Divalent Lanthanide Tetraisobutylaluminates: Reactivity and Living Isoprene Polymerization.

Lanthanide (Ln) tetraisobutylaluminates constitute key components in commercial 1,3-diene polymerization catalysts, and likewise are the homogeneous rare-earth-metal catalysts of prime industrial importance. Discrete divalent rare-earth-metal complexes [Ln(AliBu4 )2 ] (Ln=Sm, Eu, Yb) reported here display the first structurally characterized homoleptic metal tetraisobutylaluminates. Treatment of [Ln(AliBu4 )2 ] with C2 Cl6 gives access to SmII /SmIII mixed-valence cluster [Sm6 Cl8 (AliBu4 )6 ] and the YbII cluster [Yb4 Cl4 (AliBu4 )4 ], respectively. Reaction with B(C6 F5 )3 leads to hydride abstraction and formation of arene-coordinated hydroborates such as [Sm{HB(C6 F5 )3 }2 (toluene)2 ]. Complexes [Ln(AliBu4 )2 ] engage in single-component isoprene polymerization, affording high cis-1,4 polyisoprenes with narrow molecular weight distributions. Binary [Yb(AliBu4 )2 ]/[HNPhMe2 ][B(C6 F5 )4 ] fabricates polyisoprene in a perfectly living manner. The catalytically active species are scrutinized by NMR spectroscopy.

Discovery of Chlorophyll d: Isolation and Characterization of a Far-Red Cyanobacterium from the Original Site of Manning and Strain (1943) at Moss Beach, California.

We have isolated a chlorophyll-d-containing cyanobacterium from the intertidal field site at Moss Beach, on the coast of Central California, USA, where Manning and Strain (1943) originally discovered this far-red chlorophyll. Here, we present the cyanobacterium's environmental description, culturing procedure, pigment composition, ultrastructure, and full genome sequence. Among cultures of far-red cyanobacteria obtained from red algae from the same site, this strain was an epiphyte on a brown macroalgae. Its Qyin vivo absorbance peak is centered at 704-705 nm, the shortest wavelength observed thus far among the various known Acaryochloris strains. Its Chl a/Chl d ratio was 0.01, with Chl d accounting for 99% of the total Chl d and Chl a mass. TEM imagery indicates the absence of phycobilisomes, corroborated by both pigment spectra and genome analysis. The Moss Beach strain codes for only a single set of genes for producing allophycocyanin. Genomic sequencing yielded a 7.25 Mbp circular chromosome and 10 circular plasmids ranging from 16 kbp to 394 kbp. We have determined that this strain shares high similarity with strain S15, an epiphyte of red algae, while its distinct gene complement and ecological niche suggest that this strain could be the closest known relative to the original Chl d source of Manning and Strain (1943). The Moss Beach strain is designated Acaryochloris sp. (marina) strain Moss Beach.

Polymeric dimethylytterbium and the terminal methyl complex (TptBu,Me)Yb(CH3)(thf).

Divalent ytterbium bis(trimethylsilyl)amides [Yb{N(SiMe3)2}2]2 and Yb[N(SiMe3)2]2(thf)2 react with purified methyllithium to amorphous dimethylytterbium [YbMe2]n. The characterisation was performed by 171Yb and 13C CP/MAS NMR spectroscopy as well as by conducting protonolysis reactions with HC5Me5 and HTptBu,Me, affording known (C5Me5)2Yb(OEt2) and new (TptBu,Me)Yb(CH3)(thf).

The Seed of Goal-Related Doubts: A Longitudinal Investigation of the Roles of Failure and Expectation of Success Among Police Trainee Applicants.

Various theories on personal goal striving rely on the assumption that failure raises doubts about the goal. Yet, empirical evidence for an association between objective failure experiences and doubts about personal long-term goals is still missing. In a longitudinal field study, applicants for a job as a police trainee (n = 172, M age = 25.15; 55 females and 117 males) were accompanied across three measurement times over a period of five months. We investigated the effects of failure and initial expectation of success (in the standardized selection process) on doubts regarding the superordinate goal of becoming a police officer. As hypothesized, both failure and low initial expectation of success as well as their interaction led to increased goal-related doubts over time. The findings provide first empirical evidence for the role of failure in the emergence of goal-related doubts in personal long-term goals and, therefore, the disengagement process as it is hypothesized in various theories on goal striving and life-span development.

Far-red light acclimation in diverse oxygenic photosynthetic organisms.

