Laser flash photolysis (193 nm) of 1,1-dimethyl-(1-sila)cyclobut-2-ene in hexane solution leads to the formation of a transient species [Formula: see text] assigned to 1,1-dimethyl-1,3-(1-sila)butadiene on the basis of its UV absorption spectrum (λmax = 312 nm), and reactivity toward methanol (kMeOH = (3.6 ± 0.1) × 109 M−1 s−1; kH/kD = 1.3 ± 0.1), ethanol (kEtOH = (2.41 ± 0.06) × 109 M−1 s−1), tert-butanol (kBuOH = (1.8 ± 0.1) × 109 M−1 s−1; kH/kD = 1.5 ± 0.1), and oxygen [Formula: see text]. Experiments using isooctane and acetonitrile as solvent are also described. In acetonitrile, the lifetime of the silene is shortened considerably compared to hydrocarbon solvents, presumably due to quenching by adventitious water. In isooctane, under conditions of low excitation intensity, the siladiene decays with clean pseudo-first-order kinetics and a maximum lifetime of ~ 5 μs at 23 °C. The decay rate constant varies only slightly with temperature over the 20–60 °C range, leading to Arrhenius activation parameters of Ea = 0.5 ± 0.2 kcal/mol and log A = 5.7 ± 0.2. While steady state irradiation experiments suggest that in the absence of silene traps the predominant fate of the silabutadiene is thermal ring closure to regenerate the precursor, it is concluded that the rate constants and activation parameters for decay of the siladiene measured by flash photolysis represent a composite of those due to thermal electrocyclic ring closure (with Ea > ~3 kcal/mol) and reaction with adventitious quenchers (probably water, with Ea < 0). The measured Arrhenius parameters for reaction of the siladiene with methanol in isooctane (Ea = −2.6 ± 0.3 kcal/mol and log A = 7.6 ± 0.3) are consistent with this proposal. The potential and limitations of the use of 193-nm laser excitation for flash photolysis studies in solution are discussed. Keywords: far-UV, silene, flash photolysis, kinetics, electrocyclic.
1,1-二甲基-(1-硅)环丁-2-烯在己烷溶液中进行激光闪光光解(193 nm),导致产生一种瞬态物种 [Formula: see text],根据其紫外吸收光谱(λmax = 312 nm)和对甲醇的反应性(kMeOH = (3.6 ± 0.1) × 109 M−1 s−1>; kH/kD = 1.3 ± 0.1)、乙醇(kEtOH = (2.41 ± 0.06) × 109 M−1 s−1>)、叔丁醇(kBuOH = (1.8 ± 0.1) × 109 M−1 s−1>;kH/kD = 1.5 ± 0.1)和氧气 [Formula: see text],被归属为1,1-二甲基-1,3-(1-硅)丁二烯。还描述了在异辛烷和乙腈作为溶剂的实验。在乙腈中,硅烯的寿命相比烃类溶剂明显缩短,可能是由于被偶发水熄灭。在异辛烷中,在低激发强度条件下,硅二烯以清洁的伪一级动力学衰减,最大寿命约为23°C时的5 μs。在20–60°C范围内,衰减速率常数随温度变化仅略微变化,导致阿伦尼乌斯激活参数为 Ea = 0.5 ± 0.2 kcal/mol 和 log A = 5.7 ± 0.2。尽管稳态照射实验表明,在缺乏硅烯陷阱的情况下,硅丁二烯的主要命运是热环闭合以再生前体,但结论是,通过闪光光解测量的硅二烯的衰减速率常数和激活参数代表了热电环闭合(Ea > ~3 kcal/mol)和与偶发熄灭剂(可能是水,Ea < 0)反应的复合。在异辛烷中硅二烯与甲醇反应的阿伦尼乌斯参数(Ea = −2.6 ± 0.3 kcal/mol 和 log A = 7.6 ± 0.3)与该提议一致。讨论了在溶液中使用193nm激光激发进行闪光光解研究的潜力和局限性。关键词:远紫外,硅烯,闪光光解,动力学,电环闭合。