Robert D. Pike

Electrophilic reactivity of coordinated cyclic π-hydrocarbons

Abstract A large number of transition metal complexes are known that contain cyclic π -hydrocarbon ligands. In many cases, coordination to the metal imparts significant electrophilic character to the hydrocarbon. In this review, the electrophilic properties of cyclic dienyl and triene complexes are examined. Featured reactions with nucleophiles include (1) single and double addition to the coordinated ring, (2) substitution of a ring substituent, e.g. chloride, (3) deprotonation of the coordinated ring or a side chain, (4) ligand substitution and (5) single electron transfer. The mechanistic aspects of these reactions are discussed with regard to electrophilic and nucleophilic reactivity, regiochemistry, stereochemistry, and detailed reaction pathways. The mechanistic principles are illustrated by selected synthetic applications.

Reversible luminescent reaction of amines with copper(I) cyanide

Copper(i) cyanide exposed to various liquid or vapor-phase amines (L) at ambient temperature produces a variety of visible photoluminescence colors via reversible formation of amine adducts. The adducts show phase matches to authentic (CuCN)L(n), n = 0.75-2.0, produced by heating CuCN with liquid amine.

Photoluminescence of 1-D copper(I) cyanide chains: a theoretical description.

Solid copper(I) cyanide occurs as extended one-dimensional chains with interesting photophysical properties. To explain the observed luminescence spectroscopy of CuCN, we report a series of computational studies using short bare and potassium-capped [Cu(n)(CN)(n+1)] (-) (n = 1, 2, 3, 4, 5, and 7) chains as CuCN models. On the basis of TD-DFT calculations of these model chains, the excitation transitions in the UV spectrum are assigned as Laporte-allowed pi-pi transitions from MOs with Cu 3d(pi) and CN pi character to empty MOs with Cu 4p and CN pi* character. Transitions between the HOMO (3d(z)) and LUMO (Cu 4p and CN pi*) are symmetry forbidden and are not assigned to the bands in the excitation spectrum. The emission spectrum is assumed to arise from transitions between the lowest triplet excited state and the ground-state singlet. The lowest energy triplet for the model networks has a bent structure due to distortions to remove the degeneracies in the partially occupied MOs of the linear triplet. The S(0)-T gap for the bent triplet chains is consistent with the emission wavelength for bulk CuCN.

Pyrimidine, pyridazine, quinazoline, phthalazine, and triazine coordination polymers of copper(I) halides

Abstract The coordination of diazine and triazine bridging ligands (B=pyrimidine (Pym), quinazoline (Qnz), pyridazine (Pdz), phthalazine (Ptz), and 1,3,5-triazine (Trz)) with CuX and CuXL (X=Cl, Br, I; L=PPh3, P(OPh)3) has been investigated. Products without phosphorus(III) ligands include [CuXB] (B=Qnz, Pdz, Ptz), [(CuX)2B] (B=Pym, Qnz, Pdz, Ptz, Trz), [(CuX)3B2] (B=Ptz, Trz), and [(CuX)3B] (B=Trz). Only CuXTrz and CuIPdz afford more than one product stoichiometry. Products with phosphorus ligands are of the types [(CuXL)B] (B=Pdz, Ptz), [(CuXL)2B] (B=Pym, Qnz, Pdz, Ptz, Trz), and [(CuXL)3B] (B=Trz). Thermogravimetic analyses of the complexes typically show step-wise losses of B and L, ultimately yielding CuX. The X-ray crystal structure of [CuBr(Qnz)] features copper atoms bridged by Br and Qnz, forming 2D sheets of fused rectangular Cu4Br2(Qnz)2 units. The X-ray structures of [(CuBr(PPh3))2B] (B=Pym, Trz) show 1D chains formed from rhomboidal (CuL)2Br2 units linked by the B ligand. The structure of [CuCl(PPh3)(Pdz)] is shown by X-ray to be a simple halide-bridged dimer. The X-ray structure of [(CuCl(P(OPh)3))3(Trz)] is a hexamer, having an oblate spheroid core. The core is composed of a Cu6Cl6 macrocycle capped with two Trz ligands.

Copper(I) Thiocyanate-Amine Networks: Synthesis, Structure, and Luminescence Behavior.

