Vinyl ligands structure

The vinyliodonium salts 52,55 and 56 exist as head-to-tail dimers in the solid state. The dimeric unit of 52 exhibits nearly equidistant intra- and intermodular P—0--T contacts and has been described as a pseudo-octahedral 12-1-4 system95. The dimeric structures of 55 and 56 are held together by P=0--T contacts collinear with the vinyl ligands, while the fluoroborate and perchlorate ions are nearly collinear with the phenyl ligands140. 

Salient structural features of CpL2Mo(rj2-CRCR2) complexes include (1) the orientation of the two Cg substituents roughly orthogonal to the MCaCj3 plane (this is opposite to the location of Cp substituents of rj -vinyl ligands which lie in the MC C plane), (2) short M—Ca distances (1.94-1.96 A) appropriate for a molybdenum-carbon double bond (174),... 

Seyferth and co-workers described the preparation and spectroscopic characteristics of a series of jU,-r, T)--allenyl-bridged complexes [Fc2-(CO)6(/i-SR)(ju,-i7, i7"-HC=C=CH2)] (34) for which the methylene protons appeared equivalent at room temperature (23). A close structural similarity between the allenyl bonding mode and that of a bridging a-ir-vinyl was noted and led to the suggestion that the allenyl and vinyl ligands underwent a similar fluxional process (Scheme 37). 

Scheme 6.37. (a) Asymmetric cyclopropanation of styrene [137], (b) Cyclopropan-ation of alkynes [137]. For menthyl structure, see Scheme 6.34. (c) Asymmetric cyclopropanation of alkenes with vinyl carbenes [139]. Inset Ligand structures. 

The original report outlined the formation of an iridapyrrole (474, Schemes 40 and 67) by thermally induced intramolecular [3 -I- 2] cycloaddition of the acetonitrile and vinyl ligands in Tp Ir(Et)(CH = CH2)(NCMe) (292). An aromatic, rather than localised, structure was established for 474 on the basis of multinuclear 1 and 2-D NMR spectra, which revealed, inter alia, the iridium-bound methine unit to have resonances (Ah 10.71, 191.3) intermediate between those typical of metal... 

An example of this reaction has been reported in which the alkylpalladium group is functionalized with a chlorobenzyl moiety, in which case intramolecular attack on the aminoacyl leads to a cyclic carbene ligand (Equation (22)). The structure of 56 has also been obtained and a Pd-G bond length of 2.01(2) A found. In both of the above cases, deprotonation of the carbon a to the carbene atom can be carried out, leading to formally anionic vinyl ligands. 

In an extension of this work, the Shibasaki group developed the novel transformation 48—>51 shown in Scheme 10.25c To rationalize this interesting structural change, it was proposed that oxidative addition of the vinyl triflate moiety in 48 to an asymmetric palladium ) catalyst generated under the indicated conditions affords the 16-electron Pd+ complex 49. Since the weakly bound triflate ligand can easily dissociate from the metal center, a silver salt is not needed. Insertion of the coordinated alkene into the vinyl C-Pd bond then affords a transitory 7t-allylpalladium complex 50 which is captured in a regio- and stereocontrolled fashion by acetate ion to give the optically active bicyclic diene 51 in 80% ee (89% yield). This catalytic asymmetric synthesis by a Heck cyclization/ anion capture process is the first of its kind. 

Both MeMn(CO)5 and PhMn(CO)5 react with acetylenes to yield vinyl ketone tetracarbonyl complexes, most likely via a pathway involving CO insertion [Eq. (18)] 14, 36). Reactions of these same alkyls with 1,3-dienes may proceed similarly 16, 95, 96). The chelating ligand o-styryldiphenyl-phosphine (L—L) converts MeMn(CO)j into two products 25) whose structures (XXII and XXIII) were elucidated by X-ray crystallography 24). An unusual migration of COMe onto L—L occurs subsequently to the initial insertion step. 

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