The selectivity of catalytic asymmetric transformations of bifunctional symmetrical substrates of... more The selectivity of catalytic asymmetric transformations of bifunctional symmetrical substrates often depends on the linker between the two reactive sites. If the catalyst controls the selectivity of reactions at both sites, the rac product will be formed in high enantiomeric ratio (er) via asymmetric amplification. Substrate control may augment this selectivity (positive cooperativity) or detract from it (negative cooperativity). Here, we investigated the effect of linker length on the selectivity of catalytic asymmetric alkylation of the bis(secondary phosphines) PhHP(CH 2) n PHPh (n = 2-6, 1a-e) with benzyl bromide using the base NaOSiMe 3 and the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl). These reactions yielded the diastereomerically and enantiomerically enriched bis(tertiary phosphines) Ph(PhCH 2)P(CH 2) n P(CH 2 Ph)Ph (n = 2-6, 2a-e). Pt-catalyzed benzylation of the model phosphines PH(Ph)((CH 2) n H) (4a-e, n = 2-6) gave enantiomerically enriched P(CH 2 Ph)(Ph)((CH 2) n H) (5a-e, n = 2-Page 1 of 27 ACS Paragon Plus Environment ACS Catalysis 2 6). The partially alkylated bis(phosphines) PhHP(CH 2) n P(CH 2 Ph)Ph (n = 2, 3, and 5, 3a-b and 3d) were prepared with different degrees of enantiomeric enrichment at the tertiary phosphine centers, then catalytically alkylated to give 2a-b and 2d. From the diastereoselectivity and enantioselectivity of the transformations 12 and 32, the selectivity of each individual alkylation step (13R or 3S; 3R2RR or 2RS; 3S2SS or 2SR) could be determined as a function of linker length, and compared to the selectivity of alkylation of the model monophosphines 4. The two alkylations of bis(secondary phosphines) 1b-e with longer linker lengths (n = 3-6) showed identical selectivity, within experimental error. This catalyst control resulted in asymmetric amplification of rac-2. In contrast, the selectivity of the first alkylation of ethano-bridged 1a was lower than that in 1b-e (negative cooperativity), but the selectivity of the second alkylation (of intermediate 3a) increased due to positive cooperativity. Possible mechanistic explanations for the observed dependence of selectivity on linker length are discussed.
Abstract This chapter reviews the chemistry of phosphiranes, phosphirenes, and their heavier anal... more Abstract This chapter reviews the chemistry of phosphiranes, phosphirenes, and their heavier analogues reported from 2008 to 2018, with focus on the structure of the three-membered rings, synthesis, and reactivity, which is dominated by relief of ring strain. Applications as ligands for transition metals and use in catalysis are also considered.
Tetrahedral main‐group compounds are normally configurationally stable, but P‐epimerization of th... more Tetrahedral main‐group compounds are normally configurationally stable, but P‐epimerization of the chiral phosphiranium cations syn‐ or anti‐[Mes*P(Me)CH2CHPh][OTf] (Mes*=2,4,6‐(t‐Bu)3C6H2) occurred under mild conditions at 60 °C in CD2Cl2, resulting in isomerization to give a syn‐enriched equilibrium mixture. Ion exchange with excess [NBu4][Δ‐TRISPHAT] (Δ‐TRISPHAT=Δ‐P(o‐C6Cl4O2)3) followed by chromatography on silica removed [NBu4][OTf] and gave mixtures of syn‐ and anti‐[Mes*P(Me)CH2CHPh][Δ‐TRISPHAT]⋅x[NBu4][Δ‐TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P‐C cleavage to yield a hyperconjugation‐stabilized carbocation, pyramidal inversion promoted by σ‐interaction of the P lone pair with the neighboring β‐carbocation, and ring closure with inversion of configuration at P.
