Molybdenum species quadruple bonds

The reaction of WCU with K2C8H8 in THF gives a reasonably air-stable material that was shown to be [W2(C8Hg)3]. The W—W bond length of 2.375 A, although long, is consistent with the presence of a quadruple bond.329 However, it is recognized that this compound (and the related chromium and molybdenum) is electronically different from other quadruply bonded species. 

The reaction of Mo(CO)6 and acetic acid is still the most convenient preparative route known for condensing two monomeric units into a compound containing a quadruple bond. In fact, facile conversion of Mo2(02CCH3)4 to chloro species occurs in concentrated hydrochloric acid to form the Mo2 Clj ion (36), which is isostructural with the Re2Clg ion. The eclipsed configuration of Mo2Clg" and the molybdenum atom separation of 2.14 A are entirely consistent with a quadruple bond in the anion as expected (33). 

Molybdenum(ll) dimers display a slightly larger span of metal—metal distances than the quadruply bound rhenium(lll) units. Certain ligand types can be associated with fairly specific metal—metal bond lengths in the molybdenum species. Thus molybdenum quadruple bonds differ in this respect from the... 

Dinuclear Species with Quadruple Bonds. Molybdenum carbonyl reacts readily with carboxylic acids to give yellow crystalline compounds Mo2(OOCR)4 which are thermally extremely stable. They have the copper... 

An example of the model complexes that point the way to potentially fascinating polymers in the future is given by the tetranuclear species 6.21 [49]. Remarkable square arrays of molybdenum-molybdenum quadruple bonds with oxalate spacers have also been prepared by simple assembly procedures, as illustrated by the formation of the complex Mog(oxalate)4(N-N)g (6.22) (N-N = di(p-methoxyphenyl)forma-midinate) (Fig. 6.11) from [Mo2(N-N)2(NCMe)2] and [oxalate] " [52]. 

This species acts as a propene metathesis catalyst even at 0°C, Apparently clean oxidation, hydrogenation, and chlorination processes can be achieved from this material to afford new metal sites. The same coordination centre as shown in Eq. 6 can also be formed from Mo2(allyl)4 [94]. In that case adsorption at 0 C did not cause loss of propene rather the molybdenum-molybdenum quadruple bond is considered... 

There have been many compounds discovered which resemble the [Re Xj,] " ions in possessing extremely short M—M distances, eclipsed conformations and, presumably. quadruple metal-metal bonds. The isoelectronic molybdenum(ll) species, [Mo Clijj , is known and both Re(lll) and Mo(Il) form a large series of carboxylaie complexes of formulas Re2(RC02)2X4, Re2(RC02)4X2. and Mo2(RC02)4 ... 

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