Phosphorus-stabilized titanium carbene complexes: synthesis, reactivity and DFT studies.

The synthesis of two novel titanium carbene complexes from the bis(thiophosphinoyl)methanediide geminal dianion 1 (SCS(2-) ) is described. Dianion 1 reacts cleanly with 0.5 equivalents of [TiCl4 (thf)2 ] to afford the bis-carbene complex [(SCS)2 Ti] (2) in 86 % yield. The mono-carbene complex [(SCS)TiCl2 (thf)] (3) can also be obtained by using an excess of [TiCl4 (thf)2 ]. The structures of 2 and 3 are confirmed by X-ray crystallography. A strong nucleophilic reactivity towards various electrophiles (ketones and aldehydes) is observed. The reaction of 3 with N,N'-dicyclohexylcarbodiimide (DCC) and phenyl isocyanate leads to the formation of two novel diphosphinoketenimines 8 a and 8 b. The bis-titanium guanidinate complex 9 is trapped as the by-product of the reaction with DCC. The X-ray crystal structures of 8 a and 9 are presented. The mechanism of the reaction between complex 3 and DCC is rationalized by DFT studies.

First stabilization of 14-electron rhodium(I) complexes by hemichelation.

Hemichelation is emerging as a new mode of coordination where non-covalent interactions crucially contribute to the cohesion of electron-unsaturated organometallic complexes. This study discloses an unprecedented demonstration of this concept to a Group 9 metal, that is, Rh(I). The syntheses of new 14-electron Rh(I) complexes were achieved by choosing the anti-[(η(6):η(6)-fluorenyl){Cr(CO)3}2] anion as the ambiphilic hemichelating ligand, which was treated with [{Rh(nbd)Cl}2] (nbd=norbornadiene) and [{Rh(CO)2Cl}2]. The new T-shaped Rh(I) hemichelates were characterized by analytical and structural methods. Investigations using the methods of the DFT and electron-density topology analysis (NCI region analysis, QTAIM theory) confirmed the closed-shell, non-covalent and attractive characters of the interaction between the Rh(I) center and the proximal Cr(CO)3 moiety. This study shows that, by appropriate tuning of the electronic properties of the ambiphilic ligand, truly coordination-unsaturated Rh(I) complexes can be synthesized in a manageable form.

Hemichelation, a way to stabilize electron-unsaturated complexes: the case of T-shaped Pd and Pt metallacycles.

A rational method of synthesis of stable neutral T-shaped 14 electron Pd and Pt complexes is proposed. It takes advantage of the ambiphilic character of the tricarbonyl(η(6)-indenyl)chromium anion, of which the main property is to behave as a hemichelating ligand, that is a nonconventional heteroditopic ligand capable of chelating a metal center by way of covalent and noncovalent bonding, thus preserving its unsaturated valence shell. The reaction of the in situ formed tricarbonyl(η(6)-2-methylindenyl)chromium anion with a series of Pd and Pt metallacycles afforded new air-stable and persistent synfacial heterobimetallic complexes in which the metallacycle binds the indenyl fragment via its metal in an η(1) fashion, leaving the fourth coordination site at the chelated metal virtually vacant. The structures of eight of these novel complexes are disclosed, and their bonding features are investigated by an array of theoretical methods based on the density functional theory (NBO, EDA, ETS-NOCV, AIM, NCI region analysis). Theory shows that the formation of these unusual structures of bimetallic synfacial η(1)-indenyl-Pd/Pt complexes is driven thermodynamically by attractive Coulombic occlusion of the fourth vacant coordination site at Pd/Pt centers by the Cr(CO)3 moiety.

Electron-deficient η1-Indenyl,η3-allylpalladium(II) complexes stabilized by fluxional non-covalent interactions.

Highly fluxional, solution-persistent, and formally electron-deficient (32e(-)) binuclear Pd(II)-C(0) complexes of 2-methyl-1H-indene were synthesized and structurally characterized by X-ray diffraction analysis. DFT investigations combined with a number of theoretical analyses of the bond framework suggest that the polar intermetallic interaction possesses no major covalent character. Instead of bearing a static metal-metal bond as suggested by structural X-ray diffraction analysis, the complexes display in solution significant fluxionality through haptotropy, i.e., a formal "oscillation" of the Pd(η(3)-allyl) moiety between two limiting η(1)-indenyl configurations.

Room temperature tandem hydroamination and hydrosilation/protodesilation catalysis by a tricarbonylchromium-bound iridacycle.

