Synthesis and X-ray crystal structures of imido and ureato derivatives of titanium(IV) phthalocyanine and their application in the catalytic formation of carbodiimides by metathesis from isocyanates

The imido titanium phthalocyanine complex [PcTi(NDip)] (Dip = 2,6-diisopropylphenyl) 2a was synthesized from [PcTiO] 1 and one eq. of DipNCO. Due to the steric demand of the Dip group, addition of another isocyanate molecule to the Ti = N functionality of 2a does not occur even at high molar ratios of DipNCO. However, 1 reacts with 2 eq. of arylisocyanates containing sterically less demanding aryl groups producing N,N'-diarylureatotitanium(iv)phthalocyanines [PcTi{κ(2)-(NR)C(O)(N'R)}] (R = p-tolyl (Tol) 3a or mesityl (Mes) 3b). The N,N' coordination (III) of the ureato ligand in 3a and 3b was proven by a single set of resonances for the aryl groups in their (1)H-NMR spectra. An N,O coordination (IV) can therefore be excluded. This is also confirmed by the X-ray crystal structure of 3a. Upon heating [PcTiO] and an excess of aryl isocyanates for 6 days, a steady evolution of CO(2) was observed and a white precipitate, identified as the corresponding diarylcarbodiimides (V), could be isolated. Therefore this reaction was applied in the metathetic conversion of two isocyanate molecules into diarylcarbodiimides (V) and CO(2). Additionally, imido titanium Pc's 2b (R = tBu) and 2c (R = Mes) were prepared by a more general synthetic strategy, reacting the potassium salt of the ligand PcK(2) with appropriate imido titanium precursors.     

The imidato-alkenyllithium route for the synthesis of the isoquinocycline-pyrrolopyrrole substructure

A convergent and effective synthesis of the pyrrolopyrrole substructure (CDEFG) of the isoquinocyclines is reported. A key step is a tin-lithium exchange of an imidato-alkenyltin compound (a ring G equivalent) and the subsequent acylation with a lactone. The resulting acetal is used successfully for the ring F closure to the pyrrolopyrrole. The sole formation of the isoquinocycline N,O-acetal epimer is in accordance with the proposed mechanism for the isomerization of quinocyclines to isoquinocyclines.     

Improving the sensitivity of future GW observatories in the 1�C10?Hz band: Newtonian and seismic noise

The next generation gravitational wave interferometric detectors will likely be underground detectors to extend the GW detection frequency band to frequencies below the Newtonian noise limit. Newtonian noise originates from the continuous motion of the Earth??s crust driven by human activity, tidal stresses and seismic motion, and from mass density fluctuations in the atmosphere. It is calculated that on Earth??s surface, on a typical day, it will exceed the expected GW signals at frequencies below 10 Hz. The noise will decrease underground by an unknown amount. It is important to investigate and to quantify this expected reduction and its effect on the sensitivity of future detectors, to plan for further improvement strategies. We report about some of these aspects. Analytical models can be used in the simplest scenarios to get a better qualitative and semi-quantitative understanding. As more complete modeling can be done numerically, we will discuss also some results obtained with a finite-element-based modeling tool. The method is verified by comparing its results with the results of analytic calculations for surface detectors. A key point about noise models is their initial parameters and conditions, which require detailed information about seismic motion in a real scenario. We will describe an effort to characterize the seismic activity at the Homestake mine which is currently in progress. This activity is specifically aimed to provide informations and to explore the site as a possible candidate for an underground observatory. Although the only compelling reason to put the interferometer underground is to reduce the Newtonian noise, we expect that the more stable underground environment will have a more general positive impact on the sensitivity. We will end this report with some considerations about seismic and suspension noise.     

Synthesis and Crystal Structures of Axially Substituted Titaniumphthalocyanines and Preparation of PcTi@SBA‐15 and PcTi&TiOx@SBA‐15 Materials

Four axially substituted titanium(IV)phthalocyanines of formula trans‐[PcTi(OSiPh₃)₂], [PcTi{(NH)₂C₆H₄}], [PcTi(η²‐S₂)], and [PcTi=S] were prepared starting from the reactive species N,N′‐di‐4‐tolylureato(phthalocyaninato)titanium(IV). The prepared compounds were characterized by using UV/Vis‐spectroscopy, FT‐IR and raman spectroscopy, TGA, elementalanalysis and MALDI‐TOF measurements. The compound trans‐[PcTi(OSiPh₃)₂] crystallizes from chlorobenzene in the triclinic space group P with a = 10.4160(8) Å, b = 11.2160(8) Å, c = 13.1495(9) Å, α = 114.124(5)°, β = 99.452(6)°, γ = 96.174(6)°, and Z = 1. [PcTiS₂] crystallizes from chlorobenzene in the monoclinic space group P2₁/n with a = 13.114(3) Å, b = 9.752(2) Å, c = 20.975(5) Å, β = 100.46(2), and Z = 4. The crystal structures of both compounds are discussed. The reactive ureato complex could also successfully be anchored onto SBA‐15 and TiO_x@SBA‐15 materials using the apical ureato ligand as a good leaving group for the reaction with the silanol groups of the host material.     

Enantioconvergent photoredox radical-radical coupling catalyzed by a chiral-at-rhodium complex

Racemic α-chloro imidazol-2-yl-ketones undergo an enantioconvergent photoactivated C–C bond formation with N-aryl glycines catalyzed by a single bis-cyclometalated chiral-at-rhodium catalyst in yields of up to 80% and up to 98% enantiomeric excess(ee). Control experiments support a mechanism which is initiated by a single electron transfer from N-aryl glycinate to the photochemically excited rhodium-bound α-chloro imidazol-2-yl-ketone, followed by chloride fragmentation of the α-chloroketone, decarboxylation of the glycinate, and a subsequent highly stereocontrolled radical-radical coupling. This work showcases the ability of the chiral rhodium catalyst to serve a dual function as chiral Lewis acid and at the same time as the photoredox active species upon substrate binding.     

Asymmetric Photocatalysis by Intramolecular Hydrogen‐Atom Transfer in Photoexcited Catalyst–Substrate Complex

3‐(2‐Formylphenyl)‐1‐pyrazol‐1‐yl‐propenones undergo an asymmetric photorearrangement to benzo[d]cyclopropa[b]pyranones with up to >99 % ee, which is catalyzed by a bis‐cyclometalated rhodium catalyst in the presence of visible light. Mechanistic experiments and DFT calculations support a mechanism in which a photoexcited catalyst/substrate complex triggers an intramolecular hydrogen‐atom transfer followed by a highly stereocontrolled hetero‐Diels–Alder reaction. In this reaction scheme, the rhodium catalyst fulfills multiple functions by 1) enabling visible‐light π→π* excitation of the catalyst‐bound enone substrate, 2) facilitating the hydrogen‐atom transfer, and 3) providing the asymmetric induction for the hetero‐Diels–Alder reaction.