Showing papers by "Shiro Hikichi published in 2010"

Tuning the Stability and Reactivity of Metal‐bound Alkylperoxide by Remote Site Substitution of the Ligand

Abstract: An alkylperoxonickel(II) complex with hydrotris(3,5-diisopropyl-4-bromo-1-pyrazolyl)borate, [Ni(II)(OOtBu)(Tp(iPr2,Br))] (3 a), is synthesized, and its chemical properties are compared with those of the prototype non-brominated ligand derivative [Ni(II)(OOtBu)(Tp(iPr2))] (3 b; Tp(iPr2)=hydrotris(3,5-diisopropyl-1-pyrazolyl)borate). Same synthetic procedures for the prototype 3 b and its precursors can be employed to the synthesis of the Tp(iPr2,Br) analogues. The dimeric nickel(II)-hydroxo complex, [(Ni(II)Tp(iPr2,Br))(2)(mu-OH)(2)] (2 a), can be synthesized by the base hydrolysis of the labile complexes [Ni(II)(Y)(Tp(iPr2,Br))] (Y=NO(3) (1 a), OAc (1 a')), which are obtained by the metathesis of NaTp(iPr2,Br) with the corresponding nickel(II) salts, and the following dehydrative condensation of 2 a with the stoichiometric amount of tert-butylhydroperoxide yields 3 a. The unique structural characteristics of the prototype 3 b, that is, highly distorted geometry of the nickel center and intermediate coordination mode of the O--O moiety between eta(1) and eta(2), are kept in the brominated ligand analogue 3 a. The introduction of the electron-withdrawing substitutents on the distal site of Tp(R) affects the thermal stability and reactivity of the nickel(II)-alkylperoxo species.

Coordination Properties of Organoborate Ligands – Steric Hindrance Around the Distal Boron Center Directs the Conformation of the Dialkylbis(imidazolyl)borate Scaffold

Abstract: Alkylmethylbis(imidazolyl)borate ligands, [B(Im N-Me ) 2 (alkyl)-M e ] - (L alkyl ; alkyl = methyl and n-butyl), have been synthesized by nucleophilic substitution from the chloride to the corresponding alkyl derivative on the boron center of the chloroborate precursor. In homoleptic complexes of nickel(II) with L alkyl , [Ni II (L alkyl ) 2 ] (1 alkyl ) one of the two alkyl groups on the boron atom faces the nickel(II) center to form a C-H...M interaction. In the analogous homoleptic nikel(II) complexes of the hydride, phenyl, and methoxy derivatives 1 x (X = H, Ph, OMe), the boron-attached CH 3 moieties do not turn towards the metal center. Steric repulsion between the methyl substituent on the imidazolyl ligands and the boron-attached methyl group directs the orientation of the alkyl groups on L alkyl . In the solution state the molecular structures of 1 alkyl observed in the solid state are retained. Mixed-ligand complexes, [Ni II (L alkyl )(Tp iPr2 )] (2 alkyl ). can be synthesized by reaction of [Ni II (Y)(Tp iPr2 )] (Y = Cl, NO 3 ) with L alkyl through selective ligand metathesis. In 2 Me , one methyl group of L Me approaches the nickel center retaining the bent conformation of the two imidazolyl groups. Conversely, the carbon atoms of the boron-attached nBu and Me groups of L Bu are located away from the nickel center, and the orientation of the two imidazolyl groups is almost coplanar in 2 Bu . The structural characteristics of these nickel(II) complexes demonstrate the flexibility of the dialkybis(imidazolyl)borate scaffold.