Crystallographic report: Tricarbonyl(η5‐cyclopentadienyl)(dichloroindium) molybdenum

In the solid state, [{Cp(CO)₃Mo}InCl₂]∞ forms a one‐dimensional coordination polymer in which the indium atoms are coordinated by four chlorine atoms (In? Cl: 2.448(2)–3.004(2) Å) and a {Cp(CO)₃Mo} group (In? Mo: 2.750(1) Å) in a distorted trigonal bipyramidal environment. Copyright © 2004 John Wiley & Sons, Ltd.     

Subphthalocyaninato Boron(III) Hydride: Synthesis,Structure and Reactivity

Subphthalocyanine (SubPc) chemistry has been limited so far by their high sensitivity toward strong nucleophiles. In particular, the substitution of the axial chlorine atom by a nucleophilic group in the case of less-reactive SubPcs, such as those bearing electron-withdrawing peripheral substituents, presents some limitations and requires harsh conditions. By taking advantage of the electrophilic character of DIBAL-H, it has been possible to prepare for the first time SubPc-hydride derivatives that exhibit high reactivity as hydroboration reagents of aldehydes. This hydride transfer requires using a typical carbonyl activator (trimethylsilyl triflate) and only one equivalent of aldehyde, affording SubPcs with an axial benzyloxy group in good yield. This transformation has proven to be a useful alternative method for the axial functionalisation of dodecafluoroSubPc, a paradigmatic SubPc derivative, by using electrophiles for the first time. Considering the increasing interest in SubPcs as electron-acceptor semiconductors with remarkable absorption in the visible range to replace fullerene in organic photovoltaic (OPV) devices, it is of the utmost importance to develop new synthetic methodologies for their axial functionalisation.     

Synthetic Routes to Coumarin(Benzopyrone)-Fused Five-Membered Aromatic Heterocycles Built on the α-Pyrone Moiety. Part II: Five-Membered Aromatic Rings with Multi Heteroatoms

Coumarins are natural heterocycles that widely contribute to the design of various biologically active compounds. Fusing different aromatic heterocycles with coumarin at its 3,4-position is one of the interesting approaches to generating novel molecules with various biological activities. During our continuing interest in assembling information about fused five-membered aromatic heterocycles, and after having presented mono-hetero-atomic five-membered aromatic heterocycles in Part I. The current review Part II is intended to present an overview of the different synthetic routes to coumarin (benzopyrone)-fused five-membered aromatic heterocycles with multi-heteroatoms built on the pyrone ring, covering the literature from 1945 to 2021.     

Generation of Dicoordinate Boron(I) Units by Fragmentation of a Tetra‐Boron(I) Molecular Square

Reduction of carbene‐borane adduct [(cAAC)BBr₂(CN)] (cAAC=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐ylidene) cleanly yielded the tetra(cyanoborylene) species [(cAAC)B(CN)]₄ presenting a 12‐membered (BCN)₄ ring. The analysis of the Kohn–Sham molecular orbitals showed significant borylene character of the B^I atoms. [(cAAC)B(CN)]₄ was found to reduce two equivalents of AgCN per boron center to yield [(cAAC)B(CN)₃] and fragmented into two‐coordinate boron(I) units upon reaction with IMeMe (1,3,4,5‐tetramethylimidazol‐2‐ylidene) to yield the corresponding tricoordinate mixed cAAC‐NHC cyanoborylene. The analogous cAAC‐phosphine cyanoborylene was obtained by reduction of [(cAAC)BBr₂(CN)] in the presence of excess phosphine.     

