Natural bond orbital analysis of the electronic structure of [L nM(CH 3)] and [L nM(CF 3)] complexes

Andrés G. Algarra, Vladimir V. Grushin*, Stuart A. MacGregor

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


An analysis of the geometries and electronic structures of a series of [L nM(CX 3)] species (where X = H, F) is presented, on the basis of density functional theory (DFT) and the natural bonding orbital (NBO) approach. Computed geometries show that L nM-CF 3 bonds can be up to 0.1 Å shorter than the equivalent L nM-CH 3 bonds, although the extent of this shortening varies considerably depending on the L nM fragment. Evidence for CF 3 having a higher trans influence than CH 3 is seen, but this is most apparent in systems where the L nM-CF 3 bond is itself shorter. NBO calculations show that the computed charge at the metal center is usually slightly more negative (or less positive) in the [L nM(CF 3)] species compared to that of its CH 3 congener. Further detailed NBO analyses on the [(H 3P) 3Rh(CX 3)] (1), trans-[(H 3P) 2Pt(Cl)(CX 3)] (2), [(OC) 5Mn(CX 3)] (3), and [Pt(H) 3(CX 3)] 2- (8) pairs indicate a significantly higher M←CX 3 σ interaction when X = F. The L nM-CF 3 σ bond is computed to have much higher C 2s character and is also enhanced by contributions from the C-F σ* orbitals. In contrast, any M→C-F(σ*) π back-donation is relatively weak, being at most 8% of the magnitude of M←CF 3 σ interaction, while M→C-H(σ*) π back-donation is negligible in the [L nM(CH 3)] congeners. The metal-based d orbitals are computed to be between 0.4 and 0.7 eV lower in energy in the [L nM(CF 3)] species. Thus, CH 3/CF 3 replacement has two significant, apparently counterdirecting, effects, in that it both maintains and indeed can increase the electron density at the metal center, while at the same time causing a stabilization of the metal-based d orbitals. These effects account for the enhanced reactivity of [L nM(CF 3)] species toward nucleophiles and form a basis for understanding the reactivity of [L nM(CF 3)] species in the literature. Implications for the Pd-catalyzed trifluoromethylation of aryl halides ArX are discussed: in particular, the balance between Ar-CF 3 reductive elimination from [L nPd(Ar)(CF 3)] and the propensity of this species to undergo transmetalation (and hence catalyst deactivation) in the presence of [L nPd(Ar)(X)] species.

Original languageEnglish
Pages (from-to)1467-1476
Number of pages10
Issue number4
Publication statusPublished - 27 Feb 2012


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