Organolanthanide-catalyzed synthesis of phosphine-terminated polyethylenes. Scope and mechanism.

Primary and secondary phosphines are investigated as chain-transfer agents for organolanthanide-mediated olefin polymerization. Ethylene polymerizations were carried out with [Cp'(2)LnH](2) and Cp'(2)LnCH(SiMe(3))(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Sm, Y, Lu) precatalysts in the presence of dicyclohexyl-, diisobutyl-, diethyl-, diphenyl-, cyclohexyl-, and phenylphosphine. In the presence of secondary phosphines, high polymerization activities (up to 10(7) g of polymer/(mol of Ln.atm ethylene.h)) and narrow product polymer polydispersities are observed. For lanthanocene-mediated ethylene polymerizations, the phosphine chain-transfer efficiency correlates with the rate of Ln-CH(SiMe(3))(2) protonolysis by the same phosphines and follows the trend H(2)PPh >> H(2)PCy > HPPh(2) > HPEt(2) approximately HP(i)()Bu(2) > HPCy(2). Under the conditions investigated, dicyclohexylphosphine is not an efficient chain-transfer agent for Cp'(2)LaPCy(2)- and Cp'(2)YPCy(2)-mediated ethylene polymerizations. Diisobutylphosphine and diethylphosphine are efficient chain-transfer agents for Cp'(2)La-mediated polymerizations; however, phosphine chain transfer does not appear to be competitive with other chain-transfer pathways in Cp'(2)Y-mediated polymerizations involving diisobutylphosphine. Regardless of the lanthanide metal, diphenylphosphine is an efficient chain-transfer agent for ethylene polymerization. Polymerizations conducted in the presence of primary phosphines produce only low-molecular-weight products. Thus, Cp'(2)Y-mediated ethylene polymerizations conducted in the presence of phenylphosphine and cyclohexylphosphine produce low-molecular-weight phenylphosphine- and cyclohexylphosphine-capped oligomers, respectively. For Cp'(2)YPPh(2)-mediated ethylene polymerizations, a linear relationship is observed between M(n) and [diphenylphosphine](-)(1), consistent with a phosphine protonolytic chain-transfer mechanism.

Organolanthanide-catalyzed synthesis of phosphine-terminated polyethylenes.

Organolanthanide-mediated hydrophosphination and ethylene polymerization are coupled in a catalytic cycle to produce diphenylphosphine-terminated polyethylenes. The resulting polymers were characterized by 1H, 13C, and 31P NMR, GPC, and DSC and compared spectroscopically to the model compound, 1-eicosyldiphenylphosphine oxide. High activities (107 g polymer/(mol Ln.atm ethylene.h)) and narrow polydispersities were observed in the polymerization/chain transfer process. Polyethylene molecular weights were found to be inversely proportional to diphenylphosphine concentration, supporting a chain transfer mechanism. The present discovery represents the first case in which an electron-rich phosphine functions efficiently as a chain transfer agent in a single-site fn/d0-mediated olefin polymerization process.

Intramolecular hydroamination/cyclization of conjugated aminodienes catalyzed by organolanthanide complexes. Scope, diastereo- and enantioselectivity, and reaction mechanism.

Organolanthanide complexes of the general type Cp'(2)LnCH(TMS)(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Sm, Y; TMS = SiMe(3)) and CGCSmN(TMS)(2) (CGC = Me(2)Si(eta(5)-Me(4)C(5))((t)()BuN)) serve as effective precatalysts for the rapid, regioselective, and highly diastereoselective intramolecular hydroamination/cyclization of primary and secondary amines tethered to conjugated dienes. The rates of aminodiene cyclizations are significantly more rapid than those of the corresponding aminoalkenes. This dienyl group rate enhancement as well as substituent group (R) effects on turnover frequencies is consistent with proposed transition state electronic demands. Kinetic and mechanistic data parallel monosubstituted aminoalkene hydroamination/cyclization, with turnover-limiting C=C insertion into the Ln-N bond to presumably form an Ln-eta(3) allyl intermediate, followed by rapid protonolysis of the resulting Ln-C linkage. The rate law is first-order in [catalyst] and zero-order in [aminodiene]. However, depending on the particular substrate and catalyst combination, deviations from zero-order kinetic behavior reflect competitive product inhibition or self-inhibition by substrate. Lanthanide ionic radius effects and ancillary ligation effects on turnover frequencies suggest a sterically more demanding Ln-N insertion step than in aminoalkene cyclohydroamination, while a substantially more negative DeltaS( double dagger ) implies a more highly organized transition state. Good to excellent diastereoselectivity is obtained in the synthesis of 2,5-trans-disubstituted pyrrolidines (80% de) and 2,6-cis-disubstituted piperidines (99% de). Formation of 2-(prop-1-enyl)piperidine using the chiral C(1)-symmetric precatalyst (S)-Me(2)Si(OHF)(CpR)SmN(TMS)(2) (OHF = eta(5)-octahydrofluorenyl; Cp = eta(5)-C(5)H(3); R = (-)-menthyl) proceeds with up to 71% ee. The highly stereoselective feature of aminodiene cyclization is demonstrated by concise syntheses of naturally occurring alkaloids, (+/-)-pinidine and (+)-coniine from simple diene precursors.

Synthesis and characterization of volatile, fluorine-free beta-ketoiminate lanthanide MOCVD precursors and their implementation in low-temperature growth of epitaxial CeO(2) buffer layers for superconducting electronics.

A new class of volatile, low-melting, fluorine-free lanthanide metal-organic chemical vapor deposition (MOCVD) precursors has been developed. The neutral, monomeric Ce, Nd, Gd, and Er complexes are coordinatively saturated by a versatile, multidentate ether-functionalized beta-ketoiminato ligand series, the melting point and volatility characteristics of which can be tuned by altering the alkyl substituents on the keto, imino, and ether sites of the ligand. Direct comparison with conventional lanthanide beta-diketonate complexes reveals that the present precursor class is a superior choice for lanthanide oxide MOCVD. Epitaxial CeO(2) buffer layer films can be grown on (001) YSZ substrates by MOCVD at significantly lower temperatures (450-650 degrees C) than previously possible by using one of the newly developed cerium beta-ketoiminate precursors. Films deposited at 540 degrees C have good out-of-plane (Deltaomega = 0.85 degrees ) and in-plane (Deltaphi = 1.65 degrees ) alignment and smooth surfaces (rms roughness approximately 4.3 A). The film growth rate decreases and the films tend to be smoother as the deposition temperature is increased. High-quality yttrium barium copper oxide (YBCO) films grown on these CeO(2) buffer layers by pulsed organometallic molecular beam epitaxy exhibit very good electrical transport properties (T(c) = 86.5 K, J(c) = 1.08 x 10(6) A/cm(2) at 77.4 K).