Molybdenum triple bonds

M.H. Chisholm, J.F. Coming, J.C. Huffman, The molybdenum-molybdenum triple bond. 14. Preparation and characterization of mixed alkoxy-thiolate compounds of formula Mo2(OR)2(SAr)4. Inorg. Chem. 23, 754-757 (1984)... 

The Novel Reactivity of the Molybdenum-Molybdenum Triple Bond in Cp2Mo2(CO)4... 

An ordering of the ease of adduct formation (HCsCH Me=CMe PhCsCH> CF3C=CH>CF3C=CCF3 PhC=CPh) shows both a steric and electronic dependence. The yields are 60%. Allene also adds to the molybdenum triple bond as a four-electron donor ° ... 

A 2,5di-(tert-butyl)phospholyl complex containing a molybdenum-molybdenum triple bond synthesis, molecular structure, and coordination chemistry of [Mo2(PC4H2Bu 2)2(CO)4] <94CC2459>. 

The molybdenum-molybdenum triple bond in this complex is 2.2 A long, whereas the length of a single Mo-Mo bond is 2.78 A in the dimer [Cp(CO)3Mo-Mo(CO)3Cp] which is its precursor. The shortening is indeed very large. 

Cummins complex Mo(NRAr)3 is an interesting one, because it allows both the formation of a dinitrogen complex and the cleavage of the very strong nitrogen-nitrogen bond in N2 (942 kJ mol ) at room temperature to form two nitrogen-molybdenum triple bonds (680 kJ- mol each) ... 

Dinuclear stmctures are known for molybdenum(III) in a series of air and moisture sensitive compound containing multiple Mo—Mo bonds. Examples include Mo2(N(CH2)2)g (Fig- 5b) and Mo2(CH2Si(CH2)3)g in which there is a strong Mo—Mo bond, presumably of triple-bond character (28). 

Chemistry of compounds containing metal to metal triple bonds between molybdenum and tungsten. M. H. Chisholm and F. A. Cotton, Acc. Chem. Res., 1978,11, 356-362 (66). 

The cr2 tta triple bond between molybdenum and tungsten atoms developing the chemistry of an inorganic functional group. M. H. Chisholm, Angew. Chem., Int. Ed. Engl., 1986,25,21 (70). 

Figure 6.13 Activation and cleavage of the N2 triple bond on molybdenum as discussed in reference 33.

Molybdenum imido alkylidene complexes have been prepared that contain bulky carboxylate ligands such as triphenylacetate [35]. Such species are isola-ble, perhaps in part because the carboxylate is bound to the metal in an r 2 fashion and the steric bulk prevents a carboxylate from bridging between metals. If carboxylates are counted as chelating three electron donors, and the linear imido ligand forms a pseudo triple bond to the metal, then bis(r 2-carboxylate) species are formally 18 electron complexes. They are poor catalysts for the metathesis of ordinary olefins, because the metal is electronically saturated unless one of the carboxylates slips to an ri1 coordination mode. However, they do react with terminal acetylenes of the propargylic type (see below). 

One of the first isolated and structurally characterized phosphido complexes [(t-Bu Ph"N)3Mo=P] (la) was obtained from the reaction of a molybde-num(III) complex with P4 in 79% yield (Eq. 1) [8]. The molybdenum starting material [(f-Bu Ph"N)3Mo] is planar, and the three unpaired electrons are localized on the Mo atom [10], engendering an ideal environment for the reduction of white phosphorus and formation of the triple bond, la can transfer the phosphido ligand to another complex [(t-BuPhN)3Moj via a het-erocumulene intermediate to give [(t-BuPhN)3Mo=Pj (lb) [11] (Eq. 2). 

The analogous reaction of 3 with W2(OrBu)6 gave a brown solution, from which a yellow, microcrystalline material could be isolated. Based on spectroscopic data the latter was formulated as [Cy7Si70i2]2W2(p-H)(0tBu) (158). Cleavage of the Mo = Mo triple bond in 157 occurred upon treatment of this compound with NO (two equivalents) to afford the dimeric nitrosyl molybdenum silsesquioxane complex [Cy7Si70i2]2Mo2(NO)2 (159). °°... 

Again several alkyls add—molybdenum, chromium, iron, cobalt, nickel, the alkali metal alkyls and aluminum alkyls react. A tin alkoxide has recently been studied by Russian workers and found to add to acetylenes. Mercury chloride, of course, adds and two cobalt—cobalt bonded compounds add to acetylene. The second is questionable because it dissociates in solution and the reaction may be a radical reaction, one cobalt adding to each end of the triple bond. 

Of considerable interest are reactions in which the metal-metal bond order changes. So far, there are no known examples in which a W—W triple bond is converted to a W—W quadruple bond, a reaction which is known for molybdenum.289 However, several reactions in which the W—W triple bond is oxidized are known. The preparation of alkoxo clusters of WIV have been mentioned (Section 37.5.4.1) and the reaction in which W=W reacts with RC CR or RC=N to give mononuclear complexes containing the W=CR and WssN units have been discussed (Section 37.3.3). 

Chisholm and Cotton have summarized their successful efforts characterizing metal-metal triple bonds in molybdenum(III) and tungsten(III) compounds containing no bridging ligands (46). This realm of strong homo-nuclear metal-metal bonds was unknown prior to the 1970s, and the rapid development and exploitation of the chemistry of these dimers provide an... 

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