Phosphine-Dependent Selective Cross-Dimerization between Terminal Alkylacetylene and Silylacetylene by Iridium(I) Guanidinate Complex-Phosphine System

Abstract

The new iridium(I)-guanidinate complex served as an efficient catalyst for phosphine-dependent selective cross-dimerization between silylacetylene and terminal alkyl- or arylacetylene. Especially, in case of cross-dimerization between silylacetylene and alkylacetylene, E/Z selectivity of resulting enynes could be controlled by changing phosphine.

alkynes - enynes - coupling - dimerizations - iridium

References and Notes

For recent example of transition-metal-catalyzed homodimerization of alkynes, see:

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Synthesis of {Ir[(N ₂ ( i -Pr) ₂ CN( i -Pr) ₂ ](cod)} (1) A solution of [IrCl(cod)]₂ (281 mg, 0.42 mmol) in THF (5 mL) was cooled to -78 ˚C, and then a THF solution of Li[(N₂ (i-Pr)₂CN(i-Pr)₂], which was prepared by the reaction of the DIC (0.13 mL, 0.84 mmol) with LDA solution (1.8 M in heptane-THF-ethylbenzene solution, 0.48 mL, 0.86 mmol) at -78 ˚C, was added. The mixture was allowed to warm to r.t. After 4 h, the volatiles were removed under reduced pressure. The residual solid was extracted with toluene and the filtrate was evaporated off under high vacuum to give orange complex 1 (278 mg, 0.53 mmol, 63%). ^¹H NMR (400 MHz, C₆D₆): δ = 0.96 (d, J = 6.4 Hz,
12 H, i-PrCH₃), 1.23 (d, J = 6.9 Hz, 12 H, i-PrCH₃), 1.39 (d, J = 7.8 Hz, 4 H, cod), 2.20 (br, 4 H, cod), 3.43 (sept, J = 6.9 Hz, 2 H, i-PrCH), 3.80 (sept, J = 6.4 Hz, 2 H, i-PrCH), 4.09 (br, 4 H, cod). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = 22.8, 25.0, 32.5, 47.1, 48.6, 58.9 (cod, i-Pr), 128.5 (cod), 179.7 (NCN). Anal. Calcd for C₂₁H₄₀IrN₃: C, 47.88; H, 7.65; N, 7.98. Found: C, 47.82; H, 7.60; N, 8.00.

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Crystal Data for 1
C₂₁H₄₀IrN₃, MW = 526.79, monoclinic, P2₁/n, a = 20.5195 (4) Å, b = 15.5067 (4) Å, c = 27.6890 (4) Å, β = 102.4145 (16)˚, V = 8604.4 (3) Å₃, Z = 16, D _calc = 1.626 g/cm^³, µ (Mo Kα) = 62.328 cm^-¹, 84841 measured reflections, 24677 independent (R _int = 0.063), 13318 observed [I > 2σ(I)]. R1 = 0.0353, wR2 = 0.0903 (all data). Atomic coordinates, thermal parameters, bond distances, and angles have been deposited at the Cambridge Crystallographic Data Center. CCDC number: 668977.

<A NAME="RU07608ST-10">10</A>

General Procedure for Homodimerization of Terminal Alkynes (Table 1 and Scheme 2)
The mixture of 1 (16 mg, 0.03 mmol), toluene (3 mL), phosphine (16 mg, 0.06 mmol), and terminal alkyne (1.0 mmol) was charged in a sealed tube under argon atmosphere. After stirring for 6 h at 80 ˚C, the solvent was removed, and the residue was chromatographed on SiO₂, using hexane or Et₂O-hexane (1:3) as eluent. The solvent was removed to give dimeric product 3 or 4.

<A NAME="RU07608ST-11">11</A>

Results of dimerization of 1-octyne(2a) catalyzed by 1-trialkylphosphine system; 1-Et₃P: yield 60%, E/Z = 42:58; 1-n-Pr₃P: yield 79%, E/Z = 40:60

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<A NAME="RU07608ST-13">13</A>

