A Significant but Constrained Geometry Pt -> Al Interaction: Fixation of CO2 and CS2, Activation of H-2 and PhCONH2

作者：Devillard Marc; Declercq Richard; Nicolas Emmanuel; Ehlers Andreas W; Backs Jana; Saffon Merceron Nathalie; Bouhadir Ghenwa^*; Slootweg J Chris^*; Uhl Werner^*; Bourissou Didier^*

来源：Journal of the American Chemical Society, 2016, 138(14): 4917-4926.

DOI：10.1021/jacs.6b01320

Reaction of the geminal PAl ligand [Mes(2)PC(=CHPh)AltBu(2)] (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 interaction in 2, despite the strain associated with the four-membered cyclic structure. The Pt center dot center dot center dot Al distance is short [2.561(1) angstrom], the Al center is in a pyramidal environment [Sigma(C-Al-C) = 346.6 degrees], 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 eta(1)-CO2 coordination. Reaction of 2 with CS2 affords the crystalline complex 4, in which the PPtP framework is bent, the CS2 molecule is eta(2)-coordinated to Pt, and one S atom interacts with Al. The Pt complex 2 also smoothly reacts with H-2 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 H-2 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.

• 出版日期2016-4-13