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Cobalt-Catalyzed Regio- and Enantioselective Markovnikov 1,2-Hydrosilylation of Conjugated Dienes Huanan Wen, Kuan Wang, Yanlu Zhang, Guixia Liu, and Zheng Huang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b04481 • Publication Date (Web): 14 Jan 2019 Downloaded from http://pubs.acs.org on January 15, 2019
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ACS Catalysis
Cobalt-Catalyzed Regio- and Enantioselective Markovnikov 1,2-Hydrosilylation of Conjugated Dienes Huanan Wen†, Kuan Wang†, Yanlu Zhang†, Guixia Liu† and Zheng Huang*,†,‡ †State
Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China. ‡Chang-Kung Chuang Institute, East China Normal University, Shanghai 200062, China Supporting Information Placeholder ABSTRACT: The asymmetric 1,2-Markovnikov hydrosilylation of conjugated dienes with primary silane catalyzed by a quinoline-oxazoline cobalt complex has been described. This protocol provides an efficient approach to chiral allyl dihydrosilanes with high regioselectivity and enantioselectivity (up to 96% ee). The catalyst system is effective for a wide array of conjugated dienes, including mono- and 1,2-disubstituted dienes with aryl and/or alkyl substituents. Further, the products are applied to the synthesis of polyorganosiloxanes (organo-silicone copolymers) containing side chains of enantioenriched allylic functionalities using a pyridine-oxazoline cobalt-catalyzed step-growth polymerization with terephthalaldehyde. The result of a deuterium-labelling experiment involving the reaction of PhSiD3 and 1,3-pentadiene suggests the hydrosilylation most likely proceeds through the modified Chalk-Harrod mechanism involving the 1,2-insertion of the terminal double bond of the diene into the Co−Si bond. KEYWORDS: cobalt, conjugated dienes, allylsilane, polyorganosiloxane, hydrosilylation, asymmetric catalysis
INTRODUCTION Transition metal-catalyzed hydrosilylation reactions of conjugated dienes have been extensively studied,1,2 but enantioselective methods for 1,2-Markovnikov hydrosilylation remain underdeveloped. Such a transformation encounters both regioand enantioselectivity challenges. Among the reported catalytic methods of diene hydrosilylation, 1,4-addition reactions prevail in part because of the propensity to form -allyl transition metal intermediates (Scheme 1a).1,2 Although a handful of catalysts are now known for diene 1,2-hydrosilylation with anti-Markovnikov3 or Markovnikov4 selectivity, there has been only one example for asymmetric version of 1,2-Markovnikov hydrosilylation with limited success: a difluorphos Co complex catalyzed 1,2-hydrosilylation of three 1-aryl-substituted dienes with moderate enantioselectivity (overall range of ee: 76−80%),4b whereas known catalysts cannot effect asymmetric 1,2-Markovnikov hydrosilylation of alkyl-substituted dienes. Herein we disclose the development of bidentate oxazoline-based Co complexes, one of which catalyzes 1,2-Markovnikov hydrosilylation of various mono- and 1,2-disubstituted conjugate dienes bearing aryl and/or alkyl substituents with unprecedented levels of regio- and enantiocontrol (Scheme 1b). Products of enantioselective 1,2-Markovnikov diene hydrosilylation, chiral allylsilanes, are highly valuable building blocks, as demonstrated by their wide applications in asymmetric synthesis of natural products.5 Moreover, allyl dihydrosilanes derived from primary silane can potentially act as coupling reagents by hydrosilylating unsaturated compounds. Such a strategy may be further extended to the synthesis of functional organo-silicone copolymers that contain chiral allylic branchings by reacting allyl dihydrosilane with suitable bifunctional monomers. It is worth noting that such chiral allyl dihydrosilanes are difficult to access by the existing methods for asymmetric allylsilane synthesis, such as catalytic cross-coupling6 and allylic substitution reactions.7
Scheme 1. Catalytic hydrosilylation of conjugated dienes a) Classical 1,4-hydrosilylation H [Si]H [M] + R proposed R -allyl intermediates Ref. 1
[Si] [Si]
or
R
H Ref. 2
b) This work: asymmetric 1,2-Markovnikov hydrosilylation SiH2Ph PhSiH3 (QuinOx)Co SiH2Ph + [CoI] H R R R R' R' R' proposed R = Ar or Alk >99:1 rr R' = H, Ar or Alk up to 96% ee 1,2-insertion intermediate
RESULTS AND DISCUSSION Based on our earlier observations of Markovnikov-selective hydrosilylations of alkenes8 or alkynes9 using Co complexes of tridentate ligands, which was attributed to inherent 1,2-insertion preference of C−C multiple bond into a Co−Si bond of CoI silyl intermediates,8,10 we envisioned that Co complexes supported by suitable chiral ligands might engender regio- and enantioselective 1,2-Markovnikov diene hydrosilylation. The less hindered terminal C=C bond of 1,3-dienes may undergo facile 1,2-insertion into the Co−Si bond (see the proposed intermediate in Scheme 1b), thus avoiding the formation of a -allyl intermediate that would lead to the common 1,4-hydrosilylation. Given the superior performance of oxazoline-containing tridentate ligands in Co-catalyzed asymmetric hydrofunctionalizations of alkenes11 and alkynes,12 we initially tested the iminopyridine-oxazoline (IPO) Co complexes (Table 1).11a,b Upon activation with NaBEt3H,13 (IPO)CoCl2 complex 1a (2.0 mol %) with an iPr substituent at the oxazoline proved 1,2-Markovnikov selective for the hydrosilylation of 1-phenyl-1,3-butadiene 3a with PhSiH3. The reaction in THF at 25 °C furnished allyl dihydrosilane (S)-4a in 72% NMR yield with 95:5 rr without any detectable 1,4-hydrosilylation product.
