Rhodium-catalysed isomerisation of allylic alcohols in water at ambient temperature

Single Site Supported Cationic Rhodium(I) Complexes for the Selective Redox Isomerization of Allylic Alcohols

“…Very recently,w ef ound ac ationic Rh I complex that catalyzes the isomerization of allylic alcohols with low catalyst loadings and water as the sole solventata mbient temperatures. [13] Althoughe xcellent resultsh ave been achieved in the isomerization of allylic alcohols using the abovementioned complexes (up to 99 %y ield under mild reaction conditions), we observedt hat the separation of the products from trace amountso ft he metal catalysts was sometimes difficult. Immobilizationo ft he transition-metalc omplexes onto an inorganic support could overcome this problem.…”

“…Cleavage of the CÀOH bond was not observed fora ny of the substrates. We propose the mechanism shown in Scheme 4, similar to that proposed by Trost [44] and us, [11][12][13] and studied theoreticallyb yC adierno, Sordo, and Gimeno [7] for homogeneous complexes.I ti nvolves 18 ( …”

“…[4,5] Several complexeso fr hodium have been successfully immobilized on mesoporous silica materials and used as catalysts in different reactions, such as hydrogenations, [23,24] hydroformylations, [25] acetylene cyclotrimerization, [26] and transfer hydrogenation. [27] These results, together with our experience on the isomerizationo fa llylic alcohols using ac ationic rhodium complexi nw ater, [13] prompted us to evaluate the activity of such complexes immobilized on inorganic supports.…”

“…The majority of these are water soluble complexes used in biphasic solvent systems( water/organic solvent). [13,21] To the besto fo ur knowledge, there is only one example in which at ransition-metal complex (Ru(OH) x )w as immobilizedo nto an inorganic support (Al 2 O 3 )a nd used in the isomerization of allylic alcohols. [22] The catalytic system was intrinsically heterogeneous and could be recycled.…”

“…[4,5] It is only in the last few years that metal complexesw ere found to catalyze the reaction under mild reactionc onditions with high efficiency and selectivity. [6][7][8][9][10][11][12][13] Previously,w ereported the use of RuÀCl [10,11] and RhÀCl [12] complexes together with potassium tert-butoxide (KOtBu) as ac ocatalyst for this reactioni no rganic solvents. Very recently,w ef ound ac ationic Rh I complex that catalyzes the isomerization of allylic alcohols with low catalyst loadings and water as the sole solventata mbient temperatures.…”