Dissociation from Mo

The cationic precursor complex [Mo(NO)2(MeCN)4]2+ is itself prepared from [Mo(CO)3(MeCN)3] and [NO]PF6 in MeCN.26 The exchange reactions of the MeCN in this dication have been studied by NMR, two MeCN ligands being relatively easily dissociated. It is assumed that these are irons to the cis NO groups. The cationic complexes [Mo(acac)(NO)2(MeCN)2]+ and [MoCl(NO)2(MeCN)3]+ have also been prepared, the former in which the MeCN groups are mutually trans does not dissociate MeCN, whereas the latter exchanges the one MeCN which is trans to NO.28... 

Molybdenum is a metal of the second transition series, one of the few heavy elements known to be essential to life. Its most stable oxidation state, Mo(VI), has 4d orbitals available for coordination with anionic ligands. Coordination numbers of 4 and 6 are preferred, but molybdenum can accommodate up to eight ligands. Most of the complexes are formed from the oxycation Mo(VI)022+. If two molecules of water are coordinated with this ion, the protons are so acidic that they dissociate completely to give Mo(VI)042, the molybdate ion. Other oxidation states vary from Mo(III) to Mo(V). 

In these lower oxidation states, the tendency for protons to dissociate from coordinated ligands is less, e.g., Mo(III)(H20)63+ does not lose protons even in a very basic medium. Molybdenum tends to form dimeric... 

As described earlier (see Section IV,B) the monoalkylation of coordinated dinitrogen in frons-IMf MdppeM iM = Mo or W) is rate limited by dinitrogen dissociation from the substrate (A, Scheme 3i (88, 8.9). 

This effect is readily understandable, because tetra-substituted complexes should have very significant steric interactions. Steric interactions are also shown to be important in dissociations from cw-Mo(CO)4L2 complexes. ... 

Bonds to Sulphur or Selenium.— Values for the dissociation energies (Do) of the diatomic species PS, PSe, and PTe, determined by Knudsen-cell mass spectrometry, are 438, 360, and 294 kJ mol 1, respectively.583 Some 3lP n.m.r. data for P4S3 in the polycrystalline state584 and in a nematic phase are now available.585 Displacement of one carbon monoxide group from Mo(CO)6 occurs on reaction with P4S3, giving (84),586 and crystal data show... 

In a series of experiments, the rate of phosphine dissociation from cis-Mo(CO)4L2 (L = phosphine) was determined for several phosphines. The overall reaction in each case was of the form... 

A radical, by definition, is a molecule that has a single unpaired electron in an orbital. A free radical is a radical capable of independent existence. (Radicals formed in an enzyme active site during a reaction, for example, are not considered free radicals unless they can dissociate from the protein to interact with other molecules.) Radicals are highly reactive and initiate chain reactions by extracting an electron from a neighboring molecule to complete their own orbitals. Although the transition metals (e.g., Fe, Cu, and Mo) have single electrons in orbitals, they are not usually considered free radicals because they are relatively stable, do not initiate chain reactions, and are bound to proteins in the cell. 

Siemankowski RF, Wiseman MO, White HD (1985) ADP dissociation from actomyosin subfragment 1 is sufficiently slow to limit the unloaded shortening velocity in vertebrate muscle. Proc Natl Acad Sci U S A 82 658662 Sivaramakrishnan M, Burke M (1982) The free heavy chain of vertebrate skeletal myosin subfragment 1 shows full enzymatic activity. J Biol Chem 257 11021105 Small JV (1977) Studies on isolated smooth muscle cells The contractOe apparatus. J Cell Sci 24 327349... 

Siemankowski RF, Wiseman MO, White HD (1985) ADP dissociation from actomyosin subfragment 1 is sufficiently slow to limit the unloaded shortening velocity in vertebrate muscle. Proc Natl Acad Sci U S A 82 658-662... 

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