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Unfortunately, the enantioselectivity was unsatisfactory, with 50% ee favoring the (S)-enantiomer (entry 1). The tBu analog 1b was more enantioselective than 1a, giving (S)-4a in 68% ee (entry 2). Next we turned to bidentate oxazoline-containing ligands. A series of new pyridine/quinoline-oxazoline chiral CoII dichloride complexes were prepared (Figure 1). The incorporation of a Me substituent at the C6-position of the pyridine moiety is key to form a mononuclear complex, whereas the unsubstituted pyridine-oxazoline (HPyOxiPr) (L1, Table 1) was previously reported to form a dinuclear species [L12Co][CoCl4].14 The reaction of the Me-substituted ligands (MePyOxR) with CoCl2 in THF afforded four-coordinate complexes 2a-2d in high yields. Two quinoline-oxazoline (QuinOxR) complexes 2e, 2f were obtained in a similar manner. The mononuclear structures were confirmed by X-ray diffraction analysis of 2b and 2f, which revealed a tetrahedral coordination geometry (see Figure 1). O
O N Me PyOx or
N
N
Co
CoCl2 O N
N
N
R
Cl
THF
Cl O N
N
R
Co
QuinOx
Cl
Cl
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for the hydrosilylation of the Z-1-phenyl-1,3-butadiene (Z)-3a, with >95% (Z)-3a remaining intact (entry 14).16 Table 1. Evaluation of cobalt catalysts for hydrosilylation of 3a with PhSiH3a + PhSiH3
Ph (E)-3a
R = iBu, 2a, MePyOxiBu, 94% iPr, 2b, MePyOxiPr, 97% R sBu, 2c, MePyOxsBu, 93% tBu, 2d, MePyOxtBu, 97% or
R R = iPr, 2e, QuinOxiPr, 96% tBu, 2f, QuinOxtBu, 95%
(S/R)-4a
Yield [%]
rr
ee [%]
1
1a
72
95:5
50 (S)
2 3
1b 2a
88 85
94:6 >99:1
68 (S) 9 (S)
4
2b
91
>99:1
6 (S)
5
2c
89
>99:1
2 (S)
6
2d
96
>99:1
28 (R)
7b
[L12Co][CoCl4]
71
90:10
15 (R)
8c
[L22Co][CoCl4]
90
93:7
19 (R)
9
2e
95
>99:1
4 (R)
10
2f
93
>99:1
94 (R)
11d
2f
45
>99:1
87 (R)
12e
2f
61
>99:1
83 (R)
13f 14g
2f 2f
NR 99:1 rr (entries 3-6). However, all reations resulted in low enantioselectivity. Introducing a larger substituent at the oxazoline led to declined selectivity for the (S)-enantiomer (9% ee for iBu (2a), 6% ee for iPr (2b), and 2% ee for sBu (2c)). The run with the tBu variant (2d) resulted in enrichment of the (R) isomer (28% ee). The inversion of the stereochemistry implies that the selectivity springs from the synergistic interaction of the oxazoline and pyridine components. To probe the effect of the pyridine component on the selectivity, two truncated ligands (L1, L2) lacking the Me substituent at the pyridine moiety were tested. Submission of the precatalysts formed in situ from CoCl2 and L1/L2 to the hydrosilylation led to a modest drop in regioselectivity, and the (R)-enantiomer was formed preferentially (15% ee for HPyOxiPr L1 and 19% ee for HPyOxtBu L2) (entries 7, 8). Motivated by the observed change of enantioselectivity with modified pyridine components, the quinoline-oxazoline complexes (2e, f) were further examined. (QuinOxiPr)CoCl2 1e with an iPr-substituted oxazoline yielded 4a with high rr, but low ee (4%, entry 9). Delightfully, the tBu-substituted analog (QuinOxtBu)CoCl2 2f is highly regio- and enantioselective, furnishing (R)-4a in 93% yield with >99:1 rr and 94% ee (entry 10).15 The hydrosilylations of 3a with other activators, such as MeLi and EtMgBr, have also been carried out, which were active for the silylation, albeit with a drop of the yield (entries 11, 12). The control reaction without an activator afforded no hydrosilylation products (entry 13). The catalytic activity is sensitive to the geometry of the diene; 2f was found to be inactive
Ph
THF, 25 oC, 12 h
Precat.
