Enrique Pérez-Carreño

A Simple Preparation of Pyridine‐Derived N‐Heterocyclic Carbenes and Their Transformation into Bridging Ligands by Orthometalation

Cat-ionic nickel(II) or palladium(II) complexes that have beenprepared in the laboratories of Raubenheimer, Herrmann, orFrenking by oxidative addition (or oxidative substitution) ofthe C X(X=halogen) bond of N-alkyl (or N-aryl) halopyr-idinium (or haloquinolinium, haloacridinium, etc.) salts toappropriate metal(0) precursors.

Cationic Heterocycles as Ligands: Synthesis and Reactivity with Anionic Nucleophiles of Cationic Triruthenium Clusters Containing C‐Metalated N‐Methylquinoxalinium or N‐Methylpyrazinium Ligands

The cationic cluster complexes [Ru3(CO)10(mu-H)(mu-kappa2N,C-L1Me)]+ (3+; HL1=quinoxaline) and [Ru3(CO)10(mu-H)(mu-kappa2N,C-L2Me)]+ (5+; HL2=pyrazine) have been prepared as triflate salts by treatment of their neutral precursors [Ru3(CO)10(mu-H)(mu-kappa2N,C-Ln)] with methyl triflate. The cationic character of their heterocyclic ligands is responsible for their enhanced tendency to react with anionic nucleophiles relative to that of hydrido triruthenium carbonyl clusters that have neutral N-heterocyclic ligands. These clusters react instantaneously with methyl lithium and potassium tris-sec-butylborohydride (K-selectride) to give neutral products that contain novel nonaromatic N-heterocyclic ligands. The following are the products that have been isolated: [Ru3(CO)9(mu-H)(mu3-kappa2N,C-L1Me2)] (6; from 3+ and methyl lithium), [Ru3(CO)9(mu-H)(mu3-kappa2N,C-L1HMe)] (7; from 3+ and K-selectride), [Ru3(CO)9(mu-H)(mu3-kappa2N,C-L2Me2)] (8; from 5+ and methyl lithium), and [Ru3(CO)9(mu-H)(mu3-kappa2N,C-L2HMe)] (11; from 5+ and K-selectride). Whereas the reactions of 3+ lead to products that arise from the attack of the corresponding nucleophile at the C atom of the only CH group adjacent to the N-methyl group, the reactions of 5+ give mixtures of two products that arise from the attack of the nucleophile at one of the C atoms located on either side of the N-methyl group. The LUMOs and the atomic charges of 3+ and 5+ confirm that the reactions of these clusters with anionic nucleophiles are orbital-controlled rather than charge-controlled processes. The N-heterocyclic ligands of all of these neutral products are attached to the metal atoms in nonconventional face-capping modes. Those of compounds 6-8 have the atoms of a ligand C=N fragment sigma-bonded to two Ru atoms and pi-bonded to the other Ru atom, whereas the ligand of compound 11 has a C-N fragment attached to a Ru atom through the N atom and to the remaining two Ru atoms through the C atom. A variable-temperature 1H NMR spectroscopic study showed that the ligand of compound 7 is involved in a fluxional process at temperatures above -93 degrees C, the mechanism of which has been satisfactorily modeled with the help of DFT calculations and involves the interconversion of the two enantiomers of this cluster through a conformational change of the ligand CH(2) group, which moves from one side of the plane of the heterocyclic ligand to the other, and a 180 degrees rotation of the entire organic ligand over a face of the metal triangle.