Diastereoselective coordination of racemic secondary phosphines (PHRR′) to Cu(I) precursors conta... more Diastereoselective coordination of racemic secondary phosphines (PHRR′) to Cu(I) precursors containing chiral bis(phosphines) (diphos*) was explored as a potential route to P-stereogenic phosphido complexes. Reaction of [Cu(NCMe) 4 ]-[PF 6 ] with chiral bis(phospholanes) gave [Cu(diphos*) 2 ][PF 6 ] (diphos* = (R,R)-Me-DuPhos (1), (R,R)-Et-DuPhos (2), or (R,R)-Me-FerroLANE) (3)) or the mono(chelates) [Cu-(diphos*)(NCMe) n ][PF 6 ] (diphos* = (R,R)-i-Pr-DuPhos, n = 2 (4); diphos* = (R,R)-Me-FerroLANE, n = 1 (5)). Treatment of [Cu(NCMe) 4 ][PF 6 ] with diphos* and PHMe(Is) (Is = 2,4,6-(i-Pr) 3 C 6 H 2) gave mixtures of diastereomers of [Cu((R,R)-i-Pr-DuPhos)(PHMe(Is))(NCMe)][PF 6 ] (6) and [Cu((R,R)-Me-FerroLANE)(PHMe(Is))][PF 6 ] (7); two of the three expected isomers of the bis(secondary phosphine) complexes [Cu((R,R)i-Pr-DuPhos)(PhHP(CH 2) n PHPh)][PF 6 ] (n = 2 (8); n = 3 (9)) were formed preferentially in related reactions. Reaction of the halide-bridged dimers [Cu((R,R)-i-Pr-DuPhos)(X)] 2 or [Cu((R,R)-Me-FerroLANE)(I)] 2 with PHMe(Is) gave the labile adducts Cu((R,R)-i-Pr-DuPhos)(PHMe(Is))(X) (X = Cl (10), Br (11), I (12)) and Cu((R,R)-Me-FerroLANE)(PHMe-(Is))(I) (13). Complexes 1, 6, and 8−11 were structurally characterized by X-ray crystallography. Variable temperature NMR studies of 6 and 8 showed that the secondary phosphine ligands underwent reversible dissociation. Deprotonation of 6 or 7 generated the P-stereogenic phosphido complexes Cu(diphos*)(PMeIs) (diphos* = (R,R)-i-Pr-DuPhos (14) or (R,R)-Me-FerroLANE) (17)), observed by 31 P NMR spectroscopy, but decomposition also occurred. Density functional theory calculations were used to characterize the diastereomers of thermally unstable 17 and the inversion barrier in a model copperphosphido complex. These observations provided structure−property relationships which may be useful in developing catalytic asymmetric reactions involving secondary phosphines and P-stereogenic copper phosphido intermediates.
Alkylation of MeC(CH2PHPh)3 1 with 2-cyanobenzyl bromide and NaOSiMe3 using the catalyst precurso... more Alkylation of MeC(CH2PHPh)3 1 with 2-cyanobenzyl bromide and NaOSiMe3 using the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl) gave a mixture of tris(phosphines) enriched in C3-MeC(CH2PPh(CH2(o-C6H4CN))3 3; Cu-catalyzed phosphination yielded C1-enriched 3. Oxidation of 3 by sulfur or H2O2 formed MeC(CH2P(E)Ph(CH2(o-C6H4CN))3 (E = S 4; E = O 5). Repeated recrystallization gave a low yield of (R,R,R)-4, which was crystallographically characterized. Tris(phosphine) 3 was formed with a diastereomeric ratio (dr = C3/C1) of 2.1(2) and enantiomeric ratios of 54(10) and 3.8(7) for C3-3 and C1-3 respectively, which showed that the selectivity of the triple alkylation was not the same at each site (substrate control).
