Comparative Studies on Ether−Phosphine-Assisted Exchange Processes in the Rhodium(III) and Iridium(III) Complexes ClMH2(P⌒O)(P∼O)

• Published in: Organometallics 1997-07, Vol.16 (15), p.3531-3535
• Main Authors: Lindner, Ekkehard, Gierling, Karlheinz, Keppeler, Berthold, Mayer, Hermann A
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om970105j

The rhodium and iridium complexes ClRhH2(P⌒O)(P∼O) (2a,b) and ClIrH2(P⌒O)(P∼O) (3a) (P⌒O = η2(P,O) coordination, P∼O = η1(P) coordination of Cy2PCH2CH2OCH3 (a) and Cy2PCH2C4H7O (b); C4H7O = tetrahydrofuranyl) were subjected to dynamic NMR studies. They exhibit a fast fluxional behavior both of the two ether oxygen donors and of the two cis hydrides at room temperature. The exchange of the hydrides is assisted by the fact that one of the ether moieties simulates an external solvent. The complexes 2a,b show the same behavior as is suggested for the coordinatively unsaturated species ClRhH2(PPh3)2, which is generally postulated to be an active intermediate in the catalytic hydrogenation of olefins. In the course of the formation of 3a from its ortho-metalated (4a; = η2(P,CH2) coordination of Cy2PCH2CH2OCH2) and dihydrogen, one C−H bond of the methoxy group and an additional Ir−H bond were formed. This was confirmed by the corresponding reaction of 4a with D2 to give the analogous dideuterium complex 3a‘. The opposite behavior was observed when 4a was treated with DCl:  one C−D and one Ir−Cl bond were formed in the complex Cl2IrH(P⌒O)(P∼O) (5a; one Cy2PCH2CH2OCH2D ligand) while the hydride remained at the metal. The 103Rh chemical shift has been determined for compound 2b.