DE2365439B2 - Process for the preparation of homo- and copolymers of episulphides and co- or terpolymers from episulphides with monomers of the vinylic type and / or monomers of the lactone type and block copolymers of episulphides as well as episulphide and vinyl monomers - Google Patents

Description

CH ₃ - SO - (CH ₂ ) * - SO - CH ₃

CH ₃ -SO

SO-CH ₃

Φ— SO— (CHj) ₆ -SO- *

Φ = phenyl

CH ₃ -SO ₂ - (CHj) ₄ -SO ₂ -CH ₃

The catalyst used according to the invention is preferably obtained by reacting metal-donating Agent / disulfoxide or disulfone or polyderivative in a ratio of 1: 1

Mixtures of these can also be used as polar solvents in the process according to the invention. Is preferably carried out at temperatures ranging from -20 to + 4O ⁰ C.

The concentration of the catalyst is preferably between 0.01% and 1%, based on the fed moles of monomers! or monomers. Among those in the method according to the invention Usable monomers may be mentioned, for example: as episulfides:

Ethylene sulfide, propylene sulfide,
Isobutene episulphide, styrene episulphide, vinylcyclohexene episulphide,
Allyloxy-2,3-epithiopropane,

Butadiene monoepisulfide;
as monomers of vinylic type: acrylonitrile, methacrylonitrile,
Methyl methacrylate, styrene,
Methyl vinyl ketone, acrylamide.

The copolymers that can be prepared can be random or block copolymers.

The following examples serve to illustrate the invention.

Manufacture of the catalysts

Catalyst A

Production of

Il Il

CH ₃ -S- (CH ₂ J ₆ -S-CH ₃

and the corresponding reaction product with Li-butyl

In a three-necked flask equipped with a stirrer, dropping funnel and thermometer, in one

Argon flow 4.6 g (17OmMoI) NaH introduced, and 100 cc of dimethylsulfoxide are slowly added dropwise with stirring The mixture is stirred for 6 hours at + 4O ⁰ C and then filtered and titrated. The reaction mixture, which is 95 mmol

Na ⁺ -CH ₂ -S-CH ₃
contains, is with 48 mmol

Br-CHi-CH ₂ -CH ₂ -CH ₂ -Br

diluted with 10 ecm DMSO, implemented The reaction is slightly exothermic. The reaction is kept at 60 ° C. for 8 hours, DMSO is removed by vacuum distillation, ether is added and then the whole thing is filtered and washed cold with 50 ecm THF.

The solid is extracted with hot THF, the extract in tetrahydrofuran with anhydrous ether precipitated and then filtered and dried, 5.6 g (yield = 56%)

CH ₃ - S - (CH 1) ₆ - S - CH ₃

receives

In a previously vented 250 ccm three-necked flask equipped with a cooler, dropping funnel and thermometer, 4.1 g (19.4 mmol) are obtained under an argon atmosphere

CH ₃ -S- (CH ₂ J ₆ -S-CH ₃

Il Il

ο ο

introduced and then 200 ecm anhydrous Dioxane added (dehydration of the dioxane by ÜAIH4). It will be based on complete dissolution Heated to 40 to 50 ° C, and 40 mmol of Li-butyl in hexane solution are slowly added.

A noticeable evolution of gas is observed and the temperature rises to + 55 ° C. The formation of a white precipitate is observed towards the end of the reaction. The mixture is stirred for 3 hours at 5O ⁰ C, the mixture was filtered, washed repeatedly with THF in the heat to excess Li-Butyl, and possibly unreacted product to remove and dried 1 to 2 hours at the vacuum pump. The product dried in this way is dissolved in hexamethylphosphoramide (HMPA).

Characterization:

a) Elemental analysis

Calculated: C 43, H 7.2, S 28, Li 6.4%;
found: C 42, H 7.5, Li 6.4%;

b) mn C ₂ H ₅ Br:

Into a 100 cc three-necked flask that has been vented beforehand and was equipped with a stirrer, dropping funnel and thermometer, were under an argon atmosphere 0.2 g (0.90 mmol) of catalyst A were introduced and 50 ecm of tetrahydrofuran (THF) was added.

a white suspension formed. 6 mmol C ₂ H ₅ Br were added and stirring was continued for 16 hours at 30 ⁰ C a clear solution which was evaporated to dryness, to give to give a white hygroscopic solid, which had a molecular weight of 266 in the mass spectrum, corresponds to the sum of two C ₂ H ₅ groups with catalyst A.

