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Zhaomin Hou

Publications and source records attributed to Zhaomin Hou.

15 recordsLinked to original sources
PubMed2006

Hydrogenation of carbon monoxide by tetranuclear rare earth metal polyhydrido complexes. Selective formation of ethylene and isolation of well-defined polyoxo rare earth metal clusters.

The reaction of the tetranuclear rare earth metal polyhydrido complexes {Cp'Ln(mu-H)2}4(THF) (Cp' = C5Me4SiMe3, Ln = Y (1a), Lu (1b)) with carbon monoxide (1 atm) yielded ethylene and the corresponding tetraoxo cubane complexes (Cp'Ln)4(mu3-O)4 (Ln = Y (5a), Lu (5b)). Stepwise formation of some key reaction intermediates, such as oxymethylene complexes (Cp'Ln)4(mu-OCH2)(mu-H)6(THF) (Ln = Y (2a), Lu (2b)), enolate species (Cp'Y)4(OCH=CH2)(mu-O)(mu-H)5(THF) (3), and dioxo complex (Cp'Y)4(mu3-O)2(mu-H)4(THF) (4), was confirmed. The molecular structures of 2a, 4, and 5b were determined by X-ray diffraction studies.

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PubMed2006

Pi-conjugated aromatic enynes as a single-emitting component for white electroluminescence.

By use of the organolanthanide catalysts Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) and (C5Me5)2LaCH(SiMe3)2, carbazole-substituted phenyl enynes (Z)-CPEY and (E)-CPEY were synthesized, respectively, with excellent regio- and stereoselectivity through the catalytic dimerization of the corresponding terminal alkyne. These new pi-conjugated compounds, in particular, the (E)-enyne isomer (E)-CPEY, act as an excellent single-emitting component for white organic light-emitting devices (WOLEDs), as a result of combination of the blue emission from an isolated molecule with the longer-wavelength emissions (green and orange-red) from excimers. The (E)-CPEY-based double-layer device emitted almost pure white light with CIE coordinates of (0.32, 0.33), maximum brightness of 1395 cd m-2, and maximum current efficiency of 2.07 cd A-1. This is perhaps the purest white emission ever reported for a single-emitting-component WOLED. The quality of the white emission remained almost unchanged under varying driving voltages, demonstrating an advantageous potential of single-emitting-component WOLEDs.

Journal Article↗
PubMed2005

Catalytic addition of terminal alkynes to carbodiimides by half-sandwich rare earth metal complexes.

The catalytic addition of terminal alkynes to carbodiimides has been achieved for the first time by use of half-sandwich rare earth metal complexes, such as {Me2Si(C5Me4)(NPh)}Y(CH2SiMe3)(THF)2, which offers a straightforward, atom-economic route to the N,N'-disubstituted propiolamidines which contain a conjugated C-C triple bond, a new family of amidines which were difficult to prepare by other means. A rare earth metal amidinate species was confirmed to be a true catalytic species in this process, thus demonstrating for the first time that an amidinate unit, though being often used as an ancillary ligand for various organometallic complexes, can itself participate in a catalytic reaction under appropriate conditions.

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PubMed2005

Unprecedented isospecific 3,4-polymerization of isoprene by cationic rare earth metal alkyl species resulting from a binuclear precursor.

The isospecific 3,4-polymerization of isoprene has been achieved for the first time by use of a combination of a binuclear rare earth metal dialkyl complex, such as [Me2Si(C5Me4)(mu-PCy)YCH2SiMe3]2 (Cy = cyclohexyl), and an equimolar amount of [Ph3C][B(C6F5)4] as a catalyst system. A DFT calculation suggested that a binuclear monocationic monoalkyl species, such as [Me2Si(C5Me4)(mu-PCy)Y(mu-CH2SiMe3)Y(mu-PCy)(C5Me4)SiMe2]+, in which the alkyl group bridges the two metal centers, could be the true catalyst species.

Butadienes↗
PubMed2004

Scandium half-metallocene-catalyzed syndiospecific styrene polymerization and styrene-ethylene copolymerization: unprecedented incorporation of syndiotactic styrene-styrene sequences in styrene-ethylene copolymers.

