Coordination and Coupling of OH-Functionalized C2 Units at a Single Metal Center: The Synthesis of Alkynyl(Vinylidene), Alkynyl(Enyne), Bis(Alkynyl)Hydrido, Enynyl, and Hexapentaene Rhodium Complexes from Propargylic Alcohols as Precursors.

Abstract

The reaction of [Rh(η3 -C3 H5 )-(PiPr3 )2 ] (1) with HCCCH(Ph)OH yields the alkynyl(vinylidene) complex trans-[Rh{CCCH(Ph)OH}{CCH-CH(Ph)OH}(PiPr3 )2 ] (2), while from 1 and HCCCPh2 OH the alkynyl-(enyne)metal derivative trans-[Rh(CCCPh2 OH){n2 -(E)-Ph2 (OH)CCCCHCH-CPh2 OH} (PiPr3 )2 ] (3) is obtained. On treatment with 1-alkyn-3-ols HCCCR2 OH (R = Me, Ph, iPr), the highly reactive π-benzyl compound [Rh(n3 -CH2 Ph)(PiPr3 )2 ] (4) yields the five-coordinate complexes [RhH(CCCR2 OH)2 (PiPr3 )2 ] (5-7) of which those with R = Me and Ph can be converted to the alkynyl(vinylidene)metal isomers trans-[Rh(CCCR2 OH)(CCH-CR2 OH)-(PiPr3 )2 ] (8, 9). Compounds 8 and 9 react with L' = CO and isocyanides by migration of the alkynyl ligand to the vinylidene unit to give the enynylrhodium(I) complexes trans-[Rh{n1 -(Z)-C(CCCR2 OH)CH-CR2 OH}(L')(PiPr3 )2 ] (10, 11: L' = CO; 12-15: L' = CNR'). Cleavage of the Rh-C s̀-bond of 10 with CF3 -CO2 H affords trans-[Rh(n1 -O2 CCF3 )-(CO)(PiPr3 )2 ] (16) and the enyne (E)-Me2 (OH)CCCCHCH-CMe2 OH (17). Compounds 5-7 react with L' = CO and isocyanides to give the octahedral 1:1 adducts [RhH(CCCR2 OH)2 (L')(P-iPr3 )2 ] (18-20 and 24-27), of which the CO derivatives 18-20 readily eliminate HCCCR2 OH to yield trans-[Rh-(CCCR2 OH)(CO)(PiPr3 )2 ] (21-23). On treatment of 6 or 9 (R = Ph) with Al2 O3 in the presence of chloride ions, besides trans-[RhCl(CCCPh2 )(P-iPr3 )2 ] (28) the hexapentaenerhodium(I) complex trans-[RhCl(n2 -Ph2 CCCCCCPh2 )(PiPr3 )2 ] (29) is formed. The kinetically preferred isomer trans-[RhCl(n2 -Ph2 CCCCCCPh2 )(P-iPr3 )2 ] (33) has been prepared from [RhCl(PiPr3 )2 ]2 and Ph2 CCCCCCPh2 ; it rearranges smoothly at room temperature to the thermodynamically more stable isomer 29. The molecular structures of 7 and 29 have been determined.