Iridium complexes, supported

Although highly active pincer-PCP-li catalysts have been designed for the dehydrogenation of alkanes, selective systems remain elusive [139]. Pincer-type NHC-based iridium complexes have been also tested in such a challenging reaction. Iridium complexes supported by pincer-NHC ligands described by... 

An X-ray crystal structure of 55, redrawn as Fig. 10, supported the formulation of the complex as that of a peroxo system. Further, the structure demonstrated that no interactions between the [Of-] ligand and the borate moiety were possible because of the relative arrangement of the [Of-] and borate ligands about the iridium center. Such interactions were implicated in the oxygen-initiated decomposition of the iridium complex of 52, while the lack of reactivity of the iridium complexes of 53 and 54 was attributed to steric factors arising from the alkyl chains connecting the sulfur atoms. 

A kinetic study by Harrod and Smith of oxidative addition to a square planar cationic iridium complex also supports the three-center mechanism (258). The rate law is first order in the iridium complex and first order in hydrosilane. Determination of the activation parameters indicated a moderate activation enthalpy (AH — 5-6 kcal/mol) and a large negative activation entropy (AS — -47 e.u.) No variations were observed on changing the solvent. Harrod and Smith concluded that oxidative addition proceeds via a concerted three-center transition state in which little bond-making or bond-breaking had occurred. The activation enthalpy was attributed to a deformation of the square planar complex on its approach to the transition state. 

Polystyrenes have also been used to support chromophores useful in organic light-emitting diodes (OLEDs). Week and coworkers have attached tris(2-phenylpyridine) iridium complexes to aminomethylated polystyrene using a Schiff base reaction, 4 [21]. There was no major diminution of the desirable luminescence properties of the iridium complexes (high emission quantum yields of 0.23 and lifetimes of about a microsecond). Similar results have been reported for aluminum and boron 8-hydroxy quinoline complexes tethered to polystyrene using Schiff base condensation [22]. 

Itsimo [25] has also shown that polymer-supported OPEN monosulfonamides containing sulfonated pendent group (Scheme 16) are able to catalyze the HTR reduction of ketones in water with sodium formiate as hydrogen donor (S/C = 100). However, TsDPEN immobilized on polystyrene crosslinked or not, polymer 30 and 31 respectively, shrank in water. Sodium /j-styrene sulfonate was copolymerized with chiral A-(vinylbenzene-p-sulfonyl)-DPEN (20) imder radical polymerization conditions with or without DVB leading respectively to ligand 32 and 33. Control of the balance hydrophilicity/hydrophobieity of the polymer support is carried out by changing the salt from Na to quaternary ammonium. All of these polymers swelled in water, and their respective ruthenium, rhodium or iridium complexes were prepared. Compared to sodium salt polymer-supported catalyst from 32a and 33a, ammonium... 

The hydrogen atom of the central cyclopentadiene ring can be displaced by potassium with t-BuOK to form the K(CgoMe5) complex in which the potassium atom can then be displaced to form iridium complexes such as Ir(ri5-C6oMe5)(CO)2 [Matsuo, Iwashita and Nakamura Organometallics 24 89 2005], and with rhodium to form Rh(ri5-C6oMe5)(CO)2 [Sawamuia, Kuninobu and Nakamura Chem Soc 122 12407 2000], structures which are supported by X-ray structure analyses. The same cyclopentadiene can complex with Fe and cyclopentadiene (Cp) to form a hybrid of buckyferrocene Fe(C6oMe5)Cp [Sawamura et al. J Am Chem Soc 124 9354 2002, Nakamura Pure Appl Chem 75 427 2003],... 

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