On treatment with 1 equiv of [Ph3C][B(C6F5)4], the scandium half-sandwich bis(alkyl) complex (C5Me4SiMe3)Sc(CH2SiMe3)2(THF) showed extremely high activity (up to 1.36 x 104 kg of sPS/(mol Sc.h)) and syndiospecificity (rrrr > 99%) for the polymerization of styrene at room temperature in toluene. More remarkably, this catalyst system could also effect the syndiospecific copolymerization of styrene with ethylene to yield styrene-ethylene copolymers having syndiotactic styrene-styrene sequences. The styrene content in the copolymers could be easily controlled by changing the styrene feed and could reach higher than 80 mol %. This is the first example of formation of such types of styrene-ethylene copolymers, which are expected to show novel properties.

Journal Article↗
PubMed2004

Hydrogenation of carbon dioxide and aryl isocyanates by a tetranuclear tetrahydrido yttrium complex. Isolation, structures, and CO2 insertion reactions of methylene diolate and mu3-oxo yttrium complexes.

The reaction of carbon dioxide with a tetranuclear tetrahydrido yttrium complex [(C5Me4SiMe3)Y(mu-H)]4(L) (L = Me3SiCC(H)C(H)CSiMe3) (1) rapidly afforded the corresponding bis(methylene diolate) complex [(C5Me4SiMe3)Y]4(mu-O2CH2)2(L) (2), while the reactions of an aryl isocyanate with 1 led to selective formation of the mu3-oxo complex [(C5Me4SiMe3)Y]4(mu-O)( mu-H)2(L) (5) or [(C5Me4SiMe3)Y]4(mu-O)2(L) (7), depending on the substrate ratio. Both the methylene diolate and the oxo complexes can undergo CO2 insertion reactions to give the corresponding carbonate complexes. These reactions not only yield a new series of polynuclear yttrium complexes having novel structures but also shed new light on the mechanistic aspects of the heterogeneous hydrogenation of COmicron2. The high reactivity of the polynuclear mu3-oxo yttrium complexes 5 and 7 could also make them novel molecular models for study of metal oxide-supported catalysts.

Journal Article↗
PubMed2004

Tetranuclear rare earth metal polyhydrido complexes composed of "(C5Me4SiMe3)LnH2" Units. Unique reactivities toward unsaturated C-C, C-N, and C-O bonds.

The tetranuclear Lu and Y polyhydrido complexes [(C5Me4SiMe3)Ln(mu-H)2]4(THF) (Ln = Lu, Y) undergo novel multiple hydrogenation reactions with unsaturated organic compounds such as benzonitrile, gamma-butyrolactone, styrene, and 1,4-bis(trimethylsilyl)-1,3-butadiyne to afford a series of structurally characterizable polynuclear complexes that possess novel structures and are otherwise difficult to access. Most of these reactions are unprecedented and can be attributed to the unique cooperative effects of multiple active sites in the polyhydrido rare earth metal complexes.

Journal Article↗
PubMed2003

Novel Z-selective head-to-head dimerization of terminal alkynes catalyzed by lanthanide half-metallocene complexes.

Various terminal alkynes have been cleanly dimerized into the corresponding head-to-head (Z)-enynes by use of the half-metallocene lutetium alkyl complexes Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) (Ar = Ph, C6H3Me2-2,6, C6H2Me3-2,4,6) as catalysts. Aromatic C-Cl, C-Br, and C-I bonds, which are known to be extremely susceptible to reductive cleavage by transition metals, survived in the present reactions. The corresponding dimeric alkynide species [Me2Si(C5Me4)(NAr)Lu(mu-CCR)]2 are thought to be the true catalysts, some of which have been isolated and structurally characterized. These alkynide species were thermally stable and soluble at the reaction temperatures (80-110 degrees C), but they precipitated upon cooling to room temperature after completion of the reaction. Therefore, this catalyst system works homogeneously but can be separated and reused, thus constituting the first example of a recyclable catalyst system for the dimerization of terminal alkynes and also the first example of (Z)-selective head-to-head dimerization of aromatic terminal alkynes.

Journal Article↗
PubMed2003

New reactions of 1-alkynes catalyzed by transition metal complexes.

