Cationic platinum (II) complexes bearing substituted bipyridyl ligands ([bipyPt(L)Ph]+ , L = labile ligand) have been shown to be efficient and selective olefin hydroarylation catalysts. To expand this genre of chemistry, we became interested in studying neutral tris(pyrazol-1-yl)alkane ligands on platinum to examine how a third proximal donor ligand within the coordination sphere of platinum would affect the catalytic olefin hydroarylation reactivity. Herein, we present our preliminary results and progress. Reaction of Ph2Pt(SEt2)2 with tris(3,5-dimethylpyrazol-1-yl)methane (HC(3,5-Me-pz)3, pz = pyrazolyl, Mp) or 1,1,1-tris-(3,5-dimethylpyrazol-1-yl)-2-(trimethylsiloxy)ethane ((CH3)3SiOCH2C(3,5-Me-pz)3, pz = pyrazolyl, Sp) yields the square planar complexes, (κ2-N,N-Mp)PtPh2 (1) and (κ2-N,N-Sp)PtPh2 (2). Complex 1 reacts rapidly with hydrochloric acid in diethyl ether to form an isolable, cationic Pt(IV) intermediate, [(κ3-N,N,N-Mp)PtPh2(H)]Cl (3), then slowly transforms to (κ2-N,N-Mp)PtPhCl (4), after reductive elimination of benzene under prolonged heating at reflux. Complex 2 reacts cleanly with hydrochloric acid to produce (κ2-N,N-Sp)PtPhCl (5) with no observable formation of a cationic Pt(IV) intermediate, which we believe is due to the steric profile of the trimethylsiloxy group that prevents coordination of the free 3,5-dimethylpyrazolyl arm. Compound 5 cleanly reacts with silver tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (AgBArF′, [B{3,5-CF3(C6H3)}4]) in acetonitrile to produce [ (κ2-N,N-Sp)PtPh(NCMe)][BArF’] (6). All compounds have been characterized by 1H NMR and/or single crystal X-ray crystallography. Compound 6 is notable as it may show promising olefin hydroarylation reactivity in our future studies.

Tris(3,5-dimethylpyrazol-1-yl)methane and 1,1,1-tris-(3,5-dimethylpyrazol-1-yl)-2-(trimethylsiloxy)ethane platinum compounds: Synthesis, reactivity and structure

251st National Meeting (2016)

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