Enyl complexes

When heated under reflux in benzene or methanol, in the absence of hydrogen, isomerisation of the terminal olefin of the pent-4-enyl phosphine n=3) is completed in less than 5 hours to yield the cis-pent-3-enyl phosphine complex. For the but-3-enyl complex ( =2) the isomerisation to the but-2-enyl phosphine complex is incomplete even after 88 hours. The mechanism involves a i-allyl hydride intermediate, whose stability, as in the case of the hydrogenation studies, is controlled by the... 

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. ... 

John G. R., Kane-Maguire, L. A. P., and Eabom, C., Chem. Commun. 481 (1975) (Elimination of SiMe3 groups in the reaction of cationic metal-7r-enyl complexes with aryltrimethylsilanes). 

Unlike the alkyl and aryl-substituted methylenecyclopropanes discussed above, both cis- and franj-Feist s esters undergo chloropalladation with proximal 1,2-ring opening, to give isomeric n3-[3-chloro-l,2-bis(methoxycarbonyl)but-3-enyl]palladium complexes (equation 331)397. Formation of the but-3-enyl complexes is rationalized by sequential... 

The hydrogenation of trans-l-phenyl-1,3-butadiene has been discussed49 in terms of the mechanism originally proposed,45 and 773-allyl species were invoked. NMR studies on the hydrogenation of butadiene have shown that Tj -but-2-enyl and r 3-l-methylallyl complexes are present in the reaction mixture. With isoprene, an q1 -methylbut-2-enyl complex was observed.50 By using a two-phase system and a phase-transfer catalyst, the turnover numbers attainable with conjugated dienes can be increased to about 30.51... 

Enyl complexes (continued) reactivity, 8, 373 reductive elimination, 8, 380 structure and bonding, 8, 368 thermal decomposition, 8, 374 via transmetallation, 8, 367 transmetallation to metals, 8, 374 with niobium, 5, 87 with Pd 7i-complexes... 

No simple ri2- or >j4-diene complexes could be detected from the reaction of tricarbonyl-f7s-cyclopentadienylmethylmolybdenum (73) (87,88) with 1,3-butadiene (la). The reaction mixture contains four enyl complexes (74-77). The enyl ligands are formed from 1,3-butadiene by acetyl (74-76) or methyl... 

Small differences are found for the Mn—C bond lengths of C-l to C-3 [215.4(1), 213.5(1), and 207.9(1) pm], in contrast to >y3-enyl complexes, in which the central carbon atom is closer to the metal than the terminal ones (171,215). However, there is good agreement with the bond lengths found in [Mn(CO)3b/3 CH-C6H8CH3)] (47,48). The distance of C-4 from Mn-1... 

Section VII describes Cp and related V-ligand halocarbonyl complexes, and Section VIII is concerned with the little-studied Tj6-arene halocarbonyl complexes. Finally, Section IX briefly discusses the halocarbonyl complexes of molybdenum(II) and tungsten(II) containing V-cycloheptatrienyl as a ligand. As Green and Ng9 have reviewed cycloheptatrienyl and -enyl complexes of the early transition metals, only one reference in this area is given. 

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). 

Note that the cis isomer lacks an improper axis of rotation and is tbereftire chiral, but that the trans isomer has a plane of symmetry and will be achiral in the absence of an asymmetric carbon in the phoq hine ligand. As in the case of the previously encountered cyclopentat enyl complex (page 476), it can be argued whether the co ination number is S or 9. fn either semantic interi etatiDn these compounds are of considerable intoest since isomerism in nine-coordinate complexes is even less well documented than in those with coordination number S. 

Chemistry of coordination complexes and organometallic compounds. Allyl and enyl complexes Allyl-transition metal systems... 

Whilst reaction of acyl chloride 303 with Na[Co(CO)3(PEt3)] affords the oxocyclobut-enyl complex 306" by ring expansion and CO loss, analogous treatment with NaRe(CO)5 delivers the non-fluxional // -cyclopropenylrhenium compound 305" . In the latter case, compound 304 loses carbon monoxide with concomitant migration of the cyclopropenyl moiety from carbonyl to rhenium as an allylic rearrangement rather than a 1,2-shift. 

Parameters for the -perfluoroallylcobalt complex [164], formed by the reaction of perfluoroallyl iodide with Zn[Co(CO)4)2 are given with the structure. (85) The prop-l-enyl complex [165], identified as trans about the double bond by the large value of 7(F-F), was also formed, and an octet at 3 -41-6, with coupling constants similar to those of... 

In reaction (30), the addition of the Fe—H to butadiene gives a cis-trans isomeric mixture of the Fe-but-2-enyl complex which is the 1 4 addition product. There is no evidence for the formation of either the 1 3 or 1 2 addition product (102). 

The simplest mechanism that can be put forward which covers these points is one where the rate-determining slow step is the opening of a chloride bridge bond. Coordination of a diene at the vacant site thus created and the subsequent H-transfer reaction to give the enyl complex are then expected to be very fast. 

Bochmann et have shown that the methide abstraction by FAB occurs not only from a transition metal complex but from an aluminum cyclopentadi-enyl complex. CpzAlCHs, to produce the aluminoce-nium cation ion pair Cp2Al+MeB(C6F5)3 (72 eq 41), which is an effective cationic initiator for the polymerization of isobutylene. 

The enyl-palladium bond formed can further be transformed by different means i.e. hydrogen transfer to the enyl system creates an alkene system and free alkene or hydrogen transfer from the enyl complex yields the starting or isomerized diene. 

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