N
2f
SiH2Ph
Entry
iPr
2b
precat. (2.0 mol %) NaBEt3H (6.0 mol %)
N
Co Cl
N R PyOx H R = iPr, PyOxiPr L1 tBu, HPyOxtBuL2 N
(IPO)CoCl2 R R = iPr, 1a tBu, 1b
H
Conditions: 3a (0.3 mmol), PhSiH3 (0.6 mmol) in THF (3 mL). Yields and rr values (1,2-Markovnikov product:1,2-anti-Markovnikov product) were determined by 1H NMR with dibromomethane as an internal standard, and ee values were determined by chiral HPLC. bFormed In situ from CoCl2 and HPyOxiPr L1. cFormed In situ from CoCl2 and HPyOxtBu L2. dMeLi, instead of NaBEt H, was used as activator. eEtMgBr, instead of 3 NaBEt3H, was used as activator. fWithout an activator. g(Z)-3a was used as the substrate. a
The scope of conjugated 1,3-dienes for asymmetric 1,2-Markonikov hydrosilylation was then explored by using 2f as the precatalyst (Table 2). Despite the structural diversity of the substrates, all reactions of 1- and 1,2-substituted conjugated dienes offered exclusive regioselectivity for 1,2-Markonikov products when using PhSiH3 (one exception was the case with Ph2SiH2 as the reagent, vide infra), and most reactions gave high ee values (90%). 1-Aryl-substituted dienes (see Table 2a) with both electron- donating and -withdrawing groups on the arene were suitable substrates. The position of the substituents had little impact on the hydrosilylation. For example, three substrates with a Me-substituent at the para, meta, or ortho position respectively yielded the corresponding allylsilanes (4b-d) with comparable selectivity. Halogen (F, Cl, and Br) (4i-m), amine (4n), CF3O (4o), ether (4p, q), thioether (4r), and acetal (4u) functionalities were tolerated. The ester group in 3s is subject to reduction with silanes.17 Thus it is relatively impressive that using Ph2SiH2 (a less reactive silane compared to PhSiH3) afforded the desired product 4s in 42% yield, 91:9 rr and 83% ee. The dienes with heterocyclic (4t, 89% ee) and 1-naphthyl (4v, 89% ee) substituents performed well. To demonstrate scalability, the hydrosilylation of 3a was performed on a 10 mmol scale using 1.0% of 2f, delivering 2.3 g of 4a in 95% yield, >99:1 rr and 93% ee (Table 2a). The catalytic system is efficient for diene hydrosilylation with primary arylsilane other than PhSiH3. The reactions using silanes containing Cl or MeO substituent at the para position of aryl ring afforded the 1,2-Markonikov products in high yields with high
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ACS Catalysis enantioselectivities (4w, 87% ee; 4x, 94% ee). A sterically. desired product 4y with high ee value (93%), albeit in moderate hindered arylsilane with two ortho-Me substituents furnished the Table 2. Cobalt-catalyzed asymmetric hydrosilylation of various conjugated dienes with PhSiH3a R
+ R' 3
ArSiH3
SiH2Ar
2f (2.0 mol %), NaBEt 3H (6.0 mol %)
R
THF, RT, 12 h
4
R'
a) 1-monosubstituted dienes SiH2Ph
SiH2Ph Ph
4a, 95% (2.3 g) 93% ee b
Ph
SiH2Ph
4b, 85% 92% ee
SiH2Ph
SiH2Ph
SiH2Ph
4h, 80% 93% ee
SiH2Ph
4n, 85% 87% ee
Me 2N SiHPh 2
EtO 2C
b) multisubstituented dienes SiH2Ph * 4af, d 72%, 96:4 dr
4o, 53% 90% ee
CF3O
4f, 94% 94% ee
tBu
SiH2Ph 4k, 79% 93% ee
Cl
SiH2Ph
OMe
SiH2Ph
4q, 85% 94% ee
SiH2Ph
4t, 80% 89% ee
4u, 96% 88% ee
O
SiH2Ph ( )7
* 4aa, 89%, 90% ee
* 4ab, 82%, 89% ee
*
4ag, d 67%, 91% ee
* nC6H13 4ah, d 51%, 81% ee
SiH2Ph
*
* 4ae, f 95%
4ad, f 76%
SiH2Ph Ph
4r, 87% 96% ee
MeS
SiH2Ph TBSO
* 4ac, 79%, 90% ee
SiH2Ph Ph
Ph
SiH2Ph
SiH2Ph ( )8
SiH2Ph Ph
88% 92% ee
SiH2Ph
SiH2Ar Ar = p-ClC6H 4, 4w, 83%, 87% ee p-MeOC6H 4, 4x, 96%, 94% ee 2,6-Me2C6H 3, 4y, d,e 56%, 93% ee
O 4v, d
4l, 77% 94% ee
Br
SiH2Ph
4p, 92% 93% ee
MeO
SiH2Ph
SiH2Ph
SiH2Ph * 4z, 88%, 92% ee
4j, 75% 93% ee
SiH2Ph
O
4s, c
( )6
4e, 86% 92% ee
SiH2Ph
4i, 81% 95% ee
F
SiH2Ph
* 42%, 91:9 rr, 83% ee
SiH2Ph
SiH2Ph
F
4g, 81% 94% ee
4m, 76% 95% ee
iPr
4d, 83% 91% ee
4c, 79% 94% ee
F 3C
Br
SiH2Ph
Ph
*
SiH2Ph
SiH2Ph
Ph
Ph 4ai, d,e 42%, 93% ee
Ph
4aj, g 33%, 0% ee
4ak, 99:1 rr) and high enantioselectivity (89-92% ee). The reaction of a triene with PhSiH3 proceeded smoothly without isomerization or hydrosilylation of the isolated internal C=C bond (4ac, 90% ee). The diene containing a TBSO-functionalized alkyl chain underwent regioselectively (4ad), and simple 1,3-pentadiene was hydrosilylated to the corresponding allylsilane (4ae) in high yield with exclusive 1,2-Markovnikov regioselectivity (the ee values for these two products could not be determined by HPLC). The hydrosilylation of isoprene and 1,3-butadiene, however, gave mixtures of 1,4- and 1,2-addition products, with the former as the major products (see Supporting Information for product distributions). The Co-catalyzed asymmetric hydrosilylation was not limited to terminally monosubstituted 1,3-dienes. 1,2-Disubstitued dienes were hydrosilylated with PhSiH3 effectively using 5.0% of 2f (Table 2b). 1,2-Dialkyl-substituted diene derived from (-)-perillaldehyde underwent the hydrosilylation to form 4af in 72% yield and 96:4 d.r.. 2-Methyl-1-phenyl-substituted diene gave 4ag in 67% yield with 91% ee, while the substitution of n-hexyl for methyl led to a reduced yield and enantioselectivity (4ah, 81% ee). 1,2-Diphenyl 1,3-butadiene (3ai) was less reactive than 3ag and 3ah, but did form the desired product 4ai in 42%
yield and 93% ee after a prolonged reaction time of 24 h. 1,1-Diphenyl 1,3-butadiene (3aj) was presumably too sterically bulky to undergo the hydrosilylation. In line with this assertion, switching 2f to the less hindered precatalyst 2b gave 4aj in 33% yield, but without any enantiocontrol. 1,4-disubstituted diene (3ak, however, failed to react. Scheme 2. Derivatizations of chiral allyl dihydrosilanea OH Ph
H Si
5, 86%, 93% ee
Ph
H2O2, KHCO3
Bn
Ph 6, 90%, 2.4:1 d.r. Ph 93% ee & 92% ee
a)
(R)-4a (93% ee)
b) Ph
Ph
H Si
Ph
Ph 7, 71%, 2.1:1 d.r. 92% ee & 87% ee
aCatalysts
used for the hydrosilylation reactions: a) (S)-(IPO)FeBr2 (5.0%), NaBEt3H (15%); b) Co(acac)2 (5.0%), XantPhos (5.0%), NaOtBu (10%).
