Reactions of iridium bis(phosphinite) pincer complexes with protic acids

Abstract

Iridium pincer complexes [C 6 H 3 2,6 (OPBu t 2 ) 2 ]Ir(H)Cl (10) and [4 EtOOCC 6 H 2 2,6 (OPBu t 2 ) 2 ]Ir(H)Cl (11) react with protic acids undergoing metallation of one of the tert butyl groups to form double cyclometallated products [4 R C 6 H 2 2 (OPBu t 2 ) 6 (OP(Bu t )CMe 2 CH 2 )]IrCl (12, R = H; 13, R = COOEt), which are stable in air. Complex 12 reacts with CO and Bu t NC giving the corresponding 18 electron complexes [C 6 H 3 2 (OP Bu t 2 ) 6 (OP(Bu t )CMe 2 CH 2 )]Ir(L)Cl (14, L = CO; 15, L = CNBu t ). The structure of com pound 14 was established by X ray diffraction analysis.Homogeneous catalytic dehydrogenation of saturated hydrocarbons is one of the most important problems of organometallic chemistry, the solution of which should promote more rational use of hydrocarbon raw materials. 1 At the same time, the solution of this problem will allow one to accomplish functionalization of a wide class of com pounds containing unactivated C-H bonds. 2 Iridium compounds play an important role here. 3 In the field of study of homogeneous catalysts for dehydrogenation, 4 the most prominent results were achieved using complexes of the type A and B (see .Several years ago, we also began our study on dehydro genation of alkanes. We succeded in the development of complexes of the type C containing pincer ligands based on metallocenes (ferrocene and ruthenocene), 9 which ex hibited unprecedent activity in the dehydrogenation of alkanes and at present are the most active catalysts for this reaction.A necessity to compare electronic and steric properties of the pincer ligands obtained by us with analogous prop erties of ligands studied by other researches was the reason for the synthesis and more detailed study of chemical prop erties of complexes of the type B (for example, we de scribed reactions of complex 3 with CO and CNBu t ).In addition, in order to immobilize dehydrogenation catalysts on polymeric (or dendrimeric) supports we in troduced various functional groups (COOR, CONR 2 , CH 2 NR 2 ) into the pincer ligand of complexes of the type B.In the attempt to modify the substituents indicated, it was found that acidic or basic reagents very often react with the iridium atom instead of a functional group to form a mixture of unidentified products. These observations prompted us to more detailed study of the reaction of known 8 iridium bis(phosphinite) complex 10 and its ana logs with various reactive compounds, in particular, with protic acids.

C–H Bond Activation by Cationic Iridium(III) NHC Complexes: A Combined Experimental and Computational Study

“…Upon cooling, these resonances decoalesced into two pairs of sharp signals, which are attributed to the two sets of NHC C–H and N–Me groups (one proximal and one distal to the CO ligand; Figure , inset). The infrared spectrum of 5b exhibits one carbonyl band with a stretching frequency appropriate for a cationic Ir III monocarbonyl (2024 cm –1 ) . The complex [Cp*Ir­(PMe 3 )­Me­(CO)] + shows a higher value for ν CO (2035 cm –1 ), consistent with the assertion that 3b is more electron-rich than its PMe 3 -ligated counterpart.…”

Formation of a C–C double bond from two aliphatic carbons. Multiple C–H activations in an iridium pincer complex

“… 10 During the formation of 4 from 1 , three C sp 3 –H bonds are activated intramolecularly in addition to one external C sp 2 –H bond. Cyclometallation of tert -butyls 11 or other groups 12 , 13 bound to phosphorus is not unprecedented in the chemistry of iridium pincer complexes, but in the case of 4 it results in the formation of a new C–C double bond. To the best of our knowledge, this is the first example where the main product is the result of the formation of a C–C double bond from non-activated C sp 3 –H bonds.…”

Impact of Backbone Substituents on POCOP-Ni Pincer Complexes: A Structural, Spectroscopic, and Electrochemical Study

“…Our group has also shown that in the cationic complexes [(POCOP)Ni(NCMe)] + the P -substituents have greater influence on structures and reactivities relative to chloride substituents at the 3- and 5-positions (with respect to the metallated carbon) . In contrast to these sporadic and limited studies for POCOP-Ni systems, the impact of ring- and P -substituents on the properties of POCOP-Ir complexes has been investigated in much more detail . Similar studies have been reported on NCN-Ni and NCN-Pt complexes …”