Intramolecular exchange of coordinated and dangling phosphines in pentacarbonyl group 6 complexes of 1,1,2-tris(diphenylphosphino)ethane

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• 作者：Richard L. Keiter ; Ping Ye ; Ellen A. Keiter ; John William Benson ; Weiying Lin ; Douglas E. Br ; t ; Joel S. Southern ; Arnold L. Rheingold ; Ilia Guzei ; Kraig A. Wheeler ; Lew W. Cary
• 关键词：Group 6 pentacarbonyls ; Linkage isomerization ; Phosphine exchange ; Through-space coupling
• 刊名：Inorganica Chimica Acta
• 出版年：2010
• 出版时间：15 December 2010
• 年：2010
• 卷：364
• 期：1
• 页码：176-184
• 全文大小：730 K

文摘

The linkage isomers, (OC)₅M[κ¹-PPh₂ CH₂CH(PPh₂)₂] 1 and (OC)₅M[κ¹-PPh₂ CH(PPh₂)CH₂PPh₂] 2 (M = Cr, Mo and W) exist in equilibrium at room temperature. Equilibrium constants for 1Cr  2Cr, 1Mo  2Mo and 1W  2W at 25 °C in CDCl₃ are 2.61, 5.0 and 4.74, respectively. Enthalpy favors the forward reaction (ΔH = −13.5, −12 and −12.2 kJ mol⁻¹, respectively) while entropy favors the reverse reaction (ΔS = −37.6, −28 and −28.2 J K⁻¹ mol⁻¹, respectively). Isomerization is much faster than chelation with 1Mo  2Mo  1W  2W > 1Cr  2Cr. Enthalpies of activation for 1Cr  2Cr and 1W  2W are 119.0 and 92.6 kJ mol⁻¹, respectively, and entropies of activation are 1.4 and −28.2 J K⁻¹ mol⁻¹, respectively. Isomerization is 10⁴ times faster for these complexes than for (OC)₅M[κ¹-PPh₂CH₂CH₂P(p-tolyl)₂]. A novel mechanism is proposed to account for the rate differences. The X-ray crystal structure of 2W shows that the phosphorus atom of the short phosphine arm lies very close to a carbon atom of the W(CO)₄ equatorial plane (3.40 Å) which could allow “through-space” coupling, accounting in part for the observation of long-range J_PC and J_PW coupling. The X-ray structure of (OC)₅W[κ¹-PPh₂ C(CH₂)PPh₂] 5W has been determined for comparison to 2W.