Ligands hydrocarbon

The analogous dimerization of alkynes over Fe(C0)5 is not applicable, so clearly a different route towards alkynylated derivatives of 25 was needed. Comparison of 25 to cymantrene suggests that metallation of the hydrocarbon ligand should be the route of choice for the synthesis of novel substituted cyclobutadienes. In the literature, addition of organolithium bases (MeLi, BuLi) to the CO ligands with concomitant rearrangement had been observed [25]. But the utilization of LiTMP (lithium tetramethylpiperidide, Hafner [26]) or sec-BuLi as effectively non-nucleophilic bases led to clean deprotonation of the cyclobuta-... 

Such organometallic dehydroannulenes A are expected to be formed as mixtures of diastereomers differing only with regard to the relative position of the organometallic fragments (above or below the plane of the large hydrocarbon ligand) with respect to each other. In respective diastereomers, only the spatial... 

Propyhdyne formed from propene on lr4 supported on y-Al203 was observed by IR and NMR spectroscopies [38]. When ethene or propene was brought in contact with oxide-supported lr4 [39,40], Ire [39,40], or Rhe (A.M. Argo and B.C. Gates BC, impubhshed results) in the presence of H2, hydrocarbon hgands were formed (namely, alkyls and /r-bonded alkenes), which have been inferred from IR spectra to be intermediates in hydrogenation to make alkanes, as discussed later. The population of these hydrocarbon ligands on the supported clusters depends sensitively on the conditions, such as reactant partial pressures and temperature. 

III. Carbonyl Complexes Not Containing -Bonded Hydrocarbon Ligands 319... 

CARBONYL COMPLEXES NOT CONTAINING xr-BONDED HYDROCARBON LIGANDS... 

While the majority of group 4B metal carbonyl complexes contain 7r-bonded hydrocarbon ligands, most notably 17-cyclopentadienyl, recent studies by Wreford and co-workers have led to the identification and isolation of three novel phosphine-stabilized titanium carbonyl complexes (12,13). 

Without question the vast majority of group 4B metal carbonyl complexes contain a metallocene framework. Only two carbonyl complexes of group 4B have been reported that contain 77-bondcd acyclic hydrocarbon ligands that are not metallocenes. 

Figure 4. IR spectra in D -doped liquid Kr at -120°C of (OC) Cr(ol) and of the photolysis product (OC) Cr(ol)(D ) [ol = trans-cyclooctene]. D2 was used rather than H2 to avoid potential spectral overlap of any V(H-H) bands with bands due to the hydrocarbon ligand.

Similarly, the complex 3 was formed from 3,3-dimethylcyclopropene and 2,2 -bipyridyl( 4-cy-cloocta-l,5-diene)nickel, which on treatment with maleic anhydride at 25 °C gave anti-3,3,6,6-tetramethyltricyclo[3.1.0.02,4]hexane (4) in >90% yield. Displacement of the hydrocarbon ligand from 3 with 3,3-dimethylcyclopropene proceeds at > 90"C. Since the complex 3 is regenerated in this step, 3 is the catalyst in the cyclodimerization of the cyclopropene.120... 

The air-sensitive violet complex thus formed was treated with methyl-magnesium bromide and then hydrolyzed to give /rans-Ph(Me3Si)C= CPh(SiMe3) (90, 91). Apparently, this is the first example of transfer of silyl groups from a metal to a coordinated hydrocarbon ligand. It seems that a similar step is involved in the dehydrogenative cis double silylation of acetylenes catalyzed by diethyl(bipyridyl)nickel(II) (156). 

In an inert atmosphere, excess chloromethyldifluorophosphine was distilled on cycloheptatriene molybdenum tricarbonyl, and the hydrocarbon ligand was readily displaced in a mildly exothermic reaction, requiring a reaction time of as little as 20 to 30 minutes. A high boiling colorless liquid (b.p. 127° at 0.05 mm.) was isolated by distillation, which could be shown to be the expected molybdenum tricarbonyl derivative, formed according to ... 

Using the Spectra of Hydrocarbon Ligands in Metal-Cluster Compounds as Models for Spectra from Analogous Surface Species... 

Fig. 4. Structural diagrams for C2 hydrocarbon ligands on metal clusters that are available as model compounds for chemisorbed surface species, numbered in accordance with the entries in Table IV (M = metal atom).

Fig. 5. A summary of the infrared absorption bands exhibited by hydrocarbon ligands on metal atoms in various model compounds. Surface species on metals may give absorptions varying by ca. 50 cm 1 from the band positions in the model-compound spectra in the fingerprint region below 1400 cm. The patterns of band-positions and intensities are significant. M indicates MSSR-allowed modes for an analogous species on a flat surface when the adsorbed species is on a site of high symmetry (--) indicates other absorptions that may occur for adsorption on less symmetrical sites or on small metal particles, vs—very strong s—strong ms—medium strong m—medium mw—medium weak w—weak.

Figure 5 collects together information on bands of medium (m) or strong (s) intensity expected on metal surfaces for most of the possible types of C and C2 hydrocarbon ligands. Relationships between the latter structures are set out systematically in Scheme 2, (M = cr-bonded metal atom M = -bonding to metal). In this scheme the parent adsorbate hydrocarbons are indicated by solid rectangular outlines, and dashed rectangles encompass those surface species that can be derived from the parent without breaking the CH bonds.

Numerous synthetically useful carbon-carbon bond-forming reactions are based on the fact that unsaturated hydrocarbon ligands bound to electrophilic transition metal moieties are activated toward addition of nucleophiles. Normally the metal moiety in such complexes is a neutral or cationic metal carbonyl group. Prominent and well-studied examples include [Cr(arene)(CO)3] complexes (covered in Chapter 2.4, this volume),1 [Fe(dienyl)(CO)3]+ complexes (covered in Chapter 3.4, this volume),2 [FeCp(CO)2(alkene)]+ complexes3 and [M(CO) (diene)] complexes.4... 

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