[Cp2TiNi(S2N2)2] – The First Organometallic Derivative of [Ni(S2N2H)2]

The synthesis and structural characterization of the first organometallic derivative of [Ni(S₂N₂H)₂] ( 1 ) are reported. Treatment of K₂[Ni(S₂N₂)₂] ( 2 ) with stoichiometric amounts of [Cp₂TiCl₂] in boiling toluene afforded black, crystalline [Cp₂TiNi(S₂N₂)₂] ( 3 ) in 50 % yield. According to a single‐crystal X‐ray diffraction study, the novel heterobimetallic complex 3 comprises a nearly planar TiNi(S₂N₂)₂ arrangement. The Ti···Ni separation in 3 is 2.8348(5) Å, a value that is typical for bridged early‐late heterobimetallic complexes.     

In search of the [PhB(mu-N(t)Bu)2]2As. radical: experimental and computational investigations of the redox chemistry of group 15 bis-boraamidinates

DFT calculations for the group 15 radicals [PhB(mu-N(t)Bu)2]2M. (M = P, As, Sb, Bi) predict a pnictogen-centered SOMO with smaller contributions to the unpaired spin density arising from the nitrogen and boron atoms. The reactions of Li 2[PhB(mu-NR)2] (R = (t)Bu, Dipp) with PCl 3 afforded the unsolvated complex LiP[PhB(mu-N(t)Bu)2] 2 ( 1a) in low yield and ClP[PhB(mu-NDipp)2] (2), both of which were structurally characterized. Efforts to produce the arsenic-centered neutral radical, [PhB(mu-N (t) Bu) 2] 2As., via oxidation of LiAs[PhB(mu-N(t)Bu)2]2 with one-half equivalent of SO 2Cl 2, yielded the Zwitterionic compound [PhB(mu-N (t) Bu) 2As(mu-N(t)Bu)2B(Cl)Ph] (3) containing one four-coordinate boron center with a B-Cl bond. The reaction of 3 with GaCl3 produced the ion-separated salt, [PhB(mu-N(t)Bu)2] 2As (+)GaCl 4 (-) ( 4), which was characterized by X-ray crystallography. The reduction of 3 with sodium naphthalenide occurred by a two-electron process to give the corresponding anion [{PhB(mu-N(t)Bu)2} 2As] (-) as the sodium salt. Voltammetric investigations of 4 and LiAs[PhB(mu-N (t) Bu) 2] 2 ( 1b) revealed irreversible processes. Attempts to generate the neutral radical [PhB(mu-N(t)Bu)2] 2As. from these ionic complexes via in situ electrolysis did not produce an EPR-active species.     

Ni[(EPiPr2)2N]2 complexes: stereoisomers (E = Se) and square-planar coordination (E = Te)

The reaction of ((i)Pr 2PE) 2NM.TMEDA (M = Li, E = Se; M = Na, E = Te) with NiBr 2.DME in THF affords Ni[(SeP (i)Pr 2) 2N] 2 as either square-planar (green) or tetrahedral (red) stereoisomers, depending on the recrystallization solvent; the Te analogue is obtained as the square-planar complex Ni[(TeP (i)Pr 2) 2N] 2.     

PCP-bridged chalcogen-centred anions: coordination chemistry and carbon-based reactivity

Since the discovery of the stabilising influence of thiophosphinoyl groups in methanediides by Le Floch et al. (Angew. Chem. Int. Ed., 2004, 43, 6382), numerous transition metal, lanthanide and actinide complexes of bis(thiophosphinoyl) carbene ligands have been investigated with an emphasis on the electronic structure and reactivity of the metal-carbon bonds. This Perspective begins by discussing main group (s- and p-block) complexes of this ligand and draws attention to differences compared to their d and f-block analogues. Investigations targeting the heavy chalcogen analogues of the Le Floch ligand have revealed an unusual carbon-based reactivity that led to the discovery of novel multidentate chalcogen-centred ligands as both monomers and, upon oxidation, dimers linked by dichalcogenido functionalities. Studies of main group and coinage metal complexes have established the flexibility and redox-activity of these novel anionic ligands.     

