Switching and Extension of a [c2]Daisy-Chain Dimer Polymer

We report the synthesis of a [c2]daisy-chain dimer via ruthenium-catalyzed ring-closing olefin metathesis. Confirmation of the interlocked nature of the structure was achieved through single-crystal X-ray diffraction analysis. The dimer could be readily switched from the bound to the unbound conformation by treatment with 3.0 equiv of KOH and subsequently reprotonated by treatment with 3.0 equiv of HPF_6. Azide functionalization of the dimer enabled incorporation in linear step-growth polymer chains using the alkyne-azide “click” reaction. Gel permeation chromatography coupled with multiangle laser light scattering analysis showed the polymers contained 22 dimers and had a radius of gyration of 14.8 nm. Acylation of the amines of the dimers sterically forced elongation of the interlocked units, and MALLS analysis of the polymer showed a 48% increase in the R_g (21.4 nm)

Terminal ruthenium carbido complexes as σ-donor ligands

The terminal carbido ligand of (Pcy_3)_2(Cl)_2RuC coordinates to other metal centers in a σ-donor fashion, as in (Pcy_3)_2(Cl)_2Ru≡C–Pd(Cl)_2(Sme_2) and (Pcy_3)_2(Cl)_2Ru≡C–Mo(CO)_5

The Avifauna of Buldir Island, Aleutian Islands, Alaska

We studied the avifauna of Buldir Island, Aleutian Islands, Alaska, between 1972 and 1984. During the study 126 forms of 125 species were recorded, including first North American records for 6 species and first Aleutian records for 4 others. Due to the absence of mammalian predators and rich food resources nearby, 32 species, 21 of them seabirds, bred at Buldir. Breeding populations totaled approximately 1.8 million pairs of birds, primarily storm-petrels (Oceanodroma spp.) and auklets (Aethia spp.). Buldir's suite of breeding alcids - 12 species - may be the most diverse of any seabird colony in the world. Our data on migrants suggest that Buldir is near the eastern edge of the Japan-Kuril Islands-Kamchatka flyway. All migrant and breeding species recorded are discussed in an annotated list.Key words: Buldir Island, Aleutian Islands, Beringia region, zoogeography, breeding birds, migrant birds, Bering Sea, subarctic seabirdsMots clés: île Buldir, îles Aléoutiennes, Béringie, zoogéographie, oiseaux nidificateurs, oiseaux migrateurs, mer de Béring, oiseaux de mer subarctique

(Dicyclohexylphosphino)borane, BH_3PH(C_6H_(11))_2, a Precursor to Water-Soluble Phosphine Ligands

(Dicyclohexylphosphino) borane is a precursor in the synthesis of water-soluble phosphines. The boranato group can be removed quantitatively under mild conditions

Latent Olefin Metathesis Catalysts Featuring Chelating Alkylidenes

The synthesis of a series of ruthenium-based metathesis catalysts featuring imine donors chelated through the alkylidene group is described. The relative placement of the imine carbon−nitrogen double bond (exocyclic vs endocyclic) has a major impact on the initiation behavior. When used in metathesis applications, catalysts with an endocyclic imine bond show latent behavior and a high degree of tunability. The incorporation of additional donor atoms is an additional strategy for controlling initiation behavior. These latent catalysts could be useful in high-temperature applications

A Diphenylcyclopropene Complex of Tungsten, [WCl_2O(PMePh_2)_2(η^2-3,3-diphenylcyclopropene)], Precursor to a Tungsten–Oxo–Olefin Metathesis Catalyst

The title compound, dichlorobis(methyldiphenylphosphine-P) [(1,2-[η])-3,3-diphenylcyclopropene]oxotungsten, [WCl_2O(C_(15)H_(12))(C_(13)H_(13)P)_2], is a mononuclear complex of tungsten with an approximately octahedral environment around the metal atom. The ligand, 3,3-diphenylcyclopropene, is bonded to the W atom in a [η]^2-geometry with effectively identical metal-to-carbon bond distances [W-C1 = 2.133 (7) Å and W-C2 2.131 (7) Å]

Novel η^3- Vinylcarbene Complexes Derived from Ruthenium-Based Olefin Metathesis Catalysts

Electron-rich, disubstituted alkynes react with (H_2IMes)(PCy_3)(Cl)_2Ru═CHPh (1; H_2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) to form phosphine-free η^3-vinylcarbene complexes. An X-ray diffraction study on (H_2IMes)(Cl)_2Ru[η^3-(CHPh)(CPh)(CPh)] (2) confirms the unusual structure. These complexes are relevant to the mechanisms of olefin metathesis and alkyne polymerization

Decomposition of a Key Intermediate in Ruthenium-Catalyzed Olefin Metathesis Reactions

Dinuclear ruthenium complex, with a bridging carbide and a hydride ligand, and methyltricyclohexylphosphonium chloride result from thermal decomposition of olefin metathesis catalyst, (ImesH_2)(PCy)_3)(Cl)_2Ru CH_2. Involvement of dissociated phosphine in the decomposition is proposed. The dinuclear complex has catalytic olefin isomerization activity, which can be responsible for competing isomerization processes in certain olefin metathesis reactions

Discovery of Northern Fur Seals (Callorhinus ursinus) Breeding on Bogoslof Island Southeastern Bering Sea

A small group of northern fur seals (Callorhinus ursinus) including one male with two females, each with a small pup, and two lone males were discovered on Bogoslof Island, Alaska in the Bering Sea on 20 July 1980. This is the first evidence of breeding on Bogoslof, or on any island in the eastern Bering Sea other than the Pribilof Islands. We suggest that these fur seals require breeding islands adjacent to the continental shelf break where they are supported by the pelagic food web characteristic of the oceanic and outer shelf domains.Key words: fur seal, Callorhinus ursinus, Steller sea lion, Eumetopias jubatus, Aleutian Islands, Bering SeaMots clés: otarie à fourrure, Callorhinus ursinus, otarie, Eumetopias jubatus, îles Aléoutiennes, mer de Bérin

Conformations of N-Heterocyclic Carbene Ligands in Ruthenium Complexes Relevant to Olefin Metathesis

The structure of ruthenium-based olefin metathesis catalyst 3 and model π-complex 5 in solution and in the solid state are reported. The N-tolyl ligands, due to their lower symmetry than the traditional N-mesityl substituents, complicate this analysis, but ultimately provide explanation for the enhanced reactivity of 3 relative to standard catalyst 2. The tilt of the N-tolyl ring provides additional space near the ruthenium center, which is consistent with the enhanced reactivity of 3 toward sterically demanding substrates. Due to this tilt, the more sterically accessible face bears the two methyl substituents of the N-aryl rings. These experimental studies are supported by computational studies of these complexes by DFT. The experimental data provides a means to validate the accuracy of the B3LYP and M06 functionals. B3LYP provides geometries that match X-ray crystal structural data more closely, though it leads to slightly less (0.5 kcal mol^(−1)) accuracy than M06 most likely because it underestimates attractive noncovalent interactions