Mechanism of O2 Activation and Methanol Production by (Di(2-pyridyl)methanesulfonate)PtIIMe(OHn)(2–n)– Complex from Theory with Validation fro
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- 作者：Wei-Guang Liu ; Anna V. Sberegaeva ; Robert J. Nielsen ; William A. Goddard ; III ; Andrei N. Vedernikov
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：February 12, 2014
- 年：2014
- 卷：136
- 期：6
- 页码：2335-2341
- 全文大小：501K
- ISSN：1520-5126
文摘
The mechanism of the (dpms)PtIIMe(OHn)(2鈥?i>n)鈭?/i> oxidation in water to form (dpms)PtIVMe(OH)2 and (dpms)PtIVMe2(OH) complexes was analyzed using DFT calculations. At pH < 10, (dpms)PtIIMe(OHn)(2鈥?i>n)鈥?/sup> reacts with O2 to form a methyl Pt(IV)鈥揙OH species with the methyl group trans to the pyridine nitrogen, which then reacts with (dpms)PtIIMe(OHn)(2鈥?i>n)鈥?/sup> to form 2 equiv of (dpms)PtIVMe(OH)2, the major oxidation product. Both the O2 activation and the O鈥揙 bond cleavage are pH dependent. At higher pH, O鈥揙 cleavage is inhibited whereas the Pt-to-Pt methyl transfer is not slowed down, so making the latter reaction predominant at pH > 12. The pH-independent Pt-to-Pt methyl transfer involves the isomeric methyl Pt(IV)鈥揙OH species with the methyl group trans to the sulfonate. This methyl Pt(IV)鈥揙OH complex is more stable and more reactive in the Pt-to-Pt methyl-transfer reaction as compared to its isomer with the methyl group trans to the pyridine nitrogen. A similar structure鈥搑eactivity relationship is also observed for the SN2 functionalization to form methanol by two isomeric (dpms)PtIVMe(OH)2 complexes, one featuring the methyl ligand trans to the sulfonate group and another with the methyl trans to the pyridine nitrogen. The barrier to functionalize the former isomer with the CH3 group trans to the sulfonate group is 2鈥? kcal/mol lower. The possibility of the involvement of Pt(III) species in the reactions studied was found to correspond to high-barrier reactions and is hence not viable. It is concluded that the dpms ligand facilitates Pt(II) oxidation both enthalpically and entropically.