López-Serrano Joaquín, Duckett Simon B, Aiken Stuart, Almeida Leñero Karina Q, Drent Eite, Dunne John P, Konya Denis, Whitwood Adrian C
Department of Chemistry, University of York, Heslington, York, U.K.
J Am Chem Soc. 2007 May 23;129(20):6513-27. doi: 10.1021/ja070331c. Epub 2007 May 1.
The complexes [Pd(bcope)(OTf)2] (1a), where bcope is (C8H14)PCH2-CH2P(C8H14), and [Pd(tbucope)(OTf)2] (1b), where tbucope is (C8H14)PC6H4CH2P(tBu)2, catalyze the conversion of diphenylacetylene to cis- and trans-stilbene and 1,2-diphenylethane. When this reaction was studied with para-hydrogen, the characterization of Pd(bcope)(CHPhCH2Ph) (2a) and Pd(tbucope)(CHPhCH2Ph) (2b) was achieved. Magnetization transfer from the alpha-H of the CHPhCH2Ph ligands in these species proceeds into trans-stilbene. This process has a rate constant of 0.53 s-1 at 300 K in methanol-d4 for 2a, where DeltaH = 42 +/- 9 kJ mol-1 and DeltaS = -107 +/- 31 J mol-1 K-1, but in CD2Cl2 the corresponding rate constant is 0.18 s-1, with DeltaH = 79 +/- 7 kJ mol-1 and DeltaS = 5 +/- 24 J mol-1 K-1. The analogous process for 2b was too fast to monitor in methanol, but in CD2Cl2 the rate constant for trans-stilbene formation is 1.04 s-1 at 300 K, with DeltaH = 94 +/- 6 kJ mol-1 and DeltaS = 69 +/- 22 J mol-1 K-1. Magnetization transfer from one of the two inequivalent beta-H sites of the CHPhCH2Ph moiety proceeds into trans-stilbene, while the other site shows transfer into H2 or, to a lesser extent, cis-stilbene in CD2Cl2, but in methanol it proceeds into the vinyl cations Pd(bcope)(CPh=CHPh)(MeOD) (3a) and Pd(tbucope)(CPh=CHPh)(MeOD) (3b). When the same magnetization transfer processes are monitored for 1a in methanol-d4 containing 5 microL of pyridine, transfer into trans-stilbene is observed for two sites of the alkyl, but the third proton now becomes a hydride ligand in Pd(bcope)(H)(pyridine) (5a) or a vinyl proton in Pd(bcope)(CPh=CHPh)(pyridine) (4a). For 1b, under the same conditions, two isomers of Pd(tbucope)(H)(pyridine) (5b and 5b') and the neutral dihydride [Pd(tbucope)(H)2] (7) are detected. The single vinylic CH proton in 3 and the hydride ligands in 4 and 5 appear as strong emission signals in the corresponding 1H NMR spectra.
配合物[Pd(bcope)(OTf)₂]（1a，其中bcope为(C₈H₁₄)PCH₂ - CH₂P(C₈H₁₄)）和[Pd(tbucope)(OTf)₂]（1b，其中tbucope为(C₈H₁₄)PC₆H₄CH₂P(tBu)₂）可催化二苯乙炔转化为顺式和反式芪以及1,2 - 二苯乙烷。当用仲氢研究该反应时，实现了Pd(bcope)(CHPhCH₂Ph)（2a）和Pd(tbucope)(CHPhCH₂Ph)（2b）的表征。这些物种中CHPhCH₂Ph配体的α - H的磁化转移进入反式芪。在氘代甲醇 - d₄中，该过程在300 K时对于2a的速率常数为0.53 s⁻¹，其中ΔH = 42 ± 9 kJ mol⁻¹，ΔS = -107 ± 31 J mol⁻¹ K⁻¹，但在二氯甲烷 - d₂中相应的速率常数为0.18 s⁻¹，ΔH = 79 ± 7 kJ mol⁻¹，ΔS = 5 ± 24 J mol⁻¹ K⁻¹。2b的类似过程在甲醇中太快而无法监测，但在二氯甲烷 - d₂中，300 K时反式芪形成的速率常数为1.04 s⁻¹，ΔH = 94 ± 6 kJ mol⁻¹，ΔS = 69 ± 22 J mol⁻¹ K⁻¹。CHPhCH₂Ph部分两个不等价β - H位点之一的磁化转移进入反式芪，而另一个位点在二氯甲烷 - d₂中显示转移到H₂或在较小程度上转移到顺式芪，但在甲醇中它转移到乙烯基阳离子Pd(bcope)(CPh = CHPh)(MeOD)（3a）和Pd(tbucope)(CPh = CHPh)(MeOD)（3b）。当在含有5 μL吡啶的氘代甲醇 - d₄中对1a监测相同的磁化转移过程时，观察到烷基的两个位点向反式芪的转移，但第三个质子现在在Pd(bcope)(H)(吡啶)（5a）中成为氢化物配体或在Pd(bcope)(CPh = CHPh)(吡啶)（4a）中成为乙烯基质子。对于1b，在相同条件下，检测到Pd(tbucope)(H)(吡啶)（5b和5b'）的两种异构体以及中性二氢化物[Pd(tbucope)(H)₂]（7）。3中的单个乙烯基CH质子以及4和5中的氢化物配体在相应的¹H NMR光谱中表现为强发射信号。
