Claims:1. A POCNP Pincer ligand consisting of at least one compound selected from Formula-I(A), and Formula-I(B),

wherein, R? and R? are at least one independently selected from the group consisting of C1 to C10 alkyl groups; and R1 and R2 are at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups.
2. A POCNP-Iridium Pincer complex consisting of at least one compound selected from Formula-II(A), and Formula-II(B), the POCNP-Iridium Pincer complex being a product of reaction of the POCNP Pincer ligand as claimed in claim 1 and at least one iridium salt;

wherein, R? and R? are at least one independently selected from the group consisting of C1 to C10 alkyl groups; and R1 and R2 are at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups.
3. The POCNP-Iridium Pincer complex as claimed in claim 2, wherein the iridium salt is at least one selected from the group consisting of chlorobis(cyclooctene)iridium(I)dimer [Ir(COE)2Cl]2, and bis(1,5-cyclooctadiene)diiridium(I) dichloride [Ir(COD)Cl]2.
4. A process for preparing the POCNP Pincer ligand as claimed in claim 1, the process comprising reaction of at least one compound selected from the group consisting of Formula-III(A), and Formula-III(B),
;
wherein, R1 and R2 are at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups;
with at least one halodialkylphosphine of Formula-IV,
R'R"PX - Formula-IV
wherein, R? and R? are at least one independently selected from the group consisting of C1 to C10 alkyl groups; and X is a halogen selected from the group consisting of Cl, Br, and I.
5. The process as claimed in claim 4, wherein the compound of Formula-III(A) is 6-hydroxyindole, the compound of Formula-III(B) is 2-hydroxycarbazole, and the halodialkylphosphine is at least one selected from the group consisting of chlorodiisopropylphosphine, and di-tert-butylchlorophosphine.
6. The process as claimed in claim 4 comprising the following steps:
- stirring a mixture comprising at least one compound selected from the group consisting of Formula-III(A) and Formula-III(B), and at least one first base in at least one first fluid medium at a temperature in the range of 10 ?C to 50 ?C for a period of 2 hours to 20 hours to obtain a reaction mixture;
- adding a mixture of at least one halodialkylphosphine of Formula-IV, and the first fluid medium to the reaction mixture and stirring the resultant mixture at a temperature in the range of 10 ?C to 50 ?C for a period of 2 hours to 20 hours to obtain a product mixture; and
- separating the first fluid medium from the product mixture to obtain a residue containing the POCNP Pincer ligand.
7. The process as claimed in claim 6, wherein the first fluid medium is tetrahydrofuran; and the first base is at least one selected from the group consisting of potassium tert-butoxide, and sodium tert-butoxide.
8. A process for preparing POCNP-Iridium Pincer complexes as claimed in claim 2, the process comprising heating a mixture comprising at least one POCNP Pincer ligand, and at least one iridium salt in at least one third fluid medium at a temperature in the range from 100 °C to 150 ?C, followed by the separation of the third fluid medium to obtain a crude POCNP-Iridium Pincer complex, and purifying the crude POCNP-Iridium Pincer complex to obtain the POCNP-Iridium Pincer complex.
9. A process for dehydrogenation of alkane using POCNP-Iridium Pincer complex as claimed in claim 2, the process comprising heating a mixture of at least one alkane, at least one hydrogen acceptor and at least one second base in at least one fourth fluid medium at a temperature in the range from 160 to 210 ?C in the presence of the POCNP-Iridium Pincer complex, to obtain dehydrogenated alkane.
10. The process as claimed in claim 9, wherein the hydrogen acceptor is tert-butylethylene, the second base is at least one selected from the group consisting of potassium tert-butoxide, and lithium tert-butoxide, and the fourth fluid medium is selected from a group consisting of toluene, xylene and mesitylene.
, Description:FIELD
The present disclosure relates to a catalyst, particularly iridium based Pincer complexes.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
A POCNP Pincer ligand is a tridentate ligand that binds with a metal at three sites; one phosphorous atom of phosphinite group, one phosphorous atom of phosphinous amide group and a carbon of an aromatic framework. The phosphinite group is in the form of a phosphorous-oxygen (P-O) bond and phosphinous amide group is in the form of a phosphorous-nitrogen (P-N) bond.
BACKGROUND
A Pincer ligand is a type of chelating agent that binds to three adjacent coplanar sites, usually on a transition metal in a meridional configuration. The Pincer complex obtained from the complexation of the Pincer ligand and a transition metal attain a planer framework. The Pincer complexes catalyze chemical transformations with high selectivity.
A POCNP Iridium Pincer complex can be used for dehydrogenation of alkanes. It is desired that the POCNP Iridium Pincer complexes are stable at high temperature.
Further, in general, processes for the preparation of Iridium Pincer complexes are associated with various drawbacks such as being a multistep and tedious process and having low yield.
There is, therefore, felt a need to provide a POCNP Iridium Pincer complex that is stable at high temperature and a simple process for preparing the POCNP Iridium Pincer complex with high yield.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
It is another object of the present disclosure to provide POCNP-Iridium Pincer complexes that are stable at high temperature.
It is yet another object of the present disclosure to provide a simple process for preparing POCNP-Iridium Pincer complexes in high yield.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
In one aspect, the present disclosure provides POCNP Pincer ligand consisting of at least one compound selected from Formula-I(A), and Formula-I(B).

