Hemilabile β-Aminophosphine Ligands Derived from 1,3,5-Triaza-7-phosphaadamantane: Application in Aqueous Ruthenium Catalyzed Nitrile Hydration

Abstract

A series of β-aminophosphines derived from 1,3,5-triaza-7-phosphaadamantane (PTA) are described. PTA-CHPhNHPh (1), PTA-CH(p-C(6)H(4)OCH(3))NHPh (2), and PTA-CPh(2)NHPh (3) were prepared in good yield (62-77%) by reaction of lithiated PTA with the corresponding imine followed by hydrolysis. Compounds 1 and 2 were synthesized as pairs of diastereomers which were separated by successive recrystallization from THF/hexane. Compounds 1-3 are somewhat soluble in water (S(25)(o) = 4.8 (1), 4.9 (2), 2.7 (3) g/L). Upon coordination to Ru(II) arene centers both monodentate (κ(1)-P) [RuCl(2)(η(6)-toluene)(1-3)] and bidentate (κ(2)-P,N) [RuCl(η(6)-toluene)(1-3)]Cl coordination modes were observed. Ru(II) arene complexes 4-6 exhibited hemilabile behavior transitioning between κ(1)-P and κ(2)-P,N coordination upon change in solvent or addition of a coordinating ligand such as Cl(-) or CH(3)CN. Complexes (4-6) were found to be active air stable catalysts for the aqueous phase hydration of various nitriles with TOF up to 285 h(-1) and TON of up to 97,000 observed.

Metal-catalyzed nitrile hydration reactions: The specific contribution of ruthenium

“…Interestingly, [RuCl 2 (PTA) 4 ] tolerated the presence of air and the catalytic reactions could be carried under atmospheric conditions (no inert atmosphere required). The arene-ruthenium(II) complex 25, containing a β-aminophosphine ligand derived from 1,3,5-triaza-7-phosphaadamantane (PTA), proved to be also active in water under aerobic conditions (Scheme 11) [38]. Thus, using a 5 mol% of this complex, various aromatic and aliphatic organonitriles could be transformed into the corresponding amides in moderate to good yields after 24 h of heating (TOF up to 3 h -1 ).…”

Ruthenium-Catalyzed Amide-Bond Formation

“…More likely, the intrinsic basic nature of the pendant amino group of the aryl-phosphines would increase the concentration of the more nucleophilic hydroxide anion in the solution, thus accelerating the hydration process ( Figure 2). The use as auxiliary ligands derived from the aminophosphine PTA (1,3,5-triaza-7-phosphaadamantane) and related water-soluble "cage-like" phosphines has led in recent years to highly efficient ruthenium catalysts for nitrile hydration in pure water [40][41][42][43][44]. Complexes 4-8 are the most representative examples (Figure 3).…”

“…Interestingly, performing the catalytic hydration of benzonitrile with only 0.001 mol% of complexes 5 and 6 turnover numbers of 22000 and 97000, respectively, could be attained. However, very long reaction times of 97 (5) [42] and 14 (6) [44] days were needed to achieve such a high productivity. It is also worthy of note that, after selective crystallization of the final amides, recycling of the aqueous phase containing complexes 4 (2 times) [40] and 5 (6 times) [42] was possible.…”

Water soluble diphosphine ligands based on 1,3,5-triaza-7-phosphaadamantane (PTA-PR2): Synthesis, coordination chemistry, and ruthenium catalyzed nitrile hydration

“…[1][2][3] Ruthenium compounds have been utilized as catalysts for nitrile hydration with [(η 6 -arene)RuCl 2 PR 3 ] complexes as some of the most efficient and versatile catalysts with good substrate tolerance. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Ruthenium complexes of 1,3,5-triaza-7-phosphaadamtane (PTA) [11,12,[15][16][17] and derivatives [10] have exhibited high activity and selectivity for the hydration of nitriles to amides. We have shown that some ruthenium complexes with PTA or PTA derivatives are active for nitrile hydration in the presence of air, removing the need to run these reactions under inert atmosphere.…”