355840-60-7Relevant academic research and scientific papers
The steric effect of o-tolyl ligand on the fluxionality behavior of some binuclear organoplatinum(II) complexes with bis(diphenylphosphino)methane as bridging ligand
Hashemi, Majid,Rashidi, Mehdi
, p. 982 - 989 (2007/10/03)
A series of binuclear organoplatinum(II) complexes of general formula cis,cis-[R2Pt(μ-SMe2)(μ-dppm)Pt(o-MeC 6H4)2], 3a-3d, in which R = Ph, p-MeC 6H4, m-MeC6H4 or p-MeOC 6H4, were prepared by the reaction of monomeric precursors [Pt(o-MeC6H4)2(dppm)] and cis-[PtR 2(SMe2)2]. The binuclear dialkyl analogs, in which R = Me (3e) or R2 = {(CH2)4} (3f), were prepared by the reaction of cis-[Pt(o-MeC6H4)2 (SMe2)2] and [PtR2 (dppm)]. The complexes were fully characterized by multinuclear (1H, 13C, 31P, 195Pt) NMR spectroscopy each as a mixture of syn and anti isomers (depending on the relative orientations of Me substituents on o-tolyl ligands) and each isomer was shown to have a rigid structure. Other binuclear analogs cis,cis-[R2Pt(μ-SMe2)(μ-dppm) PtR2′], 3g-3j, in which R is a less steric demanding aryl groups m-MeC6H4 or p-MeOC6H4, and R′ = Me or R2′={(CH2)4}, were prepared by the reaction of cis-[PtR2(SMe2)2] and [PtR2′(dppm)], and shown to have fluxional structures.
Unexpected selectivities in C-H activations of toluene and p-xylene at cationic platinum(II) diimine complexes. New mechanistic insight into product-determining factors
Johansson,Ryan,Romming,Tilset
, p. 6579 - 6590 (2007/10/03)
The C-H activation of toluene and p-xylene at cationic PtII diimine complexes (N-N)Pt(CH3)(H2O)+BF4- (N-N = Ar-N=CMe-CMe=N-Ar; 1(BF4-), Nf-Nf, Ar = 3,5-(CF3)2C6H3); 2(BF4-), N′N′, Ar = 2,6-(CH3)2C6H3) has been investigated. The reactions were performed at ambient temperature in 2,2,2-trifluoroethanol (TFE), and after complete conversion of the starting material to mixtures of Pt-aryl/Ptbenzyl complexes and methane, acetonitrile was added to trap the products as more stable acetonitrile adducts. In the reactions with toluene, the relative amounts of products resulting from aromatic C-H activation were found to decrease in the order (N-N)Pt(m-tolyl)(NCMe)+ > (N-N)Pt(p-tolyl)(NCMe)+ > (N-N)Pt(o-tolyl)(NCMe)+ for both 1 and 2. Unlike the reaction at 1, significant amounts of the benzylic activation product (N′-N′)Pt(benzyl)(NCMe)+ were concurrently formed in the C-H activation of toluene at 2. The C-H activation of p-xylene revealed an even more remarkable difference between 1 and 2. Here, the product ratios of (N-N)Pt(xylyl)(NCMe)+ and (N-N)Pt(p- methylbenzyl)(NCMe)+ were found to be 90:10 and 7:93 for reactions at 1 and 2, respectively. The elimination of toluene from (Nf-Nf)Pt(Tol)2 species (3a-c; a, Tol= o-tolyl; b, Tol = m-tolyl; c, Tol = p-tolyl) after protonolysis with 1 equiv of HBF4 was investigated. Most notably, protonation in neat TFE followed by addition of acetonitrile gave a 77:23 mixture of (Nf-Nf)Pt(mtolyl)(NCMe)+ (4b) and (Nf-Nf)Pt(p-tolyl)(NCMe)+ (4c) from all three isomeric bis(tolyl) complexes 3a-c. The presence of acetonitrile during the protonation reactions resulted in considerably less isomerization. This behavior is explained by an associative mechanism for the product-determining displacement of toluene by the solvent. For the C-H activation reactions, our findings suggest the existence of a dynamic equilibrium between the isomeric intermediates (N-N)Pt(aryl)(CH4)+ (aryl = tolyl/benzyl from 1; xylyl/p-methylbenzyl from 2). The observed selectivities might then be explained by steric and electronic effects in the pentacoordinate transition -state structures for the solvent-induced associative elimination of methane from these intermediates.
