| Transition metal polyarene compounds have been extremely important in the exploration of low-valent transition metal chemistry because they often function as synthetic precursors for new and unique molecules. The first group 4 species of this type, tris(naphthalene)zirconate, was prepared and characterized in 1994, while its titanium and hafnium analogs have remained elusive. Herein, the successful isolation and characterization of tris(naphthalene(2-)hafnate, the first arene complex to contain hafnium in a formally negative oxidation state, and tris(naphthalene)titanate(2-), the first tris-polyarene species of the first row transition metals, are reported. For the first time, a series of tris(polyarene)metalates has been isolated and in this work, their chemistries are described in detail.;A number of reactions of [M(eta-C10H8)3 ]2-, M = Ti, Zr, Hf, are reported, many of which establish these species as sources of "naked" metal dianions. For example, all three compounds react with anthracene to provide a second series of tris(polyarene)metalates, [M(eta-C14H10)3]2-, M = Ti, Zr, Hf. However, additional reactivity studies indicate that the chemistry of tris(naphthalene)titanate(2-) is quite different from that of the heavier group 4 metals. Thus, reactions with ethylene, pyrene, and 1,3,5,7-cyclooctatetraene (COT) all proceed differently with [Ti(eta-C10H8) 3]2- than with [M(eta4-C10H 8)3]2-, M = Hf, Zr. In the case of the former, reactions with ethylene generate unknown products, while reactions with the ligands pyrene and COT result in the formation of paramagnetic 17-electron complexes, bis(ligand)titanate(1-). The heavier tris(naphthalene)metalates(2-) react with ethylene to generate the metallacyclopentanes, [M(eta 4-C10H8)2(C4H8)] 2-, M = Hf, Zr, which are structurally distinct;from the previously isolated tantalum species, [Ta(eta-C10H 8)2(C4H8)]-. In reactions of [M(eta4-C10H8)3] 2-, M = Hf, Zr, with pyrene, only the formation of pyrene radical anion is observed, but their reactions with COT produce the novel tris(COT)metalates(2-).;These species, [M(eta-COT)3]2-, M = Hf, Zr, are much less reducing than their naphthalenemetalate precursors, suggesting that the COT ligands remove considerable electron density from the respective metal centers. In fact, X-ray crystal structures show that two COT ligands are bound in eta3-allyl fashion and only one is bound as a substituted eta4-butadiene ligand. These data are indicative of metal centers that are much closer to tetravalent than dianionic. Tris(cyclooctatetraene)hafnate(2-) and --zirconate(2-) show no tendency to combine with CO under ambient conditions. However, they do react readily with Me3SnCl to produce the unexpected species, [M(eta-COT)2Cl]-, M = Hf, Zr. Previous reactions of low-valent titanium and zirconium species with Me3SnCl resulted only in the formation of M-Sn bonds.;Finally, a high yield one-pot synthesis of [Ti(CO)6] 2- has been established and its chemical reactivity has been expanded upon. For instance, a general procedure for the preparation of [PPN][Ti(CO) 4(eta3-BH4)] from [Ti(CO)6] 2- is reported. This product undergoes reactions with a number of ligands to provide novel titanium(0) carbonyls, many of which have been characterized only by IR spectroscopy. However, its reaction with K[S2CN(CH 2)5] generates [Ti(CO)4{S2CN(CH 2)5}]-, which has been well characterized and is reported in this work. Also, this work has established HgCl2 as a useful two electron oxidant of [Ti(CO)6]2- and in the presence of Cp- and tacn, the titanium(0) tetracarbonyls, [CpTi(CO)4]- and Ti(CO)4(tacn) are generated. |
