1-methallyl -complexes, preparation

In contrast to the tricarbonyl halide complexes, it is the exo conformation of () -allyl)FeCp(CO) complexes (163) which is preferred, and at equilibrium only traces of the endo isomer can be observed. Existing crystal structures of members of this class are of the exo conformation.Reasonable percentages of the endo conformer are realized upon low-temperature photolyses of their () -allyl)Fp precursors, however, and the activation barrier to endolexo conversion has been determined to be AG = 100.8kJmol for the 2-methallyl complex. In addition, the anti isomers, which can be prepared stereospecifically from the (j7 -allyl)Fp complexes, isomerize to the syn isomers with brief heating. The Fe NMR spectra are known for several of the complexes where CO has been replaced by a phosphine or phosphite (145) the chemical shift is highly dependent on the nature of the phosphorus ligand. ... 

Treatment of Cp"Cr(Ti -Cot), Cp" = Cp, Cp with (EtCN)3M(CO)3, M = Mo, W and Fe2(CO)9 affords the complexes [(Cp Cr)(CO)3M][ i-Cot], M = Fe, Cr, W, Cp = Cp and I(Cp Cr)(CO)3Crl/i-Cot, Cot = Cyclooctatetrane, which have been spectroscopically characterised. Bimetallic complexes containing bis(tetramethylcyclopentadienyl) dimethylsilane bridges have been prepared from the reaction of arene tricarbonyl molybdenum complexes with the silyl substituted cyclopentadienyl derivative. The synthesis of pinanylcyclopentadienes followed by metallation and reaction with Mo(CO)s and Mel gives the chiral (-)-[(ii -C5Me4-3-pinanyl)(CO)3Me], which has been structurally characterised. The chiral methallyl complexes CpMo(NO)X(Ti -2-methallyl) X = camphorsulfonate have been resolved and the reactions of the... 

Some of the evidence for such structures comes from the change in product distribution of the butenes as a function of cyanide concentration when butadiene is hydrogenated with pentaeyanocobaltate(II) catalyst or when the a butenyl complex is reduced with the hydride complex [HCo(CN)5] . Thus 1-butene is the major product in the presence of excess CN, and major product in the absence of excess cyanide. The 1-butene presumably arises from the cleavage of a tr complex, and the 2-butene via an intermediate w-allyl complex. The Tr-allyl complexes of cobalt tricarbonyl are well-characterized and can be prepared either from butadiene and HCo(CO)4 or from methallyl halide and NaCo(CO)4 [49). 

Success was obtained with Ru3(CO)i2 as catalyst precursor [6], but the most efficient catalysts were found in the RuCl2(arene)(phosphine) series. These complexes are known to produce ruthenium vinylidene spedes upon reaction with terminal alkynes under stoichiometric conditions, and thus are able to generate potential catalysts active for anti-Markovnikov addition [7]. Similar results were obtained by using Ru(r]" -cyclooctadiene)(ri -cyclooctatriene)/PR3 as catalyst precursor [8]. (Z)-Dienylcarba-mates were also regio- and stereo-selectively prepared from conjugated enynes and secondary aliphatic amines (diethylamine, piperidine, morpholine, pyrrolidine) but, in this case, RuCl2(arene) (phosphine) complexes were not very efficient and the best catalyst precursor was Ru(methallyl)2(diphenylphosphinoethane) [9] (Scheme 10.1). 

Ru(methallyl)2(cyclooctadiene) is prepared by addition of polymeric dichloro(cy-clooctadiene)ruthenium to a suspension of (2-methylpropenyl)magnesium chloride in diethyl ether, and stirring at room temperature for 1.5 h. After hydrolysis with cold water at -40 °C, the reaction mixture is extracted twice with diethyl ether. Evaporation of the solvent furnishes a gray powder in 80 % yield. This complex (2.0 g, 6.26 mmol) and 2.6 g (6.10 mmol) l,3-bis(diphenylphosphino)butane are... 

Other i73-allyl ruthenium complexes of type 44 have been prepared from la with allylmercury chlorides (allyl, methallyl, crotyl, 1-and 2-phenylallyl, and l-acetyl-2-methylallyl) (45). 

Anhydrous CrClj reacts with xs C3H5MgCI in ether at —30 to — 20°C to form red, volatile Cr( -C3H5)3 in ca. 60% yield . A detailed procedure is available, and Cr(// -methallyl)3 and Cr( j -crotyl)3 are prepared similarly . These 15-electron complexes are electron-pair acceptor acids and form stable adducts with donor bases such as pyridine and dioxane. Heating Cr(r/ -C3H5)3 in refluxing dioxane affords brown... 

Ruthenium-Catalyzed Hydrogenations. Ru-DuPhos complexes are commonly prepared by reacting [RuCl2(cod)] with methallylmagnesium chloride to generate [Ru(cod)(methallyl)2] which when treated with DuPhos and HX forms the catalytically active complex (DuPhos)RuX2. The procedure can be performed in a single pot or in stepwise fashion. Ru-DuPhos complexes effectively reduce a variety of substrates to provide chiral materials. 

The ligand dihydrobis(3,4,5-tribromopyrazol-l-yl)borate, (BpBr3), and its derivative [Mo(BpBr3)(t 3-methallyl)(CO)2] have been prepared and characterized by Trofimenko and coworkers who compared the structure of the Mo complex with that of [Mo(Bp )(t 3-methallyl) (C O) 2 ].152... 

Preparation. The complex is prepared from 2-methallyl bromide and nickel carbonyl in 85% yield by the method of Semmelhack and Helquist (4, 353). Reaction with carbonyl compounds. The complex reacts with aldehydes and ketones to produce homoallylic alcohols ... 

CpMo(NO)(7t-2-methallyl)X (X = (S)-(+)-10-camphorsulfonate) complexes 50 and 51 were prepared and separated from each other by resolving a diastereomeric mixture of CpMo(NO)(L)(7t-2-methylallyl) 49 (L = (+)- l(S)-camphorsulfonate) through fractional crystallization. In a typical run the yields of (-)-(S)-50 (97% de) and (+)-(R) 51 (de = 98%) were 14% and 38%, respectively. For these chiral compounds, replacing their camphorsulfonate group with halides allows generating enan-tiomerically pure CpMo(NO)X(ti-methallyl) (X = halides)[(-)-(5)-S2,... 

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