INTRODUCTION:

Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal¹. Typical organometallic compounds are organozinc compounds such as ClZnCH₂C(=0)OEt, organocuprates such as Li[CuMe₂](lithium dimethylcuprate), organomagnesium compounds such as Grignard reagents MeMgI (iodo methyl magnesium)and MgCH₂CH₃(diethyl magnesium), and organolithium such as n-butyl lithium². In past organometallic chemistry was not a particular field of interest for many chemists due to the fact that the metal-carbon bonds seen thus far were inherently unstable.

The beginning of organometallic chemistry came about very unexpectedly. The earliest successful synthesis of an organometallic compound can be credited to Willium. C. Zeise, a Danish scientist. The compound was produced in a reaction of ethanol with the mixture of PtCl₂ and PtCl₄ in the presence of KCl. The notable contribution to organometallic chemistry is from Edward Frank land at the turn of the 20th century³ Frank land tried to treat organic halides with metals

2EtI + Zn → ZnI₂ + EtEt

Where, “Et” is an ethylene group.

The only reported occurrences in nature of compounds which might be considered to be organometallic are those of moissanite, SiC, and of Cohen it (FeCoNi)₃C. Both compounds have been found in meteorites. The great stability of organomtallic compound warrants the prediction that others may be found.

Types of organometallic compounds:

Organometallic compounds are of two types:

Simple organometallic compounds:

Simple organometallic compounds are those which have only hydrocarbon radical or hydrogen atom attached to the metal atom, e.g. (C₂H₅)₄Pb, (CH₃)₃SnH.

Mixed organometallic compounds:

Mixed organometallic compounds are those, which have groups other than hydrocarbon radicals or hydrogen atom, also attached directly to the metal atom. e.g. C₂H₅MgBr, (C₄H₉)₂SnCl₂ etc. Organometallic compounds are generally low melting solids, liquids, and gasses at ordinary temperature. They are usually soluble in non-polar or weakly polar organic solvents such as alkenes, toluene, ether or even alcohols.

Organometallic compounds reacts chemically with Me₄Ti and decomposes at room temperature .All organometallic compounds are thermodynamically unstable to oxidation. But many of them are also kinetically unstable to oxidation at room temperature. Organometallic compounds particularly Grignard’s reagent and organolithium compounds find uses in the synthesis of various organic compounds to attack hydrocarbon groups.

Aside from the intrinsically interesting nature of organometallic compounds, many organometallic compounds form useful catalysts and consequently are of significant commercial interest. One of the most interesting things about organometallic compounds is that they can be used as homogeneous catalyst in processes where all the reacting partners are present in one phase, usually the liquid one. Organo zinc compounds, first prepared by Frank land in 1848, are used extensively in organic synthesis⁴. The preparative way of organozinc reagents of the type RZnX play an important role in the reactivity and stability of these compounds^5-8. Organozinc reagents have different reactivity and selective properties than the analogous Grignard Reagent and used in cross-coupling reaction^8-10. Michael addition and electrophilic amination reactions¹¹.

In 1965, X-ray diffraction showed the structure to consist of an iron atom sandwiched between two parallel C₅H₅ rings. The details of the structure proved somewhat controversial, with the initial study indicating the rings to be in a staggered conformation. Electron diffraction studies of gas phase ferrocene, however, showed the rings to be eclipsed, or very nearly so. More recent X-ray diffraction studies of solid ferrocene have identified several crystalline phases, with an eclipsed conformation at 98K and with conformations having the rings slightly twisted in higher temperature crystalline modifications¹².

The preparation and properties of organolead halides and oxides have already been considered. Organolead hydrides are not known. Hydroxide derivatives are not numerous, and they are so distinctly amphoteric in character that their solution is rather difficult. Oxidation of a hexaalkyldilead provides a unique way of obtaining such hydroxides Triphenyllead derivatives of fatty acids may be prepared from tetraphenyllead and the appropriate acid by refluxing in xylene, illustrating further the effect of even weak acids on the carbon-lead bond. The products are waxy solids of moderate melting point. Organolead derivatives of alcohols are much less common than the analogous compounds of silicon, germanium, and tin, probably because oxides form instead. Like the three lighter elements of the group, however, lead forms sodium derivatives of the type R₃PbNa¹³.

