The reactions of so called “tuck-in” permethyl zirconocene compounds Cp*(η5-η1-C5Me4CH2)ZrX (X = Cl (1a), C6H5 (1b), CH3 (1c)) with the highly electrophilic boranes HB(C6F5)2 and B(C6F5)3 are described. The products are zwitterionic olefin polymerization catalysts. Reactions with 1a and 1b yielded single products cleanly, but reactions with tuck-in methyl starting material 1c gave mixtures. Spectroscopic and structural studies showed that the electrophilic zirconium center in the product zwitterions was stabilized by a variety of mechanisms. In the products of reaction between 1a and 1b with HB(C6F5)2, Cp*[η5,η1-C5Me4CH2B(C6F5)2(μ-H)]ZrX (X = Cl (2a), 74%), C6H5 (2b, 62%)), the metal is chelated by a pendant hydridoborate moiety. Chloride product 2a was characterized crystallographically. In the reaction of B(C6F5)3 with 1a, the fluxional zwitterionic product Cp*[η5-C5Me4CH2B(C6F5)3]ZrCl (3a, 84%) is stabilized by a weak donor interaction between one of the ortho fluorine atoms of the −CH2B-(C6F5)3 counterion and the zirconium center (Zr−F = 2.267(5) Å). In the product of the reaction between 1b and B(C6F5)3, Cp*[η5-C5Me4CH2B(C6F5)3]ZrC6H5 (3b, 82%), a similar ortho-fluorine interaction was found in a yellow kinetic product (y-3b), which converted upon heating gently to a thermodynamic orange polymorph (o-3b) in which the zirconium center is compensated via an agostic interaction from an ortho C−H bond of the phenyl group and an interaction between the methylene group of the −CH2B-(C6F5)3 counteranion. These compounds were both characterized by X-ray crystallography. Zwitterion o-3b reacts with H2 to form the zwitterionic hydride Cp*[η5-C5Me4CH2B(C6F5)3]ZrH (4, 77%), characterized by NMR spectroscopy and X-ray crystallography to reveal a return to the ortho-fluorine mode of stabilization. Compounds 2a, 3a, o-3b, and 4 were all found to be active ethlyene polymerization catalysts; the chloride derivatives required minimal amounts of methylaluminoxane (MAO) to alkylate the zirconium center. Polymerization data are discussed in light of the structural findings for the catalysts employed.

Organometallic derivatives of scandium and yttrium supported by a bulky salicylaldiminato ligand were prepared from the tris(alkyl) precursors [M(CH2SiMe2R)3(THF)2] (M = Sc, 1-Sc R ; M = Y, 1-Y R ; R = CH3, Ph) via alkane elimination. The new precursors 1-M Ph are convenient alternatives to the 1-M Me derivatives, due to their higher thermal stability and crystallinity; 1-Sc Ph has been characterized crystallographically. Reaction of these compounds with 1 equiv of protio ligand gives isolable mono(ligand) bis(alkyl) derivatives only for 1-Y; for other derivatives 1-Sc, mixtures were obtained. The products of the former reaction retain either two (2-Y Ph ) or one (3-Y Ph ) THF ligands; both of these compounds have been characterized crystallographically. In solution, both exhibit fluxional exchange between two geometric isomers which were characterized by variable-temperature NMR spectroscopy. Heating solutions of either compound leads to facile ligand redistribution. Reactions of tris(alkyls) 1 with 2 equiv of protio ligand gives the five-coordinate, THF-free bis(ligand) mono(alkyl) complexes 4-M R . These compounds are highly thermally stable, decomposing at temperatures above 140 °C via a pathway involving metalation of one of the N-aryl isopropyl methyl groups. The derivatives 4-Sc Me and 4-Y Ph have been structurally characterized, as well as the product of thermolysis of 4-Sc Me , the nonorganometallic four-coordinate complex 5-Sc. Both 4-Sc Me and 4-Y Ph react slowly but cleanly with H2. The former yields a product, 7-Sc, derived from transfer of the in situ formed scandium hydride to the aldimine carbon of one of the ligands. The yttrium product, however, is the D 2-symmetric dimeric μ-hydride complex 6-Y, characterized by spectroscopic and crystallographic methods. A survey of 6-Y’s reactivity toward deuterated solvents, d 2 -6-Y, ethylene, (trimethylsilyl)acetylene, [HB(C6F5)2]2, benzophenone, pyridine, and THF suggests that it does not dissociate into a monomeric hydride but reacts as a dimer. Nonetheless, products from the reactions of (trimethylsilyl)acetylene, [HB(C6F5)2]2, benzophenone, pyridine, and THF were isolated and characterized spectroscopically and, in the case of the product from the benzophenone reaction, crystallographically. Finally, reactions of mono(alkyls) 4-Sc Me and 4-Y Ph with a further 1 equiv of protio ligand gave nonorganometallic tris(ligand) coordination complexes, both of which were structurally and spectroscopically characterized. The scandium derivative 8-Sc contained an O-bound κ1-salicylaldiminato ligand, while for 8-Y, containing the larger Y nucleus, all three ligands were chelating in the normal κ2 bonding mode.

The ring closure of 1,2-diisopropylhydrazine and 1,1-bis(phenylchloroboryl)ethane produced a heterocyclic compound with a CB 2 N 2 framework. Deprotonation of this precursor yielded 1,2-diisopropyl-4-methyl-3,5-diphenyl-1,2-diaza-3,5-diborolyl, a cyclopentadienyl analogue containing only one carbon atom in the ring skeleton. Lithium, sodium, and potassium salts of the new ligand have been prepared and characterized. The structures of both monomeric and polymeric sodium metallocenes, as well as the structures of polymeric potassium metallocenes incorporating the new heterocycle, have been determined by single-crystal X-ray diffractometry. These structures reveal not only many similarities but also significant differences in the coordination behavior of the new ligand compared with that of the carbon-based analogue.