Utilising a Proton-Responsive 1,8-Naphthyridine Ligand for the Synthesis of Bimetallic Palladium and Platinum Complexes.

We present four proton-responsive palladium and platinum complexes, [MCl2 (R PONNHO)] (M=Pd, Pt; R=i Pr, t Bu) synthesised by complexation of PdCl2 or PtCl2 (COD) with the 1,8-naphthyridine ligand R PONNHO. Deprotonation of [MCl2 (tBu PONNHO)] switches ligand coordination from mono- to dinucleating, offering a synthetic pathway to bimetallic PdII and PtII complexes [M2 Cl2 (tBu PONNO)2 ]. Two-electron reduction gives planar MI -MI complexes [M2 (tBu PONNO)2 ] (M=Pd, Pt) containing a metal-metal bond. In contrast to the related nickel system that forms a metallophosphorane [Ni2 (tBu PONNOPONNO)], an unusual phosphinite binding mode is observed in [M2 (tBu PONNO)2 ] containing close phosphinite-naphthyridinone P⋅⋅⋅O interactions, which is investigated spectroscopically, crystallographically and computationally. The presented proton-responsive and structurally-responsive R PONNHO and bimetallic R PONNO complexes offer a novel platform for future explorations of metal-ligand and metal-metal cooperativity with palladium and platinum.

Oxidative Addition and ß-Hydride Elimination by a Macrocyclic Dinickel Complex: Observing Bimetallic Elementary Reactions.

The dinickel(I) complex Ni2 (tBu PONNOPONNO), featuring a planar macrocyclic diphosphoranide ligand tBu PONNOPONNO, offers a unique architectural platform for observing bimetallic elementary reactions. Oxidative addition reactions of alkyl halides produce dinickel(II) complexes of the type Ni2 (µ-R)(µ-X)(tBu PONNOPONNO). However, when R=Et ß-hydride elimination is observed to form a dinickel monohydride, with the rate dependent on the nature of X. DFT studies suggest a new mechanism for bimetallic ß-hydride elimination, where the rate dependence arises from the steric pressure imposed by the X group on the opposing trans face of the dinickel macrocycle. This work enhances understanding of bimetallic elementary reactions, particularly ß-hydride elimination, which have not been well-explored for dinuclear systems.

Bimetallic Nickel Complexes Supported by a Planar Macrocyclic Diphosphoranide Ligand.

Metal-metal cooperativity is emerging as an important strategy in catalysis. This requires appropriate ligand scaffolds that can support two metals in close proximity. Here we report nickel-promoted formation of a dinucleating planar macrocyclic ligand that can support bimetallic dinickel(II) and dinickel(I) complexes. Reaction outcomes can be tuned by variation of the substituents and reaction conditions to favour dinucleating macrocyclic, mononucleating macrocyclic or conventional pincer architectures.

Correction to "Substrate Dynamics Contribute to Enzymatic Specificity in Human and Bacterial Methionine Adenosyltransferases".

[This corrects the article DOI: 10.1021/jacsau.1c00464.].

Synthesis of an expanded pincer ligand and its bimetallic coinage metal complexes.

An expanded pincer ligand tBu-PONNOP (2,7-bis(di-tert-butylphosphinito)-1,8-naphthyridine) has been synthesised and its coordination to coinage metals has been studied. Bimetallic complexes were produced with metal halide salts of the type [M2X2(tBu-PONNOP)] (X = Cl, M = Au, Ag, Cu; X = I, M = Cu) with a varying degree of interaction with the naphthyridyl backbone in the order Au < Ag < Cu. The salts [Ag2(tBu-PONNOP)2][BArF4]2 (ArF = 3,5-C6H3(CF3)2) and [Ag2(NCMe)2(tBu-PONNOP)]X2 (X = BArF4, PF6) were prepared, which may serve as a source of tBu-PONNOP via transmetallation.

Substrate Dynamics Contribute to Enzymatic Specificity in Human and Bacterial Methionine Adenosyltransferases.

Protein conformational changes can facilitate the binding of noncognate substrates and underlying promiscuous activities. However, the contribution of substrate conformational dynamics to this process is comparatively poorly understood. Here, we analyze human (hMAT2A) and Escherichia coli (eMAT) methionine adenosyltransferases that have identical active sites but different substrate specificity. In the promiscuous hMAT2A, noncognate substrates bind in a stable conformation to allow catalysis. In contrast, noncognate substrates sample stable productive binding modes less frequently in eMAT owing to altered mobility in the enzyme active site. Different cellular concentrations of substrates likely drove the evolutionary divergence of substrate specificity in these orthologues. The observation of catalytic promiscuity in hMAT2A led to the detection of a new human metabolite, methyl thioguanosine, that is produced at elevated levels in a cancer cell line. This work establishes that identical active sites can result in different substrate specificity owing to the effects of substrate and enzyme dynamics.

Metal coordination to a dimetallaoctatetrayne.

The reactions of the ditungstaoctatetrayne [(Tp*)(CO)2W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])W(CO)2(Tp*)] with several metal complexes have been investigated. Addition of [Co2(CO)8] occurs across the internal C[triple bond, length as m-dash]C bonds, whereas [AuCl(SMe2)] initially delivers 'AuCl' across the W[triple bond, length as m-dash]C carbyne bonds before undergoing further reaction to oxidise the tungsten and replace the carbonyl ligands with chloride in [(Tp*)Cl2W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])WCl2(Tp*)] with retention of the ditungstaoctatetrayne bridge. Reaction with [AuCl(PR3)] (R = Ph, Cy) in the presence of AgPF6 prevents this oxidation and adds [AuPR3]+ across the W[triple bond, length as m-dash]C bonds to give dicationic derivatives. Finally, the reaction with [Pt(nbe)3] (nbe = norbornene, bicyclo[2.2.1]hept-2-ene) and 1,5-cyclooctadiene (COD) adds a 'Pt(COD)' unit to one or both tungsten-carbon bonds, allowing both the mono- and diplatinum complexes to be isolated.