Triple-Decker Iron and Cobalt Complexes Featuring a Bridging 1,2-Diboratabenzene Ligand.

Neutral triple-decker iron and cobalt complexes with a bridging 1,2-diboratabenzene ligand were accessed by reactions of a dilithium 1,2-diboratabenzene reagent with [Cp*FeCl] and [Cp*CoCl], respectively. While 1,2-diboratabenzene metal complexes are known, these represent the first examples of the ligand bridging two metals.

Unlocking metal coordination of diborylamides through ring constraints.

A cyclic lithium diborylamide compound was synthesized and crystallographically characterized, revealing strong Li-N bonding in sharp contrast to previous linear diborylamides. Two iron(II) diborylamide complexes were also synthesized, including a 2-coordinate Fe bis(diborylamide) complex. The present cyclic diborylamide represents a new addition to the growing scope of amide ligands.

Electrochemical C-H bond activation cationic iridium hydride pincer complexes.

A C-H bond activation strategy based on electrochemical activation of a metal hydride is introduced. Electrochemical oxidation of ( PCP)IrH ( PCP is [1,3-( BuPCH)-CH]) in the presence of pyridine derivatives generates cationic Ir hydride complexes of the type [( PCP)IrH(L)] (where L = pyridine, 2,6-lutidine, or 2-phenylpyridine). Facile deprotonation of [( PCP)IrH(2,6-lutidine)] with the phosphazene base -butylimino-tris(pyrrolidino)phosphorane, BuP(pyrr), results in selective C-H activation of 1,2-difluorobenzene (1,2-DFB) solvent to generate ( PCP)Ir(H)(2,3-CFH).

Mechanism of Chemical and Electrochemical N Splitting by a Rhenium Pincer Complex.

A comprehensive mechanistic study of N activation and splitting into terminal nitride ligands upon reduction of the rhenium dichloride complex [ReCl(PNP)] is presented (PNP = N(CHCHP tBu)). Low-temperature studies using chemical reductants enabled full characterization of the N-bridged intermediate [{(PNP)ClRe}(N)] and kinetic analysis of the N-N bond scission process. Controlled potential electrolysis at room temperature also resulted in formation of the nitride product [Re(N)Cl(PNP)].

A Ruthenium Hydrido Dinitrogen Core Conserved across Multielectron/Multiproton Changes to the Pincer Ligand Backbone.

A series of ruthenium(II) hydrido dinitrogen complexes supported by pincer ligands in different formal oxidation states have been prepared and characterized. Treating a ruthenium dichloride complex supported by the pincer ligand bis(di-tert-butylphosphinoethyl)amine (H-PNP) with reductant or base generates new five-coordinate cis-hydridodinitrogen ruthenium complexes each containing different forms of the pincer ligand. Further ligand transformations provide access to the first isostructural set of complexes featuring all six different forms of the pincer ligand.

Ammonia Synthesis from a Pincer Ruthenium Nitride via Metal-Ligand Cooperative Proton-Coupled Electron Transfer.

The conversion of metal nitride complexes to ammonia may be essential to dinitrogen fixation. We report a new reduction pathway that utilizes ligating acids and metal-ligand cooperation to effect this conversion without external reductants. Weak acids such as 4-methoxybenzoic acid and 2-pyridone react with nitride complex [(H-PNP)RuN] (H-PNP = HN(CHCHPBu)) to generate octahedral ammine complexes that are κ-chelated by the conjugate base.

Efficient Bimolecular Mechanism of Photochemical Hydrogen Production Using Halogenated Boron-Dipyrromethene (Bodipy) Dyes and a Bis(dimethylglyoxime) Cobalt(III) Complex.

A series of Boron-dipyrromethene (Bodipy) dyes were used as photosensitizers for photochemical hydrogen production in conjunction with [Co(III)(dmgH)2pyCl] (where dmgH = dimethylglyoximate, py = pyridine) as the catalyst and triethanolamine (TEOA) as the sacrificial electron donor. The Bodipy dyes are fully characterized by electrochemistry, X-ray crystallography, quantum chemistry calculations, femtosecond transient absorption, and time-resolved fluorescence, as well as in long-term hydrogen production assays. Consistent with other recent reports, only systems containing halogenated chromophores were active for hydrogen production, as the long-lived triplet state is necessary for efficient bimolecular electron transfer.

Neutral Fe(IV) alkylidenes, including some that bind dinitrogen.

Neutral, formally Fe(IV) alkylidene species are sought as plausible olefin metathesis catalysts, and the synthesis of several is described herein. The complexes are prepared via nucleophilic attack (Nu = MeLi, PhCH2K, 2-picolyllithium, Me2PCH2Li, MePhPCH2Li, Ph2PCH2Li) at the imine of cationic [mer-{κ-C,N,C-(C6H4-yl)-2-CH=N(2-C6H4-C(iPr)=)}Fe(PMe3)3][B(3,5-CF3-C6H3)4]. In contrast, MeMgCl and mesityllithium displaced and deprotonated bound PMe3, respectively.

Fe(iv) alkylidenes protonation of Fe(ii) vinyl chelates and a comparative Mössbauer spectroscopic study.

Treatment of -MeFe(PMe) with di-1,2-(-2-(pyridin-2-yl)vinyl)benzene ((bdvp)H), a tetradentate ligand precursor, afforded (bdvp)Fe(PMe) (-PMe) and 2 equiv. CH, C-H bond activation. Similar treatments with tridentate ligand precursors PhCH[double bond, length as m-dash]NCH(-CH[double bond, length as m-dash]CHPh) ((pipp)H) and PhCH[double bond, length as m-dash]N(2-CCMe-Ph) ((pipa)H) under dinitrogen provided -(pipp)Fe(PMe)N () and -(pipvd)Fe(PMe)N (), respectively; the latter one C-H bond activation, and a subsequent insertion of the alkyne into the remaining Fe-Me bond.

Making hydrogen from water using a homogeneous system without noble metals.

A photocatalytic noble metal-free system for the generation of hydrogen has been constructed using Eosin Y (1) as a photosensitizer, the complex [Co(dmgH)(2)pyCl](2+) (5, dmgH = dimethylglyoximate, py = pyridine) as a molecular catalyst, and triethanolamine (TEOA) as a sacrificial reducing agent. The system produces H(2) with an initial rate of approximately 100 turnovers per hour upon irradiation with visible light (lambda > 450 nm). Addition of free dmgH(2) greatly increases the durability of the system addition of 12 equiv of dmgH(2) (vs cobalt) to the system produces approximately 900 turnovers of H(2) after 14 h of irradiation.