Orthometalation reactions in trifluoroacetate dirhodium(II) compounds. Molecular structure of Rh2(O2CCF3)2[(C6H4)PPh2]2·(PPh3)2·2(C7H8)

Abstract Rh 2 (O 2 CCF 3 ) 3 [(C 6 H 4 )PPh 2 ]·(HO 2 CCF 3 ) 2 reacts with PPh 3 yielding the doubly metalated compound Rh 2 (O 2 CCH 3 ) 2− [(C 6 H 4 )PPh 2 ] 2 ·(HO 2 CCF 3 ) 2 . The reaction proceeds via a reactive intermediate with an equatorial phosphine, Rh 2 (η 2 -O 2 CCF 3 )(μ-O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ](PPh 3 )·(HO 2 CCF 3 ), which can also be generated in moderate yield under photochemical conditions. The structure of the PPh 3 bis-adduct Rh 2 (O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ] 2 ·(PPh 3 ) 2 ·2(C 7 H 8 ) has been determined by X-ray diffraction. M r =1663.27, orthorhombic, space group Fdd 2, a =41.748(9), b =21.620(5), c =17.375(5) A, V =15683(6) A 3 , Z =8, D x =1.41 g cm −3 . Mo Kα radiation (graphite crystal monochromator, λ=0.71073 A), μ(Mo Kα)=5.57 cm −1 , F (000)=6800, T =293 K. Final conventional R factor=0.035 for 2789 ‘observed’ reflections and 422 variables. The molecule shows crystallographic two-fold axis symmetry through the RhRh bond. One toluene solvent molecule slightly disordered is present in the asymmetric unit.

Ring Opening and Bidentate Coordination of Amidinate Germylenes and Silylenes on Carbonyl Dicobalt Complexes: The Importance of a Slight Difference in Ligand Volume

The reactions of [Co2 (CO)8 ] with one equiv of the benzamidinate (R2 bzam) group-14 tetrylenes [M(R2 bzam)(HMDS)] (HMDS=N(SiMe3 )2 ; 1: M=Ge, R=iPr; 2: M=Si, R=tBu; 3: M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co2 {κ(1) MM(R2 bzam)(HMDS)}(CO)7 ] (4: M=Ge, R=iPr; 5: M=Si, R=tBu; 6: M=Ge, R=tBu), which contain a terminal κ(1) M-tetrylene ligand. Whereas the Co2 Si and Co2 Ge tert-butyl derivatives 5 and 6 are stable at 20 °C, the Co2 Ge isopropyl derivative 4 evolved to the ligand-bridged derivative [Co2 {μ-κ(2) Ge,N-Ge(iPr2 bzam)(HMDS)}(μ-CO)(CO)5 ] (7), in which the Ge atom spans the CoCo bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate-tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group-14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate NR groups. The disubstituted derivatives [Co2 {κ(1) MM(R2 bzam)(HMDS)}2 (CO)6 ] (8: M=Ge, R=iPr; 9: M=Si, R=tBu; 10: M=Ge, R=tBu), which contain two terminal κ(1) M-tetrylene ligands, have been prepared by treating [Co2 (CO)8 ] with two equiv of 1-3 at 20 °C. The IR spectra of 8-10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3-diarylimidazol-2-ylidenes), whereas that of silylene 2 is even higher.

Triazolopyridines. Part 11. Ylides derived from 2-Acylmethyltriazolopyridinium salts.

Abstract Ylides derived from 2-acylmethyltriazolopyridinium salts (2a) -(2c) react with methyl or ethyl propiolate and with dimethyl acetylenedicarboxylate to give ylides (3a)–(3e), (6) or (7). In some cases 1:2 adducts are formed, shown to be the novel ylides (8a)–(8d); an X-ray diffraction confirms structure (8a).

Diastereoselective intramolecular Diels-Alder reaction of the furan diene. A facile access to enantiopure epoxy tetrahydroisoindolines

Abstract 2-(2′-Furfuryl)-N-acryloyl tetrahydro-1,3-benzoxazine 2a participates in diastereoselective intramolecular Diels-Alder reaction in very mild conditions leading to two diastereoisomeric exo -adducts with good diastereoselectivity. Chromatographic separation of both adduts, and further elimination of the menthol appendage allows to prepare enantiopure iso -indoline derivatives in excellent chemical yields.

