Platinum compounds, stereochemistry

Entries 79, 80, and 83- 86 show that the potent reducing agent LiAlH4 cleaves a variety of silicon-metal bonds, giving a hydridosilane. Nucleophilic attack by H is indicated a discussion of the associated stereochemistry is deferred until Section IV,E. When the silicon-platinum compounds shown in entries 85 and 86 are reduced, metallic platinum is formed, but the metal-containing products in other cases have not generally been identified. Equation (63) provides an example of a compound with a robust Si-Fe bond that resists reductive cleavage (237) (cf. Section III,C,3). 

The chemistry of the zerovalent state in nickel, palladium, and platinum compounds is reviewed. After a historical introduction in which the development of this chemistry is analyzed in terms of the current theory of the stabilization of low valency states, the most interesting classes of zerovalent compounds are described. The stability and properties of these compounds are discussed and related to the nature of the ligands and the coordinated metal. The catalytic properties of these zerovalent derivatives toward olefins, diolefins, and acetylenes are considered in connection with the facility of ligands exchange, the variation of coordination number, and the stereochemistry. A discussion of the % bond is reported. 

SERS-spectroscopy has been used to clarify the specific binding modes of the powerful anti-tumor agent cis-Pt(NH3)2Cl2 and an inactive Pt-complex [Pt-(dien)Cl]Cl The presence or absence of specific SERS bands of platinum compounds yields information concerning the stereochemistry of Pt binding to DNA. This is a further... 

The first strong attack upon the concept of valence follows two pages later "the difference in valences is a somewhat obscure concept because valence itself is not a clear concept" (KT 49). (This is one of the passages quoted verbatim by Jorgensen (20y, see also (7).) The attack is prepared at a metaphorical level with many nouns, verbs, and adjectives belonging to the semantic field of the opposition obscure/clear, and is followed by a triumphant exclamation "Thus a stereochemistry of cobalt compounds and platinum compounds appears alongside the stereochemistry of carbon compounds and nitrogen compounds "(WB 300 KT 50). 

Table 27.2 Oxidation states and stereochemistries of compounds of nickel, palladium and platinum...

Yoshida has studied anodic oxidations in methanol containing cyanide to elucidate the electrode processes themselves.288 He finds that, under controlled potential ( 1.2 V), 2,5-dimethylfuran gives a methoxynitrile as well as a dimethoxy compound (Scheme 57). Cyanide competes for the primary cation radical but not for the secondary cations so that the product always contains at least one methoxy group. On a platinum electrode the cis-trans ratio in the methoxynitrile fraction is affected by the substrate concentration and by the addition of aromatic substances suggesting that adsorption on the electrode helps determine the stereochemistry. On a vitreous carbon electrode, which does not strongly adsorb aromatic species, the ratio always approaches the equilibrium value. 

Introduction of the allene structure into cycloalkanes such as in 1,2-cyclononadiene (727) provides another approach to chiral cycloalkenes of sufficient enantiomeric stability. Although 127 has to be classified as an axial chiral compound like other C2-allenes it is included in this survey because of its obvious relation to ( )-cyclooctene as also can be seen from chemical correlations vide infra). Racemic 127 was resolved either through diastereomeric platinum complexes 143) or by ring enlargement via the dibromocarbene adduct 128 of optically active (J3)-cyclooctene (see 4.2) with methyllithium 143) — a method already used for the preparation of racemic 127. The first method afforded a product of 44 % enantiomeric purity whereas 127 obtained from ( )-cyclooctene had a rotation [a]D of 170-175°. The chirality of 127 was established by correlation with (+)(S)-( )-cyclooctene which in a stereoselective reaction with dibromocarbene afforded (—)-dibromo-trans-bicyclo[6.1 0]nonane 128) 144). Its absolute stereochemistry was determined by the Thyvoet-method as (1R, 87 ) and served as a key intermediate for the correlation with 727 ring expansion induced... 

The triple bond can be reduced with hydrazine to form the vinyl complex with a cis stereochemistry about the carbon-carbon double bond (equation 223).617 The five types ol reaction between platinum acetylide complexes and aprotic compounds A—B have beer summarized. These are (a) oxidative addition (A—B is I2, IBr, ICN, Mel etc.) (b) insertior (A—B is C2(CN)4) (c) addition across the triple bond to form vinyl complexes (A—B is CF3COCI, o-tetrachloroquinone, Br, NOC1) (d) insertion into the C—H bond (A—B is (CFs)2CO) and (e) formation of five-coordinate adducts.618... 

The principal application of NMR with compounds of the platinum group metals has been in the study of their stereochemistry. Cis and trans isomers of the Pt(PR3)2L2 and Pt(PR3)2X4 type are identified easily because of the difference in the coupling constants as discussed above. 

Stan s some one hundred articles dealt with the synthesis, structure, stereochemistry, and biological properties of coordination compounds, including the anticancer activity of platinum complexes optical rotatory dispersion circular dichroism the Pfeiffer Effect in metal complexes inorganic nomenclature and the application of computer techniques to chemical and information problems. A prominent educator, he edited three books on inorganic and coordination chemistry. 

Cis addition is a characteristic feature of the hydrosilylation of acetylenic compounds in the presence of platinum catalysts. This is in marked contrast to the trans addition giving cis adduct on using free radical initiators (193). Free radical hydrogermylation (23) and hydrostannyhtion (194) also proceed with trans stereochemistry. 

The synthesis and antitumour properties of DACH platinum(II) complexes containing a variety of different types of leaving ligand have been reported [38, 39, 60-67]. Although early studies with the compounds were content to utilize mixtures of geometric and optical isomers, the realization that the stereochemistry of the DACH ligand influenced antitumour activity underscored the importance of working with isomerically pure forms of the diamine [68-70],... 

Many of the complexes for which 7p M data have been collected are those of platinum(II) and rhodium(I) compounds. These are square planar complexes and the highest microsymmetry corresponding to this stereochemistry is In this symmetry group, the d 2 orbital and the s orbital on the acceptor transform as A g, so there will be three molecular orbitals involving the s orbital of the metal instead of... 

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