01734nas a2200217   4500008004100000022001400041245011900055210006900174260007700243300001400320520087400334653002601208653003601234653002801270653001401298653001301312100001901325700002701344700001701371856012801388       2014                        eng d  a1434-194800aNature of the active site in ziegler-natta olefin polymerization catalysis systems - a computational investigation0 aNature of the active site in zieglernatta olefin polymerization   aBOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANYbWILEY-V C H VERLAG GMBHcOCT  a5063-50763 a<p>Pull quantum chemical calculations with density functional theory (DET) show that a principal role of donors in Ziegler-Nana (ZN) oh-din polymerization catalysts is to coordinate to the metal center at the active sites on the MgCl2 surface. Thereby, the behavior of the catalyst is modulated to favor insertion over termination and, thus, polymerization occurs. This is shown to be true for a range of different donors. The calculations indicate that active sites that feature anionic chloride ligands at the titanium center (the conventional model for the active site) would lead to lower-molecular-weight riolymers. If an -OC2H5 group were present instead of a chloride ligand, the active site would much more effectively produce long chain polymers. Therefore, the current work provides important new insights into the nature of the ZN polymerization process.</p>10aAlkene polymerization10aDensity functional calculations10aheterogeneous catalysis10aInsertion10aPolymers1 aKumawat, Jugal1 aGupta, Virendra, Kumar1 aVanka, Kumar  uhttps://library.ncl.res.in/content/nature-active-site-ziegler-natta-olefin-polymerization-catalysis-systems-computational-002512nas a2200265   4500008004100000022001400041245010800055210006900163260000800232300001100240490000800251520162600259653001801885653001401903653002001917653001801937653002301955653002601978100002302004700002102027700001702048700002602065700002502091856013002116       2022                        eng d  a0022-328X00aReactivity of four coordinate iridium complex towards hydrogen: an experimental and computational study0 aReactivity of four coordinate iridium complex towards hydrogen a  cMAY  a1223170 v9653 a<p>
	Reaction of a four coordinate, 16-electron Ir complex, [Ir-(iPr)4(POCOP)(PPh3)] (4 ) (((iPr)4)(POCOP= 2,6-bis(di-isopropyl phosphinito)benzene, kappa(3)-C6H3-1,3-[OP((iPr))(2)](2)), with H-2 resulted in an oxidative addition product, cis-dihydride complex, cis-[Ir(H)(2) ((iPr)4)(POCOP)(PPh3)] ( cis-5 ) presumably via the intermediacy of a sigma complex, [Ir(eta(2)-H-2)((iPr)4)(POCOP)(PPh3)]. The cis-dihydride complex completely isomerizes to the trans-dihydride complex trans-[Ir(H)(2) ((iPr)4)(POCOP)(PPh3)] ( trans-5 ) under ambient conditions in about 3 h. It was found that the steric and electronic features on the iridium center have significant influence on the approach of H-2 onto the metal center followed by oxidative addition and isomerization. The isomerization process was studied in detail and all the mechanistic aspects have been elucidated using a combination of both experimental work and computation. The cis-dihydride complex isomerizes to the trans-dihydride by compensating the trans influence of the strongly trans-directing hydride ligand. A mechanism involving the exchange of the position of PPh3 with a hydride ligand cis to itself via PPh3 dissociation and re-coordination thereby resulting in the formation of the trans-dihydride complex, has been proposed for the isomerization. The cis-dihydride was found to be a highly active catalyst for hydrogenation of ethy-lene. A competing reactivity study of cis-dihydride between isomerization versus insertion of C2H4 into the Ir-H bond, was studied experimentally and computationally. (c) 2022 Elsevier B.V. All rights reserved.</p>
10aHydrogenation10aInsertion10airidium complex10aisomerization10aOxidative addition10aReductive elimination1 aAgrawal, Nisha, K.1 aDash, Soumya, R.1 aVanka, Kumar1 aNethaji, Munirathinam1 aJagirdar, Balaji, R.  uhttps://library.ncl.res.in/content/reactivity-four-coordinate-iridium-complex-towards-hydrogen-experimental-and-computational