Roles of π-Alkyne, Hydride–Alkynyl, and Vinylidene Metal Species in the Conversion of Alkynes into Vinylidene: New Theoretical Insights

The transformation of acetylene into vinylidene, as promoted by the metal fragment [(pp3)Co]+ [pp3 = P(CH2CH2PPh2)3], is unimolecular and features the hydride–acetylide species as an intermediate. The paper describes a detailed ab initio study of the reaction, in particular with regard to the step involving 1,3-H shift. The best computational results are obtained by mimicking the pp3 ligand with actual ethylenic chains rather than with single PH3 molecules. The keypoints along the two-step reaction path (π-acetylene, hydride–acetylide, and vinylidene complexes, as well as intermediate transition states) have been optimized for CoI and RhI derivatives at the MP2 level. For the fragment [(pp3)Co]+, the barrier associated with transformation of the hydride–acetylide intermediate to vinylidene (20.6 kcal/mol) is easier to surmount compared to that for reversion to the reactants (28.6 kcal/mol). The situation is reversed for the analogous RhI system, with the initial π-acetylene adduct being slightly more stable. Although higher in energy, the hydride–acetylide species is the experimentally detected product of the reaction of acetylene with the fragment [(pp3)Rh]+. The salient chemical aspects of the 1,3-H shift are discussed in terms of perturbation theory arguments. Parallel EHMO calculations, which have provided a relatively good consistency with the ab initio results, allow the proposal of an orbital rationale for the mode of migration of the hydride ligand along the substantially linear Co–Cα–Cβ grouping.

Synthesis of indenyl-ruthenium(II) σ-alkynyl complexes via nucleophilic addition of (1R)-(+)- and (1S)-(−)-camphor enolates on the allenylidene group of [Ru(CCCPh2)(η5-C9H7)(PPh3)2][PF6]: Efficient synthesis of novel optically pure vinylidene derivatives

Abstract The diphenylallenylidene complex [Ru(CCCPh 2 )(η 5 -C 9 H 7 )(PPh 3 ) 2 ][PF 6 ] ( 1 ) regioselectively reacts at the C γ atom with the lithium enolate derived from (1 R )-(+)-camphor to yield σ-alkynyl derivative [Ru{CCCPh 2 (C 10 H 15 O)}(η 5 -C 9 H 7 )(PPh 3 ) 2 ] ( 2 ). Complex 2 was obtained as a non-separable mixture of two diastereoisomers, i.e. (1 R ,3 S ,4 R )- 2 and (1 R ,3 R ,4 R )- 2 (ca. 3:2 ratio), in which the alkynyl fragment is located in exo or endo disposition on the camphor skeleton, respectively. Protonation of this mixture with HBF 4 ·Et 2 O affords the vinylidene derivative [Ru{CC(H)CPh 2 (C 10 H 15 O)}(η 5 -C 9 H 7 )(PPh 3 ) 2 ][BF 4 ] ( 3 ) as a single diastereoisomer, i.e. (1 R ,3 S ,4 R )- 3 , showing an exo disposition of the vinylidene group. The structure of complex (1 R ,3 S ,4 R )- 3 has been confirmed by X-ray diffraction. The molecular structure shows the typical pseudo-octahedral three-legged piano-stool geometry around the ruthenium atom, which is linked to the phosphorus atoms of the PPh 3 ligands, to the η 5 -bonded indenyl ligand, and to an almost linear vinylidene chain (RuC(1)C(2)=165.6 (18)°) with a RuC(1) bond length of 1.88 (2) A. Demetalation of (1 R ,3 S ,4 R )- 3 , by treatment with acetonitrile at reflux, yields the terminal alkyne HCCCPh 2 (C 10 H 15 O) ( 4 ) and the nitrile complex [Ru(NCMe)(η 5 -C 9 H 7 )(PPh 3 ) 2 ][BF 4 ] ( 5 ). Compound 4 was obtained as a non-separable mixture of two diastereoisomers, i.e. (1 R ,3 S ,4 R )- 4 and (1 R ,3 R ,4 R )- 4 (ca. 3:1 ratio). Related reactions starting from diphenylallenylidene 1 and the (1 S )-(−)-camphor enolate are also reported.