Catalyst B

Implementation of

CH ₃ -S- (CHj) ₆ -S-CH ₃

O O

with NaNH ₂

In a flask equipped with a tight Quickfit glass stirrer and a dropping funnel with a jacket, are introduced, and 0.39 g (10 mmol) of NaNH ₂ - 70 ⁰ C dissolved in 40 cc of liquid ammonia. 5 mmoles

CH ₃ - S - (CH ₂ ) ₆ - S - CH ₃

suspended in 40 ecm THF are added. The mixture is stirred for a further 10 hours at -45 ° C., NH ₃ is removed, and the content of dry solids is used for the polymerization.

Characterization with BrC ₂ H ₅ is carried out on part of the solid as in the case of catalyst A. The product obtained appears in the mass spectrum in accordance with a structure similar to the preceding structure.

Catalyst C

Implementation of Mg (C ₂ Hs) ₂ and
OO

CH ₃ -S- (CH ₂ J ₆ -S-CH ₃

In a flask equipped with a magnetic stirrer, dropping funnel and condenser, 0.5 g (2.4 mmol)

CH ₃ -S- (CH ₂ ) ₆ -S-CH ₃

introduced and dissolved with 70 ecm THF at +40 ⁰ C. 4.8 mmol of Mg (C ₂ H _{5 I 2 dissolved} in 20 ecm of tetrahydrofuran are then added. The formation of a precipitate and the simultaneous evolution of a gas are observed, which disappears after 30 minutes of aging.

The temperature of +40 ⁰ C is maintained for 18 hours. The opalescent solution is concentrated and precipitated with hexane, filtered, washed with tetrahydrofuran and hexane to remove the unreacted products, and dried, and the precipitate is used in the polymerization.

Catalyst D
Implementation of Zn—

and

CH ₃ -S- (CH ₂ ) SS-CH ₃
OO

Following the procedure of Example 3, 0.75 mmol

CH ₃ -S- (CH 2) ₆ -S-CH ₃

Il Il

ο ο

reacted with 0.75 mmol Zn (C ₂ H ₅ ^ in THF

It occurs gas evolution and the solution opalized The temperature door 16 is held transmitting at +50 ⁰ C, the solution is concentrated and extracted with hexane precipitated washed with THF and hexane, dried, and the precipitation is used in the polymerization.

Catalyst E.

Implementation of AlH ₃ N (CH ₃ ), and
CH ₃ -S- (CH ₂ J ₆ -S-CH ₃

Il Il

ο ο

After the procedure described above, 0.57 mmol

CH ₃ - S - (CH ₂ I ₆ - S - CH ₃

Il Il

O O

reacted with 0.57 mmol of AlH ₃ N (CH ₃ J ₃ in 40 ecm of toluene. The temperature of 60 ° C. is maintained for 1 hour, the precipitate is filtered, washed with THF and toluene and dried and used in the polymerization.

Table I.

Catalyst F

Precipitation of CH ₃ -SO ^ CH ^ -SO ₂ -CH ₃
and reaction with Li-butyl

In a three-necked flask equipped with a stirrer, dropping funnel and condenser, 1 g (4.7 mmol)

CH ₃ -S- (CH ₂ J ₆ -S-CH ₃

10

introduced and dissolved in the smallest possible amount of glacial acetic acid. The mixture is heated to 70 ^° C. and the necessary amount of H ₂ O ₂ is added dropwise. The reaction is ^{kept at 70 °} C. for 10 hours and then left to stand overnight. A white precipitate forms, which is crystallized from alcohol. The product is carefully dried in vacuo. 1.05 g (87%) of the desired product were obtained.

After the procedure described for catalyst A, 1.05 g (4.1 mmol)

CH ₃ -S0 ₂ - (CH ₂ ) ₆ -SO-CH ₃

reacted with 8.2 mmol of Li-butyl. The product was dried and dissolved in HMPA.

Characterization:

a) Elemental analysis

Calculated: C 38.0, H 6.2, S 25.2, Li 5.5%;
found: C 37.5, H 6.0, Li 5.7%;

b) with BrC ₂ H ₅ .

The reaction has been described in detail for catalyst A. The mass spectroscopic analysis corresponds to a compound with a molecular weight of 298.

