School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA.
Dalton Trans. 2018 Jul 3;47(26):8807-8816. doi: 10.1039/c8dt01857j.
The synthesis of alkylphosphine-substituted α-diimine (DI) ligands and their subsequent addition to Ni(COD)2 allowed for the preparation of (iPr2PPrDI)Ni and (tBu2PPrDI)Ni. The solid state structures of both compounds were found to feature a distorted tetrahedral geometry that is largely consistent with the reported structure of the diphenylphosphine-substituted variant, (Ph2PPrDI)Ni. To explore and optimize the synthetic utility of this catalyst class, all three compounds were screened for benzaldehyde hydrosilylation activity at 1.0 mol% loading over 3 h at 25 °C. Notably, (Ph2PPrDI)Ni was found to be the most efficient catalyst while phenyl silane was the most effective reductant. A broad scope of aldehydes and ketones were then hydrosilylated, and the silyl ether products were hydrolyzed to afford alcohols in good yield. When attempts were made to explore ester reduction, inefficient dihydrosilylation was noted for ethyl acetate and no reaction was observed for several additional substrates. However, when an equimolar solution of allyl acetate and phenyl silane was added to 1.0 mol% (Ph2PPrDI)Ni, complete ester C-O bond hydrosilylation was observed within 30 min at 25 °C to generate propylene and PhSi(OAc)3. The scope of this reaction was expanded to include six additional allyl esters, and under neat conditions, turnover frequencies of up to 990 h-1 were achieved. This activity is believed to be the highest reported for transition metal-catalyzed ester C-O bond hydrosilylation. Proposed mechanisms for (Ph2PPrDI)Ni-mediated carbonyl and allyl ester C-O bond hydrosilylation are also discussed.
烷基膦取代的α-二亚胺（DI）配体的合成及其随后与 Ni(COD)2 的加成允许制备（iPr2PPrDI）Ni 和（tBu2PPrDI）Ni。这两种化合物的固态结构均被发现具有扭曲的四面体形几何形状，这与报道的二苯基膦取代变体（Ph2PPrDI）Ni 的结构基本一致。为了探索和优化该催化剂类别的合成实用性，在 25°C 下以 3 小时、1.0mol%的负载量对所有三种化合物进行了苯甲醛氢硅烷化活性筛选。值得注意的是，（Ph2PPrDI）Ni 是最有效的催化剂，而苯基硅烷是最有效的还原剂。然后对广泛的醛和酮进行了氢硅烷化，将硅醚产物水解得到了良好收率的醇。当尝试探索酯还原时，发现乙酸乙酯的二氢硅烷化效率不高，并且对其他几种底物没有反应。然而，当将等摩尔的乙酸烯丙酯和苯基硅烷溶液加入到 1.0mol%（Ph2PPrDI）Ni 中时，在 25°C 下 30 分钟内观察到完全的酯 C-O 键氢硅烷化，生成丙烯和 PhSi(OAc)3。该反应的范围扩大到包括另外六个烯丙基酯，在纯条件下，达到了高达 990 h-1 的周转频率。据信，这是报道的过渡金属催化酯 C-O 键氢硅烷化中活性最高的。还讨论了（Ph2PPrDI）Ni 介导的羰基和烯丙基酯 C-O 键氢硅烷化的可能机制。
