Probing individual steps of dynamic exchange with P-31 EXSY NMR spectroscopy: Synthesis and characterization of the [E7PtH(PPh3)](2-) Zintl ion complexes [E = P, As]

Ethylenediamine (en) solutions of E-7(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, a nd deuterium labeling studies show that the order of hydrogen sources follo ws the sequence en > CH3CN > DMSO > DMF in the synthesis of 1. The [E7PtH(P Ph3)](2-) anions have C-1 point symmetry with unperturbed nortricyclane-lik e E-7(3-) ligands bound eta (2) to square planar (PtH)-H-pi(PPh3)(+) center s. Complex 1 is dynamic in solution whereby the PtH(PPh3)(+) fragment shift s from the top to bottom of the P-7 cluster (an eta (2) -> eta (4) -> eta ( 2) shift) and spins in the P-4 face in a concerted process to give apparent C-2 nu symmetry. We have shown that P-31 EXSY NMR experiments at -78 degre esC permit the separation of the two processes and show that shifting is si milar to 20 times faster than spinning (k(shift) = 160 s(-1), k(spin) = 8 s (-1)).