Synthesis, spectroscopic and structural characterization of tertiary phosphine tellurium dihalides Et3PTeX2(X = Cl, Br, I)

The reactions of triethylphosphine telluride with SO2Cl2 or I2 produced the first structurally characterized tellurium-containing tertiary phosphine chalcogen dihalides, Et3PTeCl2 and Et3PTeI2, respectively, in good yields. The corresponding dibromide, Et3PTeBr2, was obtained by an in situ reaction between Et3PTeCl2 and two equivalents of Me3SiBr. This series of compounds has been characterized in the solid state by X-ray structural analyses and in solution by multinuclear NMR spectra. The structures of Et3PTeX2(X = Cl, Br, I) all show a T-shaped geometry around tellurium with weak Te...halogen interactions giving rise to centrosymmetric dimers. NMR data indicate that Et3PTeI2 exhibits the weakest P-Te bond in solution. The ionic complexes, [(Et3PO)2H]2[Te2I6] and [(Et3PO)2H]2[TeI4], were isolated from THF solutions of Et3PTeI2 and characterized by X-ray structural determinations.     

Zinc complexes of anionic NPPN and NP(S)PN ligands and rearrangement to the isomeric NPNP and NP(S)NP ligands in mercury complexes

The lithium (imido)diphosphineimide Li(Et2O)[DippNPhP-P((n)Bu)PhNDipp] (1) (Dipp = 2,6-(i)Pr2C6H3) undergoes simple metathesis reactions with equimolar amounts of zinc halides, ZnCl2 and (t)BuZnBr, to give the respective N,N'-chelated complexes {Zn(micro-Cl)[DippNPhP-P((n)Bu)PhNDipp]}2 (2) and (t)BuZn[NDippPhP-P((n)Bu)PhNDipp] (3). In contrast, the reaction of two equivalents of complex 1 with HgCl2 affords the rearranged bis(imidodiphosphinoamine) complex, Hg[PhP([double bond, length as m-dash]NDipp)(micro-NDipp)P((n)Bu)Ph]2 (4), where the ligand acts as a P-centered anion. The (imido)diphosphineimide backbone of remains intact on oxidation with elemental sulfur to afford the lithium (imido)diphosphineimine sulfide complex, Li(Et2O)[DippNPhP(S)-P((n)Bu)PhNDipp] (6). Reactions of 6 with group 12 metal halides show similar behaviour to those of complex 1. The N,N' chelated metathesis products RZn[DippNPhP(S)-P((n)Bu)PhNDipp] (7, R = Cl; 8, R = (t)Bu) are obtained on reaction with ZnCl2 and (t)BuZnBr, respectively. Isomerization of the ligand backbone occurs on reaction of 6 with HgCl2 to form the homoleptic P,S-chelated mercury complex Hg[Ph(S)P(=NDipp)(micro-NDipp)P((n)Bu)Ph]2 (9). Complexes 2, 3, 4, 6, 8 and 9 have been characterized by X-ray crystallography.     

Melting of discrete vortices via quantum fluctuations

We consider nonlinear boson states with a nontrivial phase structure in the three-site Bose-Hubbard ring, quantum discrete vortices (or q vortices), and study their "melting" under the action of quantum fluctuations. We calculate the spatial correlations in the ground states to show the superfluid-insulator crossover and analyze the fidelity between the exact and variational ground states to explore the validity of the classical analysis. We examine the phase coherence and the effect of quantum fluctuations on q vortices and reveal that the breakdown of these coherent structures through quantum fluctuations accompanies the superfluid-insulator crossover.     

Small Chvátal Rank

We propose a variant of the Chvátal-Gomory procedure that will produce a sufficient set of facet normals for the integer hulls of all polyhedra {x : A x ≤ b} as b varies. The number of steps needed is called the small Chvátal rank (SCR) of A. We characterize matrices for which SCR is zero via the notion of supernormality which generalizes unimodularity. SCR is studied in the context of the stable set problem in a graph, and we show that many of the well-known facet normals of the stable set polytope appear in at most two rounds of our procedure. Our results reveal a uniform hypercyclic structure behind the normals of many complicated facet inequalities in the literature for the stable set polytope. Lower bounds for SCR are derived both in general and for polytopes in the unit cube.