Abstract
AbstractFive sets of group 14 sextet cyclic unsaturated divalent species including carbenes (1X), silylenes (2X), germylenes (3X), stannylenes (4X), and plumbylenes (5X) are compared and contrasted at B3LYP/AUG‐cc‐pVTZ//B3LYP/6‐311 + G* and MP2/AUG‐cc‐pVTZ//MP2/6‐311 + G* levels of theory, where X = H, F, Cl, and Br. The scrutinized carbenes consisting of cyclonona‐3,5,7‐trienylidene (1H) and its 2,2,9,9‐tetrahalo derivatives (1Cl, 1Br) appear as boat shaped minima except for 1H which turns out as a boat shaped transition state for having a negative force constant. All of carbenes (1H, 1Cl, and 1Br) have triplet ground states except for 1F. In contrast, all of the corresponding 2X‐ 5X metallylenes appear as singlet boat shaped minima on their potential energy surfaces. Stability (estimated by ΔEs‐t, ie, energy gap between singlet [s] and triplet states) appear as a function of size and decreases by going down in group 14 column: 5X > 4X > 3X > 2X > 1X. Exclusive of carbene set, within other four sets stability decreases by going down in group 17 column: Br > Cl > F > H. Hence, singlet 2,2,9,9‐tetrabromocyclonona‐3,5,7‐trienplumbylene, 5Br, appears as the most stable sextet divalent with no tendency for dimerization. Comparison is extended to the structural parameters, band gap, nucleophilicity, electrophilicity, isodesmic reactions, and dimerization.
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