Pseudooctahedral

Coordination compounds of vanadium are mainly based on six coordination, in which vanadium has a pseudooctahedral stmcture. Coordination number four is typical of many vanadates. Coordination numbers five and eight also are known for vanadium compounds, but numbers less than four have not been reported. The coordination chemistry of vanadium has been extensively reviewed (8—12) (see Coordination compounds). 

Figure 13.11 Structure of the binuclear anion [Sbj OCle] " showing the bridging oxygen and chlorine atoms and the pseudooctahedral coordination about Sb the O atom is at the common apex of the face-shared square pyramids and the lone-pairs are trans- to this below the SbCU bases. The bridging distances Sb-Cl are substantially longer than the terminal distances Sb-Cl,.

SF4 is unusual in apparently acting both as an electron-pair acceptor and an electron-pair donor (amphoteric Lewis acid-base). Thus pyridine forms a stable 1 1 adduct C5H5NSF4 which presumably has a pseudooctahedral (square-pyramidal) geometry. Likewise CsF (at 125°) and Me4NF (at —20°) form CsSFs and [NMe4]+[SFs] (Fig. 15.21a). By contrast, SF4 behaves as a donor to form 1 1 adducts with many Lewis acids the stability decreases in the sequence SbFs > AsFs > IrFs > BF3 > PF5 > ASF3. In view of the discussion on... 

Thermal arene exchange of tetramethylthiophene with [(/ -cymene)RuCl2]2 affords 130 (89JA8828), which on reaction with AgBE4 and excess tetramethylthiophene yields 131. The Ru—S thiophenic cluster, 132, was synthesized by reaction of 130 with (Mc3Si)2S followed by anionic metathesis and formation of the PFg salt. The coordination geometry around each ruthenium atom is pseudooctahedral. 

Dinuclear complexes with hydroxide bridged dizinc centers were synthesized with a ligand based on the phthalazine framework.455 The dizinc complex of 1,4-bis(2,2 -dipyridylmethyl)phtha-lazine (49) is bridged by the phthalazine moiety, a water molecule, and a hydroxide ion. Both centers are pseudooctahedral with two pyridine donors and a water molecule occupying the remaining coordination sites. 

The model predicts that frontier orbital-controlled addition at position (1) should be favorable for octahedral or pseudooctahedral complexes of... 

Reactions of this pseudooctahedral complex have been studied in particular detail by the Davies group at Oxford and the Liebeskind group in the United States because of its potential use as a chiral auxiliary for control of the absolute stereochemistry of various reactions of the acyl enolate. Both R-( — )-l and S-( + )-1 are now available commercially (Fluka), but at a prohibitive cost ( 125.60 per gram). 

The water proton NMRD of the pseudooctahedral Co(H20)g (reported in Fig. 13) shows almost field-independent water proton relaxation rate values in the 0.01-60 MHz region (47). Therefore, the (Os c = 1 a nd of course the co/Cc = l dispersions must occur at fields higher than 60 MHz. This provides an upper limit value for Tig equal to 4 x 10 s. Such a low Tig value is consistent with the low water proton relaxation rate values. By using the SBM theory, Tie at 298 K can be estimated to be about 10 s. It can be larger, if the presence of a probable static ZFS is taken into account (47). When measurements are performed in highly viscous ethyleneglycol the observed rates are similar to those obtained in water. This suggests that Tig is also similar and, therefore, it is rotation-independent (47). 

Pseudooctahedral complexes of the N4 donor cyclam of type [Mn(cyclam)X2]Y, where X and Y are a range of monovalent anions, have been reported." The efficacy of a complex of this type (with X = Y = Cl) as an oxidation catalyst has been probed. In another study both manganese(II) and manganese(III) complexes of the tetraaza macrocycle (175) have been characterized and were shown to be of types [MnLCy O.SHCl and [MnL(N3)2]N3. The traw -octahedral structures of both species have been confirmed by X-ray diffraction studies. 

Manganese(III) complexes of a number of phenolate pendant arm macrocycles related to the above have also been reported. Thus, both l,4,7-tris(2-hydroxybenzyl)-l,4,7-triazacyclononane and l,4,7-tris(3-t-butyl-2-hydroxybenzyl)-l,4,7-triazacyclononane, on tris-deprotonation, afford monomeric pseudooctahedral complexes with this ion." ... 

Re(NPh)(maltolate)2(PPh3)]" has been isolated upon addition of Na(BPh4)7 The complex has a pseudooctahedral structure with cw-maltolate ligands (209). 

Pseudooctahedral coordination of rhenium(III) centers has also been found for mixed-ligand complexes with tertiary phosphines and A-heterocyclic thiols which coordinate as their neutral thione tautomers. A representative example with thiazoline-2-thiol (HSthiaz) has been characterized structurally. The paramagnetic complex [ReCl3(HSthiaz)2(PPh3)] (235) contains the HSthiaz ligands in trans position. ... 

A better synthetic route for the pseudooctahedral complexes, however, is the ligand exchange starting from [ReCl3(PPh3)2(CH3CN)]. ... 

Structure 10.4 Model of transition states A and B suitable for proton-hydride exchange processes obtained by extendend Hiickel theory calculations on the basis of symmetrical pseudooctahedral geometry (H+ and represent the acid). (From ref. 7.)... 

---