Recently discovered catalytic reactions with ruthenium and lanthanide metal complexes have extended the scope of 1-alkynes as useful reagents. The specific formation of aryl-substituted (Z)-1,3-enzymes via the dimerization of HC(triple bond) CR(1) (R(1) = aryl) has been attained using dimeric lanthanide complexes, the catalytic activity of which appears to be unaffected by time. The dimerization of HC(triple bond) CR(2) (R(2) = t-Bu, SiMe(3)) catalyzed by Ru(cod)(cot)/PR(3) or RuH(2)(PPh(3))(3) produces a good yield of butatrienes (Z)R(2)CH=C=C=CHR(2) with a high degree of selectivity. Under certain conditions, HC(triple bond) C=SiMe(3) dimerizes to yield exclusively (Z)-M(3)Si-C(triple bond) C-CH=CH-SiMe(3). The hydration of HC(triple bond)CR(3) (R(3) = alkyl, aryl) catalyzed by RuCl(2)/PR'(3) or CpRuCl(PR"(3))(2) has realized the first example of anti-Markovnikov regioselectivity in an addition reaction of water that produces aldehydes R(3)CH(2)bond;CHO. The application of this reaction to propargylic alcohols has lead to their formal isomerization to alpha,beta-unsaturated aldehydes. In contrast, the addition of amines R(4)bond;NH(2) (R(4) = aryl) to HCtbond;CR(5) (R(5) = alkyl, aryl) conforms to Markovnikov's rule to produce ketimines R(5)bond;(C=NR(4))bond;CH(3) when catalyzed by a Ru(3)(CO)(12)/additive. Since the reaction can be performed in air without the need for any solvents, it enables the practical synthesis of aromatic ketimines, which are difficult to prepare by conventional methods. The synthesis of indoles using deactivated anilines is one practical application of this reaction. The mechanisms of some of these reactions have been analyzed in detail with the aid of theoretical calculations.

Journal Article↗
PubMed1996

Heteroleptic Lanthanide Complexes with Aryloxide Ligands. Synthesis and Structural Characterization of Divalent and Trivalent Samarium Aryloxide/Halide and Aryloxide/Cyclopentadienide Complexes.

Synthesis of a new class of heteroleptic samarium aryloxide complexes has been achieved by the use of homoleptic samarium(II) bis(aryloxide) Sm(OAr)(2)(THF)(3) (1, Ar = C(6)H(2)Bu(t)(2)-2,6-Me-4) as a starting material, which is easily obtained by reaction of Sm(N(SiMe(3))(2))(2)(THF)(2) with 2 equiv of ArOH in THF. 1 reacts with 1 equiv of SmI(2) in THF to give Sm(II) mixed aryloxide/iodide [(ArO)Sm(&mgr;-I)(THF)(3)](2) (2), which adopts a dimeric structure via very weak Sm.I (3.534(2) Å) interactions. Reaction of 2 with C(5)Me(5)K in THF/HMPA affords the corresponding Sm(II) aryloxide/cyclopentadienide (C(5)Me(5))Sm(OAr)(HMPA)(2) (3). Oxidation of 1 with 0.5 equiv of I(2) in THF gives monomeric samarium(III) aryloxide/iodide (ArO)(2)SmI(THF)(2) (4), while the similar reaction of 1 with ClCH(2)CH(2)Cl or (t)BuCl in THF affords dimeric samarium(III) aryloxide/chloride [(ArO)(2)Sm(&mgr;-Cl)(THF)](2) (5). Crystal data for 1: monoclinic, space group P2(1), a = 9.903(3) Å, b = 16.718(5) Å, c = 13.267(2) Å, beta = 95.17(2) degrees, V = 2187(2) Å(3), Z = 2, D(c) = 1.223 g cm(-)(3), R = 0.0634. Crystal data for 2.2THF: monoclinic, space group P2(1)/a, a = 18.330(6) Å, b = 14.320(4) Å, c = 13.949(3) Å, beta = 103.16(2) degrees, V = 3563(2) Å(3), Z = 2, D(c) = 1.46 g cm(-)(3), R = 0.0606. Crystal data for 3: triclinic, space group P&onemacr;, a = 10.528(1) Å, b = 12.335(2) Å, c = 19.260(2) Å, alpha = 101.33(1) degrees, beta = 95.230(9) degrees, gamma = 108.54(1) degrees, V = 2293.1(5) Å(3), Z = 2, D(c) = 1.25 g cm(-)(3), R = 0.0358. Crystal data for 4: monoclinic, space group C2/c, a = 17.191(7) Å, b = 10.737(6) Å, c = 21.773(7) Å, beta = 98.80(3) degrees, V = 3971(3) Å(3), Z = 4, D(c) = 1.44 g cm(-)(3), R = 0.0467. Crystal data for 5: monoclinic, space group P2(1)/n, a = 13.750(3) Å, b = 17.231(3) Å, c = 14.973(6) Å, beta = 95.81(2) degrees, V = 3529(2) Å(3), Z = 2, D(c) = 1.31 g cm(-)(3), R = 0.0557.

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