Mono- and bis-amidinate 2,6-xylylimido vanadium chlorides: synthesis, structure, and reactivity.
(2010)
Journal - Dalton transactions (Cambridge, England : 2003)
Abstract :
Salt metathesis of (2,6-xylylimido) vanadium trichloride () with the unsolvated or the TMEDA lithium p-Et benzamidinate complexes ( and , respectively, in 1 : 2 V : Li molar ratio) yields bis[N,N'-bis(trimethylsilyl) p-Et benzamidinate](2,6-xylylimido)VCl () as dark brown, diamond-shaped crystals. When equimolar amounts of complexes and are reacted, a mixture of the bis () and mono () imidovanadium amidinates results. A similar mixture is also obtained by a ligand metathesis reaction of the bis amidinate complex and complex . When the synthesis of the mono amidinate is attempted with the TMEDA lithium amidinate complexes or the 3-pyridyl derivative () (in 1 : 1 V : Li molar ratio) a redox reaction takes place to produce (kappa(2)-TMEDA)(2,6-xylylimido)V(IV)Cl(2) () as crystalline, mustard-yellow plates. The activity of complex in ethylene polymerization was negligible with MAO or MAO\(CPh(3))(+)[B(C(6)F(5))(4)](-) as co-catalysts.
Chemoselectivity Diversity in the Reaction of LiNC(6)F(5)SiMe(3) with Nitriles and the Synthesis, Structure, and Reactivity of Zirconium Mono- and Tris[2-(2-pyridyl)tetrafluorobenzimidazolate] Complexes.
(2010)
Journal - Inorganic chemistry
Abstract :
Unlike the reaction of LiNTMS(2)·TMEDA (TMS = SiMe(3); TMEDA = tetramethylethylenediamine) with 2-cyanopyridine, which results in the nearly exclusive formation of the amidinate, (Me(3)SiNC(6)F(5))Li·TMEDA (1) reacts with 2-cyanopyridine in toluene to yield quantitatively the lithium pyridyltetrafluorobenzimidazolate complex [C(6)F(4)N(2)C(2-C(5)H(4)N)]Li·TMEDA (3). In this work, the reactivity of complex 1 toward aromatic nitriles Ar-CN (Ar = Ph, o-OMeC(6)H(4), C(6)F(5), 2-pyridyl) was examined. Whereas complex 1 fails to react with o-methoxybenzonitrile, its reaction with benzonitrile or pentafluorobenzonitrile gives triphenyl-1,3,5-triazine (4) or the hexacoordinate lithium polymer [LiN(4-NCC(6)F(4))(C(6)F(5))·THF·TMEDA](n) (7), respectively. When 1 is reacted with 2-cyanopyridine in tetrahydrofuran (THF), the benzimidazolate coordination polymer {[C(6)F(4)N(2)C(2-C(5)H(4)N)]Li·THF}(n) (5) is obtained. Herein we discuss how this diverse chemoselectivity in the reaction of the examined lithium N-silylated amides LiNRTMS·TMEDA (R = TMS, C(6)F(5)) with nitriles is influenced by the electronic properties of the nitrile or amide substituents and by the ability of these substituents to interact with the lithium or silicon atoms. Further, we present the syntheses and structures of zirconium tris(pyridyltetrafluorobenzimidazolate) chloride (10) and zirconium bis(dimethylamido)(pyridyltetrafluorobenzimidazolate) chloride·THF (11) complexes. These complexes, the first prepared zirconium mono- and tris(benzimidazolate)s, were crystallographically characterized and examined in the polymerization of propylene with methyl aluminoxane (1:1000 Zr/Al molar ratio).
Synthesis of lithium N-pentafluorophenyl, N'-trimethylsilyl 2-pyridylamidinate and its cyclization to lithium tetrafluoro-2-(2-pyridyl)benzimidazolate via a Me3SiF elimination. Coordination chemistry, reactivity, and mechanism.
(2009)
Journal - Inorganic chemistry (United States )
Abstract :
When N-trimethylsilylpentafluoro aniline reacts with BuLi in the presence of THF or TMEDA, the corresponding THF (2) or TMEDA (4) lithium anilides are obtained. Complex 4 is monomeric in the solid state, with a distorted trigonal pyramidal coordination geometry at the lithium center. The strong C-F-->Li interaction in this complex is also accompanied by the elongation of the C-F bond. Mild heating of complex 4 with 2-cyanopyridine results in rapid evolution of Me(3)SiF to quantitatively yield the tetrafluoro-2-(2-pyridyl)benzimidazolate lithium complex (6). From the reaction mixture of complex 4 the asymmetric N-trimethylsilyl, N'-pentafluorophenyl-2-pyridylamidinate lithium complex (5) was isolated as a dormant intermediate. Complex 5 possesses several unusual bonding features with the most notably being a very short Si-N bond length and a rare kappa(1)-Z-syn amidinate bonding mode. A mechanism that includes silicon assisted C-F bond activation is proposed for the cyclization reaction based on the structural parameters of complexes 5 and 6, and on (1)H, (19)F, and (13)C NMR studies.
Lithium Furyl and Pyridyl Amidinates as Building Blocks in Coordination Polymers, Ladder and Cage Structures.
(2009)
Journal - Inorganic chemistry
Abstract :
Lithium N,N'-bis(trimethylsilyl)heterocyclic amidinate complexes with 3- and 4-pyridyl and 3-furyl carbon substituents were prepared by addition of the corresponding nitriles to LiN(SiMe(3))(2) (LiNTMS(2)) solution. In the presence of N,N,N',N' tetramethylethylene diamine (TMEDA), both pyridyl amidinates crystallize as coordination polymers with an amidinate-Li-pyridyl backbone. The 4-pyridyl derivative (7) creates a linear polymer with amidinate-Li-TMEDA units as side chains, whereas the 3-pyridyl polymer (6) has a two-dimensional (2D) network structure in which TMEDA serves as a cross-linker. Solvation of the reaction mixture of 3-furonitrile and LiNTMS(2) with TMEDA affords the monomeric 3-furyl amidinate Li TMEDA complex (3). Crystals of the Li(2)O complex {[3-furyl-C-(NTMS)(2)Li](4).Li(2)O}.C(7)H(8) (4) are obtained from toluene by partial hydrolysis of the unsolvated 3-furyl amidinate (2). Degradation of the polymer (7) to monomeric units can be achieved by solvation in toluene or by reaction with TMS(2)NLi.TMEDA that affords crystals of the complex {NTMS(2)Li.[4-C(5)H(4)N-C(NTMS)(2)Li.TMEDA]}(2).(NTMS(2)Li.TMEDA) (8). The formation of these aggregates can be rationalized by directed substitution of TMEDA with pyridyl moieties and by the laddering principle.