Comparison of the oxidation of dinuclear cyclopentadienyl iron diphosphine complexes with the bridging ligands −CN and −CC(CH2)2Cn

Abstract The alkynyliron complex [Fe(CCCH 2 CH 2 CN)(dppe)(C 5 H 5 )] ( 2 ) (dppe = Ph 2 PCH 2 CH 2 PPh 2 ) prepared from [Fe(CCCH 2 CH 2 CN)(CO) 2 (C 5 H 5 )] ( 1 ) and dppe under UV irradiation, reacted with HBF 4 Et 2 O in tetrahydrofuran and with NH 4 [PF 6 ] in CH 2 Cl 2 to give the cationic vinylidene derivative [Fe(CCHCH 2 CH 2 CN) (dppe)(C 5 H 5 )][A] (A = BF 4 ( 3a ) or PF 6 ( 3b )), which can be reconverted to 2 with K 2 CO 3 in CH 2 Cl 2 . The compound [(C 5 H 5 )(dppe)Fe-NC-CH 2 CH 2 -CCH][PF 6 ] ( 4 ), which is a tautomeric form of 3 was prepared by reaction of [Fe(I)(dppe)(C 5 H 5 )] with the alkyne HCCCH 2 CH 2 CN in the presence of NH 4 [PF 6 ] in CH 2 Cl 2 . The dinuclear compound [(C 5 H 5 )(dppe)FeCCH 2 CNFe(dppe)C 5 H 5 ) [PF 6 ] ( 5 ), which is unstable, can be formed by reaction of 2 with [Fe(NCMe)(dppe)(C 5 H 5 ]PF 6 in CH 2 Cl 2 . Its electrochemical oxidation shows that there is no electronic interaction between the two metal centres. Extended Huckel molecular orbital calculations have been carried out on the model complexes [(C 5 H 5 )(PH 3 ) 2 FeCCCH 2 CH 2 -CNFe(PH 3 ) 2 (C 5 H 5 )] + ( 7 ) and [(C 5 H 5 )(PH 3 ) 2 FeCNFe(PH 3 ) 2 (C 5 H 5 )] + ( 8 ).

Novel indenyl half-sandwich osmium(II) complexes. X-ray structure of [Os{CC(H)But}(η5-C9H7)(PPh3)2][PF6]·OEt2

Abstract Reaction of LiC9H7 with [OsBr2(PPh3)3] gives the complex [Os(η5-C9H7)Br(PPh3)2] (1). The analogous complex [Os(η5-C9H7)I(PPh3)2] (2) is obtained from the metathesis reaction of [Os(η5-C9H7)Cl(PPh3)2] with NaI. The treatment of [Os(η5-C9H7)X(PPh3)2] with NaOMe leads to the hydride derivative [Os(η5-C9H7)H(PPh3)2] (3) which can be protonated with HBF4 to yield the cationic complex [Os(η5-C9H7)H2(PPh3)2][BF4] (4). Abstraction of the halide ligand in complexes [Os(η5-C9H7)X(PPh3)2] with NaPF6 or AgBF4 followed by the treatment with NCMe or terminal alkynes yield complexes [Os(η5-C9H7)(NCMe)(PPh3)2][BF4] (6) and [Os{ COCH 2 (CH 2 ) 3 C H2}(η5-C9H7)(PPh3)2][PF6] (7), respectively. X-ray crystal structure of the vinylidene derivative [Os{CC(H)tBu}(η5-C9H7)(PPh3)2][PF6] is reported along with variable temperature NMR studies.