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The donor properties of five different PCcarbeneP ligands are assessed by evaluation of the CO stretching frequencies in iridium(i) and rhodium(i) carbonyl cations. The ligands feature dialkyl phosphine units (R = (i)Pr or (t)Bu) linked to the central benzylic carbon by either an ortho-phenylene bridge, or a 2,3-benzo[b]thiophene linker; in the former, substituent patterns on the phenyl linker are varied. The carbonyl complexes are synthesized from the (PCcarbeneP)M-Cl starting materials via abstraction of the chlorides in the presence of CO gas. In addition to the expected mono carbonyl cations, products with two carbonyl ligands are produced, and for the rhodium example, a novel product in which the second carbonyl ligand adds reversibly across the Rh[double bond, length as m-dash]C bond to give an η(2) ketene moiety was characterized. The IR data for the complexes shows the 2,3-benzo[b]thiophene linked system to be the poorest overall donor, while the phenyl bridged ligands incorporating electron donating dialkyl amino groups para to the anchoring carbene are very strongly donating pincer arrays.

Terfestatin A, a specific inhibitor of auxin signaling, has been synthesized from a known aromatic aldehyde in 21% overall yield via five steps. The first total synthesis of terfestatin B with potent neuroprotective activity has also been accomplished in eight steps from the same aromatic aldehyde in 30% overall yield through a common intermediate. The key feature of this synthesis is the utilization of the aldehyde functionality of the starting material both as a directing group for regioselective O-protection and as a masked hydroxy group.

The isolation and study of carbenes with σ-donating and π-accepting properties stronger than those of N-heterocyclic carbenes (NHCs) have been regarded as one of the big challenges in carbene chemistry. We have investigated the properties of 1,8-disubstituted xanthylidene-based compounds by using two different approaches: The photolysis-induced formation of free carbenes and the synthesis of the corresponding metal–carbene complexes by oxidative addition. The former study revealed that the carbene unsubstituted at the 1- and 8-positions is kinetically more reactive than the parent xanthylidene and that the substituents at the 1- and 8-positions are less effective in generating carbenes by photolysis. However, oxidative addition of palladium(0) to the 1,8-diphenyl-substituted precursor successfully afforded a low-coordinate 14-electron palladium(II)–carbene complex. This unusual complex is stabilized by agnostic interactions involving an adjacent phenyl group. This complex is the second example of a stable cationic 14-electron palladium(II)–carbene complex to have been reported so far.

A rarely investigated octaisopropylporphyrin (OiPP) was successfully prepared by an alternative synthetic route with organic reactions. Introduction of an electron-donating butyl group at the meso-position of OiPP nickel(II) and copper(II) complexes induced structural perturbation on the porphyrin cores. Structural distortion of nickel(II) complexes decreased slightly upon introduction of a butyl group; however, structural change of the copper complexes showed opposite behavior. These results indicate that structural deformation of the OiPP metal complexes with a meso-substituent was determined by the central metal.

Unter Verwendung eines cyclischen (Alkyl)(amino)carben(CAAC)-Liganden konnten neutrale, CAAC-stabilisierte Radikale mit einer Borylfunktion durch Reduktion der entsprechenden Halogenboranaddukte erhalten werden. Die Duryl-substituierte Radikalspezies wurde vollstandig mithilfe von Rontgenstrukturanalyse, EPR-Spektroskopie und DFT-Rechnungen charakterisiert. Die hier isolierten Spezies weisen eine grosere Spindichte auf dem Borzentrum als bekannte Borylradikale auf. Weiterhin erwies sich die Titelverbindung unter inerten Bedingungen in Losung wie auch im Feststoff als uberaus temperaturstabil. Elektrochemische Untersuchungen lassen auf die Erzeugung eines stabilen formalen Borylanions schliesen.

The most anti-aromatic 16π porphyrin, an octaethylporphyrin (OEP) zinc(II) complex with no substituents at the meso-positions was generated as a highly unstable species from the reaction of the corresponding 18π porphyrin using strong oxidants such as AgSbF 6/ I 2 or SbF 5. The porphyrin showed a significant blue-shift unique to 16π porphyrins in its UV-vis spectrum. 1 H NMR measurements revealed an evident high-field shift of the meso-protons of the porphyrin ring, thereby establishing that the novel 16π porphyrin has the strongest anti-aromaticity reported so far.

