Complexes tetracoordinated

While for silyl and germyl cation complexes tetracoordination of the element prevails, stannyl cations favor pentacoordination. That is, the trigonal-bipyramidal environment of the Sn atom in the diwater complex of the stannylium ion Me3Sn ... 

While for silyl and germyl cation complexes tetracoordination of the element prevails, stannyl cations favor pentacoordination. That is, the trigonal-bipyramidal environment of the Sn atom in the diwater complex of the stannylium ion Me3Sn + [Me3Sn(H20)2]+ 84178 has its counterpart in the tetrahedral structure of the pro-tonated silanol 85.116 The structure of the bis(acetonitrile)tricyclohexyltin hexa-fluoroantimonate 86 SbF6179 reveals pentacoordination for the tin atom,180 while all... 

However, conversion of alkenylalanes into the corresponding a7e-complexes (tetracoordinated aluminum) by addition of methyllithium or n-butyllithium enhances their reactivity toward carbon electrophilesP ... 

Pd(n) complexes tetracoordinated by a tridentate (pincer) Ugand and a monodentate ligand. 

Very recently, the first disulfur complexes of a tetracoordinated transition metal PtS2[P(Ar)Me2]2 (Ar=Tbt, Bbt) were synthesized by the reaction of ze-rovalent platinum complexes Pt[P(Ar)Me2]2> generated by treatment of the dichloride complexes PtCl2[P(Ar)Me2]2 with lithium naphthalenide, with elemental sulfur (Scheme 6) [37]. Since the use of excess elemental sulfur also... 

Summary of Facial Stereoselectivity in Aldol and Mukaiyama Reactions. The examples provided in this section show that there are several approaches to controlling the facial selectivity of aldol additions and related reactions. The E- or Z-configuration of the enolate and the open, cyclic, or chelated nature of the TS are the departure points for prediction and analysis of stereoselectivity. The Lewis acid catalyst and the donor strength of potentially chelating ligands affect the structure of the TS. Whereas dialkyl boron enolates and BF3 complexes are tetracoordinate, titanium and tin can be... 

Complexes formed by tetradentate siderophores involve stepwise complex formation and therefore, have somewhat different equilibria from their hexadentate analogs. Initial chelation will occur with a tetracoordinate FeL complex forming. A subsequent equilibrium then occurs, where the FeL complexes will react in a 2 1 stoichiometry with free ligands in solution to form a single Fe2L3 complex (coordinated water and charges not shown for clarity). 

A tetracoordinated complex (20)4 was actually isolated. Complex 20 in the presence of ethylene forms the coordinated complex 21, as can be seen from H NMR. Complex 21 is a model of the intermediate for the additional reaction to form C6 dienes. The model catalyst had been shown to be a codimerization catalyst under more severe conditions (high temperature), although the rate of reaction was very slow compared to the practical systems. These studies are extremely useful in demonstrating the basic steps of the codimerization reactions taking place on the Ni atom. The catalytic cycle based on these model complexes as visualized by Tolman is summarized in Scheme 7. A more complete scheme taking into consideration by-product formation can be found in Tolman (40). 

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