General Procedure for Cross-Dimerization of Silylacetylene with Terminal Alkynes (Table 2 and Scheme 3) The mixture of 1 (25 mg, 0.05 mmol), toluene (3 mL), phosphine (26 mg, 0.10 mmol), silylacetylene (1.0 mmol), and terminal alkyne (2.0 mmol) was charged in sealed tube under argon atmosphere. After stirring for 6 h at 80 ˚C, the solvent was removed, and the residue was chromatographed on SiO₂, using hexane as eluent. Homo-dimer was eluted first. Then the eluate containing cross-dimer 5 was obtained. The solvent was removed to give cross-dimer 5 as colorless or pale-yellow oil.
Spectral Data for New Compounds
Product (E)-5d: ^¹H NMR (400 MHz, CDCl₃): δ = 0.18 (s,
9 H, SiMe₃), 0.87 (d, J = 7.0 Hz, 6 H, CH₃), 1.20-1.30 (m,
2 H, CH₂), 1.50-1.60 (m, 1 H, CH), 2.00-2.20 (m, 2 H, CH₂), 5.50 (dt, J = 15.8, 1.8 Hz, 1 H, CH=CH), 6.21 (dt, J = 15.8, 7.0 Hz, 1 H, CH=CH). ^¹³C{^¹H} NMR (100 MHz, CDCl₃):
δ = 0.0 (s, SiMe₃), 22.4, 27.3, 30.9, 37.6 (s, C₆H₁₃), 92.4, 104.2 (s, C=C), 109.4, 146.5 (C=C). HRMS (EI): m/z [M - Me]⁺ calcd for C₁₁H₁₉Si: 179.1256; found: 179.1259.
Product (Z)-5d: ^¹H NMR (400 MHz, CDCl₃): δ = 0.19 (s,
9 H, SiMe₃), 0.90 (d, J = 6.4 Hz, 6 H, CH₃), 1.20-1.30 (m,
2 H, CH₂), 1.50-1.60 (m, 1 H, CH), 2.30-2.40 (m, 2 H, CH₂), 5.46 (d, J = 10.5 Hz, 1 H, CH=CH), 5.95 (dt, J = 10.5, 7.6 Hz, 1 H, CH=CH). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = 0.0 (s, SiMe₃), 22.4, 27.3, 30.9, 37.6 (s, C₆H₁₃), 88.7, 92.4 (s, C=C), 109.4, 146.5 (C=C). HRMS (EI): m/z [M - Me]⁺ calcd for C₁₁H₁₉Si: 179.1256; found: 179.1213.
Product (E)-5e: ^¹H NMR (400 MHz, CDCl₃): δ = 0.17 (s,
9 H, SiMe₃), 3.43 (d, J = 6.9 Hz, 2 H, CH₂), 5.53 (dt, J = 15.6, 1.8 Hz, 1 H, CH=CH), 6.35 (dt, J = 15.6, 6.9 Hz,
1 H, CH=CH), 7.10-7.40 (m, 5 H, Ph). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = -0.1 (s, SiMe₃), 39.3 (s, CH₂Ph), 93.5, 103.7 (s, C=C), 111.0, 126.4, 128.5, 128.7, 138.6, 144.2 (S, C=C, Ph). HRMS (EI): m/z [M]⁺calcd for C₁₄H₁₈Si: 214.1178; found: 214.1169.
Product (Z)-5e: ^¹H NMR (400 MHz, CDCl₃): δ = 0.22 (s,
9 H, SiMe₃), 3.67 (d, J = 7.3 Hz, 2 H, CH₂), 5.60 (d, J = 11.0 Hz, 1 H, CH=CH), 6.10 (dt, J = 10.6, 7.3 Hz, 1 H, CH=CH), 7.10-7.40 (m, 5 H, Ph). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = -0.02 (s, SiMe₃), 36.5 (s, CH₂Ph), 99.0, 101.8 (s, C=C), 109.9, 126.2, 128.5, 128.5, 139.7, 143.2 (S, C=C, Ph). HRMS (EI): m/z [M]⁺ calcd for C₁₄H₁₈Si: 214.1178; found: 214.1158.
Product (E)-5g: ^¹H NMR (400 MHz, CDCl₃): δ = 0.22 (s,
