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pmgbapm 2012-5-5 02:01 AM

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[[i] 本帖最後由 pmgbapm 於 2018-8-24 11:05 AM 編輯 [/i]]

pmgbapm 2012-5-6 02:15 AM

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[[i] 本帖最後由 pmgbapm 於 2018-8-24 11:05 AM 編輯 [/i]]

jmlo 2012-5-6 11:40 AM

回覆 2# 的帖子

Your proposal looks reasonable. The two vinylsilanes are formed from silyl group migration followed by beta-H elimination.

jmlo 2012-5-6 11:44 AM

回覆 1# 的帖子

2) The cycle starts with CO addition to Ni. Then there are two possibilities: (i) beta-H transfer from C2H5 to CO and eliminates C2H4; (ii) migration of C2H5 to CO to form acyl group. The step (i) goes on with the migration of the other C2H5 group to produce diethylketone. Similarly, the step (ii) can move on by C2H5 migration; instead it produces propanal.

I think you can convert the ideas above to a mechanism. :loveliness:

jmlo 2012-5-6 12:09 PM

回覆 1# 的帖子

4(i) The synthesis consists of the following steps:
step 1: [CpFe(CO)2]2 + 2KBHEt3  ---->  2K[CpFe(CO)2]
step 2: K[CpFe(CO)2] + CH3I  ----> CpFe(CO)2(CH3)
step 3: CpFe(CO)2(CH3) + PMe3  ---->  CpFe(CO)(COCH3)(PMe3)

notes:
(i) Step 1 is the reductive cleavage of the Fe-Fe bond.
(ii) Step3 is a simple insertion reaction of nucleophile (e.g. CO, SO2, PR3) in acetonitrile as solvent. Sometimes heat is needed. This reaction is usually accompanied by migration of CH3 group. i.e.,
M(CO)L + PR3  ----> M(COL)(PR3)

pmgbapm 2012-5-6 04:41 PM

[quote]2) The cycle starts with CO addition to Ni. Then there are two possibilities: (i) beta-H transfer from C2H5 to CO and eliminates C2H4; (ii) migration of C2H5 to CO to form acyl group. The step (i) goes on with the migration of the other C2H5 group to produce diethylketone. Similarly, the step (ii) can move on by C2H5 migration; instead it produces propanal.

I think you can convert the ideas above to a mechanism.[/quote]
唔知你個意思係咪好似version 1 咁 : [img]http://i155.photobucket.com/albums/s286/pmgbapm/V1.jpg[/img]


但我又做過一題, 有d 靈感唔知關唔關trans, cis時 (b-elimination)
see":
[img]http://i155.photobucket.com/albums/s286/pmgbapm/6-1.jpg[/img]

呢個係我根據呢題所做的version 2, 唔知有沒錯到, 可唔可以接受,  Thank you very mucHH~~Jmlo兄:loveliness: :loveliness:
[img]http://i155.photobucket.com/albums/s286/pmgbapm/V2.jpg[/img]
p.s b-H elimination 畫少左個 product H2C=CH2

[[i] 本帖最後由 pmgbapm 於 2012-5-6 04:56 PM 編輯 [/i]]

pmgbapm 2012-5-6 05:09 PM

Some extra quesion
[img=626,299]http://i155.photobucket.com/albums/s286/pmgbapm/Q7.jpg[/img]
Q7(iii)唔肯定答得岩唔岩, 好像有點亂來:D  Plz help me to check~ thx
[img]http://i155.photobucket.com/albums/s286/pmgbapm/A2P7.jpg[/img]


係其他題目見到 , 唔明點解第三個product係 50%,  唔係1:1:1咩?
[img]http://i155.photobucket.com/albums/s286/pmgbapm/QQ5.jpg[/img]

iv: 所以唔肯定呢題係咪有4個product, ratio 都係1:1:1:1
[img]http://i155.photobucket.com/albums/s286/pmgbapm/iv.jpg[/img]

[[i] 本帖最後由 pmgbapm 於 2012-5-6 05:21 PM 編輯 [/i]]

jmlo 2012-5-7 05:59 AM

回覆 6# 的帖子

[quote] 但我又做過一題, 有d 靈感唔知關唔關trans, cis時 (b-elimination) [/quote]
Yes. Reductive elimination requires the two leaving groups cis to each other in the organometallic compound.

[quote] 呢個係我根據呢題所做的version 2, 唔知有沒錯到, 可唔可以接受 [/quote]
It seems also okay, but I would suggest the following changes.
(i) I don't think the beta-H elimination would occur directly from the starting material. It should proceed after CO is added to Ni.
(ii) In order for CO to add to Ni, one of the Ni-P bonds has to be broken, opening a vacant site for CO. Here we propose this because we would like to maintain the coordination number of 4 around Ni all the time.
(iii) If so, the reaction can go through the following paths.
(dppe)Ni(Et)2  ---->  (R2PCH2CH2PR2)Ni(Et)2   (*)
(R2PCH2CH2PR2)Ni(Et)2 + CO   ----> (R2PCH2CH2PR2)Ni(CO)(Et)2

path 1: (R2PCH2CH2PR2)Ni(CO)(Et)2   ---->  (R2PCH2CH2PR2)Ni(CO)HEt + C2H4     (**)
(R2PCH2CH2PR2)Ni(CO)HEt  ---->  (dppe)Ni(COH)Et  (***)
(dppe)Ni(COH)Et  ---->  (dppe)Ni + CH3CH2COH

path 2: (R2PCH2CH2PR2)Ni(CO)(Et)2  ---->  (dppe)Ni(COEt)Et
(dppe)Ni(COEt)Et  ---->  (dppe)Ni + CH3CH2COCH2CH3

notes:
(*) (dppe) = bidentate mode; (R2PCH2CH2PR2) = monodentate mode
(**) The beta-H elimination yields the H ligand cis to CO. The H ligand is then transferred to C=O group, followed by reductive elimination to produce propanal.
(***) Similarly, the beta-H elimination of the other Et group yields the H trans to CO. In this case, the Et migration takes place first followed by reductive elimination to produce propanal.

jmlo 2012-5-7 06:32 AM

回覆 7# 的帖子

[quote] Q7(iii)唔肯定答得岩唔岩, 好像有點亂來  Plz help me to check~ thx [/quote]
Your answer makes sense. :loveliness:

jmlo 2012-5-7 08:45 AM

回覆 7# 的帖子

[quote] 係其他題目見到 , 唔明點解第三個product係 50%,  唔係1:1:1咩? [/quote]
I think the given answer is wrong. The reaction starts with CH3 migration to a CO group cis to it. Hence, there are only three possibilities.

[quote] iv: 所以唔肯定呢題係咪有4個product, ratio 都係1:1:1:1 [/quote]
I think so if there is no CO scrambling.
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