Oxygenic photosynthesis has historically been considered limited to be driven by the wavelengths of visible light. However, in the last few decades, various adaptations have been discovered that allow algae, cyanobacteria, and even plants to utilize longer wavelength light in the far-red spectral range. These adaptations provide distinct advantages to the species possessing them, allowing the effective utilization of shade light under highly filtered light environments. In prokaryotes, these adaptations include the production of far-red-absorbing chlorophylls d and f and the remodeling of phycobilisome antennas and reaction centers. Eukaryotes express specialized light-harvesting pigment-protein complexes that use interactions between pigments and their protein environment to spectrally tune the absorption of chlorophyll a. If these adaptations could be applied to crop plants, a potentially significant increase in photon utilization in lower shaded leaves could be realized, improving crop yields.

Cu+ Contributes to the Orange Carotenoid Protein-Related Phycobilisome Fluorescence Quenching and Photoprotection in Cyanobacteria.

Photosynthesis starts with absorption of light energy by using light-harvesting antenna complexes (LHCs). Overexcitation of LHCs and subsequent photosystems, however, is damaging and can be lethal. The orange carotenoid protein (OCP) protects most cyanobacteria from photodamage by dissipating excessive excitation energy harvested by phycobilisomes (PBS, LHCs) as heat. OCP has two states: the orange, inactive OCP (OCPO) and the red, active OCP (OCPR), with the latter able to bind PBS at a ratio of 2:1 and execute photoprotection. Conversion of OCPO to OCPR is driven by blue light absorption. Previous work indicated that in the presence of Cu2+, photoactivation of OCP can result in it being locked in its red form OCPR. The molecular mechanism of such chemical conversion, however, remains unclear. Here, we demonstrated that Cu+ can convert OCPO to OCPR under anaerobic conditions independent of light illumination. Interestingly, in the presence of Cu2+ and ascorbic acid, a ubiquitous reductant in photosynthetic organisms, the conversion of OCPO to OCPR can also take place spontaneously in the dark, indicative of a locked OCPR-Cu+ complex. Furthermore, our functional and structural studies indicate that OCPR-Cu+ can interact with PBS and trigger PBS fluorescence quenching. We hypothesize that copper ion, a redox-active component, may synergistically play an important role in the regulation of nonphotochemical quenching in cyanobacteria under stress conditions.

Chasing Multiple Bonding Interactions between Alkaline-Earth Metals and Main-Group Fragments.

Formally dianionic ligands such as alkylidenes or organoimidos play a major role in the organometallic chemistry of transition metals and are an emerging topical area of f-element chemistry. The pursuit and development of main-group-metal congeners has been tackled sporadically but is clearly lacking behind. The pronounced ionic bonding in particular, prevailing in alkali and alkaline-earth (Ae) metal derivatives, proved cumbersome. Recent substantial progress in the respective field of divalent Ae chemistry has been triggered by the implementation of new synthesis strategies involving new AeII precursors and tailor-made ligands. The main emphasis of this Minireview will be on the synthesis and reactivity of well-defined Group 2 alkylidenes, organoimides, silylenes, and phosphandiides.

Excitation energy transfer in the far-red absorbing violaxanthin/vaucheriaxanthin chlorophyll a complex from the eustigmatophyte alga FP5.

This work highlights spectroscopic investigations on a new representative of photosynthetic antenna complexes in the LHC family, a putative violaxanthin/vaucheriaxanthin chlorophyll a (VCP) antenna complex from a freshwater Eustigmatophyte alga FP5. A representative VCP-like complex, named as VCP-B3 was studied with both static and time-resolved spectroscopies with the aim of obtaining a deeper understanding of excitation energy migration within the pigment array of the complex. Compared to other VCP representatives, the absorption spectrum of the VCP-B3 is strongly altered in the range of the chlorophyll a Qy band, and is substantially red-shifted with the longest wavelength absorption band at 707 nm at 77 K. VCP-B3 shows a moderate xanthophyll-to-chlorophyll a efficiency of excitation energy transfer in the 50-60% range, 20-30% lower from comparable VCP complexes from other organisms. Transient absorption studies accompanied by detailed data fitting and simulations support the idea that the xanthophylls that occupy the central part of the complex, complementary to luteins in the LHCII, are violaxanthins. Target analysis suggests that the primary route of xanthophyll-to-chlorophyll a energy transfer occurs via the xanthophyll S1 state.

Lewis-Acid Stabilized Organoimide Complexes of Divalent Samarium, Europium, and Ytterbium.

