Rhenium polyhydride complexes

H-D Exchange Reaction of Borane-Lewis Base Adducts by Rhenium Polyhydride Complexes... 

Thus we examined the reactions of borane-Lcwis base adducts with rhenium polyhydride complexes to synthesize highly fluxional polyhydride(borane) complexes. However, treatment of several boranes with the rhenium complexes in deuterated solvents resulted in an unexpected reaction H-D exchange between the boranes and solvents. This is the first example of H-D exchange between sp2 carbon and sp3 boron, and closely associated with metal-catalyzed deuteration of alkanes.4... 

In this regard a more significant determination should be obtained from a study of the polyhydride complexes [ReH7(PR3)2], in that (i) if the complex is a classical hydride the rhenium atom would be in its maximum oxidation state (+ 7) and, therefore, could not undergo further oxidation processes (ii) if the complex is a non-classical hydride, the rhenium atom would be in a lower oxidation state and, consequently, could display oxidation processes. 

A reversible deprotonation for a 17-electron hydride complex was shown for the stable cationic cobalt(II) hydride complex [CoH CH3C(CH2PPh2)3 (PEtj)]BPh4, yielding a presumed Co(0) neutral species. Although the latter species could not be isolated and fully characterized, it was shown that it can be reprotonated to yield the Co(II) hydrido species back [40]. Polyhydride complexes have also been shown to readily lose protons. Early examples have been provided by Walton on rhenium compounds, e.g. ReH5(PR3)3 derivatives [101], on the basis of electrochemical investigations. 

With rhenium there are several possible or probable H2 complexes as well as some cases that are very equivocal. It is believed that the [Re(PR3)2H8]+ ion, obtained by protonation of ReH7(PR3)2 must contain at least one H2 ligand, since a classical structure containing eight H ligands exceeds the possible valence of rhenium. Other protonated species, e.g., [Re(PR3)3H<]+, may well be classical polyhydrides. It is to be noted that protonation occurs only at low temperature otherwise there is a reaction such as the following in which H2 is evolved ... 

One of the characteristic features of rhenium is its tendency to form stable complexes in a high oxidation state such as Re(VI) and Re(VII) and a series of rhenium 0x0-alkyls and a variety of polyhydrides of this type have been extensively studied. 

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