Kazuyuki Tatsumi

Electronic structures of tris(cyclopentadienyl)uranium(IV)-ligand complexes

Abstract We present a systematic molecular orbital study of the electronic and geometrical structure of complexes containing the Cp3U fragment bonded to a variety of organic ligands. Nature of UC bonding is variegated, as is incarnated in a remarkable range of UC distances. As measured by overlap populations, covalency in the UC(alkyl) σ bond is strong, but very weak in the case of the UCp π bond. Covalency in the UCHPR3 and UCCR bonds is even enhanced due to additional interactions, more for the former, indicating the presence of partial multiple bond character.

Linear vs. bent MOR bonds in d0 metal alkoxides: X-ray crystal structure of (C5Me5)Ta(StBu)3(OnBu) and EHMO analysis

Abstract The tantalum n-butoxide complex of Cp★Ta(S t Bu) 3 (O n Bu) ( 1 ) (CP★  C 5 Me 5 ) has been isolated as a minor product from the reaction of Cp★TaCl 4 with LiS t Bu in THF. The crystal structure of 1 consists of two crystallographically independent molecules with distinctly different TaOC angles, where a larger angle is associated with a longer TaO bond and vice versa . EHMO calculations on the model CpTa(SH) 3 (OH) showed that the potential energy curve against the TaOH angle is in fact flat while the TaO overlap population decreases as the TaOH bond bends. Crystallographic data: 1 , space group P 2 1 , a = 9.134(4), b = 12.078(7), c = 27.74(2) A, β = 92.39(6)°; Z = 4; 4515 reflections with I > 3.0σ,( I ); R = 0.038, R w = 0.052.

An MO study on structures and reactivity of organoactinides based on the extended Hückel method: actinide bis(cyclopentadienyl) complexes

Abstract This contribution describes a brief summary of extended Huckel MO characterization of bis(cyclopentadienyl) (Cp) complexes of actinides. Some Cp * 2 AnL 2 molecules (An=actinide; Cp * =pentamethylcyclopentadienyl; L=η 2 -pyrazolate, η 2 -acyl, etc.) assume 20-electron structures violating the EAN rule. Our calculations show the observed geometries to be in fact electronically most stable, in contrast to the d-metal analogs which exhibit a strong tendency to obey the EAN rule. Characteristic features of the Cp 2 An fragment orbitals are emphasized. The electronic origins of the unusual alkyl deformation in Cp * 2 Th(CH 2 CMe 3 ) 2 are also ascribable to the unique bonding ability of the actinide fragment.

Catalysis by low-valent diamagnetic transition-metal complexes of the cis—trans isomerization of azobenzenes

Abstract Diamagnetic hydrido complexes, MH 2 (η-C 5 H 5 ) 2 (M = MO and W) and zerovalent d 10 complexes, ML 2-4 (M = Pt, Pd and Ni) are catalytically active in the cis—trans isomerization of azobenzenes and their p -substituted derivatives. The importance of a π interaction between the catalyst and azobenzene in inducing the isomerization is shown by (1) kinetic studies, (2) steric and electronic effects, and (3) a semi-empirical INDO calculation. By considering the π acidity of an NN linkage, a π-basic metal species is suggested as playing a vital role in the isomerization.

Rigidity of the unsymmetric coordination geometry of the two dithiolates in (C5Me5)Ta(norbornane-exo-2,3-dithiolate)2

Abstract We have synthesized (C 5 Me 5 )Ta(norbornane-exo-2,3-dithiolate) 2 and found that the two dithiolate ligands coordinate to Ta with opposite orientations with respect to CP★. In the 1 H NMR time scale, this unique geometry is rigid up to 100°C.

New Aspects of Carbanion Chemistry. Structure of Pentadienyl Anions and Butenediyl Dianions and their Roles in Organic and Inorganic Syntheses

Pentadienylpotassium exhibits the U-shaped (Z,Z)-geometry in ethereal solution as confirmed by trimethylsilylation and by the NMR measurement while solvated pentadienyllithium assumes the W-shaped (E,E)-geoemtry. The EHMO calculation on the pentadienylpotassium indicates the substantial stability of the U-shaped geometry. A variety of transmetallation of pentadienylpotassium is summarized briefly. A novel preparative method of 2-butene-l,4-diylmagnesium, one of the allylic dianions, is also described. This bifunctional magnesium compound serves as a versatile reagent in organic and inorganic syntheses.

On the Uranium-To-Carbon Bonds in Cp3UL Complexes

In this paper we study the nature of U-C bonding in Cp3UL complexes based on the extended Huckel molecular orbital method. A remarkable range of observed U-C distances parallels the calculated overlap populations. Covalency in the U-C (alkyl) σ bond is strong, while the U-Cp π bond has a very weak covalent character, if any. On the other hand, covalency in the U-CHPR3 and U-CCR bonds is enhanced, as measured by overlap population, due to additional π interactions indicating the presence of partial U-C multiple bond character. An analysis is also presented of the similarities and differences in the σ and π bonding capabilities of the organic ligands to U and a typical d transition metal, Fe.