A chromiumtricarbonyl-bound iridacycle displays novel catalytic virtues for the conversion of terminal aromatic alkynes into racemic N-phenyl, 1-arylethylamines by tandem hydro-amination and hydrosilation/protodesilation reactions under mild "one pot" conditions.

Revisiting the molecular roots of a ubiquitously successful synthesis: nickel(0) nanoparticles by reduction of [Ni(acetylacetonate)2].

The widely used preparation of Ni(0) nanoparticles from [Ni(acac)(2)] (acac=acetylacetonate) and oleylamine, often considered to be a thermolysis or a radical reaction, was analyzed anew by using a combination of DFT modeling and designed mechanistic experiments. Firstly, the reaction was followed up by using TGA to evaluate the energy barrier of the limiting step. Secondly, all the byproducts were identified using NMR spectroscopy, mass spectrometry, FTIR, and X-ray crystallography. These methods allowed us to depict both main and side-reaction pathways. Lastly, DFT modeling was utilized to assess the validity of this new scheme by identifying the limiting steps and evaluating the corresponding energy barriers. The oleylamine was shown to reduce the [Ni(acac)(2)] complex not through a one-electron radical mechanism, as often stated, but as an hydride donor through a two-electron chemical reduction route. This finding has strong consequences not only for the design of further nanoparticles syntheses that use long-chain amine as a reactant, but also for advanced understanding of catalytic reactions for which these nanoparticles can be employed.

Room temperature reversible C-H activation mediated by a Pt(0) center, and stoichiometric biphenyl formation via solvent activation.

Room temperature reversible C-H activation mediated by a designed diphosphine platinum complex is presented. These findings are demonstrated through mechanistic studies involving kinetics, isotopic effects, and corroborated by DFT calculations. The coupling between two unactivated aromatic derivatives is also demonstrated.

Synthesis of planar chiral iridacycles by cationic metal π-coordination: facial selectivity, and conformational and stereochemical consequences.

Facial selectivity during the π-coordination of pseudo-tetrahedral iridacycles by neutral (Cr(CO)(3)), monocationic (Cp*Ru(+)), and biscationic (Cp*Ir(2+)) metal centers was directly influenced by the coulombic imbalance in the coordination sphere of the chelated Ir center. We also showed by using theoretical calculations that the feasibility of the related metallacycles that displayed metallocenic planar chirality was dependent to the presence of an electron-donating group, such as NMe(2), which contributed to the overall stability of the complexes. When the π-bonded moiety was the strongly electron-withdrawing Cp*Ir(2+) group, the electron donation from NMe(2) resulted in major conformational changes, with a barrier to rotation of about 17 kcal mol(-1) for this group that became spectroscopically diastereotopic (high-field (1)H NMR spectroscopy). This peculiar property is proposed as a means to introduce a new type of constitutional chirality at the nitrogen center: planar chirality at tertiary aromatic amines.

Transmetalation of a nucleophilic carbene fragment: from early to late transition metals.

Early transition metal nucleophilic carbene complexes have been used as stoichiometric carbene transfer agents in a transmetalation process.

Room-temperature palladium-catalyzed Negishi-type coupling: a combined experimental and theoretical study.

An air-stable, bulky electron-accepting phosphine ligand (phosphabarrelene) allows the easy reduction of a Pd(II) precursor to a Pd(0) complex, highly active in room-temperature Negishi-type cross-coupling. DFT calculations show that the use of the electron-accepting ligand favors both transmetalation (TM) and reductive-elimination (RE) processes (see scheme; OA = oxidative addition).

Synthesis and structure of divalent thulium borohydrides, and their application in ε-caprolactone polymerisation.

The new divalent thulium compound [Tm(BH(4))(2)(DME)(2)] could be prepared by reduction of [Tm(BH(4))(3)(THF)(3)] or from TmI(2) and KBH(4). It was used as a precursor to the divalent [(Tp(tBu,Me))Tm(BH(4))(THF)] by reaction with potassium tris(2-tBu-4-Me)pyrazolylborate (KTp(tBu,Me)). Both Tm(II) compounds were found active as ε-caprolactone polymerisation catalysts.

Straightforward four-component access to spiroindolines.

Spiroindolines could be synthesized via a very convenient one-pot procedure combining a Ugi coupling and a new copper-catalyzed oxidative process at a peptidyl position. Due to the nature of the first step, this method offers a straightforward access to complex alkaloids with four points of molecular diversity.

