BETA-HYDRIDE ELIMINATION FROM METHOXO VS ETHYL LIGANDS - THERMOLYSIS OF (DPPE)PT(OCH3)2, (DPPE)PT(CH2CH3)(OCH3) AND (DPPE)PT(CH2CH3)2
BETA-HYDRIDE ELIMINATION FROM METHOXO VS ETHYL LIGANDS - THERMOLYSIS OF (DPPE)PT(OCH3)2, (DPPE)PT(CH2CH3)(OCH3) AND (DPPE)PT(CH2CH3)2
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DOI：
10.1021/ja00276a018
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发表时间：
1986-08-06
影响因子：
15
通讯作者：
BERCAW, JE
中科院分区：
文献类型：
--
作者：
BRYNDZA, HE;CALABRESE, JC;BERCAW, JE
背景技术在历史上，制备VIII族（8-10族）金属的烷醇盐和酰胺络合物比制备含β-氢取代基的类似烷基物质更困难。此外，后金属醇盐的化学只是最近才被探索，而金属烷基络合物的反应已经研究了很多年。[2]通常认为这类物质具有弱的金属-氧键，这是由于硬碱配体与相对较软的第VIII族（第8-10族）金属中心的相互作用很弱。分离醇盐配合物的困难以及它们分解（可能是通过β-氢化物消除）为金属氢化物的容易性3增加了这些假设的可信度;人们假设弱MO键通过提高基态来降低β-氢化物消除反应的固有势垒醇盐相对于烷基的自由能。与此解释一致，含β-氢原子的铂醇盐的合成在含吸电子取代基的物质中最成功地完成4，并且可比的氢氧化物和酚盐络合物通常比醇盐类似物稳定得多。[5] Whitesides、Yamamoto和其他人提供了极好的实验研究，表明从铂（II）烷基中消除β-氢最容易通过膦配体从P2PtR 2络合物中解离，然后烷基和氢化物配体的β-消除和还原偶联来进行。6在高膦配体浓度下或使用螯合双膦配体时，来自16电子起始材料的较高能量/3-消除与解离途径竞争。[6]我们现在报告，类似的铂醇盐表现出相同的行为，并提供了两类化合物之间有趣的比较。
Background It has been historically more difficult to preparealkoxide and amide complexes of the group VIII (groups 8-10) metals than to prepare comparable alkyl species containing/3-hydrogensub-stituents. In addition, thé chemistry of late-metal alkoxides has only recently been explored1 while reactions of metal alkyl com-plexes have been studiedfor many years. 2 The commonly held perception that suchspecies have weak metal-oxygen bonds has been attributed to the suspected poor interaction of hard base ligands with relatively soft group VIII (groups 8-10) metal centers. The difficulty in isolating alkoxide complexes and the ease with which they decompose (presumably by/3-hydride elimination) to metal hydrides3 adds credence to these hypotheses; it has been assumed that weak MO bonds lower the intrinsic barrier to/3-hydride elimination reactions by raising the ground-state free energies of alkoxides relative to alkyls. Consistent with this interpretation, synthesis of platinum alkoxides containing/3-hy-drogen atoms has been accomplished most successfully in species containing electron-withdrawing substituents4 and comparable hydroxide and phenoxide complexes are generally much more stable than alkoxide analogues. 5 Whitesides, Yamamoto, and others have provided elegant la-beling studies which show/3-hydrogen elimination from platinum (II) alkyls most easily takes place by dissociation of phosphine ligands from P2PtR2 complexesfollowed by^-elimination and reductive coupling of alkyl and hydride ligands. 6 At high phosphine ligand concentrations or with chelatingbis-phosphine ligands, a higher energy/3-elimination from the 16-electron starting materials becomes competitive with the dissociative route. 6 We now report that analogous platinum alkoxides show the same behavior and provide interesting comparisons between the two classes of compounds.