Me-DuPhos)(CH 2 Cl)(Cl) (4). Treatment of [Rh(COD)(Cl)] 2 with (R,R)-Me-DuPhos at low temperature... more Me-DuPhos)(CH 2 Cl)(Cl) (4). Treatment of [Rh(COD)(Cl)] 2 with (R,R)-Me-DuPhos at low temperature in THF or CH 2 Cl 2 afforded [Rh((R,R)-Me-DuPhos)(Cl)] 2 (5). At room temperature, these reactions also gave the byproduct [Rh((R,R)-Me-DuPhos) 2 ][Cl], which was prepared independently as the BF 4 salt 6. When 5 was generated in CH 2 Cl 2 , oxidative addition of both CeCl bonds yielded the bridging carbene complex (Rh ((R,R)-Me-DuPhos)(Cl)) 2 (µ-Cl) 2 (µ-CH 2) (8). Both 6 and 8 were crystallographically characterized.
A range of P-containing ene-diynes suitable for desymmetrization was prepared via a two-step proc... more A range of P-containing ene-diynes suitable for desymmetrization was prepared via a two-step process starting from phosphorus oxychloride. In the presence of the Hoveyda-Grubbs II catalyst, these substrates underwent diastereoselective enyne ring-closing metathesis leading to various synthetically useful P-stereogenic heterocycles featuring an exocyclic alkynyl group. These products are amenable to further functional manipulation.
Reaction of the enantiomerically enriched P-stereogenic phosphiranes syn-(RP,SC)-Mes*PCH2CH(Ph) (... more Reaction of the enantiomerically enriched P-stereogenic phosphiranes syn-(RP,SC)-Mes*PCH2CH(Ph) (syn-1) and anti-(SP,SC)-Mes*PCH2CH(Ph) (anti-2, Mes* = 2,4,6-(t-Bu)3C6H2) with metal complex precursors gave Au(L)(Cl) (L = 1 (3); L = 2 (4)), trans-ML2Cl2 (L = 1, M = Pd (5), Pt (6)), Pd(η3-C3H5)(L)(Cl) (L = 1 (7)), and trans-RhL2(CO)(Cl) (L = 1 (8); L = 2 (9)); 3, 4, 7, and 9 were crystallographically characterized. Phosphirane coordination resulted in shortening of the P–C bonds and increased bond angles at P, consistent with rehybridization at phosphorus. A comparison of complexes of phenylphosphirane and phenyldimethylphosphine using IR spectra, coupled with DFT studies using electronic decomposition analysis (EDA) and natural orbitals for chemical valence (NOCV), indicated that phosphiranes are slightly poorer σ-donors than the analogous phosphines and that the π-acceptor properties of these ligands are similar. Pauli repulsion, dispersion, and electrostatic attraction are also important factors in deter...
Angewandte Chemie (International ed. in English), Jan 23, 2018
Nucleophilic substitution results in inversion of configuration at the electrophilic carbon cente... more Nucleophilic substitution results in inversion of configuration at the electrophilic carbon center (S 2) or racemization (S 1). The stereochemistry of the nucleophile is rarely considered, but phosphines, which have a high barrier to pyramidal inversion, attack electrophiles with retention of configuration at P. Surprisingly, cyclization of bifunctional secondary phosphine alkyl tosylates proceeded under mild conditions with inversion of configuration at the nucleophile to yield P-stereogenic syn-phosphiranes. DFT studies suggested that the novel stereochemistry results from acid-promoted tosylate dissociation to yield an intermediate phosphenium-bridged cation, which undergoes syn-selective cyclization.
... (b) Collman, JP; Hegedus, LS; Norton, JR; Finke, RG Principles and Applications of Organotran... more ... (b) Collman, JP; Hegedus, LS; Norton, JR; Finke, RG Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987. ... Ana García,Julio Gómez, Elena Lalinde, and M. Teresa Moreno. Organometallics 2006 25 (16), 3926-3934. ...
