Adduct Formation and Single and Double Deprotonation of Cp*(PMe3)Ir(H)2 with Main Group Metal Alkyls and Aryls: Synthesis and Structure of Three Novel Ir−Al and Ir−Mg Heterobimetallics

Publisher Summary This chapter discusses a review of the anionic transition-metal hydrides. A large portion of homogeneous catalytic processes of import to the reduction of unsaturated organics, the reduction and homologation of oxycarbon compounds, and the use of carbon monoxide as a reducing agent have as catalysts, catalyst precursors, or mechanistically required intermediates, anionic transition-metal hydride complexes. Encapsulated in a cryptand ligand, the interaction of [K(crypt.222)]+ with an equatorial CO oxygen of μ-HCr2(CO)10– is predictably less perturbing of the anion. Asymmetric hydride bridges are observed for inherently asymmetric dimmers, such as μ-H[Mo(CO)5] [Mo(CO)4PPh3]– in which the Mo–H distance to the more electron-rich Mo center, Mo(CO)4PPh3, is considerably longer than that to the more electron-poor Mo(CO)5. The X-ray diffraction study revealed a distorted octahedral disposition of ligands about Ru. The crystal structure of the nonsolvated lithium salt of H5W(PMe3)3– disclosed a tetrameric cluster with alternating distances (2.77 and 2.93 A) between Li and W, suggesting the presence of μ–H ligands, which could not be located by X-ray crystallographic methods. Infrared and nuclear magnetic resonance spectroscopies are the primary tools for analyzing the solution structures of transition-metal hydrides. The metal–hydrogen stretch should also be useful for the analysis of the electronic character of a particular anion; however, this vibrational frequency is rarely available because of the fact that it is usually a weak and broad absorption or is obscured by other absorptions, such as v(CO) bands.

Anionic Transition Metal Hydrides

Preparation et proprietes chimiques de l′inorganomagnesien Cp(DPPE)FeMgBr

4 – Magnesium, Calcium, Strontium and Barium

Reduction of Fp2 (Fp = CpFe(CO)2) or [Co(CO)3(PCy3)]2 (15) with Mg-mercury amalgam gave [Mg{TM(L)}2(THF)]2 (TM(L) = Fp or Co(CO)3(PCy3) (19)) in which the TM is bonded to two Mg atoms. Reduction of 15 with Ca-, Sr-, Ba-, Yb-, Eu- and Sm-mercury amalgam gave a series of compounds “M{Co(CO)3(PCy3)}2(THF)n” (M = Ae or Ln) in which the M–Co bonding varies with the charge-to-size ratio of M. For M = Ca or Yb (24), each metal forms one M–Co bond and one M(μ-OC)Co η1-isocarbonyl linkage. With M = Sr (21) or Eu (25), a switch from M–Co bonding to side-on (η2) CO ligand coordination is found. SmII{Co(CO)3(PCy3)}2(THF)3 disproportionates in pentane to form SmIII{Co(CO)3(PCy3)}3(THF)3 containing two SmIII–Co bonds, in contrast with 25, showing the importance of the Ln charge on Ln–TM bonding. Diffusion NMR spectroscopy found that in solution, 21 and 24 are dimeric compounds [M{Co(CO)3(PCy3)}2(THF)3]2 that, according to DFT calculations, contain either one (Ae = Ca) or two (Ae = Sr) Ae–Co bonds per Co atom. DFT calcu...

Probing the limits of alkaline earth-transition metal bonding: an experimental and computational study.

The dihydride [Mo(η-C5H5)2H2] reacts with bromo(cyclohexyl)magnesium to give the cyclic dimer [H(η-H5C5)2-Mo{µ-( H11C6)MgBr2Mg(OEt2)}2Mo(η-C5H5)2H], (III). The Grignard reagents MgRX (RX = PriBr, BunBr, Mel, or PhBr) give generally similar products. Derivative (III) reacts with carbon dioxide, carbon monoxide, benzyl bromide, or butadiene to give the compounds [Mo(η-C5H5)2(CO)], [Mo(η5-C5H5)(η3-C5H7)(CO)2], [Mo(η-C5H5)2(CH2Ph)2], and [Mo(η3-C4H7)(η-C5H5)2][PF6] respectively. The isopropyl analogue of (III) reacts similarly. Also, with iodomethane, the compound [MoMe(η-C5H5)2I] is formed. The methyl and phenyl analogues of (III) react with benzyl bromide to give [MoMe(η-C5H5)2(CH2Ph)] and [Mo(η-C5H5)2Ph(CH2Ph)] respectively. The dihvdride [W(η-C5H5)2H2] reacts with the Grignard reagents MgRX (RX = Mel, Pri, or PhBr) to give tungsten–magnesium compounds which appear to be generally similar to the molybdenum adducts.

Francis Pettit

Papers

Preparations and reactions of bis(η-cyclopentadienyl) compounds of molybdenum or tungsten containing covalent bonds to magnesium

PREPARATIONS AND REACTIONS OF BIS(η-CYCLOPENTADIENYL) COMPOUNDS OF MOLYBDENUM OR TUNGSTEN CONTAINING COVALENT BONDS TO MAGNESIUM