Charge-induced facial-selectivity in the formation of new cationic planar chiral iridacycles derived from aniline.

The reaction of chiral chlorido-iridacyclic 2-(4-N,N-dimethylaminophenyl)pyridines with solvato-type [Cp*M(S)(3)](q+) (M = Ru, S = MeCN, q = 1; M = Ir, S = MeC(O)Me, q = 2) complexes produces new cationic racemic planar chiral iridacycles in an efficient and diastereospecific way.

Synthesis of samarium(II) borohydrides and their behaviour as initiators in styrene and epsilon-caprolactone polymerisation.

The bisborohydrido samarium compound Sm(BH(4))(2)(THF)(2) (1) was prepared in high yield by comproportionation between Sm and 2 equivalents of Sm(BH(4))(3)(THF)(3). Reaction of 1 with KCp* (Cp* = C(5)Me(5)) afforded the half-sandwich Cp*Sm(BH(4))(THF)(2) (2). The (1)H NMR borohydride resonances of both complexes, observed at very high field, are typical of divalent Sm compounds. X-Ray single crystal analysis revealed polymeric and dimeric molecular arrangements for 1 and 2, respectively. Complex 1 was found moderately active towards styrene polymerisation when activated with Al((i)Bu)(3), or with a borate/Al combination, whereas 2 showed no activity. Ring-opening polymerisation of epsilon-caprolactone could be performed rapidly at room temperature with both initiators. Complex 2 leads to narrow polydispersities and higher activity. Two different mechanisms, by monoelectronic transfer or by insertion into the Sm-(BH(4)) bond can be proposed.

Phosphorus stabilized carbene complexes: bisphosphonate dianion synthesis, reactivity and DFT studies of O~C~O zirconium(IV) complexes.

The reactivity of the geminal dianion of tetraisopropyl methylenediphosphonate, 3, with [ZrCl4(THF)2] affords a trinuclear structure 5 in which an unprecedented triscarbene-Zr dianionic fragment is found. The overall trinuclear arrangement is assembled by PO bridging moieties. The X-ray crystal structure of 5 is presented. The reaction of complex 5 with stoichiometric amounts of pyridine affords a dinuclear complex 6 whose formulation was ascertained by an X-ray crystal structure. Complexes 5 and 6 cleanly react with aldehydes (R1)(H)CO to afford the corresponding olefin of general formula [((OiPr)2P=O)2C=C(R1)(H)]. DFT calculations which were carried out on the model complex of 5t and a hypothetical monometallic Zr complex [Zr(3)Cl2(OMe2)2] 8t indicate that the Zr-C bond only features a weak pi-interaction between the carbon atom and a vacant orbital at the metal. The polarization of the orbital towards the carbon center is consistent with the observed nucleophilic character of the carbene complexes described here.

Bonding mode of a new bis-phosphine-borane alkyl ligand to a Rh(I) species.

The stoichiometric reaction of [Rh(COD)Cl](2) with the anion resulting from the deprotonation of dppm(BH(3))(2) yielded a new alkyl Rh(I) complex; the coordination modes of the BH(3) groups are discussed on the basis of X-ray data, variable temperature multinuclear NMR experiments and DFT studies.

Micro-chlorido, micro-hydroxo-bridged dicarbonyl ruthenacycles: synthesis, structure and catalytic properties in hydrogen atom transfer.

Micro-chlorido, micro-hydroxo-bridged ruthenacycles containing the Ru(CO)2 motif were synthesized by reaction of micro-dichlorido-bridged congener complexes with water in the presence of disodium carbonate. The substitution of one chlorido ligand for one hydroxo occurs with high stereoselectivity affording essentially hydroxo-bridged ruthenacycles, whereby the OH ligand occupies axial positions with respect to the mean plane defined by the chelating ligand. According to computational DFT investigations this stereoselectivity stems from a marked transphobia of the hydroxo ligand towards the carbanion of the ruthenacycle. The catalytic properties of the title compounds in hydrogen atom transfer process and particularly in the partial hydrogenation of alkynes have been investigated.

1-phosphabarrelene complexes of palladium and their use in Suzuki-Miyaura coupling reactions.

A bulky 1-phosphabarrelene, , was obtained from the reaction of a phosphinine with benzyne; two palladium complexes of were successfully employed in the Suzuki-Miyaura coupling of several aryl chlorides with phenylboronic acid at a relatively low catalyst loading, and activated aryl chlorides were coupled at room temperature in the absence of strong bases.