ABSTRACT Catalytic asymmetric alkylation of the bis(secondary phosphines) IsHP(CH2)nPHIs (1a−e, n... more ABSTRACT Catalytic asymmetric alkylation of the bis(secondary phosphines) IsHP(CH2)nPHIs (1a−e, n = 1−5, Is = isityl = 2,4,6-(i-Pr)3C6H2) with benzyl bromide using the base NaOSiMe3 and the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl) gave the bis(tertiary phosphines) Is(PhCH2)P(CH2)nP(CH2Ph)Is (2a−e, n = 1−5) via the intermediates Is(PhCH2)P(CH2)nPHIs (4a−e, n = 1−5). The rates of these reactions depended strongly on n, in the order 1a < 1b < 1c ≈ 1d ≈ 1e. The bulkier bis(secondary phosphine) Mes*HP(CH2)2PHMes* (5, Mes* = 2,4,6-(t-Bu)3C6H2) did not undergo catalytic alkylation under these conditions. The alkylation selectivity also depended on n. Alkylation of 1b was meso-selective, while alkylation of 1a,c−e was rac-selective, occurring with similar diastereoselectivity and enantioselectivity for the longer linkers (1c−e). The product ratios suggested that the catalyst controlled the selectivity for 1d,e, while substrate control operated for ethano-bridged 1b, with negative cooperativity. Substrate control also likely occurred for 1a, for which competition from the background alkylation was significant. Analysis of the observed diastereo- and enantioselectivity for Pt-catalyzed alkylation of 1c and the mixed secondary/tertiary phosphine IsHP(CH2)3P(CH2Ph)Is (4c) yielded quantitative information on the selectivity of both P−C bond-forming steps, which was consistent with predominant catalyst control, altered slightly by the influence of the substrate.
1. Experimental Section 2. X-ray Crystallographic Details General Experimental Details. Unless ot... more 1. Experimental Section 2. X-ray Crystallographic Details General Experimental Details. Unless otherwise noted, all reactions and manipulations were performed in dry glassware under a nitrogen atmosphere at 20 °C in a dry box or using standard Schlenk techniques. Petroleum ether (bp 38-53 °C), CH 2 Cl 2 , ether, THF, and toluene were dried over alumina columns similar to those described by Grubbs. 1 NMR spectra were recorded using Varian 300 or 500 MHz spectrometers. 1 H or 1 3 C NMR chemical shifts are reported vs Me 4 Si and were determined by reference to the residual 1 H or 13 C solvent peaks. 3 1 P NMR chemical shifts are reported vs H 3 PO 4 (85%) used as an external reference. Coupling constants are reported in Hz, as absolute values unless noted otherwise. Unless indicated, peaks in NMR spectra are singlets.
Enantioselective tandem alkylation/arylation of primary phosphines with 1-bromo-8-chloromethylnap... more Enantioselective tandem alkylation/arylation of primary phosphines with 1-bromo-8-chloromethylnaphthalene catalyzed by Pt(DuPhos) complexes gave P-stereogenic 1-phosphaacenaphthenes (AcePhos) in up to 74% ee. Diastereoselective formation of four P-C bonds in one pot with bis(primary) phosphines gave C2-symmetric diphosphines, including the o-phenylene derivative DuAcePhos, for which the rac isomer was formed with high enantioselectivity. These reactions, which appear to proceed via an unusual metal-mediated nucleophilic aromatic substitution pathway, yield a new class of heterocycles with potential applications in asymmetric catalysis.
The racemic secondary phosphine PH(Me)(Is) (1, Is = 2,4,6-(i-Pr)3C6H2) was coupled with PhI in th... more The racemic secondary phosphine PH(Me)(Is) (1, Is = 2,4,6-(i-Pr)3C6H2) was coupled with PhI in the presence of NaOSiMe3 and the catalyst Pd((R,R)-Me-Duphos)(Ph)(I) (3) to give P(Ph)(Me)(Is) (2) in up to 78% ee. The intermediate phosphido complex Pd((R,R)-Me-Duphos)(Ph)(P(Me)(Is)) (5a,b) was observed as a mixture of diastereomers by low-temperature 31P NMR. The rate of interconversion of 5a,b by phosphorus inversion is greater than or equal to that of reductive elimination, which suggests that the enantiodetermining step occurs after Pd-P bond formation.
