Solvent-mediated chemoselective reduction of aldehydes by using tributyltin hydride in methanol, aqueous organic solvents, or water: An environmentally benign process

Versatile Catalytic Hydrogenation Using A Simple Tin(IV) Lewis Acid

“…[13] Specifically,o ur interest was drawn to stannylium ion "R 3 Sn + "( R = alkyl) LAs; [14] these are isolobal with Ar 3 B species commonly employed in FLP chemistry,and have been calculated to possess similar hydride ion affinities (DG H À = 65.83 and 64.95 kcal mol À1 for nBu 3 Sn-H and [H-B(C 6 F 5 ) 3 ] À respectively), [15] suggesting that they ought to demonstrate comparable reactivity in FLP H 2 activation and hydrogenation reactions.F urthermore,C = Or eductions by R 3 SnH in protic media are well known to occur via ionic hydride transfer. [16] Crucially,however, these LAs interact only much more weakly with hydroxylic species [for example, (nBu 3 Sn·x H 2 O) + ;pK a (H 2 O) = 6.25]. [17] Manners et al have previously investigated the use of nBu 3 SnOTf (an nBu 3 Sn + equivalent;T f= CF 3 SO 2 )a saL A partner in FLP chemistry, [13a] but reported that it was not capable of activating H 2 when combined with the strong amine base TMP (2,2,6,6-tetramethylpiperidine) at 50 8 8C, whereas the B(C 6 F 5 ) 3 /TMP FLP readily cleaves H 2 ,e ven at room temperature; [18] this result was attributed to the poorer electrophilicity of the Sn compound, and it is evident that the Sn-OTf interaction is strong enough to substantially reduce the Lewis acidity of the nBu 3 Sn + fragment.…”