Terminal carbonyl groups

Carbonyl groups that are attached to two metal atoms simultaneously are called bridging carbonyls, whereas those attached to only one metal atom are referred to as terminal carbonyl groups. The structures of Mn2(CO)10, Tc2(CO)10, and Re2(CO)10 actually involve only a metal-metal bond, so the formulas are more correctly written as (CO)5M-M(CO)5. Two isomers are known for Co2(CO)8. One has... 

The experimental evidence shows that the carbon of terminal carbonyl groups is positively polarized (or polarizable) and, contrary to the behaviour of free carbon monoxide, is easily attacked by strong nucleophiles (OH-, OR-) a behaviour which is general in the chemistry of metal carbonyls. Moreover, the negative polarisation (or polarizability) of oxygen atoms of carbonyl groups, particularly bridging carbonyls, is illustrated by the facile formation of adducts with Lewis acids as shown inEq. (16) 7. ... 

A different method of reduction involves the reaction with strong base, such as OH- and OR-. In this case, the primary reaction is nucleophilic attack on a carbon atom of a terminal carbonyl group as shown by the formation of a carboalkoxy group on reaction with alkoxide ... 

Figure 20 illustrates the molecular structure of [Fe3(CO)i2]ld It consists of a triangle of iron atoms. Two CO molecules assume a bridging position with respect to one Fe-Fe side (Fe2-Fe3), rendering this side shorter by about 0.1 A with respect to the other two sides bearing only terminal carbonyl groups. 

As is evident from Figure 21, the triangular [Ru3(CO)i2] and [Os3(CO)i2] display only terminal carbonyl groups. 

The presence of three triply bridging, three doubly bridging and nine terminal carbonyl groups obviously causes inequivalence in the Co-Co bond lengths. 

This reaction is general and proceeds smoothly and quantitatively in light petroleum at room temperature each triple bond of a diync reacts independently. The complexes are diamagnetic, and show bands in their infrared spectra characteristic of terminal carbonyl groups, but no bands due to bridging carbonyl groups or a C C stretching vibration. 

Dinuclear carbonyl anions [M2(CO)8X3] were obtained through a two-electron transfer to protons by treatment of [M(CO)6]- with HX (X = Cl, OAc, OMe) (equation 82).526 The anion has Civ symmetry. The niobium atoms are heptacoordinated with four terminal carbonyl groups each and three bridging chlorides located at the vertices of an approximately equatorial... 

Preliminary data on the salt [NEt4]2[Mo2Ni4(CO)i4] indicate a structure with Dih symmetry based on an equatorial Ni4(CO)6 rhombus with two Mo (CO) 4 groups placed above and below the plane (111). It is probable that there are only terminal carbonyl groups. 

In the carbide rhodium clusters, the Rh—C distances of the terminal carbonyl groups are significantly longer than those of the noncarbide derivatives, whereas the corresponding C—0 distances are shorter (see Table II). This trend indicates a decrease in backbonding to the carbonyl... 

In the carbonylmetalates the main absorption of terminal carbonyl groups is fairly well related to the ratio of the number of metal atoms to... 

Q Terminal carbonyl groups Edge bridging carbonyl groups Face bridging carbonyl groups... 

The dynamic properties of (/j5-Cp)2Fe2(CO)3[P(OPh)3] have been studied by n.m.r. Two processes occur cis-trans isomerism and scrambling of bridging and terminal carbonyl groups. It was found that both processes have the same rate and activation parameters within experimental error and this is in complete agreement with the mechanism proposed by Adams and Cotton and discussed earlier in this... 

The [Osi8Hg3(C)2(CO)42]2 clusteris composed of two tricapped octahedral Os9(C)(CO)2iunits sandwiching a Hg3 triangle (Fig. 19.4.3(b)). Each corner Os atom in the top and bottom faces has three terminal carbonyl groups, and the remaining Os atoms each have two. 

The core of the [Fe6Ni6(N)2(CO)24]2- cluster comprises a central Ni6 octahedron that shares a pair of opposite faces with two Ni3Fe3 octahedra, as shown in Fig. 19.4.3(c). The interstitial N atoms occupy the centers of the Ni3Fe3 octahedra. Each Fe atom has two terminal carbonyl groups, and each Ni atom has one. 

The metal atoms in [Ru8(P)(CO)22] constitute a square antiprismatic assembly [Fig. 19.4.3(e)], Two opposite slant edges are each bridged by a carbonyl group. Each Ru bridged atoms has two terminal carbonyl groups, and each... 

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