With 4a readily produced on gram-scale by our method (vide supra), the synthetic utility of chiral allyl dihydrosilane was investigated (Scheme 2). The Fleming-Tamao oxidation of 4a gave a chiral allyl alcohol 5 in 86% yield without racemization (93% ee).18 Using (S)-(IPO)FeBr2 (see Supporting Information (SI) for its structure) as the precatalyst,19 the asymmetric anti-Markovnikov hydrosilylation of styrene with 4a proceeded at RT to give a tertiary silane 6 with an enantioenriched Si-stereocenter in 2.4:1 d.r. and 90% yield.20 Furthermore, the asymmetric hydrosilylation of phenylacetylene with a cobalt
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catalyst of XantPhos11d, 21 formed allyl vinylsilane 7 with 2.1:1 d.r.. Next, we explored the possibility of synthesizing polyorganosiloxanes by polyhydrosilylation using chiral allyl dihydrosilane and dicarbonyl compound as the monomers. The alternating organo-silicone copolymers, which are conventionally synthesized by condensation of (,-bis)silanol22 or polyhydrosilylation with ,-dihydrooligosiloxanes,23 have garnered widespread attention because these materials combine the mechanical properties of organic polymers with the surface properties of silicones.24 We first investigated the reactivity of the secondary allylsilane toward sequential dual-hydrosilylation by running a model reaction between 4a and benzaldehyde (2 equiv). Initial efforts were focused on classical precious metal hydrosilylation catalysts. However, Wilkinson catalyst Rh(PPh3)3Cl was inactive for the hydrosilylation, whereas [Ir(cod)OMe]2 gave the monohydrosilylation product (only one Si−H bond of 4a involved) (see SI). Excitingly, the Co complex (MePyOxiPr)CoCl2 (2b) was found be highly efficient for the dual-hydrosilylation: the reaction catalyzed by (rac)-2b/NaBEt3H formed allyl bis(oxo)silane 8 in 93% yield with complete retention of the configuration at the carbon stereocenter (93% ee) (Scheme 3a). Scheme 3. Synthesis of chiral polyorganosiloxane
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regioselectivity, the Chalk-Harrod mechanism must proceed via a -allyl cobalt intermediate (C) formed by hydrometalation, whereas the modified Chalk-Harrod mechanism must occur via an intermediate (F) formed by 1,2-insertion of the terminal C=C bond of 1,3-dienes into the Co−Si bond (see Figure 2a and 2b for these two simplified catalytic cycles). The reaction of 1,3-pentadiene 3ae with PhSiD3 yielded a single product CH3CH=CHCH(SiPhD2)CH2D 11 with the D- and Si-atom added to the C1 and C2 positions of 1,3-pentadiene, respectively (Figure 2c). This result argues strongly against the Chalk-Harrod mechanism because silylation of the putative allyl intermediate [Co](CH3CHCHCHCH2D) C would otherwise form two products CH3CH=CHCH(SiPhD2)CH2D (11) and CH3CH(SiPhD2)CH=CHCH2D (11’) in an approximate 1:1 ratio. Thus, the 1,2-insertion of the terminal double bond of 1,3-dienes into the Co−Si bond (E → F) is likely to be the enantio-determining step (the plausible enantio-determining transition state that accounts for the observed selectivity is depicted in the Supporting Information). a) Chalk-Harrod mechanism R B
(rac)-2b (5.0 mol %) Si(OBn)2Ph 2 PhCHO NaBEt3H (15.0 mol %) + Ph 8, 93%, 93% ee (R)-4a (93% ee) THF, RT, 8 h [D28 = -7.8 (c = 0.27 M, CH2Cl2)
a)
b)
(R)-4a (93% ee) +
OHC
CHO 9
[L12Co][CoCl4] (2.5 mol %) NaBEt3H (15 mol %) THF, RT, 60 h
O
H2 C
Ph H2 C O Si
[Co]-H
n
Ph 10, 74%, Mw = 8,700, PDI = 1.8 [D22 = -5.3 (c = 0.49 M, CH2Cl2)
