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The catalytic hydroboration of imines, nitriles, and carbodiimides is a powerful method of preparing amines which are key synthetic intermediates in the synthesis of many value-added products. Imine hydroboration has perennially featured in notable reports while nitrile and carbodiimide hydroboration have gained attention recently. Initial developments in catalytic hydroboration of imines and nitriles employed precious metals and typically required harsh reaction conditions. More recent advances have shifted toward the use of base metal and main group element catalysis and milder reaction conditions. In this survey, we review metal and nonmetal catalyzed hydroboration of these unsaturated organic molecules and group them into three distinct categories: precious metals, base metals, and main group catalysts. The TON and TOF of imine hydroboration catalysts are reported and summarized with a brief overview of recent advances in the field. Mechanistic and kinetic studies of some of these protocols are also presented. 

Convergent paired electrolysis combines both anodic and cathodic reactions simultaneously in an electrochemical transformation. It provides a highly energy‐efficient and divergent approach to conventionally challenging and useful structures. However, the physical separation of the two half‐electrode reactions makes it extremely difficult to couple the intermediates arising from the two electrodes. In this concept article, four strategies used in convergent paired electrolysis will be discussed from the perspective of the reaction mechanism: a) metal‐catalyzed convergent paired electrolysis, b) convergent paired electrolysis enabled by persistent radical effects, c) microfluidic chemistry applied to convergent paired electrolysis, and d) alternating current electrolysis.

 

α‐Diimine ligands have contributed extensively to the coordination chemistry of the majority of the transition metals; bis(arylimino)acenaphthene ligands (BIANs) have been widely studied and found to offer great versatility in their application as supporting ligands in catalytic transformations. In recent years, BIAN‐based iron complexes have proven effective in mediating a number of reductive transformations which includes hydrosilylation, hydroboration and hydrogenation chemistries. This review highlights the most recent contributions to the field. In our initial 2015 communication, we disclosed that the arene‐capped Fe(0) species^ArBIAN−Fe(toluene) mediates aldehyde and ketone hydrosilylation with exceptional activity under solvent‐free conditions. This led us to the discovery that such systems were capable of the hydrosilylation of imines and esters, the hydroboration of imines, aldehydes, ketones, alkenes, and alkynes and even the ring‐opening polymerization ofrac‐lactide. Spectroscopic and computational studies have firmly established the importance of redox non‐innocence in BIAN complexes and detailed mechanistic studies have revealed the importance of spin‐state‐crossing in catalysis. Although this work represents only a small component of advances in iron catalysis, our efforts have proven influential in Fe‐based approaches to reductive transformations and is likely to continue to inform the design of Fe‐based catalysts.

 

Iron complexes [BIAN]Fe(I)(η⁶‐toluene) (M1) and [BIAN]FeCl₂(M2) (BIAN=bis(2,6‐diisopropylaniline)acenaphthene) were found to be viable catalysts for the regioselective hydroboration of alkynes and alkenes. The hydroboration of alkynes and alkenes in the presence of HBpin and an activator at 70 °C afforded linear vinyl and alkyl boronic esters, respectively. Selectivity up to 98% was observed for alkyl boronic esters and exclusive formation of trans product was observed for vinyl boronic esters.

 

Arylation of carbonyls, one of the most common approaches toward alcohols, has received tremendous attention, as alcohols are important feedstocks and building blocks in organic synthesis. Despite great progress, there is still a great gap to develop an ideal arylation method featuring mild conditions, good functional group tolerance, and readily available starting materials. We now show that electrochemical arylation can fill the gap. By taking advantage of synthetic electrochemistry, commercially available aldehydes (ketones) and benzylic alcohols can be readily arylated to provide a general and scalable access to structurally diverse alcohols (97 examples, >10 gram‐scale). More importantly, convergent paired electrolysis, the ideal but challenging electrochemical technology, was employed to transform low‐value alcohols into more useful alcohols. Detailed mechanism study suggests that two plausible pathways are involved in the redox neutral α‐arylation of benzylic alcohols.

 

Arylation of carbonyls, one of the most common approaches toward alcohols, has received tremendous attention, as alcohols are important feedstocks and building blocks in organic synthesis. Despite great progress, there is still a great gap to develop an ideal arylation method featuring mild conditions, good functional group tolerance, and readily available starting materials. We now show that electrochemical arylation can fill the gap. By taking advantage of synthetic electrochemistry, commercially available aldehydes (ketones) and benzylic alcohols can be readily arylated to provide a general and scalable access to structurally diverse alcohols (97 examples, >10 gram‐scale). More importantly, convergent paired electrolysis, the ideal but challenging electrochemical technology, was employed to transform low‐value alcohols into more useful alcohols. Detailed mechanism study suggests that two plausible pathways are involved in the redox neutral α‐arylation of benzylic alcohols.

 

The syntheses of the 2,9‐dimesityl‐1,10‐phenanthroline (dmesp) metal complexes, [Cu(dmesp)(MeCN)]PF₆(1), [Cu(dmesp)₂]PF₆(2), Fe(dmesp)Cl₂(3), Co(dmesp)Cl₂(4), Ni(dmesp)Cl₂(5), Zn(dmesp)Cl₂(6), Pd(dmesp)MeCl (7), Cu(dmesp)Cl (8), and Pd(dmesp)₂Cl₂(9), in good to high yields are described. These complexes were characterized by¹H and¹³C NMR spectroscopy, HR–MS (ESI and/or APPI), and elemental analysis (CHN). The solid‐state structures of complexes1–8were determined by single‐crystal X‐ray analysis and their photophysical properties were also characterized. To demonstrate the versatility of this new platform, complexes3–5,8, and9were employed in the catalytic oligomerization of ethylene using modified methyl aluminoxane (MMAO) as the cocatalyst, where Co(II) and Ni(II) complexes (4and5, respectively) were found to exhibit moderate selectivity for catalytic dimerization of ethylene to butenes over tri‐ or tetramerization. Complex8is an effective catalyst of both the commonly encountered “click” reaction and amine arylation chemistries. Complexes6and9were found to be excellent catalysts for Friedel‐Crafts alkylation and Suzuki‐Miyaura coupling, respectively.