A Fluorinated Cobalt(III) Porphyrin Complex for Hydroalkoxylation of Alkynes

Abstract

A fluorinated cobalt(III) porphyrin complex [Co(TPFPP)- (Fig. 1). This method compares well with the earlier procedures catalyzed by Hg, 6,7) Pd, [8][9][10] Pt, 9,11,12) Au, [13][14][15][16][17][18][19][20][21][22] Ir [23][24][25][26] and Zn. 27)The active pentafluorophenylated Co III catalyst 1a was developed by structural modification of 1b used previously for alkyne hydration 2) (Fig. 1). Reaction of tetrakis(pentafluorophenyl) porphyrin (H 2 TPFPP) and cobalt(II) acetate 28) followed by aerobic oxidation in the presence of HNTf 2 and recrystallization from a mixture of chloroform, ethanol, and hexane afforded 1a in 67% yield. X-Ray structural analysis of 1a indicated that (1) the cobalt center adopts octahedral geometry, with porphyrin ligand in the equatorial positions and ethanol in the apical positions (Fig. 2); (2) Figure S1(a)].The catalyst 1a was found to be more reactive than 1b in the hydroalkoxylation of phenylacetylene (2a) with methanol (Table 1, entries 1 vs. 7). When a mixture of 2a (2.0 mmol), 1a (0.05 mol%), and HNTf 2 (0.18 mol%) in methanol (0.9 mL, 11 equiv) was heated at 70°C for 4 h under aerobic conditions, acetal 3a was obtained in 97% yield (entry 1).29) The initial turnover frequency (TOF) was 4000 h −1 (t=12 min). This value is comparable to those of gold catalysts and higher than those of catalysts based on other metals (entry 2). 30) Hydroalkoxylation of 2a in the absence of HNTf 2 required higher catalyst loading (entries 3 and 4). The reaction proceeded under N 2 atmosphere, but yielded 3a in a lower yield than that under air (entry 5 vs. entry 1). Double hydroalkoxylation of 2a at 27°C (room temperature) afforded acetal 3a in 97% yield (entry 6). Co III TPPCl [TPP=5,10,15, porphyrin] was less reactive than 1a and 1b (entry 8 vs. entries 1 and 7). The reaction hardly proceeded with analogous metal complexes such as Fe III TPPCl or Mn III TPPCl under otherwise identical conditions (entries 9 and 10).* To whom correspondence should be addressed. e-mail: h_naka@nagoya-u.jp

Catalytic Transfer Hydration of Cyanohydrins to α-Hydroxyamides

“…During the course of our recent study seeking efficient methods for catalytic hydration of unsaturated organic compounds, we found that the use of palladium chloride and carboxamide − allows the hydration of acetone cyanohydrin ( 1a ). The conversion of nitriles to amides by palladium chloride and acetamide was initially described by Maffioli et al as a reverse reaction of the dehydration of amides to nitriles .…”

Water as a key ingredient in the synthesis of platinum H‐phosphonate complexes and catalytic cascade reactions involving the hydration of alkynes and hydrogen/deuterium exchange reaction

“…It is worth mentioning that the reaction is specific to water. Acetophenone was formed in the system, and no evidence of hydroalkoxylation reaction products was detected 35 …”

Applications of Fluorous Porphyrinoids: An Update†

“…Ushimaru et al . (61) reported that the fluorinated Co(III) porphyrinoid, CoTPPF 20 ‐NTf 2 ·2C 2 H 5 OH (where Tf = CF 3 SO 2 ) can catalyze the conversion of both aliphatic and aromatic terminal alkynes into acetals in excellent yield. These can then be further functionalized by attacking the acetals with desired nucleophiles.…”