The high efficiency demonstrated in the model reaction suggests that Co-catalyzed step-growth polymerization using allyl dihydrosilanes as the monomers is feasible. Bifunctional terephthalaldehyde 9 was selected as the comonomer. (rac)-2b/NaBEt3H was active for the polyhydrosilylation reaction between 9 and 4a (1 equiv), but yielded low molecular weight (MW) polymer (see SI for GPC data). A screen of other Co catalysts developed in this work revealed that the use of a less sterically hindered ligand has a beneficial effect on the generation of high MW copolymer: the polymerization catalysed by [L12Co][CoCl4] with the less congested HPyOxiPr ligand L1 created relatively high MW copolymer 10 (Mw = 8,700, PDI = 1.8) (Scheme 3b). NMR analysis of the reaction mixture revealed the disappearance of the signals for the CHO group of 9 and for the SiH group of 4a, and the appearance of the signal for the CH2 units between the aryl rings and O-atoms. Noteworthily, the allylic moieties remained intact during the polyhydrosilylation process (see SI for spectra). Although the enantiopurity of 10 cannot be determined, the data obtained by chiroptical methods in combination with the observed stereochemistry for 8 resulting from the model reaction strongly support the generation of chiral polymer. Despite the rigid backbones composed of perfectly alternating aromatic rings and silicone units, the pale gray solid material of 10 exhibits good solubility in common organic solvents, such as THF and DMF. Although a full understanding of the mechanism for the cobalt-catalyzed Markovnikov 1,2-hydrosilylation of conjugated dienes needs additional computational and experimental studies, a deuterium-labeling experiment provides evidence in support of the modified Chalk-Harrod mechanism (alkene insertion into a Co−Si bond) versus the Chalk-Harrod mechanism (alkene insertion into a Co−H bond). To accommodate the observed
[Co] H R
A
SiH2Ph H *
R
[Co] R
H C
PhSiH3 b) modified Chalk-Harrod mechanism R
[Co] SiH2Ph
R E
[Co] SiH2Ph
1,2insertion
D
SiH2Ph H *
R
R PhSiH3 c)
4
2 3
+ PhSiD3
1
2f (2.0 mol %) NaBEt3H (6.0 mol %) THF, RT, 12 h
SiH2Ph [Co] * F
SiD2Ph * CH2D 11, 82%
SiD2Ph CH2D 11', not formed
Figure 2. a) Simplified Chalk-Harrod and b) modified Chalk-Harrod mechanism that account for the observed regioselectivity for Co-catalyzed diene hydrosilylation; c) deuterium-labling experiment supporting the modified Chalk-Harrod mechanism. CONCLUSIONS In conclusion, we report the first general asymmetric 1,2Markovnikov hydrosilylation of conjugated dienes with excellent regio- and stereoselectivity using an easily-accessible quinoline-oxazoline Co catalyst. The hydrosilylation is applicable to a wide variety of 1,3-dienes with aromatic and aliphatic
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ACS Catalysis substituents. In addition, the chiral allyl dihydrosilane product can be used for Co-catalyzed polyhydrosilylation of dicarbonyls, thereby offering an efficient approach to novel polyorganosiloxanes containing chiral, reactive allylic groups as side chains, which are expected to undergo further alkene functionalization and hold promise for synthesis of chiral crosslinked networks. EXPERIMENTAL SECTION General Procedure for Cobalt-Catalyzed 1,2-Hydrosilylation of Conjugated Dienes. In an Ar-filled glovebox, to a solution of 2f (2.3 mg, 6.0 µmol) in 3.0 mL of THF, conjugated dienes 3 (0.3 mmol, 1.0 equiv) and ArSiH3 (0.6 mmol, 2.0 equiv) were added. After the solution was cooled to -30 ºC, a solution (1.0 M in THF) of NaBEt3H (18 µL, 18.0 µmol) was slowly added. The reaction mixture was stirred for 12 h at RT and then was quenched by exposing the solution to air. The resulting solution was concentrated in vacuum and the residue was purified by chromatography on silica gel eluting with ethyl acetate/petroleum ether to give the product 4.
ASSOCIATED CONTENT AUTHOR INFORMATION Corresponding Author
[email protected] Notes The authors declare no competing financial interest.
Supporting Information Experimental procedures and characterization data. This material is available free of charge via the Internet at http://pubs.acs.org.
ACKNOWLEDGMENTS Financial support was provided by the Ministry of Science and Technology of China (2016YFA0202900, 2015CB856600), NSFC (21825109, 21732006, 21432011, 21602236), and Chinese Academy of Sciences (XDB20000000, QYZDB-SSW-SLH016), and Science and Technology Commission of Shanghai Municipality (17JC1401200).
