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2 Homometallic Alkoxides

2 Homometallic Alkoxides

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292 Alkoxo and Aryloxo Derivatives of Metals<br />

Figure 4.47 Structure of [W2⊲ -<br />

OPr i ⊳2⊲OPr i ⊳4⊲OCMeDCMeO⊳2]<br />

(H atoms omitted).<br />

the one in the axial position (2.42 ˚A)owingtothetrans influence of the carbyne<br />

(W C, 1.77 ˚A). 312 See also [W2⊲ -OBu t ⊳2⊲OBu t ⊳4⊲CMe⊳2] (Table 4.11). 323<br />

The unsymmetrical chloride methoxide [Cl2⊲MeO⊳2W⊲ -OMe⊳2W⊲OMe⊳3Cl] also<br />

has the edge-shared bi-octahedral structure. 313 The remarkable compound [W2⊲ -<br />

OCH2Bu t ⊳⊲ -H⊳⊲ -I⊳⊲OCH2Bu t ⊳5⊲Me2NH⊳] (WDW, 2.456 ˚A) has the confacial bioctahedral<br />

structure with three different bridging groups. 314 A similar hydrido-bridged<br />

confacial bi-octahedral structure was also found in [W2⊲ -OC5H9-c⊳2⊲ -H⊳⊲OC5H9c⊳5⊲Me2NH⊳](WDW,<br />

2.438 ˚A). 315 Reaction of the latter compound gave rise to the novel<br />

alkyl, alkene complex [Et⊲C2H4⊳⊲c-C5H9O⊳W⊲ -OC5H9-c⊳3W⊲OC5H9-c⊳3] (W–W,<br />

2.668 ˚A) in which the confacial bridging is sustained by three alkoxo ligands. Other<br />

related molecules are [W2⊲ -OC5H9-c⊳2⊲ -CH2CCH2⊳⊲OC5H9-c⊳6], [W2⊲ -OC5H9c⊳3⊲OC5H9-c⊳5f<br />

2 -OC(CH2)3CH2g], [W2⊲ -OPr i ⊳3⊲OPr i ⊳4H⊲ 2 -OCPh2⊳], and [W2⊲ -<br />

OPr i ⊳2⊲ - 2 -HNCPhDCPhN] in which the nitrogen-containing ligand is both chelating<br />

and bridging. 316<br />

Reaction of xylylisonitrile ⊲2,6-Me2C6H3NC⊳ with W2⊲OBu t ⊳6 gave the dinuclear<br />

[W2⊲ -OBu t ⊳2⊲ -CNC6H3Me2⊳⊲OBu t ⊳4] (W–W, 2.525 ˚A) in which the fivecoordinated<br />

metals are in a face-sharing bi-square pyramidal configuration with<br />

the carbon atom of the bridging isonitrile occupying the apical position. 316 See<br />

also [W2⊲tftb⊳6⊲CNC6H3Me2⊳2] (Table 4.11). 322 With W2⊲OPr i ⊳6 the unsymmetrical<br />

[W2⊲ -OPr i ⊳2⊲ -CNC6H3Me2⊳⊲OPr i ⊳4⊲py⊳] species was formed. One metal is in<br />

distorted octahedral and the other is in square pyramidal coordination in a confacial<br />

bridged structure. 316<br />

Reaction of the tetranuclear W4⊲OBu i ⊳12 with nitric oxide gave the centrosymmetrical<br />

dinuclear [W2⊲ -OBu i ⊳2⊲OBu i ⊳4⊲NO⊳2⊲py⊳2] with the edge-shared isobutoxobridged<br />

bi-octahedral structure. 317 The isobutoxo bridges are unsymmetrical with the<br />

W–O bond trans to the linear NO ligand being longer (2.204 ˚A) than the one trans to<br />

the terminal isobutoxo ligand (2.054 ˚A).<br />

A number of binuclear organoimido alkoxo complexes have been studied. The<br />

edge-shared bi-octahedral structure was found for [W2⊲ -OMe⊳2⊲OMe⊳6⊲NPh⊳2].<br />

The practically linear (W�NC, 174 Ž ) imido group is trans to a bridging methoxo

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