An investigation of ethylene rotational barriers for 5-coordinate d8 metal bis-ethylene complexes

Abstract

The successful isolation and structural characterization of (CF3PCP)Ir(C2H4)2 is reported, which confirms a rare example of axial and equatorial ethylene coordination in a TBP coordination environment. DFT studies indicate a moderate barrier to ethylene rotation for the equatorial C2H4 group (ΔG‡=19.0kcalmol−1), and a negligible rotational barrier for the axial C2H4 (ΔG‡=1.2kcalmol−1). DFT analyses of ethylene rotational barriers for a series of known symmetrical (equatorial/equatorial) and asymmetric (equatorial/axial) bis ethylene Ir(I) complexes are consistent with previously reported experimental rotational barriers. In the case of the asymmetric systems ([9]aneS3)Ir(C2H4)2+ and (Tp)Ir(C2H4)2, a separate equatorial C2H4 rotational barrier is not observed due to facile conformational exchange of axial and equatorial ethylene coordination sites. Conformational exchange is not observed for (CF3PCP)Ir(C2H4)2.