[(Ph3P)3M(X)]（M = Rh，Ir）的流变性。[（Ph3P）3Ir（Cl）]的红色和橙色形式。哪种膦从Wilkinson 催化剂中更快地解离？

Fluxionality of [(Ph3P)3M(X)] (M = Rh, Ir). The red and orange forms of [(Ph3P)3Ir(Cl)]. Which phosphine dissociates faster from Wilkinson's catalyst?

机构信息

Central Research & Development, E. I. DuPont de Nemours & Co., Inc., Experimental Station, Wilmington, Delaware 19880, USA.

出版信息

J Am Chem Soc. 2010 Sep 1;132(34):12013-26. doi: 10.1021/ja1039693.

DOI:10.1021/ja1039693

PMID:20687561

Abstract

NMR studies of intramolecular exchange in [(Ph(3)P)(3)Rh(X)] (X = CF(3), CH(3), H, Ph, Cl) have produced full sets of activation parameters for X = CH(3) (E(a) = 16.4 +/- 0.6 kcal mol(-1), DeltaH(double dagger) = 16.0 +/- 0.6 kcal mol(-1), and DeltaS(double dagger) = 12.7 +/- 2.5 eu), H (E(a) = 10.7 +/- 0.2 kcal mol(-1), DeltaH(double dagger) = 10.3 +/- 0.2 kcal mol(-1), and DeltaS(double dagger) = -7.2 +/- 0.8 eu), and Cl (E(a) = 16.3 +/- 0.2 kcal mol(-1), DeltaH(double dagger) = 15.7 +/- 0.2 kcal mol(-1), and DeltaS(double dagger) = -0.8 +/- 0.8 eu). Computational studies have shown that for strong trans influence ligands (X = H, Me, Ph, CF(3)), the rearrangement occurs via a near-trigonal transition state that is made more accessible by bulkier ligands and strongly donating X. The exceedingly fast exchange in novel [(Ph(3)P)(3)Rh(CF(3))] (12.1 s(-1) at -100 degrees C) is due to strong electron donation from the CF(3) ligand to Rh, as demonstrated by computed charge distributions. For weaker donors X, this transition state is insufficiently stabilized, and hence intramolecular exchange in [(Ph(3)P)(3)Rh(Cl)] proceeds via a different, spin-crossover mechanism involving triplet, distorted-tetrahedral [(Ph(3)P)(3)Rh(Cl)] as an intermediate. Simultaneous intermolecular exchange of [(Ph(3)P)(3)Rh(Cl)] with free PPh(3) (THF) via a dissociative mechanism occurs exclusively from the sites cis to Cl (E(a) = 19.0 +/- 0.3 kcal mol(-1), DeltaH(double dagger) = 18.5 +/- 0.3 kcal mol(-1), and DeltaS(double dagger) = 4.4 +/- 0.9 eu). Similar exchange processes are much slower for [(Ph(3)P)(3)Ir(Cl)] which has been found to exist in orange and red crystallographic forms isostructural with those of [(Ph(3)P)(3)Rh(Cl)].

摘要

[(Ph(3)P)(3)Rh(X)] (X = CF(3), CH(3), H, Ph, Cl) 的分子内交换的 NMR 研究产生了 X = CH(3) 的完整的活化参数集（E(a) = 16.4 +/- 0.6 kcal mol(-1)，DeltaH(double dagger) = 16.0 +/- 0.6 kcal mol(-1)，和 DeltaS(double dagger) = 12.7 +/- 2.5 eu），H（E(a) = 10.7 +/- 0.2 kcal mol(-1)，DeltaH(double dagger) = 10.3 +/- 0.2 kcal mol(-1)，和 DeltaS(double dagger) = -7.2 +/- 0.8 eu），和 Cl（E(a) = 16.3 +/- 0.2 kcal mol(-1)，DeltaH(double dagger) = 15.7 +/- 0.2 kcal mol(-1)，和 DeltaS(double dagger) = -0.8 +/- 0.8 eu）。计算研究表明，对于强反式影响配体（X = H，Me，Ph，CF(3)），重排通过近乎三角过渡态发生，该过渡态由较大配体和强供体 X 更易接近。新型[(Ph(3)P)(3)Rh(CF(3))]（在-100°C 时为 12.1 s(-1)）中非常快速的交换归因于来自 CF(3)配体的强电子给体对 Rh 的作用，这由计算得到的电荷分布证明。对于较弱的供体 X，这种过渡态没有得到充分稳定，因此 [(Ph(3)P)(3)Rh(Cl)] 中的分子内交换通过涉及三重态、扭曲四面体 [(Ph(3)P)(3)Rh(Cl)] 的不同的自旋交叉机制进行，该中间物为自旋交叉机制。通过解离机制，[(Ph(3)P)(3)Rh(Cl)] 与游离的 PPh(3)（THF）的同时的分子间交换仅从反式位（E(a) = 19.0 +/- 0.3 kcal mol(-1)，DeltaH(double dagger) = 18.5 +/- 0.3 kcal mol(-1)，和 DeltaS(double dagger) = 4.4 +/- 0.9 eu）发生。[(Ph(3)P)(3)Ir(Cl)] 中的类似交换过程要慢得多，该物质已经发现存在于橙色和红色结晶形式中，与 [(Ph(3)P)(3)Rh(Cl)] 的结晶形式相同。