Complexes tricoordinated

The acute-angle coordinations were similarly predicted for tricoordinated metal complexes [66]. The acute O-Al-O angles of trihydrated aluminum clusters were reported [67]. 

Silver(I) complexes are known with the tris(pyrazolyl)borate [HB(pz)3] and the methyl, phenyl, bromo, or trifluoromethyl-substituted derivatives. The structure of the silver tri(pyrazolyl)borato species has been a puzzle since it was first reported.385,386 It was suggested that the structure could be oligomeric, but recently the crystal structure of the compound [Ag HB(3,5-Me2pz)3 ]2 shows that it has a dimeric structure387 where the silver(I) centers are tricoordinated by a bidentate arm of one ligand and a monodentate arm of the other ligand (29). The related complexes [Ag HB(4-Brpz)3 ]2, [Ag HB(4-Mepz)3 ]2, [Ag HB(3,5-Me2pz)3 ]2, [Ag HB(3-Mepz)3 ] , [Ag B(pz)4 ], and... 

Complexes with borane can be obtained due to the presence of the tricoordinated phosphorus atom [Eq. (103)] (90IZV1120). When heated... 

The aryl-substituted derivatives of [Bi(SeC6H2R3-2,4,6)3] (R = Me, Pr, Bu) are the only isolated examples of selenolate complexes. They have been characterized by mp, elemental analysis, NMR spectroscopy, and thermal gravimetric analysis, and the solid-state structure of the isopropyl-substituted derivative reveals a tricoordinate environment for bismuth [Bi-Se 2.630(8)-2.711(8) A Se-Bi-Se 92.3(2)-103.3(2)°], imposed by the steric bulk of the ligands (38). 

Haubenstock, H., Asymmetric Reductions with Chiral Complex Aluminum Hydrides and Tricoordinate Aluminum Reagents, 14, 231. 

Many species that are tricoordinate in monomeric form are actually tetracoordinate in oligomeric form, or when complexed with donor ligands (e.g., in ether solvents). 

The modification of lithium aluminum hydride with chiral auxiliary reagents has resulted in several highly effective reagents, particularly for the reduction of aryl alkyl ketones and a,0-acetylenic ketones. Applications of several of these reagents to key reduction steps in more complex syntheses have been highly successful. Chiral tricoordinate aluminum reagents have given lower enantiomeric excesses of alcohols. 

ASYMMETRIC REDUCTIONS WITH CHIRAL COMPLEX ALUMINUM HYDRIDES AND TRICOORDINATE ALUMINUM REAGENTS 231... 

The stereodetermining step has been postnlated to occnr during the exchange between the molecule of solvent (S) bonded to the tricoordinated Li of 62 (Figure 4) and the oxirane in one of the two possible conformations 51 and 52 (Scheme 28). A new complex is thus obtained in which the conformation of the oxirane is fixed. Then a fast depolymerization followed by the -deprotonation step gives the aUylic alcohol. Thus, as opposed to type A HCLA bases, the stereodiscrimination could occur prior to the fi-deprotonation (TS), during the formation of an initial complex, also called initial state (IS, Scheme 28)5 -s . 66. 

Figure 13.8. Analysis of alkene binding to different tricoordinated metal complexes.

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