Arylazopyrazoles: azoheteroarene photoswitches offering quantitative isomerization and long thermal half-lives.

Arylazopyrazoles, a novel class of five-membered azo photoswitches, offer quantitative photoswitching and high thermal stability of the Z isomer (half-lives of 10 and ∼1000 days). The conformation of the Z isomers of these compounds, and also the arylazopyrroles, is highly dependent on the substitution pattern on the heteroarene, allowing a twisted or planar geometry, which in turn has a significant impact on the electronic spectral properties of the compounds.

Contraction and expansion of the silicon scaffold of stable Si6R6 isomers.

The reactivity of two stable Si(6)R(6) clusters (4 and 5, R = 2,4,6-(i)Pr(3)C(6)H(2)) with unsymmetrical substitution patterns (including Si, SiR, and SiR(2) vertices) is reported. In order to account for the importance of such clusters as model systems for transient intermediates in the deposition of elemental silicon, we here propose the term "siliconoids" for silicon clusters with unsaturated valencies. With the hexasilaprismane 8a, a saturated-i.e., non-siliconoid-Si(6)R(6) isomer is accessible from a suitable Si(3) precursor. Thermal redistribution of the substituents converts 1,1,2-trichlorocyclotrisilane 6 into the corresponding 1,2,3-derivative 7 prior to the requisite reductive coupling step leading to 8a. On the other hand, a stable expanded Si(11)-siliconoid 9 was isolated as a minor side product of the thermal isomerization of 4 to 5, thus providing a first example of siliconoid cluster expansion in the condensed phase. In the solid-state structure, the two unsubstituted vertices of 9 strongly interact in a staggered propellane-like fashion. Oxidative cluster contraction of a siliconoid scaffold is observed upon treatment of siliconoid 5 with a large excess of iodine in refluxing toluene, thus providing access to a highly functionalized hexaiodocyclopentasilane 11 in high yield. Conversely, chlorination of the isomeric 4 with BiCl(3) as a mild source of Cl(2) results in a complex mixture of products from chlorination of the unsubstituted vertices as well as σ-bonds of the cluster framework of 4. The main product, 1,2-dichlorotricyclo[2.2.0.0(2,5)]hexasilane 12, undergoes thermal cluster contraction to give tricyclo[2.1.0.0(2,5)]pentasilane 14 with an exohedral chlorosilyl group.

Amino-oxetanes as amide isosteres by an alternative defluorosulfonylative coupling of sulfonyl fluorides.

Bioisosteres provide valuable design elements that medicinal chemists can use to adjust the structural and pharmacokinetic characteristics of bioactive compounds towards viable drug candidates. Aryl oxetane amines offer exciting potential as bioisosteres for benzamides-extremely common pharmacophores-but are rarely examined due to the lack of available synthetic methods. Here we describe a class of reactions for sulfonyl fluorides to form amino-oxetanes by an alternative pathway to the established SuFEx (sulfonyl-fluoride exchange) click reactivity. A defluorosulfonylation forms planar oxetane carbocations simply on warming. This disconnection, comparable to a typical amidation, will allow the application of vast existing amine libraries. The reaction is tolerant to a wide range of polar functionalities and is suitable for array formats. Ten oxetane analogues of bioactive benzamides and marketed drugs are prepared. Kinetic and computational studies support the formation of an oxetane carbocation as the rate-determining step, followed by a chemoselective nucleophile coupling step.

Design, Synthesis, and Conformational Analysis of Oligobenzanilides as Multifacial α-Helix Mimetics.

The design, synthesis, and conformational analysis of an oligobenzanilide helix mimetic scaffold capable of simultaneous mimicry of two faces of an α-helix is reported. The synthetic methodology provides access to diverse monomer building blocks amenable to solid-phase assembly in just four synthetic steps. The conformational flexibility of model dimers was investigated using a combination of solid and solution state methodologies supplemented with DFT calculations. The lack of noncovalent constraints allows for significant conformational plasticity in the scaffold, thus permitting it to successfully mimic residues i, i+2, i+4, i+6, i+7, and i+9 of a canonical α-helix.

Computer-aided molecular design of solvents for accelerated reaction kinetics.

Solvents can significantly alter the rates and selectivity of liquid-phase organic reactions, often hindering the development of new synthetic routes or, if chosen wisely, facilitating routes by improving rates and selectivities. To address this challenge, a systematic methodology is proposed that quickly identifies improved reaction solvents by combining quantum mechanical computations of the reaction rate constant in a few solvents with a computer-aided molecular design (CAMD) procedure. The approach allows the identification of a high-performance solvent within a very large set of possible molecules. The validity of our CAMD approach is demonstrated through application to a classical nucleophilic substitution reaction for the study of solvent effects, the Menschutkin reaction. The results were validated successfully by in situ kinetic experiments. A space of 1,341 solvents was explored in silico, but required quantum-mechanical calculations of the rate constant in only nine solvents, and uncovered a solvent that increases the rate constant by 40%.

Synthesis, characterisation and complexation of phosphino disilenes.

