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1. Synthesis and characterization of a tert- butyl ester-substituted titanocene dichloride: ^t-BuOOC Cp ₂ TiCl ₂

   https://doi.org/10.1107/S2056989020011834  

   McCarthy, Jackson S.; McMillen, Colin D.; Pienkos, Jared A.; Wagenknecht, Paul S. (October 2020, Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   Bis[η 5 -( tert -butoxycarbonyl)cyclopentadienyl]dichloridotitanium(IV), [Ti(C 10 H 13 O 2 ) 2 Cl 2 ], was synthesized from LiCp COO t -Bu using TiCl 4 , and was characterized by single-crystal X-ray diffraction and 1 H NMR spectroscopy. The distorted tetrahedral geometry about the central titanium atom is relatively unchanged compared to Cp 2 TiCl 2 . The complex exhibits elongation of the titanium–cyclopentadienyl centroid distances [2.074 (3) and 2.070 (3) Å] and a contraction of the titanium–chlorine bond lengths [2.3222 (10) Å and 2.3423 (10) Å] relative to Cp 2 TiCl 2 . The dihedral angle formed by the planes of the Cp rings [52.56 (13)°] is smaller than seen in Cp 2 TiCl 2 . Both ester groups extend from the same side of the Cp rings, and occur on the same side of the complex as the chlorido ligands. The complex may serve as a convenient synthon for titanocene complexes with carboxylate anchoring groups for binding to metal oxide substrates. 

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2. Interpreting inorganic compositional depth profiles to understand the rate-limiting step in vapor phase infiltration processes

   https://doi.org/10.1039/D3CP01517C  

   Balogun, Shuaib A.; Ren, Yi; Lively, Ryan P.; Losego, Mark D. (May 2023, Physical Chemistry Chemical Physics)

   Vapor phase infiltration (VPI) is a post-polymerization modification technique that infuses inorganics into polymers to create organic–inorganic hybrid materials with new properties. Much is yet to be understood about the chemical kinetics underlying the VPI process. The aim of this study is to create a greater understanding of the process kinetics that govern the infiltration of trimethyl aluminum (TMA) and TiCl 4 into PMMA to form inorganic-PMMA hybrid materials. To gain insight, this paper initially examines the predicted results for the spatiotemporal concentrations of inorganics computed from a recently posited reaction–diffusion model for VPI. This model provides insight on how the Damköhler number (reaction versus diffusion rates) and non-Fickian diffusional processes (hindering) that result from the material transforming from a polymer to a hybrid can affect the evolution of inorganic concentration depth profiles with time. Subsequently, experimental XPS depth profiles are collected for TMA and TiCl 4 infiltrated PMMA films at 90 °C and 135 °C. The functional behavior of these depth profiles at varying infiltration times are qualitatively compared to various computed predictions and conclusions are drawn about the mechanisms of each of these processes. TMA infiltration into PMMA appears to transition from a diffusion-limited process at low temperatures (90 °C) to a reaction-limited process at high temperatures (135 °C) for the film thicknesses investigated here (200 nm). While TMA appears to fully infiltrate these 200 nm PMMA films within a few hours, TiCl 4 infiltration into PMMA is considerably slower, with full saturation not occurring even after 2 days of precursor exposure. Infiltration at 90 °C is so slow that no clear conclusions about mechanism can be drawn; however, at 135 °C, the TiCl 4 infiltration into PMMA is clearly a reaction-limited process, with TiCl 4 permeating the entire thickness (at low concentrations) within only a few minutes, but inorganic loading continuously increasing in a uniform manner over a course of 2 days. Near-surface deviations from the uniform-loading expected for a reaction-limited process also suggest that diffusional hindering is high for TiCl 4 infiltration into PMMA. These results demonstrate a new, ex situ analysis approach for investigating the rate-limiting process mechanisms for vapor phase infiltration. 

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3. Catalytic intramolecular hydroamination of aminoallenes using titanium complexes of chiral, tridentate, dianionic imine-diol ligands

   https://doi.org/10.1039/C8DT05156A  

   Sha, Fanrui; Mitchell, Benjamin S.; Ye, Christopher Z.; Abelson, Chase S.; Reinheimer, Eric W.; LeMagueres, Pierre; Ferrara, Joseph D.; Takase, Michael K.; Johnson, Adam R. (January 2019, Dalton Transactions)

