The enthalpy for the substitution reaction cis-[PdRf2(THF)2] + 2 L →cis-[PdRf2L2] + 2THF (THF = tetrahydrofuran) has been measured in THF by calorimetric methods for Rf = 3,5-dichloro-2,4,6-trifluorophenyl, L = PPh3, AsPh3, SbPh3, PMePh2, PCyPh2, PMe3, AsMePh2, or L2 = dppe (1,2-bis(diphenylphosphino)ethane), dppf (1,1′-bis(diphenylphosphino)ferrocene). The values determined show that the substitution enthalpy has a strong dependence on the electronic and steric properties of the ligand. The study of the consecutive substitution reactions cis-[PdRf2(THF)2] + L →cis-[PdRf2L(THF)] + THF, and cis-[PdRf2L(THF)] + L →cis-[PdRf2L2] + THF has been carried our for L = PPh3 and L = PCyPh2. The first substitution is clearly more favorable for the bulkier leaving ligand, but the second gives practically the same ΔH value for both cases, indicating that the differences in steric hindrance happen to compensate the electronic differences for both ligands. The X-ray structures of cis-[PdRf2(PMePh2)2], cis-[PdRf2(dppe)] and cis-[PdRf2(dppf)] are reported.
通过量热方法在THF中测量了取代反应cis-[PdRf2(THF)2] + 2 L →cis-[PdRf2
L2] + 2THF(THF =
四氢呋喃)的焓变,其中Rf = 3,5-二
氯-2,4,6-三
氟苯基,L = PPh3、AsPh3、SbPh3、PMePh2、PCyPh2、PMe3、AsMePh2或
L2 = dppe(1,2-双(二苯膦)
乙烷)、dppf(1,1'-双(二苯膦)
二茂铁)。测定值表明,取代焓强烈依赖于
配体的电子和立体性质。对连续取代反应cis-[PdRf2(THF)2] + L →cis-[PdRf2L(THF)] + THF和cis-[PdRf2L(THF)] + L →cis-[PdRf2
L2] + THF的研究进行了L = PPh3和L = PCyPh2的情况。第一次取代显然对较大的离去
配体更有利,但第二次取代实际上在两种情况下给出了相同的ΔH值,表明立体阻碍的差异恰好补偿了两种
配体的电子差异。报道了cis-[PdRf2(PMePh2)2]、cis-[PdRf2(dppe)]和cis-[PdRf2(dppf)]的X射线结构。