Metal Complexes (M = Zn, Sn, and Pb) of 2-Phosphinobenzenethiolates: Insights into Ligand Folding and Hemilability

Electrocatalytic syngas generation with a redox non-innocent cobalt 2-phosphinobenzenethiolate complex

A cobalt complex supported by the 2-(diisopropylphosphaneyl)benzenethiol ligand was synthesized and its electronic structure and reactivity were explored. X-ray diffraction studies indicate a square planar geometry around the cobalt center with a trans arrangement of the phosphine ligands. Density functional theory calculations and electronic spectroscopy measurements suggest a mixed metal-ligand orbital character, in analogy to previously studied dithiolene and diselenolene systems. Electrochemical studies in the presence of 1 atm of CO₂ and Brønsted acid additives indicate that the cobalt complex generates syngas, a mixture of H₂ and CO, with faradaic efficiencies up to >99%. The ratios of H₂ : CO generated vary based on the additive. A H₂ : CO ratio of ∼3 : 1 is generated when H₂O is used as the Brønsted acid additive. Chemical reduction of the complex indicates a distortion towards a tetrahedral geometry, which is rationalized with DFT predictions as attributable to the populations of orbitals with σ*(Co-S) character. A mechanistic scheme is proposed whereby competitive binding between a proton and CO₂ dictates selectivity. This study provides insight into the development of a catalytic system incorporating non-innocent ligands with pendant base moieties for electrochemical syngas production.

Reaction of stannylene phosphorus Lewis pairs with dichlorides of germanium, tin and lead - the formation of base stabilized stannyl stannylenes/germylenes and redox reaction with PbCl2

The reaction of intramolecular stannylene phosphorus Lewis pairs with heavier dichlorides of group 14 (GeCl2, SnCl2, PbCl2) is reported. Phosphine base stabilized stannyl germylenes/stannylenes were formed by the oxidative addition of an E-Cl bond to the stannylene tin atom (E = Ge, Sn). In solution, a dynamic equilibrium between two diastereomeric configurations was observed. With PbCl2 a redox reaction towards elemental lead and the dichlorinated tin(iv) compound was found. All compounds were characterized by X-ray diffraction, NMR spectroscopy and elemental analysis.

Hemilability-Driven Water Activation: A NiII Catalyst for Base-Free Hydration of Nitriles to Amides

The Ni^II complex 1 containing pyridyl- and hydroxy-functionalized N-heterocyclic carbenes (NHCs) is synthesized and its catalytic utility for the selective nitrile hydration to the corresponding amide under base-free conditions is evaluated. The title compound exploits a hemilabile pyridyl unit to interact with a catalytically relevant water molecule through hydrogen-bonding and promotes a nucleophilic water attack to the nitrile. A wide variety of nitriles is hydrated to the corresponding amides including the pharmaceutical drugs rufinamide, Rifater, and piracetam. Synthetically challenging α-hydroxyamides are accessed from cyanohydrins under neutral conditions. Related catalysts that lack the pyridyl unit (i.e., compounds 2 and 4) are not active whereas those containing both the pyridyl and the hydroxy or only the pyridyl pendant (i.e., compounds 1 and 3) show substantial activity. The linkage isomer 1' where the hydroxy group is bound to the metal instead of the pyridyl group was isolated under different crystallization conditions insinuating a ligand hemilabile behavior. Additional pK_a measurements reveal an accessible pyridyl unit under the catalytic conditions. Kinetic studies support a ligand-promoted nucleophilic water addition to a metal-bound nitrile group. This work reports a Ni-based catalyst that exhibits functional hemilability for hydration chemistry.

Chirality at metal and helical ligand folding in optical isomers of chiral bis(naphthaldiminato)nickel(ii) complexes

Ni-Schiff base complexes combine ligand chirality, chirality at metal, and helical ligand folding in a concerted way.

Lead(II) nitrate and hexafluorosilicate complexes with neutral diphosphine coordination

Rare examples of phosphine complexes of lead(II) are reported. The reaction of Pb(NO3)2 with Me2P(CH2)2PMe2, o-C6H4(PMe2)2 or Et2P(CH2)2PEt2 (L-L) in H2O/MeCN gave white [Pb(L-L)(NO3)2], irrespective of the ratio of reagents used. The X-ray structures of [Pb{Me2P(CH2)2PMe2}(NO3)2] and [Pb{o-C6H4(PMe2)2}(NO3)2] reveal chelating diphosphines and κ(2)-NO3(-) groups occupying one hemisphere about the lead centre with single oxygen bridges to two further nitrate groups from neighbouring molecules completing a distorted eight-coordinate geometry. Using Pb(SiF6)·2H2O produced [Pb{o-C6H4(PMe2)2}(H2O)(SiF6)]·H2O which has a chelating diphosphine, the water molecule and a coordinated SiF6(2-) group (which could be described as either κ(1)- or asymmetric κ(3)-coordinated to the lead), with further Pb-F interactions to neighbouring molecules producing a chain polymer structure. The structure of [Pb{o-C6H4(PMe2)2}(DMF)2(SiF6)]·DMF was also determined and contains dimers with fluorosilicate bridges. Adventitious oxygen readily form diphosphine dioxide complexes, and the structures of [Pb{Et2(O)P(CH2)2P(O)Et2}2(NO3)2] and [Pb{Me2P(CH2)2PMe2}{Me2(O)P(CH2)2P(O)Me2}][BF4]2·½MeNO2 produced in this way were determined. The former contains eight-coordinate lead with κ(2)-NO3(-) groups and bridging diphosphine dioxides, which results in an infinite polymer. In the latter the diphosphine is chelated but the diphosphine dioxide bridges between Pb(ii) centres, with coordinated BF4(-) groups completing a very distorted ten-coordinate moiety. Attempts to isolate similar complexes with o-C6H4(PPh2)2 or o-C6H4(AsMe2)2 were unsuccessful.