1. INTRODUCTION
Inorganic diluents or dispersants that are insoluble in the melt have been known as additives to control the rate of solid-solid reactions. Addition of a high melting point inert solid to a melt can be used to control the rate of a solvent-free reaction just as the rates of some reactions are controlled by solvents. A good example is in a solventless substitution reaction of Mn(CO)4(PPh3)Br with PPh3, a range of dispersants or diluent (KBr, Al2O3, Na2SO4, NaNO2, SiO2, Na2CO3, NaC2H3O2, NaNO3, sucrose and TiO2) are ground and filtered only to provide a comparable particle size. The reaction was investigated and monitored by in situ DRIFTS. The result of the above study showed that the chemical nature of the diluent matrix influenced the rate of the solventless reaction. Therefore, when the reaction was carried out in sucrose and SiO2, the rate of the reaction was fastest. When Al2O3 and TiO2 were used, the reaction was slower [1]. Also the role of the nature of the solid dispersant or diluent has been investigated in solventless reactions involving thallium salts of tris (pyrazolylborate). The grinding of thallium salts of tris (pyrazolylborate), Tp with Mn(II), Co(II) and Ni(II) salts in an agate mortar has been reported to yield Mn, Co and Ni tris (pyrazolylborate) metal complexes of the type TpMCl via a substitution type of reaction [2]. Supramolecular complexes of the formula [CoIII(η5-C5H4COOH) (η5-C5H4COO)]2⋅M+X− were formed when organometallic zwitterion [CoIII(η5-C5H4COOH)(η5-C5H4COO)] reacts quantitatively as a solid polycrystalline phase with a number of crystalline alkali salts MX (M = K+, Rb+, Cs+,3-1310024\fc13284c-361b-4127-8e63-1022a593f9b0.jpg" width="45.219998550415" height="34.4849992752075 " />; X = Cl–, Br–, I–, 3-1310024\29d7d096-1f39-4689-87ad-5c6868d4b5bf.jpg" width="38.094998550415" height="34.4849992752075 " />[1].
In the same vein, manual grinding of the organometallic complex [Fe(η5-C5H4COOH)2] with a number of solid bases, namely 1,4-diazabicyclo[2.2.2]octane, C6H12N2, 1,4-phenylenediamine, p-(NH2)2C6H4, piperazine, HN(C2H4)2NH, trans-1,4-cyclohexanediamine, p-(NH2)2C6H10, and guanidinium carbonate [(NH2)3C]2[CO3], generates quantitatively the corresponding adducts[HC6H12N2][Fe(η5-C5H4COOH)(η5-C5H4COO)], [HC6H8N2][Fe(η5-C5H4COOH)(η5-C5H4COO)], [H2C4H10N2][Fe(η5-C5H4COO)2], [H2C6H14N2][Fe(η5-C5H4COO)2].2H2O, and
[C(NH2)3]2[Fe(η5-C5H4COO)2].2H2O, respectively [3].
Therefore, environmental concerns in synthetic chemistry have led to a reconsideration of reaction methodologies. This has resulted in investigations into atom economy, the use of supercritical CO2, ionic liquids, and other procedures to reduce the disposal problems associated with most chemical reactions. One obvious route to reduce waste entails generation of chemicals from reagents in the absence of solvents [4]. Little is known about reactivity patterns of organometallic complexes in the solid state, until it was discovered that organometallic complexes, of the type CpML4, undergo cis-trans ligand isomerization reactions in the solid state [5-8].
Hence, in this study we report on the effect of pelleting on organometallic compounds, transand cis-[(η5-C5H4Me) Mo(CO)2PPh3I]. Attempt were made on the effect of diluents on iron organometallic complexes [(η5-C5H5) Fe(CO)23-1310024\e1087c33-064d-4bc7-b291-e5e6d072c263.jpg" width="47.594998550415" height="34.4849992752075 " />][3-1310024\9eadef61-a1ab-4b3d-9fd0-3ed09a4b1e0d.jpg" width="38.094998550415" height="34.4849992752075 " />], as its influenced the products formed after pellet formation. Hence these diluents KBr, KCl, NaCl, CaCl2, NaNO3, BaSO4, CaCO3 and Al2O3 were screened for either good pellet formation or set out reactions with the complexes. It was observed that BaSO4, CaCO3 and Al2O3 could not form a good pellet for FT IR measurement of the complexes. A simple process of forming a good pellet for FT IR measurement could generate a reaction because of high amount of energy involved. In general, when two solids are ground together, the heat generated in the grinding process may be sufficient to either create a melt at the surface or completely melt the solid reagents. This could arise from the generation of a “hot spot” (an exotherm) [1,9] that could lead to a self-sustaining reaction.
2. EXPERIMENTAL
2.1. General
(η5-C5H4Me)Mo(CO)3I were prepared by the standard procedures used to synthesise other ring-substituted analogues [10,11]. TrimethylamineN-oxide dihydrate (Aldrich) was used as received. All reactions were carried out using standard Schlenk techniques under nitrogen.