9 H, SiMe₃), 2.34 (s, 3 H, CH₃), 6.12 (d, J = 16.5 Hz, 1 H, CH=CH), 6.98 (d, J = 16.5 Hz, 1 H, CH=CH), 7.10-7.30 (m, 4 H, Ar). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = 0.0 (s, SiMe₃), 21.5 (s, CH₃), 96.4, 104.6 (s, C=C), 106.9, 126.2, 129.0, 129.4, 138.9, 142.4 (s, C=C, Ph). HRMS (EI): m/z [M]⁺ calcd for C₁₄H₁₈Si: 214.1178; found: 214.1171.
Product (E)-5h: ^¹H NMR (400 MHz, CDCl₃): δ = 0.11 (s,
9 H, SiMe₃), 3.81 (s, 3 H, CH₃, 6.16 (d, J = 19.2 Hz, 1 H, CH=CH), 6.48 (d, J = 19.2 Hz, 1 H, CH=CH), 6.84 (d, J = 9.2 Hz, 2 H, Ar), 7.37 (d, J = 9.2 Hz, 2 H, Ar). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = -1.6 (s, SiMe₃), 55.2 (s, OCH₃), 88.4, 89.9 (s, C=C), 113.9, 128.4, 132.1, 133.0, 144.7, 159.6 (s, C=C, Ph). HRMS (EI): m/z [M]⁺ calcd for C₁₄H₁₈OSi: 230.1127; found: 230.1133.
Product (E)-5i: ^¹H NMR (400 MHz, CDCl₃): δ = 0.80-2.20 (m, 16 H, C₆H₁₃, i-PrCH), 1.07 (br d, 18 H, i-PrCH₃), 5.52 (dt, J = 16.0, 1.4 Hz, 1 H, CH=CH), 6.20 (dt, J = 16.0, 6.9 Hz, 1 H, CH=CH). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = 11.3, 14.1, 22.6, 28.6, 28.9, 31.7, 33.1 (s, C₆H₁₃, i-PrCH), 18.6 (s, i-PrCH₃), 88.5, 106.1 (s, C=C), 109.8, 145.8 (s, CH=CH). HRMS (EI): m/z [M]⁺ calcd for C₁₉H₃₆Si: 292.2586; found: 292.2583.
Product (Z)-5i: ^¹H NMR (400 MHz, CDCl₃): δ = 0.80-2.40 (m, 16 H, C₆H₁₃, i-PrCH), 1.09 (br d, 18 H, i-PrCH₃), 5.50 (d, J = 10.5 Hz, 1 H, CH=CH), 6.0 (m, 1 H, CH=CH). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ = 11.3, 14.1, 22.6, 28.8, 29.0, 30.4, 31.7 (s, C₆H₁₃, i-PrCH), 18.6 (s, i-PrCH₃), 94.6, 103.9 (s, C=C), 109.6, 145.2 (s, CH=CH). HRMS (EI): m/z [M]⁺ calcd for C₁₉H₃₆Si: 292.2586; found: 292.2587.
Product (E)-5j: ^¹H NMR (400 MHz, CDCl₃): δ = 0.11 (s,
6 H, SiMe₂), 0.80-2.20 (m, 13 H, C₆H₁₃), 0.94 (s, 9 H, t-Bu), 5.50 (d, J = 15.8 Hz, 1 H, CH=CH), 6.21 (dt, J = 15.8, 7.0 Hz, 1 H, CH=CH). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ =
-4.6 (s, SiMe₂), 14.1, 16.6, 22.6, 28.6, 28.8, 31.6, 33.1 [s, C₆H₁₃, C(CH₃)₃], 26.1 [s, C(CH₃)₃], 90.6, 104.8 (s, C=C), 109.6, 146.2 (s, CH=CH). HRMS (EI): m/z [M]⁺ calcd for C₁₆H₃₀Si: 250.2117; found: 250.2116.
Product (Z)-5j: ^¹H NMR (400 MHz, CDCl₃): δ = 0.13 (s,
6 H, SiMe₂), 0.80-2.40 (m, 13 H, C₆H₁₃), 0.96 (s, 9 H, t-Bu), 5.48 (d, J = 10.8 Hz, 1 H, CH=CH), 5.96 (dt, J = 10.8, 7.4 Hz, 1 H, CH=CH). ^¹³C{^¹H} NMR (100 MHz, CDCl₃): δ =
-4.6 (s, SiMe₂), 14.1, 16.6, 22.6, 28.7, 28.9, 30.3, 31.6 [s, C₆H₁₃, C(CH₃)₃], 26.1 [s, C(CH₃)₃], 96.6, 102.8 (s, C=C), 109.2, 145.6 (s, CH=CH). HRMS (EI): m/z [M]⁺ calcd for C₁₆H₃₀Si: 250.2117; found: 250.2108.

<A NAME="RU07608ST-14">14</A>

Formation ratio of (E)-5a/(E)-3a = 77:23 (determined by ^¹H NMR).

<A NAME="RU07608ST-15">15</A>

Result of cross-dimerization between 2c and 2a catalyzed by 1-Et₂PhP system: yield 88%, E/Z = 9:91.