Examples 1 and 2

The polymerization tests are carried out in a 250 cc vessel that has previously been vented and under argon is held. First, the catalyst A is introduced with the solvent and then the monomer. The tests are kept in a thermostatic bath at 30 ° C. The important ones Data are given in Table I.

30th

example
No. Monomer lot Catalyst A solvent lot Conversion
lung ['/] Type 60 mmol lot Art 25 ecm % dl / g 1 Ethylene sulfide 63 mmoles 0.03 mmol HMPA 5-20 ecm 100 n / A. 2 Propylene sulfide = Hexamethylphosphoramide.
= Tetrahydrofuran.
= not determined. 0.05 mmol HMPA-THF 100 2.24 toI. 30 C HMPA
THF
n / A

Example 3

Following the procedure described above, 0.05 mmol of the reaction product of

CH ₃ -S- (CH ₂ ) ₆ -S-CH ₃

Il Il

with NaNH ₂ (catalyst B) in 25 ecm THF under argon in a vented vessel. Afterward

63 mmol propylene sulfide are added. The experiment is carried out in a thermostatic bath at 30 ° C. 4.65 g (yield 100%) of a polymer with a value for [η] in toluene at 30 ° C. of 2.10 dl / g are obtained.

Example 4

One works in the usual way in a vented vessel under argon, but using 0.05 mmol des from

CH ₃ -SO ₂ - (CH ₂ ) ₆ -SO _: -CH ₃

Catalyst made with Li-Butyl (Catalyst F) in 25 ecm solvent (5 ecm HMPA + 20 ecm THF). 63 mmoles of propylene sulfide are added and the experiment is carried out in a thermostatic bath at 30.degree carried out.

4.65 g (100% yield) of polymer are obtained with a value for [η] = 1.84 dl / g at 30 ° C. in toluene.

Example 5

Using the procedure described, 25 mg of the reaction product of
and

O O

CH ₃ - S - (CH ₂ ) ₆ - S - CH ₃

(Catalyst C) placed under argon in a vented vessel, whereupon they are dissolved in 30 ecm HMPA and 63 mmol propylene sulfide are added. The polymerization is carried out at 30.degree. C., 4.4 g (yield 98%) of a polymer having a value for [η] = 1.32 dl / g in toluene at 30.degree. C. being obtained.

Example 6

Using the procedures described above, 0.05 mmol of the reaction of Zn (C ₂ Hs) ₂ and

CH ₃ -S- (CH ₂ ) ₆ -S -CH ₃

10

15th

20 (Catalyst D) obtained precipitate and dissolved in HMPA, whereupon 76 mmol of propylene sulfide are added. The polymerization is carried out at 30 ° C; 3.4 g (yield 61%) of a polymer with a value for [τ /] = 1.86 dl / g in toluene at 30 ° C. are obtained.

Example 7

Using the procedures described above, 0.05 mmol of the by reaction of AIH ₃ N (CH ₃ J ₃ and

CH ₃ -S- (CH ₂ ) ₆ -S-CH ₃

25 product obtained (catalyst E) introduced into and kept under argon vessel. They are suspended in 20 cm of HMPA and 57 mmoles of propylene sulfide are added. The polymerization is carried out at 3O ⁰ C to give 3 g (yield 70%) of a polymer having a value of [η] = 1.80 dl / g in toluene at 30 ° C.

Examples 8-13

The copolymerization and terpolymerization experiments were carried out in a 250 ccm vessel, which has been previously vented and kept under argon. First was the catalyst A with introduced the solvent and then the mixture of monomers. The attempts were made in carried out in a thermostatic bath at 30 ° C. The data are given in Table II.

Table II

At- monomer

No. Type Quantity

Comonomer

Kind of amount

Termonomic Cat. A

Type amount amount

solvent

8 propylene- 45 mmoles ethylene- 19 mmoles
sulfide sulfide

9 propylene- 63 mmoles acrylonitrile 10 mmoles
sulfide

10 propylene- 63 mmoles allyloxy-2.3-3.15 mmoles sulfide epithio-

propane

11 propylene- 63 mmoles ethylene- 24 mmoles allyloxy-2,3-6,14 mmoles sulfide sulfide epithio-

propane

12 propylene- 76 mmoles methacrylic-II mmoles
sulfide nitrile

13 propylene- 67 mmol acrylic- 3 mmol allyloxy-2,3- 4 mmol sulfide nitrile epithio-

