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Description:
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This dissertation investigates three topics in the field of multiple -bonded metal chemistry .
The first topic concerns the synthetic and theoretical considerations of ditungsten
formamidinates and guanidinates compounds . This work presents an enhanced synthetic path to
the W2 (hpp )4 molecule (Hhpp = 1 ,3 ,4 ,6 ,7 ,8 -hexahydro -2H -pyrimido[1 ,2 -a]pyrimidine ) . The
reflux of W (CO )6 with Hhpp in o -dichlorobenzene at 200 oC produces W2 (hpp )4Cl2 in a one -pot
reaction in 92 % yield . This compound is stable and easily stored for further use , and it can be
efficiently reduced in a one -step reaction to the most easily ionized compound W2 (hpp )4 . This
work also examines the electronic structure and geometry of the intermediates W2 (à µ -CO )2 (à µ -
hpp )2 (à ·2 -hpp )2 and W2 (hpp )4Cl2 .
The second topic concerns the theoretical investigation by DFT of the electronic
structure of [Mo2] units bridged by oxamidate ligands or bridging hydride ions ([Mo2] =
(Mo2 (DArF )3 , where DArF is the anion of a diarylformamidine ) . It is shown that the effect of the
gauche conformation of the à ± oxamidate isomers is due to steric interactions , and that the planar
à ² oxamidate isomers have an electronic structure similar to that of naphthalene when it is doubly
oxidized . The [Mo2] (à µ -H )2[Mo2] compound shows interdimetal unit interactions between the à ´
orbitals of the two [Mo2] units . These interactions are theoretically predicted and experimentally
observed by a decrease in the [Mo2] - - -[Mo2] distance with a one -electron oxidation of [Mo2] (à µ -
H )2[Mo2] . The final topic concerns the magnetic and structural properties of two Ru2 (DArF )4Cl
compounds . The compounds with Ar = p -anisyl (para ) and m -anisyl (meta ) both show different
temperature dependence of their molar magnetic susceptibility , Ã Â . For the para compound , there
is a Boltzmann distribution between a à  *3 ground state and a à ´*2à  * upper state , and this is
confirmed by a temperature dependence of the Ru -Ru bond length : 2 .4471 (5 ) Ã Â at 23 K and
2 .3968 (5 ) à  at 300 K . For the meta compound , a à ´*2à  *configuration persists over the range of
23 -300 K as shown by an invariant Ru -Ru bond length and its molar magnetic susceptibility . |