Reversible Dihydrogen Activation and Catalytic H/D Exchange with Group 10 Heterometallic Complexes**

Abstract

Reaction of a hexagonal planar palladium complex featuring a [PdMg 3 H 3 ] core with H 2 is reversible and leads to the formation of a new [PdMg 2 H 4 ] tetrahydride species alongside an equivalent of a magnesium hydride co-product [MgH]. While the reversibility of this process prevented isolation of [PdMg 2 H 4 ], analogous [PtMg 2 H 4 ] and [PtZn 2 H 4 ] complexes could be isolated and characterised through independent syntheses. Computational analysis (DFT, AIM, NCIPlot) of the bonding in a series of heterometallic tetrahydride compounds (Ni-Pt; Mg and Zn) suggests that these complexes are best described as square planar with marginal metal-metal interactions; the strength of which increases slightly as group 10 is descended and increases from Mg to Zn. DFT calculations support a mechanism for H 2 activation involving a ligand-assisted oxidative addition to Pd. These findings were exploited to develop a catalytic protocol for H/D exchange into magnesium hydride and zinc hydride bonds.

Low-Valent Transition Metalate Anions in Synthesis, Small Molecule Activation, and Catalysis

“…Ion-pairing interactions can occur in the absence of a cation sequestering agent. While studies by Fürstner, Hevia, − Mountford, ,,, Crimmin, − Wolf, Peters, − ,− and Lu, ,− among other contributions, illustrate that ion-pairing is a frequent phenomenon, only a handful of the investigations explicitly address the influence of such interactions on their reactivity. However, from these investigations it has become clear that the countercation may have profound influence on the reaction patterns, stoichiometric or catalytic, of metalates.…”

“…The deformation from the trigonal planar to the hexagonal planar configuration was found to have a low energy penalty at the expense of the M–E bond, as evidenced by the corresponding Walsh diagram. Furthermore, it is noteworthy that 706 reversibly reacts with molecular hydrogen to form the tetrahydride species [PdH 4 {Mg­( Ar nacnac)} 2 ] ( 711 , Ar nacnac = [CH­(ArNCMe) 2 ] − ; Ar = Dipp) and the dimer [( Ar nacnac)­Mg­(μ-H)] 2 ( 712 ) . In contrast, the heavier analogues [PtH 4 ­{Mg­( Ar nacnac)} 2 ] ( 713 ) and related [PtH 4 ­{Zn­( Ar nacnac)} 2 ] ( 714 ) feature [M II H 4 ] 4– fragments interacting with two cationic Mg or Zn moieties and, therefore, cannot be described as low-valent metalates.…”

Photochemical H2 activation by an Zn–Fe heterometallic: a mechanistic investigation

“…In the past few years there has been growing interest in using heterometallic complexes for H 2 activation. Transition metal complexes supported by Lewis-acidic B, [1][2][3] Al, 4 Zn, 5,6 Mg, 7,8 and Sn 9,10 ligands have all been documented to react with H 2 under thermal conditions. Despite the rapid growth of this area, examples of photolytic H 2 splitting using these types of heterometallic complexes are rare.…”

Dihydrogen Cleavage by a Zinc–Zinc Bond of a Heteroleptic Dizinc(I) Cation

“…While oxidative addition of dihydrogen dominates the formation of transition metal hydrides, binuclear oxidative addition across an unsupported metal–metal bond has also been recognized to cleave dihydrogen . Since the report by Power et al on facile dihydrogen activation by RGeGeR (R = C 6 H 3 -2,6-(C 6 H 3 -2,6- i Pr 2 ) 2 ) in 2005, heterolysis of dihydrogen by heterobimetallic complexes with main group and transition metals such as Ni–B, Fe–B, Pt–Mg/B, , Pt–Al, Rh–Sn, Fe–Ge/Sn, and Ni–Mg has been developed . Although some heterobimetallic metal–zinc complexes featuring a transition metal ( IV , VI ) − and a main group metal ( V ) , activate dihydrogen (Scheme ), hydrogenation catalysis by zinc complexes remains scarce.…”