X-ray structures versus NMR signals in pentacoordinate [PtX2(η2-CH2CH2)(Me2phen)] (X=Cl, Br, I) complexes

Hindrance, Donor Ability of Men∩NN Chelates and Overall Stability of Pentacoordinate [PtCl2(η2‐CH2=CH2)(Men∩NN)] Complexes as Observed by η2‐Olefin 1JPt,C Modulation: An NMR Study

“…In the last case, the Pt-η 2 -olefin system should be similar to a metallacyclopropane system. In this work, we observed that, in contrast to the 1 H and 13 C NMR values of the η 2 -olefin, the 1 J Pt,C coupling constants are not [19] and [PtBr 2 (η 2 -C 2 H 4 )(Me 2 phen)] (B), [16] evidencing the close contacts, in the trigonal equatorial plane, originated between the diimine Me groups and the η 2 -olefin; van der Waals radii are used for the space fill (white = H; gray = C; green = Cl; brown = Br; blue = N; Pt atoms are not visible in this perspective).…”

“…Elemental analyses were performed with a CHN Eurovector EA 3011. [30] [PtCl 2 (η 2 -CH 2 =CH 2 )(bpy)] (3), [10,39] [PtCl 2 (η 2 -CH 2 =CH 2 )(Mebpy)] (Me3), [10] [PtCl 2 (η 2 -CH 2 =CH 2 )(phen)] (4), [10] and [PtCl 2 (η 2 -CH 2 =CH 2 )(Me 2 phen)] (Me 2 4), [16,20] were synthesized by reported methods (for these complexes, only additional here discussed new NMR spectroscopic data, collected at 263 K, are reported in the Supporting Information). The new pentacoordinate complexes, discussed in this work, were synthesized by an extension of previously reported methods.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16] Although some very stable pentacoordinate complexes are well known, [17][18][19][20] [PtXY(η 2 -alkyne)(_ NN)] and [PtXY(η 2 -alkene)(_ NN)] complexes generally undergo characteristic decomposition patterns, including loss of alkyne or alkene, loss of an axial ligand, chelate ring opening, reductive elimination, and insertion of the unsaturated ligand into a σ-bond. [18] In this context, the main decomposition pattern generally involves the formation of reactive cationic intermediates of the type [PtX(η 2 …”

“…This intramolecular contact, in the case of Me 2 phen Me groups and η 2 -ethene, was also evident in the previously reported X-ray structures of [PtX 2 (η 2 -CH 2 =CH 2 )(Me 2 phen)] (X = halide, Figure 3). [16,20,49] The previous discussion clearly demonstrates that the 1 H and 13 C NMR chemical shifts of the η 2 -olefin are very much influenced by the surrounding groups and therefore cannot provide easily interpretable information on the nature of the Pt-η 2 -olefin bond. This bond could shift, in principle, from a simple π-interaction, in which the olefin donates its π-electron density to the metal, to a more complex situation that also involves electron back-donation from the metal valence orbitals to the empty π* orbital of the η 2 -olefin.…”

Pauling Electronegativity On/Off Effects Assessed by 13C and 29Si NMR Spectroscopic Analysis

“…[3] This effect indicatest he frequentlyo bserved decrease in the NMR chemical shift for an ucleus on increasingt he atomicw eighto ft he halogen atom(s) bound to that nucleus. [5] The high number of different and sometimes mutuallyc onflictinge xplanations proposed to rationalize the opposite NHD and IHD trends is remarkable. [3] Nevertheless,d ue to the complexity of the observed NMR effectsi ns everalc ases, every attempt to interpret experimental data by using simple, descriptive,a nd practical models unfortunately fails.…”