Catecholborane

Abstract: Previously, we reported the palladium-catalyzed cross-coupling reaction of 1-alkenylboron compounds with various vinylic or aryl halides in the presence of base to provide corresponding coupling products in good yields, stereoand regioselectively. The recent progress of such reactions is discussed. Most recently, it has been found that B-alkylorganoboranes react readily with vinylic halides or haloarenes in the presence of special palladium catalyst and base. Furthermore, even the most difficult cross-coupling of B-alkyl-9-BBN with alkyl iodides has been demonstrated to proceed smoothly to give coupling alkane derivatives in moderate yields under special conditions. Finally, it will be discussed that B-alkyl-9-BBN derivatives react with iodoalkanes under carbon monoxide atmosphere in the presence of potassium phosphate and a catalytic amount of Pd(PPh,),, yielding unsymmetrical ketones in excellent yields. The reaction is extremely accelerated by irradiation of light. RECENT PROGRESS OF CROSS-COUPLING REACTION U S I N G 1 -ALKENYLBORANES Previously we reported a simple and versatile synthesis leading to conjugated (E,E)-, (E,Z)-, (Z,E)-, and (Z,Z)alkadienes (ref. 1) via a cross-coupling reaction of (E)or (Z)-1-alkenyldisiamylboranes or 2-[(E)-l-alkenyl1-1,3,2benzodioxaboroles (B-1-alkenylcatecholboranes) with either (E)or (Z)-1-alkenyl halides in the presence of a catalytic amount of palladium catalyst and base in benzene. The coupling with (E)-1-alkenylboronic acids or their esters prepared by hydroboration of alkynes with catecholborane always gives the expected dienes in 80-90% yields, while the coupling reactions with (Z)-1-alkenyldisiamyl(Ia) or (Z)-1-alkenyldicyclohexylboranes (Ib) give relatively poor yields of the coupling products (4), less than 50%. One of the major reasons for this difficulty appears to be due to the side reaction arising from the two alkyl groups on boron atom. In order to overcome this, we have attempted to use (Z)-1-alkenylboronates (3), f i t prepared by Brown and Imai (ref. 2). The reactions 1 a : R~ = siamyi 1 b : R2 cyclohexyl

Abstract: Nickel hydride with a diphosphinite-based ligand catalyzes the highly efficient reduction of CO2 with catecholborane, and the hydrolysis of the resulting methoxyboryl species produces CH3OH in good yield. The mechanism involves a nickel formate, formaldehyde, and a nickel methoxide as different reduced stages for CO2. The reaction may also be catalyzed by an air-stable nickel formate.

Abstract: In this work, we report that organocatalyst 1-Bcat-2-PPh2–C6H4 ((1); cat = catechol) acts as an ambiphilic metal-free system for the reduction of carbon dioxide in presence of hydroboranes (HBR2 = HBcat (catecholborane), HBpin (pinacolborane), 9-BBN (9-borabicyclo[3.3.1]nonane), BH3·SMe2 and BH3·THF) to generate CH3OBR2 or (CH3OBO)3, products that can be readily hydrolyzed to methanol. The yields can be as high as 99% with exclusive formation of CH3OBR2 or (CH3OBO)3 with TON (turnover numbers) and TOF (turnover frequencies) reaching >2950 and 853 h–1, respectively. Furthermore, the catalyst exhibits “living” behavior: once the first loading is consumed, it resumes its activity on adding another loading of reagents.