Complexes of Group 4 metallocenes in the +3 oxidation state and amidoborane or phosphidoborane function as efficient precatalysts for the dehydrocoupling/dehydrogenation of amine-boranes, such as Me(2) NH⋅BH(3). Such Ti(III) -amidoborane complexes are generated in [Cp(2)Ti]-catalyzed amine-borane dehydrocoupling reactions, for which diamagnetic M(II) and M(IV) species have been previously postulated as precatalysts and intermediates.
The water-soluble complexes [(Cp′OR)RuCl(PTA) 2 ] (Cp′OR ) η 5 -1-alkoxy-2,4-di-tert-butyl-3-neopentylcyclopentadienyl; R ) Me, Et; PTA ) 1,3,5-triaza-7-phosphaadamantane) are considerably more cytotoxic (ca. 2 orders of magnitude) than the cyclopentadienyl analogue [CpRuCl(PTA) 2 ] (i.e., IC 50 ) 4-10 Vs >1000 µM, depending on the cell line). The structure of [(Cp′OMe)RuCl(PTA) 2 ] is reported, together with that of the precursor [(Cp′OEt)Ru(µ-Cl)] 2 .
The reaction between CO2 and propylene oxide in the presence of Nb(EtO)5 and 4-dimethylaminopyridine leads to the formation of an acyclic carbonate through an unprecedented pathway.
A chloro-bridged Ru III complex of formula [Cp ∧ RuCl 2 ] 2 (Cp ∧ ) η 5 -1-methoxy-2,4-tert-butyl-3neopentylcyclopentadienyl) (1) was obtained in a single step by reaction of [RuCl 3 (solv) n ] with tertbutylacetylene in methanol. Complex 1 showed polymorphism and crystallized in two distinct forms: an isomer, 1a, with no significant metal-metal interactions (Ru‚‚‚Ru ) 3.684(1) or 3.743(1) Å) and an isomer, 1b, in which the Ru atoms are 2.960(2) Å apart from each other. In solution, a temperaturedependent equilibrium between the two isomers is established. When the reaction of [RuCl 3 (solv) n ] with tert-butylacetylene was carried out in ethanol, the chloro-bridged dimer 2, with an ethoxy instead of a methoxy group attached to the cyclopentadienyl ligand, was formed. Complex 1 was found to be a versatile starting material for the synthesis of mononuclear half-sandwich complexes. With phosphine ligands or norbornadiene (nbd), the 16 ecomplexes [Cp ∧ RuCl(PCy 3 )] (3), [Cp ∧ RuCl(PPh 3 )] (4), and [Cp ∧ RuCl-(PnBu 3 )] ( 5), the 17 ecomplex [Cp ∧ RuCl 2 (PPh 3 )] ( 7), and the 18 ecomplexes [Cp ∧ RuX(PPh 2 RPPh 2 )] (X ) H, Cl; R ) CH 2 , C 2 H 4 ; 8-11) and [Cp ∧ RuCl(nbd)] (12) were obtained. Crystallographic analyses show that the Ru-P bond lengths in these complexes are longer than in corresponding pentamethylcyclopentadienyl complexes.
The methoxy-bridged Ru II complex [Cp ∧ Ru(µ-OMe)] 2 (Cp ∧ ) η 5 -1-methoxy-2,4-di-tert-butyl-3neopentylcyclopentadienyl) was obtained from the Ru III complex [Cp ∧ RuCl(µ-Cl)] 2 by reaction with K 2 CO 3 in methanol. In the presence of EtOH, the complex was converted into the ethoxy-bridged dimer [Cp ∧ Ru(µ-OEt)] 2 . Due to the steric demand of the Cp ∧ π-ligand, complex [Cp ∧ Ru(µ-OMe)] 2 behaves differently than the parent complex [Cp*Ru(µ-OMe)] 2 . Reaction with Me 3 SiCl in the presence of LiCl gave the electronically unsaturated complex [Cp ∧ Ru(µ-Cl)] 2 , whereas a tetrameric structure had been reported for the analogous Cp* complex. In contrast to the expected addition reaction, a monomeric complex [Cp ∧ Ru(CO) 2 (CO 2 Me)] was obtained by ligand insertion of CO in the Ru-OMe bond. Moreover, an unprecedented transformation of cyclooctadiene into ethylbenzene in the coordination sphere of Ru was observed. Complex [Cp ∧ Ru(µ-OMe)] 2 was found to act as a highly active catalyst for atom transfer radical cyclization (ATRC) reactions on a diverse range of substrates such as N-substituted dichloroand trichloroacetamides, enamides, ethers, and esters.
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