Probing the Limits of Alkaline Earth鈥揟ransition Metal Bonding: An Experimental and Computational Study
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- 作者：Matthew P. Blake ; Nikolas Kaltsoyannis ; Philip Mountford
- 刊名：Journal of the American Chemical Society
- 出版年：2015
- 出版时间：September 30, 2015
- 年：2015
- 卷：137
- 期：38
- 页码：12352-12368
- 全文大小：1146K
- ISSN：1520-5126
文摘
Reduction of Fp2 (Fp = CpFe(CO)2) or [Co(CO)3(PCy3)]2 (15) with Mg-mercury amalgam gave [Mg{TM(L)}2(THF)]2 (TM(L) = Fp or Co(CO)3(PCy3) (19)) in which the TM is bonded to two Mg atoms. Reduction of 15 with Ca-, Sr-, Ba-, Yb-, Eu- and Sm-mercury amalgam gave a series of compounds 鈥淢{Co(CO)3(PCy3)}2(THF)n鈥?(M = Ae or Ln) in which the M鈥揅o bonding varies with the charge-to-size ratio of M. For M = Ca or Yb (24), each metal forms one M鈥揅o bond and one M(渭-OC)Co 畏1-isocarbonyl linkage. With M = Sr (21) or Eu (25), a switch from M鈥揅o bonding to side-on (畏2) CO ligand coordination is found. SmII{Co(CO)3(PCy3)}2(THF)3 disproportionates in pentane to form SmIII{Co(CO)3(PCy3)}3(THF)3 containing two SmIII鈥揅o bonds, in contrast with 25, showing the importance of the Ln charge on Ln鈥揟M bonding. Diffusion NMR spectroscopy found that in solution, 21 and 24 are dimeric compounds [M{Co(CO)3(PCy3)}2(THF)3]2 that, according to DFT calculations, contain either one (Ae = Ca) or two (Ae = Sr) Ae鈥揅o bonds per Co atom. DFT calculations in combination with Ziegler Rauk energy decomposition and atoms in molecules analysis were used to assess the nature and energy of Ae鈥揅o bonding in a series of model compounds. The Ae鈥揅o interaction energies decrease from Be to Sr, and toward the bottom of the group, side-on (畏2) CO ligand coordination competes with Ae鈥揅o bonding. The PCy3 ligand plays a pivotal role by increasing solubility in nondonor solvents and the Ae鈥揅o interaction energy.