Recent work, both in this research group and elsewhere, has shown that the a,a'-diiminopyridine ligand [a,a'-{2,6-(iPr) 2 PhN¼C(Me)} 2 (C 5 H 3 N)], well known for its ability to form highly active polymerization catalysts, [1] can be involved in the organometallic transformations of metal centers. Alkylating agents may attack not only the imino function [2] but also all of the pyridine ring carbon atoms [3,4] and even the nitrogen atom. [5] In addition, dimerization may be achieved by imine reductive coupling [4] or by the cycloaddition of two pyridine rings to form a tricyclic system. [4] In parallel with all of these transformations, either one or both of the CH 3 groups attached to the imine functions may be partly deprotonated. [4,5] In this unusual variety of transformation, the metal center coordinated to the ligand may engage in redox reactions and may either lower or even increase its oxidation state. [3,6, 7] This behavior illustrates the unique ability of this ligand system to a) accept negative charge with preferential spin-density localization on the imine groups and on the pyridine N and C para atoms, and b) to engage in internal redox processes with the coordinated metal. The ability of the ligand to accept or to donate negative charge to the metal is paramount to the fine-tuning of the redox potential of the metal, and of its Lewis acidity which, in turn, determines the catalytic behavior of the metal complex.Given the above scenario, we became interested in clarifying the ability of this remarkable ligand system to accept negative charge. For this purpose, we have carried out the reduction of [a,a'-{2,6-(iPr) 2 PhN ¼ C(Me)} 2 (C 5 H 3 N)] with strong reductants such as Li and [Li(naphthalenide)], in the absence of transition metals. Herein we describe our findings.The reactions were carried out by treating a solution of [a,a'-{2,6-(iPr) 2 PhN¼C(Me)} 2 (C 5 H 3 N)] with either metallic Li under argon or [Li(naphthalenide)] under nitrogen in THF. Regardless of the stoichiometric ratio, the reduction with Li afforded a mixture of [a,a'-{2,6-(iPr) 2 PhN ¼ C(Me)} 2 -(C 5 H 3 N)][Li(thf)] 3 (1) and [{a-[2,6-(iPr) 2 PhN ¼ C(Me)]}-{a'-[2,6-(iPr) 2 PhN-C(¼CH 2 )]}C 5 H 3 N][Li(thf)] 2 [Li(thf) 2 ](2) through a readily reproducible process. Both species contain a trianionic ligand (Scheme 1). Separation of the two extremely air-sensitive species was possible because of their relative solubilities in hexane. However, we observed that reactions carried out at low temperature with 3 equiv of [Li(naphthalenide)] afforded 2 as the only isolated compound (67 %) and no evidence for the presence of 1.The connectivity of 1 was elucidated by an X-ray crystal structure (Figure 1). The complex contains the intact ligand, which adopts the usual chelating tridentate conformation COMMUNICATIONS

Reaction of CrCl 3 (THF) 3 with 3 equiv of R-M [R ) Me 3 CCH 2 (a), Me 3 SiCH 2 (b)] afforded either the previously reported tetravalent homoleptic R 4 Cr (1a, b) [M ) MgCl] or the unprecedented divalent and tetranuclear homoleptic [R 2 Cr] 4 (2b) [M ) Li]. Both types of compounds display a remarkable chemical inertness toward proton transfer agents but readily react with ethylene.

Recent work, both in this research group and elsewhere, has shown that the a,a'-diiminopyridine ligand [a,a'-{2,6-(iPr) 2 PhN¼C(Me)} 2 (C 5 H 3 N)], well known for its ability to form highly active polymerization catalysts, [1] can be involved in the organometallic transformations of metal centers. Alkylating agents may attack not only the imino function [2] but also all of the pyridine ring carbon atoms [3,4] and even the nitrogen atom. [5] In addition, dimerization may be achieved by imine reductive coupling [4] or by the cycloaddition of two pyridine rings to form a tricyclic system. [4] In parallel with all of these transformations, either one or both of the CH 3 groups attached to the imine functions may be partly deprotonated. [4,5] In this unusual variety of transformation, the metal center coordinated to the ligand may engage in redox reactions and may either lower or even increase its oxidation state. [3,6, 7] This behavior illustrates the unique ability of this ligand system to a) accept negative charge with preferential spin-density localization on the imine groups and on the pyridine N and C para atoms, and b) to engage in internal redox processes with the coordinated metal. The ability of the ligand to accept or to donate negative charge to the metal is paramount to the fine-tuning of the redox potential of the metal, and of its Lewis acidity which, in turn, determines the catalytic behavior of the metal complex.Given the above scenario, we became interested in clarifying the ability of this remarkable ligand system to accept negative charge. For this purpose, we have carried out the reduction of [a,a'-{2,6-(iPr) 2 PhN ¼ C(Me)} 2 (C 5 H 3 N)] with strong reductants such as Li and [Li(naphthalenide)], in the absence of transition metals. Herein we describe our findings.The reactions were carried out by treating a solution of [a,a'-{2,6-(iPr) 2 PhN¼C(Me)} 2 (C 5 H 3 N)] with either metallic Li under argon or [Li(naphthalenide)] under nitrogen in THF. Regardless of the stoichiometric ratio, the reduction with Li afforded a mixture of [a,a'-{2,6-(iPr) 2 PhN ¼ C(Me)} 2 -(C 5 H 3 N)][Li(thf)] 3 (1) and [{a-[2,6-(iPr) 2 PhN ¼ C(Me)]}-{a'-[2,6-(iPr) 2 PhN-C(¼CH 2 )]}C 5 H 3 N][Li(thf)] 2 [Li(thf) 2 ](2) through a readily reproducible process. Both species contain a trianionic ligand (Scheme 1). Separation of the two extremely air-sensitive species was possible because of their relative solubilities in hexane. However, we observed that reactions carried out at low temperature with 3 equiv of [Li(naphthalenide)] afforded 2 as the only isolated compound (67 %) and no evidence for the presence of 1.The connectivity of 1 was elucidated by an X-ray crystal structure (Figure 1). The complex contains the intact ligand, which adopts the usual chelating tridentate conformation ZUSCHRIFTEN

Acute encephalitis can be life-threatening, especially in the immunocompromised population. Viruses are the main infectious agents, with varicella zoster virus (VZV) a common cause. Neuropsychiatric symptoms are well documented, but it is rare for mania to be the only symptom on presentation. Here, we report a case of hypomania in a 31-year-old white British heterosexual man who following investigation was found to be HIV positive and subsequently diagnosed with VZV encephalitis. To date, we are unaware of any similarly reported cases. It is important to raise awareness of atypical HIV presentations to improve clinical outcomes for patients.

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