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(Ph2PCtriple bond; length of mdashCR)]− and neutral fac-[ReBr(CO)3(Ph2PCtriple bond; length of mdashCR)2] (R = Ph, Tol, tBu) complexes have been prepared and the crystal structures of fac-[ReBr2(CO)3(Ph2PCtriple bond; length of mdashCTol)]− and fac-[ReBr(CO)3(Ph2PCtriple bond; length of mdashCtBu)2] have been determined by X-ray crystallography, evidencing the presence of the uncoordinated alkyne in all these compounds. The phosphinoalkyne (o-Tol)2PCtriple bond; length of mdashCPh 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)2PCtriple bond; length of mdashCPh}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.