R? and R? can be at least one independently selected from the group consisting of C1 to C10 alkyl groups; and R1 and R2 can be at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups.
In another aspect, the present disclosure provides a POCNP-Iridium Pincer complex consisting of at least one compound selected from Formula-II(A), and Formula-II(B), the POCNP-Iridium Pincer complex being a product of reaction of the POCNP Pincer ligand of the present disclosure and at least one iridium salt.

R? and R? can be at least one independently selected from the group consisting of C1 to C10 alkyl groups; and R1 and R2 can be at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups.
In accordance with the embodiments of the present disclosure, the iridium salt is at least one selected from the group consisting of chlorobis(cyclooctene)iridium(I)dimer [Ir(COE)2Cl]2, and bis(1,5-cyclooctadiene)diiridium(I) dichloride [Ir(COD)Cl]2.
In yet another aspect, the present disclosure provides a process for preparing the POCNP Pincer ligand of the present disclosure by reaction of at least one compound selected from Formula-III(A), and Formula-III(B),
;
wherein, R1 and R2 are at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups;
with at least one halodialkylphosphine of Formula-IV,
R'R"PX ….. Formula-IV,
wherein, R? and R? are at least one independently selected from the group consisting of C1 to C10 alkyl groups; and X is a halogen selected from the group consisting of Cl, Br, and I.
In accordance with the embodiments of the present disclosure, the compound of Formula-III(A) can be 6-hydroxyindole, compound of Formula-III(B) can be 2-hydroxycarbazole, and halodialkylphosphine can be at least one selected from the group consisting of chlorodiisopropylphosphine, and di-tert-butylchlorophosphine.
The process for preparing the POCNP Pincer ligand of the present disclosure involves the following steps.
At least one compound selected from the group consisting of Formula-III(A) and Formula-III(B), and at least one first base are stirred in at least one first fluid medium at a temperature in the range of 10 ?C to 50 ?C for a period of 2 hours to 20 hours to obtain a reaction mixture.
A mixture of at least one halodialkylphosphine of Formula-IV, and the first fluid medium is added to the reaction mixture and the resultant mixture is stirred at a temperature in the range of 10 ?C to 50 ?C for a period of 2 hours to 20 hours to obtain a product mixture.
The first fluid medium is separated from the product mixture to obtain a residue containing the POCNP Pincer ligand.
In accordance with the embodiments of the present disclosure, the first fluid medium can be tetrahydrofuran, and first base can be at least one selected from the group consisting of potassium tert-butoxide, and sodium tert-butoxide.
In yet another aspect, the present disclosure provides a process for preparing POCNP-Iridium Pincer complexes of the present disclosure. The process involves heating a mixture comprising at least one POCNP Pincer ligand of Formula-I(A), and Formula-I(B), and at least one iridium salt in at least one third fluid medium at a temperature in the range from 100 °C to 150 ?C, followed by the separation of the third fluid medium to obtain a crude POCNP-Iridium Pincer complex. The crude POCNP-Iridium Pincer complex can be purified to obtain the POCNP-Iridium Pincer complex.
In accordance with the embodiments of the present disclosure, the molar ratio of POCNP Pincer ligand and the iridium salt can be 2:1.
In still another aspect, the present disclosure provides a process for dehydrogenation of alkane using POCNP-Iridium Pincer complex of the present disclosure. The process involves heating a mixture of at least one alkane, at least one hydrogen acceptor and at least one second base in at least one fourth fluid medium at a temperature in the range from 160 to 210 °C in the presence of POCNP-Iridium Pincer complex of the present disclosure.
The POCNP-Iridium Pincer complexes of the present disclosure are prepared using a simple process in high yield. These POCNP-Iridium Pincer complexes dehydrogenate alkanes with high turnover numbers. Further, the POCNP-Iridium Pincer complexes of the present disclosure have high thermal stability.
DETAILED DESCRIPTION
A Pincer ligand is a tridentate ligand that binds with a metal at three sites in one plane. A POCNP Pincer ligand provides a binding site via phosphorous atom of the phosphinite group, a binding site via phosphorous atom of the phosphinous amide group, and a binding site through a carbon on aromatic framework, for complexation with the metal. Thus, a Pincer ligand forms complex with the metal through two metal-phosphorous (M-P) bonds and one metal–carbon bond [M-C(aryl) bond].
In general the conventional processes for preparation of Iridium Pincer complexes are associated with various drawbacks such as being a multistep and tedious process and having low yield.
The present disclosure envisages a simple process for preparing the POCNP-Iridium Pincer complexes with high yield. Further, POCNP-Iridium Pincer complexes that are stable at high temperature are envisaged.
In one aspect, the present disclosure provides POCNP Pincer ligand consisting of at least one compound selected from Formula-I(A), and Formula-I(B).

