An unusual new reaction of α-olefins with

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proposed for the mechanism of the reaction. Keywords: synthesis, catalysis ..... in an argon current over LiAlH 4. The Grignard reagents were prepared by the.

CHEMICAL TRANSFORMATIONS OF O R G A N I C C O M P O U N D S A N UNUSUAL NEW REACTION OF a - O L E F I N S W I T H MAGNESIUM n - A L K Y L D E R I V A T I V E S C A T A L Y Z E D BY C P 2 Z r C ! 2

U. M. Dzhemilev, O. S. Vostrikova, R. M. Suitanov, and I. N. Batalina

UDC 542.97:547.313:547.254.6

The reaction of organomagnesium compounds (OMC) containing alkyl radicals of normal structure with a-olefins, resulting in the formation of alkenylorganomagnesium compounds and accompanied by hydride transfer was discovered and systematical~ investigated. A scheme providing for tile formation of zirconacyclopentane complexes was proposed for the mechanism of the reaction. Keywords: synthesis, catalysis, ct-olefins, organomagnesium compounds, zirconium, complex, mechanism, zirconacyclopemanes.

We previously demonstrated the possibility of regioselective carbomagnesiation of c~-olefins and some norbornene derivatives Et2Mg and reagents of the EtMgZ type [1-3]. The CP2ZrC12-catalyzed reaction of styrene and substituted styrenes with magnesium n-alkyl derivatives results in the formation of disubstituted magnesium cyclopentanes [4, 5]. We investigated the Cp2ZrCl2-catalyzed reaction of a-olefins with magnesium alkyls to expand the area of application of reactions of catalytic carbomagnesiation and cyclometallization. We found as a result that magnesium n-alkyl derivatives, beginning with n-Pr2Mg , react with a-olefins, basically yielding acyclic alkenylorganomagnesium compounds. A mixture of propane and propylene (-20:1) is separated in the reaction of equimolar amounts of n-Pr2Mg with 1octene in the presence of 5 mole % Cp2ZrCI2 (20 h, 20°C, ether). Monodeuterated alkenyls (1-4) and vic-dimethyldideutero. alkanes (5-7) were identified in the products of deuterolysis of the reaction mass; this suggests the formation of alkenylorganomagnesium compounds (8-11) and 3,4-disubstituted magnesium cyclopentanes (12-14) (Scheme 1) during the reaction. Note that the organomagnesium compounds (OMC) formed contain a smaller number of hydrogen atoms than the starting OMC and olefin together. The excess n-Pr2Mg acts as the acceptor of the hydrogen "surpluses", and it undergoes reducing splitting at the M g - C bond. Actually, propane is separated and a sediment corresponding to the empirical formula MgH 2 .nEt20 (where n varies from 0.5 to 1.5 in the different experiments) is formed during the reaction. In addition, hydrogen is liberated during hydrolysis or deuterolysis of the reaction mass, indicating the presence of soluble hydrides of the HMgR type. In the reaction of t-octene with n-PrMgBr, the reaction takes place more slowly and ends after 40-45 h. The composition of the products formed is the same, but there is no insoluble residue. HMgBr, easily soluble in ether, is probably formed instead of MgH 2 in this case. Increasing the temperature to 80°C causes predominant formation of product 11 with an overall increase in the reaction rate (Table 1). The same effect can be obtained by using an excess of the starting olefin. Selective formation of other products of the reaction could not be attained. An lIA-fold excess of the starting OMC with respect to the olefin is the optimum ratio of the starting reagents for obtaining maximum conversion (Fig. 1). After attaining maximum conversion, the molar ratio of products formed virtually does not change (Fig. 2), which shows that they are stable and do not undergo further transformations in the reaction conditions.

Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1187-1196, May, 1992. Original article submitted July 2, 1991.

936

1063-5211/92/4105-0936512.50

o1993 Plenum Publishing Corporation

Scheme 1

/x~..4- / \

n-Pr~Mg+- /

• '(

""\ / \ /

/""%~'~

l

~,. MgH~.nEt~O

1 [Zrl

(

\ /

\

\

./

\\

.rng

/

\

mg

i

mg

(

f

/

\

Mg (14)

(11)

.

\

Mg (12)

(8)

,)

/

/

Mg (i3)

(9, 10)

t DCI ,DeO

F

/

l) \J

/\.,'"\,/'\_/'\,,'\/"\ .) !

+ /',..,." \ . / . , . / ' , . , . / 2 " , , / - . , . , , - " .. + / \ , / % . I

\

D

-..

D

D (4)

(7)

)L + D

(I)

D (5)

D

L \__/\/'\/\,,

t l

.,) ,,,,. D

(:L 3)

D (6)

The composition and yield of products of the reaclion of n-Pr2Mg with 1-octene in the presence of Cp2ZrCl 2 (based on the results of GLC of the products of deuterolysis of the reaction mass) are reported below: Compound Yield, %

l-octene 2

2 25

3 5

4 56

6 10

7 2

Scheme 2 mg ~"

,

R~/\ /\Rt /--N Mg

~A)

R l / "/'--N , AR~ \ / Mg

(~)

mg f/t_/z'% ~_ R ~ _ / X _ M g Z

Cp:ZrCl~.

