A nickel bis(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni(P(Cy)2N(t-Bu)2)2](BF4)2 (P(Cy)2N(t-Bu)2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the Ni(II) complex gives three isomers of the doubly protonated Ni(0) complex [Ni(P(Cy)2N(t-Bu)2H)2](BF4)2. Using the pKa values and Ni(II/I) and Ni(I/0) redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni(P(Cy)2N(t-Bu)2)2](2+) was determined to be -7.9 kcal mol(-1). The catalytic rate observed in dry acetonitrile for the oxidation of H2 depends on base size, with larger bases (NEt3, t-BuNH2) resulting in much slower catalysis than n-BuNH2. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt3 and t-BuNH2. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H2 using n-BuNH2 as a base and with added water, a turnover frequency of 58 s(-1) is observed at 23 °C.

Three paramagnetic heterobimetallic lantern complexes of the form [PtM(tba) 4 (OH 2 )] (M ¼ Fe, 1; Co, 2; Ni, 3; tba ¼ thiobenzoate) have been prepared in a single-step, bench-top procedure. In all three cases, a lantern structure with Pt-M bonding is observed in solution and in the solid state. Compound 1 is a monomer whereas 3 exists as a dimer in the solid state via a Pt/Pt metallophilic interaction. Compound 2 has been characterized in forms with (2a, purple) and without (2b, yellow) Pt/Pt metallophilic interactions. The dimers 2a (J ¼ À10 cm À1 , based on the spin Hamiltonian Ĥ ¼ À2J (S A $S B )) and 3 (J ¼ À60 cm À1 ) exhibit antiferromagnetic coupling between the two first-row metal ions in the solid state via a Pt/Pt non-covalent metallophilic interaction. The electronic structure ofNi, units have been studied with DFT calculations, confirming the relative spin-state energies observed and the antiferromagnetic exchange pathway through four d z 2 orbitals. The compounds 2a and 3 are the first examples of antiferromagnetic coupling through an unbridged M/M contact.

We report a synthetic nickel complex containing proton relays, [Ni(P(Ph)2N(C6H4OH)2)2](BF4)2 (P(Ph)2N(C6H4OH)2 = 1,5-bis(p-hydroxyphenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclo-octane), that catalyzes the production of H2 in aqueous acetonitrile with turnover frequencies of 750-170,000 s(-1) at experimentally determined overpotentials of 310-470 mV.

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