R? and R? can be at least one independently selected from the group consisting of C1 to C10 alkyl groups; and R1 and R2 can be at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups.
In accordance with the embodiments of the present disclosure, R? and R? can be independently selected from the group consisting of methyl, ethyl, isopropyl, tert-butyl, cyclopentyl, cyclohexyl and adamantyl.
The oxygen atom and the nitrogen atom of the POCNP Pincer ligands of the present disclosure are separated by 3 carbon atoms. Both the nitrogen atom and the oxygen atom of the heterocyclic aromatic compound bear a dialkylphosphine group each. Due to this spatial relationship between the oxygen atom and the nitrogen atom, phosphorous atoms of the phosphinite group and the phosphinous amide group are suitably positioned for the formation of a POCNP-metal Pincer complex.
In another aspect, the present disclosure provides a POCNP-Iridium Pincer complex consisting of at least one compound selected from Formula-II(A), and Formula-II(B), the POCNP-Iridium Pincer complex being a product of reaction of the POCNP Pincer ligand of the present disclosure and at least one iridium salt.

R? and R? can be at least one independently selected from the group consisting of C1 to C10 alkyl groups; and R1 and R2 can be at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups.
The POCNP-Iridium Pincer complexes derived from ligands of Formula-I(A) and Formula-I(B) are represented by Formula-II(A) and Formula-II(B) respectively.
In accordance with the embodiments of the present disclosure, the iridium salt is at least one selected from the group consisting of chlorobis(cyclooctene)iridium(I)dimer [Ir(COE)2Cl]2, and bis(1,5-cyclooctadiene)diiridium(I) dichloride [Ir(COD)Cl]2.
The POCNP-Iridium Pincer complexes of the present disclosure can be used for dehydrogenation of alkanes.
In yet another aspect, the present disclosure provides a process for preparing the POCNP Pincer ligand of the present disclosure by reaction of at least one compound selected from the group consisting of Formula-III(A), and Formula-III(B),
;
wherein, R1 and R2 are at least one independently selected from the group consisting of hydrogen, electron withdrawing groups, and electron donating groups;
with at least one halodialkylphosphine of Formula-IV,
R'R"PX ….. Formula-IV
wherein, R? and R? are at least one independently selected from the group consisting of C1 to C10 alkyl groups; and X is a halogen selected from the group consisting of Cl, Br, and I.
In accordance with the embodiments of the present disclosure, the compound of Formula-III(A) can be 6-hydroxyindole, compound of Formula-III(B) can be 2-hydroxycarbazole, and halodialkylphosphine can be at least one selected from the group consisting of chlorodiisopropylphosphine, and di-tert-butylchlorophosphine.
The process for preparing the POCNP Pincer ligand of the present disclosure comprises the following steps.
At least one compound selected from the group consisting of Formula-III(A) and Formula-III(B), and at least one first base are stirred in at least one first fluid medium at a temperature in the range of 10 ?C to 50 ?C for a period of 2 hours to 20 hours to obtain a reaction mixture.
A mixture of at least one halodialkylphosphine of Formula-IV, and the first fluid medium is added to the reaction mixture and the resultant mixture is stirred at a temperature in the range of 10 ?C to 50 ?C for a period of 2 hours to 20 hours to obtain a product mixture.
The first fluid medium is separated from the product mixture to obtain a residue containing the POCNP Pincer ligand.
The residue containing the POCNP Pincer ligand can be extracted with at least one second fluid medium.
In accordance with one embodiment of the present disclosure, the reaction is carried out at room temperature.
The halodialkylphosphines used in the process of the present disclosure are non-pyrophoric and cheaper as compared to the corresponding dialkylphosphines, which can be used for preparing certain Pincer ligands.
In accordance with one embodiment of the present disclosure, the molar ratio of the at least one compound selected from the group of Formula-III(A) or Formula-III(B) and the halodialkylphosphine can be 1:2.
In accordance with the embodiments of the present disclosure, the first fluid medium can be tetrahydrofuran.
In accordance with the embodiments of the present disclosure, the first base can be at least one selected from the group consisting of potassium tert-butoxide, and sodium tert-butoxide.
The POCNP Pincer ligands derived from compound of Formula-1(B) may contain two rotamers. These two rotamers can be at least partially separated by recrystallization from at least one second fluid medium.
