Synopsis of Trifluoromethyl Metal Structural Data

Because the trifluoromethyl group has some of the attributes of a halogen and some of an alkyl, there are two obvious comparisons for the molecular structures of trifluoromethyl organometallic compounds. The first is to chlorides, compounds in which the CFj group has replaced a halide of equivalent electronegativity (76). Recently, the structure of CpCr(NO)2CF3 has been obtained, and within experimental uncertainty. 

Typically, the difference between the M—CH3 and M—CF3 bond lengths in similar complexes is ca. 0.05 A with the latter expected to be the shorter. In Ir(CO)I(CH3XCF3XPPh3)2, however, the reverse is true in that the Ir—CH3 bond appears to be somewhat (ca. 0.03 A) shorter than the Ir—CF3 bond (67). 

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