Previously unreported octaisopropyltetraphenylporphyrin (OiPTPP) was prepared from 3,4-diisopropylpyrrole, an unstable previously unisolated heterocyclic compound. Purification of the free-base 18π porphyrin required conversion to its 18π zinc(II) complex, chromatographic separation, and acid mediated demetalation. Oxidation of the 18π porphyrin with SbCl5 furnished metal-free 16π octaisopropyltetraphenylporphyrin (OiPTPP). X-ray structural determination revealed that the novel species is the most distorted 16π porphyrin to date. The time course of decomposition of the oxidized species monitored by UV-vis spectra implied that the introduction of high steric repulsion was effective for enhancing stability of the 16π porphyrin. The reaction of metal-free 16π OiPTPP with LiBF4 followed by Pd2(dba)3 gave the corresponding 18π OiPTPP palladium(II) complex via reduction of the OiPTPP lithium(I) complex as previously reported for 16π octaisobutyltetraphenylporphyrin (OiBTPP). The new 18π porphyrin system could be characterized by the X-ray analysis of the 18π OiPTPP palladium(II) complex. The X-ray structure of the 18π metal complex also indicated that the distortion of the porphyrin ring had become larger than that of previously known 18π porphyrins

Utilizing a cyclic (alkyl)(amino)carbene (CAAC) as a ligand, neutral CAAC-stabilized radicals containing a boryl functionality could be prepared by reduction of the corresponding haloborane adducts. The radical species with a duryl substituent was fully characterized by single-crystal X-ray structural analysis, EPR spectroscopy, and DFT calculations. Compared to known neutral boryl radicals, the isolated radical species showed larger spin density on the boron atom. Furthermore, the compound that was isolated is extraordinarily stable to high temperatures under inert conditions, both in solution and in the solid state. Electrochemical investigations of the radical suggest the possibility to generate a stable formal boryl anion species.

A two-electron oxidation of the Cu(II) (9) and Zn(II) (12) complexes of tetraphenyltetrabenzoporphyrin (TPTBP) results in the formation of stable antiaromatic [(TPTBP)Cu(II)(H(2)O)](2+)⋅2 [SbF(6)](-) (10) and [(TPTBP)Zn(II)(H(2)O)(2)](2+)⋅2 [SbF(6)](-) (13) with 16π electrons on the inner ligand perimeter. X-ray structures of the parent TPTBP complexes, the dications, and singly oxidized species [(TPTBP)Cu(II)](⋅+)[SbF(6)](-) (11) reveal that the use of TPTBP rather than a porphyrin ligand reduces the degree of nonplanarity in the 16π-electron species relative to the parent 18π complex. Significant high-field shifts of the (1)H NMR signals of the outer ring protons and large positive values in calculations of nucleus-independent chemical shifts on the central cavity of the porphyrin ring provide unambiguous evidence for the antiaromatic character of the 16π Zn(II) species. A combination of magnetic circular dichroism spectroscopic studies and TD-DFT calculations on both the Zn(II) and Cu(II) species demonstrates that the main electronic bands of the dicationic species can be readily assigned by using Michl's 4N perimeter model. Femtosecond transient absorption studies clearly demonstrated that the number of π electrons on the inner ligand perimeter and the configuration of the central metal ion play a critical role in the excited-state relaxation dynamics. Redox potentials for conversion between the 16π, 17π, and 18π systems were measured by cyclic voltammetry in dichloromethane and benzonitrile, and UV/Vis spectra of each oxidation/reduction product were monitored by thin-layer spectroelectrochemistry.

Small GTPase Ras is one of the G proteins. It was shown that the crystal structure of the GTPase domain strikingly resemble to that of ATP driven motor proteins myosin and kinesin. We have previously demonstrated that incorporation of photochromic molecules in the functional sites of kinesin enable the photo-regulation of their ATPase activities. Therefore, it is expected that Ras may be also regulated using photochromic molecules. In this study, basic experiments were performed in order to photoregulate GTPase activity of Ras. A new fluorescent GTP analogue, NBD-GTP was synthesized in order to monitor the GTPase Ras.NBD-GTP showed initial burst enhancement of the fluorescent intensity by 120% when GDP free Ras was added and subsequently slow increase of fluorescence. The results may suggest that the initial burst of fluorescence reflects the binding of GTP to the free GTPase site of Ras, and the slow phase corresponds to the formation of Ras-GDP-Pi state. Quantitative analysis of cysteine residue on the surface of Ras using DTNB revealed that one of the intrinsic three cysteine locates on the surface. However, SH group reactive photochromic molecule, 4-phenylazophenyl maleimide (PAM) was not incorporated into the cysteine residues of wild type Ras. We designed the cDNA encoding the ras, which has an additional reactive cysteine residue at near 12, 59 and 61, which are suggested as an essential for GTPase activity. We prepared Ras mutant T59C that have a reactive cysteine residue in the functional key region for the signal transduction. Incorporation of PAM into T59C abolished GTP binding and GTP hydrolysis of the mutant. UV and Visible light photo irradiation did not alter the GTPase activity of the mutant modified with PAM.

With the objective of preparing an isolable triplet carbene, we have carried out the oxidation of an allenic compound bearing two thioxanthene moieties (5). Relatively weak oxidants such as Ph3C+BF4 – gave 8, which is the conjugate acid of 5, as a result of a one-electron oxidation followed by hydrogen abstraction, whereas relatively strong oxidants such as SbCl5 furnished a dicationic ketal (9) as a consequence of oxidation and demethylation. Computations on the supposed dicationic intermediate suggest that the singlet state is more stable than the triplet state by 6.7 kcal mol–1 and that the reason for this peculiarity is because the singlet state is essentially a vinyl cation stabilized by a coordinating methoxy group.