Hydride donors structural types

Finally, Figure 5.40 displays the surprising structure of the (PtH2)2 dimer, an anti-H-bond n—a donor-acceptor complex. As expected, the leading NBO donor-acceptor interaction is of npt crptH type, but the attack by npt is now on the backside of the cjrh NBO, leading to unusual Pt - -Pt—H coordination to the hydride antibond as depicted in Fig. 5.40b. 

Monomeric dialkylaluminum hydrazides with terminal hydrazido groups (A, Scheme 2) were observed only in those cases in which donor ligands such as ether molecules (28 to 30) or hydride ions (26) saturate the aluminum atoms to yield coordination numbers of four. In the absence of Lewis bases dimers are formed of the monoaluminum and monogallium monohydrazido derivatives, a trimer has never been detected by crystal structure determinations. Three different types of structures were reported ... 

Additional information on electronic structure comes from a NMR study of a closely related series of compounds of the type (Cp )2Hf(X)(H), where X is H, Me, OH, NH2, NHMe, or NMe2. Bercaw and co-workers observed that in the H-NMR spectrum the metal-bonded H atom becomes more shielded as the tt donor ability of X increases (51). The hydride chemical shifts corresponding to X are 8 15.6, 13.1, 10.2, 9.3, 9.1, and 11.5, respectively. Clearly, the tt interaction of the main group ligand with the metal is important in compounds of this type. 

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