Tp iPr Research Articles

Synthesis and characterization of enolato-cobalt and -nickel complexes bearing Tp iPr 2 ligand, [Tp iPr 2M(XCHY)] n [Tp iPr 2=hydrotris(3,5-diisopropylpyrazolyl)borato; n=1, 2], obtained from hydroxometal complexes, (μ-OH) 2(MTp iPr 2) 2, and active methylene compounds, CH 2XY

Reaction of hydroxo-cobalt and -nickel complexes, (Tp iPr 2 M) 2(μ-OH) 2 ( 1) [M=Co ( 1 Co), Ni ( 1 Ni); Tp iPr 2 : hydrotris(3,5-diisopropylpyrazolyl)borato], with active methylene compounds, CH 2XY ( 2) [X/Y=CN/COPh ( 2a); CN/CN ( 2b); COCH 2CMe 2CH 2CO ( 2d: dimedone); COMe/COOMe ( 2e); COOMe/COOMe ( 2f)], in the presence of a drying agent (e.g. Na 2SO 4) results in the dehydrative condensation to give N/O-bound enolato complexes with monomeric chelated structure Tp iPr2 MXCHY ( 3e and 3f), or dimeric cyclic structure (Tp iPr 2 M) 2(μ-XCHY) 2 ( 3a, 3b, and 3d). In contrast, treatment of 1 with methyl cyanoacetate ( 2c) gives the κ 2-carboxylato complex, Tp iPr 2 M(κ 2-OOCCH 2CN) ( 4c), via hydrolysis of the ester moiety by the action of the OH functional group in 1. The reaction pathway (enolato formation vs. ester hydrolysis) is a combined result of various factors including the acidity of the CH moiety in 2, rigidity of the enolato skeleton, and relative thermodynamic stability of possible structures. Molecular structures of 3b Co-2py, 3e Co-MeCN, 3f Ni and 4c Ni determined by X-ray crystallography reveal the formation the N/O-bound structure, where the negative charge is widely delocalized over the enolato functional group. No isomerization to C-bound enolate, Tp RM-CHXY, is observed, even when a less sterically hindered ligand, Tp Me 2 , is employed. Reaction of 3a Co and 3a Ni with benzaldehyde carried out as a preliminary study of the reactivity of the obtained enolato complexes 3 affords the metallacyclic products Tp iPr2C oO-C(Ph)-C(CN-CoTpiPr2)-CHPh-C(CN)-C(Ph)-O ( 5) (characterized by X-ray crystallography as a 2MeCN adduct) and Tp iPr2N iO-C(Ph)-C(CN-H)-CHPh-C(CN)-C(Ph)-O ( 6), respectively, by way of double condensation of PhCHO with two enolato functional groups.

Characterization of a dinuclear Mn(II) tri(μ-carboxylato) complex with the hindered hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (=Tp iPr 2) ligand: intramolecular hydrogen bonding interaction between the protonated Tp iPr 2 and Mn-coordinating carboxylate ligands

A dinuclear Mn(II) di(μ-hydroxo) complex having hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (=Tp iPr 2 ) reacted with benzoic acid to yield a dinuclear Mn(II) tri(μ-carboxylato) complex, Tp iPr 2 Mn-(μ-OBz) 3-Mn(Tp iPr 2 H). X-ray crystallography reveals the unsymmetrical coordination environments for the manganese centers. One of the two Tp iPr 2 ligands, which bound to the five-coordinated Mn center, is protonated by the action of the third carboxylic acid and the resulting non-Mn-binding N–H moiety forms an intramolecular hydrogen bond with the oxygen donor of a carboxylate ligand. Steric congestion in the bimetallic core results in the large separation of the manganese centers bridged by the syn- anti carboxylate ligand.

