Bond transition metal complexes

Sigma-bonded transition metal complexes are able to polymerize a range of vinyl monomers, the only limitation being that the monomer should not have groups that react chemically with the transition metal compound. An important observation is that styrene and its derivatives are polymerized by the sigma complexes. In this respect they differ from the jr-allyl compounds that show no reactivity at all toward these monomers. A reasonable explanation for this is that the mechanism of the initiation is different... 

The band at 1600 cm-1 due to a double-bond stretch shows that chemisorbed ethylene is olefinic C—H stretching bands above 3000 cm-1 support this view. Interaction of an olefin with a surface with appreciable heat suggests 7r-bonding is involved. Powell and Sheppard (4-1) have noted that the spectrum of olefins in 7r-bonded transition metal complexes appears to involve fundamentals similar to those of the free olefin. Two striking differences occur. First, infrared forbidden bands for the free olefin become allowed for the lower symmetry complex second, the fundamentals of ethylene corresponding to v and v% shift much more than the other fundamentals. In Table III we compare the fundamentals observed for liquid ethylene (42) and a 7r-complex (43) to those observed for chemisorbed ethylene. Two points are clear from Table III. First, bands forbidden in the IR for gaseous ethylene are observed for chemisorbed ethyl-... 

TABLE I. Bi- and Polynuclear Metal-Metal Bonded Transition Metal Complexes."... 

Similarity to the C,H7 anion is apparent if you allow each phosphorus a Jone pair of electrons, which gives five p orbitals (with six electrons) available for it bonding. Transition metal complexes containing P, rings, however, were known prior to the synthesis of the free P5 ligand (see Chapter 15) "M Examples are [( -CjMe Fet 5-... 

Contrary to the rich organometallic chemistry of cyclopropylacetylenes with main group elements, tr-bonded transition metal complexes of the alkynes are rare. Nevertheless, the single example given in the literature is of a stable crystalline compound, which permits insight into the structure of cyclopropylethynyl complexes in the solid state. 

Models for the understanding of oxidative addition and reductive elimination in two-centered systems are provided by reactions of M—M bonded transition metal complexes " and main group systems ". ... 

The photochemical reaction of 7,8-B9HioCHP and 7,9-B9HioCHP with Fe(CO)5 and Mn2(CO)io gives complexes in which the phosphacarba-borane ligand has replaced a CO group, giving a-bonded transition-metal complexes. ... 

Multiply Bonded Transition Metal Complexes of Heavier Main Group Elements... 

M. T. Benson, T. R. Cundari, Y. Li, and L. A. Strohecker, Int.. Quantum Chem., Symp., 28, 181 (1994). Effective Core Potential Study of Multiply Bonded Transition Metal Complexes of the Heavier Main Group Elements. 

---