Synthesis and Characterisation of [(en)2Co]3+ Complexes Coordinated by Substituted Thiourea Ligands

Abstract

Substituted thiourea ligands bind in a bidentate manner forming a four-membered ring through the sulfur atom and a deprotonated thiourea nitrogen atom when reacted with [(en)2Co(OSO2CF3)2]+ in tetramethylene sulfone. Reaction of unsymmetrical ligands results in the formation of coordination isomers, some of which can be separated by column chromatography using Sephadex SPC-25. Coordination isomers are easily distinguishable based on visible and 1H NMR spectroscopy . Twelve para-substituted and one meta-substituted ligands were studied: N,N′-dibenzylthiourea (1a); N-(R)phenyl-N′-benzylthiourea {R = H (2a), NO2 (2b), CH3 (2c)}; N-(R)phenyl-N′-(R′)phenylthiourea {R, R′: H, H (3a), H, CH3 (3b), OCH3, NO2 (3c), CH3, NO2 (3d)}; N-methyl-N′-(R)phenylthiourea {R = H (4a), CH3 (4b), OCH3 (4c), NO2 (4d), 3-CH3 (4e)}. The solid state structure (X-ray) of one isomer of Co-4a as its perchlorate salt confirms the coordination mode suggested by 1H NMR spectroscopy and shows that the Co–N bond trans to the coordinated thiourea sulfur induces a structural trans effect of 0.019 Å.

Reaction of 2-Pyridylmethylthiourea Derivatives with [(en)2Co(OSO2CF3)2]+ Induces Hypodentate Coordination of an Ethylenediamine Ligand

“…STEs as large as 0.03 Å have been observed in structures containing deprotonated urea ligands. [2,17] While the STEs observed here are larger than those observed in our previous report, [1] they are more consistent with data that we have collected on related structures (J. Krause and L. Roecker, unpubl. data).…”

“…4a-c) in which the added ligand coordinates in a bidentate manner consistent with the established reactivity of related ligands. [1,2] The target complex (Fig. 4c), however, was not isolated because the pyridylthiourea ligand bonded in a tridentate manner (Fig.…”

“…4d) through the open coordination site arising from cleavage of a Co-N(en) bond. That the ligand is capable of bonding in a tridentate manner is not unexpected as evidenced by coordination of similar ligands such as thiosemicarbazones [3] and the ability of the thiourea moiety to form four-membered rings, [1] but rupture of the Co-N(en) bond, which allowed it to do so, was unexpected. Hypodentate coordination [4] of ethylenediamine has been documented previously in Co III complexes of [(en) 2 (Cl)CoN-H 2 CH 2 CH 2 NH 3 ] 3þ , [5,6] [(NH 3 ) 5 CoNH 2 CH 2 CH 2 NH 3 ] 4þ , [7] and [(en) 2 Co(NH 2 CH 2 CH 2 NH 3 ) 2 ] 5þ , [8] but they are prepared by a different synthetic route.…”

“…Details of how coordination though the thiourea moiety affects bond lengths and angles within the ligand has been recently described and the results obtained here are consistent with those observations. [1] The four-membered ring has a bite angle of 72.04 (7)8 with the Co III centre with the remaining angles of the ring being 76.9(1)8, 109.3(2)8, and 101.6(2)8 for the Co-S-C, N-C-S, and Co-N-C angles, respectively. This arrangement is facilitated by deformation of the trigonal planar environment about the thiourea carbon atom with bond angles of 109.3(2)8, 125.7(3)8, and 124.9(2)8 along with lengthening of the C-S bond to 1.741(3) Å from the 1.68(1) Å found in non-coordinated thiourea ligands.…”

“…Substituted thiourea ligands that do not contain a pyridyl group coordinate to the [(en) 2 Co] 3þ subunit in a bidentate manner through the thiourea sulfur atom and a deprotonated nitrogen atom (Fig. 2), [1] while the urea analogues of the ligands illustrated in Fig. 1 coordinate in a bidentate manner through the pyridyl nitrogen and deprotonated exo urea nitrogen atom (Fig.…”