A series of metal-organic networks of CuSCN were prepared by direct reactions with substituted pyridine and aliphatic amine ligands, L. Thiocyanate bridging is seen in all but 1 of 11 new X-ray structures. Structures are reported for (CuSCN)L sheets (L = 3-chloro- and 3-bromopyridine, N-methylmorpholine), ladders (L = 2-ethylpyridine, N-methylpiperidine), and chains (L = 2,4,6-collidine). X-ray structures of (CuSCN)L(2) are chains (L = 4-ethyl- and 4-t-butylpyridine, piperidine, and morpholine). A unique N-thiocyanato monomer structure, (CuSCN)(3-ethylpyridine)(3), is also reported. In most cases, amine ligands are thermally released at temperatures <100 °C. Strong yellow-to-green luminescence at ambient temperature is observed for the substituted pyridine complexes. High solid state quantum efficiencies are seen for many of the CuSCN-L complexes. Microsecond phosphorescence lifetimes seen for CuSCN-L are in direct contrast to the nanosecond-lifetime emission of CuSCN. MLCT associated with pyridine π* orbitals is proposed as the excitation mechanism.

Bi(OTf)3–, TfOH–, and TMSOTf–Mediated, One-Pot Epoxide Rearrangement, Addition and Intramolecular Silyl-Modified Sakurai (ISMS) Cascade Toward Dihydropyrans: Comparison of Catalysts and Role of Bi(OTf)3

Catalytic quantities of bismuth(III) triflate efficiently initiate the rearrangement of epoxides to aldehydes, which subsequently react with (Z)-δ-hydroxyalkenylsilanes to afford 2,6-disubstituted 3,6-dihydro-2H-pyrans. Isolated yields of desired products using Bi(OTf)(3) were compared with yields obtained when the reactions were run with TfOH and TMSOTf in the presence and absence of several additives. These studies, as well as NMR spectroscopic analyses, indicate an initial Lewis acid/base interaction between Bi(OTf)(3) and substrates providing TfOH in situ.

Carbonyl-twisted 6-acyl-2-dialkylaminonaphthalenes as solvent acidity sensors.

Derivatives of 2-propionyl-6-dimethylaminonaphthalene (PRODAN) with twisted carbonyl groups were investigated as highly responsive sensors of H-bond donating ability. The PRODAN derivative bearing a pivaloyl group (4) was prepared. The torsion angle between the carbonyl and naphthalene is 26° in the crystal. It shows solvatochromism that is similar to five other PRODAN derivatives (1-3, 5, 6). Twisted-carbonyl derivatives 3, 4, and 6 show strong fluorescence quenching in protic solvents. The order of magnitude of the quenching is linearly related to the H-bond donating ability of the solvent (SA) but not to other solvent properties. Binary mixtures of protic solvents show specific interaction effects with respect to quenching and solvatochromism. Aggregation in water is an issue with the pivaloyl derivatives.

Efficient Entry to the [2.2.2]-Diazabicyclic Ring System via Diastereoselective Domino Reaction Sequence

A domino reaction sequence involving aldol condensation, alkene isomerization, and intramolecular hetero-Diels-Alder cycloaddition for the synthesis of [2.2.2]-diazabicyclic structures is reported. Excellent diastereofacial control during the cycloaddition is enforced with a removable chiral phenyl aminal diketopiperazine substituent. The reaction sequence rapidly generates molecular complexity and is competent with both enolizable and nonenolizable aldehyde substrates (nine examples total). Progress toward the synthesis of malbrancheamide B, a protypical member of the [2.2.2]-diazabicyclic natural product family, is also disclosed.

Synthesis of (±)-acetylnorloline via stereoselective tethered aminohydroxylation.

Loline alkaloids exhibit a strained ether-bridged pyrrolizidine skeleton and possess insecticidal and insect antifeedant properties. The synthesis of acetylnorloline, a prototypical member of the alkaloid family, is described. Central to the route is a stereoselective tethered aminohydroxylation (TA) of a homoallylic carbamate. Allylic (A1,3) strain is exploited to enforce diastereofacial selectivity during the aminohydroxylation.

Diels–Alder Cycloaddition of Chiral Nonracemic 2,5-Diketopiperazine Dienes

Preparation of a chiral, nonracemic 2,5-diketopiperazine diene has enabled the investigation of intermolecular hetero-Diels-Alder cycloadditions. The diketopiperazine diene is reactive with both electron-rich and -deficient alkene substrates. Diastereofacial control in the cycloaddition is enforced with a removable aminal substituent. This study partly illuminates the regiochemical, stereoelectronic, and reactivity preferences of the diketopiperazine cycloaddition as well as provides a direct diastereoselective synthetic route to bicyclo[2.2.2]diazaoctane structures.