| This thesis reports the synthesis and spectral characterization, including x-ray diffraction, of the cobalt-cobalt multiple-bonded Co(,2)((eta)('5)-C(,5)Me(,5))(,2)((mu)(,2)-CO)(,2) dimer as well as of six other clusters which can be visualized as resulting from the addition of M(,x)(CO)(,y) and M(C(,n)R(,n))(CO)(,z) species across its cobalt-cobalt double bond-viz. Co(,4)((eta)('5)-C(,5)Me(,5))(,2)(CO)(,4)((mu)(,2)-CO)((mu)(,3)-CO)(,2),;C(,5)H(,4)Me)(,2)((mu)(,2)-CO)(,2)((mu)(,3)-CO), CrCo(,2)((eta)('5)-C(,5)Me(,5))(,2)((eta)('6)-C(,6)H(,5)Me)((mu)(,2)-CO)(,3).;((mu)(,3)-CO), MnCo(,2)((eta)('5)-C(,5)Me(,5))(,2)((eta)('5)-C(,5)H(,4)Me)((mu)(,2)-CO)(,3)((mu)(,3)-CO), and.;FeCo(,2)((eta)('5)-C(,5)Me(,5))(,2)((eta)('4)-C(,4)H(,4))((mu)(,2)-CO)(,3)((mu)(,3)-CO).;FeCo(,2)((eta)('5)-C(,5)Me(,5))(,2)(CO)(,3)((mu)(,2)-CO)(,2)((mu)(,3)-CO), Co(,3)((eta)('5)-C(,5)Me(,5))(,2)((eta)('5)-.;A comparative structural analysis of the {Co(,2)((eta)('5)-C(,5)Me(,5))(,2)((mu)(,2)-CO)(,2)}('n) dimers (n = -1, 0) has provided definite experimental evidence in support of the Pinhas-Hoffmann calculated model giving the enegy-level ordering of the frontier MO's; this model places the unpaired electron of the monoanion with the out-of-plane (pi)*(,yz) MO (of b(,2) representation under C(,2v)-m2m symmetry) which is strongly antibonding with respect to the two metal atoms.;An X-ray diffraction analysis of Co(,4)((eta)('5)-C(,5)Me(,5))(,2)(CO)(,4)((mu)(,2)-CO)((mu)(,3)-CO)(,2) has revealed a new type of tetrahedral metal cluster containing both doubly and triply bridging carbonyl ligands as well as terminal carbonyl and C(,5)Me(,5) ligands. This complex can be viewed, at least conceptually, as an adduct formed by the net insertion of a Co(,2)(CO)(,4)((mu)(,2)-CO) fragment across the Co-Co double bond of Co(,2)((eta)('5)-C(,5)Me(,5))(,2)((mu)(,2)-CO)(,2).;A designed photochemical synthetic procedure for obtaining mixed-metal clusters in reasonable quantities under mild conditions has been demonstrated by a series of reactions of the double-bonded metal-metal dimer, Co(,2)((eta)('5)-C(,5)Me(,5))(,2)((mu)(,2)-CO)(,2), with photogenerated M(CO)(,x) and M(C(,n)R(,n))(CO)(,y) species. The five triangularly bonded dicobalt-metal clusters procured by the net insertion of electronically equivalent, photogenerated Cr((eta)('6)-C(,6)H(,5)Me)(CO)(,2), Mn((eta)('5)-C(,5)H(,4)Me)(CO)(,2), Fe((eta)('4)-C(,4)H(,4))(CO)(,2),;Fe(CO)(,4), and Co((eta)('5)-C(,5)H(,4)Me)(CO) fragments across the Co-Co double bond of Co(,2)((eta)('5)-C(,5)Me(,5))(,2)((mu)(,2)-CO)(,2) were found from spectral and X-ray crystallographic analyses to separate into two distinct structural series.;The MCo(,2)((eta)('5)-C(,5)Me(,5))(,2)((mu)(,2)-CO)(,3)((mu)(,3)-CO) series {composed of three members designated by M being Cr((eta)('6)-C(,6)H(,5)Me) (1), Mn((eta)('5)-C(,5)H(,4)Me).;(2), and Fe((eta)('4)-C(,4)H(,4)) (3)} possesses one triply bridging and three double bridging carbonyl ligands, while the MCo(,2)((eta)('5)-C(,5)Me(,5))(,2)((mu)(,2)-CO)(,2)((mu)(,3)-CO) series {consisting of two members denoted by M being Fe(CO)(,3) (4) and Co((eta)('5)-C(,5)H(,4)Me) (5)} has one triply bridging but only two doubly bridging carbonly ligands. These electronically equivalent metal clusters, which were conveniently photogenerated at ambient temperatures in 27-45% yields, were not obtained from corresponding thermal reactions. All five compounds were characterized by IR, ('1)H NMR, and mass spectral measurements; the detailed molecular configurations of compounds 2-5 were also determined from single crystal X-ray diffraction studies. The results of this systematic investigation clearly indicate that photochemically assisted insertion reactions across a metal-metal multiple bond may provide a highly useful synthetic pathway for acquiring a variety of new transition metal clusters heretofore unobtainable by other routes. |
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