Guido D. Frey

Ferrocenyl aryl ethers can be synthesized in good yields by Cu(I)/phosphine-catalyzed coupling reactions from iodoferrocene or 1,1′-dibromoferrocene and various phenols in toluene, using Cs₂CO₃ or K₃PO₄ as a base. For the first time a solid-state structure of a ferrocenyl-1,1′-diaryl ether [1,1′-di(4-tert-butylphenoxy)ferrocene] has been determined from single-crystal X-ray data. The mixed ferrocenyl aryl ether 1-(4-tert-butylphenoxy)-1′-(2,4-dimethylphenoxy)ferrocene was prepared in a two-step synthetic protocol.

The crystal structure of 1-(1H-pyrazol-4-yl)ethanone (commonly known as 4-acetylpyrazole; C₅H₆N₂O) was determined from single-crystal X-ray data at 173 K: monoclinic, space group P2₁/n (no. 14), a = 3.865(1), b = 5.155(1), c = 26.105(8) Å, β = 91.13(1)°, V = 520.0(2) ų and Z = 4. The adjacent molecules assemble into a wave-like ribbon structure in the solid state, linked by strong intermolecular N-H...N hydrogen bonds between the pyrazole rings and a weak C-H...O=C hydrogen bond involving the carbonyl group. The ribbons are stacked in the solid state via weak π interactions between the pyrazole rings.

The title compound Al-NacNac is isolobal to the imidazol-2-ylidene (NHC); the latter is considered as a nucleophilic carbene. However, the title compound is different from a typical carbene, as aluminum is a heavier group 13 element with a predominant inert s orbital. Its singlet ground state is a poor Lewis donor (acceptor) toward white phosphorus, but its corresponding lowest energy triplet state forms a strong Al–P bond with (opened) white phosphorus. The reaction of Al-NacNac with white phosphorus proceeds in two steps: after the addition of a first carbene analogue, a second one is added, resulting in a transient biradicaloid species. This undergoes facile subsequent rearrangement, and a final ring closure reaction leads to the observed product with a bicyclobutane moiety. It is determined by intramolecular bond formation of two phosphorus centered radicals. Finally, a structure with a large singlet–triplet energy separation is formed. An analogy to the noninnocent ligand character as well as the exciplex view of the monoadduct of white phosphorus with the Al-NacNac system is drawn.

The article contains sections titled: 1. Introduction 2. Saturated Aldehydes 2.1. Physical Properties 2.2. Chemical Properties 2.3. Production 2.4. Individual Saturated C ₅ –C ₁₃ Aldehydes 2.4.1. C ₅ Aldehydes 2.4.2. C ₆ Aldehydes 2.4.3. C ₇ Aldehydes 2.4.4. C ₈ Aldehydes 2.4.5. C ₉ Aldehydes 2.4.6. C ₁₀ Aldehydes 2.4.7. C ₁₁ Aldehydes 2.4.8. C ₁₂ Aldehydes 2.4.9. C ₁₃ Aldehydes 3. Unsaturated Aldehydes 3.1. Physical Properties 3.2. Chemical Properties 3.3. Production 3.4. Individual Unsaturated C ₅ –C ₁₁ Aldehydes 3.4.1. C ₅ Alkenals 3.4.2. C ₆ Alkenals 3.4.3. C ₈ Alkenals 3.4.4. C ₁₀ Alkenals 3.4.5. C ₁₁ Alkenals 4. Hydroxyaldehydes 4.1. Properties 4.2. Production 4.3. Individual Hydroxyaldehydes 4.3.1. 3‐Hydroxypropanal 4.3.2. 3‐Hydroxybutanal (Acetaldol) 4.3.3. 4‐Hydroxybutanal 4.3.4. 2,2‐Dimethyl‐3‐hydroxypropanal (Hydroxypivaldehyde) 4.3.5. 2‐Ethyl‐3‐hydroxyhexanal (Butyraldol) 4.3.6. 3,7‐Dimethyl‐7‐hydroxyoctanal (Hydroxycitronellal) 5. Dialdehydes 5.1. Properties 5.2. Production 5.3. Individual Dialdehydes 5.3.1. Succinaldehyde (1,4‐Butanedial) 5.3.2. Glutardialdehyde (1,5‐Pentanedial) 5.3.3. TCD Dialdehyde 6. Acetals 6.1. Properties 6.2. Production 6.3. Uses 7. Quality Control 8. Analysis 9. Storage, Transportation, and Environmental Regulations 10. Economic Aspects