Group 13 elements donor adducts

It did not prove possible to synthesize a substituent-free Ga complex with formula Cp (CO)2Fe Fe(CO)4 Ga (Scheme 13).43 Addition of bipy to 30 resulted in halide elimation, but the main group element in the product 31 was coordinated by the bipy ligand. Upon addition of dppe, however, substitution of the carbonyl ligands occurred instead along with halide ion elimination to produce the substituent-free Ga complex 32. It has a linear coordination environment (Fe-Ga-Fe angle = 176.01(4)°), and the Ga-Fe bond distances are much shorter than in those related adducts where donor ligands are also bound to the Ga atom.43 The authors attributed the non-observation of the carbonyl derivative to a need for an electron-rich metal center to stabilize the Fe-Ga bond via 7r-backdonation. 

A similar coordirmtion sphere at silicon is found in unsaturated Si=E compounds (E = element of group 14-16) and their donor adducts (coordination numbers 3 and 3+1). Attached to coordination number three at silicon the existence of silicenium cations is still controversely discussed in the literature. While some experiments are interpreted as evidence for their existence in the condensed phase, theoretical calculations do not support the formulation of donor free silicenium cations. However, there seems to be no doubt about the verfication of inter- and intramolecular donor stabilized cationic species (coordination numbers 3+1 and 3+2, respectively). 

Hermtann, W.A. Kuehn. F.E. Mattner. M.R. Artus. G.R.J. Geisberger. M.R. Con-eia. J.D.G. Multiple bonds between transition metals and main-group elements. 163. Nitrogen-donor adducts of organorhenium(VII) oxides Structural and catalytic aspects. J. Organomet. Chem. 1997, 538. 203-209. 

For alkoxides of the Group I and II elements and the lanthanides, typical adducts involve coordinating O-donors such as Et20 or THF. For example, the sparingly soluble, anhydrous aryloxide LiOAr (OAr = 2,6-di-r-butylphenoxide) will dissolve in ethers to give dimeric adducts of the type [(OAr )Li(L)]2 (L = Et20, THF, py), which have been structurally characterized.22 ... 

Trihalides of the Group VA elements are pyramidal (C3v) with an unshared pair of electrons on the central atom. Typically, the molecules are Lewis bases, and they form acid-base adducts and metal complexes. In accord with the hard-soft interaction principle, these species are better electron pair donors toward soft electron pair acceptors. Therefore, most of the complexes of these EX3 molecules contain second and third row transition metals or first row metals in low oxidation states. 

The trihalides (except the fluorides), and other R3M compounds such as the trialkyls, triaryls, mixed R2MX compounds, and A1H3, all function as Lewis acids, forming 1 1 adducts with a great variety of Lewis bases. This is one of the most important aspects of the chemistry of the Group 13 elements. The Lewis acidity of the A1X3 groups (where X = Cl, CH3, etc.) has been extensively studied thermodynamically, and basicity sequences for a variety of donors have been established. 

Amine N-oxides, phosphine oxides, arsine oxides, and related ligands. The prototypical system for extraction of the uranyl ion from aqueous solution into organic solvent is tributylphosphate in hydrocarbons such as kerosene. This has stimulated interest in understanding the coordination chemistry of actinyl ions with P=0 (and related) functional groups in order to optimize extraction efficiency or discrimination among actinides to be separated. Of all classes of neutral group 16-atom donor ligands, phosphine oxide adducts are the most common examples of complexes of transuranic elements (Np, Pu). 

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