Nickel macrocycles with complex hydrides—new avenues for hydrogen storage research

A multifaceted approach to hydrogen storage

“…The PP 3 ligand is a chelate rather than a macrocycle, with the potentially advantageous property of enforcing a cis geometry, and is a logical next step in donor strength after amines and thioethers. It forms [NiH(PP 3 )]BF 4 by reaction with complex hydrides either in solution 85 or mechanochemical synthesis, 86 and has shown itself to be resistant to destruction even from such powerful reducing agents as LiAlH 4 .…”

Diaqua[(1R,2S,4R,8R,9S,11R)-2,9-dimethyl-1,4,8,11-tetraazacyclotetradecane]nickel(II) dichloride dihydrate

“…For uses of the title compound, see: Kimura et al (1992); Liang et al (2002); Burrows et al (1992Burrows et al ( , 1988; Kelly et al (1999); Churchard et al (2010). For the synthesis of the ligand, see: Beck & Lang (2003); Beck et al (1998.…”

Variable Borohydride Hapticity in Nickel(II) Scorpionate Complexes [(TpR,Me)Ni(ηn‐BH4)]: TpR,Me = hydrotris{3‐R‐5‐methyl‐1‐pyrazolyl}borate; R = Ph, n = 3 vs. R = Me, n = 4

“…Reactions of borohydride anion with nickel salts and complexes are of interest as routes to metal hydrides and metal borides for catalytic reduction, and hydrogenation,, , as well as H 2 storage , . A related consideration is the biological activity of nickel‐dependent hydrogenases .…”

“…The 3‐center B–H–M bonding and variable hapticity of transition metal–borohydride complexes are also relevant as models for alkane coordination at transition metal centers . Synthesis and characterization of stable nickel borohydride complexes therefore attain some importance; despite some early synthetic and spectroscopic work,, only a handful of nickel borohydride complexes have been structurally characterized , . Attention is also called to structurally characterized complexes of derivative ligands with 3‐center Ni–H–B bonds , …”

“…Aside from the foregoing discussion, an important aspect of borohydride coordination chemistry is the remarkable versatility of this anion as a ligand; it can coordinate to a single metal ion through one, two or three B–H bonds, and can also bridge between metals in an even greater variety , . The Cambridge Structural database, reports only 11 discrete examples of nickel borohydride complexes,, yet four distinct bonding modes were observed (Scheme ). The earliest structure, reported in 1978, was the diamagnetic trans ‐[(R 3 P) 2 Ni(H)(η 3 ‐BH 4 )] (R = cyclohexyl) , , .…”