A Significant but Constrained Geometry Pt→Al Interaction: Fixation of CO2 and CS2, Activation of H2 and PhCONH2

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• 作者：Marc Devillard ; Richard Declercq ; Emmanuel Nicolas ; Andreas W. Ehlers ; Jana Backs ; Nathalie Saffon-Merceron ; Ghenwa Bouhadir ; J. Chris Slootweg ; Werner Uhl ; Didier Bourissou
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：April 13, 2016
• 年：2016
• 卷：138
• 期：14
• 页码：4917-4926
• 全文大小：601K
• 年卷期：0
• ISSN：1520-5126

文摘

Reaction of the geminal PAl ligand [Mes₂PC(═CHPh)AltBu₂] (1) with [Pt(PPh₃)₂(ethylene)] affords the T-shape Pt complex [(1)Pt(PPh₃)] (2). X-ray diffraction analysis and DFT calculations reveal the presence of a significant Pt→Al interaction in 2, despite the strain associated with the four-membered cyclic structure. The Pt···Al distance is short [2.561(1) Å], the Al center is in a pyramidal environment [Σ(C–Al–C) = 346.6°], and the PCAl framework is strongly bent (98.3°). Release of the ring strain and formation of X→Al interactions (X = O, S, H) impart rich reactivity. Complex 2 reacts with CO₂ to give the T-shape adduct 3 stabilized by an O→Al interaction, which is a rare example of a CO₂ adduct of a group 10 metal and actually the first with η¹-CO₂ coordination. Reaction of 2 with CS₂ affords the crystalline complex 4, in which the PPtP framework is bent, the CS₂ molecule is η²-coordinated to Pt, and one S atom interacts with Al. The Pt complex 2 also smoothly reacts with H₂ and benzamide PhCONH₂ via oxidative addition of H–H and H–N bonds, respectively. The ensuing complexes 5 and 7 are stabilized by Pt–H→Al and Pt–NH–C(Ph) = O→Al bridging interactions, resulting in 5- and 7-membered metallacycles, respectively. DFT calculations have been performed in parallel with the experimental work. In particular, the mechanism of reaction of 2 with H₂ has been thoroughly analyzed, and the role of the Lewis acid moiety has been delineated. These results generalize the concept of constrained geometry TM→LA interactions and demonstrate the ability of Al-based ambiphilic ligands to participate in TM/LA cooperative reactivity. They extend the scope of small molecule substrates prone to such cooperative activation and contribute to improve our knowledge of the underlying factors.