propane

0.0128 mmol HMPA 20 ecm

0.015 mmol DMSO 20 ecm

0.033 mmol DMSO 20. ecm

0.015 mmol HMPA 20 ecm

0.037 mmol DMSO 25 ecm

0.25 mmol DMSO 40 cm

ίο

Table II (continued)

example composition 80% - Ethylene sulfide 20% l ·.] 30 C Conversion No. 75% - Acrylonitrile 25% 30 C lung 95% - Allyloxy-2,3- 5% dl / g 80 C % 8th Propylene sulfide epithio-propane 1.89 toluene 98 9 Propylene sulfide 60% - Ethylene sulfide 33% 2.17CHCl., 30 C 100 10 Propylene sulfide 83% - Methacrylonitrile 17% 2.20 toluene 30 C 100 74% - Acrylonitrile 19% 30 C 11 Propylene sulfide ATE 6% 1.15 toluene 97 12th Propylene sulfide 0.46 DMFA 65 13th Propylene sulfide 0.7 CHCl ₃ 76

DMSO = dimethyl sulfoxide.

DMFA = dimethylformamide.

ATE = allyloxy-2,3-epithio-propane (allyl tiranyl ether).

n / A. = not determined.

The following are the technological features of the polymers produced in Examples 10, II and 13 after vulcanization using the following recipe:

Polymer 100 parts

Antioxidant 1 part

Stearic acid 1 part

Carbon black 50 parts

ZnO 5 parts

Mercaptobenzothiazole 0.5 parts

Tetramethylthiuram disulfide 1 part

Sulfur 2 parts

The vulcanization was carried out at 145 ° C. Polymer from Example 10

Polymer of example

Module kg / cm ²

Cr *) Ar **)

100% 200% 300% kg / cm ² %

7th 34 69 15th 52 112 30th 58 124 45 61 - 60 59 -

103

147 142 124 121 114

505 260 205 190 180

*) Cr = breaking strength.
**) Ar = elongation at break.

Permanent deformation

20 8 4 2 2

45 minutes

30th

35 module kg / cm

100% 200% 300%

15th 51 30th 62 45 66 60 72

132

Cr Ar 135 Last 175 de Ver 160 forming kg / cm ² % 145 % 145 4th 125 0 118 0 111 0

40 polymer of example

_Minu . th

_Modulus in kg / cm ²

100% 200% 300%

19 51 63 55 66

32 96

101

41

Cr Ar 445 Last 285 de Ver 195 forming kg / cm ² % 295 % 48 160 8th 115 6th 119 4th 128 6th 100 0

55

Examples 14 to 17

The polymerization experiments for the production of Block copolymers were carried out in a 250 cc reactor which had been previously vented and was kept under argon.

First, the catalyst A was mixed with the solvent introduced and then the monomer. After completion of the polymerization of the first monomer after 5-8 hours the polymer obtained is dissolved with 50 ecm of THF and the second monomer becomes added, the reaction being terminated at the temperature of 30.degree. The data are given in Table III

Table III

example
No.

Monomer 1

Art

lot

Monemeres 2
Art

lot

catalyst
Type A

Propylene sulfide
Propylene sulfide
Propylene sulfide

63 mmoles 63 mmoles 63 mmoles

Ethylene sulfide

Acrylonitrile

Methacrylonitrile

40 mmol
35 mmol
10 mmol

0.064 mmol
0.04 mmol
0.015 mmol

Table 111 (continued)

Example No. Solvent

Composition conversion 7g

14 HMPA 20ccm

15 HMPA 20ccm

16 HMPA 20ccm

Tf = melting temperature.

Tg - glass transition temperature.

PS = propylene sulfide.

PS 65% ES 35%

PS 70% ACN 30%

PS 90% MACN 10%

ES = ethylene sulfide.

ACN = acrylonitrile. MACN = methacrylonitrile.

90%
90%
90%

-42 C; 200 C (7JO
-39 C; 95 C
nd

In addition to the data listed in Table III, the polymeric nature of the products obtained proved by fractional extraction experiments, eliminating the presence of mechanical mixtures of the two homopolymers is excluded.

