Orthoalkylation of Aromatic Ketimine with the Vinyl Group in Polybutadiene Using a Rhodium(I) Catalyst

Abstract

Chemical modification of polybutadiene was achieved by orthoalkylation of aromatic ketimine with the vinyl group of ­polybutadiene using a rhodium(I) catalyst. A high 2-acylphenyl group-impregnation ratio was observed with low vinyl group poly­butadiene, likely due to decreased steric congestion between the pendant orthoalkylated groups in the modified polybutadiene.

C-H activation - homogeneous catalysis - transition metal - polymer - rhodium

References and Notes

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13

1a, 1b and 1c were purchased from Aldrich Chemical Co. and polymer specifications are as follows: 1a: MW = 3,400, 100% vinyl, M _w /M _n = 1.26; 1b: MW = 1,300, 43% vinyl and 57% internal, M _w /M _n = 1.09; 1c: MW = 1,500, 27% vinyl and 73% internal olefins, M _w /M _n = 1.08.

14

Typical Procedure for the Catalytic Reaction of 1 and 2 under 3 (Scheme 1, Scheme 2): A screw-capped pressure vial (1 mL) was charged with polybutadiene (1, 0.5 mmol), (PPh₃)₃RhCl (3, 0.025 mmol), ketimine (2, 1.0 mmol) and toluene (150 mg). The solution was stirred in a preheated oil bath (130 °C) for 3 h. After the reaction, the mixture was hydrolyzed using aq. HCl (4 N, 5 mL) and THF (5 mL) for 12 h and the product purified by column chromatography (SiO₂, n-hexane-EtOAc, 8:1). [18]

15

The degree of orthoalkylation (a) of the vinyl could be calculated by the following equation: incorporation rate a (%) = a/(a + b + c) Ž 100%; a = A/2, b = B/2, c = C-B/2. A is the area of 2.81-2.94 ppm (α-CH₂ to CO); B is the area of 4.9-5.0 ppm (vinylic CH₂); C is the area of 5.3-5.6 ppm (vinylic -CH in the vinyl group and internal -CH=C- isomerized from the vinyl group).

16

In o-acylphenyl-group-incorporated polybutadiene, the integration ratio of methylene hydrogens (ArCH₂CH ₂ )-methyl hydrogens of the acetyl group in the ¹H NMR spectra is regarded as 2/3 if these two peaks are not clearly separated. In the case of o-heptanoylphenyl-incorporated polybutadiene, it is presumed that the integration ratio of methylene hydrogens (ArCH₂CH ₂ )-α-methylene hydrogens of the heptanoyl group is 2/2 since these two peaks overlap.

17

The amount of orthoalkylation (a) of the vinyl groups could be calculated by the following equation; incorporation rate = a/(a + b + c) Ž 100%; (a is the orthoalkylated vinyl group, b is the unreacted terminal olefin, c is the isomerized from the vinyl group, and d is the unreacted internal olefin). a = A/2, b = B/2, c = C-B/2-D/2, (a + b + c)/d = 43/57; A is the area of 2.81-2.94 ppm (α-CH₂ to CO); B is the area of 4.9-5.0 ppm (vinylic CH₂); C is the area of 5.3-5.6 ppm (internal -CH=CH- and vinylic -CH).