The selectivity of catalytic asymmetric transformations of bifunctional symmetrical substrates of... more The selectivity of catalytic asymmetric transformations of bifunctional symmetrical substrates often depends on the linker between the two reactive sites. If the catalyst controls the selectivity of reactions at both sites, the rac product will be formed in high enantiomeric ratio (er) via asymmetric amplification. Substrate control may augment this selectivity (positive cooperativity) or detract from it (negative cooperativity). Here, we investigated the effect of linker length on the selectivity of catalytic asymmetric alkylation of the bis(secondary phosphines) PhHP(CH 2) n PHPh (n = 2-6, 1a-e) with benzyl bromide using the base NaOSiMe 3 and the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl). These reactions yielded the diastereomerically and enantiomerically enriched bis(tertiary phosphines) Ph(PhCH 2)P(CH 2) n P(CH 2 Ph)Ph (n = 2-6, 2a-e). Pt-catalyzed benzylation of the model phosphines PH(Ph)((CH 2) n H) (4a-e, n = 2-6) gave enantiomerically enriched P(CH 2 Ph)(Ph)((CH 2) n H) (5a-e, n = 2-Page 1 of 27 ACS Paragon Plus Environment ACS Catalysis 2 6). The partially alkylated bis(phosphines) PhHP(CH 2) n P(CH 2 Ph)Ph (n = 2, 3, and 5, 3a-b and 3d) were prepared with different degrees of enantiomeric enrichment at the tertiary phosphine centers, then catalytically alkylated to give 2a-b and 2d. From the diastereoselectivity and enantioselectivity of the transformations 12 and 32, the selectivity of each individual alkylation step (13R or 3S; 3R2RR or 2RS; 3S2SS or 2SR) could be determined as a function of linker length, and compared to the selectivity of alkylation of the model monophosphines 4. The two alkylations of bis(secondary phosphines) 1b-e with longer linker lengths (n = 3-6) showed identical selectivity, within experimental error. This catalyst control resulted in asymmetric amplification of rac-2. In contrast, the selectivity of the first alkylation of ethano-bridged 1a was lower than that in 1b-e (negative cooperativity), but the selectivity of the second alkylation (of intermediate 3a) increased due to positive cooperativity. Possible mechanistic explanations for the observed dependence of selectivity on linker length are discussed.
Abstract This chapter reviews the chemistry of phosphiranes, phosphirenes, and their heavier anal... more Abstract This chapter reviews the chemistry of phosphiranes, phosphirenes, and their heavier analogues reported from 2008 to 2018, with focus on the structure of the three-membered rings, synthesis, and reactivity, which is dominated by relief of ring strain. Applications as ligands for transition metals and use in catalysis are also considered.
Tetrahedral main‐group compounds are normally configurationally stable, but P‐epimerization of th... more Tetrahedral main‐group compounds are normally configurationally stable, but P‐epimerization of the chiral phosphiranium cations syn‐ or anti‐[Mes*P(Me)CH2CHPh][OTf] (Mes*=2,4,6‐(t‐Bu)3C6H2) occurred under mild conditions at 60 °C in CD2Cl2, resulting in isomerization to give a syn‐enriched equilibrium mixture. Ion exchange with excess [NBu4][Δ‐TRISPHAT] (Δ‐TRISPHAT=Δ‐P(o‐C6Cl4O2)3) followed by chromatography on silica removed [NBu4][OTf] and gave mixtures of syn‐ and anti‐[Mes*P(Me)CH2CHPh][Δ‐TRISPHAT]⋅x[NBu4][Δ‐TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P‐C cleavage to yield a hyperconjugation‐stabilized carbocation, pyramidal inversion promoted by σ‐interaction of the P lone pair with the neighboring β‐carbocation, and ring closure with inversion of configuration at P.