REFERENCES (1) For examples of 1,4-addition with Si-added to the terminal carbon: (a) Lappert, M. F.; Nile, T. A.; Takahashi, S. Homogeneous catalysis: II. ziegler systems as catalysts for hydrosilylation. J. Organomet. Chem. 1974, 72, 425-439. (b) Gustafsson, M.; Frejd, T. Regioselectivity in the rhodium catalysed 1,4-hydrosilylation of isoprene. Aspects on reaction conditions and ligands. J. Organomet. Chem. 2004, 689, 438-443. (c) Hilt, G.; Lüers, S.; Schmidt, F. Cobalt(I)-Catalyzed Diels-Alder, 1,4-Hydrovinylation and 1,4-Hydrosilylation Reactions of Non-Activated Starting Materials on a Large Scale. Synthesis 2004, 634-638. (d) Wu, J. Y.; Stanzl, B. N.; Ritter, T. A Strategy for the Synthesis of Well-Defined Iron Catalysts and Application to Regioselective Diene Hydrosilylation. J. Am. Chem. Soc. 2010, 132, 13214-13216. (e) Pop, R.; Cui, J. L.; Adriaenssens, L.; Comte, V.; Le Gendre, P. [Me2C(C5H4)2TiMe2]: An Open-Bent Titanocene Catalyst for the Hydrosilylation of Bulky 1,3-Dienes. Synlett 2011, 679-683. (f) Srinivas, V.; Nakajima, Y.; Ando, W.; Sato, K.; Shimada, S. Bis(acetylacetonato) Ni(II)/NaBHEt3-catalyzed hydrosilylation of 1,3-dienes, alkenes and alkynes. J. Organomet. Chem. 2016, 809, 57-62. (2) For asymmetric 1,4-addition with H-added to the terminal carbon: (a) Han, J. W.; Hayashi, T. Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes. Tetrahedron: Asymmetry 2010, 21, 2193-2197, and references therein. (b) Okada, T.; Morimoto, T.; Achiwa, K. Asymmetric Hydrosilylation of Cyclopentadiene and Styrene with Chlorosilanes Catalyzed by Palladium Complexes of Chiral (-N-Sulfonylaminoalkyl)phosphines. Chem. Lett. 1990, 19, 999-1002. (c)
Hatanaka, Y.; Goda, K.-i.; Yamashita, F.; Hiyama, T. Catalytic asymmetric hydrosilylation of conjugated dienes: Effective control of regio- and enantioselectivities. Tetrahedron Lett. 1994, 35, 7981-7982. (d) Marinetti, A.; Ricard, L. Phosphetanes as Chiral Ligands for Catalytic Asymmetric Reactions: Hydrosilylation of Olefins. Organometallics 1994, 13, 3956-3962. (e) Ohmura, H.; Matsuhashi, H.; Tanaka, M.; Kuroboshi, M.; Hiyama, T.; Hatanaka, Y.; Goda, K.-i. Catalytic asymmetric hydrosilylation of 1,3-dienes with difluoro(phenyl) silane. J. Organomet. Chem. 1995, 499, 167-171. (f) Park, H. S.; Han, J. W.; Shintani, R.; Hayashi, T. Asymmetric hydrosilylation of cyclohexa-1,3-diene with trichlorosilane by palladium catalysts coordinated with chiral phosphoramidite ligands. Tetrahedron: Asymmetry 2013, 24, 418-420. (3) (a) Parker, S. E.; Börgel, J.; Ritter, T. 1,2-Selective Hydrosilylation of Conjugated Dienes. J. Am. Chem. Soc. 2014, 136, 4857-4860. (b) Greenhalgh, M. D.; Frank, D. J.; Thomas, S. P. Iron-Catalysed Chemo-, Regio-, and Stereoselective Hydrosilylation of Alkenes and Alkynes using a Bench-Stable Iron(II) Pre-Catalyst. Adv. Synth. Catal. 2014, 356, 584-590. (c) Ibrahim, A. D.; Entsminger, S. W.; Zhu, L.; Fout, A. R. A Highly Chemoselective Cobalt Catalyst for the Hydrosilylation of Alkenes using Tertiary Silanes and Hydrosiloxanes. ACS Catal. 2016, 6, 3589-3593. (d) Raya, B.; Jing, S.; Balasanthiran, V.; RajanBabu, T. V. Control of Selectivity through Synergy between Catalysts, Silanes, and Reaction Conditions in Cobalt-Catalyzed Hydrosilylation of Dienes and Terminal Alkenes. ACS Catal. 2017, 7, 2275-2283. (4) (a) Hu, M.; He, Q.; Fan, S.; Wang, Z.; Liu, L.; Mu, Y.; Peng, Q.; Zhu, S. Ligands with 1,10-phenanthroline scaffold for highly regioselective iron-catalyzed alkene hydrosilylation. Nat. Commun. 2018, 9, 221, DOI: 10.1038/s41467-017-02472-6. (b) Sang, H. L.; Yu, S.; Ge, S. Cobalt-catalyzed regioselective stereoconvergent Markovnikov 1,2-hydrosilylation of conjugated dienes. Chem. Sci. 2018, 9, 973-978. (5) (a) Panek, J. S.; Yang, M. Diastereoselective additions of chiral (E)-crotylsilanes to -alkoxy and -alkoxy aldehydes. A one-step, silicon-directed tetrahydrofuran synthesis. J. Am. Chem. Soc. 1991, 113, 9868-9870. (b) Hu, T.; Panek, J. S. Enantioselective Synthesis of the Protein Phosphatase Inhibitor (−)-Motuporin. J. Am. Chem. Soc. 2002, 124, 11368-11378. (c) Su, Q.; Panek, J. S. Total Synthesis of (−)-Apicularen A. J. Am. Chem. Soc. 2004, 126, 2425-2430. (d) Tinsley, J. M.; Roush, W. R. Total Synthesis of Asimicin via Highly Stereoselective [3+2] Annulation Reactions of Substituted Allylsilanes. J. Am. Chem. Soc. 2005, 127, 10818-10819. (e) Va, P.; Roush, W. R. Total Synthesis of Amphidinolide E. J. Am. Chem. Soc. 2006, 128, 15960-15961. (f) Binanzer, K.; Fang, G. Y.; Aggarwal, V. K. Asymmetric Synthesis of Allylsilanes by the Borylation of Lithiated Carbamates: Formal Total Synthesis of (−)-Decarestrictine D. Angew. Chem. Int. Ed. 2010, 49, 4264-4268. (g) Wu, J.; Pu, Y.; Panek, J. S. Divergent Synthesis of Functionalized Carbocycles through Organosilane-Directed Asymmetric Alkyne–Alkene Reductive Coupling and Annulation Sequence. J. Am. Chem. Soc. 2012, 134, 18440-18446. (6) (a) Hayashi, T.; Konishi, M.; Ito, H.; Kumada, M. Optically active allylsilanes. 