New mixed ligand complexes of dicyclopentadienyl titanium(IV) derived from sterically congested heterocyclic β-diketones and N-protected amino acids

Abstract

The interaction of titanocenedichloride with various monofunctional bidentate ligands in different stoichiometric ratios affords products of variable compositions depending upon the nature of the ligands and experimental conditions. [1][2][3] An exhaustive survey of the literature reveals that a large number of dicyclopentadienyl titanium(IV) complexes of the types [Ti(C 5 H 5 ) 2 ClL], [TiC 5 H 5 ClL 2 ] and [Ti(C 5 H 5 ) 2 L 2 ] (where L = monofunctional bidentate ligand) have been synthesised and extensively studied 4-6 due to their interesting chemistry and applications. Metallocene catalysts 7-9 are put to use for the industrial polymerisation of alkenes. [10][11][12][13] It is reported that some of the derivatives of titanocenedichloride exhibit an antitumour effect, 14,15 this has provided an impetus for further studies in this field.N-protected amino acids and heterocyclic β-diketones are the potential organic ligands which have aroused much interest because of their interesting bonding patterns 16,17 and potential biological applications of their metal complexes. [18][19][20] Much interest has been focused on the chemistry of complexes of these ligands with group IV and XIV metals. 16,17,[21][22][23][24][25][26] However, there is no literature report on the synthesis of mixed ligand complexes of titanocenedichloride derived from these ligands. As an extension of the work described in our previous communications, 22,27 it was considered relevant to prepare mixed ligand complexes of dicyclopentadienyl titanium(IV) of these potential organic ligands. The present work has the objective of seeking more information concerning the nature of bonding and comparative ligating capability of these ligands towards dicyclopentadienyl titanium(IV). Results and discussionDicyclopentadienyl titanium(IV) complexes of general formula [TiCp 2 LA] where LH= RCOC:C(OH)N(C 6 H 5 )N:CCH 3 and AH = HOOC-CHR'NC(O)C 6 H 4 C(O) [R = -C 6 H 5 , -CH 3 , -C 2 H 5 and R' = -H, -CH 2 C 6 H 5 , -CH 3 and -CH(CH 3 ) 2 ]have been synthesised by the interaction of titanocenedichloride with congested heterocyclic β-diketones (LH) and N-protected amino acids (AH) in the presence of triethylamine in a 1:1:1:2 molar ratio in refluxing THF solution, see below.After filtering off triethylamine hydrochloride formed during the reaction and stripping the volatile fraction under reduced pressure, coloured solid powders were obtained which were recrystallised from CHCl 3 /n-hexane mixture in 48 to 56% yield. These solid derivatives have sharp melting points and are highly soluble in common organic solvents like THF, benzene and chloroform. The newly synthesized mixed ligand complexes of dicyclopentadienyl Ti(IV) derived from N-protected amino acids and heterocyclic β-diketones were subjected to spectral (IR, 1 H NMR and 13 C NMR) studies and information inferred from these studies has been used to diagnose the nature of bonding and to elucidate the plausible structures of these complexes. IR spectral studiesThe IR spectra of these complexes are record...

Some new N-protected amino acid derivatives of phenylboronic acid: preparation, structural chemistry and insight into structural aspects based on spectroscopic studies

“…υ (CO) sym and υ (COO) asym bands are merged and appeared as a broad band at ∼ 1690 cm -1 . In the IR spectra of boron derivatives, this band shifts in the region 1725 ± 5 cm -1 which indicates the unidentate nature of the ligands (Verma et al, 2004). The unidentate nature of N-protected aminoacids is further supported by the magnitude of ∆ υ [ ∆ υ = υ (COO) asym -υ (COO) sym ] calculated for these boron derivatives.…”

“…Various potential organic ligands have been used for the synthesis of organic derivatives of organoboron(III) (Singh et al, 2005;Swami et al, 2009;Yadav et al, 2010). N-Protected amino acids are an important class of organic ligands which display a diversifi ed mode of bonding (Saxena et al, 1991(Saxena et al, , 1992Surana and Saxena, 1996;Verma et al, 2004;Joshi et al, 2005;Sharma et al, 2007;Gupta et al, 2009) and their metal complexes exhibit signifi cant biological activities (Saxena et al, 1991). In view of the interesting results obtained in our previous communications (Gupta et al, 2010a,b;Sharma et al, 2010) and as an extension of our ongoing research work concerning the synthesis of organic derivatives of some trivalent and tetravalent elements, it was considered relevant to study the ligating capability of N-protected amino acids towards PhB(OH) 2 .…”

Structural insights into some sterically demanding heterocyclic β-diketones: Optimized molecular structure, optimized energy, stability and Mulliken charge distribution based on DFT analysis

“…The charge distribution at O1' and O2' demonstrates the highest electron density sites in heterocyclic β-diketones. In our previous research work, these heterocyclic β-diketones were used as a very promoising organic ligands for the synthesis of different metal complexes involving these sites in bonding [18][19][20][26][27][28] .…”

Synthesis, Structural, and Antibacterial Studies of Some Mixed Ligand Complexes of Zn(II), Cd(II), and Hg(II) Derived From Citral Thiosemicarbazone and N-Phthaloyl Amino Acids

“…26 Recently, a publication reported on the synthesis and characterization of mixed ligand complexes of titanocene dichloride derived from heterocyclic β-diketonates and N-protected amino acids. 27 However, there are no literature reports on the synthesis of mixed ligand complexes derived from thiosemicarbazone of citral and N-phthaloyl amino acids. As an extension of work described in our previous communications, 28,29 in the present communication we report the synthesis, structural, and antibacterial studies of some mixed ligand complexes of transition metals derived from these potential organic ligands.…”