In accordance with the embodiments of the present disclosure, the second fluid medium can be selected from the group consisting of n-pentane, n-hexane, and n-heptane.
The process of the present disclosure provides the POCNP Pincer ligands with a yield in the range from 80% to 94%.
The process of the present disclosure provides a simple process for preparing the POCNP Pincer ligands. Further, yield of POCNP ligand prepared by the process of the present disclosure is high.
In yet another aspect, the present disclosure provides a process for preparing POCNP-Iridium Pincer complexes of the present disclosure. The process involves the following steps.
A mixture comprising at least one POCNP Pincer ligand, and at least one iridium salt in at least one third fluid medium, is heated at a temperature in the range from 100 to 150 ?C, followed by the separation of the third fluid medium, to obtain a crude POCNP-Iridium Pincer complex. The crude POCNP-Iridium Pincer complex can be purified to obtain the POCNP-Iridium Pincer complex with high purity.
In accordance with the embodiments of the present disclosure, Iridium salt can be at least one selected from the group consisting of chlorobis(cyclooctene)iridium(I)dimer [Ir(COE)2Cl]2 and bis(1,5-cyclooctadiene)diiridium(I) dichloride [Ir(COD)Cl]2.
In accordance with one embodiment of the present disclosure, the molar ratio of the POCNP pincer ligand and the iridium salt can be 2:1.
In accordance with the embodiments of the present disclosure, the third fluid medium can be at least one selected from the group consisting of toluene, xylene and mesitylene.
The purification of the POCNP-Iridium Pincer complex can be carried out by trituration with n-pentane and n-hexane.
The yield of the purified POCNP-Iridium Pincer complex is in the range from 60% to 71%.
The present disclosure provides a simple process for preparing the POCNP-Iridium Pincer complexes. Further, the process of the present disclosure provides POCNP-Iridium Pincer complexes in high yield.
In still another aspect, the present disclosure provides a process for dehydrogenation of alkanes using POCNP-Iridium Pincer complex of the present disclosure.
The process involves heating a mixture of at least one alkane, at least one hydrogen acceptor and at least one second base in at least one fourth fluid medium at a temperature in the range from 160 to 210 °C in the presence of POCNP-Iridium Pincer complex of the present disclosure, to obtain dehydrogenated alkane. The dehydrogenated alkane can be alkenes and/or diene.
In accordance with the embodiments of the present disclosure, the second base can be at least one selected from the group consisting of potassium tert-butoxide, and lithium tert-butoxide.
In accordance with the embodiments of the present disclosure, the fourth fluid medium can be selected from a group consisting of toluene, xylene and mesitylene.
It is observed that the POCNP-Iridium Pincer complexes of the present disclosure are stable up to 210 ?C.
In accordance with the embodiments of the present disclosure, the alkane can be at least one selected from the group consisting of C1 to C10 alkanes.
In accordance with the embodiments of the present disclosure, the alkane can be at least one selected from the group consisting of n-butane, and isobutane.
In accordance with the embodiments of the present disclosure, the hydrogen acceptor is tert-butylethylene. Other hydrogen acceptors can also be used for dehydrogenation of alkane.
In accordance with an exemplary embodiment of the present disclosure, the POCNP-Iridium Pincer complex is used for dehydrogenation of n-butane. The products of dehydrogenation are butenes and butadiene. The butenes can be a mixture of 1-butene, cis-2-butene and trans-2-butene.
In accordance with the embodiments of the present disclosure, alkane dehydrogenation is carried out in the presence of the POCNP-Iridium Pincer complex of the present disclosure with a catalyst turnover number in the range from 100 to 1500.
In accordance with one embodiment of the present disclosure, the alkane is a C4-stream containing a mixture of n-butane and isobutane. The POCNP-Iridium Pincer complex of the present disclosure dehydrogenates isobutane, which is a branched alkane, in preference to n-butane, which is a straight chain alkane.
The POCNP-Iridium Pincer complex of the present disclosure can be immobilized on supports selected from the group consisting of alumina, silica, zeolites, resins, and metal surfaces. The immobilization may involve physical adsorption process or covalent bond linkage.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.

