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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Diaminocarbenes; Calculation of Barriers to Rotation about C_(carbene)-N Bonds, Barriers to Dimerization, Proton Affinities, and ~(13)C NMR Shifts
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Diaminocarbenes; Calculation of Barriers to Rotation about C_(carbene)-N Bonds, Barriers to Dimerization, Proton Affinities, and ~(13)C NMR Shifts

机译：二氨基卡宾; C_（碳烯）-N键旋转的势垒，二聚化的势垒，质子亲和力和〜（13）C NMR位移的计算

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摘要

Barriers to rotation about the C_(carbene)-N bonds in diaminocarbene (H_2N)_2C 1a, bis(dimethylamino)carbene ((CH_3)_2N)_2C 1b, the related formamidinium ions (H_2N)_2CH~+ 2a and ((CH_3)_2N)_2CH~+ 2b, and the Li~+ complexes (H_2N)_2CLi~+ 3a and ((CH_3)_2N)_2CLi~+ 3b have been calculated using density-functional theory in order to study the extent of #pi#-bond stabilization of the carbene center. Experimental barriers from DNMR are reported for 1b and 2b and compared with those for bis(diisopropylamino)carbene 1c and the N,N,N',N'-tetraisopropyl-formamidinium ion 2c; rotational barriers computed for 1b and 2b including thermal corrections compare well with experiment. The dimerization of 1a and 1b have been studied with (full) geometry optimization up to the levels QCISD(T)/cc-pVDZ//MP2/cc-pVDZ and B3LYP/cc-pVDZ//B3LYP/cc-pVDZ method. It is shown that the transition state geometries for the dimerizations of 1a and 1b have C_2 and C_1 symmetry, respectively, the latter being strongly polarized. The possible involvement of catalysis by protons and lithium ions in the dimerization processes is discussed. Calculations of the proton affinities of 1a, 1b, and some related species are reported. ~(13)C NMR shielding constant calculations on a series of diaminocarbenes have been performed using the gauge-including atomic orbitals (GIAO) method. The variation in the extremely downfield-shifted ~(13)C NMR signal of the carbene carbon in 1a, 1b, and related species is reproduced reasonably well by GIAO calculations, the latter being 2-8 ppm more upfield than the experimentally observed signals. It is shown that the paramagnetic contributions to the shielding tensor at the carbene nucleus play an important role in the chemical shift changes upon substitution in the RXC(NR_2) species.
机译：二氨基卡宾（H_2N）_2C 1a，双（二甲基氨基）卡宾（（CH_3）_2N）_2C 1b，相关的甲ami离子（H_2N）_2CH〜+ 2a和（（CH_3）中的C_（碳烯）-N键的旋转障碍为了研究＃pi＃-的程度，已使用密度泛函理论计算了_2N）_2CH〜+ 2b和Li〜+配合物（H_2N）_2CLi〜+ 3a和（（CH_3）_2N）_2CLi〜+ 3b卡宾中心的键稳定。报告了1b和2b的DNMR实验壁垒，并与双（二异丙基氨基）卡宾1c和N，N，N'，N'-四异丙基-甲ami离子2c进行了比较;为1b和2b计算的旋转障碍（包括热校正）与实验进行了比较。 1a和1b的二聚化已通过（完全）几何优化研究到QCISD（T）/ cc-pVDZ // MP2 / cc-pVDZ和B3LYP / cc-pVDZ // B3LYP / cc-pVDZ方法。结果表明，1a和1b二聚化的过渡态几何分别具有C_2和C_1对称性，后者是强极化的。讨论了质子和锂离子催化可能参与的二聚化过程。报告了1a，1b和一些相关物种的质子亲和力的计算。已使用量规（包括原子轨道）（GIAO）方法对一系列二氨基卡宾进行了〜（13）C NMR屏蔽常数计算。通过GIAO计算可以很好地再现1a，1b和相关物种中卡宾碳的极低场移位〜（13）C NMR信号的变化，后者比实验观察到的信号高2-8 ppm。结果表明，在卡宾核的屏蔽张量的顺磁贡献在RXC（NR_2）物种中的化学位移变化中起重要作用。

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