Cationic Hydrogen Complexes of Rhenium. 2. Synthesis, Reactivity, and Competition Studies

Abstract

Cationic rhenium dihydrogen complexes, [Re(H2)(PR3)2(CO)3]B(Ar‘)4 (PR3 = PCy3, PiPr3, PiPrPh2, PPh3; Ar‘ = 3,5-(CF3)2C6H3), have been prepared by the protonation of ReX(PR3)2(CO)3 (X = H, CH3) with [H(Et2O)2]B(Ar‘)4 under a hydrogen atmosphere. Deuterium is incorporated into the H2 ligand when placed under a D2 atmosphere and large J HD values (30−33 Hz) are consistent with a dihydrogen formulation. Relaxation data indicate very short T 1min for these complexes. These complexes are susceptible to heterolytic cleavage of dihydrogen, and the reactivity with several bases has been investigated. Under vacuum or argon atmosphere the complexes readily lose hydrogen to form 16-electron complexes. In the solid state, [Re(PCy3)2(CO)3]B(Ar‘)4 exhibits an agostic interaction to a β C−H bond of the phosphine ligand. Variable-temperature 31P{1H} NMR spectra of [Re(PCy3)2(CO)3]B(Ar‘)4 indicate a dynamic process involving hindered rotation about the Re−P bond. Competition studies have been conducted, and the hydrogen binding affinity is higher for [Re(H2)(PCy3)2(CNtBu)3]B(Ar‘)4 (5) than for [Re(H2)(PCy3)2(CO)3]B(Ar‘)4 (2a). Similar experiments also find that 5 also binds hydrogen preferentially over W(H2)(PCy3)2(CO)3.

Preparation and Reactivity of Hydridorhenium Complexes with Polypyridine and Phosphonite Ligands

“…On this basis, we hypothesize that the reaction of [ReH(bpy)(CO) 3 ] with HBF 4 does not proceed by protonation of the Re–H bond to give an η 2 ‐H 2 ligand but involves the oxidative addition of H + to yield the formal cationic Re III derivative [ReH 2 (bpy)(CO) 3 ] + . Oxidative addition of H + to a Re I complex is rather rare3e as formation of the dihydrogen [Re]‐η 2 ‐H 2 complex is the more usual result of protonation 3i,4a,11b. The presence of the bpy ligand probably strongly influences the course of the protonation reaction that leads to the Re III species 3 .…”

Electrophilic Addition vs Electron Transfer for the Interaction of Ag+ with Molybdenum(II) Hydrides. 1. Reaction with CpMoH(PMe3)3 and the Mechanism of Decomposition of [CpMoH(PMe3)3]+

“…The protonation reaction, an extensively studied process, affords either classical M(H) 2 or non classical M(H 2 ) dihydrides by pathways a and b, respectively (see Scheme 1). [1][2][3][4][5][6][7][8][9][10][11][12][13] The 3c-2e nonclassical product may be unstable and collapse to the dihydrido complex or reductively eliminate dihydrogen (see Scheme 1, paths b.i and b.ii, respectively). The hydride abstraction reaction by the trityl cation (E + = Ph 3 C + ) [14][15][16][17] can also be viewed as an exemple of a reaction following path b.ii.…”

Brønsted–Lowry Acid Strength of Metal Hydride and Dihydrogen Complexes

“…189 The corresponding dppp complexes (entries 68, 69 vs 125, 126 ) show similar trends although in this case the osmium chloro complex is much less acidic (pK a DCM = 12.3) than the ruthenium complex (pK a DCM = 5.6). 153 133,137,138,147,149) are useful acids to establish the pK a THF scale from 12 to 19. They also provide a link to Angelici's enthalpy of protonation scale in dichloroethane solvent (DCE).…”