Multistep self-assembly of heteroleptic magnesium and sodium-magnesium benzamidinate complexes

Reaction of the magnesium bis-alkyl Mg(CH2SiMe3)(2) and the sodium amide NaHMDS (where HMDS = N(SiMe3)(2)) with benzonitrile yields the homometallic heteroleptic complex [PhC(NSiMe3)(2)Mg{mu-NC(CH2SiMe3)Ph}](2) (1). It appears that at least six independent reactions must have occurred in this one-pot reaction to arrive at this mixed benzamidinate ketimido product. Two benzonitrile solvated derivatives of Mg(CH2SiMe3)(2) (5a and 5b) have been synthesized, with 5a crystallographically characterized as a centrosymmetric (MgC)(2) cyclodimer. When, the components of 5a are allowed to react for longer, partial addition of the Mg-alkyl unit across the C N triple bond occurs to yield the trimeric species (Me3SiCH2)(2)Mg-3[mu-N=C(CH2SiMe3)Ph](4)center dot 2N CPh (6), with bridging ketimido groups and terminal alkyl groups. Finally, using the same starting materials as that which produced 1, but altering their order of addition, a magnesium bis-alkyl unit is inserted into the Na-N bonds of a benzamidinate species to yield a new sodium magnesiate complex, PhC(NSiMe3)(2)Mg(mu-CH2SiMe3)(2)Na center dot 2TMEDA (7). The formation of 7 represents a novel (insertion) route to mixed-metal species of this kind and is the first Such example to contain a bidentate terminal anion attached to the divalent metal center. All new species are characterized by H-1 and C-13 NMR spectroscopy and where appropriate by IR spectroscopy. The solid-state structures of complexes 1, 5a, and 7 have also been determined and are disclosed within

Remote functionalisation via sodium alkylamidozincate intermediates : access to unusual fluorenone and pyridyl ketone reactivity patterns

Treating fluorenone or 2-benzoylpyridine with the sodium zincate [(TMEDA)center dot Na(mu-Bu-t)(mu-TMP)Zn(Bu-t)] in hexane solution, gives efficient Bu-t addition across the respective organic substrate in a highly unusual 1,6-fashion, producing isolable organometallic intermediates which can be quenched and aerobically oxidised to give 3-tert-butyl-9H-fluoren-9-one and 2-benzoyl-5-tert-butylpyridine respectively

The applicability of the standard DIN EN ISO 3690 for the analysis of diffusible hydrogen content in underwater wet welding

The European standard ISO 3690 regulates the measurement of diffusible hydrogen in arc-welded metal. It was designed for different welding methods performed in dry atmosphere (20% humidity). Some details of the standard are not applicable for wet underwater welding. The objective of this study was to extend the applicability of DIN EN ISO 3690:2018-12 to underwater wet-shielded metal arc welding (SMAW). Four different aspects regulated within the standard were accounted for: (1) sample dimensions and number of samples taken simultaneously; (2) time limitations defined by the standard regarding the welding and the cleaning process; (3) time, temperature, and method defined for analysis of the diffusible hydrogen content; (4) normalization of the hydrogen concentration measured. Underwater wet welding was performed using an automated, arc voltage-controlled welding machine. The results are discussed in light of standard DIN EN ISO 3690, and recommendations are provided for the analysis of diffusible hydrogen content upon underwater wet welding. © 2020 by the authors

Control of the diffusible hydrogen content in different steel phases through the targeted use of different welding consumables in underwater wet welding

Due to the rising number of offshore structures all over the world, underwater wet welding has become increasingly relevant, mainly as a repair method. Welding in direct contact with water involves numerous challenges. A topic focused by many studies is the risk of hydrogen-induced cracking in wet weldments due to hardness values of up to 500 HV 0.2 in the heat-affected zone (HAZ) and high levels of diffusible hydrogen in the weld metal. The risk of cracking increases as the equivalent carbon content rises, because the potential to form martensitic structures within the HAZ rises too. Thus, high-strength steels are especially prone to hydrogen-induced cracking and are considered unsafe for underwater wet repair weldments. © 2020 The Authors. Materials and Corrosion published by Wiley-VCH Gmb

Induction Heating in Underwater Wet Welding—Thermal Input, Microstructure and Diffusible Hydrogen Content

Hydrogen-assisted cracking is a major challenge in underwater wet welding of high-strength steels with a carbon equivalent larger than 0.4 wt%. In dry welding processes, post-weld heat treatment can reduce the hardness in the heat-affected zone while simultaneously lowering the diffusible hydrogen concentration in the weldment. However, common heat treatments known from atmospheric welding under dry conditions are non-applicable in the wet environment. Induction heating could make a difference since the heat is generated directly in the workpiece. In the present study, the thermal input by using a commercial induction heating system under water was characterized first. Then, the effect of an additional induction heating was examined with respect to the resulting microstructure of weldments on structural steels with different strength and composition. Moreover, the diffusible hydrogen content in weld metal was analyzed by the carrier gas hot extraction method. Post-weld induction heating could reduce the diffusible hydrogen content by −34% in 30 m simulated water depth

Effect of the water depth on the hydrogen content in SMAW wet welded joints

Hydrogen-induced cold cracking is a huge challenge in underwater wet welding. In the present study, the influence of water depth on the diffusible and residually stored hydrogen content is investigated for the case of underwater wet shielded metal arc welding. The welding is carried out in a simulated water depth of 5, 20, 40, and 60 m with four stick electrodes specifically developed for underwater wet welding. The influence of the welding current, the arc voltage and the electrode’s composition on the diffusible hydrogen content are considered. To obtain reproducible welding conditions, a fully automated multi-axis welding system is used inside a pressure chamber. The water depth is simulated by setting the internal pressure up to 6 bar, equivalent to 60 m water depth. A large amount of samples are analysed and statistical method are used to evaluate the results. The results show a significant reduction of the diffusible hydrogen and an increase of residual hydrogen in the joining zone with increasing water depth

Structural elaboration of the surprising ortho-zincation of benzyl methyl ether

Breaking with convention, the reaction of the sodium zincate, [(TMEDA)Na(μ-TMP)(μ-tBu)Zn(tBu)] with benzyl methyl ether (PhCH2OMe) produces exclusively an ortho-zincated intermediate [(TMEDA)Na(μ-TMP)(μ-C6H4CH2OMe)Zn(tBu)] instead of the expected 'thermodynamic' α-metallated product

Potassium-mediated zincation of ferrocene and ruthenocene : potassium, the architect behind supramolecular structural variations

Direct zincation of ferrocene and ruthenocene by the synergic base [PMDETA.K(μ-TMP)(μ-Me)Zn(Me)] produces the monozincated complexes [{PMDETA.K(μ-Me)2Zn(Fc)}∞] and [{PMDETA.K(μ-Me)2Zn(Rc)}2] respectively, having similar monomeric (dinuclear) units but aggregating supramolecularly in very different polymeric and dimeric forms