trans-(6-Amino-2-pyridinio)iodobis(triphenylphosphine)palladium(II) iodide ethyl acetate solvate

Abstract

The title compound, [Pd(C 5 H 6 N 2){(C 6 H 5) 3 P} 2 ]IÁC 4 H 8 O 2 , has a square-planar geometry for Pd, coordinated by two transphosphines, an iodo, and an aminopyridyl ligand. The cation, anion and solvent molecule all lie on a crystallographic mirror plane, and are connected together by NÐHÁ Á ÁI and NÐ HÁ Á ÁO hydrogen bonds. Comment The title compound, (I), was obtained unexpectedly as a byproduct in a reaction exploring the synthesis of enantiomerically pure pyridylamino acids via palladiumcatalysed cross-coupling of serine-derived organozinc reagents with various halopyridines (Tabanella et al., 2003). It is presumably derived from the product of oxidative addition of 2-amino-6-bromopyridine to bis(triphenylphosphine)palladium(0), followed by exchange of bromide for iodide, originating from the zinc reagent. Similar products have been obtained by other researchers in related reactions (Spee et al., 2000; Bocelli et al., 1998).

Preparation of enantiomerically pure pyridyl amino acids from serine

“…Coupling of zinc reagent 2a, prepared from iodide 1a (0.31 g, 0.7 mmol) using procedure A, with 3-bromopyridine (91 µl, 0.9 mmol) using procedure C, gave 4a (0.13 g, 45%) as pale yellow solid; mp 40…”

“…According to general procedure D, 11b (0.76, 2.2 mmol) was obtained from the methyl ester 6b (1 g, 3 mmol), as a yellow solid in 75% yield; mp 165-166 ЊC, [α] D Ϫ9.0 (c 1 in acetone); found C 44.9%, H 4.9, N 7.8, C 13 H 17 N 2 O 4 Br requires C 45.2%, H 5.0, N 8.1; ν max (KBr disc)/cm Ϫ1 3378, 2985, 2973, 1737, 1687, 1548, 1165, 650; δ H (500 MHz, CDCl 3 ) 8.48 (1H, s), 7.74 (1H, d, J 7.0), 7.15 (1H, d, J 7.0), 6.02-5.98 (1H, br s), 4.48-4.45 (1H, m), 3.29-3.27 (1H, m), 3.20-3.18 (1H, m), 1.35 (9H, s) (carboxylic acid proton not observed); δ C (125 MHz, CDCl 3 ) 176.6, 156.7, 155.9, 149.5, 140.0, 125.9, 118.9, 80.0, 54.8, 38.9, 28.3; m/z (EI) 300 (33%), 288 (30), 271 (65), 244 (80), 171 (40), 57 (100).…”

“…According to general procedure D, 12 (0.61, 1.3 mmol) was obtained from the methyl ester 7b (0.72 g, 1.5 mmol) as a white solid in 87% yield; mp 156-158 ЊC; [α] D Ϫ12.0 (c 1 in acetone); found C 44.9%, H 4.9, N 7.9, C 13 H 17 N 2 O 4 Br requires C 45.2%, H 4.9, N 7.9; ν max (KBr disc)/cm Ϫ1 3330, 2980, 1725, 1686, 1518, 1166; δ H (500 MHz, CDCl 3 ) 7.58 (1H, app t, J 7.5), 7.43 (1H, d, J 7.5), 7.27 (1H, d, J 7.5), 5.81 (1H, d, J 6.0), 4.59-4.56 (1H, m), 3.36-3.26 (2H, m), 1.44 (9H, s); δ C (125 MHz, CDCl 3 ) 173.3, 158.7, 155.6, 140.4, 140.0, 126.7, 123.1, 80.4, 52.6, 38.9, 28.3; m/z (EI) 345 (MH ϩ , 80%), 300 (40), 244 (35), 201, 199 (100), 171 (95), 57 (95).…”

“…Coupling of the zinc reagent 15, prepared from 14 (0.34 g, 0.7 mmol) using general procedure A, with 2,6-dibromopyridine (0.11 g, 0.5 mmol) using procedure C, gave the product 16 (46 mg, 10%) as a yellow solid; mp 73-75 ЊC; [α] D ϩ23.8 (c 0.5 in CH 2 Cl 2 ); ν max (KBr disc)/cm Ϫ1 3341, 3003, 2976, 2932, 1724, 1520, 1222, 1154, 739; δ H (500 MHz, CDCl 3 ) 7.74 (2H, d, J 7.5), 7.67 (4H, t, J 7.0), 7.57 (4H, t, J 7.5), 7.50-7.45 (2H, m), 7.34-7.27 (4H, m), 7.17 (1H, q, J 8.0), 7.00 (2H, d, J 8.0), 6.71 (2H, d, J 8.5), 4.88-4.85 (2H, m), 4.22-4.13 (4H, m), 4.05 (2H, t, J 7.5), 3.38 (2H, dd, J AX 6.5, J AB 15.5), 3.27 (2H, dd, J BX 4.0, J AB 15.5), 1.38 (18H, s); δ C (125 MHz, CDCl 3 ) 171.2, 157.0, 156.5, 143.9, 141.1, 136.7, 127.7, 127.0, 125.5, 121.8, 119.8, 81.6, 67.1, 53.2, 47.0, 39.9, 28.0; m/z (EI) 809 (M ϩ , 18%), 708 (8), 631 (16), 587 (65), 486 (34), 430 (40), 178 (100), 165 (31).…”