   Alkylation of d - or l -phenylalanine or valine alkyl esters was carried out using methyl or phenyl Grignard reagents. Subsequent condensation with salicylaldehyde, 3,5-di- tert -butylsalicylaldehyde, or 5-fluorosalicylaldehyde formed tridentate, X 2 L type, Schiff base ligands. Chiral shift NMR confirmed retention of stereochemistry during synthesis. X-ray crystal structures of four of the ligands show either inter- or intramolecular hydrogen bonding interactions. The ligands coordinate to the titanium reagents Ti(NMe 2 ) 4 or TiCl(NMe 2 ) 3 by protonolysis and displacement of two equivalents of HNMe 2 . The crystal structure of one example of Ti(X 2 L)Cl(NMe 2 ) was determined and the complex has a distorted square pyramidal geometry with an axial NMe 2 ligand. The bis-dimethylamide complexes are active catalysts for the ring closing hydroamination of di- and trisubstituted aminoallenes. The reaction of hepta-4,5-dienylamine at 135 °C with 5 mol% catalyst gives a mixture of 6-ethyl-2,3,4,5-tetrahydropyridine (40–72%) and both Z - and E -2-propenyl-pyrrolidine (25–52%). The ring closing reaction of 6-methyl-hepta-4,5-dienylamine at 135 °C with 5 mol% catalyst gives exclusively 2-(2-methyl-propenyl)-pyrrolidine. The pyrrolidine products are obtained with enantiomeric excesses up to 17%. 

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4. The Effect of Surface Terminations on the Initial Stages of TiO ₂ Deposition on Functionalized Silicon

   https://doi.org/10.1002/cphc.202200724  

   Parke, Tyler; Silva‐Quinones, Dhamelyz; Wang, George_T; Teplyakov, Andrew_V (January 2023, ChemPhysChem)

   Abstract As atomic layer deposition (ALD) emerges as a method to fabricate architectures with atomic precision, emphasis is placed on understanding surface reactions and nucleation mechanisms. ALD of titanium dioxide with TiCl₄and water has been used to investigate deposition processes in general, but the effect of surface termination on the initial TiO₂nucleation lacks needed mechanistic insights. This work examines the adsorption of TiCl₄on Cl−, H−, and HO− terminated Si(100) and Si(111) surfaces to elucidate the general role of different surface structures and defect types in manipulating surface reactivity of growth and non‐growth substrates. The surface sites and their role in the initial stages of deposition are examined by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Density functional theory (DFT) computations of the local functionalized silicon surfaces suggest oxygen‐containing defects are primary drivers of selectivity loss on these surfaces. 

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5. Cu ₄ MnGe ₂ S ₇ and Cu ₂ MnGeS ₄ : two polar thiogermanates exhibiting second harmonic generation in the infrared and structures derived from hexagonal diamond

   https://doi.org/10.1039/D1DT02535J  

   Glenn, Jennifer R.; Cho, Jeong Bin; Wang, Yiqun; Craig, Andrew J.; Zhang, Jian-Han; Cribbs, Marvene; Stoyko, Stanislav S.; Rosello, Kate E.; Barton, Christopher; Bonnoni, Allyson; et al (December 2021, Dalton Transactions)

   The new, quaternary diamond-like semiconductor (DLS) Cu 4 MnGe 2 S 7 was prepared at high-temperature from a stoichiometric reaction of the elements under vacuum. Single crystal X-ray diffraction data were used to solve and refine the structure in the polar space group Cc. Cu 4 MnGe 2 S 7 features [Ge 2 S 7 ] 6− units and adopts the Cu 5 Si 2 S 7 structure type that can be considered a derivative of the hexagonal diamond structure. The DLS Cu 2 MnGeS 4 with the wurtz-stannite structure was similarly prepared at a lower temperature. The achievement of relatively phase-pure samples, confirmed by X-ray powder diffraction data, was nontrival as differential thermal analysis shows an incongruent melting behaviour for both compounds at relatively high temperature. The dark red Cu 2 MnGeS 4 and Cu 4 MnGe 2 S 7 compounds exhibit direct optical bandgaps of 2.21 and 1.98 eV, respectively. The infrared (IR) spectra indicate potentially wide windows of optical transparency up to 25 μm for both materials. Using the Kurtz–Perry powder method, the second-order nonlinear optical susceptibility, χ (2) , values for Cu 2 MnGeS 4 and Cu 4 MnGe 2 S 7 were estimated to be 16.9 ± 2.0 pm V −1 and 2.33 ± 0.86 pm V −1 , respectively, by comparing with an optical-quality standard reference material, AgGaSe 2 (AGSe). Cu 2 MnGeS 4 was found to be phase matchable at λ = 3100 nm, whereas Cu 4 MnGe 2 S 7 was determined to be non-phase matchable at λ = 1600 nm. The weak SHG response of Cu 4 MnGe 2 S 7 precluded phase-matching studies at longer wavelengths. The laser-induced damage threshold (LIDT) for Cu 2 MnGeS 4 was estimated to be ∼0.1 GW cm −2 at λ = 1064 nm (pulse width: τ = 30 ps), while the LIDT for Cu 4 MnGe 2 S 7 could not be ascertained due to its weak response. The significant variance in NLO properties can be reasoned using the results from electronic structure calculations. 

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