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(Ph2PCCR)]− and neutral fac-[ReBr(CO)3(Ph2PCCR)2] (R = Ph, Tol, tBu) complexes have been prepared and the crystal structures of fac-[ReBr2(CO)3(Ph2PCCTol)]− and fac-[ReBr(CO)3(Ph2PCCtBu)2] have been determined by X-ray crystallography, evidencing the presence of the uncoordinated alkyne in all these compounds. The phosphinoalkyne (o-Tol)2PCCPh 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)2PCCPh}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.

Graphical abstractPhosphinoalkynes Ph2PCCR (X = Ph; R = Ph, Tol, tBu) react with [ReBr3(CO)3]2− and the hydrolyzed complex [ReBr3–n(CO)3(H2O)n]n–2 to form anionic fac-[ReBr2(CO)3X2CCR]− or neutral fac-[ReBr(CO)3(X2PCCR)2] complexes depending on the starting precursor and independently of metal/phosphine ratio used. The same behaviour has been observed using the phosphinoalkyne with bulky groups (o-Tol)2PCCPh.Figure optionsDownload full-size imageDownload as PowerPoint slide