Photochemical substitution of ethene and hydrogen/deuterium exchange in (.eta.5-cyclopentadienyl)bis(ethene)rhodium
Photochemical substitution of ethene and hydrogen/deuterium exchange in (.eta.5-cyclopentadienyl)bis(ethene)rhodium
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(η5-环戊二烯基)双(乙烯)铑中乙烯的光化学取代和氢/氘交换
DOI：
10.1021/om00105a027
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发表时间：
1989
期刊：
影响因子：
2.8
通讯作者：
R. Perutz
中科院分区：
文献类型：
--
作者：
S. Belt;S. Duckett;D. Haddleton;R. Perutz
(C2H4)(t？2-C4H6)在CpRh(r/4-C4H6)之前形成。换算成？J2-丁二烯到β-4-丁二烯的络合物可以用光化学或热方法得到。当以CO或Bu‘NC为底物时，除生成取代产物外，还形成双核配合物(CpRhL)2(/ul)。光解方法的作用是(A)引入只能取代100℃以上的配体(ph3p，Me2SO，烯烃)，(B)形成不稳定的络合物，这些络合物不能通过热方法形成(环己烯，CH3CN，)2-丁二烯，以及(C)形成新的双核络合物[CpRh(ButNC)]2(M-ButNC)。对于不稳定的络合物，由于产物在室温或更低的温度下分解，因此可在低温下进行光解。提供了在193K甲苯溶液中光解生成CpRh(C2H4)(t？2-甲苯)的证据。取代产物的另一种途径是在253K下将CH3CN中的1光化学转化为CpRh(C2H4)(CH3CN)，然后添加配体。这些光化学反应与早期以CpRh(C2H4)和CpRh(C2H4)S(S=溶剂)为中间体的闪光光解和基质隔离实验所推断的机理是一致的。在C2D4气氛下的光解表明存在一个额外的途径，该途径导致乙烯配体内的H/D交换。这个途径可能包括1的乙烯基氢脱异构体作为不稳定的中间体。没有证据表明H/D与溶剂发生交换。配合物CpRh(C2H4)L(L=MeGSO，CH3CN，CH2=CHSiMe3)具有比已报道的其他同类配合物更高的绕Rh-乙烯键旋转的势垒。双核光产物[CpRh(Bu*Nc)]2(it-BuNc)表现出两个流动过程，第一个是两个构象围绕桥联异腈的CN键的内旋相互转化(AG*=45.7±1.6kJ mol“1)，第二个是桥联异腈和末端异腈的交换(AG*=61.8±0.8kJ mol”1)。
(C2H4)(t? 2-C4H6) is formed prior to CpRh (r/4-C4H6). Conversion of the? j2-butadiene tothe?? 4-butadiene complex can be achieved photochemically or thermally. When CO or Bu'NC are the substrates, dinuclear complexes (CpRhL) 2 (/uL) are formed in addition to substitution products. The photolysis method effects (a) the introduction of ligands that otherwise substitute only above 100 C (Ph3P, Me2SO, alkenes),(b) the formation of labile complexes which cannot be formed by thermal methods (cyclohexene, CH3CN,») 2-butadiene), and (c) the formation of the new dinuclear complex [CpRh (ButNC)] 2 (M-ButNC). For the labile complexes photolysis at low temperature is employed, since the products decompose at or below room temperature. Evidence is presented for the formation of CpRh (C2H4)(t? 2-toluene) on photolysis at 193 K intoluene solution. An alternative route to substitution products involves photochemical conversion of 1 in CH3CN to CpRh (C2H4)(CH3CN) at 253 K followed by addition of ligand. The photochemical reactions are consistent with the mechanism deduced from earlier flash photolysis and matrix isolation experiments in which CpRh (C2H4) and CpRh (C2H4) S (S= solvent) act as intermediates. Photolysis with a C2D4 atmosphere demonstrates the existence of an additional pathway which causes H/D exchange within the ethene ligand. This pathway probablyinvolves a vinyl hydrideisomer of 1 as an unstable intermediate. There is no evidence for H/D exchange with the solvent. The complexes CpRh (C2H4) L (L= MegSO, CH3CN, CH2= CHSiMe3) have a substantially higher barrier to rotation about the rhodium-ethene bond than has been reported for other complexes of this type. The dinuclear photoproduct [CpRh (Bu* NC)] 2 (it-ButNC) exhibits two fluxional processes, first interconversion of two conformersby internal rotation about the CN bond of the bridging isonitrile (AG*= 45.7±1.6 kJ mol" 1) and second exchange of bridging and terminal isonitriles (AG*= 61.8±0.8 kJ mol" 1).