Facile Si–H bond activation and hydrosilylation catalysis mediated by a nickel–borane complex

Metal–borane complexes are emerging as promising systems for study in the context of bifunctional catalysis. Herein we describe diphosphineborane nickel complexes that activate Si–H bonds and catalyze the hydrosilylation of aldehydes. Treatment of [^(Mes)DPB^(Ph)]Ni (1) ([^(Mes)DPB^Ph] = ^(Mes)B(o-Ph_2PC_6H_4)_2) with organosilanes affords the complexes [^(Mes)DPB^(Ph)](μ-H)NiE (E = SiH_2Ph (3), SiHPh_2 (4)). Complex 4 is in solution equilibrium with 1 and the thermodynamic and kinetic parameters of their exchange have been characterized by NMR spectroscopy. Complex 1 is a catalyst for the hydrosilylation of a range of para-substituted benzaldehydes. Mechanistic studies on this reaction via multinuclear NMR spectroscopy are consistent with the intermediacy of a borohydrido-Ni-siloxyalkyl species

Expanding the scope of ligand substitution from [M(S2C2Ph2] (M = Ni2+, Pd2+, Pt2+) to afford new heteroleptic dithiolene complexes

The scope of direct substitution of the dithiolene ligand from [M(S2C2Ph2)2] [M = Ni2+ (1), Pd2+ (2), Pt2+ (3)] to produce heteroleptic species [M(S2C2Ph2)2Ln] (n = 1, 2) has been broadened to include isonitriles and dithiooxamides in addition to phosphines and diimines. Collective observations regarding ligands that cleanly produce [M(S2C2Ph2)Ln], do not react at all, or lead to ill-defined decomposition identify soft σ donors as the ligand type capable of dithiolene substitution. Substitution of MeNC from [Ni(S2C2Ph2)(CNMe)2] by L provides access to a variety of heteroleptic dithiolene complexes not accessible from 1. Substitution of a dithiolene ligand from 1 involves net redox disproportionation of the ligands from radical monoanions, –S•SC2Ph2, to enedithiolate and dithione, the latter of which is an enhanced leaving group that is subject to further irreversible reactions

Deciphering the mechanism of O2 reduction with electronically tunable non-heme iron enzyme model complexes

A homologous series of electronically tuned 2,20,200-nitrilotris(N-arylacetamide) pre-ligands (H3LR) were prepared (R ¼ NO2, CN, CF3, F, Cl, Br, Et, Me, H, OMe, NMe2) and some of their corresponding Fe and Zn species synthesized. The iron complexes react rapidly with O2, the final products of which are diferric mu-oxo bridged species. The crystal structure of the oxidized product obtained from DMA solutions contain a structural motif found in some diiron proteins. The mechanism of iron mediated O2 reduction was explored to the extent that allowed us to construct an empirically consistent rate law. A Hammett plot was constructed that enabled insightful information into the rate-determining step and hence allows for a differentiation between two kinetically equivalent O2 reduction mechanisms

The impact of immediate breast reconstruction on the time to delivery of adjuvant therapy: the iBRA-2 study

Background: Immediate breast reconstruction (IBR) is routinely offered to improve quality-of-life for women requiring mastectomy, but there are concerns that more complex surgery may delay adjuvant oncological treatments and compromise long-term outcomes. High-quality evidence is lacking. The iBRA-2 study aimed to investigate the impact of IBR on time to adjuvant therapy. Methods: Consecutive women undergoing mastectomy ± IBR for breast cancer July–December, 2016 were included. Patient demographics, operative, oncological and complication data were collected. Time from last definitive cancer surgery to first adjuvant treatment for patients undergoing mastectomy ± IBR were compared and risk factors associated with delays explored. Results: A total of 2540 patients were recruited from 76 centres; 1008 (39.7%) underwent IBR (implant-only [n = 675, 26.6%]; pedicled flaps [n = 105,4.1%] and free-flaps [n = 228, 8.9%]). Complications requiring re-admission or re-operation were significantly more common in patients undergoing IBR than those receiving mastectomy. Adjuvant chemotherapy or radiotherapy was required by 1235 (48.6%) patients. No clinically significant differences were seen in time to adjuvant therapy between patient groups but major complications irrespective of surgery received were significantly associated with treatment delays. Conclusions: IBR does not result in clinically significant delays to adjuvant therapy, but post-operative complications are associated with treatment delays. Strategies to minimise complications, including careful patient selection, are required to improve outcomes for patients

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Synthesis and reactivity of novel iron complexes supported by neutral tris(phosphino)borane ligands

Of central importance to elucidating iron's role in biol. nitrogen fixation are the accessible geometries and oxidn. states of proposed iron intermediates. Our group has an ongoing interest in exploring the chem. of Fe- N_xH_y species and have successfully described terminal imide and nitride species supported by anionic tris(phosphino)borate ligands as well as terminal N_2 complexes stabilized by anionic tris(phosphino)silyl ligands in pseudo-tetrahedral and trigonal-bipyramidal geometries, resp. A single ligand scaffold capable of stabilizing low-valent complexes with a π-acidic N_2 mol., as well as high-valent complexes with a π-basic nitride ligand would certainly be of interest; accordingly, the synthesis of a series of iron complexes supported by the neutral tris(phosphino)borane ligand, [TPB^R] ([TPB^R] = (o-(R_2P)C_6H_4)_3B), R = iPr, Ph) will be presented and their structures and chem. reactivity discussed within the context of the hemi-lability of the apical Lewis-acidic borane

{N,N-Bis[2-(trimethylsilylamino)ethyl]-N′-(trimethylsilyl)ethane-1,2-diaminato(3–)-κ4N}methylzirconium(IV)

The title compound, [Zr(CH3)(C15H39N4Si3)], is a unique example of a triamidoamine-supported zirconium–methyl complex that crystallized as a monomer with trigonal–bipyramidal geometry at zirconium, featuring a Zr—C bond of 2.2963 (16) Å

A Facially Coordinating Tris-Benzimidazole Ligand for Nonheme Iron Enzyme Models

This work describes the synthesis and characterization of new ligands and iron complexes for mononuclear nonheme iron oxygenase structural models