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An Elongated Dihydrogen Complex of Iridium

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journal contribution
posted on 19.06.2003, 00:00 by Vincent Pons, D. Michael Heinekey
Reaction of [Cp*Ir(dmpm)Cl]Cl with [Et3Si]B(ArF)4 (dmpm = bisdimethyl-phosphinomethane; ArF = C6F5) under hydrogen gas affords the dicationic complex [Cp*Ir(dmpm)H2]2+ (1), which is readily deprotonated by weak bases to give [Cp*Ir(dmpm)H]+. Complex 1 exists as a mixture of two isomers (97:3). On the basis of the magnitude of 2JH-P couplings and T1 measurements, a cis-dihydride or dihydrogen complex structure is suggested for the predominant isomer 1-cis (2JH-P = 6 Hz), with the minor isomer assigned a transoid structure 1-trans (2JH-P = 20 Hz). When the preparative reaction is carried out with HD gas, the resonance in the 1H NMR spectrum assigned to 1-cis-d1 exhibitsJH-D = 9.0 Hz. The observed values of 1JH-D vary significantly with temperature, increasing from 7.0 Hz at 223K to 9.0 Hz at 300 K. The observed chemical shift of 1-cis-d1 also varies significantly with temperature. These observations are interpreted in terms of a dynamic equilibrium between a cis-dihydride and a dihydrogen complex.