Details

Autor(en) / Beteiligte

• Ruhland, Klaus
• Herdtweck, Eberhardt

Titel

Mechanistic investigation of the thermal decomposition of Biphen(OP i-Pr)PtEt 2: An entrance into C–C single bond activation?

Ist Teil von

• Journal of organometallic chemistry, 2005, Vol.690 (23), p.5215-5236

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

2005

Link zum Volltext

Quelle

Elsevier ScienceDirect Journals Complete

Beschreibungen/Notizen

• The [ 1]Pt(Ethene) complex illustrated was synthesized via thermolysis of the [ 1]PtEt 2. Mechanistic investigations show that the ethene in [ 1]Pt(Ethene) is temporarily dissociated. We investigated whether by dissociation of the ethene the bridging C–C single bond of the biphenyl fragment can be activated. Biphen(OP i-Pr) and (COD)PtCl 2 give Biphen(OP i-Pr)PtCl 2 which upon treating with ethyl Grignard forms Biphen(OP i-Pr)PtEt 2. The thermal decomposition of Biphen(OP i-Pr)PtEt 2 was investigated in the temperature range of 353–383 K. The clean and quantitative formation of the Pt(Ethene) adduct was observed. X-ray structures of a molecule in the solid state of all three reaction products and two further related complexes with phenyl fingers instead of i-Pr have been determined. For the complexes with i-Pr fingers a decisive deviation from a square plane is observed in contrast to the complexes with phenyl fingers. The P–Pt–P angle increases from about 95° in Biphen(OP i-Pr)PtCl 2 to about 120° in Biphen(OP i-Pr)Pt(Ethene), forcing the bridging C–C single bond of the biphenyl fragment as near as 4.17 Å to the Pt center. No through-space coupling between the bridging C atoms and the Pt center could be observed in 13C NMR spectroscopy. No bond lengthening of the bridging C–C single bond in the biphenyl fragment was observed in Biphen(OP i-Pr)Pt(Ethene) in comparison to the precursor complexes. The thermal decomposition of Biphen(OP i-Pr)PtEt 2 can be described by a first-order kinetic and the activation parameters were determined (temperature range: 353–383 K; Δ H ‡ = 173.8 ± 16.2 kJ/mol and Δ S ‡ = 104.7 ± 44.1 J/(mol K)). The reaction kinetics were also measured for perdeuterated ethyl groups yielding in a kinetic isotopic effect of 1.56 ± 0.14 which was almost temperature-independent. Selective deuteration at α and β position of the ethyl group, respectively, showed that β-H elimination takes place fast in comparison to the complete thermolysis. In the temperature range of 333–353 K only a scrambling of the deuterium atoms was found without further decomposition (temperature range: 333–353 K; Δ scram H ‡ = 76.1 ± 15.2 kJ/mol, Δ scram S ‡ = −80.7 ± 45.5 J/(mol K) for Biphen(OP i-Pr)PtEt 2-d 6). The ethene is not lost during the scrambling process. The scrambling process is connected with a primary KIE decisively larger than 1.56. Biphen(OP i-Pr)Pt(Ethene) exchanges the coordinated ethene with ethene in solution as proven by labeling experiments. Both a dissociative and an associative mechanism could be shown to take place as ethene exchange reaction by means of VT 1H NMR spectroscopy via line shape analysis (temperature range: 333–373 K; Δ ass H ‡ = 26.9 ± 29.6 kJ/mol, Δ ass S ‡ = −148.0 ± 87.5 J/(mol K), Δ diss H ‡ = 86.0 ± 6.5 kJ/mol, Δ diss S ‡ = 5.4 ± 17.8 J/(mol K)). The Pt(0) complex formed during the dissociative loss of ethene activates several substrates among them: O 2, H 2, H 2SiPh 2 via Si–H activation, MeI presumably via forming a cationic methyl adduct and ethane via C–H activation but it was proven that the bridging C–C single bond of the biphenyl fragment is not even temporarily broken. The materials were characterized by means of 1H NMR, 13C NMR, 31P NMR, 195Pt NMR, EA, MS, IR, X-ray analysis and polarimetric measurement where necessary.