2 Homometallic Alkoxides

294 Alkoxo and Aryloxo Derivatives of Metals
formed whilst crotonaldehyde coordinates in 2 -OC mode in [W2⊲ -
OCH2Bu t ⊳2⊲OCH2Bu t ⊳4⊲ 2 -OCHCH ž žCHCH3⊳2]. 331 In the diolate complex [W2⊲ -L⊳3],
where L D 2,5-dimethylhexane-2,5-diolate, the molecule retains the ethane-like staggered
conformation with 3 eight-membered diolate rings spanning the metal–metal triple
bond (W W, 2.363 ˚A) (Fig. 4.48). 332 In the dimethylamine adduct [W2⊲ -L⊳⊲ 2 -
L⊳2⊲Me2NH⊳2] there is one bridging diolate ligand and the other two each chelate one of
the metal atoms whilst the two amine ligands are anti to one another about the metal–metal
bond (W W, 2.320 ˚A). 332
Reactions of W2⊲OR⊳6 with CO have produced some interesting products. With
the isopropoxide the dinuclear complex [W2⊲ -OPr i ⊳2⊲ -CO⊳⊲OPr i ⊳4⊲py⊳2] (W–W,
2.499 ˚A) was obtained. This molecule has the same confacial bi-octahedral structure as
the isomorphous molybdenum complex. 234 With W2⊲OBu t ⊳6 the compound formed
[W2⊲ -OBu t ⊳2⊲ -CO⊳⊲OBu t 4 ]333 which is isomorphous and isostructural with the
molybdenum analogue. 227 Also formed in the reaction of [W2⊲OPr i ⊳6⊲py⊳2] with CO is
the interesting complex [W2⊲ -OPr i ⊳2⊲OPr i ⊳4⊲CO⊳4] in which an octahedral W⊲OPr i ⊳6
moiety acts as a bidentate bridge to the W⊲CO⊳4 moiety. 334 In this edge-sharing
bi-octahedral complex the bridges are very unsymmetrical with W–O bonds in the
W⊲OPr i ⊳6 moiety being shorter (1.96 ˚A) than those in the W⊲ -OPr i ⊳2⊲CO⊳4 moiety
(2.25 ˚A).
Reaction of the alkylidyne complex [W2⊲OBu t ⊳6⊲CMe⊳2] with CO gave the unsymmetrical
complex [W2⊲ -OBu t ⊳⊲ , 4 -C2Me2⊳⊲OBu t ⊳5⊲CO⊳] composed of two trigonal
bipyramids joined by axial ( -OBu t ) and equatorial ( -C2Me2) ligands. One W atom
is bonded to three terminal Bu t O ligands and the other to two terminal Bu t Oand
one CO ligand. 335 Addition of CO to [W2⊲OBu t ⊳6⊲CNMe2⊳2] producing bridging 2 -
ketenyl ligands in the symmetrical dimer [W2⊲ , 2 -OCCNMe2⊳2⊲OBu t ⊳6]. 335 With
[W⊲OPr i ⊳3⊲CNEt2⊳⊲py⊳2] carbonylation produced the symmetrical [W2⊲ , 2 -
Figure 4.48 Structure of
[W2⊲OCMe2C2H4CMe2O⊳3].