Carbonyl and Thiocarbonyl Complexes

The IR spectrum of CO adsorbed on dehydrated Na-Rb-Y zeolite shows that the CO interacts mainly with Rb cations, with vCO at 2157 cm Some Na -CO interaction gives rise to absorption at 2166 cm  

Carbonyl stretching wavenumbers for (35), where M = Nb or Ta, R = H, C02Me, C02Et, C(=0)Me, C(=0)Ph, C(=0)CH2Ph, CMe=CH2, CH2=CH2, etc., shift as expected with changing electron donating/withdrawing characteristics of R.  

TRIR studies on vCO modes of the initial photolysis product of [Cp Cr(CO)2]2 in heptane shows that it is the triply-bridged, CO-loss species Cp Cr(p3-CO)3CrCp. The resonance Raman spectrum of Cr(CO)4(bipy) 

The value of vCO in (36) is 1907 cm ie. very high for a bridging carbonyl -ascribed to the semibridging nature of the bonding. TRIR spectroscopy of transition metal carbonyls, e.g. W(CO)5py, showed that MLCT excited states gave broad vCO bands due to solvent-solute interactions.  

FTIR spectra were used to follow the redox behaviour of trans- and cis,mer-Mn(CO)2(ri -P2P )Fr on graphite surfaces, where P2P = Ph2P(CH2)2 2PPh. Femtosecond TRIR (vCO) was used to follow SiH bond activation in the reaction of CpMn(CO)3 and EtsSiH.  

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Carbonyl and thiocarbonyl complexes of Mes2Si have been observed in a remarkable series of experiments by Ando and coworkers144. Photolysis of Mes2Si(SiMe3)2 was carried out at 77 K in a soft (3-MP/isopentane) matrix in the presence of tetramethyl-2-indanone or its sulfur analog. The free silylene was formed initially but it slowly reacted with the carbonyl (or thiocarbonyl) compound to give the complex, which can be formulated as a silacarbonyl ylide (Scheme 8). Further photolysis converted these ylide complexes to the silaoxirane or silathiirane, reversibly. 

Carbonyl and Thiocarbonyl Complexes.—For a comprehensive survey the reader should consult the Organometallic Specialist Periodical Report. 

Carbon monosulfide is not a stable molecule, but carbon monosulfide complexes (more commonly called thiocarbonyl complexes) are known for most of the transition metals. Because of the mstability of free CS, most CS complexes have been prepared by generation of CS from CS, Cl CS, or EtOC(S)Cl in the coordination sphere of the metal, as shown in Equations 2.5, 2.6, and 2.7. Thiocarbonyl ligands vibrate between 1160 and 1410 cm" free CS (in a matrix) vibrates at 1274 cm". A detailed analysis of force constants of mixed carbonyl and thiocarbonyl complexes indicates that the CS ligand can be a weaker or stronger TT-acceptor tiian CO. Seleno- and tellurocarbonyl complexes are also known. ... 

The second problem involves the measurement of pKa values for carbonyl and thiocarbonyl derivatives. Grieg and Johnson (157) have pointed out that the measurement of pKa values for very weak bases (11) is an inaccurate and arbitrary process. Of particular difficulty for our purposes is the fact that different carbonyl derivatives may require different acidity functions. As a result of this situation, no attempt was made to make correlations of pKa data for carbonyl and thiocarbonyl derivatives with eq. (2). Because accurate pKa values can be measured for imines, these values were correlated with eq. (2), although the conformational problem remains. The imine sets were first studied by Charton and Charton (73), who correlated them with eq. (2). No correlations of data for carbonyl or thiocarbonyl derivatives with eq. (2) are extant in the literature. Bhaskar, Gosavi, and Rao (158) have reported that AG values for complex formation of substituted thioureas with iodine are a linear function of the Taft a values. Drago, Wenz, and Carlson (159) have reported similar results for complex formation between iodine and substituted amides. Oloffson (160) has reported a linear relationship between -AH for the complex of substituted N,N-dimethylamides with SbCls and the ffj constants. 

Sila-ylides from complexation of silylenes by carbonyl and thiocarbonyl compounds have been observed their chemistry is discussed in Section V.A144. The first stable... 

TRI-ju-CHLORO-CHLOROTETRAKIS(TRIPHENYLPHOS-PHINE)DIRUTHENIUM(II) COMPLEXES WITH ACETONE CARBONYL AND THIOCARBONYL LIGANDS... 

