Contents 1. Introduction 3031 1.1. Definition of the β-Diketiminato Ligand and Scope of This Review 3031 1.2. Some Significant Developments 3032 2. Preparation of β-Diketimines and Their Metal Complexes 3034 2.1. Synthesis of a β-Diketimine from a β-Diketone or 1,1,3,3-Tetraalkoxypropane 3034 2.2. Synthesis of a Metal β-Diketiminate by Nitrile or Isonitrile Insertion into a Metal−Alkyl Bond 3034 2.3. Various Other Synthetic Routes to Metal β-Diketiminates 3035 2.4. Other Synthetic Routes to β-Diketimines 3035 3. Bonding Modes and Structural Features of β-Diketiminatometal Complexes 3037 4. Discussion of Specific β-Diketiminatometal Complexes 3039

Dedicated to Professor William J. Evans on the occasion of his 60th birthdayThe continuing quest for molecular complexes of lowoxidation-state lanthanides (other than the well-known samarium(II), europium(II), and ytterbium(II)) has produced significant achievements.[1] The majority of such compounds are derivatives of neodymium, dysprosium, and thulium, [2] obtained from the corresponding molecular iodides (often prepared in situ): [NdI 2 (thf) [2c,d] or by the reduction of an appropriate Ln III derivative. [2e,f] The present state of lanthanum, cerium, praseodymium, and gadolinium redox chemistry was described by S. A. Cotton: "None of these metals exhibits a stable + 2 state in any of its compounds and … they are unlikely to form stable compounds in this state." [3] Thus, the isolation of room-temperature-stable solid La II compounds is a very unexpected and significant breakthrough in the chemistry of lanthanides.Related to the subject of this study is a large group of inorganic materials: reduced or metal-rich rare-earth-metal halides, [4] including LaI 2 (featuring an extended structure with La 5d1 electrons delocalized on a conduction band), in which a lanthanum atom can be considered as being in the + 2 oxidation state.[4b] These compounds are better treated in a materials science context, where the metal valence [5,6] rather than the oxidation state is of primary importance.Previously [8] The latter featured redox ambiguity, which was also found in cerocene [9] and bis(pentalene)-cerium, [10] in which a metal-bound ligand had readily accessible adjacent oxidation states. For the binuclear arenebridged complexes, three different metal-ligand formal charge distributions are possible: Ln 2+

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Subvalent Group 4B Metal Alkyls and Amides. Part I. The Synthesis and Physical Properties of Kinetically Stable Bis[bis(trimethysilyl)methyl]germanium(ii), -tin(ii), and -lead(ii) t

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