Coordination and coupling of OH-functionalized C-2 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

The reaction of [Rh(eta(3)-C3H5)-(PiPr(3))(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}(PiPr(3))(2)] (2), while from 1 and HC equivalent to C-CPh(2)OH the alkynyl(enyne)metal derivative trans-[Rh(C equivalent to C-CPh(2)OH){eta(2)-(E)-Ph(2)(OH)C-C equivalent to C-CH=CH-CPh(2)OH}(PiPr(3))(2)] is obtained. On treatment with 1-alkyn-3-ols HC equivalent to C-CR(2)OH (R=Me,Ph,iPr), the highly reactive pi-benzyl compound [Rh(eta(3)CH(2)Ph)(PiPr(3))(2)] (4) yields the five coordinate complexes [RhH(C equivalent to C-CR(2)OH)(2)(PiPr(3))(2)] (5-7) of which those with R=Me and Ph can be converted to the alkynyl(vinylidene)metal isomers trans-[Rh(C equivalent to C-CH2OH) (=C=CH-CR(2)OH)-(PiPr(3))(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{eta(1)-(Z)-C(C equivalent to C-CR(2-) OH)=CH-CR(2)OH}(L')(PiPr(3))(2)] (10, 11: L'=CO; 12-15: L'=CNR'). Cleavage of the Rh-C sigma-bond of 10 with CF, CO2H affords trans-[Rh(eta(1)-O2CCF3)-(CO)(PiPr(3))(2)] (16) and the enyne (E)-Me(2)(OH)C-C equivalent to C-CH=CH-CMe(2)OH (17). Compounds 5-7 react with L'=CO and isocyanides to give the octahedral 1:1 adducts [RhH(C equivalent to C-CR(2)OH)(2)(L')(PiPr(3))(2)] (18-20 and 24-27), of which the CO derivatives 18-20 readily eliminate HC equivalent to C-CR(2)OH to yield trans-[Rh- (C equivalent to C-CR(2)OH)(CO)(PiPr(3))(2)] (21-23). On treatment of 6 or 9 (R=Ph) with Al2O3 in the presence of chloride ions, besides trans-[RhCl(=C=C=CPh(2))(PiPr(3))(2)] (28) the hexapentaenerhodium(I) complex trans-[RhCl(eta(2)-Ph(2)C=C=C=C=C=CPh(2))(PtPr3)(2)] (29) is formed. The kinetically preferred isomer trans-[RhCl(eta(2)-Ph(2)C=C=C=C=C=CPh(2))(PiPr(3))(2)] (33) has been prepared from [RhCl(PiPr(3))(2)](2) and Ph(2)C=C=C=C=C=CPh(2); it rearranges smoothly at room temperature to the thermodynamically more stable isomer 29. The molecular structures of 7 and 29 have been deter mined.