Carbon monoxide ligands coordination modes

There are two principal modes of coordination of the carbon monoxide ligand in transition metal carbonyls terminal coordination, to a single metal atom, and bridging coordination, to two or more metal atoms. The Ols spectrum of Co4(CO)12, shown in Fig. 5, can be readily deconvoluted into two peaks corresponding to these two types of carbonyl groups109. This spectrum is useful for determining the relative chemical shifts for the two types because... 

This sequence leads to the formation of the unusual bridging isocyanide and carbon monoxide ligands, which act as normal two-electron donors to one Mn and donate a pair of tt electrons to the second Mn. A drawing of the in-place portion of the structure of ( t-dpm)2Mn2(/Lt-p-CH3C6H4NC)-(CO)4 is shown in Figure 5.19. " This gives details of the novel mode of isocyanide coordination. 

A fourth mode of CO-coordination is also known, namely that found in the anion [Fe4(CO)i3H] " in which, as can be observed in Fig. 2.4, one carbon monoxide ligand is coordinated by the carbon atom to all four Fe-atoms which are arranged in a butterfly configuration. As also indicated in Fig. 2.4, the CO-oxygen atom appears to be also bonded to the metal polyhedron. 

The methylene isomer 15 eliminates carbon monoxide when heated at 110°C (toluene, xylene 24 h), and yet another carbon-metal hydrogen shift takes place (75). The methylidyne species 16formed in this irreversible reaction has been characterized by its NMR spectra [S(CH) 9.36, quartet (76) 8(CH) 118.4 (CD3)2CO (77)] which implies a structure analogous to the previously known ethylidyne derivative (/i.-H)3(/i.-CCH3)-Os3(CO)io (138). NMR data obtained for partially deuterated samples of the methyl complex 14 have yielded evidence that the methyl ligand occupies an unsymmetrical bridging position between two metal centers, a coordination mode which implies significant C H Os interaction... 

From the standpoint of the present review, we will focus on compounds in which unusual and potentially reactive features of CO coordination are revealed, and on certain classes of reactions in which the conversion of CO to other chemical entities is achieved. For the purposes of determining what a reactive mode of CO coordination is and in what way the CO ligand can be activated, it is first instructive to briefly review the primary modes of carbon monoxide coordination. These are illustrated as Lewis structures... 

It is thus clear that a rigorous study of the chemical shift anisotropy, combining theory and experiment, is essential to understand at the molecular level the variation of coordination of a ligand on a metal center. This can in fact be used to understand the mode of absorption of carbon monoxide on metallic particles and metallic clusters. ... 

---