Tianshu Li

University of Toronto, Toronto, Ontario, Canada

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Publications (4)15.04 Total impact

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    ABSTRACT: Equilibrium constants (KDM) for reactions between acids and bases of the title compounds in CD2Cl2 (DM) have been determined by 31P and 1H NMR spectroscopy at room temperature. [HPCy3]BPh4 and [HPCy3]BF4, with pKDM assigned by literature convention to 9.7, have been used as the anchor compounds for the pKDM determinations. A continuous scale of pKDM values covering the range 9.7 to 5.7 is created with the acidic compounds [HPR3]BPh4. Those acids with pKDM greater than 6 are stable, while those with more acidic cations HPR3+ protonate BPh4– to produce R3PBPh3 and benzene. The literature pKTHF values reported for [HPBu2Ph]BPh4, [HPMePh2]BPh4, and [HPEtPh2]BPh4 are questionable because of this protonation reaction. NOE and PGSE 1H NMR techniques are used to show that [HPCy2Ph]BPh4 in DM exists as ion pairs and higher aggregates up to quadrupoles at the concentrations used in the acid–base studies. The new dihydrogen complexes [Ru(H2)Cl(PPh3)2(dach)]BF4 (dach = (1R,2R)-(–)-diaminocyclohexane) and [Ru(H2)Cl{tmeP2(NH)2}]BF4 (tmeP2(NH)2 = PPh2C6H4CH2NHCMe2CMe2NHCH2C6H4PPh2) were prepared by reaction of RuHCl(PPh3)2(dach) and RuHCl{tmeP2(NH)2} with HBF4. Their crystal structures are reported, and the pKDM values of their BPh4– salts were determined to be 8.6 and 6.9, respectively.Key words: acidity, dihydrogen complex, hydride, phosphonium, dichloromethane.
    No preview · Article · Feb 2011 · Canadian Journal of Chemistry
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    ABSTRACT: The reaction of RuHCl(PPh3)3 with the tetradentate ligand [PPh2((ortho-C6H4)CH2NHCH2-)]2 {ethP2(NH)2} in THF produces the new complex trans-RuHCl{ethP2(NH)2} (1) as a mixture of two isomers. The complex RuHCl{ethP2(NH)2} (1) when activated with KOtBu/KH is a very active catalyst for the hydrogenation of benzonitrile to benzylamine in toluene, more active than the known catalyst Ru(H2)2H2(PCy3)2 (2). A mixture of 1 and 2 and base also results in efficient conversion of benzonitrile to benzylamine. The complex RuHCl{tmeP2(NH)2} (3) where tmeP2(NH)2 is [PPh2((ortho-C6H4)CH2NHCMe2-)]2 is a less active catalyst for this reaction. These catalyst systems are air sensitive and extremely moisture sensitive. Experimental and theoretical (DFT) evidence is presented for a new mechanism for nitrile hydrogenation:  the successive hydrogenation of the CN triple bond and then the CN double bond of the intermediate imine by H+/H- transfer from a trans dihydride active catalyst. The amido complex RuH{tmeP2N(NH)} (4) has similar activity to 3/base for the base-free hydrogenation of benzonitrile and is moderately active for the catalytic hydration of benzonitrile. The new complex RuH(BH4){ethP2(NH)2} (7) was prepared by reacting 1 with NaBH4 but is found to be a poor catalyst for nitrile hydration.
    No preview · Article · Oct 2007 · Organometallics
  • Tianshu Li · Alan J Lough · Robert H Morris
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    ABSTRACT: Equilibrium constants (K) for reactions between acids and the conjugate base forms of a number of phosphonium salts, [HPR3][BF4], and iron hydrides, [Fe(CO)3H(PR3)2][BF4], in CD(2)Cl(2) have been determined by means of 31P and 1H NMR spectroscopy at 20 degrees C. The anchor compound chosen for pK(CD(2)Cl(2)) determinations was [HPCy3][BF4] with a pK(CD(2)Cl(2)) value of 9.7, as assigned by literature convention (Cy: cyclohexyl). A continuous scale of pK(CD(2)Cl(2)) values covering the range from 9.7 to -3 was created and correlated with the DeltaH values reported by Angelici and co-workers and literature pK(a) values. The pK(CD(2)Cl(2)) values for 15 other hydride or dihydrogen complexes of the iron group elements and of diethyl ether were also placed on this scale. The crystal structures of [Fe(CO)3H(PCy(2)Ph)2][BF4] and [Fe(CO)3(PCy(2)Ph)2] revealed that the trans-oriented, bulky, unsymmetrical phosphane ligands distort the equatorial plane of the complexes. The acidity of iron carbonyl hydrides is an important feature of the reactions of iron hydrogenase enzymes.
    No preview · Article · Feb 2007 · Chemistry
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    ABSTRACT: The new diphosphinediimine ligand PPh2C6H4CHNCMe2CMe2NCHC6H4PPh2 {tmeP2N2} is prepared by reacting NH2CMe2CMe2NH2 with 2 equiv of PPh2(C6H4-2-CHO). The diamine derivative PPh2C6H4CH2NHCMe2CMe2NHCH2C6H4PPh2 {tmeP2(NH)2} is prepared by reducing tmeP2N2 with LiAlH4. The reaction of RuHCl(PPh3)3 with tmeP2N2 in THF produces the complex trans-RuHCl{tmeP2N2}, while a similar reaction of RuHCl(PPh3)3 with tmeP2(NH)2 gives the complex trans-RuHCl{tmeP2(NH)2}, as a mixture of two isomers. The isomer with two N−H bonds syn to the Ru−H bond is converted on heating to an isomer thought to have one N−H syn to the Ru−H. The reaction of the two isomers with KOtBu under Ar in toluene produces the novel hydridoamido complex RuH{tmeP2NNH}, where the ligand is deprotonated at one nitrogen. Reaction of this amido complex with H2 gives exclusively the dihydridoamine complex trans-Ru(H)2{tmeP2(NH)2}. The complexes have been characterized by X-ray crystallography, NMR, IR, elemental analysis, and a deuterium exchange study. Complex RuH{tmeP2NNH}, or a combination of RuHCl{tmeP2(NH)2} and KOtBu, slowly catalyzes the hydrogenation of acetophenone (6 atm H2, 20 °C, benzene or 2-propanol). The catalytic cycle is thought to be similar to that for the ketone hydrogenation precatalyst trans-RuHCl{(S,S)-cyP2(NH)2)}. However in the present work both of the proposed catalysts trans-RuH2{tmeP2(NH)2} and RuH{tmeP2NNH} have been completely characterized. The tmeP2(NH)2 system, with hindering methyl groups, is less active than the cyP2(NH)2 system with a trans-1,2-substituted cyclohexyl backbone. The variable configuration of the amine nitrogens that is observed for the tmeP2(NH)2 complexes might also occur in the cyP2(NH)2 systems and could explain the inconsistent selectivity of such catalysts. The diimine complex RuHCl{tmeP2N2} reacts with KOtBu under H2 to produce the dihydridodiamine complex trans-Ru(H)2{tmeP2(NH)2}, the catalyst for the hydrogenation of acetophenone.
    No preview · Article · Nov 2004 · Organometallics