Coupling of CpCr(CO)₃and Heterocyclic Dithiadiazolyl Radicals. Synthetic, X-ray Diffraction, Dynamic NMR, EPR, CV, and DFT Studies

Abstract

The reaction of the 1,2,3,5-dithiadiazolyls (4-R-C(6)H(4)CN(2)S(2))(2) (R = Me, 2a; Cl, 2b; OMe, 2c; and CF3, 2d) and (3-NC-5-tBu-C(6)H(3)CN(2)S(2))(2) (2e) with [CpCr(CO)(3)](2) (Cp = eta(5)-C(5)H(5)) (1) at ambient temperature respectively yielded the complexes CpCr(CO)(2)(eta(2)-S(2)N(2)CC(6)H(4)R) (R = 4-Me, 3a; 4-Cl, 3b; 4-OMe, 3c; and 4-CF(3), 3d) and CpCr(CO)(2)(eta(2)-S(2)N(2)CC(6)H(3)-3-(CN)-5-(tBu)) (3e) in 35-72% yields. The complexes 3c and 3d were also synthesized via a salt metathesis method from the reaction of NaCpCr(CO)(3) (1B) and the 1,2,3,5-dithiadiazolium chlorides 4-R-C(60H(4)CN(2)S(2)Cl (R = OMe, 8c; CF(3), 8d) with much lower yields of 6 and 20%, respectively. The complexes were characterized spectroscopically and also by single-crystal X-ray diffraction analysis. Cyclic voltammetry experiments were conducted on 3a-e, EPR spectra were obtained of one-electron-reduced forms of 3a-e, and variable temperature 1H NMR studies were carried out on complex 3d. Hybrid DFT calculations were performed on the model system [CpCr(CO)(2)S(2)N(2)CH] and comparisons are made with the reported CpCr(CO)(2)(pi-allyl) complexes.

Coordination complexes of thiazyl rings — Synthesis, structure, and density functional theory (DFT) computational analysis of CpCr(CO)x(x= 2, 3) complexes of fluorinated and nonfluorinated 1λ3-1,2,4,6-thiatriazinyls with differing Cr–S bond orders

“…This bonding mode is thus very similar to what is observed in the case of the aryl 2 -DTDA complexes of type III. [33][34][35] In the latter case, we were able to show that such complexes in solution are in dynamic exchange between the exo (major) and endo (minor) isomers in solution, while, by using different remote substituents on the aryl ring, either one or the other crystallizes preferentially. However, for 6a and 6b only, the exo form has yet to be isolated and the solution behaviour seems to be dominated by a single species according to the NMR evidence.…”

“…[33][34][35] A signature feature of III and IV is that, in contrast to all previous complexes with low-valent metals, the S-S separation is almost unchanged from that of the dimeric radicals that have been crystallographically analyzed. Thus, oxidative addition, the dominant reaction of low-valent transition metals towards element-element bonds, is avoided for the first time for any thiazyl ring compound.…”

“…A very distinct histogram peak is found between 2.33 and 2.37 Å for the 2 -DTDAs, that is structures of type III and IV, which are thus found to have Cr-S bond orders of 1.3, consistent with the previously assigned -bonding character of this class. [33][34][35] Fig. 3.…”

“…31 Oxidative addition also predominates for metal complexes of 1,2,3,5-dithiadiazoyl (DTDA) radicals, RCN 2 S 2 , 30,32 although this class of thiazyl radicals affords a greater variety of adduct geometries, including metallacycles akin to II= that retain paramagnetism as well as larger clusters that are found both as diamagnetic and paramagnetic species (representative structures are shown as (A)-(E) in Chart 2 of ref. 33). …”

“…Preuss 29 has shown that intact thiazyl radicals can form coplanar complexes via a ring N atom with coordinatively saturated, nonoxidizing M(hfac) 2 complexes of Cu(II), Ni(II), and Mn(II) when an adjacent donor atom is available (i.e., a chelating "bipyridyl"-type geometry, see structures (F) and (G) in Chart 2 of ref. 33). Previously, Hursthouse and co-workers [37][38][39] reported on the preparation, by salt-metathesis routes, of complexes of Ti, Zr, Mo, Ni, and Ru in middle-oxidation states containing the Ph-S=N-t-Bu unit, but these structures have very short metal-nitrogen and rather long metal-sulfur bonds, and are therefore contraindicative of bonding to sulfur, whereas structures of type VI are not distorted in this fashion.…”