Comprehensive Study of the Thermochemistry of First-Row Transition Metal Compounds by Spin Component Scaled MP2 and MP3 Methods

• Published in: Organometallics 2004-11, Vol.23 (23), p.5581-5592
• Main Authors: Hyla-Kryspin, Isabella, Grimme, Stefan
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om049521b

The enthalpies of (i) the dissociation reactions of the carbonyl ligand in Cr(CO) n [n = 6 (1a), 5 (1b), 4 (1c)], Fe(CO)5 (2a), and Ni(CO) n [n = 4 (3a), 3 (3b), 2 (3c)], (ii) the dissociation reactions of the heteroligand L in Cr(CO)5L [L = CS (4a), Xe (4b), H2 (4c), C2H4 (4d), C2F4 (4e)], Cr(CO)3L [L = C6H6 (5a), C6Me6 (5b)], and Fe(CO)4L [L = H2 (6a), C2H4 (6b)], (iii) the deprotonation reactions of Cr(CO)3C6H6 (5a) and Fe(CO)3C4H6 (8), (iv) the protonation reaction of ferrocene (10), and (v) the hydrogenation reactions of Mn2(CO)10 (13) and Co2(CO)8 (15) were calculated at the DFT/BP86, MP2, MP3, SCS-MP2, and SCS-MP3 levels and compared with the corresponding experimental data. The set of systems studied covers different types of chemical bonding and a broad range of reaction enthalpies (from a few kcal/mol to a few hundred kcal/mol), and it is thus proposed as a general benchmark for quantum chemical methods. It is shown that the erratic behavior of the low-order MP approaches can be corrected by the newly developed spin component scaled perturbation theory (SCS-MP2, SCS-MP3). Both methods are based on a partitioning of the total correlation energy into contributions from antiparallel- (αβ) and parallel-spin (αα, ββ) pairs of electrons, followed by a unique scaling procedure of the two correlation energy terms. The calculated thermochemical data at the SCS-MP2 and SCS-MP3 levels are significantly improved as compared to those from their standard counterparts. For the dissociation processes of 1−6 the mean absolute errors are 21.0 kcal/mol (MP2), 22.3 kcal/mol (MP3), 11.6 kcal/mol (SCS-MP2), 4.1 kcal/mol (SCS-MP3), and 3.4 kcal/mol (DFT/BP86). It is shown that contrary to standard MP3, the new SCS-MP3 method is able to predict the reaction energetics for wide variety of TM compounds with an accuracy comparable to that from DFT. The SCS-MP3 enthalpy of the hydrogenation reaction of 13 (5.8 kcal/mol) agrees better with the experiment (8.7 ± 0.3 kcal/mol) than the BP86 value (1.7 kcal/mol). The SCS-MP3 proton affinity of metal-protonated ferrocene 11 (214.8 kcal/mol) and of the agostic form 12 (203.9 kcal/mol) compare well with the experimental values (206−213 kcal/mol) and contrary to MP2 do not exclude the dynamic behavior of protonated ferrocene. It is suggested that for complex chemical systems including transition metals simultanous application of DFT and SCS-MP3 methods may be helpful to increase the reliability of the predictions.