Synthesis and molecular structure of the first neutral transition-metal complex containing a linear M=C=C=C=C=CR(2) chain

The reaction of[IrH2Cl(PiPr(3))(2)] (2) with the pentadiyne derivative HC=C-C=C-CPh(2)OH (1) yields the five-coordinate compound [IrH(C=C-C=CCPh(2)OH)Cl(PiPr(3))(2)] (3), which photochemically rearranges to give the vinylidene-substituted isomer trans-[IrCl(=C=CH-C=CCPh(2)OH)(PiPr(3))(2)] (4). On treatment of 3 with pyridine,the octahedral complex [IrH(C=C-C=CCPh(2)OH)Cl(py)(PiPr(3))(2)] (5) is formed. While attempts to eliminate water from 4 (or 5) failed, the reaction of 3 with one equivalent of trifluorosulfonic acid anhydride and two equivalents of triethylamine led to the formation of trans-[IrCl(=C=C=C=C=CPh(2))(PiPr(3))(2)] (6), which is the first neutral transition-metal complex containing a C(5)R(2) ligand. The X-ray structural analysis of 6 reveals a perfect square-planar coordination geometry around the metal centre and an almost linear IrC5 chain with Ir-C-C and C-C-C bond angles of 174-179 degrees.