2.2. Preparation of a Mixture of transand cis-[(η5-C5H4Me)Mo(CO)2PPh3I]
A mixture of the cis and trans isomers were prepared in good yield by following a standard procedure in the literature [11].
2.3. Preparation of [(η5-C5H5)Fe(CO)23-1310024\9eb737ee-3b26-43f3-9d46-885bcd6022d1.jpg" width="54.719998550415" height="35.719998550415 />][3-1310024\0fbf988e-762b-4769-afe9-b2e769daa94b.jpg" width="41.6099992752075" height="35.719998550415 " />]
The procedures are the same for the preparation of [(η5- C5H5)Fe(CO)23-1310024\fc1a6ab2-3914-4a62-9598-5baf504a0167.jpg" width="47.594998550415" height="34.4849992752075 " />][3-1310024\d6c7430b-f84c-4910-b4e1-a77f554907a3.jpg" width="35.719998550415" height="34.4849992752075 " />] in the literature [12].
2.4. Refractometric Measurement to Ascertain the Purity of the Salts
Abbe Refractometer (Optic Ivymen) was used to determine the purity of the samples.
2.5. Pellets Formation
The diluents were dried for 12 hrs in an oven to ensure complete removal of moisture. About 10 mg of pure diluents (e.g. NaCl) were crushed to fine powder using an agate mortar and pestle. About 2 mg of the solid organometallic complex was added and gently ground together with diluents until fully mixed. The die set was assembled and the mixture was added into the die and goes between two stainless-steel discs and pressed to form a good, thin and transparent pellet. Opaque pellets gave poor spectra and white spots in the pellets.
3. RESULTS AND DISCUSSIONS
3.1. Preparation of the Complexes transand cis-[(η5-C5H4Me)Mo(CO)2PPh3I]
The method developed by Blumer et al. [13] for the synthesis of the related unsubstituted compounds was adopted for the synthesis of transand cis-[(η5-C5H4Me)Mo(CO)2 PPh3I]. Isomer separation was achieved by dissolving the crude material in CH2Cl2 followed by mixing with a small quantity of silica gel. The yellow powder left after removing the CH2Cl2 was chromatographed on a silica gel column (60 cm) with a 1:10 CH2Cl2/hexane mixture to afford the desired complexes [14].
3.2. Preparation of [(η5-C5H5)Fe(CO)23-1310024\e886175d-b181-4bd9-ade5-15c284f1bf17.jpg" width="54.719998550415" height="35.719998550415 />][3-1310024\f3abe69e-31a9-4de6-beb7-ecfec1cc89b2.jpg" width="41.6099992752075" height="35.719998550415 " />]
The preparation of [(η5-C5H5)Fe(CO)23-1310024\5cedcdf1-f279-457b-8c3f-7f0372ae25fc.jpg" width="47.594998550415" height="34.4849992752075 " />][3-1310024\25094a33-2ad4-434f-88f7-26fc64a18dd4.jpg" width="35.719998550415" height="34.4849992752075 " />], follows the ETC PPh3 ligand replacement for I– on (η5-C5H5) Fe(CO)2I to obtain the complexes [12]. The yield and spectroscopic information were not at variant with the established results in the literature.
3.3. Purity of the Salts
Before the formation of a good pellet suitable for FTIR measurement, the diluents were carefully dried at 10530;C until a constant weight obtained. This is to remove moisture and other volatile component in the diluents. The refractive index of the salts at the specified temperature, 33.430;C depicts the state of high purity of the salts when compared with reference refractive indexes.
3.4. Effect of Pelleting on νco in Methylcyclopentadienyl Molybdenum Dicarbonyl Triphenylphosphine Iodide Using Different Diluents
We reported earlier a thermal transformation of cisor trans-(η5-C5H4Me)Mo(CO)2(PPh3)I in the solid state where the color and shape of the starting materials showed no visible change and no obvious decomposition during the heating process [11]. The cis and trans products was achieved by means of TLC, and solution IR and NMR spectroscopy on the products after the reaction, revealed the formation of the isomer materials. The isomerisation reactions for the new complexes were studied and the general trend was for the isomerisation reaction to occur from the trans to the cis isomer dependent on electronic factors associated with ligand orientation effects. An extension of the work was on the formation of the products mixture on pelleting either the cis or the trans isomer of the complex. Figure 1 shows the isomerisation reaction during the formation of a suitable pellet for FT IR spectroscopy. While Figure 2 shows the FT IR mixture of the cis or the trans isomer of the complex.
The cis or the trans isomer gave the same IR spectra i.e a mixture of cis and trans isomer of the complex.
3-1310024\25f7dcb7-ae3d-46fa-b925-1ad892cddc21.jpg" width="434.15" height="118.93999710083 " />
Figure 1. Solid state cis/trans isomerisation reaction of (η5-C5H4Me)Mo(CO)2(PPh3)I during pelleting.
