A <i>cis</i>-IrL(CO) Group Responds to Increasing Steric Bulk of L by M−L Stretching, Not M−C−O Tilting or Bending

The crystal structures of [Ir(2-R-bq)(PPh3)2(H)(CO)]+ (bq = benzoquinolinato; R = H, i-Pr, t-Bu) show that steric interference caused by contact between the bulky pendant R groups of the bq and the C of the cis-CO is relieved by Ir−N bond stretching in the Irbq system and bending of the trans-Ph3P−Ir−PPh3 groups, rather than by tilting or bending of the CO. Ir−CO is therefore more rigid than the Ir−N and Ir−P bonds. The Ir−N stretching is aided by the presence of a high trans effect H trans to N.