The Influence of Aromaticity in Gas Chromatography Retention: The Case of Polycyclic Aromatic Sulfur Heterocycles

Aromaticity has been used as a criterion to explain the gas chromatographic (GC) retention of cata-condensed polycyclic aromatic sulfur heterocycles (PASHs) C₁₂H₈S, C₁₆H₁₀S, C₂₀H₁₂S; and peri-condensed PASHs C₁₈H₁₀S, in a GC column with 50% phenyl/50% dimethyl silphenylene polymer. To establish the aromaticity, nucleus-independent chemical shifts at the level of the molecular plane, NICS(0), and at 1 Å above the surface of the molecular plane, NICS(1), have been used. It has been found that the GC retention of cata-condensed PASHs C₁₂H₈S, C₁₆H₁₀S, and C₂₀H₁₂S is satisfactorily defined by the aromaticity of the entire molecule, and the GC retention of peri-condensed PASHs C₁₈H₁₀S is satisfactorily defined by the local aromaticity in the sulfur pentagonal ring. In addition, the positive slope between GC retention and NICS(0) of the entire molecule for cata-condensed PASHs, C₁₂H₈S and C₁₆H₁₀S, and by NICS(1) in the pentagonal ring for peri-condensed PASHs, C₁₈H₁₀S, is explained by the interaction between the electrons of the heterocycle molecule and the positive pole of the silicon atom in the GC column, as suggested with PAHs. In contrast, the negative slope between GC retention and aromaticity for cata-condensed C₂₀H₁₂S is explained by the presence of bay, cove, or fjord regions in the vicinity of the sulfur atom that generates either higher GC retention and lower aromaticity or lower GC retention and higher aromaticity.     

Solid State Dynamics of Tricarbonyl(eta-1,5-cyclohexadienylium)iron Tetrafluoroborate and Tricarbonyl(eta-1,5-cycloheptadienylium)iron Tetrafluoroborate

The dynamic behavior of [(C(6)H(7))Fe(CO)(3)]BF(4) (I) and [(C(7)H(9))Fe(CO)(3)]BF(4) (II) in the solid state has been investigated principally by NMR spectroscopy. High-resolution variable-temperature (1)H and (13)C NMR spectra indicate that both complexes have a solid state phase transition above which there is rapid reorientation of the cyclodienylium rings and fast exchange of the carbonyl groups. The transition occurs between 253 and 263 K for I and between 329 and 341 K for II. The presence of the phase transition is confirmed by differential scanning calorimetry (DSC). (57)Fe M?ssbauer spectroscopy supports the notion that complex I is highly mobile at room temperature, while II is relatively static. The activation energy for the cyclodienylium group rotation in the high-temperature phase of I is estimated from (1)H spin-lattice relaxation time measurements to be 17.5 kJ mol(-)(1). Static (13)C NMR measurements of the solid complexes in the high-temperature phase indicate that the (13)C chemical shift anisotropies are only 20-30 ppm. This is significantly less than that expected to result from motion of individual groups and thus suggests that rotation of the whole molecule is involved. A single-crystal X-ray structural determination of complex II, at 295 K, showed that the complex is tetragonal (space group P4(1), a = 10.610(1) ?, c = 21.761(3) ?, V = 2449.7(5) ?(3), rho(calc) = 1.734 g cm(-)(3)), with eight cycloheptadienyl cations and eight tetrafluoroborate anions per unit cell. In addition, powder X-ray diffraction studies of both I and II confirm that at low temperatures both complexes have a tetragonal unit cell, which transforms to a cubic unit cell above the phase transition. The powder patterns, recorded above the phase transition, support the proposal that the complexes are undergoing whole-molecule tumbling in their dynamic regimes.     

Diazadiene-isonitrile complexes of molybdenum(II) and molybdenum(III)

Summary [MoCl₃(THF)₃] reacts with CNMe and diazadienes or a diamines, NN (RN=CHCH=NR, RN=CMeCMe=NR where R = 4-C6₆H₄OMe, and Me₂NCH₂CH₂NMe₂) to give molybdenum(III) complexes [MoCl₃(CNMe) NN] and molybdenum(II) complexes [MoCl₂(CNMe)₂NN]. The i.r. and magnetic data of these complexes are interpreted on the basis of the electronic properties of the ligands.