Diastereoselective coordination of racemic secondary phosphines (PHRR′) to Cu(I) precursors conta... more Diastereoselective coordination of racemic secondary phosphines (PHRR′) to Cu(I) precursors containing chiral bis(phosphines) (diphos*) was explored as a potential route to P-stereogenic phosphido complexes. Reaction of [Cu(NCMe) 4 ]-[PF 6 ] with chiral bis(phospholanes) gave [Cu(diphos*) 2 ][PF 6 ] (diphos* = (R,R)-Me-DuPhos (1), (R,R)-Et-DuPhos (2), or (R,R)-Me-FerroLANE) (3)) or the mono(chelates) [Cu-(diphos*)(NCMe) n ][PF 6 ] (diphos* = (R,R)-i-Pr-DuPhos, n = 2 (4); diphos* = (R,R)-Me-FerroLANE, n = 1 (5)). Treatment of [Cu(NCMe) 4 ][PF 6 ] with diphos* and PHMe(Is) (Is = 2,4,6-(i-Pr) 3 C 6 H 2) gave mixtures of diastereomers of [Cu((R,R)-i-Pr-DuPhos)(PHMe(Is))(NCMe)][PF 6 ] (6) and [Cu((R,R)-Me-FerroLANE)(PHMe(Is))][PF 6 ] (7); two of the three expected isomers of the bis(secondary phosphine) complexes [Cu((R,R)i-Pr-DuPhos)(PhHP(CH 2) n PHPh)][PF 6 ] (n = 2 (8); n = 3 (9)) were formed preferentially in related reactions. Reaction of the halide-bridged dimers [Cu((R,R)-i-Pr-DuPhos)(X)] 2 or [Cu((R,R)-Me-FerroLANE)(I)] 2 with PHMe(Is) gave the labile adducts Cu((R,R)-i-Pr-DuPhos)(PHMe(Is))(X) (X = Cl (10), Br (11), I (12)) and Cu((R,R)-Me-FerroLANE)(PHMe-(Is))(I) (13). Complexes 1, 6, and 8−11 were structurally characterized by X-ray crystallography. Variable temperature NMR studies of 6 and 8 showed that the secondary phosphine ligands underwent reversible dissociation. Deprotonation of 6 or 7 generated the P-stereogenic phosphido complexes Cu(diphos*)(PMeIs) (diphos* = (R,R)-i-Pr-DuPhos (14) or (R,R)-Me-FerroLANE) (17)), observed by 31 P NMR spectroscopy, but decomposition also occurred. Density functional theory calculations were used to characterize the diastereomers of thermally unstable 17 and the inversion barrier in a model copperphosphido complex. These observations provided structure−property relationships which may be useful in developing catalytic asymmetric reactions involving secondary phosphines and P-stereogenic copper phosphido intermediates.
Alkylation of MeC(CH2PHPh)3 1 with 2-cyanobenzyl bromide and NaOSiMe3 using the catalyst precurso... more Alkylation of MeC(CH2PHPh)3 1 with 2-cyanobenzyl bromide and NaOSiMe3 using the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl) gave a mixture of tris(phosphines) enriched in C3-MeC(CH2PPh(CH2(o-C6H4CN))3 3; Cu-catalyzed phosphination yielded C1-enriched 3. Oxidation of 3 by sulfur or H2O2 formed MeC(CH2P(E)Ph(CH2(o-C6H4CN))3 (E = S 4; E = O 5). Repeated recrystallization gave a low yield of (R,R,R)-4, which was crystallographically characterized. Tris(phosphine) 3 was formed with a diastereomeric ratio (dr = C3/C1) of 2.1(2) and enantiomeric ratios of 54(10) and 3.8(7) for C3-3 and C1-3 respectively, which showed that the selectivity of the triple alkylation was not the same at each site (substrate control).