Discrete organoimide complexes of the divalent rare-earth metals samarium, europium, and ytterbium are reported. Tandem salt metathesis-protonolysis reactions using LnII bis(tetramethylaluminate) precursors [Ln(AlMe4 )2 ]n and monopotassium salts of 2,6-diisopropylaniline (H2 NDipp) and triphenylsilylamine prove viable and efficient protocols. Depending on the ionic radius of the LnII metal centers and the steric demand of the imido carbon backbone, mono- and dilanthanide arrangements of general composition [(thf)x Ln(NR)(AlMe3 )]y (Ln=Sm, Eu, Yb; R=Dipp, SiPh3 ) are found in the solid state. Complex formation and stabilization is achieved by coordination of the Lewis acid AlMe3 , which also prevents formation of higher aggregated species. The feasibility of redox chemistry is shown with the plumbocene derivative Cp*2 Pb, providing access to the corresponding monomeric LnIII half-sandwich complexes [Cp*Ln(NR)(AlMe3 )(thf)2 ] (Ln=Sm, Yb).

Synthesis of homometallic divalent lanthanide organoimides from benzyl complexes.

The reaction of LnI2(thf)2 with benzyl potassium affords the homoleptic benzyl complexes [Ln(CH2Ph)2]n of samarium, europium, and ytterbium. In the cases of Eu and Yb, the treatment of [Ln(CH2Ph)2]n with one equivalent of 2,6-diisopropylaniline gives access to tetrameric organoimide complexes [(thf)Ln(µ3-NDipp)]4, representing the first examples of homometallic Ln(ii) imides. This study revealed that the Yb(ii) organoimide chemistry is significantly different from that of calcium.

Trivalent Rare-Earth-Metal Bis(trimethylsilyl)amide Halide Complexes by Targeted Oxidations.

In contrast to previously applied salt metathesis protocols the targeted rare-earth-metal compounds Ln[N(SiMe3)2]2(halogenido) were accessed by oxidation of Ln(II) silylamide precursors. Treatment of Sm[N(SiMe3)3]2(thf)2 with 0.5 equiv of C2Cl6 or 0.25 equiv of TeBr4 in thf and crystallization thereof gave [Sm{N(SiMe3)2}2(µ-X)(thf)]2 (X = Cl, Br). A similar reaction/crystallization procedure performed with 0.5 equiv of 1,2-diiodoethane gave monomeric Sm[N(SiMe3)2]2I(thf)2. Switching to Yb[N(SiMe3)2]2(thf)2, the aforementioned oxidants generated monomeric five-coordinate complexes Yb[N(SiMe3)2]2X(thf)2 (X = Cl, Br, I). The reaction of Eu[N(SiMe3)2]2(thf)2 with 0.5 equiv of C2Cl6 in thf yielded the separated ion pair [Eu{N(SiMe3)2}3Cl][(thf)5Eu(µ-Cl)2Eu(thf)5]. Performing the chlorination in n-hexane led to oxidation followed by rapid disproportionation into EuCl3(thf) x and Eu[N(SiMe3)2]3. The bromination reaction did not afford crystalline material, while the iodination gave crystals of divalent EuI2(thf)5. Use of trityl chloride (Ph3CCl) as the oxidant in thf accomplished the Eu(III) species [Eu{N(SiMe3)2}2(µ-Cl)(thf)]2. In situ oxidation of putative [Tm{N(SiMe3)2}2(thf) x] using 0.5 equiv of C2Cl6 in thf followed by crystallization from n-hexane led to the formation of a mixture of [Tm{N(SiMe3)2}2(µ-Cl)(thf)]2 and Tm[N(SiMe3)2]3. Switching the oxidant to 0.5 equiv of 1,2-diiodoethane and crystallizing from thf repeatedly afforded the bis-halogenated complex Tm[N(SiMe3)2]I2(thf)3.

Dimethylcalcium.

