Chiral Pt(II)/Pd(II) pincer complexes that show C–H⋯Cl hydrogen bonding: Synthesis and applications to catalytic asymmetric aldol and silylcyanation reactions

Unsymmetrical, oxazolinyl-containing achiral and chiral NCN pincer ligand precursors and their complexes with palladium(II)

“…While in the case of electron-rich aryl bromides such as 4-bromoanisole, complex 4a exhibited higher activity than complex 4b (entries 9-10). Similarly, 4c was more active than 4d (entries [11][12]. Among the five Pd complexes, 4c with 4-i-Pr-oxazolinyl and 3,5-dimethyl pyrazolyl group was the most active, providing the 4-methoxybiphenyl in an excellent yield (entries 9-13).…”

“…As shown in Table 4, when the reaction was conducted in DMF at 140°C for 12 h, KFÁ2H 2 O, K 2 CO 3 and Na 2 CO 3 as a base gave excellent yields (entries 1-6). When toluene was used as solvent, excellent yields were also obtained at 110°C after 12 h with KFÁ2H 2 O, K 2 CO 3 , K 3 PO 4 Á3H 2 O and NaOH as a base (entries [7][8][9][10][11][12]. Several other solvents using K 2 CO 3 as the base were also tested.…”

“…Much of the research has focused on symmetrical NCN pincer palladium complexes, which are symmetrical with two identical N donors such as amines [5][6][7], imines [8,9], pyridines [10][11][12], oxazolines [13][14][15][16][17][18][19][20] or other N-containing heterocycles [21,22] and 2 equiv. five-membered palladacycles (Scheme 1).…”

Activation of trimethylsilyl cyanide by potassium phthalimide for facile synthesis of TMS-protected cyanohydrins

“…The cyanosilylation of carbonyl compounds is particularly suitable since the silyl protecting groups can be removed under very mild reaction conditions. The cyanohydrin trimethylsilyl ethers are generally prepared by the addition of trimethylsilyl cyanide (TMSCN), a safe and easily handled reagent compared to HCN and KCN or NaCN [3][4][5][6]21,42], to carbonyl compounds in the presence of Lewis acids [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], inorganic Lewis bases [22][23][24][25], and double activating [3,26] or bifunctional catalytic systems [27][28][29]. However, many of these methods suffer from several disadvantages such as use of heavy and expensive metal catalysts [3,[12][13][14][15][16], high catalyst loading [6,13,14,22,23], the requirement for an inert atmosphere or anhydrous solvents [11][12][13]…”

“…Complete removing or replacement of a safer solvent in a chemical process is likely to often be the greatest reduction and simplification (in the work-up as well as the reaction) that can be achieved [52]. To the best of our knowledge, most of the introduced protocols for cyanosilylation of carbonyl compounds have been reported by using toxic solvents such as DMF [21,[43][44][45], CH 3 CN [1,12,[23][24][25], CHCl 3 [40] or CH 2 Cl 2 [11][12][13][14][15][16][17]19,26,[34][35][36][37][38][39]51] and the number of methods under solvent-free conditions remains quiet limited [5,6,18,33,49]. In continuation of our interest to develop new efficient nucleophilic organocatalysts for cyanosilylation of carbonyl compounds [33][34][35], we herein disclose the application of potassium phthalimide (PPI) as an efficient organocatalyst for the addition of TMSCN to carbonyl compounds under mild and solvent-free conditions affording various cyanohydrin trimethylsilyl ethers (Scheme 1).…”