Facial configuration

Additionally, MO calculations indicate the lowest energy orientation occurs with the three strongest trans-influence ligands (two hydrides and a PPh3) in a facial configuration. Calculations on compounds IrX(CO)(PR3)2 indicates that weak donors X and strong 7r-acceptors PR3 favour addition in the XIrCO plane [134, 135],... 

Support for Schetty s postulates has been provided by X-ray crystal structure determinations. Thus the 2 1 chromium complexes (126) and (127) of the two o,o -dihydroxydiarylazo compounds 2,2 -dihydroxyazobenzene and l-(2-hydroxy-4-nitrophenylazo)-2-naphthol, respectively, have been proved89 to have meridional configurations, whilst the 2 1 chromium complex (128) of the o-carboxyarylazopyrazolone l-(4-brornophenyl)-3-methyl-4-(2-methyl-6-carboxyphenylazo)-5-pyrazolone has been proved90 to have a facial configuration. 

A similar argument can be applied to the results of later work by Idelson et al.i9 In this they prepared the chromium complex (133) by interaction of the 1 1 chromium complex of 1-phenyl-3-methyl-4-(2-hydroxy-4-cyanonaphth-l-ylazo)-5-pyrazolone and diethylenetriamine and by reaction of the azo compound with [Cr(CO)3dien]. Identical products were obtained and, since the diethylenetriamine occupies9 a facial position in [Cr(CO)3dien], it was concluded that the complex (133) had a facial configuration. Similarly, the reported77 separation of isomeric 2 1 chromium complexes of 2-amino-6-(2-hydroxy-6-nitro-4-sulfonaphth-l-ylazo)-5-naphthol-7-sulfonic acid is... 

Besides bidentate ligands, tripyrazolylborates (Tp) (see Tris(pyrazolyl)borates) derivatives, which are of anionic tridentate in facial configuration, also afford octahedral... 

Figure 4.11 (A) Dimetal complex (Co2TAPH) (N03)4. (TAPH = 6,7,8,9,12,19, 20,21,22,25-decahydro-8,8,10,21,21,23,-hexamethyl-5,26 13,18-/)/s(azo)-dibez(1,2,6,7,12,13,17,18)oxaazacyclodocosine) (B) Face-to-face Co—Co 4-porphyrin. (Reprinted from Ref 17, with permission from Elsevier.) (C) Cis and trans Co-O-O-Co facial configuration and (D) Co-corrole compounds for O2 reduction reaction. ...

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