Activation of Cp2ZrCl2 and Cp2ZrMe2 by methylaluminoxane (MAO) in toluene is largely complete at Al:Zr ratios of 100:1 to 200:1 as revealed by electrospray ionization mass spectrometry (ESI MS). The anions present undergo chlorination in the case of Cp2ZrCl2. DFT calculations reveal that chlorination of MAO is favorable and involves dissociation of Me3Al, followed by association of Me2AlCl. Ethylene polymerizations were conducted using these catalyst precursors in toluene. The activity vs [Zr] data are essentially identical, while higher MW polyethylene is formed with a narrower MWD at lower Al:Zr ratios in the case of Cp2ZrMe2. The activity vs [Zr] data could be fit to a model which invokes bimolecular deactivation of growing chains. ESI MS reveals that a dinuclear Zr2 cation with m/z 557 is formed on exposure of [Cp2Zr­(μ-Me)2AlMe2]+ to ethylene, in addition to other cations that are dinuclear with respect to Zr. Labeling experiments using ethylene-d 4 indicate that these dinuclear cations are derived from ethylene, either through direct incorporation in the case of m/z 557, or indirectly through incorporation of deuterium following e.g. β-H elimination. These experiments shed light on the need for high Al:Zr ratios for ethylene polymerization using soluble metallocene catalysts. The active catalyst [Cp2ZrR]­[MAO­(Me)] (R = H, Et or a higher homologue) suffers a second order deactivation, and thus activity improves upon dilution of the catalyst precursor at constant [Al].

Ethylene polymerization using catalysts derived from activation of zirconocene aluminohydride complexes with either methyl aluminoxane or B(C6F5)3 is reported. Variable-temperature NMR spectra of mixtures of Cp*2ZrH3AlH2 or Cp‘2ZrH3AlH2 and excess B(C6F5)3 reveal the formation of di- or polynuclear metallocenium ion-pairs featuring terminal or both terminal and bridging borohydride counteranions HB(C6F5)3 arising from hydride abstraction. At higher T, ion-pairs featuring the terminal HB(C6F5)3 counterion decompose, and the AlH3 that is liberated degrades B(C6F5)3 to furnish mixtures of (C6F5) n AlH3 - n and, in the case of Cp*2ZrH3AlH2, a new ion-pair partnered with the diborohydride counteranion [Cp*2ZrH][(μ-H)2B(C6F5)2]. The latter compound was independently prepared from Cp*2ZrH2 and HB(C6F5)2 and is active in ethylene polymerization; however it is 1000 times less active than the catalyst formed from Cp*2ZrH3AlH2 and B(C6F5)3 and so cannot account for the multisite behavior of the latter combination. There is evidence of chemical exchange between “free” or terminal HB(C6F5)3 and excess B(C6F5)3 in these mixtures, and on the basis of model studies with [ n Bu4N][HB(C6F5)3] and B(C6F5)3, this involves reversible formation of [ n Bu4N][(C6F5)3B)(μ-H)B(C6F5)3], which can be detected by 19F NMR spectroscopy in solution at low T.

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Copper nanoparticles (Cu-NPs) with sizes lower than 31 nm were prepared by wet chemical reduction using copper sulfate solution, hydrazine, and mixture of allylamine (AAm) and polyallylamine (PAAm) as stabilizing agents. The use of AAm/PAAm mixture leads to the formation of Cu and CuO nanoparticles. The resulting nanostructures were characterized by XRD, TGA, and TEM. The average particle diameters were determined by the Debye-Scherrer equation. Analysis by TGA, TEM, GS-MS, and1HNMR reveals that synthesized NPs with AAm presented a coating with similar characteristics to NPs with PAAm, suggesting that AAm underwent polymerization during the synthesis. The synthesis of NPs using AAm could be a good alternative to reduce production costs.

Treatment of RuCl2(PPh3)3 and RuHCl­(PPh3)3 with the tin compound CH2C­(Me)­CHC­(Me)­CH2SnMe3 gives the corresponding acyclic pentadienyl half-sandwich (η5-CH2C­(Me)­CHC­(Me)­CH2)­RuX­(PPh3)2 [X = Cl, (2); H, (3)]. The steric congestion in 2 is most effectively relieved by formation of the cyclometalated complex (η5-CH2C­(Me)­CHC­(Me)­CH2)­Ru(C6H4PPh2)­(PPh3) (4). Addition of 1 equiv of PHPh2 to (η5-CH2CHCHCHCH2)­RuCl­(PPh3)2 (1) affords the chiral complex (η5-CH2CHCHCHCH2)­RuCl­(PPh3)­(PHPh2) (5), while compound (η5-CH2C­(Me)­CHC­(Me)­CH2)­RuCl­(PPh3)­(PHPh2)] (6) is directly obtained from the reaction of RuCl2(PPh3)3 with CH2C­(Me)­CHC­(Me)­CH2Sn­(Me)3 and PHPh2. Treatment of RuCl2(PPh3)3 with the corresponding Me3SnCH2CHCHCHNR (R = Cy, t-Bu) affords (1-3,5-η-CH2CHCHCHNCy)­RuCl­(PPh3)2 (7) and [1-3,5-η-CH2CHCHCHN­(t-Bu)]RuCl­(PPh3)2 (8). The hydrolysis of 7, on a silica gel chromatography column, allows the isolation of RuCl­(η5-CH2CHCHCHO)­(PPh3)2 (9). The azapentadienyl complex 7 reacts with 1 equiv of PHPh2 to afford [1-3,5-η-CH2CHCHCHN­(Cy)]­RuCl­(PPh3)­(PHPh2) (10), while the corresponding product [1-3,5-η-CH2CHCHCHN­(t-Bu)]­RuCl­(PPh3)­(PHPh2) (11) from 8 is only observed through 1H and 31P NMR spectroscopy as a mixture of isomers. Two equivalents of PHPh2 gives spectroscopic evidence of [η3-CH2CHCHCHN­(t-Bu)]­RuCl­(PHPh2)3. A mixture of products [η5-CH2C­(Me)­CHC­(Me)­O]­RuCl­(PPh3)2 (12) and [η5-CH2C­(Me)­CHC­(Me)­O]­RuH­(PPh3)2 (13) is obtained from reaction of RuCl2(PPh3)3 with Li­[CH2C­(Me)­CHC­(Me)­O]. In contrast, the oxopentadienyl compound 13 is cleanly formed from RuHCl­(PPh3)3 and Li­[CH2C­(Me)­CHC­(Me)­O]. An attempt to separate compounds 12 and 13 by crystallization gives an orthometalated product [η5-CH2C­(Me)­CHC­(Me)­O]­Ru­(C6H4PPh2)­(PPh3) (14), which is the oxopentadienyl analogue to 4. The bulky [1-3,5-η-CH2C­(t-Bu)­CHC­(t-Bu)­O]­RuH­(PPh3)2 (15) analogue to 13 has also been prepared from RuHCl­(PPh3)3 and Li­[CH2C­(t-Bu)­CHC­(t-Bu)­O]. Compounds 3, 5, 6, 7, and 12–15 have been structurally characterized. The preferred heteropentadienyl orientations and the relative positions of the H, Cl, PPh3, and PHPh2 ligands have been established in the piano-stool structures for all compounds, and it can be definitively surmised that the chemistry involved in the heteropentadienyl half-sandwich compounds studied is dominated by steric effects.

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