Two a/b-fold hydrolases, KARRIKIN INSENSITIVE2 (KAI2) and Arabidopsis thaliana DWARF14 (AtD14), are necessary for responses to karrikins (KARs) and strigolactones (SLs) in Arabidopsis (Arabidopsis thaliana). Although KAI2 mediates responses to KARs and some SL analogs, AtD14 mediates SL but not KAR responses. To further determine the specificity of these proteins, we assessed the ability of naturally occurring deoxystrigolactones to inhibit Arabidopsis hypocotyl elongation, regulate seedling gene expression, suppress outgrowth of secondary inflorescences, and promote seed germination. Neither 5-deoxystrigol nor 4-deoxyorobanchol was active in KAI2-dependent seed germination or hypocotyl elongation, but both were active in AtD14-dependent hypocotyl elongation and secondary shoot growth. However, the nonnatural enantiomer of 5-deoxystrigol was active through KAI2 in growth and gene expression assays. We found that the four stereoisomers of the SL analog GR24 had similar activities to their deoxystrigolactone counterparts. The results suggest that AtD14 and KAI2 exhibit selectivity to the butenolide D ring in the 29R and 29S configurations, respectively. However, we found, for nitrile-debranone (CN-debranone, a simple SL analog), that the 29R configuration is inactive but that the 29S configuration is active through both AtD14 and KAI2. Our results support the conclusion that KAI2-dependent signaling does not respond to canonical SLs. Furthermore, racemic mixtures of chemically synthesized SLs and their analogs, such as GR24, should be used with caution because they can activate responses that are not specific to naturally occurring SLs. In contrast, the use of specific stereoisomers might provide valuable information about the specific perception systems operating in different plant tissues, parasitic weed seeds, and arbuscular mycorrhizae.Strigolactones (SLs) are carotenoid-derived phytohormones that mediate various aspects of plant development in addition to symbiotic and parasitic interactions in the rhizosphere. Originally identified as seed germination stimulants of root-parasitic weeds (Cook et al., 1966(Cook et al., , 1972, SLs have now been implicated in several processes, including inhibition of bud outgrowth to decrease shoot branching, regulation of leaf morphology, regulation of root architecture, control of secondary growth in the cambium, and association of plant roots with symbiotic fungi and nodulating bacteria (for review, see Brewer et al., 2013;Waldie et al., 2014).The isolation of several mutants in pea (Pisum sativum; rms), rice (Oryza sativa; d), petunia (Petunia hybrida; dad), and Arabidopsis (Arabidopsis thaliana; max) that exhibit dwarfism and an increased number of secondary shoots or tillers has enabled the identification of genes involved in four steps in SL biosynthesis and another three involved in signal transduction. The initial step of SL biosynthesis involves the conversion of all-trans-b-carotene into 9-cis-b-carotene by the isomerase D27. The sequential cleavage of the D27 produ...

Zerovalent carbene complexes of Pd containing the 1,3,4,5-tetramethylimidazol-2-ylidene ligand (tmiy) have been synthesized. Pd(COD)(alkene) (COD = cyclooctadiene) reacts with the nucleophilic carbene tmiy to produce the complexes Pd(tmiy)2(alkene) (alkene = maleic anhydride (MAH) (2), tetracyanoethylene (TCNE) (3)). Spectroscopic studies on the complexes provide strong evidence of the almost purely donor nature of the carbene ligand. Oxidative addition of hydrocarbyl halide and dihalide substrates to 2 and 3 yield the PdII derivatives Pd(tmiy)2(Ph)I (4), Pd(tmiy)2I2 (5), Pd(tmiy)2(4-nitrophenyl)I (6), and Pd(tmiy)2Br2 (7). The zerovalent Ni complex Ni(tmiy)2 was produced in situ from the reaction of Ni(COD)2 with tmiy, and the oxidative addition of organic halides yields Ni(tmiy)2(o-tolyl)Br (8), Ni(tmiy)2(Me)I (9), and Ni(tmiy)2I2 (10). X-ray crystal structures of complexes 8 and 10 are reported which reveal square-planar coordination with the carbene ligands inclined at significant angles to the coordination planes of the complexes. Metal to ligand bond distances are all indicative of the electron density induced on the metal center by the donor carbene ligands. Halide abstraction from 6 in the presence of n-butyl acrylate leads to migratory insertion of the olefin and elimination of the Heck coupling product. Under stoichiometric reaction conditions hydrocarbyl−imidazolium ions are also produced as byproducts. Selected complexes were tested as catalysts for the Heck reaction (Pd) and Suzuki coupling (Pd, Ni) and were found to be highly active. The observed reaction behavior is interpreted, and a mechanism for the Heck coupling is provided.

A general synthetic methodology is reported for tris(bidentate)ruthenium(II) complexes containing three different polypyridyl ligands, based on the sequential addition of the ligands to the oligomer [RuíCObCX],,. The tris-(heteroleptic) complexes were characterized by FAB mass spectrometry and NMR spectroscopy. An X-ray crystal structure determination was made for the complex [Ru(Me2bpy)(phen)(bpa)](PF6)2'C6Hi4 [C40H43F12N7P2RU, M = 1062.8; Me2bpy = 4J4'-dimethyl-2,2'-bipyridine, phen = 1,10-phenanthroline, bpa = bis(2-pyridyl)amine]: triclinic, space group PI, a = 14.57(3) k,b= 13.50(3) k, c = 12.73(3) Á, a = 68.6(2)°, ß = 63.5(1)°, = 79.8(2)°, V = 2082 Á3, Z = 2. Aspects of the electrochemistry, spectroscopy, and photophysics of the tris-(heteroleptic) species are discussed.

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The complexes {Cp*(PP)Ru}2(μ-C⋮CC⋮C) (PP = dppm 5a, dppe 5b) have been synthesized from RuCl(PP)Cp* (1a/b) via the corresponding vinylidenes [Ru(CCH2)(PP)Cp*]+ (2a/b), deprotonation (KOBut) to the ethynyls Ru(C⋮CH)(PP)Cp* (3a/b), oxidative coupling ([FeCp2][PF6]) to the bis(vinylidenes) [{Ru(PP)Cp*}2{μ-(CCHCHC)}]2+ (4a/b), and deprotonation [dbu (4a), KOBut (4b)]. Electrochemistry of 5a/b revealed the expected sequence of four 1e redox steps, which occurred at significantly lower E° values than found for the Ru(PPh3)2Cp analogue. Single-crystal X-ray structure determinations are reported for 1a/b, 2a/b, 3a/b, 4a/b, and 5a/b, together with the oxidized products [5b][PF6] n (n = 1, 2). In the monocation [5b][PF6] the Ru−C(1) [1.931(2) Å] and C−C distances [1.248−1.338(3) Å] are intermediate between those found in 5b and the dication [5b]2+. The short Ru−C [1.857(5) Å] and experimentally equal C−C distances [1.269−1.280(6) Å] in [5b][PF6]2 confirm the anticipated dicarbene-cumulene structure for the RuCCCCRu bridge.