Strong π-stacking causes unusually large anisotropic thermal expansion and thermochromism.

π-stacking in ground-state dimers/trimers/tetramers of N-butoxyphenyl(naphthalene)diimide (BNDI) exceeds 50 kcal ⋅ mol-1 in strength, drastically surpassing that for the *3[pyrene]2 excimer (∼30 kcal ⋅ mol-1; formal bond order = 1) and similar to other weak-to-moderate classical covalent bonds. Cooperative π-stacking in triclinic (BNDI-T) and monoclinic (BNDI-M) polymorphs effects unusually large linear thermal expansion coefficients (α a , α b , α c , ß) of (452, -16.8, -154, 273) × 10-6 ⋅ K-1 and (70.1, -44.7, 163, 177) × 10-6 ⋅ K-1, respectively. BNDI-T exhibits highly reversible thermochromism over a 300-K range, manifest by color changes from orange (ambient temperature) toward red (cryogenic temperatures) or yellow (375 K), with repeated thermal cycling sustained for over at least 2 y.

Cupriphication of gold to sensitize d10-d10 metal-metal bonds and near-unity phosphorescence quantum yields.

Outer-shell s0/p0 orbital mixing with d10 orbitals and symmetry reduction upon cupriphication of cyclic trinuclear trigonal-planar gold(I) complexes are found to sensitize ground-state Cu(I)-Au(I) covalent bonds and near-unity phosphorescence quantum yields. Heterobimetallic Au4Cu2 {[Au4(µ-C2,N3-EtIm)4Cu2(µ-3,5-(CF3)2Pz)2], (4a)}, Au2Cu {[Au2(µ-C2,N3-BzIm)2Cu(µ-3,5-(CF3)2Pz)], (1) and [Au2(µ-C2,N3-MeIm)2Cu(µ-3,5-(CF3)2Pz)], (3a)}, AuCu2 {[Au(µ-C2,N3-MeIm)Cu2(µ-3,5-(CF3)2Pz)2], (3b) and [Au(µ-C2,N3-EtIm)Cu2(µ-3,5-(CF3)2Pz)2], (4b)} and stacked Au3/Cu3 {[Au(µ-C2,N3-BzIm)]3[Cu(µ-3,5-(CF3)2Pz)]3, (2)} form upon reacting Au3 {[Au(µ-C2,N3-(N-R)Im)]3 ((N-R)Im = imidazolate; R = benzyl/methyl/ethyl = BzIm/MeIm/EtIm)} with Cu3 {[Cu(µ-3,5-(CF3)2Pz)]3 (3,5-(CF3)2Pz = 3,5-bis(trifluoromethyl)pyrazolate)}. The crystal structures of 1 and 3a reveal stair-step infinite chains whereby adjacent dimer-of-trimer units are noncovalently packed via two Au(I)⋯Cu(I) metallophilic interactions, whereas 4a exhibits a hexanuclear cluster structure wherein two monomer-of-trimer units are linked by a genuine d10-d10 polar-covalent bond with ligand-unassisted Cu(I)-Au(I) distances of 2.8750(8) Å each-the shortest such an intermolecular distance ever reported between any two d10 centers so as to deem it a "metal-metal bond" vis-à-vis "metallophilic interaction." Density-functional calculations estimate 35-43 kcal/mol binding energy, akin to typical M-M single-bond energies. Congruently, FTIR spectra of 4a show multiple far-IR bands within 65-200 cm-1, assignable to vCu-Au as validated by both the Harvey-Gray method of crystallographic-distance-to-force-constant correlation and dispersive density functional theory computations. Notably, the heterobimetallic complexes herein exhibit photophysical properties that are favorable to those for their homometallic congeners, due to threefold-to-twofold symmetry reduction, resulting in cuprophilic sensitization in extinction coefficient and solid-state photoluminescence quantum yields approaching unity (ΦPL = 0.90-0.97 vs. 0-0.83 for Au3 and Cu3 precursors), which bodes well for potential future utilization in inorganic and/or organic LED applications.

The curious case of mesityl azide and its reactivity with bpyNiEt2.

A DFT analysis of the reaction of bpyNiEt2 with ArN3 was performed for para-tolyl-azide (Ar = pTol), 3,5-dimethyl-phenyl-azide (Ar = mXy) and ortho-tolyl-azide (Ar = oTol), and mesityl-azide (MesN3). Of particular interest were the different products obtained for the latter (ethylene, butane, azomesitylene, mesityl-ethylamine, etc.) versus the other reagents, i.e., (bpyNi(N(Ar)Et)(Et)). Calculated thermodynamics and kinetics for metal-free reactions did not differentiate MesN3 from the other aryl azides. Once (2)bpyNiEt(•) was generated via bond homolysis, formation of ethylene by ß-H elimination was facile, as was formation of nickel-imidyl (NR(-•)) intermediates by reaction of ArN3 with bpyNiEtx (x = 0-2). On the basis of computed energetics, three reactions of bpyNiEt2 were proposed to compete: Ni-C bond homolysis, reductive elimination of butane, and nucleophilic attack (NA) by ArN3. Inspection of their temperature dependence suggested that NA and Ni-Et bond homolysis dominated at lower and higher temperatures, respectively. Calculated Ni-N and Ni-C bond dissociation free energies (BDFEs) suggested the role of radical pathways in discriminating bpyNiEt2/ArN3 reactions, and implied that the concentration of radicals such as aminyl (ArN(•)(Et)), (2)bpyNiEt(•), and Et(•) will be greatest for MesN3.

Flavin-catalyzed insertion of oxygen into rhenium-methyl bonds.

Flavins and related molecules catalyze organic Baeyer-Villiger reactions. Combined experimental and DFT studies indicate that these molecules also catalyze the insertion of oxygen into metal-carbon bonds through a Baeyer-Villiger-like transition state.