Enyl complexes preparation

Clark and Hartwell have prepared the but-3-enyl complex (CH2= =CHCH2CH2)3PRhCl (52) in which the Rh is again pentacoordinate, an X-ray study showing that the olefin groups are parallel to the equatorial plane of the trigonal bipyramidal coordination sphere as in RhBr-(tvpp). The complex shows a conductivity in methanol appropriate for ionization to LRh MeOH)+ Cl. ... 

Cu(l) and Fe(ll) complexes prepared in situ by reacting copper(l) or iron(ll) chloride with 1 equiv of ligand LI (tris(pyridin-2-ylmethyl)amine) or L2 are efficient catalysts for atom-transfer radical addition reactions. For instance, pent-4-enyl trichloroacetate was converted into 3,3,5-trichlorooxocan-2-one in 90% and 99% yield, respectively, when CuCl-Ll and CuCl-L2 were used as catalysts (Scheme 30) <2000J(P1)575>. 

Co arene chemistry has been expanded by the preparation of a number of (arene)Co(j7" -diene)+ and (arene)Co( , -enyl) complexes starting from (10). Hydrogenation of (10) in the presence of an arene and a base (piperidine or quinuclidine for obvious stabilization of coordinatively unsaturated cobalt intermediates) gives cyclooctenyl complexes (37) (equation 53). This reaction occurs with a large niunber of arenes even CeFg gives an j -arene complex. The resulting complexes (37) are moderately active catalysts in the pyridine synthesis from alkynes and nitriles (Section 5.1.4). 

Equation (57) shows another example of the preparation of a Pd(ll) enyl complex by nucleophilic attack of OH on a diene, following previous oxidation of a Pd(0) complex by a quinone. 

Obviously, substituted jc-enyl complexes only may be prepared from diene olefins. In the above addition of 7c-C5H5(CO)2Fe—H to butadiene mainly the 1,4-addition product is obtained. Similarly the 1,4-addition product is fotind with Co(CO)4H and butadiene. In this case a (r-but-2-enyI intermediate is not isolated and the reaction proceeds immediately to the 7t-methylallyl cobalt tricarbonyl which is isolated as a mixture of the... 

These c-complexes have been less extensively studied than the r 3-allyltitanium derivatives. r 1 -Allyltitanocenes can readily be prepared from the corresponding magnesium compounds by reaction with Cp2TiCl2 or by reaction of preformed r 3-allyltitanium complexes with but-2-enyl halides [36]. Crotyl-type reagents, which are accessible only in the E-iso-meric form, add to aldehydes with an anti selectivity (Scheme 13.17). 

Mercury(II) complexes of two t5T>es have been prepared (6) from pent-4-enyl diphenyl phosphine and mercuric halides. These complexes are of the formulae [LHgX2]2(X = Cl, Br, I) and LaHgXg (X = Br, I). In no case is the olefin coordinated to the metal. 

The photochemical reaction corresponds to facile insertion of la into [(f/5-indenyl)Mo(CO)3(CH3)] with formation of [(f/5-indenyl)Mo(CO)2( 3-(Z)-2-hexen-l-yl-5-one)] (90). Cationic complexes of the type [(f/5-C5Hs)-M(f/3 "-enylketone)] [PF6] (M = Rh, Ir) have been prepared recently. An -coordination of the enyl moiety and of the carbonyl function by a free pair of electrons has been discussed (91). 

Cationic sandwich complexes of the type CpCo(arene) + were first prepared by hydride abstraction from cyclohexadi-enyl cations (Section 7.1). They are accessible in broader variation from the reaction of CpCoX half-sandwich complexes with arene in the presence of AICI3. Their electrochemical reductions to the corresponding 19-electron monocations and to 20-electron neutral complexes have been studied. The stability of electron-rich sandwich complexes increases with increasing alkyl substitution in either ring despite the more negative redox potential mass spectrometry studies of bond dissociation energies of (arene)Co+ complexes corroborate these results. However, neutral sandwich complexes are not very stable in the polar solvents necessary for the reduction of mono- or dications and have been isolated only from alkyne trimerization with CpCo precursors in nonpolar solvents (Section 5.1.4). 

To test the validity of their assumption, Mootoo and Fraser-Reid prepared NPGs 12-18 and treated them with NBS in 1% aqueous acetonitrile [16]. Their results, summarized in O Table 1, showed that differently substituted NPGs could be chemoselectively liberated at the anomeric center to yield hemiacetals 19-24. Furthermore, benzylidene, silyl, p-methoxybenzyl (PMB), ethoxyethyl, and allyl protecting groups proved to be compatible with the conditions employed in the deprotection of the anomeric pent-4-enyl group. Diol 18, however, furnished a complex reaction mixture probably related to competing glycosylation processes, vide infra. 

Heterobimetallic ruthenium alkylidenes, which may be prepared by reaction of Cl2Ru(PCy3)2(CHR) with [Ru(/j-cymene)Cl2]2, [Os(/j-cymene)Cl2]2, and [Rh(terf-butylcyclopentadienyl)Cl2]2, respectively, were reported to possess significantly elevated activities in the ROMP of 1,5-cyclooctadiene (COD) and 2,2-bis(trifluormethyl)norbomene. The most active compounds obtained so far are the bimetallic complexes (/j-cymene)RuCl(M-Cl)2RuCl(CHPh)(NHC) and (Cp )RhCl( -Cl)2RuCl(CHPh)(NHC) (NHC = N-het-erocyclic carbene, Cp = pentamethylcyclopentadi-enyl) (Scheme 23). It is worth mentioning that... 

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