Alkyne complexes crystal structures

The substituted bis-Cp alkynyl-alkenyl (C5Me4R1)2Ti(G=CR2)(GH=GHR2) (Scheme 502) have been synthesized by reaction of the bis(trimethylsilyl)ethyne complex (G5Me4R1)2Ti(Me3SiC2SiMe3) with 1-alkynes the crystal structures have been determined by X-ray diffraction. Photolysis of these complexes involves dimerization processes with coupling of the two cr-ligands to give complexes with 1,4-disubstituted but-l-en-3-ynes.1287... 

The novel highly substituted spiro[4.4]nonatrienes 98 and 99 are produced by a [3+2+2+2] cocyclization with participation of three alkyne molecules and the (2 -dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 (Scheme 20). This transformation is the first one ever observed involving threefold insertion of an alkyne and was first reported in 1999 by de Meijere et al. [81]. The structure of the product was eventually determined by X-ray crystal structure analysis of the quaternary ammonium iodide prepared from the regioisomer 98 (Ar=Ph) with methyl iodide. Interestingly, these formal [3+2+2+2] cycloaddition products are formed only from terminal arylacetylenes. In a control experiment with the complex 96 13C-labeled at the carbene carbon, the 13C label was found only at the spiro carbon atom of the products 98 and 99 [42]. 

Reactions of the Ir1 complexes (289) and (290) with H2 and subsequent reaction of the dihydride products with dimethyl acetylenedicarboxylate, Me02CC CC02Me (dma), give the Ir11 complexes (291), (292), (293), and (294), as shown in Reaction Scheme 26.482 The X-ray crystal-structure determination of (294) confirms the double insertion of the alkyne into each of the Ir—H bonds of (293). 

Figure 8 The preparations and crystal structures of copper(I) alkene and alkyne complexes... 

A mononuclear tantalum-benzyne complex (121) has been prepared by thermolysis of 120 [Eq. (20)].14 An X-ray crystal structure was reported for 121. Bond lengths for the benzyne unit are given in Table III. Complex 121 exhibits a rich insertion chemistry similar to that of Ti, Zr, and Ru benzyne complexes. Insertion reactions of 121 with ethylene, 2-butyne, acetonitrile, and carbon dioxide give 122, 123, 124, and 125, respectively (Scheme 15). Diphenylacetylene does not couple with 121, presumably because of steric constraints. Reagents with acidic protons such as methanol or terminal alkynes cleave the Ta—C bond to give butyl isocyanide and carbon monoxide, but... 

X-Ray Crystal Structure Determinations of Molybdenum(II) and Tungsten(II) Halocarbonyl Alkyne Complexes Reported since 1987... 

The crystal structures of in excess of 70 hexacarbonylalkyne-dicobalt complexes have been determined by X-ray diffraction. In all cases the basic structural features are the same and can be illustrated by the structure of [Co -FjCQCFjXCO), shown in Fig. 1,Z7 The molecule has pseudo C2v symmetry in which the two cobalt atoms and the two acetylenic carbon atoms form a quasi-tetrahedral core. The carbon-carbon bond of the alkyne is in a perpendicular orientation relative to the cobalt-cobalt bond, as opposed to the parallel orientation which is also observed in dinuclear complexes with bridging alkyne ligands. The coordination around the cobalt atoms is distorted octahedral and the two tricarbonylcobalt moieties are eclipsed. 

Connelly and Orpen have used the complexes [Co2( -RC2R)(/a-dppm)2(CO)2] (R = Me, Ph, or C02Me) to test the molecular orbital description of [Co2(jU-alkyne)(CO)6] outlined in Section II,B.63a The X-ray crystal structures of [Co2( U.-MeC2Me)( U,-dppm)2(CO)2] (see Fig. 10) and [Co2(jU-PhC2Ph)(jU,-dppm)2(CO)2] show the alkyne to be orthogonal to the cobalt-cobalt bond. Oxidation affords the monocations [Co2(jU-RC2R) (/a-dppm)2(CO)2]+, and the crystal structure of [Co2(,u-MeC2Me)... 

A number of other mechanistic sequences are thought to occur in alkyne trimerizations mediated by other metal systems. Catalysts derived from Co2(CO)s follow a characteristic sequence of steps that involves exclusively dinuclear complexes (Scheme 26). The nature of the final (alkyne)3C02(CO)4 intermediate, a so-called flyover complex, is supported by both X-ray crystal structure data as well as its involvement in forming other products besides benzenes. These dinuclear cobalt systems are note-... 

One final structure in this series is the bis-TMEDA-solvated bis(phenylethynyl)magnesium species characterized as a monomer (111). ° Note the octahedral geometry of the central magnesium with two axial ethynyl ligands. This series of alkynic structures, (106)-(lil). serves to underscore the unpredictability of carbanion crystal structures. The alkynic carbanions have coordination numbers of one, two or three in these complexes. 

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