Structure and solution dynamics of a “P–N–P” ligand attached to calix[4]arene scaffold and its palladium dichloride complex

A new diphosphazane ligand, Ph₂PN(CHMe₂)P(Ph){1,3-dimethoxycalix[4]arene} (2), in which the P–N–P unit is appended to calix[4]arene backbone, and its PdCl₂ complex (3) have been synthesized. The structures of the conformers of both the compounds in solution have been elucidated with the help of two-dimensional NMR experiments. Single crystal X-ray diffraction studies reveal the partial cone and cone conformations of the calixarene unit in the ligand (2) and the Pd-complex (3), respectively.     

Enamine–azide [2+3]-cycloaddition as a method to introduce functional groups into fluorescent dyes

Fluorescent dyes are a significant research tool with various applications in modern science. However, many experiments require the preparation of covalent dye conjugates, which is impossible without the presence of a functional group on the dye molecule. Unfortunately, the introduction of such groups is often a complicated task. Herein, we report a novel approach for the introduction of functional groups into fluorescent dyes, based on the [2+3]-cycloaddition reaction of “terminal” enamines with azides. The synthesis of such “terminal” enamines is carried out by the condensation of formamide acetals with a methyl group that is influenced by a strong electron withdrawing group. Thus, the proposed functionalization technique requires only the presence of a methyl group in the relevant position of the initial non-functionalized fluorescent dye.     

The chemistry of cyclopentadienyl-ruthenacyclopentatrienes: novel carbon monoxide and isocyanide insertion reactions in [η5-C5H5)Ru(η4-C5Ph2H2NBut)Br]

Reaction of the novel ruthenacyclopentatriene [(η⁵-C₅H₅)Ru(C₄Ph₂H₂)Br] (1) with isocyanides gives the imino-2,5-diphenylcyclopentadiene complexes [(η⁵-C₅H₅Ru(η⁴-C₅Ph₂H₂NR)Br] (2, R = Me, Et, Cy, t-Bu, 2,6-Me₂C₆H₃); a novel fluxional process involving phenyl substituent rotation and imino nitrogen inversion has been identified for 2 (R = t-Bu, 2,6-Me₂C₆H₃), the interpretation of which is supported by the X-ray crystal structure determination of 2 (R = t-Bu).     

The reaction of [Ru10C(CO)24][ppn]2 with carbon monoxide to yield [Ru3(CO)12] and [Ru6C(CO)16]2−

The dianion [Ru₁₀C(CO)₂₄]²⁻ in CH₂Cl₂ reacts with CO under ambient conditions to produce quantitative amounts of the species [Ru₃(CO)₁₂] and [Ru₆C(CO)₁₆]²⁻; the hydrido-anion [HRu₁₀C(CO)₂₄]⁻ reacts similarly to form [Ru₆C(CO)₁₆]⁻.     

The influence of protecting the hydroxyl group of β-oxy-α-diazo carbonyl compounds in the competition between Wolff rearrangement and [1,2]-hydrogen shift. Density functional theory study and topological analysis of the charge density

The influence of protecting the hydroxyl group of a β-oxy-α-diazo carbonyl compound on the competition between the Wolff rearrangement (WR) and the [1,2]-hydrogen shift (HS) was investigated theoretically. Stationary points on the potential-energy surface were located with the B3LYP density functional and the 6-31G** basis set. For the basic system geometry optimisations at B3LYP/6-311+G** were performed to validate the reliability of the B3LYP/6-31G** calculations. Single-point energy calculations were carried out at the B3LYP/6-311+G** level on the B3LYP/6-31G**-optimised geometries. Further insight into the processes was achieved with the aid of the theory of “atoms in molecules” of Bader. The calculated energy barriers qualitatively predicted the yields of HS and WR obtained experimentally. In order to rationalise the calculated energy barriers, it was necessary to take into account not only the electronegativity of the protective groups but also the alignment of the migrating groups with the depletion sites at the carbene centre. Further, when the hydroxyl group was not protected the existence of an intramolecular hydrogen bond played an important role in both HS and WR. Received: 30 December 1998 / Accepted: 7 May 1999 / Published online: 4 October 1999     

Synthesis of transition-metal Lewis acid adducts of trans-[ReCl(CNR)(Ph2PCH2CH2PPh2)2] (R = alkyl). A chemical and a quantum-chemical study of electrophilic β-addition to ligating isocyanide

Treatment of trans-[ReCl(CNR)(dppe)₂] (R = Me or Bu^t, dppe = Ph₂PCH₂CH₂ PPh₂) with CoCl₂(THF)_1.5, [ReOCl₃(PPh₃)₂] or [WCl₄L₂] (L = PPh₃ or PEtPh₂) affords the dinuclear adducts [ReCl(CN(M)R)(dppe)₂] (M = CoCl₂(THF), ReOCl₃(PPh₃) or WCl₄L, respectively) (formed via electrophilic β-addition of the electron-acceptor molecules to the isocyanide ligands), which undergo dissociation oxidation (for M = CoCl₂(THF) or ReOCl₃(PPh₃)). These reactions are considered in the light of results of extended Hückel calculations.