Atom-transfer radical reactions catalyzed by a coordinatively unsaturated diruthenium amidinate, [(η5-C5Me5) Ru(μ2-i-PrNC(Me)Ni-Pr)Ru(η5-C5Me 5)]+

Yukihiro Motoyama, Shiori Hanada, Shota Niibayashi, Kazuya Shimamoto, Naoki Takaoka, Hideo Nagashima

Research output: Contribution to journalArticle

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Abstract

Atom-transfer radical cyclization (ATRC) and addition (ATRA) catalyzed by a coordinatively unsaturated diruthenium amidinate complex 4, [(η5-C5Me5)Ru(μ2-i-PrNC(Me) Ni-Pr)Ru(η5-C5Me5)]+, are investigated, and their features are compared with those of atom-transfer radical polymerization (ATRP). As an example of ATRC, a cationic diruthenium amidinate 4 is found to exhibit excellent catalytic reactivity for the cyclization of N-allyl α-halogenated acetamides including an alkaloid skeleton at ambient temperature. A catalytic species generated in situ from a halide complex, (η5-C5Me5) Ru(μ2-i-PrNC(Me)Ni-Pr)Ru(η5-C5Me 5)(X) [X=Cl, Br] and sodium salts of weakly coordinating anions such as NaPF6 and NaBPh4 also shows high catalytic activity; this actually provides a solution for a problematic instability of 4 as the practical catalyst. The in situ-generated catalyst species 4 is also active towards the intermolecular ATRA of α,α,γ-trichlorinated γ-lactam with alkenes at rt to afford the corresponding α-alkylated γ-lactams in moderate yields. Examination of ATRP of methyl methacrylate (MMA) showed that both the isolated 4 [Y=PF6] and in situ-generated 4 [Y=PF6] are effective for the polymerization of MMA in the presence of 2-bromoisobutylate as the initiator. Use of the isolated catalyst results in controlled polymerization at initial stage of the reaction; in contrast, the polymerization with in situ-generated catalyst produces poly(MMA) with wide molecular weight distribution. The isolated catalyst 4 is powerful for the activation of a C-Br bond of macromolecule initiators; BrCMe2CO 2[O(CH2)4]n-n-Bu (M n=3800; Mw/Mn=1.2) initiated ATRP of MMA even at 25°C to afford the poly(THF)-poly(MMA) block copolymer of M n=26,000 and Mw/Mn=1.2 with the aid of 4. The roles of the coordinatively unsaturated ruthenium species for these reactions are discussed.

Original languageEnglish
Pages (from-to)10216-10226
Number of pages11
JournalTetrahedron
Volume61
Issue number43
DOIs
Publication statusPublished - Oct 24 2005

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Polymerization
Methacrylates
Atom transfer radical polymerization
Cyclization
Atoms
Catalysts
Lactams
Polymethyl Methacrylate
Acetamides
Ruthenium
Alkenes
Molecular weight distribution
Macromolecules
Alkaloids
Block copolymers
Anions
Catalyst activity
Skeleton
Salts
Sodium

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Drug Discovery
  • Organic Chemistry

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Atom-transfer radical reactions catalyzed by a coordinatively unsaturated diruthenium amidinate, [(η5-C5Me5) Ru(μ2-i-PrNC(Me)Ni-Pr)Ru(η5-C5Me 5)]+. / Motoyama, Yukihiro; Hanada, Shiori; Niibayashi, Shota; Shimamoto, Kazuya; Takaoka, Naoki; Nagashima, Hideo.

In: Tetrahedron, Vol. 61, No. 43, 24.10.2005, p. 10216-10226.

Research output: Contribution to journalArticle

Motoyama, Yukihiro ; Hanada, Shiori ; Niibayashi, Shota ; Shimamoto, Kazuya ; Takaoka, Naoki ; Nagashima, Hideo. / Atom-transfer radical reactions catalyzed by a coordinatively unsaturated diruthenium amidinate, [(η5-C5Me5) Ru(μ2-i-PrNC(Me)Ni-Pr)Ru(η5-C5Me 5)]+. In: Tetrahedron. 2005 ; Vol. 61, No. 43. pp. 10216-10226.
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abstract = "Atom-transfer radical cyclization (ATRC) and addition (ATRA) catalyzed by a coordinatively unsaturated diruthenium amidinate complex 4, [(η5-C5Me5)Ru(μ2-i-PrNC(Me) Ni-Pr)Ru(η5-C5Me5)]+, are investigated, and their features are compared with those of atom-transfer radical polymerization (ATRP). As an example of ATRC, a cationic diruthenium amidinate 4 is found to exhibit excellent catalytic reactivity for the cyclization of N-allyl α-halogenated acetamides including an alkaloid skeleton at ambient temperature. A catalytic species generated in situ from a halide complex, (η5-C5Me5) Ru(μ2-i-PrNC(Me)Ni-Pr)Ru(η5-C5Me 5)(X) [X=Cl, Br] and sodium salts of weakly coordinating anions such as NaPF6 and NaBPh4 also shows high catalytic activity; this actually provides a solution for a problematic instability of 4 as the practical catalyst. The in situ-generated catalyst species 4 is also active towards the intermolecular ATRA of α,α,γ-trichlorinated γ-lactam with alkenes at rt to afford the corresponding α-alkylated γ-lactams in moderate yields. Examination of ATRP of methyl methacrylate (MMA) showed that both the isolated 4 [Y=PF6] and in situ-generated 4 [Y=PF6] are effective for the polymerization of MMA in the presence of 2-bromoisobutylate as the initiator. Use of the isolated catalyst results in controlled polymerization at initial stage of the reaction; in contrast, the polymerization with in situ-generated catalyst produces poly(MMA) with wide molecular weight distribution. The isolated catalyst 4 is powerful for the activation of a C-Br bond of macromolecule initiators; BrCMe2CO 2[O(CH2)4]n-n-Bu (M n=3800; Mw/Mn=1.2) initiated ATRP of MMA even at 25°C to afford the poly(THF)-poly(MMA) block copolymer of M n=26,000 and Mw/Mn=1.2 with the aid of 4. The roles of the coordinatively unsaturated ruthenium species for these reactions are discussed.",
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AU - Motoyama, Yukihiro

