Ligand design for site-selective installation of Pd and Pt centers to generate homo- and heteropolymetallic motifs

The modular synthesis of a series of nitrogen-rich polydentate ligands that feature a common pincer-type framework is reported. These ligands allow for site-selective installation of palladium and platinum to give rise to bi- and trimetallic complexes that have d^(8)–d^(8) interactions

Non-Markovian Quantum State Diffusion for Temperature-Dependent Linear Spectra of Light Harvesting Aggregates

Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism) no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators.Comment: 14 pages, 4 figure

A CO-Derived Iron Dicarbyne That Releases Olefin upon Hydrogenation

An iron diphosphineborane platform that was previously reported to facilitate a high degree of N_2 functionalization is herein shown to effect reductive CO coupling. Disilylation of an iron dicarbonyl precursor furnishes a structurally unprecedented iron dicarbyne complex. Several complexes related to this process are also characterized which allows for a comparative analysis of their respective Fe–B and Fe–C bonding. Facile hydrogenation of the iron dicarbyne at ambient temperature and 1 atm H_2 results in release of a CO-derived olefin

H–H and Si–H Bond Addition to Fe≡NNR_2 Intermediates Derived from N_2

The synthesis and characterization of Fe–diphosphineborane complexes are described in the context of N_2 functionalization chemistry. Iron aminoimides can be generated at room temperature under 1 atm N_2 and are shown to react with E–H bonds from PhSiH_3 and H_2. The resulting products derive from delivery of the E fragment to Nα and the H atom to B. The flexibility and lability of the Fe–BPh interactions in these complexes engender this reactivity

Regulation of nitric oxide signaling by formation of a distal receptor-ligand complex.

The binding of nitric oxide (NO) to the heme cofactor of heme-nitric oxide/oxygen binding (H-NOX) proteins can lead to the dissociation of the heme-ligating histidine residue and yield a five-coordinate nitrosyl complex, an important step for NO-dependent signaling. In the five-coordinate nitrosyl complex, NO can reside on either the distal or proximal side of the heme, which could have a profound influence over the lifetime of the in vivo signal. To investigate this central molecular question, we characterized the Shewanella oneidensis H-NOX (So H-NOX)-NO complex biophysically under limiting and excess NO conditions. The results show that So H-NOX preferably forms a distal NO species with both limiting and excess NO. Therefore, signal strength and complex lifetime in vivo will be dictated by the dissociation rate of NO from the distal complex and the rebinding of the histidine ligand to the heme

Reactions of Small Molecules Facilitated by Metal-Acceptor Interactions

The role of metal-acceptor interactions arising from M–BR3 and M–PR3 bonding is discussed with respect to reactions between first-row transition metals and N2, H2, and CO. Thermally robust, S = 1/2 (TPB)Co(H2) and (TPB)Co(N2) complexes (TPB = tris(2- (diisopropylphosphino)phenyl)borane) are described and the energetics of N2 and H2 binding are measured. The H2 and N2 ligands are bound more weakly in the (TPB)Co complexes than in related (SiP3)M(L) complexes (SiP3 = tris(2- (diisopropylphosphino)phenyl)silyl). Comparisons within and between these two ligand platforms allow for the factors that affect N2 (and H2) binding and activation to be delineated. The characterization and reactivity of (DPB)Fe complexes (DPB = bis(2- (diisopropylphosphino)phenyl)phenylborane) in the context of N2 functionalization and E–H bond addition (E = H, C, N, Si) are described. This platform allows for the one-pot transformation of free N2 to an Fe hydrazido(-) complex via an Fe aminoimide intermediate. The principles learned from the N2 chemistry using (DPB)Fe are applied to CO reduction on the same system. The preparation of (DPB)Fe(CO)2 is described as well as its reductive functionalization to generate an unprecedented Fe dicarbyne. The bonding in this highly covalent complex is discussed in detail. Initial studies of the reactivity of the Fe dicarbyne reveal that a CO-derived olefin is released upon hydrogenation. Alternative approaches to uncovering unusual reactivity using metal- acceptor interactions are described in Chapters 5 and 6, including initial studies on a new π-accepting tridentate diphosphinosulfinyl ligand and strategies for designing ligands that undergo site-selective metallation to generate heterobimetallic complexes

Evaluating Molecular Cobalt Complexes for the Conversion of N_2 to NH_3

We report a molecular Co−N_2 complex that generates a greater-than-stoichiometric yield of NH_3 (>200% NH_3 per Co−N_2 precursor) via the direct reduction of N_2 with protons and electrons. A comparison of the featured Co−N_2 complex with structurally related Co−N_2 and Fe−N_2 species shows how remarkably sensitive the N_2 reduction performance of potential precatalysts is. As discussed, structural and electronic effects are relevant to Co/Fe−N_2 conversion activity, including π basicity, charge state, and geometric flexibility