MATERIAL AND METHODS:

Synthesis of ter-butyl chloride:

(Precursor)

70ml (82.6g) of Con.HCl and 18.5g of ter-butyl alcohol was taken in two different flasks. HCl was chilled at 5-8⁰C and transferred in separating funnel then ter-butyl alcohol was added in the same separating funnel and allowed to stand for 5 min then shake well. After 20 min two different layers are formed. Ter-butyl chloride layer was at the top. The lower layer of acidic solution was drained off.

Ter-butyl chloride was washed with 10ml of sodium bicarbonate solution and then with 10ml of water. 3.0gm of anhydrous calcium chloride was added in the flask and kept it sit overnight. The cloudy liquid turned clear. Dry ter-butyl chloride was decanted into round bottom flask. 2-3 boiling chips were added and the product was distilled by distillation. The product was collected in tared container, chilled in an ice bath, product obtained (2-chloro2-methyl propane).

Synthesis of Zinc-copper couple:

40ml of 3% HCl and 49.2g of zinc powder was added in the flask. The mixture was stirred rapidly for 2 minute the supernatant was decanted. Zinc powder was washed successively with three 40ml portions of 3%HCl, five 100ml portions of distilled water, two 75ml portions of 2% aqueous copper sulfate solution, four 100ml portions of absolute ethanol, and five 100ml portions of absolute ether.

To avoid absorption of bubbles of hydrogen on zinc, washing should be done with hydrochloric acid rapidly. The absolute ethanol and absolute ether washings were decanted directly on a Buckner funnel to prevent loss of the couple, covered tightly with a rubber dam, and suction dried until it reached room temperature. The zinc-copper couple was stored overnight over phosphorous pentaoxide.

Synthesis of ter-butyl zinc chloride:

38ml of ter-butyl chloride and zinc-copper couple was added in round bottom flask. The mixture was stirrered and refluxed for one and half hour. Reaction flask was cooled with ice water, if reaction becomes too vigorous. At the end of reaction, flame was removed, the flask was allowed to cool at room temperature and the mixture was refluxed under reduced pressure and transferred from one flask to another which is immersed in an ice mixture, dry CO₂ was added. The yield of crude material was 55gm.

Synthesis of ter-butyl lead chloride:

Pure and dry magnesium ribbon is cut into small pieces and suspended in pure dry ether contained in a round bottom flask. Also added 5g of lead chloride in round bottom flask on a water bath. It is connected to a reflux condenser carrying a CaCl₂ at the other end. A crystal of iodine is added in the flask. It helps to start the reaction, but once the reaction starts, it is very vigorous and the flask is to be cooled, ter-butyl chloride is added from the above after removing CaCl₂ for a moment. When the reaction is complete a clear solution of t-butyl lead chloride in dry ether is obtained.

RESULTS AND DISCUSSION:

Ter-butyl alcohol was converted to ter-butyl chloride by shaking the alcohol in a separatory funnel with concentrated HCl, then purifying the product by a simple distillation. Ter-butyl chlorides can be converted into ter-butyl lead chloride and ter-butyl zinc chloride very readily. Alkyl lead compounds react easily with water. Any moisture present will prevent the reaction from occurring.

Table 1: TLC of Tertiary butyl chloride:

Sr. no:	Compound	Solvent ratio Methanol: Ethanol	Distance traveled by Solvent	Distance traveled by Sample	R_f
1	Tertiary butyl chloride	50: 50	5.2	4	0.769
2	″	75: 25	9	6	0.66
3	″	25: 75	7	6	0.85

Table 2: TLC of Tertiary Butyl Zinc Chloride:

Sr. No	Solvent ratio Methanol: Ethanol	Distance traveled by solvent(cm)	Distance traveled by sample(cm)	R_{f value}
1	50 : 50	5.6	4.9	0.875
2	75 : 25	6.2	5.8	0.935
3	25 : 75	6.9	6	0.869

Table 3: TLC of Tertiary Butyl lead Chloride:

Sr. no	Tertiary butyl chloride	Types of Bonds	Tertiary butyl lead chloride	Types of bonds
1	2973 cm^-1	C- H stretching	2867.54 cm^-1	CH3 ν_S
2	1471.91852 cm^-1	C-H Bending	1456.91 cm^-1	δas CH₃
3	1369.6229 cm^-1	CH₃asymmetrical	1371.09 cm^-1	δas CH₃
4	750.2792 cm^-1	C-Cl stretching	---	---

Ter- butyl zinc chloride has been prepared by the action of Zn-Copper couple and Organic halide i.e., ter-butyl chloride. Zinc-copper couple was prepared by treating zinc dust with the conc. HCl.

