Hydrogen bonds in organometallic compounds

In transition metal carbonyls, the M-C=0 group acts as a proton acceptor, which interacts with appropriate donor groups to form one or more C=0- H-X (X is O or N) hydrogen bonds. The CO ligand can function in different /i i, n-2, and ii3 modes, corresponding to a formal C-O bond order of 3, 2, and 1, respectively. Examples of hydrogen bonding formed by metal carbonyl complexes are shown below  

In organometallic compounds, the //3-CII and //2-CII2 ligands can act as proton donors to form hydrogen bonds, as shown below  

Since the acidity of /X3-CII is stronger than that of /X2-CH2, the length of a /X3-CH hydrogen bond is shorter than that of /X2-CH2. 

Neutron diffraction studies have shown that the -CH ligand in the cluster [Co(CO)3]3(at3-CH) forms three hydrogen bonds, with H-O distances of 250,253, and 262 pm. In the compound [CpMn(CO)2]2(M2-CH2), the /u.2-CH2 group forms hydrogen bonds with the O atoms of Mn-CO groups, as shown in Fig. 11.2.6. 

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There is almost no reliable information about the strength of metal-hydrogen bonds in organometallic compounds. Earlier (Section 2.2.) it was established that M-H bonds formed by (spontaneous) -elimination from metal alkyls should be stronger that their precursor, but this is an unsatisfactory and imprecise position. The dissociation... 

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