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.

Cyclopentadienyl-ruthenium half-sandwich complexes with eta(2)-bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru-catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp--)(eta(2)-RC[triple bond]CR')] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp-- (Cp--=eta(5)-1-methoxy-2,4-tert-butyl-3-neopentyl-cyclopentadienyl). Furthermore we demonstrate that [RuCl(2)(Cp==)](2) is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(eta(2)-alkyne) complexes containing {RuCl(Cp*)} (Cp*=eta(5)-C(5)Me(5)) and {RuCl(Cp--)} fragments with alkynes were investigated by DFT calculations at the M06/6-31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp-- ligand increases the activation energy required for the formation of the corresponding di(eta(2)-alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne.

No abstract

The reaction of RuCl 3 (solv.) n with tert-butylacetylene in methanol or ethanol leads to the formation of chloro-bridged half-sandwich complexes with sterically demanding cyclopentadienyl ligands, which are of high interest as starting materials for the synthesis of novel Ru catalysts. ) n ] § and 4.2 equivalents of tertbutylacetylene in methanol were heated to 55 uC, a brown powder began to precipitate after 2 h (Scheme 1). After 24 h, the mixture was cooled to 220 uC and complex 3 was isolated in 51% yield (see ESI{).Elemental analysis of complex 3 showed that a carbon-rich compound had formed (C = 50.47%). Attempts to obtain further structural information by NMR spectroscopy were not successful, indicating the presence of paramagnetic Ru III . This was confirmed by a single crystal X-ray analysis." The overall structure of complex 3 is similar to that of 2: two (g 5 -cyclopentadienyl)RuCl 2 fragments are connected by two chloro bridges to form a centrosymmetric dimer (Fig. 1). However, the cyclopentadienyl ligands show a unique substitution pattern, with two tert-butyl, one neopentyl and one methoxy group attached to the aromatic ring. Due to the presence of different side chains, the (p-ligand)Ru fragment displays planar chirality. There are two independent (p-ligand)RuCl 2 complexes in the asymmetric unit; the dimers are obtained by the symmetry operation 2x, 1 2 y, z and 1 -x, 1 -y, 1 -z, respectively. The Ru atoms in these dimers are 3.684(1) and 3.743(1) s apart from each other, and therefore not bonded to each other. 11When [RuCl 3 (solv.) n ] was reacted with tert-butylacetylene in ethanol instead of methanol, the ethoxy complex 4 was obtained in 40% yield (see ESI{). The structure of 4 is analogous to that of