Highly Efficient Hydrosilylation of Alkenes by Organoyttrium Catalysts with Sterically Demanding Amidinate and Guanidinate Ligands

The sterically demanding guanidine ArNHC(NMe2)NAr (Ar = 2,6-diisopropylphenyl, HL) reacts with Y(CH2SiMe3)3(THF)2 to give the yttrium dialkyl complex (L)Y(CH2SiMe3)2(THF) (1), which was structurally characterized. Electronic interaction of the -NMe2 group with the conjugated ligand backbone can be inferred from structural and spectroscopic data. The new yttrium guanidinate complex 1 and its related amidinate analogue [PhC(NAr)2]Y(CH2SiMe3)2(THF) are highly active and selective catalysts for alkene hydrosilylation with PhSiH3 (tof > 600 h-1 at 23 °C). For unfunctionalized olefins, full selectivity toward anti-Markovnikov products was obtained. The more electron donating guanidinate ligand affords the highest activities with heteroatom-functionalized substrates.

The effect of the amido substituent on polymer molecular weight in propene homopolymerisation by titanium cyclopentadienyl-amide catalysts

In the homopolymerisation of propene by the cyclopentadienyl-amide titanium catalyst systems [η5,η1-C5H4(CH2)2NR]TiCl2/MAO and [η5,η1-C5H4(CH2)2NR]Ti(CH2Ph)2/B(C6F5)3 (R = tBu, iPr, Me), the catalyst with the smallest substituent (Me) on the amido moiety consistently gives the highest polymer molecular weight. This differs from the trend usually observed in related catalysts with tetramethylcyclopentadienyl-amide ancillary ligands, where larger amide substituents result in higher molecular weights. Based on the present information a hypothesis is formulated in which an increased cation-anion interaction for the less sterically hindered catalyst is responsible for disfavouring chain transfer relative to chain growth.

Cationic Group 3 Alkyl Complexes with Isopropyl-Substituted Triazacyclononane-amide Ligands: Synthesis, Structure, and Thermal Decomposition Processes

Yttrium and lanthanum dialkyl complexes with the isopropyl-substituted triazacyclononane-amide monoanionic ligands [iPr2TACN-(B)-NtBu] (B = (CH2)2, L1; SiMe2, L2) are described. For Y, these were obtained by reaction of Y(CH2SiMe3)2(THF)2 with HL, whereas for La in situ peralkylation of LaBr3(THF)4 preceded reaction with HL. In C6D5Br solvent, reaction of LMR2 with [PhNMe2H][B(C6F5)4] results in rapid decomposition involving loss of propene from the ligand. This decomposition is prevented (Y) or retarded (La) in THF solvent. For yttrium, salts of the cations [LYR(THF)]+ were isolated and structurally characterized. ES-MS of these cations revealed facile desolvation. At increased nozzle voltages, fragmentation is observed with initial loss of SiMe4, followed by loss of propene. Thus decomposition is likely to involve initial cyclometalation of a ligand iPr group, followed by propene extrusion. Decomposition of [L2LaR(THF)x]+ in THF solution yields the dinuclear dication {[tBuN(Me2Si)N(C2H4)2N(C2H4)NiPr]2La2(THF)2}2+, which was structurally characterized. Kinetic data of the decomposition suggest that the process involves initial THF dissociation.

Lanthanum Tribenzyl Complexes as Convenient Starting Materials for Organolanthanum Chemistry

Simple tribenzyl complexes of lanthanum, [La(CH2C6H4-4-R)3(THF)3] (R = H (1a), Me (1b)), were prepared in a remarkably straightforward fashion from LaBr3(THF)4 and potassium benzyl reagents. Single-crystal X-ray diffraction revealed a fac arrangement of the three THF ligands and η2 binding of the benzyl groups. These compounds are convenient precursors to other organolanthanum complexes. Reaction of 1a with the amidine ArN=CPhNHAr (Ar = 2,6-Pri2C6H3) affords the corresponding mono(amidinate) dibenzyl derivative 2. Complex 1b reacts with LiCH2C6H4-4-Me to give the THF-free anion [La(CH2C6H4-4-Me)4]- (3). Reactions of 1 with 1 or 2 equiv of [PhNMe2H][B(C6X5)4] (X = H, F) generate the corresponding mono- and dicationic benzyl species [La(CH2C6H4-4-R)2(THF)4]+ (4) and [La(CH2C6H4-4-R)(THF)6]2+ (5), which were structurally characterized. Scouting ethylene polymerization experiments indicate that these species are only modestly active catalysts but suggest that the monocationic dibenzyl species is more efficient. Both neutral and cationic lanthanum benzyl complexes effect the catalytic intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine. It was also observed that polycationic La species without ancillary ligands effectively catalyze the isomerization of the substrate to (E)-2,2-dimethyl-3-pentenylamine.

Synthesis of heteroatom end-functionalized polyethene with lanthanide and transition-metal catalysts

Incorporation of heteroatom functionalities in the catalytic formation of polyolefin materials can be accomplished either by copolymerization of the olefin with an olefinic substrate that has a heteroatom-containing substituent, or by using a heteroatom-containing chain-transfer agent. In the first case the functionalities introduced are located in side-groups on the polyolefin backbone, in the second case the functionality will cap the polymer on one end of the chain. The latter strategy has been applied recently using chain-transfer agents with reactive X-H bonds (X = Si, B) in conjunction with group 3 and group 4 metal catalysts. We have sought to apply the capacity of lanthanide metallocenes to perform ethene polymerization as well as C-H activation to this chemistry, using heteroatom-containing hydrocarbons with activated C-H bonds as chain-transfer agents, and to compare this with analogous cationic group 4 metallocenes