Chemistry of chromium bis-acetylide complexes

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)2Cr(dmpe)2] n+ (R=Ph, SiMe3, SiEt3, C≡C-SiMe3 n=0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies. Graphical Abstrac

Efficient Palladium-Catalyzed Cyclotrimeriza- tion of Arynes: Synthesis of Triphenylenes**

Over the last 15 years much effort has been devoted to the preparation and characterization of transition metal complexes of arynes. [1] Parallel studies on the reactivity of these complexesÐparticularly those of Ti, Zr, As part of a project aimed at the development of new reactions of arynes promoted by metal complexes, here we report on the metal-mediated cyclotrimerization of arynes. These preliminary results show that the reaction proceeds in the presence of catalytic amounts of metal and that it has great potential for the preparation of triphenylenes, which are found at the core of many discotic liquid crystals [9] An example of the formation of triphenylene as side product of a palladium-catalyzed domino reaction has also been reported. [10] However, to the best of our knowledge, efficient preparation of triphenylenes by metalcatalyzed reaction of arynes is without precedent. Development of a catalytic procedure for the trimerization of arynes requires careful selection of the catalyst and the method for generation of the aryne. The catalyst was chosen from among the various metal systems used for trimerization of alkynes; suitable candidates contained metals such as Ni, Co, Pd, and Pt. We decided to carry out the first trials with palladium complexes because they are easy to handle and in general stable. Among the many procedures available for the generation of arynes [9] S

Bis(glycinato-kappa2N,O)dinitrosylmolybdenum(0) and bis(2-aminoethanethiolato-kappa2N,S)dinitrosylmolybdenum(0) acetonitrile monosolvate

The title compds., [Mo(C2H4NO2)2(NO)2], (I), and [Mo(C2H6NS)2(NO)2]CH3CN, (II), contain distorted octahedral complexes in which the monoanionic N,S- and N,O-bidentate ligands coordinate the molybdenum centers in different modes. The anionic O atoms of the glycinate ligands in (I) are coordinated trans to the nitrosyl ligands and the amine N atoms are located trans to each other, whereas in (II) the anionic S atoms are coordinated trans to each other and the amine N atoms are located trans to the nitrosyl ligands. Each compd. has a single complete complex in the asym. unit on a general position. Six N-HO contacts with NO distances of less than 3.2 .ANG. are obsd. in (I) between the amine groups and the nitrosyl and carboxylate O atoms. In the 1:1 solvate (II), the acetonitrile mol. forms short N-HN contacts (NN 3.3 .ANG.) contribute to the stabilization of the structure of (II

Insertion reactions of trans-Mo(dmpe)2(H)(NO) with imines.

The insertion chemistry of the hydride complex trans-Mo(dmpe)(2)(H)(NO) (1) (dmpe = bis(dimethylphosphino)ethane) with imines has been investigated. It was found that disubstituted aromatic imines RCH[double bond]NR' (R, R' = Ar) insert into the Mo-H bond of 1, while a series of various mono- and other disubstituted imines do not react. The insertion products trans-Mo(dmpe)(2)(NO)[NR'(CH(2)R)] (R = R' = Ph (2); R = Cp(2)Fe, R' = Ph (3); R = Ph, R' = Cp(2)Fe (4); R = 1-naphthyl, R' = Ph (5)) have been isolated and fully characterized by elemental analysis, IR and NMR spectroscopy, and mass spectrometry. The imine PhCH[double bond]NC(10)H(7) (C(10)H(7) = 1-naphthyl) reacted with 1 establishing an equilibrium to produce the nonisolable complex trans-Mo(dmpe)(2)(NO)[NC(10)H(7)(CH(2)Ph)] (6). The equilibrium constant for this reaction has been derived from VT-NMR measurements, and the Delta H and Delta S values of this reaction were calculated to be -48.8 +/- 0.4 kJ.mol(-1) and -33 +/- 1 J.K(-1).mol(-1) reflecting a mild exothermic process and its associative nature. Single-crystal X-ray diffraction analyses were carried out on 2-5