Enhancement of London Dispersion in Frustrated Lewis Pairs: Towards a Crystalline Encounter Complex

The encounter complex, i.e., the pre-organized assembly consisting of a Lewis acid and a Lewis base, is a fundamental concept in frustrated Lewis pair (FLP) chemistry. However, this donor acceptor complex is challenging to study due to its transient nature. Here, we present a combined theoretical and experimental investigation on the potential isolation of an encounter complex enabled by enhancement of London dispersion forces between a sterically encumbered Lewis acid and base pair. Guided by computational analyses, the FLP originating from the bulky triarylamine N(3,5-tBu2C6H3)3 and the novel triarylborane B(3,5-tBu2C6H3)3 was investigated, leading to the isolation of at 1:1 co-crystal of both FLP components

Enlightening developments in 1,3-P,N-ligand-stabilized multinuclear complexes:A shift from catalysis to photoluminescence

1,3-P,N-ligands provide the ideal spatial separation to facilitate homo and hetero metal-metal interactions to access multinuclear complexes. The rich chemistry of such complexes includes applications in coordination chemistry, metal-activation and (cooperative) catalysis. However, it has been especially the fruitful combination in photoluminescent P,N-coinage metal complexes which has renewed interest in these ligands. While the field classically focused on dinuclear species, now also coinage metal clusters have been studied for use in catalysis and photophysical applications. Reviewed are recent developments from 2009 to mid-2017

Atypical and Asymmetric 1,3-P,N Ligands : Synthesis, Coordination and Catalytic Performance of Cycloiminophosphanes

Novel seven-membered cyclic imine-based 1,3-P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These "cycloiminophosphanes" possess flexible non-isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P-kappa(1)- and P,N-kappa(2)-tungsten(0) carbonyl complexes, by determining the IR frequency of the trans-CO ligands. Complexes with [RhCp*Cl-2](2) demonstrated the hemilability of the ligands, giving a dynamic equilibrium of kappa(1) and kappa(2) species; treatment with AgOTf gives full conversion to the kappa(2) complex. The potential for catalysis was shown in the Ru-II-catalyzed, solvent-free hydration of benzonitrile and the Ru-II- and Ir-I-catalyzed transfer hydrogenation of cyclohexanone in isopropanol. Finally, to enable access to asymmetric catalysts, chiral cycloiminophosphanes were prepared from l-menthone, as well as their P,N-kappa(2)-Rh-III and a P-kappa(1)-Ru-II complexes.Peer reviewe

Base-Stabilized Nitrilium Ions as Convenient Imine Synthons

A simple and efficient methodology is presented for the synthesis of a wide range of substituted imines. It is based on stabilizing readily available, but thermally labile, <i>N</i>-alkylnitrilium triflates with pyridine or DMAP to moderately air-stable adducts. These base-stabilized imine synthons react conveniently with phosphorus- and nitrogen-based nucleophiles to amidines and phosphaamidines