Me-DuPhos)(CH 2 Cl)(Cl) (4). Treatment of [Rh(COD)(Cl)] 2 with (R,R)-Me-DuPhos at low temperature... more Me-DuPhos)(CH 2 Cl)(Cl) (4). Treatment of [Rh(COD)(Cl)] 2 with (R,R)-Me-DuPhos at low temperature in THF or CH 2 Cl 2 afforded [Rh((R,R)-Me-DuPhos)(Cl)] 2 (5). At room temperature, these reactions also gave the byproduct [Rh((R,R)-Me-DuPhos) 2 ][Cl], which was prepared independently as the BF 4 salt 6. When 5 was generated in CH 2 Cl 2 , oxidative addition of both CeCl bonds yielded the bridging carbene complex (Rh ((R,R)-Me-DuPhos)(Cl)) 2 (µ-Cl) 2 (µ-CH 2) (8). Both 6 and 8 were crystallographically characterized.
A range of P-containing ene-diynes suitable for desymmetrization was prepared via a two-step proc... more A range of P-containing ene-diynes suitable for desymmetrization was prepared via a two-step process starting from phosphorus oxychloride. In the presence of the Hoveyda-Grubbs II catalyst, these substrates underwent diastereoselective enyne ring-closing metathesis leading to various synthetically useful P-stereogenic heterocycles featuring an exocyclic alkynyl group. These products are amenable to further functional manipulation.
Reaction of the enantiomerically enriched P-stereogenic phosphiranes syn-(RP,SC)-Mes*PCH2CH(Ph) (... more Reaction of the enantiomerically enriched P-stereogenic phosphiranes syn-(RP,SC)-Mes*PCH2CH(Ph) (syn-1) and anti-(SP,SC)-Mes*PCH2CH(Ph) (anti-2, Mes* = 2,4,6-(t-Bu)3C6H2) with metal complex precursors gave Au(L)(Cl) (L = 1 (3); L = 2 (4)), trans-ML2Cl2 (L = 1, M = Pd (5), Pt (6)), Pd(η3-C3H5)(L)(Cl) (L = 1 (7)), and trans-RhL2(CO)(Cl) (L = 1 (8); L = 2 (9)); 3, 4, 7, and 9 were crystallographically characterized. Phosphirane coordination resulted in shortening of the P–C bonds and increased bond angles at P, consistent with rehybridization at phosphorus. A comparison of complexes of phenylphosphirane and phenyldimethylphosphine using IR spectra, coupled with DFT studies using electronic decomposition analysis (EDA) and natural orbitals for chemical valence (NOCV), indicated that phosphiranes are slightly poorer σ-donors than the analogous phosphines and that the π-acceptor properties of these ligands are similar. Pauli repulsion, dispersion, and electrostatic attraction are also important factors in deter...
Angewandte Chemie (International ed. in English), Jan 23, 2018
Nucleophilic substitution results in inversion of configuration at the electrophilic carbon cente... more Nucleophilic substitution results in inversion of configuration at the electrophilic carbon center (S 2) or racemization (S 1). The stereochemistry of the nucleophile is rarely considered, but phosphines, which have a high barrier to pyramidal inversion, attack electrophiles with retention of configuration at P. Surprisingly, cyclization of bifunctional secondary phosphine alkyl tosylates proceeded under mild conditions with inversion of configuration at the nucleophile to yield P-stereogenic syn-phosphiranes. DFT studies suggested that the novel stereochemistry results from acid-promoted tosylate dissociation to yield an intermediate phosphenium-bridged cation, which undergoes syn-selective cyclization.
... (b) Collman, JP; Hegedus, LS; Norton, JR; Finke, RG Principles and Applications of Organotran... more ... (b) Collman, JP; Hegedus, LS; Norton, JR; Finke, RG Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987. ... Ana García,Julio Gómez, Elena Lalinde, and M. Teresa Moreno. Organometallics 2006 25 (16), 3926-3934. ...