Cyclopentadienyl Carbonyl and Related Complexes.—Successive attack of CHs and CH3+ on [CpMn(CO)2(N2>] yields the azomethane complex [CpMn(CO>2 N-(Me)=NMe ], which can also be synthesized by oxidation of [CpMn(CO)2 MeN-(H)NHMe ]. Similar nucleophilic and electrophilic attacks on the dinitrogen complex using Ph and H+ gives [CpMn(CO)a N(Ph)=NH ]. The pyrrolyl nitrogen atom of [(> -C4H4N)Mn(CO)3] acts as a donor in the formation of the complexes [(OC)3Mn( -C4H4N)M(CO)2Cp] (M = Mn or Re).i The adducts RsP.CSa (R=Bu or Cy) have been assessed as reagents for the preparation of thiocarbonyl complexes. Unfortunately reactions such as [CpMn(CO)2(as-cyclo-octene)] with R3P,CSa lead mainly to [CpMn(CO)2(PR3)] with very low yields of [CpMn(CO)2(CS)].i ... 

In mixed complexes containing carbonyl and thiocarbonyl ligands, nucleophilic attack at co-ordinated carbon could take place either at carbonyl-C or at thiocarbonyl-C. [Fe(A -C5H5)(CO)a(CS)]+ reacts with, for example, azide ion or hydrazine by attack of the nucleophile at the thio-carbonyl-C. On the other hand, methoxide ion attacks [Ir(CO)2(CS)-(PPh3)2]+ at the carbonyl-C. ... 

Unlike the parent carbonyl compound IrCl(CO)(PPh3)2 the thiocarbonyl complex forms 1 1 adducts with the aid of the acidic cyano olefins only. The stoichiometry of the adducts of IrCl(CO)(PPh3)2 and IrCl(CS)(PPh3)2 with BX3 (X = Cl, Br) has not been satisfactorily established143. 

In so far as the decrease in chemical reactivity is an indication of diminished transition metal basicity, it was proposed143 that the thiocarbonyl complex is less basic than its carbonyl analogue. This conclusion is substantiated by the spectral shifts in Table 22 and is also in agreement with molecular orbital calculations which predict the thiocarbonyl complex to be less basic than the carbonyl complex155,156. 

Solute-solvent interactions in dithiole-thiones and -ones are attributed to localized electrostatic induction. The strength of the hetero-association complexes is determined by the distribution of the electric field around the carbonyl or thiocarbonyl group (72HCA213). 

G. R. Clark, K. Marsden, W. R. Roper, and L. J. Wright, Carbonyl, Thiocarbonyl, Selenocarbonyl, and Tellurocarbonyl Complexes Derived from a Dihalocarbene Complex of Osmium, J. Am. Chem. Soc. 102, 1206-1207 (1980). 

Few binary metal thiocarbonyls are known. Nickel tetrathiocarbonyl, Ni(CS)4, is unstable at room temperature, but many mixed carbonyl-thiocarbonyl complexes are stable and have properties similar to those of the parent carbonyl compounds. Examples are Cr(CO)5(CS), ( QH6)Cr(CO)2(CS),109 Cr(CO)3(CS)[P(OPh)3]2,° and Fe(CO)4(CS). 

Among the types of complexes found here are formyl, acyl, alkyl, and aryl carbonyls, carbonyl cyanides," " carbonyl isocyanides and acetylides," and thiocarbonyl and seleno-carbonyl complexes." Of the greatest significance, however, are the chromium carbenes, for example, (CO)sCr=C(OR)R". This chemistry has been thoroughly reviewed " nevertheless, these compounds will be briefly discussed here. 

Several diatomic ligands similar to CO are worth brief mention. Two of these, CS (thio-carbonyl) and CSe (selenocarbonyl), are of interest in part for purposes of comparison with CO. In most cases, synthesis of CS and CSe complexes is somewhat more difficult than for analogous CO complexes, because CS and CSe do not exist as stable, free molecules and do not, therefore, provide a ready ligand source.Therefore, the comparatively small number of such complexes should not be viewed as an indication of their stability. Thiocarbonyl complexes are also of interest as possible intermediates in certain sulfur transfer reactions in the removal of sulfur from natural fuels. In recent years, the chemistry of complexes containing these ligands has developed more rapidly as avenues for their synthesis have been devised. 

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