Chemistry & Biochemistry

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Browsing Chemistry & Biochemistry by Author "Ang, Chwee Y."

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    Coordination complexes of thiazyl rings: Synthesis, structure and DFT computational analysis of CpCr(CO)x (x = 2,3) complexes of fluorinated and non-fluorinated 1lamda^3-1,2,4,6-thiatriazinyls, with differing Cr—S bond orders.
    (NRC Research Press, 2015) Ang, Chwee Y.; Kuan, Seah L.; Tan, Geok K.; Goh, Lai Y.; Roemmele, Tracey L.; Yu, Xin; Boeré, René T.
    Reaction of [3,5-Ph2-C2N3S]2 with [CpCr(CO)3]2 in toluene at RT 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,  = 104.453(7)°). The Cr—S bond-length = 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 (P, a = 8.0929(8) Å; b = 10.3160(10) Å, c = 11.2405(11),  = 70.032(2)°, = 72.076(2)°, = 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,  = 97.218(2)°), also fully characterized by spectroscopy and crystallography. Their measured Cr—S bond-lengths, 2.2987(14) Å 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 DFT calculations show that the tricarbonyl complex has an unusual  bond. However, the dicarbonyl complexes of the fluorinated thiatriazinyls are -bonded.
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    Coupling of CpCr(CO)3 and heterocyclic dithiadiazolyl radicals: synthetic, X-ray diffraction, dynamic NMR, EPR, CV and DFT studies
    (ACS Publications, 2008) Lau, Hiu F.; Ang, Chwee Y.; Ng, Victor W. L.; Kuan, Seah L.; Goh, Lai Y.; Borisov, Alexey S.; Hazendonk, Paul; Roemmele, Tracey L.; Boeré, René T.; Webster, Richard D.
    The reaction of 1,2,3,5-dithiadiazolyls, (4-R-C6H4CN2S2)2 (R = Me, 2a; Cl, 2b; OMe, 2c; and CF3, 2d) and (3-NC-5-tBu-C6H3CN2S2)2 (2e) with (CpCr(CO)3]2 (Cp = η5-C5H5) (1) at ambient temperature, yielded respectively the complexes CpCr(CO)2(η2-S2N2CC6H4R) (R = 4-Me, 3a; 4Cl, 3b; 4-OMe, 3c; and 4-CF3, 3d) and CpCr(CO)2(η2-S2N2CC6H3-3-(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-C6H4CN2S2Cl (R = OMe, 8c; CF3, 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)2S2N2CH] and comparisons are made with the reported CpCr(CO)2(π-allyl) complexes.