Probing Individual Steps of Dynamic Exchange with ³¹P EXSY NMR Spectroscopy:  Synthesis and Characterization of the [E₇PtH(PPh₃)]^2- Zintl Ion Complexes [E = P, As]

Abstract

Ethylenediamine (en) solutions of E7 3- (E = P, As) react with Pt(PPh3)2(C2H4) in the presence of 4,7,13,16,21,24-hexaoxa-1,10-diazobicyclo[8.8.8]hexacosane (2,2,2-crypt) to give the transition-metal Zintl ion complexes [P7PtH(PPh3)]2- (1) and [As7PtH(PPh3)]2- (2) as isomorphic [K(2,2,2-crypt)]+ salts, respectively. The hydride ligand originates from the solvent, and deuterium labeling studies show that the order of hydrogen sources follows the sequence en > CH3CN > DMSO > DMF in the synthesis of 1. The [E7PtH(PPh3)]2- anions have C 1 point symmetry with unperturbed nortricyclane-like E7 3- ligands bound η2 to square planar PtIIH(PPh3)+ centers. Complex 1 is dynamic in solution whereby the PtH(PPh3)+ fragment shifts from the top to bottom of the P7 cluster (an η2 → η4 → η2 shift) and spins in the P4 face in a concerted process to give apparent C 2 v symmetry. We have shown that 31P EXSY NMR experiments at −78 °C permit the separation of the two processes and show that shifting is ∼20 times faster than spinning (k shift = 160 s-1, k spin = 8 s-1).

From Phosphidic to Phosphonium? Umpolung of the P4‐Bonding Situation in [CpFe(CO)(L)(η1‐P4)]+ Cations (L=CO or PPh3)

“…Computational investigation into the mechanism of exchanging the metalated phosphorus atom identified an η 1 ‐η 2 ‐η 1 “walking” mechanism as was previously reported for other η 1 ‐P 4 complexes and the heptaphosphanortricyclene‐P 7 3− moiety in [η 2 ‐P 7 {PtHPPh 3 }][K(2,2,2‐crypt)] 2 . The intermediate η 2 ‐P 4 complexes [CpFe(CO)(L)(η 2 ‐P 4 )] + at the BP86/def‐SV(P) level of theory with D3(BJ) dispersion correction are located 20 and 25 kJ mol −1 higher in energy than the structurally characterized η 1 ‐analogues for L=CO and PPh 3 .…”

Mechanisms and Beyond: Elucidation of Fluxional Dynamics by Exchange NMR Spectroscopy

“…Rather different is the dynamics of 120 in solution, where the PtH(PPh 3 ) fragment shifts from the top to the bottom of the P 7 cluster (η 2 –η 4 –η 2 shift) and spins in the P 4 face in a concerted process to give apparent C 2 V symmetry (Scheme ). Eichhorn's group have shown that shift is 20 times faster than spinning in cluster 120 …”

On the Theme of Amidiniophosphines: Synthesis and Reactivity of Benzo-, Diimidazolo-Tris-Annelated P-Aminodiazaphosphepines

“…Coalescence of the 31 P NMR signals could only be extrapolated to occur above 373 K; nevertheless, the EXSY 31 P{ 1 H} spectrum at 333 K revealed correlations between the broadening signals, thus confirming a dynamic exchange between the isomers (see experimental section and Figure 6 therein). 22 Line shape analysis of VTP 1 H NMR spectra allowed the determination of the first-order rate constant k(T) of the stereo-conversion at the variable temperature T. The Eyring plots Figures 3 and 5). 23 Almost the same value (17.0 kcal/mol) was obtained by line shape analysis of the VTP 31 P NMR spectra (Table 1, Figures 5 and 6).…”