Nonbridges species

Lewis acid-catalyzed reactions of readily ionizable alkyl halides with alkynes yield vinyl halides [207]. The regioselectivities of these additions can be rationalized by the relative stabilities of the intermediate vinyl cations. Unlike the situation described for additions to alkenes, there is no preference for anti-additions, and the stereoselectivities can be explained by the intermediacy of nonbridged species [208]. The site of nu-... 

Once the solution is acidified, there is a slow, time-dependent cleavage of higher oligomers (nuclearity > 6) into lower oligomers (Table III). One of the more persistent lower oligomers obtained from this procedure is the trimer [Cr3(OH)4(OH2)9]5+, and yields of up to 65% can be obtained. The structure of this species is the subject of some debate, as Marty proposed a nonclassical condensed structure as opposed to the more open structures observed with amine ligands (3) in the nonbridging positions (Fig. 9). 

Figure 12-21 The 31P NMR spectrum at 101.2 MHz of Pa of isotopically labeled ADR This was recovered from an experiment in which ADP containing 87 atom % of lsO in all four oxygens around Pp was allowed to undergo partial ( 20%) nonenzymatic hydrolysis to AMP and P . Peaks 1 represent the species containing no lsO bonded to Pa. Peaks 2 represent all species with lsO in the Pa-0-Pp bridge, and peaks 3 represent species with lsO in nonbridging positions at pa. These have undergone positional isotope exchange. From Lowe and Tuck.691...

Dimeric and cluster compounds containing isocyanide ligands exhibit dynamic behavior in solution. The dimer Cp2Mo2(CO)5CNMe exists as a mixture of nonbridged isomers and permutamers which are rapidly inter-converted by unimolecular processes at RT. The isocyanide passes rapidly from one metal atom to the other via carbonyl or carbonyl-isocyanide doubly bridged species (205). 

Point (b) is particularly relevant for systems such as Co2(CO)s, which exists in solution in an almost 1 1 ratio between the carbonyl-bridged form and the nonbridged form (see equation 25), and Mn2(CO)io, which is stable only in the nonbridged form both in solution and in the sohd state. Single metal metal bonds are not particularly strong for 3d systems this may explain the experimental observation that V(CO)6 is mononuclear, since intrahgand repulsion in the dinuclear species would not be compensated by a sufficiently strong vanadium vanadium bond. 

Starting dianion actually exists in two isomeric forms ([M02(82)4(/r-82)2] and [(Mo8)2(84)2(m-S2)] ) the latter form is desulfurated to give a species containing bridging and nonbridging coordination of the 82 hgand. ... 

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