Synthesis and reactivity of two-coordinate Ni(I) alkyl and aryl complexes.

Reaction of [(IPr)Ni(µ-Cl)]2 (1-Cl; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with ClMg{CH(SiMe3)2}·Et2O affords (IPr)Ni{CH(SiMe3)2} (2), a two-coordinate Ni(I) alkyl complex. An analogous two-coordinate aryl derivative, (IPr)Ni(dmp) (dmp = 2,6-dimesitylphenyl), can be similarly prepared from Li(dmp) and 1-Cl. Reaction of 2 with alkyl bromides gives the three-coordinate Ni(II) alkyl halide complex (IPr)Ni{CH(SiMe3)2}Br. Evidence for a radical mechanism is presented to explain the reaction of 2 with alkyl halides.

Cationic alkylaluminum-complexed zirconocene hydrides: NMR-spectroscopic identification, crystallographic structure determination, and interconversion with other zirconocene cations.

The ansa-zirconocene complex rac-Me(2)Si(1-indenyl)(2)ZrCl(2) ((SBI)ZrCl(2)) reacts with diisobutylaluminum hydride and trityl tetrakis(perfluorophenyl)borate in hydrocarbon solutions to give the cation [(SBI)Zr(µ-H)(3)(Al(i)Bu(2))(2)](+), the identity of which is derived from NMR data and supported by a crystallographic structure determination. Analogous reactions proceed with many other zirconocene dichloride complexes. [(SBI)Zr(µ-H)(3)(Al(i)Bu(2))(2)](+) reacts reversibly with ClAl(i)Bu(2) to give the dichloro-bridged cation [(SBI)Zr(µ-Cl)(2)Al(i)Bu(2)](+). Reaction with AlMe(3) first leads to mixed-alkyl species [(SBI)Zr(µ-H)(3)(AlMe(x)(i)Bu(2-x))(2)](+) by exchange of alkyl groups between aluminum centers. At higher AlMe(3)/Zr ratios, [(SBI)Zr(µ-Me)(2)AlMe(2)](+), a constituent of methylalumoxane-activated catalyst systems, is formed in an equilibrium, in which the hydride cation [(SBI)Zr(µ-H)(3)(AlR(2))(2)](+) strongly predominates at comparable HAl(i)Bu(2) and AlMe(3) concentrations, thus implicating the presence of this hydride cation in olefin polymerization catalyst systems.

Cationic alkylaluminum-complexed zirconocene hydrides as participants in olefin polymerization catalysis.

The alkylaluminum-complexed zirconocene trihydride cation [(SBI)Zr(µ-H)(3)(Al(i)Bu(2))(2)](+), which is obtained by reaction of (SBI)ZrCl(2) with [Ph(3)C][B(C(6)F(5))(4)] and excess HAl(i)Bu(2) in toluene solution, catalyzes the formation of isotactic polypropene when exposed to propene at -30 °C. This cation remains the sole observable species in catalyst systems free of AlMe compounds. In the presence of AlMe(3), however, exposure to propene causes the trihydride cation to be completely converted, under concurrent consumption of all hydride species by propene hydroalumination, to the doubly Me-bridged cation [(SBI)Zr(µ-Me)(2)AlMe(2)](+). The latter then becomes the resting state for further propene polymerization, which produces, by chain transfer to Al, mainly AlMe(2)-capped isotactic polypropene.

Alkylaluminum-complexed zirconocene hydrides: identification of hydride-bridged species by NMR spectroscopy.

Reactions of unbridged zirconocene dichlorides, (R(n)C(5)H(5-n))(2)ZrCl(2) (n = 0, 1, or 2), with diisobutylaluminum hydride (HAl(i)Bu(2)) result in the formation of tetranuclear trihydride clusters of the type (R(n)C(5)H(5-n))(2)Zr(mu-H)(3)(Al(i)Bu(2))(3)(mu-Cl)(2), which contain three [Al(i)Bu(2)] units. Ring-bridged ansa-zirconocene dichlorides, Me(2)E(R(n)C(5)H(4-n))(2)ZrCl(2) with E = C or Si, on the other hand, are found to form binuclear dihydride complexes of the type Me(2)E(R(n)C(5)H(4-n))(2)Zr(Cl)(mu-H)(2)Al(i)Bu(2) with only one [Al(i)Bu(2)] unit. The dichotomy between unbridged and bridged zirconocene derivatives with regard to tetranuclear versus binuclear product formation is proposed to be connected to different degrees of rotational freedom of their C(5)-ring ligands. Alkylaluminum-complexed zirconocene dihydrides, previously observed in zirconocene-based precatalyst systems activated by methylalumoxane (MAO) upon addition of HAl(i)Bu(2) or Al(i)Bu(3), are proposed to be species of the type Me(2)Si(ind)(2)Zr(Me)(mu-H)(2)Al(i)Bu(2), stabilized by interaction of their terminal Me group with a Lewis acidic site of MAO.

Hexaamminecobalt(III) aquabis(nitrilotriacetato-kappa4N,O,O',O")gadolinate(III) octahydrate.

Crystals of the title compound, [Co(NH(3))(6)][Gd(C(6)H(6)NO(6))(2)(H(2)O)].8H(2)O, were synthesized in and collected from aqueous solution. The hexaamminecobalt(III) cation has the expected octahedral geometry, while the Gd coordination sphere has the geometry of a tricapped trigonal prism, with the two nitrilotriacetate N atoms and one water molecule occupying the capping positions.