Hydrogen is the most promising fuel of the future owing to its carbon-free, high-energy content and potential to be efficiently converted into either electrical or thermal energy. The greatest technical barrier to accessing this renewable resource remains the inability to create inexpensive catalysts for the solar-driven oxidation of water. To date, the most efficient system that uses solar energy to oxidize water is the photosystem II water-oxidizing complex (PSII-WOC), which is found within naturally occurring photosynthetic organisms. The catalytic core of this enzyme is a CaMn(4)O(x) cluster, which is present in all known species of oxygenic phototrophs and has been conserved since the emergence of this type of photosynthesis about 2.5 billion years ago. The key features that facilitate the catalytic success of the PSII-WOC offer important lessons for the design of abiological water oxidation catalysts. In this Account, we examine the chemical principles that may govern the PSII-WOC by comparing the water oxidation capabilities of structurally related synthetic manganese-oxo complexes, particularly those with a cubical Mn(4)O(4) core ("cubanes"). We summarize this research, from the self-assembly of the first such clusters, through the elucidation of their mechanism of photoinduced rearrangement to release O(2), to recent advances highlighting their capability to catalyze sustained light-activated electrolysis of water. The [Mn(4)O(4)](6+) cubane core assembles spontaneously in solution from monomeric precursors or from [Mn(2)O(2)](3+) core complexes in the presence of metrically appropriate bidentate chelates, for example, diarylphosphinates (ligands of Ph(2)PO(2)(-) and 4-phenyl-substituted derivatives), which bridge pairs of Mn atoms on each cube face (Mn(4)O(4)L(6)). The [Mn(4)O(4)](6+) core is enlarged relative to the [Mn(2)O(2)](3+) core, resulting in considerably weaker Mn-O bonds. Cubanes are ferocious oxidizing agents, stronger than analogous complexes with the [Mn(2)O(2)](3+) core, as demonstrated both by the range of substrates they dehydrogenate or oxygenate (unactivated alkanes, for example) and the 25% larger O-H bond enthalpy of the resulting mu(3)-OH bridge. The cubane core topology is structurally suited to releasing O(2), and it does so in high yield upon removal of one phosphinate by photoexcitation in the gas phase or thermal excitation in the solid state. This is quite unlike other Mn-oxo complexes and can be attributed to the elongated Mn-O bond lengths and low-energy transition state to the mu-peroxo precursor. The photoproduct, [Mn(4)O(2)L(5)](+), an intact nonplanar butterfly core complex, is poised for oxidative regeneration of the cubane core upon binding of two water molecules and coupling to an anode. Catalytic evolution of O(2) and protons from water exceeding 1000 turnovers can be readily achieved by suspending the oxidized cubane, [Mn(4)O(4)L(6)](+), into a proton-conducting membrane (Nafion) preadsorbed onto a conducting electrode and electroxidizing the photoreduced butterfly...

A sequence of alkene complexes of platinum, PtCl(2)(PPh(3))(alkene) (alkene = ethylene, propene, 1-butene, cis-2-butene, 1-hexene, 1-octene, and 1-decene), has been prepared. These complexes are characterized by NMR spectroscopy, including assignment of each proton, and X-ray crystal structures of the 1-propene and 1-hexene complexes. Each complex was reacted with diethylamine. For the 1-hexene, 1-octene, and 1-decene complexes, the amine displaces the alkene. For the smaller alkenes, the diethylamine nucleophilically attacks the coordinated alkene. For propene and 1-butene, the low-temperature addition leads to the anti-Markovnikoff nucleophilic attack, which slowly converts at room temperature to the Markovnikoff product. The transformation from anti-Markovnikoff to Markovnikoff addition occurs without diethylamine dissociation.

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The compound Fe[N(SiMe 3) 2] 2 is shown to be a useful precursor to dinuclear and trinuclear iron-sulfur-silylamido complexes by reaction with thiols or thiols and sulfur in tetrahydrofuran (THF) or toluene. Reaction with 1 equiv of p-tolylthiol affords [Fe 2(mu 2-S- p-tol) 2(N(SiMe 3) 2) 2(THF) 2] ( 1); with 0.5 equiv of adamantane-1-thiol, [Fe 2(mu 2-S-1-Ad)(mu 2-N(SiMe 3) 2)(N(SiMe 3) 2) 2] ( 2) is formed. The clusters [Fe 3(mu 3-Q)(mu 2-SR) 3(N(SiMe 3) 2) 3] are available by three methods: (i) self-assembly in the systems Fe[N(SiMe 3) 2] 2/RSH/S or Se [Q = S, R = p-tol ( 3) and 1-Ad ( 5)]; (ii) reaction of 1 with Q = S or Se to yield 3 or [Fe 3Se(S- p-tol) 3(N(SiMe 3) 2) 3] ( 4); (iii) reaction of 2 with 1-AdSH and S to give 5. Structures of 1- 5 are presented. Complexes 1 and 2 contain planar Fe 2S 2 and Fe 2SN rhombs. Clusters 3- 5 contain a mixed-valence Fe 3Q(SR) 3 core with trigonal (cuboidal) geometry. Of known iron-sulfur clusters, these most closely resemble previously reported [Fe 3S(S-R-S) 3] (2-) stabilized by bidentate thiolate ligands. Complexes 1- 5, together with a small set of recently described clusters of nuclearities 2, 4, and 8, constitute a new class of iron-sulfur-silylamido clusters. Complexes 3- 5 constitute a new structure type of mixed-valence iron-sulfur clusters.

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