Monocarbonyl complexes

D. Formation of Titanocene Monocarbonyl Complexes Containing a o-Bonded Ligand... 

A monocarbonyl complex of zirconocene has been proposed by Floriani and co-workers as a transient intermediate in the carbonylation of the bridging oxymethylene complex (Cp2ZrCl)2(Ai-CH20) (57) (104,105). The assignment of 58 as the proposed intermediate to the final carbonylation product, [Cp2Zr(/i-CHO=CHO)]2 (59), was based on the appearance of a metal carbonyl band at 1970 cm-1 together with the subsequent CO-induced loss of Cp2ZrCl2. 

Figure 1 illustrates the evolution ofthe calculated vco versus the charge and coordination number of the Ni11 ion in the monocarbonyl complex. It appears that for a fixed coordination number the charge of the complex has a considerable effect on the CO frequency (about one hundred of cm-1) whereas, for a fixed formal charge ofthe complex, the addition of a neutral ligand such as H2O has a smaller effect (about ten cm-1), vco is shown to decrease linearly with increased coordination numbers. 

Figure 1. vco as a function of the charge of the monocarbonyl complex and of the Ni coordination number (ligands other than CO). 

Table 4 reports on the results obtained for the optimized geometry of the dicarbonyl complex formed on the Nin ion dicoordinated to one OH (SiO") and one H20 (SiOH) ligands. The value of the CO binding energy is -34 kcal.mol 1 for Si202H7 the cluster. These values are higher than those observed for the monocarbonyl complex. This suggests that dicarbonyl species form in competition with monocarbonyl, as observed experimentally [18]. 

For the dicarbonyl, one frequency is higher than the CO frequency in the monocarbonyl complex whereas the other one is lower, as observed experimentally. The difference with the experimental value is about 1.3%. However, the calculated monocarbonyl frequency is close to the frequency of the antisymmetric dicarbonyl vibration and this in contrast to the experimental results. Work is under way to find a dicarbonyl structure which give calculated CO frequencies close to the experimental values. 

The numbers ( ) indicate the shifts ofthe measured and calculated frequencies ofthe dicarbonyl complex with respect to the values of the corresponding monocarbonyl complex... 

Mixed Ruthenium-tii) and -(m) Complexes.—Interactions of the oxo-centred RuI 1 acetate [Ru30(C02Me)6(Me0H)3]+ and the reduced species [Ru30(C02Me)6 (MeOH)3] with carbon monoxide, sulphur dioxide, and NO have been studied.71 Scheme 5 summarizes the products obtained from the latter mixed-valency complex following carbonylation. Only a monocarbonyl complex is seen to be formed, and the... 

More subtle effects determine alkyne rotational preferences in symmetric CpM(RC=CR)L2 complexes with identical L and L ligands as described by Hoffmann and co-workers (145). The extensive molecular orbital discussion of W(CO)2(RC=CR)LX2 complexes in Section VI described the factors which remove the dicarbonyl complexes from the simple guidelines appropriate for analysis of monocarbonyl complexes. The experimental barrier of 9.1 kcal/mol measured for [CpMo(MeC=CMe)-(PMePh2)2]+ is lower than those of related L = CO, L = PR3 complexes (72), but it is certainly not negligible as might first be expected for L = L. Steric factors may account for most of the activation energy required to rotate the 2-butyne ligand in this complex. 

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