The potential of palladacycles: more than just precatalysts

The transition-metal chemistry of amidinatosilylenes, -germylenes and -stannylenes

Organomercurials in organic synthesis

Publisher Summary This chapter discusses the existing synthetic methods that permit introduction of up to four C 6 X 5 groups in the coordination sphere of palladium or platinum as well as the reactivity of the different complexes obtained. It presents much more numerous compounds with the metals in oxidation state (II), because these provide the gateway for the preparation of other complexes involving oxidation state (I), (III), or (IV), whose chemistry is more reduced in scope. All the complexes show infrared bands characteristic of the presence of the C 6 X 5 groups, most readily observed for C 6 F 5 compounds. Some of these internal absorptions are related to the skeletal symmetry of the molecule and to the oxidation state of the metal center and have therefore been used for structural diagnosis. The information obtained from infrared (IR) data is also discussed. Because the carbanions C 6 X 15 – are not strong nucleophiles, they do not displace neutral Group Vb ligands in the starting compounds MCI 2 L 2 , and bisaryl derivatives M(C 6 X 5 ) 2 L 2 are obtained. A general method that gives the four possible complexes in yields over 85% involves the addition of aqueous HCI to the corresponding tetrakis(pentahalophenyl) compound in methanolic solution (2:1 ratio) albeit half of the pentahalophenyl groups are lost as C 6 X 5 H. The title compounds have interesting possibilities for a variety of syntheses. Platinum(II) complexes cis-Pt(C 6 X 5 ) 2 L 2 undergo redox condensation with Pt(η-C 2 H 4 )(PPh 3 ) 2 in oxygen-free refluxing tetrahydrofuran to give binuclear Pt(I) complexes. The C 5 F 5 groups show strong absorptions in the 1650, 1500, 1300, 1050, 950, and 800 cm –1 regions.

Organopalladium and Platinum Compounds with Pentahalophenyl Ligands

1,2-Bis[(2,6-diisopropylphenyl)imino]acenaphthene) (dpp-bian) stabilizes gallium-gallium and zinc-gallium bonds (compounds 1-3). The compound [(dpp-bian)Ga-Ga(dpp-bian)] (2) was prepared by the reaction of GaCl3 with K3[dpp-bian] and the heterometallic [(dpp-bian)Zn-Ga(dpp-bian)] (3) was prepared by a simple one-pot reaction of [{(dpp-bian)ZnI}(2)] with GaCl3 and K4[dpp-bian]. In contrast to [(dpp-bian)Zn-Zn(dpp-bian)] (1) and 3, compound 2 is ESR silent, thus proving the dianionic character of both dpp-bian ligands. The solution ESR spectrum of 3 reveals the coupling of an unpaired electron with the gallium nuclei (69)Ga and (71)Ga (A((69)Ga)=0.97, A((71)Ga)=1.23 mT), thus confirming the presence of Zn-Ga bonds in solution. According to the results of the X-ray crystal structure analyses the metal-metal bond lengths in 2 (2.3598(3) A) and 3 (2.3531(8) A) are close to that found in 1 (2.3321(2) A). The electronic structures of compounds 2 and 3 were studied by DFT (B3 LYP/6-31G* level). The metal-metal pi bond in 2 is mainly formed by overlap of the p orbitals of Ga in the HOMO and HOMO-1, the latter showing a stronger interaction. The s and p orbitals of Ga overlap in the deeper located HOMO-17 producing a Ga-Ga sigma bond. In contrast to the Zn-Zn bond in 1, which has 95 % s character, the NBO (natural bond order) analysis of 2 reveals 67.8 % s, 32.0 % p, and 0.2 % d character for the Ga-Ga bond. Compound 3 has a doublet electronic ground state. The unpaired electron occupies the alpha HOMO-1 localized at the Zn-containing fragment. The Ga-Zn bond is mainly formed by overlap of the metal orbitals in the alpha HOMO-6 and beta HOMO-5. According to the results of the NBO analysis, the Zn wave functions are responsible for 28.7 % of the Zn-Ga bond, with 96.7 % s, 1.0 % p, and 2.3 % d character.

[(dpp-bian)Ga-Ga(dpp-bian)] and [(dpp-bian)Zn-Ga(dpp-bian)]: synthesis, molecular structures, and DFT studies of these novel bimetallic molecular compounds.

Reaction of the low-valent transition metal complexes with non-transition organometallic compounds☆

Stereochemistry of redox-demercuration of an optically active 8-(α-bromomercuriethyl)quinoline with zerovalent palladium complexes

The reaction between organomercurials and platinum(0) phosphine complexes: a new versatile synthesis of σ-bonded organoplatinum(II) compounds

Preparation and some reactions of organogermylmercuryplatinum complexes and related compounds

Further study of the reaction between zerovalent platinum complexes and organomercurials: The synthesis of stable compounds with a platinum-mercury σ-bond.

V. V. Bashilov

Papers

Reaction of the low-valent transition metal complexes with non-transition organometallic compounds☆

Stereochemistry of redox-demercuration of an optically active 8-(α-bromomercuriethyl)quinoline with zerovalent palladium complexes

The reaction between organomercurials and platinum(0) phosphine complexes: a new versatile synthesis of σ-bonded organoplatinum(II) compounds

Preparation and some reactions of organogermylmercuryplatinum complexes and related compounds

Further study of the reaction between zerovalent platinum complexes and organomercurials: The synthesis of stable compounds with a platinum-mercury σ-bond.