Experiments:
Experiment-1: Synthesis of POCNP-Iridium Pincer complex 21

Step 1 – Synthesis of POCNP Pincer ligand 20

To a solution of 6-hydroxyindole (0.5 g, 3.75 mmol) in THF (10 mL), a suspension of KOtBu (0.86 g, 7.66 mmol) in THF (10 mL) was added and the reaction mixture was stirred at room temperature for 10 hours. A solution of chlorodiisopropylphosphine (1.17 g, 7.66 mmol) in THF was added dropwise to the above solution and the resultant reaction mixture was stirred at room temperature for 12 hours. THF was evaporated under reduced pressure and the residue was extracted with n-pentane (20 mL X 2). The combined n-pentane extracts were evaporated under reduced pressure to obtain 20 (1.29 g).
Step-2: A glass pressure tube was charged with [IrCl(COE)2]2 (613 mg, 0.684 mmol), 20 (500 mg, 1.36 mmol), and 15 mL of toluene. The tube was sealed, placed in an oil bath, and heated at 135 °C for 24 hours. Toluene was removed under reduced pressure and the residue was extracted with n-pentane (50 mL X 3). Combined n-pentane extract was evaporated under reduced pressure to obtain 21.

Experiment-2: Synthesis of POCNP-Iridium Pincer complex 31

Step 1 – synthesis of POCNP Pincer ligand 30

To a solution of 2-hydroxycarbazole (1g, 5.46 mmol) in THF (10 mL), a suspension of KOtBu (1.24g, 11 mmol) in THF (10 mL) was added drop-wise and the reaction mixture was stirred at room temperature for 2 hours. A solution of di-tert-butylchlorophosphine (1.98 g, 11 mmol) in THF was added dropwise to the above reaction mixture, and the resultant reaction mixture was allowed to stir at room temperature for 12 hours. THF was evaporated under reduced pressure and the residue was extracted with n-pentane (10 mL X 3). The combined n-pentane extract was dried under reduced pressure to obtain 30.
Step-2: A glass pressure tube was charged with [IrCl(COE)2]2 (0.47 g, 0.53 mmol), 30 (0.5 g, 1.06 mmol), and 15 mL of toluene. The tube was sealed, placed in an oil bath, and heated at 135 °C for 24 hours. Toluene was removed under reduced pressure and the residue was extracted with several portions of n-hexane (50 mL X 3). The combined n-hexane extract was dried under reduced pressure to obtain 31.

Experiment-3: Synthesis of POCNP-Iridium Pincer complex 41

Step 1 – synthesis of POCNP Pincer ligand 40

To a solution of 2-hydroxycarbazole (1g, 5.46 mmol) in THF (10 mL), a suspension of KOtBu (1.24g, 11 mmol) in THF (10 mL) was added dropwise and the reaction mixture was stirred at room temperature for 2 hours. A solution of chlorodiisopropylphosphine (1.68 g, 11 mmol) in THF was added dropwise and the resultant reaction mixture was stirred at room temperature for 12 hours. THF was evaporated under reduced pressure and the residue was extracted with n-pentane (10 mL X 3). The combined n-pentane extract was evaporated under reduced pressure to obtain 40 in the form of two conformers in the ratio of approximately 1:1 (2.07 g).