The magnetic stirrer was used for the complete mixing of Zinc dust. Further aqueous CuSO₄ solution was added and successive washings with distilled water, ether and ethanol were carried out to prepare the zinc-copper couple. TLC of precursor ter-butyl chloride was noted in different solvent ratios. The solvent used as mobile phase was methanol and ethanol. The ratios were taken as 50: 50, 70: 25 and 25: 75.The Rf values of precursor noted were 0.769, 0.66, and 0.85. Distance traveled by the solvent was 4, 5 and 6 respectively is given in the Table 1.

Then TLC of ter-butyl zinc chloride was done in same ratio of solvent. Solvent flow noted was 5.6 in 50:50 ratio, and 6.2 in 75:50 and 6.9 in 25:75 solvent ratios. Distance traveled by the compound was 4.9, 5.8 and 6 respectively. The Rf values calculated were 0.875, 0.935 and 0.869. There was clear change noted between precursor and compound flow ratio. The data is given in the Table 2.

Then TLC of ter-butyl lead chloride was also done in the same ratio of solvent. Solvent flow noted was 5.8 in 1:1 ratio, 6.5 in 1:3 and 6.9 in 3:1 solvent ratio. Distance traveled by compound was 5.1, 5.9, and 6.2 respectively. The Rf values calculated were 0.879, 0.907, and 0.898. There was clear change noted between precursor and compound flow ratio. The comparison of Rf values of both precursor and compound was calculated and reported in Table 3.

In UV/VIS maximum absorbance of the ter-butyl zinc chloride was noted which is 213cm^-1.This λmax from which compound was prepared. The λmax of precursor is 221 cm^-1.The change has been noted from red shift to blue shift. The data is given in the Table 4.

Table 4: Spectroscopic Data of tertiary butyl chloride and Tertiary butyl zinc chloride

Sr. No	Compounds	λ_max
1	A	221.5
2	B	213

In UV/VIS maximum absorbance of ter-butyl lead chloride was noted which is 214 cm^-1 this λ_max then compared with precursor λ_max from which compound was prepared. The λ_max of precursor is 221 cm^-1 .The change has been noted from red shift to blue shift. The spectroscopic data for precursor and organometallic compound is given in Table 5.

Table 5: Maximum wave length (λ_max) of tertiary butyl lead chloride from UV/VIS spectroscopy:

No.	Compounds	λ_max
1	Tertiary butyl chloride	221cm^-1
2	Tertiary butyl lead chloride	214cm^-1

In FTIR change in bond frequencies was noted then these values compared with the frequencies of precursor. The types of bonds observed were CH₃ stretching at frequency 2867.54. Then asymmetrical stretching at 1456.91 and symmetrical stretching at 1371.09 was noted. The frequencies and types of bonds of precursor was noted as follows-H stretching at 2973cm^-1, C-H bending at 1471.91, CH₃ asymmetrical at 1369.70 and C-Cl stretching was noted at 750.30, there is a clear change occur between frequencies of organometallic compounds and precursor from which compound was prepared. The data is given in the Table 6 and 7 respectively.

The main technique used is GC/MS spectroscopy. Mass spectrum is used to calculate molecular formula of the compound. Fragmentation was also noted. MS gave different fragmentation of C₄H₉ m/z value noted was 57. Relative abundance is 100%. M+1 value is 4.47 and M+ 2 value is 0.08. Second fragmentation is C₃H₅, m/z value obtained was 41 at relative abundance of 18.6%. The M+1 and M+2 values are 3.32 and 0.04 respectively.