18

Compound 5aa: IR (CDCl₃): 3064, 2914, 2847, 1682 (CO), 1435, 1354, 1250, 910, 758, 696 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.68-7.12 (br m, in phenyl group), 5.39 (br s, internal -CH=), 4.91 (br s, 2 H, terminal -CH=CH ₂ ), 2.81 (br s, 2 H, ArCH₂), 2.53 (br s, 3 H, COCH₃), 2.02 (br s), 1.50-1.25 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 202.09 (CO), 143.49-125.88, 114.55, 40.03-30.86, 29.90; M _w /M _n = 1.16.
Compound 5ab: IR (CDCl₃): 2922, 2843, 1675 (CO), 1603, 1356, 1247, 1127, 1070, 1033, 910, 812, 732 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.45-6.75 (br m, in phenyl group), 5.40 (br s, internal -CH=), 4.90 (br s, terminal -CH=CH ₂ ), 3.76 (br s, 3 H, ArOCH₃), 2.87 (br s, 2 H, ArCH₂), 2.48 (br s, 3 H, COCH₃), 2.02 (br s), 1.51-1.16 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 199.56 (CO), 162.00, 147.35, 134.96-127.70, 116.80-110.67, 55.33, 39.47-32.03, 29.42; M _w /M _n = 1.13.
Compound 5ac: IR (CDCl₃): 2922, 2851, 1693 (CO), 1496, 1412, 1333, 1248, 1173, 1088, 962, 908, 830, 741 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.64-7.47 (br m, in phenyl group), 5.40 (br s, internal -CH=), 4.93 (br s, terminal -CH=CH ₂ ), 2.82 (br s, 2 H, ArCH₂), 2.57 (br s, 3 H, COCH₃), 2.16-2.02 (br s), 1.51-1.25 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 201.68 (CO), 143.82-115.09, 39.31-32.42, 30.41; M _w /M _n = 1.10.
Compound 5ad: IR (CDCl₃): 2924, 1688 (CO), 1598, 1453, 1118, 910, 735 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.86-6.92 (br m, in phenyl group), 5.58 (br s, internal -CH=), 4.97 (br s, terminal -CH=CH ₂ ), 2.94 (br s, 4 H, ArCH₂, COCH₂), 2.02 (br s), 1.71 (br s), 1.28 (br s), 0.89-0.83 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 200.90 (CO), 143.91, 139.19, 135.41, 132.35-127.87, 122.44, 44.35, 42.46, 33.50, 31.37, 29.01, 25.24, 22.64, 14.62; M _w /M _n = 1.10.
Compound 5ba: IR (CDCl₃): 2921, 2843, 1687 (CO), 1601, 1437, 1352, 1245, 1074, 967, 906, 759 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.63-7.14 (br m, in phenyl group), 5.28 (br m, internal -CH=), 4.94 (br s, terminal -CH=CH ₂ ), 2.81 (br s, 2 H, ArCH₂), 2.60 (br s, 3 H, COCH₃), 2.16 (br s), 1.72-1.21 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 202.19 (CO), 143.38, 138.17, 132.22-125.63, 35.92-29.97; M _w /M _n = 1.14.
Compound 5bb: IR (CDCl₃): 2913, 2246, 1681 (CO), 1567, 1454, 1355, 1233, 1128, 1067, 1030, 964, 911, 807, 747 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.45-6.72 (br m, in phenyl group), 5.40 (br s, internal -CH=), 4.94 (br s, terminal -CH=CH ₂ ), 3.80 (br s, 3 H, ArOCH₃), 2.89 (br s, 2 H, ArCH₂), 2.51 (br s, 3 H, COCH₃), 2.13 (br s), 1.64-1.24 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 199.68 (CO), 162.09, 147.05, 135.07-128.73, 116.99, 110.64, 55.44, 35.43-32.18, 29.60; M _w /M _n = 1.36.
Compound 5bc: IR (CDCl₃): 2922, 2853, 1694 (CO), 1496, 1412, 1332, 1249, 1128, 966, 908, 830, 735cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.64-7.14 (br m, in phenyl group), 5.40 (br s, 1 H, internal -CH=), 4.95 (br s, terminal -CH=CH ₂ ), 2.82 (br s, 2 H, ArCH₂), 2.56 (br s, 3 H, COCH₃), 2.02 (br s), 1.51-1.26 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 201.65 (CO), 143.84, 141.81, 132.36-122.73, 38.15-31.06, 30.29; M _w /M _n = 1.25.
Compound 5bd: IR (CDCl₃): 3056, 2923, 2851, 1654 (CO), 1579, 1482, 1434, 1188, 1092, 1025, 996, 909 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.48-7.17 (br m, in phenyl group), 5.38 (br s, internal -CH=), 4.97 (br s, terminal -CH=CH ₂ ), 2.83 (br s, 4 H, ArCH₂, COCH₂), 2.01 (br s), 1.68 (br s), 1.52-0.87 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 201.94 (CO), 145.82-117.59, 45.64, 32.42-24.57; M _w /M _n = 1.19.
Compound 5ca: IR (CDCl₃): 2926, 2851, 2097, 1682 (CO), 1453, 1352, 1258, 1074, 1029, 906, 750cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.64-7.22 (br m, in phenyl group), 5.40 (br s, internal -CH=), 4.95 (br s, terminal -CH=CH ₂ ), 2.82 (br s, 2 H, ArCH₂), 2.54 (br s, 3 H, COCH₃), 2.03 (br s), 1.63-1.25 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 202.23 (CO), 143.15, 138.15, 134.58-125.77, 35.73-27.63; M _w /M _n = 1.15.
Compound 5cb: IR (CDCl₃): 2922, 2853, 2248, 1681 (CO), 1567, 1454, 1354, 1233, 1121, 1067, 1030, 966, 911, 808, 737 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.68-7.25 (br m, in phenyl group), 6.73 (br s, in phenyl group), 5.40 (br s, internal -CH=), 4.94 (br s, terminal -CH=CH ₂ ), 3.80 (br s, 3 H, ArOCH₃), 2.89 (br s, 2 H, ArCH₂), 2.50 (br s, 3 H, COCH₃), 2.02 (br s), 1.49-1.35 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 199.89 (CO), 162.21, 147.27, 132.80-128.89, 116.94, 110.51, 55.60, 35.61-32.16, 29.40; M _w /M _n = 1.25.
Compound 5cc: IR (CDCl₃): 2919, 2847, 1693 (CO), 1496, 1437, 1332, 1249, 1126, 966, 892, 831, 743 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.51-7.11 (br m, in phenyl group), 5.41 (br s, internal -CH=), 4.95 (br s, terminal -CH=CH ₂ ), 2.82 (br s, 2 H, ArCH₂), 2.56 (br s, 3 H, COCH₃), 2.03 (br s), 1.62-1.22 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 201.37 (CO), 143.71-122.43, 114.50, 36.60-30.47, 27.40; M _w /M _n = 1.27.
Compound 5cd: IR (CDCl₃): 3057, 2928, 1658 (CO), 1576, 1489, 1434, 1188, 1093, 1029, 909 cm^-1; ¹H NMR (400 MHz, CDCl₃): δ = 7.52-7.20 (br m, in phenyl group), 5.39 (br s, internal -CH=), 4.96 (br s, terminal -CH=CH ₂ ), 2.84 (br s, 4 H, ArCH₂, COCH₂), 2.02 (br s), 1.64 (br s), 1.31-1.18 (br m), 0.90-0.87 (br m); ¹³C NMR (77.26 MHz, CDCl₃): δ = 196.49 (CO), 135.02-127.49, 44.56, 31.60-29.44; M _w /M _n = 1.19.