Example production of the catalysts

A) CH ₃ -S

S-CH ₃ (1) + LiBu

(I) was obtained by oxidation of

CH ₃ -S-

-S-CH ₃

(Reports 1909, 42, pages 2721-2731) with H ₂ O ₂ in acetic acid at 70 ⁰ C for 7 hours. The product was isolated after treatment with water and crystallization from ethyl alcohol (melting point 195-197 ° C). The mass spectroscopy (MS) and nuclear magnetic resonance (NMR) data confirm the proposed structure.
The following data were obtained in the mass spectrum: m / e = 172 (100), 155 (72), 219 (41), M + 234 (40), 76 (24), 50 (20), 63 (14), 75 (13 ), 109 (11). The data in brackets refer to the relative intensity.

In the NMR spectrum in CD ₃ CN (TMS standard) the following chemical shift was obtained in ppm: 8.4-7.8 (Φ, multiple ”), 3.12 (CH ₃ , singulstt).

8.0 mmol of (I) were treated in 60 cm ^{3 of} a mixture of Et ₂ O and hexamethylphosphoramide (HEMPA) (5: 1) with 16 mmol of Li-butyl (LiBu) at room temperature for 5 hours. At the end the catalyst was isolated , washed with Et ₂ O and dried. Then it was dissolved in HEMPA and used for the polymerization.

O O

Il Il

B) Φ — S— (CH ₂ ) ,, - S — Φ (Π) + NaNH ₂

Il Il

ο ο

(II) was obtained by oxidation of

with H ₂ O ₂ in acetic acid, at 80 ⁰ C, for 4 hours

The product was isolated by Behändem with H ₂ O and crystallization from ethyl alcohol (m.p. 115-116 ⁰ C). The MS and NMR data confirm the proposed structure.

The following values were obtained in mass spectroscopy: m / e = 143 (100), 77 (86), 197 (68), 55 (66),

125 (20), 141 (16), 51 (16), 29 (15), M + 338 (1).

The following chemical shifts in ppm were obtained in the NMR spectrum in CDCl ₃ (HMDS as standard): 7.9-7.45 (Φ, multiplet), 3.01 (CH ₂ , multiple), 1.75 (CH ₂ JS, multiples).

The compound (II) was _{treated with NaNH 2} in liquid NH 3. After liberation of NH3 from water to metallic Na and distillation in the held at -40 ⁰ C reaction vessel 8 mmol were added to (II) and 16 mmol NaNH _2, and the reaction was carried out for 4 hours.

At the end the NH3 was completely evaporated and 60 cm ^{3 of} a mixture of (C ₂ H _{5 I 2} O-HEMPA (5: 1) was added to the whole to obtain the catalyst which was then used for the polymerization. His Structure resulted from

Ul the product obtained by treatment with C ₂ HsBr, which, according to its MS and NMR data, has the following structure:

O CH ₂ CH ₃ CH ₃ CH ₂ O

Il I I Il

Φ- CH S CH ₂ CH S - Φ

O O

MS: m / e = 143 (100), 69 (80), 253 (57), 55 (57), 41 (38), (36), 111 (29), 83 (19), M + 394 (3).

NMR in CDCl3 (HMDS): 7.9-7.4 (Φ, multiplet), 2.76 (CHa, multiplet), 1.95-1.35 (CH? Ss . Multiples), 0.84 (CH ₃ , Triplet).

(HI) NaNH,

(III) was prepared by oxidizing the corresponding, ₅ disulfide under the same conditions as in the "previous example. The product had a melting point of 197 ° C.

His MS data were: m / e = 127 (100), 128 (48), 193 (46), 55 (40), 247 (36), M + 438 (34), 191 (22), 129 (22), 175, (16).

NMR in CD ₂ CI ₂ + CF ₃ COOD (HMDS): 8.5-7.5 (ΦΦ, multiplet), 3.38 (CH ₂ α, multiplet), 1.92 (CH ₂ β, multiples).

It was metallized in the same way as described above. The structure of the catalyst was confirmed by treatment with C ₂ H ₅ Br. The structure was obtained from the MS and NMR data

CH ₂ CH ₃

CH ₃ CH ₂

S-CH (CH _2), CH

MS: m / e = 128 (100), 127 (46), 193 (44), 303 (28), 69 (26), 55 (26), 129 (14), 41 (14), M + -494 (4).

NMR in CDCl3 (HMDS): 8.4-7.3 (ΦΦ, multiplet), 3.0 (CH, multiple), 1.8 (CH ₂ , multiplet), 0.87 (CH ₃ , triplet).

