2 Homometallic Alkoxides

X-Ray Crystal Structures of Alkoxo Metal Compounds 295
OCCNet2⊳2⊲OPr i ⊳6⊲py⊳2] also containing the bridging 2 -ketenyl ligands but the analogous
reaction with [W⊲OPr i ⊳3⊲CNMe2⊳⊲py⊳2] gave the unsymmetrical molecule [W2⊲ -
OPr i ⊳3⊲OPr i ⊳3f 2 -C2⊲NMe2⊳2g⊲CO⊳2]. The latter has a confacial bi-octahedral structure
with one W atom terminally bonded to one Pr i O and two CO ligands whilst the other
is bonded terminally to two Pr i O ligands and 2 -bonding alkyne. 335 Carbonylation of
[W2⊲hftb⊳4⊲NMe2⊳2] gave rise to the unsymmetrical dinuclear complex [W2⊲ -CO⊳2⊲ -
NMe2⊳⊲hftb⊳4⊲CO⊳⊲NMe2⊳] (hftbD OCMe⊲CF3⊳2) which has a confacial bi-octahedral
structure with one bridging NMe2 ligand and two semi-bridging carbonyls. One tungsten
is bonded terminally to two Pr i O and one CO ligand and the other tungsten is
terminally bonded to two Pr i O and one NMe2 ligand. 304
Reactions of W2⊲OR⊳6 with alkynes have led to the isolation of several interesting
complexes. From W2⊲OBu t ⊳6 and PhC2Ph two compounds were obtained: [W2⊲ -
CPh⊳2⊲OBu t ⊳4] (W–W, 2.665 ˚A) involving two tetrahedra sharing a common edge and
[W2⊲ -C2Ph2⊳2⊲OBu t ⊳4] (W–W, 2.677 ˚A). 336 With other tungsten alkoxides and other
alkynes the following binuclear complexes were characterized: [W2⊲ -OPr i ⊳2⊲ -
C2H2⊳⊲OPr i ⊳4⊲py⊳2] (W–W, 2.567 ˚A), [W2⊲ -OCH2Bu t ⊳⊲ -C2Me2⊳⊲OCH2Bu t ⊳5⊲py⊳2]
(W–W, 2.602 ˚A), and [W2⊲ -OPr i ⊳⊲ -C4Me4⊳⊲OPr i ⊳5⊲C2Me2⊳](W–W, 2.852 ˚A); 337–339
[W2⊲ -OPr i ⊳⊲ -C4H4⊳⊲OPr i ⊳5⊲C2H2⊳], 339 [W2⊲ -OBu t ⊳⊲ -C2H2⊳⊲OBu t ⊳5⊲py⊳]. 338
The binuclear complex [W2⊲ -CSiMe3⊳2⊲OPr i ⊳4] 340 reacted with acetylene giving
[W2⊲ -CSiMe3⊳⊲ -CHCHCSiMe3⊳⊲OPr i ⊳4] 340 and with 2,6-Me2C6H3NC giving
[W2⊲ -CSiMe3⊳⊲ -CCSiMe3⊳⊲OPr i ⊳4⊲NC6H3Me2⊳]. 341
Other organo-tungsten isopropoxo compounds characterized are [W2⊲ -
OPr i ⊳2⊲OPr i ⊳2⊲CH2Ph⊳2⊲ 2 -C2Me2⊳2] and[W2⊲ -C4Me4⊳⊲ -CH2Ph⊳⊲OPr i ⊳4]. 342
Interesting alkyne [W2⊲ -OBu t ⊳⊲ -C2Me2⊳⊲OBu t ⊳5⊲CO⊳] 343 and allene complexes
[W2⊲ -C3H4⊳⊲OBu t ⊳6], [W2⊲ -OBu t ⊳2⊲ -C3H4⊳⊲OBu t ⊳4⊲ 2 -C3H4⊳], and [W2⊲ -
OBu t ⊳2⊲ -C3H4⊳⊲OBu t ⊳4⊲CO⊳2] have been prepared. 344 Alkyne adducts have also
been prepared from reactions involving the neopentoxide [W2⊲OCH2Bu t ⊳6⊲py⊳2],
e.g. [W2⊲ -OCH2Bu t ⊳⊲ -C2H2⊳⊲OCH2Bu t ⊳5⊲py⊳2] and [W2⊲ -OCH2Bu t ⊲ -
C2Et2⊳⊲OCH2Bu t ⊳5⊲py⊳]. 345 Addition of ethylene gave the interesting binuclear
bis-adduct [W2⊲ -OCH2Bu t ⊳4⊲OCH2Bu t ⊳2⊲ 2 -C2H4⊳] (W–W, 2.533 ˚A) with four
unsymmetrical neopentoxo bridges between the two tungsten atoms. The longer bridge
bonds (av. 2.31 ˚A, cf. 2.00 ˚A) are trans to the terminal alkoxo or ethylene ligands. 346
This type of complex appears to be a precursor to other species formed in the reaction
of ethylene with W2⊲OR⊳6, e.g. [W2⊲ -OPr i ⊳3⊲OPr i ⊳3⊲ 2 -CH2CH2CH2CH2⊳⊲ 2 -C2H4⊳]
(W–W, 2.643 ˚A) in which the ⊲CH2⊳4 ligand is chelating one tungsten atom to
form a tungstacyclopentane ring. 347 In [W2⊲ -OPr i ⊳⊲OPr i ⊳5⊲ , 2 -CCH2CH2CH2⊳⊲py⊳]
(W–W, 2.674 ˚A) the hydrocarbyl ligand bridges two tungstens, chelating one of
them. 347
The 1,2-R2W2⊲OR⊳4 compounds also react with alkynes producing a variety of products,
e.g. [W2⊲ -OPr i ⊳2⊲OPr i ⊳2⊲C3H7-n⊳2⊲ 2 -C2Me2⊳2] (W–W, 2.681 ˚A), 348 [W2⊲ -
OPr i ⊳2⊲OPr i ⊳2⊲CH2Ph⊳2⊲ 2 -C2Me2⊳2] (W–W, 2.668 ˚A), 349 [W2⊲ -OPr i ⊳2⊲OPr i ⊳2⊲Ph⊳2⊲ 2 -
C2Me2⊳2] (W–W, 2.658 ˚A), 349 [W2⊲ -OPr i ⊳2⊲OPr i ⊳2⊲CH2Bu t ⊳2⊲CEt⊳2], 349 and
[Me2⊲Bu t O⊳W⊲ -OBu t ⊳⊲ -C2Me2⊳W⊲OBu t ⊳2⊲py⊳] (W–W, 2.622 ˚A). 349 Related molecules
are [W2⊲ -CPh⊳⊲ , 2 -C4Me4⊳H⊲OPr i ⊳4](W–W, 2.755 ˚A), 350 [W2⊲ -CSiMe3⊳⊲ , 2 -
C4Me4⊳⊲OPr i ⊳4⊲CH2SiMe3⊳] (W–W, 2.780 ˚A), 350 [W2⊲ -C2Me2⊳2⊲OPr i ⊳4] (W–W,
2.611 ˚A), 351 [W2⊲ -OCH2Bu t ⊳2f , 2 -CH2⊲CH⊳2CH2g⊲OCH2Bu t ⊳4⊲py⊳] (W–W,
2.471 ˚A), 352 and [W2⊲ -OCH2Bu t ⊳4⊲OCH2Bu t ⊳2⊲ 2 -C2H4⊳2] (W–W, 2.533 ˚A). 353 In