cyano moieties to bridge four different Cu(II) centers, creating a 1-D chain.