Step-2: A glass pressure tube was charged with [IrCl(COE)2]2 (0.5 g, 0.56 mmol), 40 (0.475 g, 1.14 mmol), and 15 mL of toluene. The tube was sealed, placed in an oil bath, and the mixture heated at 135 °C for 24 hours. Toluene was removed under reduced pressure and the solid was extracted with several portions of n-pentane (50 mL X 3). Combined n-pentane extract was evaporated under reduced pressure to obtain 41.

Experiment-4: Dehydrogenation of alkane using 21
To a Parr reactor, were added tbutyl-ethylene (TBE) (16 mL), 21, and mesitylene (8 mL) under inert atmosphere. The Parr reactor was cooled to -70 °C and charged with n-butane through a molecular sieve 4? trap. The reaction mixture was heated at 190 °C for 2 hours under stirring. The Parr reactor was cooled to 0 °C and the content was collected, weighed and analyzed by gas chromatography (GC).
The conversion was calculated as the total amount of the olefins, which was the sum of 1-butene, cis-2-butene, trans-2-butene, and butadiene. The catalyst turnover number (TON) was calculated as a molar ratio of total amount of olefin produced during an experiment to the amount of the catalyst used during that experiment. The results are shown in Table-1.
Table 1: Dehydrogenation of n-butane
Sr. No Catalyst Wt % n-butane: catalyst Butane Conversion (%) Products butadiene selectivity* TON
trans-2-butene 1-butene cis-2-butene Butadiene
1 0.45 2435 25.4 12.1 4.0 7.0 2.3 9.1 617
2 0.208 5313 11.4 6.1 1.7 3.4 0.2 1.4 604
*Butadiene selectivity = amount of butadiene/ total amount of olefins
*Catalyst Wt% is with respect to the amount of n-butane

The dehydrogenation of n-butane with a n-butane:catalyst ratio of 2435 gave the dehydrogenated products with the TON of 617 (Table 1, Sr. No. 1). There was no significant change in turnover numbers on increasing the catalyst ratio to 5313 (Table 1, Sr. No. 2). However, the butane conversion and the butadiene selectivity decreased with an increase in the catalyst ratio.

Experiment-5: Dehydrogenation of alkane using 41
The dehydrogenation of alkane was carried out using experimental procedure similar to that of experiment-4 using 41 as a catalyst. The results are shown in Table-2.
Table 2: Dehydrogenation of n-butane
Sr. No Catalyst Wt % n-butane: catalyst Butane Conversion (%) Products butadiene selectivity* TON
trans-2-butene 1-butene cis-2-butene Butadiene
1 0.33 3321 17.0 9.0 2.6 4.9 0.5 2.8 564
2 0.15 7306 11.0 5.9 1.8 3.2 0.1 1.3 803
*Butadiene selectivity = amount of butadiene/ total amount of olefins
*Catalyst Wt% is with respect to the amount of n-butane

The dehydrogenation of n-butane with a n-butane:catalyst ratio of 3321 gave the dehydrogenated products with the TON of 564 (Table 3, Sr. No. 1). On increasing the n-butane:catalyst ratio from 3321 to 7306 (Table 3, Sr. No. 2), the TON increased whereas, the butane conversion and butadiene selectivity decreased.

Experiment-6: Dehydrogenation of a C4 feed
To a Parr reactor, were added tbutyl-ethylene (TBE) (16 mL), 41 as a catalyst and mesitylene (8 mL) under inert atmosphere. The Parr reactor was cooled to -10 °C and charged with a C4 feed (containing 70% n-butane and 29% isobutane) through a molecular sieve 4? trap. The reaction mixture was heated at 190 °C for 2 hours under stirring.
The Parr reactor was cooled to 0 °C and the content was collected, weighed and analyzed by GC. The results are shown in Table-3.

Table 3: Dehydrogenation of C4 feed

Sr No Catalyst Wt % feed: cat Butane Conversion (%) Iso-Butane Conversion (%) Products % BD
TON
trans-2-butene 1-butene cis-2-butene Butadiene
1 0.29 3124 16.4 26.3 6.1 1.9 3.4 0.3 2.5 389
*%BD = amount of butadiene/ total amount of olefins
*Catalyst Wt% is with respect to the amount of feed
The dehydrogenation of C4-feed with a n-butane:catalyst ratio of 3124 gave the dehydrogenated products with the TON of 389. Isobutane was preferentially dehydrogenated.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of POCNP-Iridium Pincer complexes that:
- are prepared by a simple process; and
- can be used for alkane dehydrogenation with high turnover number.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.