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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Photochemical reactions of(eta~5-cyclopentadienyl)bis(t-butylacrylate)rhodium with silanes:Dynamics of isomer interconversion via Rh(eta~2-silane)species
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Photochemical reactions of(eta~5-cyclopentadienyl)bis(t-butylacrylate)rhodium with silanes:Dynamics of isomer interconversion via Rh(eta~2-silane)species

机译：（η〜5-环戊二烯基）双（丙烯酸叔丁酯）铑与硅烷的光化学反应：通过Rh（η〜2-硅烷）物种进行异构体互变的动力学

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The compound CpRh(C_2H_3CO_2'Bu)_21 has been synthesised as a mixture of two pairs of interconverting isomers which differ in the relative orientations of the alkene substituents.The four isomers have been fully characterised by NMR spectroscopy.When complex 1 is photolysed in the presence of a silane,HSiR_2R'[R_2R'= Et_3,Me_3,HET_2,(OMe)_3 and Me_2Cl] the corresponding Si-H oxidative addition products CpRh(SiR_2R')(H)(C_2H_3CO_2'Bu)and CpRh(H)_2(SiR_2R')_2 are formed.The Rh(III)complexes CpRh(SiR_2R')(H)(C_2H_3CO_2'Bu)exist in two isomeric forms of comparable energy which interconvert in an intramolecular process that does not involve a reversible [1,3] hydride or [1,3] silyl migration.The hydride ~1H NMR resonances for these species consequently broaden before coalescing into a single peak.For R_2R'= Et_3,the activation parameters for interchange from the major to minor isomer were DELTAH = 60.2(+-)2 kJ moL~1 and DELTAS = 8(+-)9 J mol~M K~H,while for R_2R'= Me_3 and ET_2H,DELTAH= 61.5(+-)1 kJ mo)~(-1),DELTAS = 6(+-)5 J mol~(-1)K~(-1),and DELTAH = 61.8(+-)3 kJ mol~(-1),DELTAS = 12(+-)9 J mol~(-1)K~(-1)respectively for conversion from the major isomer to the minor.For these complexes an eta~2-Rh-H-Si transition state or intermediate is consistent with the evidence.When R_2R'=(OMe)_3 and Me_2Cl the change in appearance of the hydride resonances is more complex,with the activation parameters for interchange from the major to minor isomer for the former species being DELTAH = 78.3(+-)2 kJ moL~1 and AS* = 30(+-)7 J mol~(-1)K~(-1)while for Me_2Cl the barrier proved too high to measure before decomposition occurred.The complex spectral changes could be simulated when a discrete eta~2-Rh-H-Si intermediate was involved in the isomer interconversion process and hence silane rotation in all these systems is proposed to involve two isomers of CpRh(eta~2-HSiR_2R')(C_2H_3CO_2~tBu).
机译：化合物CpRh（C_2H_3CO_2'Bu）_21是由两对相互转化的异构体的混合物合成而成的，这些异构体在烯烃取代基的相对方向上有所不同。四种异构体已通过NMR光谱进行了全面表征。硅烷，HSiR_2R'[R_2R'= Et_3，Me_3，HET_2，（OMe）_3和Me_2Cl]的存在下，相应的Si-H氧化加成产物CpRh（SiR_2R'）（H）（C_2H_3CO_2'Bu）和CpRh（H）形成了_2（SiR_2R'）_2。Rh（III）络合物CpRh（SiR_2R'）（H）（C_2H_3CO_2'Bu）存在两种可比较能量的异构形式，它们在不涉及可逆性的分子内过程中相互转化[1 ，3]氢化物或[1,3]甲硅烷基迁移。因此，这些物质的氢化物〜1H NMR共振在聚结成单个峰之前变宽。对于R_2R'= Et_3，从主异构体交换到次异构体的活化参数为DELTAH = 60.2（+-）2 kJ moL〜1且DELTAS = 8（+-）9 J mol〜MK〜H，而对于R_2R'= Me_3和ET_2H，DELTAH = 61。 5（+-）1 kJ mol〜（-1），DELTAS = 6（+-）5 J mol〜（-1）K〜（-1），DELTAH = 61.8（+-）3 kJ mol〜（ -1），DELTAS = 12（+-）9 J mol〜（-1）K〜（-1），分别从主要异构体转变为次要异构体。对于这些配合物，η〜2-Rh-H-Si跃迁当R_2R'=（OMe）_3和Me_2Cl时，氢化物共振的外观变化更为复杂，前者从主要异构体向次要异构体交换的活化参数为DELTAH = 78.3（+-）2 kJ moL〜1且AS * = 30（+-）7 J mol〜（-1）K〜（-1），而对于Me_2Cl，势垒过高，无法在分解发生之前进行测量。当异构体互变过程涉及离散的eta〜2-Rh-H-Si中间体时，可以模拟这种变化，因此，在所有这些系统中，硅烷旋转被提议包含CpRh（eta〜2-HSiR_2R'）（C_2H_3CO_2的两个异构体〜tBu）。

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