Allene complex

The following intermediate complex has also been isolated 121)  

This structure gives support for the proposal of an ionic monohaptoacety- 

Structural Parameters op Transition Metal-Allene Complexes 1 

A series of nickel triad complexes ML3(allene) (Table VII) were prepared (122, 123, 139) and studied in solution by means of H NMR spectroscopy. Consistent with a planar molecular structure, 

The Pt(0) complexes are in general rather stable, except for Pt(PPh )2-(TMA) (TMA = tetramethylallene). In solution, the latter shows a signal due to free TMA in addition to those of the complexed ligand, indicating dissociation  

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Because of the exceptional C-F bond strength, the successful preparation of a-halocyclopropyl c-complexes is realized by substitution of 1-bromo-l-fluoro-trans-2,3-dimethylcyclopropane 179 with Fp [90], Silica gel column chromatography of the thus obtained cr-complex 180 results in ring opening to the alcohol 181 as a single stereoisomer. The allene complex 182 is produced by treatment with BF3OEt2, indicating that 181 is derived from 182 and water. The 7i-allyl complex 183 is formed by photolysis via a disrotatory process. 

Acetylene and Allene Complexes Their Implication in Homogeneous Catalysis, 14, 245... 

Insertion of an allene molecule into the Pd-H bond, with regeneration of the starting allene complex 8 which then re-enters the catalytic cycle. In the absence of allene, extensive Pd black formation was observed. 

The photochemical reaction of diiron //-alkcnylidc complexes with diazo compounds leads to -allene complexes, which can be cleaved by several methods to yield allenes, for example allenic esters [32]. 

In 1997, Backvall and Jonasson published a procedure for the 1,2-oxidation of terminal allenes 7 [5]. In this case the reaction conditions were chosen so that the (vinyl)palladium complex equilibrates back to the allene complex. Using bromide instead of chloride as a nucleophile, the 2-bromo-jt-allyl complex 9 is the major intermediate present in the reaction mixture. A catalytic reaction was developed with the use of 5 mol% palladium acetate and p-benzoquinone (BQ) as terminal oxidant (Scheme 17.5). 

Nucleophilic attack on 45 (R = H) by four equivalents of Li[HBEt3], followed by addition of iodomethane, affords the p-allene complex (48) in a reaction which involves reduction of a coordinated CO and linkage to the vinylidene within the coordination sphere (57, 70) ... 

A number of readily reversible cr-7r rearrangements have been observed wherein a labile ligand such as carbon monoxide is lost by pyrolysis or photolysis, producing a coordinatively unsaturated metal center, which then regains coordinative saturation by means of a tr-n rearrangement. For example, irradiation of o--alkyl-7r-cyclopentadienyl-molybdenum tricarbonyl (15) produces the rr-allene complex (16) (25). These... 

B. Hydrocarbyl 7i-complexes 1. rj2-Alkene, alkyne, and allene complexes... 

The allene complexes 123-125 were also determined to adopt trigonal bipyramidal structures with the allene unit assuming a stereochemically rigid position in the trigonal plane, even at 110 °C. In the case of 1,1 -dimethylallene (124), coordination is exclusively through the CH2=C-double bond,54,55 while for methylallene (125) at least two of the four possible geometric isomers were obtained, though their stereochemistry remains undetermined, due to the complexity of the spectra (Chart 1). 

Among unique transformations on the metallacyclobutene framework, allene complexes of cobalt can be prepared by fluoride-induced desilylation of cobaltacyclobutene complex 39 three isomeric complexes bearing the same disubsituted allene are obtained (Equation 41) <1998JA1100>. 

The behavior of allene (1,2-propadiene) and its derivatives as ligands in transition metal complexes has been investigated for more than 20 years (197,198). Allene may be coordinated by only one C=C double bond to a metal (197,199), or it may link to two metal centers as a 2 2 or 3 1 electron donor. Dinuclear /i-f/2l2-allene complexes are known for Mo (200,201), W (201), Mn (202-203), and Rh (199,204). In [Fe2(CO)7(/ -f/3 1-C3H4)] a bonding mode (205,206). In the course of the reaction, often two or more allene molecules become connected with transition metal complexes. Two allenes linked by C-2 yield tetramethyl-eneethane (207,208), which is stabilized by coordination on Fe (205,208), Ni (270), or Pd (210,211). 

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