88303-54-2Relevant academic research and scientific papers
A multinuclear NMR investigation of stannous chloride promoted ligand exchange of platinum phosphole complexes
Holt, Mark S.,Jeffrey Macdougall,Mathey, Fran?ois,Nelson, John H.
, p. 449 - 453 (2008/10/08)
A thorough investigation by 31P{1H}, 119Sn, and 195Pt{1H} NMR spectroscopy of solutions containing dichlorobis(1-R-3,4-dimethylphosphole)platinum(II) (L2PtCl2) and SnCl2 under a variety of conditions [various solvents, substituents (R = CH3, n-C4H9, t-C4H9, C6H5, and C6H5CH2), stoichiometries, times, and temperatures] demonstrated that the addition of solid anhydrous SnCl2 to solutions of the phosphole complexes labilizes these phosphole complexes toward complete ligand exchange producing several species in solution. These include cis- and trans-L2Pt(SnCl3)Cl, trans-L2Pt(SnCl3)2, cis-L2PtCl2, and, surprisingly, the pentacoordinate species L3PtCl2. The L3PtCl2 species are significant as their presence demonstrates that addition of a chloride acceptor (SnCl2) to a solution of a noble-metal complex not only labilizes the metal-chloride bond as anticipated but also labilizes the other metal-ligand bonds as well.
Intra- and intermolecular equilibria and their pertinence to the mechanism of cis-trans isomerization of L2PtX2 complexes: Four- and five-coordinate platinum phosphole complexes
Macdougall, J. Jeffrey,Nelson, John H.,Mathey, Francois
, p. 2145 - 2153 (2008/10/08)
A series of platinum(II) complexes of the type L2PtX2 (L = 1-R-3,4-dimethylphosphole; R = -CH3, -n-C4H9, -t-C4H9, -C6H5, -CH2C6H5; X = Cl-, Br-, I-) have been prepared and characterized by elemental analyses, physical properties, conductance measurements, infrared spectroscopy, and 1H, 13C{1H}, 31P{1H}, and 195Pt{1H} NMR spectroscopy. All complexes are nonelectrolytes in chloroform and methanol solutions and most possess the cis geometry in solution as well as in the solid state. Variable-temperature 31P{1H} and 195Pt{1H} NMR spectroscopy and conductance studies of the equilibrium L2PtX2 + L ? L3PtX2 have been analyzed in terms of intra- and intermolecular equilibria of the pentacoordinate species L3PtX2. The formation of L3PtX2 is enthalpy favored and entropy disfavored. The relative thermodynamic stability of the L3PtX2 complexes is a function of ligand steric bulk; the smaller ligand gives the greater stability. The stereochemical rigidity of the L3PtX2 complexes is inversely proportional to ligand steric bulk: the larger the ligand, the more rigid the L3PtX2 complex. The relationship of these observations to the mechanism of cis-trans isomerization of L2MX2 (M = Pd, Pt) is discussed. Coordination chemical shift relationships of the form Δδ(31P) = A[δ(31Pligand)] + B were found for the four-coordinate L2PtX2 complexes and for both of the magnetically inequivalent phosphole ligands in the five-coordinate L3PtX2 complexes. The complexes cis-L2PtBrCl, which are intermediates in the bromide ligand substitution reactions of cis-L2PtCl2, were isolated and characterized. They demonstrate that anion ligand substitution of cis-L2PtCl2 complexes occurs with complete retention of configuration. This is direct evidence of the kinetic trans effect. In contrast, iodide substitution of L2PtCl2 to produce L2PtI2 is accompanied by some cis-trans isomerization, as mixtures of cis- and trans-L2PtI2 are formed in these reactions. This is evidence of the thermodynamic trans effect. The L2PtBrCl complexes react with excess L to form L3PtBrCl rather than [L3PtBr]Cl or [L3PtCl]Br in support of the contention that the equilibrium can be best described as L2PtX2 + L ? L3PtX2 and not as L2PtX2 + L ? [L3PtX]X. Thus, five-coordinate complexes and not ionic four-coordinate complexes are formed in solutions of L2PtX2 upon addition of excess ligand (L). The implications of this in regard to consecutive anion displacement for isomerization of L2PtX2 complexes is discussed.