Carrying out the polymerizations

1) According to the procedure described in the examples of the application documents, 63 mmoles of propylene sulfide (PS) were polymerized with 0.025 mmoles of the catalyst A obtained above. After 4 hours at room temperature, 4.6 g of a polymer with a value for 4.6 g of a polymer with a value for M ™ _t = 3.38 dl / g are obtained.

3) 63 mmoles of PS were polymerized with 0.0315 mmoles of the catalyst C obtained above. After 1 hour at room temperature, 4.6 g of a polymer with a value for [vll

= 3.83 dl / g.

50

2) 6.3 mmol of PS was polymerized with 0.0315 mmol of the catalyst B obtained above After 1 hour at room temperature, one obtained

4) The reactor was charged with 50 cm ^{3 of} THF, 10 cm ^{3 of} HEMPA, 45 mmol of ES (ethylene sulfide), 550 mmol of PS and 0.025 mmol of the catalyst B prepared above. After 2 hours at room temperature, quantitative yields of a copolymer formed from 55 MOF / 0 ES and 55 mol% PS with a value for were obtained

= 3.18 dl / g.

Claims (3)

Patent claims: 1. A process for the preparation of homopolymers and copolymers of episulfides, copolymers or terpolymers from episulfides with monomers of the vinylic type and / or monomers of the lactone type and block copolymers of episulfides and episulfide and vinyl monomers, characterized in that the reaction in a Temperature between -4O ⁰ C and + 10O ⁰ C in a solvent of polar nature in the presence of 0.001% to 5%, based on the fed moles of the monomer or monomers, of a catalyst is carried out by the reaction of a metal from groups IA , HA or IHA of the periodic table or its hydride, alkyl and amino derivatives with a compound which contains at least two groups SO and SO ₂ and is selected from the compounds which have one or more repeating units of the type in their molecule R — IX— (R'U, —Y —R " where X and Y, which can be the same or different, are SO or SO ₂ groups, R and R "are methylene, alkyl groups with 2 to 10 carbon atoms, cycloalkyl, aryl, arylalkyl, alkylcycloalkyl groups or divalent radicals which can react with one another to form a ring; R 'represents a divalent arylene, cycloalkylene, alkylarylene, alkylcycloalkylene radical or a methylene chain with a carbon number of 0 to 20; .ti is selected from 0 and 1 and η is an integer, which can be 1,2 or 3, in a ratio between 10 and 0.3 in the presence of aliphatic or aromatic hydrocarbons, tetrahydrofuran, dioxane, hexamethylphosphoramide or liquid ammonia as solvents at a temperature between -80 and + 80 ⁰ C was obtained. 2. The method according to claim 1, characterized in that the polar solvent is selected is made from hexamethylphosphoramide, dimethyl sulfoxide, Ν, Ν'-dimethylacetamide, tetrahydrofuran, dimethylfirmamide, Pyridine, acetonitrile, dioxane, morpholine, formylmorpholine, ethers and their mixtures. 3. The method according to claim 1 or 2, characterized in that the monomers used or the monomers used are selected from ethylene sulfide, propylene sulfide, acrylonitrile, Methyl acrylate, methacrylonitrile. In GB-PS 10 59 492 the polymerization of episulfides with catalysts based on the oxides various metals. However, low yields and low polymers are obtained Molecular weights. The object of the invention is to provide a process for the production of homopolymers and copolymers of episulphides and copolymers or terpolymers of episulphides with monomers of the vinylic type and / or monomers of the lactone type and block copolymers of episulfides as well as episulfide and vinyl monomers. the high molecular weight products in provides improved yields This object is achieved by the method characterized in the patent claims For the definition of the metal in Groups IA, IIA and IHA of the Periodic Table of the Elements, reference is made to the "Handbook of Chemistry and Physics" by Chemical Rubber Publishing Co. (39th edition). Examples of metals or their derivatives which are particularly suitable for the process _{according to the invention are Li, Na, K, LiH, CaH 2} , NaH, ZnH ₂ , LiR, ZnR ₂ , MgR ₂ , AlH ₃ B, AlR ₃ , UNH ₂ , Mg, Mg (NH ₂ J ₂ , where R is hydride, alkyl or amino and B is Lewis base Examples of the compounds of the formula I which can be used are: