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

The reaction of [3,5-Ph2-C2N3S]2 with [CpCr(CO)3]2 in toluene at room temperature forms an adduct via a Cr–S bond, formulated as CpCr(CO)3SN3C2Ph2, which has fitting NMR, IR, and combustion analysis data. The structure was determined by a single-crystal X-ray structure diffraction study (P21/n, a = 8.4611(17) Å, b = 20.509(4) Å, c = 11.757(2) Å, β = 104.453(7)°). The Cr–S bond length of 2.4908(11) Å corresponds to a bond order of 1.0 from >90 values for CpCr(CO)x or Cp*Cr(CO)x moieties (x = 2, 3) bonded to S, which are used to establish a Pauling-type bond order scale specific to this class of compounds. Similar reactions of fluorinated thiatriazinyls derived from [3-Ph-5-CF3-C2N3S]2 or [4-MeOC6H4-5-CF3-C2N3S]2 are accompanied by the loss of CO to produce CpCr(CO)2SN3C2PhCF3 (P1, a = 8.0929(8) Å, b = 10.3160(10) Å, c = 11.2405(11) Å, α = 70.032(2)°, β = 72.076(2)°, γ = 82.375(2)°) and CpCr(CO)2SN3(CCF3)(C6H4OCH3) (P21/c, a = 8.1311(7) Å, b = 24.284(2) Å, c = 9.1025(8) Å, β = 97.218(2)°), also fully characterized by spectroscopy and crystallography. Their measured Cr–S bond lengths, 2.2987(14) and 2.2965(11) Å, correspond to bond orders of 1.5. (U/R)B3PW91/6-311+G(2df,2p)//B3PW91/6-31G(2d,p) hybrid density functional theory (DFT) calculations show that the tricarbonyl complex has an unusual σ bond. However, the dicarbonyl complexes of the fluorinated thiatriazinyls are π bonded.