3-1310024\d24ced23-75b9-4924-a63b-ae2b13c1513a.jpg" width="438.99500579834" height="626.905023193359 " />
Figure 2. shows the FT IR spectrum of the isomer mixture in the solid state in NaCl.
Therefore, it does not matter the isomer started with in the course of solid state transformation reaction, an equilibrium ratio of 30/70 (trans/cis) will still be achieved. This result shows that the solid state isomerisation of (η5-C5H4Me)Mo(CO)2(PPh3)I still maintain a bidirectional reaction process. The IR spectra show very strong peaks at νco 1957, 1947 and strong peaks at 1867, 1853 cm–1. As shown in Figures 2 and 3.
The individual IR cis/trans isomer will therefore show at 1947 and 1853/1957 and 1867 cm–1. The solution IR spectra gave, cis = 1961, 1875 and trans = 1963, 1882 cm–1 in dry CHCl3 [11]. It should be noted that the same isomerisation products were obtained for the halide salts of group I investigated, namely, KCl, KBr and NaCl, Figure 3.
It is therefore possible to draw out some information on pelleting in the IR measurement of this complex:
1) Most of the solid state IR measurement of the organometallic complex of the type (η5-C5H4Me)Mo(CO)2 (PPh3)I on pelleting will give isomer mixture.
2) It can results in facile synthesis of cis/trans- (η5-C5H4Me) Mo(CO)2(PPh3)I.
3) It can leads to isomerisation reaction as in this process.
3-1310024\ff57c36c-719c-43f5-9771-29e5d15fafbb.jpg" width="408.025" height="610.280023193359 " />
Figure 3. shows the FT IR spectra of the isomer mixture in the solid state in different diluents.
4) It is a fast reaction.
5) It is a neat and greener reaction.
Hence, when two solids are ground or pelleting together, the heat generated in the process set out a reaction to generate an exotherm that could then lead to a self-sustaining reaction [1,9]. It is not unlikely that no other product(s) formed during the creation of a suitable pellet for IR measurement. It is also not unlikely that there is halides exchange, a possibility of Iodide in the complex exchange for Chloride or Bromide in the diluents during the formation of a good pellet for FT IR measurement. Supporting evidence in Figure 3 revealed that there is a change in the absorption intensity especially when pelleting the complex with KBr, while the intensities of NaCl and KCl remain constant.
A non isomeric organometallic product of the type [η5-(C5H5)Fe(CO)2PPh3]+[PF6]– was investigated to determine the effect of the diluents through FT IR measurement and as a control for whether the solid state transformation of the (η5-C5H4Me)Mo(CO)2(PPh3)I complex actually occurred. Figure 4 shows the spectrum of the [η5-(C5H5)Fe(CO)2PPh3]+[PF6]– complex in NaCl diluent after pelleting.
It was abserved that very strong peaks at νco 2008 and 2049 cm–1 correspond to the absorption of CO attached to the iron centre. A lower wave number of this kind reflects the degree of back bonding to the carbon monoxide ligand. The peaks position in the solid state is not significantly different from the peaks position in solution IR that occurred at 2014 and 2062 cm–1 in dry CHCl3 [12] Figure 5 depicts the behaviour of complex in different diluents.
3-1310024\797b00b9-91e1-4009-bd56-688ab7bda225.jpg" width="437.75998840332" height="406.79001159668 " />
Figure 4. FTIR Spectrum of [η5-(C5H5)Fe(CO)2PPh3]+[PF6]– in NaCl.
3-1310024\b596bd16-7363-46b4-8727-f76bb9818681.jpg" width="438.99500579834" height="516.230023193359 " />
Figure 5. FTIR Spectra of [η5-(C5H5)Fe(CO)2PPh3]+[PF6]– in different diluents.
The same pattern was therefore observed in the diluents used. This could informed that these diluents are suitable for the formation of good pellet for IR without decomposition. It is therefore possible that the anion exchange reaction, (where Cl– or Br–) exchange for 3-1310024\f74ecf21-57a8-45f8-8ac1-1cb7f14b3bbd.jpg" width="35.719998550415" height="34.4849992752075 " /> did not occur because from our experience the halide counter anion are not very stable as the 3-1310024\adee6c29-da57-4d0a-b611-eb4edf201bea.jpg" width="35.719998550415" height="34.4849992752075 " /> anion. It could therefore infered that isomerization actually took place on pelleting cis/trans-(η5-C5H4Me)Mo(CO)2(PPh3)I and no isomerisation on [η5-(C5H5)Fe(CO)2PPh3]+[PF6]– during pelleting.
4. CONCLUSION
It was established that pelleting can generate enough heat to set up a chemical reaction. Therefore on forming a suitable pellet using different diluents of group I metal salts leads to the isomerisation reactions of transforming cis to trans and the reverse, until isomeric mixture of cis/trans (30/70) is achieved.
5. ACKNOWLEDGEMENTS
We wish to thank the Redeemer’s university for providing enabling environment and facilities for this research work.
NOTES