Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

Studies from authors’ group (at the University of Tennessee) on alkylidene complexes and α-H migration in alkyl alkylidyne complexes, leading to unusual tautomerization equilibria between bis-alkylidenes and alkyl alkylidynes, are reviewed. Preparation of silyl alkylidene complexes (Me₃ECH₂)₂Ta(CHEMe₃)(SiR₃) [R₃ = (SiMe₃)₃, E = C, 3a, Si, 3b; R₃ = Bu^tPh₂, E = C, 4a, Si, 4b] and the pathway in the formation of 3b are discussed first. Pathways in the formation of archetypical Schrock-type alkyl alkylidenes (Me₃ECH₂)₃TaCHEMe₃ (E = C, 5a; Si, 5b), including the work using Ta(CD₂CMe₃)₅ (21-d₁₀) to confirm that it is the precursor to (Me₃CCD₂)₃TaCDCMe₃ (5a-d₇), are then considered. Tautomerization of silyl alkylidyne (Me₃CCH₂)₂W(CCMe₃)(SiBu^tPh₂) (6a) with bis-alkylidene (Me₃CCH₂)W(CHCMe₃)₂(SiBu^tPh₂) (6b) as well as (Me₃SiCH₂)₃W(CSiMe₃)(PR₃) [R₃ = Me₃, 7a; Me₂Ph, 8a; Me₂(CH₂)₂PMe₂ (DMPE-P), 9a] with (Me₃SiCH₂)₂W(CHSiMe₃)₂(PR₃) (R₃ = Me₃, 7b; Me₂Ph, 8b; DMPE-P, 9b) [P refers to a dangling P atom in Me₂P(CH₂)₂PMe₂] is covered next. Finally the conversion of the tungsten phosphine tautomerization mixtures to alkyl alkylidene alkylidyne (Me₃SiCH₂)W(CHSiMe₃)(CSiMe₃)(PR₃)₂ [(PR₃)₂ = (PMe₃)₂, 10; (PMe₂Ph)₂, 11; DMPE, 12], including its pathway, is presented.     

Z-Selective hydroamidation of terminal alkynes with secondary amides and imides catalyzed by a Ru/Yb-system

A catalyst system formed in situ from bis(2-methallyl)cycloocta-1,5-diene-ruthenium(II) [(cod)Ru(met)₂], 1,4-bis(dicyclohexylphosphino)butane (dcypb) and ytterbium(III) triflate hydrate (Yb(OTf)₃) was found to catalyze the addition of nitrogen nucleophiles to terminal alkynes under mild conditions to stereoselectively form the Z-enamide or Z-enimide products. Various secondary amides and imides could be added across the triple bond of a range of aliphatic and aromatic alkynes. The new bimetallic catalyst system sets new standards with regard to scope and selectivity for the synthesis of Z-configured anti-Markovnikov enamides.     

Synthesis, luminescence properties of a novel aromatic carboxylic acid (L) and corresponding Eu(III) and Tb(III) compounds as well as the binding characteristics of L with bovine serum albumin (BSA)

A novel polyamino polycarboxylic pyridine derivative ligand, N,N,N¹,N¹-(2,6-bis((3-(aminoethyl)-5-methyl-1H-pyrazol-1-yl)methyl)pyridine)hexakis(acetic acid) (L), was designed and synthesized with the motive that it is able to sensitize the emission of lanthanides. Its corresponding Eu(III) and Tb(III) complexes Na₄EuLCl₃·3H₂O and Na₄TbLCl₃·5H₂O were successfully prepared. The ligand and the complexes were characterized by elemental analysis, IR, MS, NMR and TG-DTA. The luminescence properties of the compounds in solid state were investigated; each complex had very narrow emission bands and strong luminescence intensity up to about 10,000. The TG-DTA studies showed that the initial decomposition temperature of both complexes was over 250 °C, elucidating the complexes had a high thermal stability. Meanwhile, the comparison with similar complexes suggested that the ligand with more coordination sites possessed more efficient antenna effect. To explore the potential medicinal value of L, the binding interaction of L and bovine serum albumin (BSA) was carried out by fluorescence spectrum. The studies indicated that the reaction between L and BSA was a static quenching procedure. The binding site number n and binding constant Ka were calculated according to the double logarithm regression equation. The thermodynamic parameters showed the Van der Waals and hydrogen bond interactions were the mainly impulse to the reaction.