1. Preparation by palladium-catalyzed asymmetric Grignard cross-coupling and anti stereochemistry in electrophilic substitution reactions. J. Am. Chem. Soc. 1982, 104, 4962-4963. (b) Hayashi, T.; Konishi, M.; Kumada, M. Optically active allylsilanes. 2. High stereoselectivity in asymmetric reaction with aldehydes producing homoallylic alcohols. J. Am. Chem. Soc. 1982, 104, 4963-4965. (c) Hofstra, J. L.; Cherney, A. H.; Ordner, C. M.; Reisman, S. E. Synthesis of Enantioenriched Allylic Silanes via Nickel-Catalyzed Reductive Cross-Coupling. J. Am. Chem. Soc. 2018, 140, 139-142. (7) (a) Schmidtmann, E. S.; Oestreich, M. Mechanistic insight into copper-catalysed allylic substitutions with bis(triorganosilyl) zincs. Enantiospecific preparation of -chiral silanes. Chem. Commun. 2006, 3643-3645. (b) Kacprzynski, M. A.; May, T. L.; Kazane, S. A.; Hoveyda, A. H. Enantioselective Synthesis of Allylsilanes Bearing Tertiary and Quaternary Si-Substituted Carbons through Cu-Catalyzed Allylic Alkylations with Alkylzinc and Arylzinc Reagents. Angew. Chem. Int. Ed. 2007, 46, 4554-4558. (c) Delvos, L. B.; Vyas, D. J.; Oestreich, M. Asymmetric Synthesis of a-iral Allylic Silanes by Enantioconvergent g-selective Copper(I)‐Catalyzed Allylic Silylation. Angew. Chem. Int. Ed. 2013, 52, 4650-4653. (d) Takeda, M.; Shintani, R.; Hayashi, T. Enantioselective Synthesis of a-Tri- and a -Tetrasubstituted Allylsilanes by Copper-Catalyzed Asymmetric Allylic Substitution of Allyl Phosphates with Silylboronates. J. Org. Chem, 2013, 78, 5007-5017.
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(8) Du, X.; Zhang, Y.; Peng, D.; Huang, Z. Base-Metal-Catalyzed Regiodivergent Alkene Hydrosilylations. Angew. Chem. Int. Ed. 2016, 55, 6671-6675. (9) (a) Guo, J.; Lu, Z. Highly Chemo-, Regio-, and Stereoselective Cobalt-Catalyzed Markovnikov Hydrosilylation of Alkynes. Angew. Chem. Int. Ed. 2016, 55, 10835-10838. (b) Zuo, Z.; Yang, J.; Huang, Z. Cobalt-Catalyzed Alkyne Hydrosilylation and Sequential Vinylsilane Hydroboration with Markovnikov Selectivity. Angew. Chem. Int. Ed. 2016, 55, 10839-10843. (10) (a) Chu, W.; Gilbert-Wilson, R.; Rauchfuss, T. B.; van Gastel, M.; Neese, F. Cobalt Phosphino--Iminopyridine-Catalyzed Hydrofunctionalization of Alkenes: Catalyst Development and Mechanistic Analysis. Organometallics 2016, 35, 2900-2914. (b) Du, X.; Huang, Z. Advances in Base-Metal-Catalyzed Alkene Hydrosilylation. ACS Catal. 2017. 7. 1227-1243. (11) (a) Zhang, L.; Zuo, Z.; Wan, X.; Huang, Z. Cobalt-Catalyzed Enantioselective Hydroboration of 1,1-Disubstituted Aryl Alkenes. J. Am. Chem. Soc. 2014, 136, 15501-15504. (b) Chen, J.; Xi, T.; Ren, X.; Cheng, B.; Guo, J.; Lu, Z. Asymmetric cobalt catalysts for hydroboration of 1,1-disubstituted alkenes. Org. Chem. Front. 2014, 1, 1306-1309. (c) Zhang, H.; Lu, Z. Dual-Stereocontrol Asymmetric Cobalt-Catalyzed Hydroboration of Sterically Hindered Styrenes. ACS Catal. 2016, 6, 6596-6600. (d) Cheng, B.; Lu, P.; Zhang, H.; Cheng, X.; Lu, Z. Highly Enantioselective Cobalt-Catalyzed Hydrosilylation of Alkenes. J. Am. Chem. Soc. 2017, 139, 9439-9442. (12) (a) Guo, J.; Cheng, B.; Shen, X.; Lu, Z. Cobalt-Catalyzed Asymmetric Sequential Hydroboration/Hydrogenation of Internal Alkynes. J. Am. Chem. Soc. 2017, 139, 15316-15319. (b) Guo, J.; Shen, X.; Lu, Z. Regio- and Enantioselective Cobalt-Catalyzed Sequential Hydrosilylation/ Hydrogenation of Terminal Alkynes. Angew. Chem. Int. Ed. 2017, 56, 615-618. (c) Wen, H.; Wan, X.; Huang, Z. Asymmetric Synthesis of Silicon-Stereogenic Vinylhydrosilanes by Cobalt-Catalyzed Regio- and Enantioselective Alkyne Hydrosilylation with Dihydrosilanes. Angew. Chem. Int. Ed. 2018, 57, 6319-6323. (13) Bouwkamp, M. W.; Bowman, A. C.; Lobkovsky, E.; Chirik, P. J. Iron-Catalyzed [2π+2π] Cycloaddition of α,ω-Dienes: The Importance of Redox-Active Supporting Ligands. J. Am. Chem. Soc. 2006, 128, 13340-13341. (14) Guo, J.; Liu, H.; Bi, J.; Zhang, C.; Zhang, H.; Bai, C.; Hu, Y.; Zhang, X. Pyridine–oxazoline and quinoline–oxazoline ligated cobalt complexes: Synthesis, characterization, and 1,3-butadiene polymerization behaviors. Inorg. Chim. Acta 2015, 435, 305-312. (15) The absolute configuration of 4a was determined by oxidizing it to the corresponding allyl alcohol, which was assigned by comparison with reported optical rotations. See: Chen, F.; Zhang, Y.; Yu, L.; Zhu, S. Enantioselective NiH/Pmrox-Catalyzed 1,2-Reduction of -Unsaturated Ketones. Angew. Chem. Int. Ed. 2017, 56, 2022-2025. (16) The lack of reactivity of Z-1-phenyl-1,3-butadiene is presumably due to steric effect. The formation of a cobalt diene complex with a s-cis form, a putative catalytic intermediate (cf Figure 2) would be sterically unfavorable because of the repulsion between the Ph group of the coordinated diene and ligand.
