Synthesis and Bonding in the Diamagnetic Dinuclear Tantalum(IV) Hydride Species ([P<sub>2</sub>N<sub>2</sub>]Ta)<sub>2</sub>(μ-H)<sub>4</sub> and the Paramagnetic Cationic Dinuclear Hydride Species {([P<sub>2</sub>N<sub>2</sub>]Ta)<sub>2</sub>(μ-H)<sub>4</sub>}<sup>+</sup>I<sup>-</sup> ([P<sub>2</sub>N<sub>2</sub>] = PhP(CH<sub>2</sub>SiMe<sub>2</sub>NSiMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>PPh):  The Reducing Ability of a Metal−Metal Bond Michael D. Fryzuk Samuel A. Johnson Steven J. Rettig 10.1021/om000359w.s001 https://acs.figshare.com/articles/journal_contribution/Synthesis_and_Bonding_in_the_Diamagnetic_Dinuclear_Tantalum_IV_Hydride_Species_P_sub_2_sub_N_sub_2_sub_Ta_sub_2_sub_-H_sub_4_sub_and_the_Paramagnetic_Cationic_Dinuclear_Hydride_Species_P_sub_2_sub_N_sub_2_sub_Ta_sub_2_sub_-H_sub_4_sub_sup_sup_I_sup_-_sup_/3762861 The controlled reaction of the Ta(V) trimethyl species [P<sub>2</sub>N<sub>2</sub>]TaMe<sub>3</sub>, where [P<sub>2</sub>N<sub>2</sub>] = PhP(CH<sub>2</sub>SiMe<sub>2</sub>NSiMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>PPh, under 0.5 atm of hydrogen gas produces a partially hydrogenated Ta(V) species, ([P<sub>2</sub>N<sub>2</sub>]TaMe<sub>2</sub>(H), of unknown structure. Under 4 atm of hydrogen gas, further hydrogenation does not produce the complex [P<sub>2</sub>N<sub>2</sub>]TaH<sub>3</sub>; instead, reduction of the tantalum center occurs to yield the dinuclear Ta(IV) hydride ([P<sub>2</sub>N<sub>2</sub>]Ta)<sub>2</sub>(μ-H)<sub>4</sub>. This diamagnetic tetrahydride fails to react with many reagents, including ethylene and carbon monoxide; however, upon addition of iodomethane, {([P<sub>2</sub>N<sub>2</sub>]Ta)<sub>2</sub>(μ-H)<sub>4</sub>}<sup>+</sup>I<sup>-</sup> is produced as a paramagnetic green crystalline solid. The number of hydrides in this reaction product was confirmed by a deuterium labeling study. The results of a variable-temperature magnetic susceptibility study of this tetrahydride cation can be partially modeled with the Curie−Weiss law and a large correction for temperature-independent magnetism. Ab initio calculations using density functional theory were performed in an attempt to further understand the influence of the macrocyclic ligand in the bonding in these complexes. 2000-08-24 00:00:00 Ab initio calculations CH P 2 N 2 hydrogen gas Ta