The salt metathesis reaction between homoleptic calcium bis(trimethylsilyl)amide [Ca{N(SiMe3)2}2]2 and "halide-free" methyllithium allowed for the isolation of X-ray-amorphous dimethylcalcium [CaMe2]n in good yields and purities. The formation of [CaMe2]n was proven by microanalysis and NMR/FTIR spectroscopic methods as well as a series of derivatization reactions. Despite slowly decomposing thf, [CaMe2]n could be crystallized from chilled thf solutions as the heptametallic adduct [(thf)10Ca7Me14]. Reaction of [CaMe2]n with CaI2 in thf led to the dimeric complex [(thf)3Ca(Me)(I)]2, whereas in tetrahydropyran (thp) the trinuclear complex [(thp)5Ca3(Me)5(I)] was obtained, both representing the first crystallographically characterized heavy-Grignard compounds with methyl groups as the hydrocarbyl ligand. While protonolysis of [CaMe2]n with the superbulky proligand HTptBu,Me in nonpolar solvents gave homoleptic (TptBu,Me)2Ca, reaction in donor solvents (thf, thp) afforded the monomeric complexes [(TptBu,Me)Ca(Me)(thf)] and [(TptBu,Me)Ca(Me)(thp)], which are the first examples bearing terminal Ca-CH3 functionalities. Grignard-type nucleophilic methyl-group transfer to hexamethylacetone gave access to the dimeric alkoxide complexes [(thf)Ca(OCtBu2Me)2]2 and [(tBu2CO)Ca(µ2-OCtBu2Me)3Ca(OCtBu2Me)]. Finally, addition of the Lewis acid GaMe3 to [CaMe2]n led to the corresponding tetramethylgallate compound [Ca(GaMe4)2]n.

Characterization of a newly isolated freshwater Eustigmatophyte alga capable of utilizing far-red light as its sole light source.

Oxygenic phototrophs typically utilize visible light (400-700 nm) to drive photosynthesis. However, a large fraction of the energy in sunlight is contained in the far-red region, which encompasses light beyond 700 nm. In nature, certain niche environments contain high levels of this far-red light due to filtering by other phototrophs, and in these environments, organisms with photosynthetic antenna systems adapted to absorbing far-red light are able to thrive. We used selective far-red light conditions to isolate such organisms in environmental samples. One cultured organism, the Eustigmatophyte alga Forest Park Isolate 5 (FP5), is able to absorb far-red light using a chlorophyll (Chl) a-containing antenna complex, and is able to grow under solely far-red light. Here we characterize the antenna system from this organism, which is able to shift the absorption of Chl a to >705 nm.

Subcellular pigment distribution is altered under far-red light acclimation in cyanobacteria that contain chlorophyll f.

Far-Red Light (FRL) acclimation is a process that has been observed in cyanobacteria and algae that can grow solely on light above 700 nm. The acclimation to FRL results in rearrangement and synthesis of new pigments and pigment-protein complexes. In this study, cyanobacteria containing chlorophyll f, Synechococcus sp. PCC 7335 and Halomicronema hongdechloris, were imaged as live cells with confocal microscopy. H. hongdechloris was further studied with hyperspectral confocal fluorescence microscopy (HCFM) and freeze-substituted thin-section transmission electron microscopy (TEM). Under FRL, phycocyanin-containing complexes and chlorophyll-containing complexes were determined to be physically separated and the synthesis of red-form phycobilisome and Chl f was increased. The timing of these responses was observed. The heterogeneity and eco-physiological response of the cells was noted. Additionally, a gliding motility for H. hongdechloris is reported.

Synthesis and Reactivity of Discrete Calcium Imides.

Protonolysis of dibenzylcalcium with triphenylsilylamine affords a thf-coordinated tetrametallic calcium imide with a heterocuboid core structure. The use of calcium bis(tetramethylaluminate) as a precursor for tandem salt metathesis/protonolysis reactions with alkali metal amides of 2,6-diisopropylaniline and triphenylsilylamine provides access to Lewis acid stabilized monocalcium imides of the type [(thf)4 Ca(µ2 -NR)(µ2 -Me)AlMe2 ]. Treatment of [(thf)4 Ca(µ2 -NSiPh3 )(µ2 -Me)AlMe2 ] with phenylsilane results in H-Si addition across the Ca-N imido bond, producing a homoleptic calcium amidoaluminate complex and putative CaH2 whereas reaction with phenylacetylene leads to protonation of an AlMe moiety to yield the dimeric complex [(thf)Ca{NSiPh3 }{AlMe2 (CCPh)}]2 .

Assessing the Brønsted basicity of diaminoboryl anions: reactivity toward methylated benzenes and dihydrogen.

Treatment of toluene or p-xylene with diaminoboryllithium results in consecutive reactions, involving boryl-anion-mediated deprotonation at the benzylic position followed by nucleophilic substitution at the boron center, producing benzylborane species and LiH. Diaminoboryllithium also cleaves H2 heterolytically affording diaminohydroborane and LiH, while the reaction of lithium diaminoboryl(bromo)cuprate with H2 takes place accompanied by reduction of Cu(I) to give diaminohydroborane, LiH, and Cu(0).