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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 23, Number 1
BKCSDE 23(1)
January 20, 2002 

Amine and Olefin Complexes of Pt(II) Having a PCP-Pincer Ligand
Soonheum Park
Platinum, Amine, Olefin, Equilibrium constant.
Pt(2,6-(Cy2PCH2)2C6H3)(OTf) (OTf = CF3SO3- ) readily reacts with various amines to afford cationic amine complexes [Pt(2,6-(Cy2PCH2)2C6H3)(amine)](OTf) (amine = NH3, NHMe2, NHC4H8, NH2Ph, NH2(Tol-p)) in high yields. These complexes have been fully characterized by IR, 1H-, 19F{1H}-, and 31P{1H}-NMR spectroscopy, and elemental analyses. Reaction of Pt(2,6-(Cy2PCH2)2C6H3)(OTf) with acrylonitrile quantitatively produced the π-olefinic complex [Pt(2,6-(Cy2PCH2)2C6H3)(CH2=CHCN)](OTf), which is only stable in solution in the presence of acrylonitrile. Attempt at isolating this complex in the pure solid state was failed due to partial decomposition into Pt(2,6-(Cy2PCH2)2C6H3)(OTf). The equilibrium constants (Keq = [Pt(PCP)-(NH2R)+ ][CH2=CHCN]/[Pt(PCP)(CH2=CHCN)+ ][NH2R]: [Pt(2,6-(Cy2PCH2)2C6H3)(CH2=CHCN)]+ + NH2R ⇔ [Pt(2,6-(Cy2PCH2)2C6H3)(NH2R)]+ + CH2=CHCN; R = Ph, p-tolyl) were calculated to be 0.28 (for R = Ph) and 3.1 (R = p-tolyl) at 21 ℃. The relative stability of the σ-donor amine versus the π-olefinic acrylonitrile complex has been found largely dependent upon the amine-basicity (pKb), implicating that acrylonitrile practically competes with amine in the platinum coordination sphere. On the contrary to the formation of the acrylonitrile complex, no reaction of Pt(2,6-(Cy2PCH2)2C6H3)(OTf) with other olefins such as ethylene, styrene and methyl acrylate was observed.
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