AU - Hanada, Shiori

AU - Niibayashi, Shota

AU - Shimamoto, Kazuya

AU - Takaoka, Naoki

AU - Nagashima, Hideo

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N2 - Atom-transfer radical cyclization (ATRC) and addition (ATRA) catalyzed by a coordinatively unsaturated diruthenium amidinate complex 4, [(η5-C5Me5)Ru(μ2-i-PrNC(Me) Ni-Pr)Ru(η5-C5Me5)]+, are investigated, and their features are compared with those of atom-transfer radical polymerization (ATRP). As an example of ATRC, a cationic diruthenium amidinate 4 is found to exhibit excellent catalytic reactivity for the cyclization of N-allyl α-halogenated acetamides including an alkaloid skeleton at ambient temperature. A catalytic species generated in situ from a halide complex, (η5-C5Me5) Ru(μ2-i-PrNC(Me)Ni-Pr)Ru(η5-C5Me 5)(X) [X=Cl, Br] and sodium salts of weakly coordinating anions such as NaPF6 and NaBPh4 also shows high catalytic activity; this actually provides a solution for a problematic instability of 4 as the practical catalyst. The in situ-generated catalyst species 4 is also active towards the intermolecular ATRA of α,α,γ-trichlorinated γ-lactam with alkenes at rt to afford the corresponding α-alkylated γ-lactams in moderate yields. Examination of ATRP of methyl methacrylate (MMA) showed that both the isolated 4 [Y=PF6] and in situ-generated 4 [Y=PF6] are effective for the polymerization of MMA in the presence of 2-bromoisobutylate as the initiator. Use of the isolated catalyst results in controlled polymerization at initial stage of the reaction; in contrast, the polymerization with in situ-generated catalyst produces poly(MMA) with wide molecular weight distribution. The isolated catalyst 4 is powerful for the activation of a C-Br bond of macromolecule initiators; BrCMe2CO 2[O(CH2)4]n-n-Bu (M n=3800; Mw/Mn=1.2) initiated ATRP of MMA even at 25°C to afford the poly(THF)-poly(MMA) block copolymer of M n=26,000 and Mw/Mn=1.2 with the aid of 4. The roles of the coordinatively unsaturated ruthenium species for these reactions are discussed.

AB - Atom-transfer radical cyclization (ATRC) and addition (ATRA) catalyzed by a coordinatively unsaturated diruthenium amidinate complex 4, [(η5-C5Me5)Ru(μ2-i-PrNC(Me) Ni-Pr)Ru(η5-C5Me5)]+, are investigated, and their features are compared with those of atom-transfer radical polymerization (ATRP). As an example of ATRC, a cationic diruthenium amidinate 4 is found to exhibit excellent catalytic reactivity for the cyclization of N-allyl α-halogenated acetamides including an alkaloid skeleton at ambient temperature. A catalytic species generated in situ from a halide complex, (η5-C5Me5) Ru(μ2-i-PrNC(Me)Ni-Pr)Ru(η5-C5Me 5)(X) [X=Cl, Br] and sodium salts of weakly coordinating anions such as NaPF6 and NaBPh4 also shows high catalytic activity; this actually provides a solution for a problematic instability of 4 as the practical catalyst. The in situ-generated catalyst species 4 is also active towards the intermolecular ATRA of α,α,γ-trichlorinated γ-lactam with alkenes at rt to afford the corresponding α-alkylated γ-lactams in moderate yields. Examination of ATRP of methyl methacrylate (MMA) showed that both the isolated 4 [Y=PF6] and in situ-generated 4 [Y=PF6] are effective for the polymerization of MMA in the presence of 2-bromoisobutylate as the initiator. Use of the isolated catalyst results in controlled polymerization at initial stage of the reaction; in contrast, the polymerization with in situ-generated catalyst produces poly(MMA) with wide molecular weight distribution. The isolated catalyst 4 is powerful for the activation of a C-Br bond of macromolecule initiators; BrCMe2CO 2[O(CH2)4]n-n-Bu (M n=3800; Mw/Mn=1.2) initiated ATRP of MMA even at 25°C to afford the poly(THF)-poly(MMA) block copolymer of M n=26,000 and Mw/Mn=1.2 with the aid of 4. The roles of the coordinatively unsaturated ruthenium species for these reactions are discussed.

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