The treatment of disilenide Tip2SiSi(Tip)Li (1, Tip = 2,4,6-iPr3C6H2) with P-chloro phosphines affords the phosphino disilenes (2a-d; a: R = Ph, b: R = iPr, c: R = Cy, d: R = tBu), which were characterised by multinuclear NMR spectroscopy for 2a-d and a single crystal X-ray diffraction study in case of 2c. As an alternate synthetic method, the diphenyl derivative 2a could also be prepared by reaction of LiPPh2 with the thermally unstable iododisilene, Tip2SiSi(Tip)I (3), which in turn was obtained by oxidation of 1 with stoichiometric amounts of iodine. Providing the first example for a SiSi bond with an iodo functionality, disilene 3 was fully characterised by multinuclear NMR and X-ray diffraction. The thermal rearrangement of phosphine disilene 2avia a C­H insertion reaction yields the diastereomeric mixture of a 1-phospha-2,3-disilaindane 4. The structure of the cis-diastereomer of 4 was determined by X-ray diffraction. Finally, the synthesis of first transition metal complex of 2a and 2b by their coordination to the [Pd(PCy3)] fragment is reported. The solid state structure of complex 5a reveals η2-coordination of the SiSi bond of the phosphino disilene 2a with an intermediate bonding mode between π-complex and metallacyclopropane rather than coordination of the phosphino group.

A study of (binap)(enyne)tetracarbonyldicobalt(0) complexes.

Four (binap)(enyne)tetracarbonyldicobalt(0) complexes have been synthesised and their reactivity monitored by variable temperature (31)P NMR spectroscopy. Formation of (binap)dicarbonylhydridocobalt(-1) 12 occurred at temperatures between 35 and 55 degrees C, depending on the nature of the alkene and alkyne components of the enyne. The structure of 12 was determined by X-ray crystallography, and its presence under Pauson-Khand reaction conditions was verified by NMR spectroscopy.

Structures of Sb(OC(6)H(3)Me(2)-2,6)(3) and Sb(OEt)(5) x NH(3): the first authenticated monomeric Sb(OR)(n) (n = 3, 5).

The first monomeric antimony alkoxides, Sb(OC(6)H(3)Me(2))(3) (1) and Sb(OEt)(5) x NH(3) (2), have been crystallographically characterized. The former adopts a trigonal pyramidal geometry, while the latter is octahedral about antimony; hydrogen bonding between NH(3) and SbOEt groups in Sb(OEt)(5) small middle dotNH(3) creates a one-dimensional lattice arrangement. Reaction of pyridine with SbCl(5) in EtOH/hexane yields the salt [Hpy(+)](9)[Sb(2)Cl(11)(5)(-)][Cl(-)](4) (3), which has also been crystallographically characterized. Crystallographic data: 1, C(24)H(27)O(3)Sb, a = 10.9080(2), b = 11.9660(2), c = 17.7260(4) A, alpha = 109.740(1) degrees, monoclinic P2(1)/c (unique axis a), Z = 4; 2, C(10)H(28)NO(5)Sb, a = 7.7220(1), b = 19.0700(2), c = 21.6800(3) A, beta = 93.4960(7) degrees, monoclinic P2(1)/c, Z = 8; 3, C(45)H(54)Cl(15)N(9)Sb(2), a = 13.4300(2), b = 14.4180(2), c = 17.4180(3) A, alpha = 82.7650(7), beta = 77.5570(7), gamma = 70.7670(7) degrees, triclinic P1, Z = 2.

Synthesis and characterization of novel homoleptic N,N-dialkylcarbamato complexes of antimony: precursors for the deposition of antimony oxides.

A series of tris(N,N-dialkylcarbamato)antimony(III) complexes, Sb(O(2)CNR(2))(3) (R = Me, Et, Pr(i)()), have been synthesized and are the first members of this class of compound to have been crystallographically characterized. Sb(O(2)CNMe(2))(3) (1) exists as a weakly bound dimer, whereas its diethyl and diisopropyl analogues (2, 3) are monomeric. In addition, tetrakis(N,N-diethylcarbamato)tin(IV) (4) has been prepared for comparison and shown by single-crystal X-ray analysis to exhibit the relatively rare SnO(8) coordination. Crystallographic data: for 1, a = 8.7520(5) A, b = 14.2970(8) A, c = 11.8150(7) A, beta = 108.029(2) degrees, monoclinic, P2(1)/c, Z = 4; for 2, a = b = 14.4690(2) A, c = 16.6740(2) A, trigonal, Rthremacr;, Z = 6; for 3, a = 11.9881(2) A, b = 11.6521(3) A, c = 19.8780(6) A, beta = 90.401(1) degrees, monoclinic, P2(1)/n, Z = 4; for 4, a = 13.9654(2) A, b = 12.0817(2) A, c = 16.6752(2) A, beta = 108.1960(7) degrees, monoclinic, C2/c, Z = 4. Sb(O(2)CNMe(2))(3) has been used as a single-source precursor in the low-pressure chemical vapor deposition of the senarmonite form of Sb(2)O(3).