A series of new, dicationic platinum(II) CNC pincer complexes were prepared and characterized by NMR and X-ray diffraction analysis. Oxidative addition of methyl iodide and iodine yielded the mostly unstable platinum(IV) complexes, which readily underwent reductive elimination to yield the platinum(II) precursors. Nonetheless, a platinum(IV) iodide adduct was isolated and was characterized by X-ray diffraction analysis. Additionally, a platinum(II) ethylene complex was isolated and found to be a moderately active yet highly selective catalyst in the co-dimerization of 2-methyl-2-butene with ethylene.

A set of heterogenized olefin-metathesis catalysts, which consisted of Ru complexes with the H(2)ITap ligand (1,3-bis(2',6'-dimethyl-4'dimethyl aminophenyl)-4,5-dihydroimidazol-2-ylidene) that had been adsorbed onto a silica support, has been prepared. These complexes showed strong binding to the solid support without the need for tethering groups on the complex or functionalized silica. The catalysts were tested in the ring-opening-ring-closing-metathesis (RO-RCM) of cyclooctene (COE) and the self-metathesis of methyl oleate under continuous-flow conditions. The best complexes showed a TON>4000, which surpasses the previously reported materials that were either based on the Grubbs-Hoveyda II complex on silica or on the classical heterogeneous Re(2)O(7)/B(2)O(3) catalyst.

An attractive strategy for achieving solar-thermal energy conversion is to harvest sunlight in the form of activated chemical bonds through photoisomerization of a suitable molecule that can release, on demand, such stored and transportable energy by thermal reversal to its original form.[1] When such reversible isomerizations entail significant topological alterations, they provide blueprints for eliciting further functions, for example in switches, machines, datastorage, sensors, and other devices. [1,2] Because of their expanded tunability and generally favourable electronic absorption regimes, organometallic complexes are advantageous in this respect, yet have remained relatively unexplored.[3] Among them, topologically simplest are metallohaptotropic arrays in which a single metal moiety photomigrates, thermally reversibly, to a higher-energy position along a fused p framework, without the assistance of additives.[4] Only two such systems are known, [Mo(PMe 3 ) 3 ] complexes of indole and quinazoline, discovered as part of a study focusing on catalytic hydrogenations of heterocycles. [5] We report 1) the photothermal reversibility of {CpCo} complexes of linear phenylenes [6] by a novel mode of haptotropism, namely, h 4 :h 4 from one cyclobutadiene ring to another (Scheme 1); 2) the first X-ray structures of metalated linear phenylenes, illustrating the aromatization of the ligand on complexation; 3) mechanistic aspects of the isomerization cycles; and 4) a DFT study providing a detailed picture of how the {CpCo} unit moves across the arene separating the two cyclobutadiene rings.The new complexes, 2, 5, and 6-8, were made from the respective 2,3,6,9-tetraethynyl linear [3]phenylene, 1,2,4,5-tetraethynylbenzene, and 2,3-diethynylbiphenylene ([D 2 ] for 8) synthons and their cocyclization with bis(trimethylsilyl)-acetylene (BTMSA) in the presence of stoichiometric [CpCo(CO) 2 ] (MeCp for 7), a strategy employed previously Scheme 1. Photo-thermal cycles of CpCo-phenylene complexes.

Polycyclic aromatic hydrocarbons have emerged as key components of future (opto)electronic and other nanodevices. [1] Functional constraints, such as air-sensitivity, instability, unfavorable band-gap, insolubility, and encumbered processability require tunable synthetic approaches to specific targets. [2] We report the Ni-catalyzed cycloaddition of alkynes to the angular phenylene motif, [3,4] which engenders novel sterically and electronically activated extended phenacenes [5] with extensive selectivity. The potential of phenacenes as components for light-emitting diodes, field-effect transistors, and superconductors has been discovered only recently. [6] In principle, the angular phenylene frame could undergo attack by alkynes at either the bay (full arrows) or the nonbay region (open arrows), which, if complete and regiochemically pristine, would furnish only one of the two extremes, phenacenes or helicenes, respectively ( Figure 1). In the absence of such selectivity, the number of possible products is substantial: 5 for parent system 1, 17 for angular [4]phenylene 2, and 6 for C 3 -symmetric [4]phenylene 3. We report a more optimistic experimental picture that is associated with an unexpected bifurcation in mechanism, as pinpointed by DFT computations.The results of a comparative study of the [Ni(cod)-(PMe 3 ) 2 ]-catalyzed cycloaddition (cod = 1,5-cyclooctadiene) of diphenylacetylene (dpa) to equimolar amounts of 1, 2, and 3, respectively, under identical reaction conditions are shown in Table 1. [7] Inspection of the product structures reveals remarkable selectivity toward the formation of phenacene (sub)units derived from multiple insertions, even though only one equivalent of alkyne reagent is present. Consequently, varying amounts of starting phenylenes are recovered, but the mass balances are good to excellent.Each one of the ensuing topologies (six of which were detailed by X-ray analysis; Table 1) [7] exhibits unique features as a result of p-activation through benzocyclobutadienofusion and/or extreme s-distortion from planarity caused by the crowded 4,5-diphenylphenanthrene [8] substructures. Thus, yellow 4 presents the unknown benzo[3,4]cyclobuta[1,2-a]phenanthrene connectivity. [9] Its phenyl groups are rotated extensively relative to the attached p-core (as also seen for the other structures), the center of one of which (at C11) is located directly above H10 of the biphenylene fragment (distance 2.496 ), causing extraordinary shielding of this nucleus (d = 4.01 ppm!). This phenomenon is also observed for 6, 7, and 9. [7,10] The activation of the phenanthrene nucleus is structurally evident in the change in the sequence of bond alternation in the annelated terminal ring [7] and in the electronic spectrum [e.g., highest l max = 420 nm; cf. phenanthrene: 345 nm, or the "hexagonal squeeze" [11] [4]phenacene (chrysene): 360 nm]. [12] These effects are even more pronounced in the [a,i] and [a,c] doubly fused and topologically new [13] red phenanthrenes (air sensitive) 6 [l max = 484 nm; cf.[5]phenac...

We report on a series of six new pyridinealkoxidebridged first and second generation ruthenium carbenes with similar or even higher activity in ring-opening metathesis polymerization (ROMP), cross metathesis (CM), and ring closing metathesis (RCM) reactions than state-of-the-art catalysts. The new precatalysts show an extraordinarily high stickiness to commercially available silica, which significantly enhances their adsorptive separation from unprocessed reaction mixtures.