Compounds containing carbonyl ligands

The reaction of [Tc2(CO)io] in CCI4 solution with I2 is extremely slow. Direct action of F on Tc2(CO)io]° at 100 °C in sealed ampules yielded the dimer [Tc2(CO)4lj2 which was converted to Tc(CO)5l] by high-pressure carbonylation. Ihe diamagnetic, colorless compound absorbs in the IR at 2000, 2024, 2055, and 2146 cm again in agreement with C4V symmetry [622], lire temperature dependence of the [Tc(CO)5ll vapor pressure was determined [627], 

Heating the pentacarbonyl halides to 100 °C in air resulted in complete conversion to the tetracarbonyl dimers within 24 h. The monomers also were observed lo lose 

CO slowly when standing in solution at room temperature [622], The conversion of [Tc(CO)5X]° does not stop at [Tc(CO)4X]2°, but after prolonged boiling in chlorobenzene it is said to be completely converted into [Tc(CO)3X 4°  

A technetium tricarbonyl hydroxide Tc(CO)3(OH)] ° was reported to be synthesized by heating KTCO4 with an exeess of formic acid in an autoclave at 170-180 °C for 3-4 h. lire colorless compound was characterized by elemental analysis, the IR spectrum, and the X-ray powder diffraction pattern [632], A rhenium compound of the composition ]Re(CO)3(OH)]4 exhibits a similar IR spectrum and has a tetra-meric structure in which the corners of a cube arc formed by alternating Re(CO)3 and OH groups [633]. 

A unique cubane-type cluster of Tc(I) is the compound Na[Tc3(CO)9(OCH3)4j that was shown to be an intermediate product formed by the incomplete carbonylation of NaTc04 conducted in CH3OH  

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Fig. 15.16 Geometry (linear vs. bent) of nitrosyl ligands correlated with the hybridization of the nitrogen atom and parallel correlations for analogous compounds containing carbonyl ligands.

Since the early work dealing with Zeise s salt, many complexes have been prepared with the formula [PtL(C2H4)X2], where L = quinoline, pyridine, or ammonia and X=C1 , Br , I, or N()2. Similar compounds have been prepared that contain other alkenes than C2H4. Many of the complexes containing dienes, trienes, and tetraenes as ligands also contain carbonyl ligands. In fact, metal carbonyls are frequently starting complexes from which alkene complexes are obtained by substitution reactions. 

Dimeric and cluster compounds containing isocyanide ligands exhibit dynamic behavior in solution. The dimer Cp2Mo2(CO)5CNMe exists as a mixture of nonbridged isomers and permutamers which are rapidly inter-converted by unimolecular processes at RT. The isocyanide passes rapidly from one metal atom to the other via carbonyl or carbonyl-isocyanide doubly bridged species (205). 

There are several recent reviews of the photochemistry of transition metal complexes 3,4,5,29,30,45,466,514,518,580)> the most comprehensive being 4>. However, these papers deal mainly with ionic coordination compounds containing inorganic ligands only one 466> is devoted to photochemical substitution reactions of metal carbonyls and their derivatives, while in another 4> this subject is discussed in a short paragraph. 

Polynuclear Carbonyls. Several stmctures consist of dinuclear metal carbonyls as shown in stmctures (4)—(6). The metal atoms in Mn2(CO) Q, as also for technetium and rhenium, are held together by a metal—metal bond and the compound contains 10 terminal CO ligands, five coordinated to each atom. The CO ligands of Mn2(00) 0 adopt a staggered configuration as illustrated in stmcture... 

Ziegler-Natta catalyst for polymerization of alkenes. Considerable attention has been directed to double-bonded Fischer carbenes of Cr and W, the Schrock carbenes of Ta and Ti, and cyclic polyene ligands of Fe, Co, Cr, and U. Carbonyls of transition metals from groups 6 to 10 of the periodic table include both the monomeric compounds such as Cr(CO)g, Fe(CO)5, Ni(CO)4 and those with two metal groups such as Mn2(CO)io and Co2(CO)s, which is used industrially for hydroformylation. Although their source has not been identified, it has been shown that volatile compounds from landfills contain carbonyls of Mo and W (Feldmann and Cullen 1997). 

Thermolysis of 12 with frans-cinnamaldehyde afforded the insertion compound 19, formed through the di-insertion of two carbonyl ligands into the C—Si bond of 12. The reaction of 12 with fumaronitrile yielded the cyclization product 20. X-ray study revealed 20 to be a cyclization product which contains two types of disilyl moieties, imino and N,N-bis(silyl)amino, which are connected by a five-membered ring. 

Fischer carbenes characteristically contain a number of electron-withdrawing carbonyl ligands while the typical Ru, Os, or Ir carbene complexes described above frequently contain several cr-donor ligands. The metal centers in these former compounds, then, are rather electron-deficient, with nucleophilic attack at Ca being a favorable reaction. 

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