Making a Robust Carbon−Cobalt(III) Bond

Abstract

The coordination ion with a well-characterized carbon-cobalt(III) bond, the (1,4,7-triazacyclononane)(1,6-diamino-3-thia-4-hexanido)cobalt(III) dication, [Co(tacn)(C-aeaps)](2+) (aeaps, for aminoethylaminopropylsulfide), has been reacted with iodomethane, and the S-methyl thionium derivative has been isolated. The crystal structure of the resulting [Co(tacn)(C-aeaps-SCH(3))]Br(3) x 3 H(2)O at 122 K has been determined by X-ray diffraction techniques to verify the structure. The crystal structure determination shows that the carbon-cobalt bond length is even shorter (2.001(4) A) than in [Co(aeaps)(C-aeaps)](2+) (2.026(3) A), while its trans elongating effect is less pronounced. The (1,4,7-triazacyclononane)(1,6-diamino-3-thia-4-hexanido)cobalt(III) dication [Co(tacn)(C-aeaps)](2+) (aeaps, for aminoethylaminopropylsulfide) reacts relatively fast with acid, for example, with NH(4)(+) to form a sulfur-bound aeaps ligand. The [Co(tacn)(C-aeaps-SCH(3))](3+) ion is remarkably robust in strongly acidic aqueous solution in spite of the supposed high basicity of the carbon anion. However, with a large excess of iodide, the methyl group can be removed as iodomethane. The experimentally obtained distances around cobalt(III) for the three involved coordination ions are compared to those computed from DFT with different standard choices for functionals and basis sets. The agreements range from poor to modest depending of the choice of functionals. It is noteworthy, however, that a sulfur 3p orbital in [Co(tacn)(C-aeaps)](2+) participates in bonding to cobalt(III), having implications for the transformation between the carbon- and sulfur-bound forms of the aeaps ligand.

The accuracy of DFT-optimized geometries of functional transition metal compounds: a validation study of catalysts for olefin metathesis and other reactions in the homogeneous phase

“…Here we have to limit ourselves to offering a first impression of the kind of generality that can be expected, by including also a set of 10 TM complexes different from those analyzed above; see Scheme 2 and Table 2. The complexes involve transition metals of all three rows and count well-known alkene metathesis (19)(20), polymerization (21)(22)(23), oligomerization (24), hydroformylation (25,26), and hydrogenation (27), catalyst precursors. The derivative of Vaska's complex, with two oxidatively added hydride ligands (28), completes the set and underlines the focus on catalytic organometallic chemistry in the selection of representative complexes.…”

“…For most TM complexes of practical use, structures from X-ray diffraction analyses remain the only standard against which to validate, and a number of such studies have been reported. [23][24][25][26][27][28][29] The overall impression from these studies is, as was noted above for validation studies against gas-phase geometries, that the functionals of choice depend heavily on the particular chemical system under study.…”

Reaction of a Co(III)-Peroxo Complex and NO: Formation of a Putative Peroxynitrite Intermediate

“…The presence of two chloride ions outside of the coordination sphere satisfied the charge of the central metal ion. The average Co–N distance (1.982 Å) was found to be within the range of analogous reported complexes …”

Macrocyclic coordination chemistry

“…Tacn has been used as a ligand system to produce a stable cobalt(III)-carbon bonded compound. 10 The six coordinate compound starts with an N 5 S coordination sphere followed by deprotonation of an aminoalkylsulfide ligand and a switch from S to C bonding which can then be locked in place by methylation of the sulfur. The data from the X-ray structural determination and DFT calculations were used to rationalise the bonding.…”