Dendrimer−Phosphine Complexes with Platinum(0) at the Core

Babu, Balaji; Obora, Yasushi; Ohara, Daisuke; Koide, and Shigehiro; Tsuji, Yasushi

doi:10.1021/om010687b

Cited by 35 publications

(28 citation statements)

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“…[2,3] In the course of our studies, [3] we found that a bowl-shaped [4] phosphane ligand markedly enhances the rate of rhodium-catalyzed hydrosilylation of ketones. [1] So far, most P ligands are rather small, and their design and modification have hitherto been performed within close proximity of the P atom.…”

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Rate Enhancement with a Bowl‐Shaped Phosphane in the Rhodium‐Catalyzed Hydrosilylation of Ketones

et al. 2003

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Since the nature of P ligands is very important in transitionmetal-catalyzed reactions, a wide variety of these ligands has been designed to realize high catalytic activity and selectivity. [1] So far, most P ligands are rather small, and their design and modification have hitherto been performed within close proximity of the P atom. Recently, several large (nanosized) phosphorus ligands were developed for transition-metalcatalyzed reactions. [2,3] In the course of our studies, [3] we found that a bowl-shaped [4] phosphane ligand markedly enhances the rate of rhodium-catalyzed hydrosilylation of ketones. [5] The two triarylphosphanes tris(2,2'',6,6''-tetramethyl-mterphenyl-5'-yl)phosphane [6] (denoted as P(tm-tp) 3 ) and tris(m-terphenyl-5'-yl)phosphane (denoted as P(tp) 3 ) were prepared and compared with common phosphanes in the rhodium-catalyzed hydrosilylation of cyclohexanone with a trisubstituted silane (Table 1). P(tm-tp) 3 was first prepared in 2001 [6a] and its Pd 0 complex [Pd{P(tm-tp) 3 } 2 ] was reported in 2002. [6b] In the presence of catalytic amounts of P(tm-tp) 3 and [{RhCl(C 2 H 4 ) 2 } 2 ] (P/Rh = 2), the reaction proceeded smoothly in benzene at room temperature over 3 h, and cyclohexanol was obtained in 97 % yield after desilylation (Table 1, entry 1). In contrast, the same reaction with P(tp) 3 afforded the product in only 25 % yield (entry 2). Furthermore, other representative triarylphosphanes (entries 3-6) and trialkylphosphanes (entries 7-9) were also much less effective than P(tm-tp) 3 . With these ligands (entries 2-9), the reactions were sluggish at room temperature, and much longer reaction times (40-500 h) were required to obtain the products in good yields (70-95 %). A kinetic study indicated that the P(tm-tp) 3 catalyst system (entry 1) realized 154, 31, and 28 times faster reactions than PPh 3 (entry 3), P(tp) 3 (entry 2), and P(o-tol) 3 (entry 5), respectively. [7] Benzene is a better solvent than CH 2 Cl 2 in the reactions of entries 1-3.The rate enhancement with P(tm-tp) 3 was further confirmed with various silanes and ketones, and compared with P(tp) 3 and PPh 3 (Table 2). With HSiEt 3 (Table 2, entries 1-3) or HSiMePh 2 (entries 4-6), the hydrosilylation of cyclohexanone proceeded much faster with P(tm-tp) 3 (entries 1 and 4) than with P(tp) 3 (entries 2 and 5) and PPh 3 (entries 3 and 6). Furthermore, in the hydrosilylation of various ketones such as acetophenone (entries 7-9), 2-octanone (entries 10-12), and (À)-menthone (entries 13-15), rate enhancement with P(tmtp) 3 was also evident. As catalyst precursor, the cationic rhodium complex [Rh(cod) 2 ]BF 4 (cod = cyclooctadiene) showed a similar rate enhancement with P(tm-tp) 3 (entries 16-18). P(tm-tp) 3 is a much more efficient than P(tp) 3 , although the two ligands strongly resemble each other. The structures of P(tm-tp) 3 and P(tp) 3 were optimized by HF/6-31G(d) calculations [8a] on initial structures generated by CON-P R R R R A B B 3 R= Me: P(tm-tp) 3 R= H: P(tp) 3 Table 1: Effects of ligands in the hydrosilylat...

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Rate Enhancement with a Bowl‐Shaped Phosphane in the Rhodium‐Catalyzed Hydrosilylation of Ketones

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“…6 Mono-(3a-c) and bidentate (3d-e) dendrimer-phosphine ligands connecting Frećhet type poly(benzylether) unit were synthesized as shown in Figure 2. The defect-free monodisperse nature of 3 was confirmed by 31 P NMR and ESI mass spectra.…”

Section: Pd-catalyzed Aerobic Oxidation Of Alcohols With Pyridine Ligmentioning

confidence: 99%

“…3 In this review, we summarize recent progress from our laboratoty in the field of nano-sized dendrimer pyridine and phosphine ligands having tetraphenylphenyl-, 4 m-terphenyl-, 5 and poly(benzylether) moieties. 6 These ligands show remarkable catalytic performance in Pd-catalyzed alcohol oxidation 4 and Rh-catalyzed ketone hydrosilylation. 5 In addition, we synthesized novel phosphine ligands having calixarene moieties (phosphinocalixarenes).…”

