Thermodynamic Modulation of Dihydrogen Activation Through Rational Ligand Design in Ge-Ni Complexes.

A family of chelating aryl-functionalized germylene ligands has been developed and employed in the synthesis of their corresponding 16-electron Ni complexes (DippGeAr·Ni·IPr; Dipp = {[PhPCHSi(Pr)](Dipp)N}; IPr = [{(H)CN(Dipp)}C:]; Dipp = 2,6-PrCH). These complexes demonstrate the ability to cooperatively and reversibly activate dihydrogen at the germylene-nickel interface under mild conditions (1.5 atm H, 298 K).

T-shaped Ni Systems Featuring Cationic Tetrylenes: Direct Observation of L/Z-type Ligand Duality, and Alkene Hydrogenation Catalysis.

We report a facile synthetic method for accessing rare T-shaped Ni species, stabilised by low-coordinate cationic germylene and stannylene ligands which behave as Z-type ligands toward Ni . An in-depth computational analysis indicates significant Ni →E donation (E=Ge, Sn), with essentially no E→Ni donation. The tetrylene ligand's Lewis acidity can be modulated in situ through the addition of a donor ligand, which selectively binds at the Lewis acidic tetrylene site.

Cationic Tetrylene-Iron(0) Complexes: Access Points for Cooperative, Reversible Bond Activation and Open-Shell Iron(-I) Ferrato-Tetrylenes.

The open-shell cationic stannylene-iron(0) complex 4 (4=[ DippSn⋅Fe⋅IPr] ; Dipp={[Ph PCH Si( Pr) ](Dipp)N}; Dipp=2,6- Pr C H ; IPr=[(Dipp)NC(H)] C:) cooperatively and reversibly cleaves dihydrogen at the Sn-Fe interface under mild conditions (1.5 bar, 298 K), in forming bridging hydrido-complex 6. The One-electron oreduction of the related Ge -Fe complex 3 leads to oxidative addition of one C-P linkage of the Dipp ligand in an intermediary Fe complex, leading to Fe phosphide species 7.

Accessing cationic tetrylene-nickel(0) systems featuring donor-acceptor E-Ni triple bonds (E = Ge, Sn).

We describe facile synthetic methods for accessing linear cationic tetrylene nickel(0) complexes [DippE·Ni(PPh)] (E = Ge (4) and Sn (5); Dipp = [(iPrSi)(Dipp)N]), which feature donor-acceptor E-Ni triple bonds. These species are readily accessed in a one-pot protocol, combining the bulky halo-tetrylenes DippECl (E = Ge (1) and Sn (2)), Ni(cod), PPh, and Na[BAr]. Given the diamagnetic nature of 4 and 5, they each contain a formal zero-valent Ni centre, making the E-M triple bonds in these complexes unique compared to previously reported metal tetrylidyne complexes, which typically feature covalent/ionic bonding.

Geometrically Constrained Cationic Low-Coordinate Tetrylenes: Highly Lewis Acidic σ-Donor Ligands in Catalytic Systems.

A novel non-innocent ligand class, namely cationic single-centre ambiphiles, is reported in the phosphine-functionalised cationic tetrylene Ni complexes, [ DippENi(PPh ) ] (4 a/b (Ge) and 5 (Sn); Dipp={[Ph PCH SiR ](Dipp)N} ; R=Ph, Pr; Dipp=2,6- Pr C H ). The inherent electronic nature of low-coordinate tetryliumylidenes, combined with the geometrically constrained [N-E-Ni] bending angle enforced by the chelating phosphine arm in these complexes, leads to strongly electrophilic E centres which readily bind nucleophiles, reversibly in the case of NH . Further, the Ge centre in 4 a/b readily abstracts the fluoride ion from [SbF ] to form the fluoro-germylene complex DippGe(F)Ni(PPh ) 9, despite this Ge centre simultaneously being a σ-donating ligand towards Ni .

Reversible metathesis of ammonia in an acyclic germylene-Ni complex.

Carbenes, a class of low-valent group 14 ligand, have shifted the paradigm in our understanding of the effects of supporting ligands in transition-metal reactivity and catalysis. We now seek to move towards utilizing the heavier group 14 elements in effective ligand systems, which can potentially surpass carbon in their ability to operate 'non-innocent' bond activation processes. Herein we describe our initial results towards the development of scalable acyclic chelating germylene ligands ( /), and their utilization in the stabilization of Ni complexes ( /), which can readily and reversibly undergo metathesis with ammonia with no net change of oxidation state at the Ge and Ni centres, through ammonia bonding at the germylene ligand as opposed to the Ni centre.