An approach to the O 2 activating mononuclear non-heme Fe enzymes: structural characterization of Fe(II)–acetato complex and formation of alkylperoxoiron(III) species with the highly hindered hydrotris(3-tert-butyl-5-isopropyl-1-pyrazolyl)borate

Structural characterization of an Fe(II)–acetato complex and attempts to synthesize mononuclear Fe(III) dioxygen complexes bearing the highly sterically demanding Tp tBu, iPr (=hydrotris(3-tert-butyl-5-isopropyl-1-pyrazolyl)borate) ligand have been investigated. X-ray crystallography reveals that the acetato complex consists of the distorted square pyramidal Fe(II) center as found for the previously reported O 2-reactive Tp iPr 2 derivative. In contrast to the less hindered Tp iPr 2 , (=hydrotris(3,5-diisopropyl-1-pyrazolyl)borate) complexes, oxidative addition of O 2 to the coordinatively unsaturated Fe(II) centers of the acetato and a hydroxo complexes with Tp tBu, iPr has never been observed in any conditions. Reaction of the ferrous hydroxo complex with ROOH (R=H, alkyl) results in the formation of the thermally unstable intermediates. Especially, the Fe(III)-alkylperoxo complex is characterized by UV–Vis, ESR and resonance Raman spectroscopy. The extremely bulky Tp tBu, iPr ligand hinders the approach of the exogenous O 2 molecule to the Fe(II) centers but stabilizes the unstable Fe(III)alkylperoxo intermediate enough to be detected.

Synthetic routes for hydrotris(pyrazolyl)borate complexes of rhodium(III)

The reaction of the alkali metal salt of several hydrotris(pyrazolyl)borate anions (Tp 3R,4R,5R) with RhCl 3·3H 2O in MeOH gave complexes of the type [Tp 3R,4R,5RRhCl 2(MeOH)] (Tp 3R,4R,5R = Tp Me, Tp Me2, Tp Me,4Me, Tp Me2,4Cl, Tp iPr and Tp iPr,4Br ). While the reaction of Na[Tp Me2] with [RhCl 3(MeCN) 3] in MeCN gave [Tp Me2RhCl 2(Pz Me2H)] ( 18), that of Na[Tp CF3,Me] gave [Tp CF3,MeRhCl 2(MeCN)]. The X-ray crystal structure of 18 (space group P 1 ̄ , a = 10.949(8), b = 11.415(8), c = 24.16(2) Å; α = 95.40(7), β = 91.39(7), γ = 115.37(5)°; Z = 4, R = 0.032, R w = 0.035 for 3813 observed reflections) shows that the rhodium atom has an octahedral geometry. The reaction of Na[Tp Me,Ph] with RhCl 3·3H 2O or [RhCl 3(MeCN) 3] gave mer-[RhCl 3(Pz Ph,Me) 3] while M[Tp CF3,CF3] (M = Na or Tl) did not react with either rhodium substrate. The complexes [Tp 3R,4R,5RRhCl 2(L)] (L = MeOH and MeCN) react with Cl − in CHCl 3 forming the corresponding [Tp 3R,4R,5RRhCl 3] − anions (Tp 3R,4R,5R = Tp, Tp Me, Tp Me2, Tp Me2,4Me, Tp Me2,4Cl, Tp iPr , Tp iPr,4Br , Tp CF3,Me). The X-ray crystal structure of [PPh 4][Tp Me2RhCl 3] ([ PPh 4 ] [ 25]) (space group P2 1/ c, a = 16.301(1), b = 9.9830(6), c = 26.337(1) Å; β = 101.97(3)°; Z = 4, R=0.052, R w = 0.060 for 4264 observed reflections) shows octahedral coordination at rhodium. A molecular modeling study using the structural data for 25 indicates that steric interactions between (a) the CF 3-substituents in position 5 on the pyrazolylborate and (b) the CF 3-substituents in position 3 and the other ligands present in the coordination sphere, may prevent the formation of rhodium(III) complexes with Tp CF3,CF3.

Reductive activation of dioxygen: A new concept for the catalytic oxidation

Transition metal–dioxygen complexes, which have been studied intensively in relevance to the active species of oxygenation with dioxygen molecule, are classified according to the extent of electron transfer from the metal center(s) to the O 2 ligand. A new O 2-activation method via a higher valent bis(μ-oxo) dimetal species resulting from extensive electron transfer is proposed on the basis of the results of our bioinorganic studies on the dioxygen complexes supported by the hydrotris(3,5-diisopropylpyrazolyl)borate ligand (Tp iPr ).