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Transition‐Metal Complexes with Nanosized Phosphine and Pyridine Ligands — Catalysis, Fluxional Behavior and Molecular Recognition

2007

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“…19,27) By employing the corresponding water-soluble 1Gn[CO 2 K]-palladium complex as a catalyst, an aqueous media Suzuki-Miyaura reaction was carried out smoothly, and thus a hydrophobic dendron was effective as a reaction field in the case of aqueous media organic syntheses. 19,27,29,30) We wish to report herein the synthesis of a series of dendrimers with a bidentate phosphine core ligand having carboxy groups at the peripheral layer 2Gn[CO 2 H] (n=0-2), [31][32][33][34][35] as shown in Fig. 1, and an aqueous media Suzuki-Miyaura reaction and Tsuji-Trost reaction catalyzed by the corresponding water-soluble dendritic phosphine 2Gn[CO 2 K]-palladium complex.…”

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Synthesis of Dendrimers with a Bidentate Phosphine Core Ligand Having Carboxy Groups at the Peripheral Layer and Their Application to Aqueous Media Cross-Coupling Reactions

Fujita

Hattori

2016

CHEMICAL & PHARMACEUTICAL BULLETIN

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We prepared a series of dendrimers with a bidentate phosphine core ligand having carboxy groups at the peripheral layer. By employing the corresponding water-soluble dendritic phosphine-palladium complex as a catalyst, the aqueous media Suzuki-Miyaura reaction and Tsuji-Trost reaction proceeded to provide the corresponding cross-coupling product.Key words dendrimer; phosphine; catalyst With the many environmental challenges faced by the world today, organic reactions that can be conducted in water without the use of harmful organic solvents have been a subject of increasing interest. As a potential solvent, water is not only non-toxic and non-flammable solvent, but also cheap and readily available.1-4) Accordingly, various water-soluble ligands have been synthesized in order to carry out organic reactions in purely aqueous reaction media, and the corresponding water-soluble organometallic catalyst has been applied to aqueous media organic syntheses. [5][6][7][8][9] Dendrimers are fascinating molecules due to the unique physical and chemical properties resulting from their welldefined hyperbranched frameworks.10-14) Metallodendrimers with a functional or catalytic site at their core have received considerable attention, because their solubility and physical properties can be altered by peripheral modification. 15-18)For example, by the introduction of hydrophilic groups to the peripheral layer of a hydrophobic dendron, water-soluble dendritic unimolecular micelles can be prepared.19-28) Some water-soluble dendrimers have been used as catalysts for aqueous media organic syntheses by our group 19,26,27) and by others. 28) We have synthesized a series of dendrimers with a phosphine core ligand having carboxy groups at the peripheral layer 1Gn[CO 2 H] (n=0-2); these are monodentate phosphine ligands, as shown in Fig. 1. 19,27) By employing the corresponding water-soluble 1Gn[CO 2 K]-palladium complex as a catalyst, an aqueous media Suzuki-Miyaura reaction was carried out smoothly, and thus a hydrophobic dendron was effective as a reaction field in the case of aqueous media organic syntheses. 19,27,29,30) We wish to report herein the synthesis of a series of dendrimers with a bidentate phosphine core ligand having carboxy groups at the peripheral layer 2Gn[CO 2 H] (n=0-2), [31][32][33][34][35] as shown in Fig. 1, and an aqueous media Suzuki-Miyaura reaction and Tsuji-Trost reaction catalyzed by the corresponding water-soluble dendritic phosphine 2Gn[CO 2 K]-palladium complex. The Suzuki-Miyaura reaction and Tsuji-Trost reaction have become one of the most powerful cross-coupling methods.36,37) These cross-coupling reactions have been widely used in the synthesis of a variety of fine chemicals and pharmaceutical products, as well as in materials science. From the perspective of green chemistry, the development of the aqueous media Suzuki-Miyaura reaction [38][39][40] and Tsuji-Trost reaction 41,42) is a very attractive field, as water is an environmentally benign solvent.* To whom correspondence should be addressed. e-...

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Dendrimer−Phosphine Complexes with Platinum(0) at the Core

Cited by 35 publications

References 91 publications

Rate Enhancement with a Bowl‐Shaped Phosphane in the Rhodium‐Catalyzed Hydrosilylation of Ketones

Rate Enhancement with a Bowl‐Shaped Phosphane in the Rhodium‐Catalyzed Hydrosilylation of Ketones

Transition‐Metal Complexes with Nanosized Phosphine and Pyridine Ligands — Catalysis, Fluxional Behavior and Molecular Recognition

Synthesis of Dendrimers with a Bidentate Phosphine Core Ligand Having Carboxy Groups at the Peripheral Layer and Their Application to Aqueous Media Cross-Coupling Reactions

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