-4 R : ~ ( t ) ~ \ /'%-.-~R v'~) +

mg

RI/~/~'\ R~ ' ~ ' j ~ ' ~ R : ~

"-I"

\Mg/

Rz (C)

In going from n-Pr2Mg and n-PrMgBr to the next terms of the homologous series of n-alkyls (for example, (n-C4Hg)2Mg, (n-C6H13)2Mg), all characteristics of the reaction are preserved. The OMC formed can be separated into three groups as a function of the composition of the hydrocarbon radical (Scheme 2): A) OMC whose hydrocarbon radical is formed of two mole937

Y~La mole % fO0

+q ot

80

Yl:~ta, wt. %

lO0[

-J =7

o I-o~en~

2

60

qO S

'

J 5

2O 0

q

f

0.250.?

i.O

l.,~ 2.8

2.5

3.0

5

n-PrzMg/ l-oct~ne

20

gO

720

70

Fig. 1 Fig. 2 Fig. 1. Yield and composition of products of the reaction of 1-octene with n-Pr2Mg vs nPr2Mg:l-octene ratio ([C]n.Pr2Mg = 1.5 mmole/ml, 20 h, n-PrzMg:Cp2ZrCl 2 = 100:2, 20°C, ether): 1) 1-octene; 2) 2 + 3 + 6; 3) 4 + 7. Fig. 2. Yield of products of the reaction (Scheme 1) vs time (n-Pr2Mg:l-octene:CpzZrC12 = 150:100:2, 20°C, ether [C]n.Pr2Mg = 1.25 mmole/ml): 1) 1-octene; 2) 4; 3) 2; 4) 6; 5) 3; 6) 7.

cules of the starting olefin; they are formed in the largest amount; B) OMC whose hydrocarbon radical is formed of molecules of the starting olefin and the radical of the starting OMC; C) OMC, whose hydrocarbon radical is formed of two radicals of the starting OMC; they are formed in the smallest amount. If the hydrocarbon radical of the starting OMC contains the same number of carbon atoms as the starting a-olefin, as in the reaction of (n-C6H13)2Mg with 1-hexene or (n-CsH17)2Mg with 1-octene, for example, a single deuteroalkene 4 (15) and dimethyldideuteroalkane 7 (16) are formed after deuterolysis of the reaction mass.

l

/~_/~

1. Cp2ZrCl 2

+ R_/~\

n4

,%,

:L D C I . D . O

-

. (4, 15a,

95% (n = Pr) 90% (R = C~Hu) R = C~Hn (4, 7); Pr (15a, b, t6).

D

1)

D

b)

(7, 16)

15a/15b ~ 5

The activity of different a-olefins and n-alk2,,lmagnesium derivatives in the reaction is approximately the same. For example, in the reaction of an equimolar mixture of 1-hexene and 1-octene with n-Pr2Mg , conversion of otefins after 5 h was respectively 16 and 18%. Conversion of (n-C6H13)2Mg and (n-C9H19)2Mg in the reaction with 1-octene was 21 and 23%, respectively, in a similar experiment. The structure of the type B alkenyl-OMC formed was a function of the nature of the starting reagents in many experiments. A mixture of isomeric products 17 and 18 which differ by the position and configuration of the double bond is formed in the reaction of (n-C6H13)2Mg with 1-octene (or (n-CsH17)2Mg with 1-hexene):

D

( R1--/~\--)2Mg

+

I. Cp~ZrCl~

D

U

t

2. D C I - D ~ O

R2

./~ (if)

R1 -~ Pr; R~ = CnHu.

938

(iS)

TABLE 1. Composition and Yield of Products of the Reaction of n-Pr2Mg with 1-Octene as a Function of the Temperature (products of deuterolysis of the reaction mass, G L C results; n-Pr2Mg:l-Octene:CpzZrCl 2 = 150:100:2, ether, 1 h, [C]n-Pr2Mg = 1.7 mmole/ml) Reactioa temperature,-°C

Composition of reaction mass,

Conversion of l-octene. 4

2

0.5 2.0

5 ti 23 35 60

25 35 50 60 80

6

3

i

-

-

4 6.0 22.0 34.0 58.0

7

0.5 t.0 t.0 t.0 2.0

170 -

On the contrary, the reaction of n-Pr2Mg with l-octene or allylbenzene results in the formation of alkenyl-OMC containing a double bond only in the fragment of the hydrocarbon radical corresponding to the initial olefin: D

/

1. Cp2ZrCl~

n-Pr~Mg + R - - / / ~

.a. DEI-D:O )

i D--//~//~R (2, 3. 19)

(

-- R - - / \ / ~ ' - R (4, 20)

R = C~Hn (2, 3. 4); Ph (19. 20). A similar effect is also observed in the reaction of (n-C6Ht3)2Mg with allylbenzene:

( R == Pr.

{

........

÷ 0---

'

D

)- B- - / ' \ / ~ -

2. I)CI .D~O

(2|)

O

+ 20

Note the rigorously fLxed position of the double bonds in the hydrocarbon radicals of all alkenyl-OMC between the C 4 and C 5 atoms counting from the magnesium atom. These results show that we have discovered a new catalytic reaction of n-magnesium alkyls with a-olefins. The structure and composition of the products formed suggest the possible occurrence of the reaction via intermediate zireonacyclopentane complexes. Actually, the participation of metallocycles containing transition metal atoms in the role of catalytically active intermediates of many reactions promoted by these metals has recently been demonstrated [6]. We propose the following probable scheme of the mechanism of the reaction (Scheme 3). Scheme 3 R'(") R"O)

CpzZrC1q

%--/

F-'-- 2 R ' ~ .gz

( ) (28)

K_~2ELM~z

_ _

,c,,).(~~ ,, ,, R '"-?/V

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