Reductions of M{N(SiMe3)2}3 (M = V, Cr, Fe): Terminal and Bridging Low-Valent First-Row Transition Metal Hydrido Complexes and "Metallo-Transamination"

Synthesis and Reactivity of Bis-tris(pyrazolyl)borate Lanthanide/Aluminum Heterobimetallic Trihydride Complexes

Molecular heterobimetallic hydride complexes of lanthanide (Ln) and main-group (MG) metals exhibit chemical properties unique from their monometallic counterparts and are highly reactive species, making their synthesis and isolation challenging. Herein, molecular Ln/Al heterobimetallic trihydrides [Ln(Tp)2(μ-H)2Al(H)(N″)] [2-Ln; Ln = Y, Sm, Dy, Yb; Tp = hydrotris(1-pyrazolyl)borate; N″ = N(SiMe3)2] have been synthesized by facile insertion of aminoalane [Me3N·AlH3] into the Ln-N amide bonds of [Ln(Tp)2(N″)] (1-Ln). Thus, this is a simple synthetic strategy to access a range of Ln/Al hydrides. Reactivity studies demonstrate that 2-Ln is a heterobimetallic hydride, with evidence for the cooperative nature of 2-Ln shown by the catalytic amine-borane dehydrocoupling under ambient conditions in contrast to its monomeric counterparts.

Hydrides, Halides, and Polymers: Some Unexpected Intermediates on the Routes to First-Row Transition Metal M{N(SiMe3)2}n (n = 2, 3) Complexes

The reaction of 2 equiv of LiN(SiMe₃)₂·Et₂O with TiCl₃(NMe₃)₂ or VCl₃(NMe₃)₂ afforded the dimeric, halide bridged complexes [Ti(μ-Cl){N(SiMe₃)₂}₂]₂ (1) or [V(μ-Cl){N(SiMe₃)₂}₂]₂ (2) in moderate yields. The reduction of titanium complex 1 with 3 equiv of 5% (wt) Na/NaCl gave the mixed metal titanium/sodium hydride cluster Ti₂(μ-H)₂{N(SiMe₃)₂}₃{N(SiMe₃)(SiMe₂CH)}(Na) (3), which was formed by activation of two C-H bonds at a single methyl group of one of the bis(trimethylsilyl)amide ligands. Attempts to form the analogous vanadium complex by reduction of 2 gave only intractable products. Treatment of Co{N(SiMe₃)₂}₂ with 1 equiv of BrN(SiMe₃)₂ (which was previously shown to give the unique three-coordinate cobalt(III) trisamide Co{N(SiMe₃)₂}₃) afforded the polymeric [(μ-Br)Co{μ-N(SiMe₃)(SiMe₂CH₂CH₂Me₂Si)(Me₃Si)μ-N}Co(μ-Br)]_∞ (4) as a second product, which was shown by a structural analysis to possess a carbon-carbon bond formed between the two ligands. Attempts to isolate manganese and iron complexes analogous to 4 were unsuccessful. The role of bromine in these reactions was further studied by examining the reaction of 0.5 equiv of elemental bromine with [Mn{N(SiMe₃)₂}₂]₂ or [Co{N(SiMe₃)₂}₂]₂, which for manganese was shown to give the previously reported manganese trisamide Mn{N(SiMe₃)₂}₃ but for cobalt gives the dimeric amide-bridged [Co(Br){μ-N(SiMe₃)₂}]₂ (5).

Poly(2-Hydroxyethyl methacrylate-co-N,N-dimethylacrylamide)-Coated Quartz Crystal Microbalance Sensor: Membrane Characterization and Proof of Concept

Application-oriented hydrogel properties can be obtained by modifying the synthesis conditions of the materials. The purpose of this study is to achieve customized properties for sensing applications of hydrogel membranes based on poly(2-hydroxyethyl methacrylate), HEMA and N,N-dimethylacrylamide, DMAa. Copolymer p(HEMA-co-DMAa) hydrogels were prepared by varying the DMAa monomer ratio from 0-100% in 20% increments. Hydrogel membranes were characterized by attenuated infrared spectroscopy. Swelling and sorption were evaluated using cation solutions. Copolymers were also synthesized on the gold surface of quartz crystal microbalances (QCM) as coating membranes. A proof of concept was conducted for approaching the design and development of QCM sensors based on P(DMAa-co-HEMA)-membranes. Results showed that the water and ion adsorption capacity of hydrogel membranes increased with higher DMAa content. Membranes are not selective to a specific location but did show different transport features with each cation. The QCM coated with the selected membrane presented linear relationships between resonance frequency and ions concentration in solution (10-120 ppm). As a consequence, hydrogel membranes obtained are promising for the development of future biosensing devices.