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(17) (a) Bézier, D.; Venkanna, G. T.; Castro, L. C. M.; Zheng, J.; Roisnel, T.; Sortais, J. B.; Darcel, C. Iron-Catalyzed Hydrosilylation of Esters. Adv. Synth. Catal. 2012, 354, 1879-1884. (b) Mukhopadhyay, T. K.; Flores, M.; Groy, T. L.; Trovitch, R. J. A Highly Active Manganese Precatalyst for the Hydrosilylation of Ketones and Esters. J. Am. Chem. Soc. 2014, 136, 882-885. (18) Fleming, I.; Henning, R.; Parker, D. C.; Plaut, H. E.; Sanderson, P. E. J. The phenyldimethylsilyl group as a masked hydroxy group. J. Chem. Soc. Perkin Trans. 1. 1995, 317-337. (19) (a) Zuo, Z.; Zhang, L.; Leng, X.; Huang, Z. Iron-catalyzed asymmetric hydrosilylation of ketones. Chem. Commun. 2015, 51, 5073-5076. (b) Chen, J.; Cheng, B.; Cao, M.; Lu, Z. Iron-Catalyzed Asymmetric Hydrosilylation of 1,1-Disubstituted Alkenes. Angew. Chem. Int. Ed. 2015, 54, 4661-4664. (20) An independent run using the racemic precatalyst (rac)-(IPO)FeBr2 gave 2.0:1 d.r., suggesting that the asymmetric induction of the chiral C-stereogenic center on the hydrosilylation process exists, although on a modest level. (21) Wu, C.; Teo, W. J.; Ge, S. Cobalt-Catalyzed (E)-Selective anti-Markovnikov Hydrosilylation of Terminal Alkynes. ACS Catal. 2018, 8, 5896-5900. (22) For examples, see: (a) Paulasaari, J. K.; Weber, W. P. Ruthenium-Catalyzed Hydrosilation Copolymerization of Aromatic -Diketones with 1,3-Tetramethyldisiloxane. Macromolecules 1998, 31, 7105-7107. (b) Li, C.; Zhang, D.; Wu, L.; Fan, H.; Wang, D.; Li, B. Ring-Opening Copolymerization of Mixed Cyclic Monomers: A Facile, Versatile and Structure-Controllable Approach to Preparing Poly(methylphenylsiloxane) with Enhanced Thermal Stability. Ind. Eng. Chem. Res. 2017, 56, 7120-7130. (23) For examples, see: (a) Curry, J. W. The Synthesis and Polymerization of Organosilanes Containing Vinyl and Hydrogen Joined to the Same Silicon Atom. J. Am. Chem. Soc. 1956, 78, 1686-1689. (b) Mabry, J. M.; Runyon, M. K.; Weber, W. P. Poly(silyl ether)s by Ruthenium-Catalyzed Hydrosilylation Polymerization of Aliphatic -Dimethylsilyloxy Ketones and Copolymerization of Aliphatic -Diketones with -Dihydridooligodimethylsiloxanes. Macromolecules 2002, 35, 2207-2211. (c) Bruña, S.; González-Vadillo, A. M.; Nieto, D.; Pastor, C. J.; Cuadrado, I. Redox-Active Macrocyclic and Linear Oligo-Carbosiloxanes Prepared via Hydrosilylation from 1,3-Divinyl-1,3-Dimethyl-1,3-Diferrocenyldisiloxane. Macromolecules 2012, 45, 781-793. (d) Lázaro, G.; Iglesias, M.; Fernández-Alvarez, F. J.; Sanz Miguel, P. J.; Pérez-Torrente, J. J.; Oro, L. A. Synthesis of Poly(silyl ether)s by Rhodium(I)–NHC Catalyzed Hydrosilylation: Homogeneous versus Heterogeneous Catalysis. ChemCatChem 2013, 5, 1133-1141. (24) (a) Putzien, S.; Nuyken, O.; Kühn, F. E. Functionalized polysilalkylene siloxanes (polycarbosiloxanes) by hydrosilylation—Catalysis and synthesis. Prog. Polym. Sci. 2010, 35, 687-713. (b) Yilgör, E.; Yilgör, I. Silicone containing copolymers: Synthesis, properties and applications. Prog. Polym. Sci. 2014, 39, 1165-1195. (c) Eduok, U.; Faye, O.; Szpunar, J. Recent developments and applications of protective silicone coatings: A review of PDMS functional materials. Prog. Org. Coat. 2017, 111, 124-163.
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ACS Catalysis
For Table of Contents Only PhSiH3 +
R
R R'
R = Ar, Alk R' = H, Ar, Alk
SiH2Ph
2.0% (QuinOx)-Co N
R'
N
R = Ph, R' = H
Co Cl
30 examples avg 91% ee >99:1 rr
OHC
Cl
2.5% Mw = 8,700, PDI = 1.8 [D22 = -5.3
H O C H
CHO (HPyOx)-Co
Ph H C O Si n H * Ph
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