Table 7: FTIR spectrum of Tertiary Butyl lead chloride

Sr. no:	Type of Bonds	Frequency
1	CH₃δ s	2867.54
2	δas CH₃	1456.91
3	δas CH₃	1371.09

Third fragmentation is C₄H₇, m/z values obtained is 55 at relative abundance of 22.5%. The M+1 and M+2 values are 4.43 and 0.07 respectively. Data is given in Table 8 and figure is attached.

Table 8: (GC-MS): Fragmentation pattern of Tertiary Butyl Zinc Chloride

Formula	m/z value	Relative abundance	M+1	M+2
C₄H₉	57	100	4.47	0.08
C₃H₅	41	18.6	3.32	0.04
C₄H₇	55	21.5	4.43	0.07

GC/MS gave different fragmentation of C₄ H₉. m/z value noted was 57. Relative abundance is 100% .M + 1 value was 4.47 and M + 2 value was 0.08 Second fragmentation was C₃H₅ , m/z value obtained was 41 at relative abundance of 18.6%. The M + 1 and M + 2 values were 4.47 and 1.28 respectively. Third fragmentation was C₄H₇. Which gives the molecular formula 55 .The relative abundance of this fragment noted was 22.5.The M +1 and M + 2 values were 4.43 and 0.07 respectively. The data is given in Table 9 and figure is attached.

Table 9: Gas Chromatography – Mass spectroscopy (GC-MS)

Fragmentation of Tertiary Butyl Lead chloride:

Formula	m /z value	Relative abundance	M+1	M+2
C₄H₉	57	100	4.47	0.08
C₃H₅	41	18.6	3.32	0.04
C₄ H₇	55	22.5	4.43	0.07

CONCLUSION:

Furthermore, the compounds were characterized by its boiling point, Solubility and TLC. The purity of the compounds was determined by thin layer chromatography. Various analytical techniques were also used to characterize the compounds. UV/VIS spectroscopy used for the quantitative analysis by using Beer’s Lambert law, the functional group determination was carried out by FTIR spectroscopy.

The identification of the compounds was established by the comparison of its IR spectrum with that of the authentic sample. The most efficient technique was GC-MS, used for the separation of chemical compound and also the structure determination of the compound. The molecular weight was confirmed by the mass spectrum obtained from GC-MS.

REFERENCES:

1. Hegedus LS and Haim A. Chem. 1967; 6: 664.

2. Corey EJ and Hegedus LS. J Am Soc.1968; 90: 2417.

3. Hegedus LS and Stiverson RK. J Am Soc.1974; 96: 3250.

4. Frankland E. Liebigs. Ann Chem.1848; 71:171.

5. Erdik E.Organozinc Reagents in organic synthesis. Edited by Boca Raton and Aldrich FL.CRC Press, Inc.1996; Catalog Number Z28,12-7.

6. Rieke RD and Hanson.Tetrahedron.1997; 53:1925.

7. Hanson MV et al. Tetrahedron Lett. 1994; 35:7205.

8. Cintas P. Activated Metals in organic Synthesis. Edited by Boca Raton and Aldrich FL.CRC Press, Inc.1993; Catalog Number Z24, 607-7.

9. Miller JA and Farrell RP. Tetrahedron Lett.1998; 39:7275.

10. Zhu L et al. J Org Chem.1991; 56:1445.

11. Negishi E et al. ibid.1997; 42:1821.

12. Encyclopedia information about organometallic chemistry. The Columbia Electronic Encyclopedia, Sixth Edition, Columbia University Press. Licensed from Columbia University Press. 2003.

13. Inorganic Chemistry. www.BlogHog.biz.

Received on 03.06.2010 Modified on 02.07.2010

Asian J. Research Chem. 3(4): Oct. - Dec. 2010; Page 1011-1014

Sr No	Tertiary butyl chloride	Type of Bonds	Tertiary butyl zinc chloride	Types of bonds
1	2973cm^-1	C-H Stretching	2867.54cm^-1	CH₃νs
2	1471.9185cm^-1	C-H Bending	1456.91cm^-1	δas CH₃
3	1369.6229cm^-1	CH₃ asymmetrical	1371.09cm^-1	δas CH₃
4	750.2792cm^-1	C-Cl stretching	-	-

INTRODUCTION:

Compounds

Sr. no:

Type of Bonds

Table 9: Gas Chromatography – Mass spectroscopy (GC-MS)