Rhenium carbonyl compounds with (diphenyl)phosphinoalkynes and a sterically hindered phosphinoalkyne

The synthesis and characterization of two series of rhenium carbonyl complexes with P-coordinated phosphinoalkynes are reported. The anionic fac-[ReBr2(CO)3(Ph2PC{triple bond, long}CR)]- and neutral fac-[ReBr(CO)3(Ph2PC{triple bond, long}CR)2] (R = Ph, Tol, tBu) complexes have been prepared and the crystal structures of fac-[ReBr2(CO)3(Ph2PC{triple bond, long}CTol)]- and fac-[ReBr(CO)3(Ph2PC{triple bond, long}CtBu)2] have been determined by X-ray crystallography, evidencing the presence of the uncoordinated alkyne in all these compounds. The phosphinoalkyne (o-Tol)2PC{triple bond, long}CPh with bulky groups linked to the phosphorus atom was prepared in order to avoid the coordination of two phosphinoalkynes in cis-position around the rhenium metal. As a result, surprisingly the complex fac-[ReBr(CO)3{(o-Tol)2PC{triple bond, long}CPh}2] was obtained. The crystal structure of this compound was determined confirming the cis-coordination of two bulky phosphinoalkynes in an octahedral rhenium atom. The electronic properties of the uncoordinated alkyne in these new rhenium complexes was analyzed, based on 13C NMR data and was compared with reported data on iron complexes. The results obtained indicate that the electronic characteristics of uncoordinated alkynes are similar in both families of complexes. Thus, the different reactivity observed between rhenium and iron complexes is related to the different nature of metallic fragments rather than to electronic features of uncoordinated alkynes. © 2008 Elsevier B.V. All rights reserved.