Reaction of Ta(NMe2)5 with O2: Formation of Aminoxy and Unusual (Aminomethyl)amide Oxo Complexes and Theoretical Studies of the Mechanistic Pathways

Dioxygen Splitting by a Tantalum(V) Complex Ligated by a Rigid, Redox Non-Innocent Pincer Ligand

The reaction of TaMe₃ Cl₂ with the rigid acridane-derived trisamine H₃ NNN yields the tantalum(V) complex [TaCl₂ (NNN^cat )]. Subsequent reaction with dioxygen results in the full four-electron reduction of O₂ yielding the oxido-bridged bimetallic complex [{TaCl₂ (NNN^sq )}₂ O]. This dinuclear complex features an open-shell ground state due to partial ligand oxidation and was comprehensively characterized by single crystal X-ray diffraction, LIFDI mass spectrometry, NMR, EPR, IR and UV/VIS/NIR spectroscopy. The mechanism of O₂ activation was investigated by DFT calculations revealing initial binding of O₂ to the tantalum(V) center followed by complete O₂ scission to produce a terminal oxido-complex.

Tantalum(iv) pyrazolate: new wine in the old wineskin

Homoleptic binuclear Ta(iv) pyrazolate [Ta₂(pz)₈] with Ta–Ta distance of 3.1895(7) Å was obtained in a reaction of Ta(NMe₂)₅ with unsubstituted pyrazole Hpz.

Syntheses and characterization of hepta-coordinated Group 4 amidinate complexes

Hepta-coordinated Group 4 amidinate complexes have been synthesized and characterized by ¹⁵N chemical shifts through ¹H–¹⁵N gHMBC NMR.

Reactions of d(0) tungsten alkylidyne complexes with O2 or H2O. Formation of an oxo siloxy complex through unusual silyl migrations

(Me3SiCH2)3(Me3SiC≡)W←O=PMe3 (1), an adduct between (Me3SiCH2)3W≡CSiMe3 (2) and O=PMe3, reacts with O2 to give O=W(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2 with H2O yields 3 and the trimer [(μ-O)W(CH2SiMe3)2(=O)(THF)]3 (4). In the reaction of D2O with 2, 3-d(n) and methane isotopologues CH2D2, CHD3 and CD4 have been observed.

Theoretical study on the mechanism of Ni-catalyzed alkyl-alkyl Suzuki cross-coupling

Ni-catalyzed cross-coupling of unactivated secondary alkyl halides with alkylboranes provides an efficient way to construct alkyl-alkyl bonds. The mechanism of this reaction with the Ni/L1 (L1=trans-N,N'-dimethyl-1,2-cyclohexanediamine) system was examined for the first time by using theoretical calculations. The feasible mechanism was found to involve a Ni(I)-Ni(III) catalytic cycle with three main steps: transmetalation of [Ni(I)(L1)X] (X=Cl, Br) with 9-borabicyclo[3.3.1]nonane (9-BBN)R(1) to produce [Ni(I)(L1)(R(1))], oxidative addition of R(2) X with [Ni(I)(L1)(R(1))] to produce [Ni(III)(L1)(R(1))(R(2))X] through a radical pathway, and C-C reductive elimination to generate the product and [Ni(I)(L1)X]. The transmetalation step is rate-determining for both primary and secondary alkyl bromides. KOiBu decreases the activation barrier of the transmetalation step by forming a potassium alkyl boronate salt with alkyl borane. Tertiary alkyl halides are not reactive because the activation barrier of reductive elimination is too high (+34.7 kcal mol(-1)). On the other hand, the cross-coupling of alkyl chlorides can be catalyzed by Ni/L2 (L2=trans-N,N'-dimethyl-1,2-diphenylethane-1,2-diamine) because the activation barrier of transmetalation with L2 is lower than that with L1. Importantly, the Ni(0)-Ni(II) catalytic cycle is not favored in the present systems because reductive elimination from both singlet and triplet [Ni(II)(L1)(R(1))(R(2))] is very difficult.