Metal atoms conjugated dienes

Other reactions of dienes with metal atoms are only of a limited synthetic use. Dibenzylideneacetone (PhCH=CH—CO—CH=CHPh DBA) reacts with palladium vapor to afford Pd2(DBA)3, a complex in which the coordination is through the two C=C units and does not involve the C=0 (5, 92). Cobalt vapor undergoes an extremely complicated reaction with 1,4-pentadiene, producing pentenes, C5H6, and various polymers as well as the organometallic product, HCo( 1,3-pen tadiene)2, which involves isomerization from a nonconjugated to a conjugated diene (104, 110). 

The above type of bonding is assumed to occur in other metal-olefin and metal-acetylene complexes (172). Acetylenes have two mutually perpendicular sets of ir-orbitals and are therefore capable of being bonded to one or to two metal atoms both types of complexes are known. When the hydrocarbon is a nonconjugated polyolefin e.g., cyclo-octa-1,5-diene, each C C bond interacts independently with the metal atom. In complexes of conjugated polyolefins, e.g., cyclopentadiene, infrared and nuclear magnetic resonance studies (99) indicate that it is not yet possible to distinguish between structure (IV), in which each C C bond independently contributes two --electrons to the metal-olefin bonding, and structure (V), in which... 

Figure 5.3 Schematic presentation of the formation of a ciy-1,4 diad (isotactic in the case of the terminally monosubstututed dienes) versus a 1,2 diad (syndiotactic) in the polymerisation of conjugated dienes. The last inserted monomeric unit (as an r 3-allylic ligand) is below the plane, the incoming coordinating monomer is above the plane and the transition metal atom is on the plane...

It should be noted that trans- 1,4-polymers formed by anti —> syn isomerisation, i.e. via the pathway (c)-(e)-(b) [scheme (10)] when the monomer is coordinated to a metal atom as an s-cis-rf ligand, are produced by various catalysts, especially by soluble ones. It is also worth noting that polymers with a trans-1,4 structure of monomeric units are formed by heterogeneous catalysts via the pathway (a)-(b) or (a )-(b) [scheme (10)] from the (Z)-isomers of conjugated dienes such as CH2=CH-CH=CHR, for which the s-trans-rf or s-trans-rf coordination is preferred and the s-cis-rf coordination is unfavoured [13,193],... 

The insertion of the coordinating diene monomer proceeds via an t]3-allylic species. The metal atom with the attached copolymer chain terminated by such a species gives its two coordination sites to be occupied by the -allylic group. This allows the next coordination of only one additional a-olefm. After insertion of the coordinating 7-olefin, two coordination sites at the metal atom are again available, and they are preferably complexed by another conjugated diene molecule. 

Chiral Metal Atoms in Optically Active Organo-Transition-Metal Compounds, 18, 151 13C NMR Chemical Shifts and Coupling Constants of Organometallic Compounds, 12, 135 Compounds Derived from Alkynes and Carbonyl Complexes of Cobalt, 12, 323 Conjugate Addition of Grignard Reagents to Aromatic Systems, 1, 221 Coordination of Unsaturated Molecules to Transition Metals, 14, 33 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365 Diene-Iron Carbonyl Complexes, 1, 1... 

Conjugated 1,3-dienes can coordinate to a single metal atom or may bridge two metals of the cluster. Most commonly the diene coordinates to a single metal atom in the cis conformation, as in (29). The diene is found in the s-trans conformation bridging two metals in Os3(CO)io(l,3-butadiene) (30). 

Conjugated dienes codeposited with metal atoms yield unique materials. All the transition metals form complexes with 1,3-butadiene at low temperature , but only the Mo- and W-butadiene complexes are stable in the homoleptic form The other early transition metals simply yield oligomers or polymers of butadiene upon matrix... 

Dienes, chelating reaction with metal atoms 5.S.2.5.3 Dienes, conjugated reaction with metal atoms 5.S.2.4.6 [-Dienyl complexes from organoaluminums 5.8.2.11.3 from organoborons 5.8.2.11.1 from organomercurials 5.8.2.11.2 from organotins 5.8.2.11.1... 

In most complexes, acyclic 1,3-dienes are coordinated as cis planar ligands. However, compounds in which such acyclic groups are coordinated to the metal atom in their trans forms are also known. Conjugated dienes may also function as bridging ligands in polynuclear compounds in which the C —C double bonds are attached to two central atoms. Each 4e ligand has four molecular orbitals (Figure 8.1... 

The thermal reaction of cis or trans 1,4-poly(butadiene) with iron carbonyls results in geometrical isomerization of the alkenyl moieties and formation of polymers containing conjugated diene) iron tricarbonyl units. In the course of our continuing studies of the formation of stable colloidal iron dispersions by thermal decomposition of metal carbonyls in the presence of functional polymers, some aspects of this work have been repeated. Our objective was to isolate the soluble organometallic polymer which was intermediate to particle nucleation and independently examine the intramolecular condensation of metal atoms to yield metal clusters and metal particles. In this paper, the structure of the intermediate obtained on thermolysis of an excess of FeCCO) in a dilute xylene solution of c/5-poly(butadiene) has been described. 

Reactions with Dienes. Conjugated dienes and norbomadiene displace two terminal carbonyl groups from first one and then both metal atoms of the octacarbonyl (eq 33). ... 

---