ABSTRACT Catalytic asymmetric alkylation of the bis(secondary phosphines) IsHP(CH2)nPHIs (1a−e, n... more ABSTRACT Catalytic asymmetric alkylation of the bis(secondary phosphines) IsHP(CH2)nPHIs (1a−e, n = 1−5, Is = isityl = 2,4,6-(i-Pr)3C6H2) with benzyl bromide using the base NaOSiMe3 and the catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl) gave the bis(tertiary phosphines) Is(PhCH2)P(CH2)nP(CH2Ph)Is (2a−e, n = 1−5) via the intermediates Is(PhCH2)P(CH2)nPHIs (4a−e, n = 1−5). The rates of these reactions depended strongly on n, in the order 1a < 1b < 1c ≈ 1d ≈ 1e. The bulkier bis(secondary phosphine) Mes*HP(CH2)2PHMes* (5, Mes* = 2,4,6-(t-Bu)3C6H2) did not undergo catalytic alkylation under these conditions. The alkylation selectivity also depended on n. Alkylation of 1b was meso-selective, while alkylation of 1a,c−e was rac-selective, occurring with similar diastereoselectivity and enantioselectivity for the longer linkers (1c−e). The product ratios suggested that the catalyst controlled the selectivity for 1d,e, while substrate control operated for ethano-bridged 1b, with negative cooperativity. Substrate control also likely occurred for 1a, for which competition from the background alkylation was significant. Analysis of the observed diastereo- and enantioselectivity for Pt-catalyzed alkylation of 1c and the mixed secondary/tertiary phosphine IsHP(CH2)3P(CH2Ph)Is (4c) yielded quantitative information on the selectivity of both P−C bond-forming steps, which was consistent with predominant catalyst control, altered slightly by the influence of the substrate.
1. Experimental Section 2. X-ray Crystallographic Details General Experimental Details. Unless ot... more 1. Experimental Section 2. X-ray Crystallographic Details General Experimental Details. Unless otherwise noted, all reactions and manipulations were performed in dry glassware under a nitrogen atmosphere at 20 °C in a dry box or using standard Schlenk techniques. Petroleum ether (bp 38-53 °C), CH 2 Cl 2 , ether, THF, and toluene were dried over alumina columns similar to those described by Grubbs. 1 NMR spectra were recorded using Varian 300 or 500 MHz spectrometers. 1 H or 1 3 C NMR chemical shifts are reported vs Me 4 Si and were determined by reference to the residual 1 H or 13 C solvent peaks. 3 1 P NMR chemical shifts are reported vs H 3 PO 4 (85%) used as an external reference. Coupling constants are reported in Hz, as absolute values unless noted otherwise. Unless indicated, peaks in NMR spectra are singlets.
Enantioselective tandem alkylation/arylation of primary phosphines with 1-bromo-8-chloromethylnap... more Enantioselective tandem alkylation/arylation of primary phosphines with 1-bromo-8-chloromethylnaphthalene catalyzed by Pt(DuPhos) complexes gave P-stereogenic 1-phosphaacenaphthenes (AcePhos) in up to 74% ee. Diastereoselective formation of four P-C bonds in one pot with bis(primary) phosphines gave C2-symmetric diphosphines, including the o-phenylene derivative DuAcePhos, for which the rac isomer was formed with high enantioselectivity. These reactions, which appear to proceed via an unusual metal-mediated nucleophilic aromatic substitution pathway, yield a new class of heterocycles with potential applications in asymmetric catalysis.
The racemic secondary phosphine PH(Me)(Is) (1, Is = 2,4,6-(i-Pr)3C6H2) was coupled with PhI in th... more The racemic secondary phosphine PH(Me)(Is) (1, Is = 2,4,6-(i-Pr)3C6H2) was coupled with PhI in the presence of NaOSiMe3 and the catalyst Pd((R,R)-Me-Duphos)(Ph)(I) (3) to give P(Ph)(Me)(Is) (2) in up to 78% ee. The intermediate phosphido complex Pd((R,R)-Me-Duphos)(Ph)(P(Me)(Is)) (5a,b) was observed as a mixture of diastereomers by low-temperature 31P NMR. The rate of interconversion of 5a,b by phosphorus inversion is greater than or equal to that of reductive elimination, which suggests that the enantiodetermining step occurs after Pd-P bond formation.
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