Synthesis and reactivity of dinuclear rhodium complexes with RhCCHR and RhCCCRR′ units as building blocks

The reaction of [Rh{κ2-O2S(O)CF3}(PiPr3)2] (1) with ethynylferrocene in the presence of KF affords the substituted vinylidene complex trans-[RhF{CCH(C5H4)Fe(C5H5)}(PiPr3)2] (2) which upon treatment with the butadiyne derivative Ph3SnCCCCSnPh3 produces the chain-like compound trans-[(μ-CCCC){Rh(CCH(C5H4)Fe(C5H5))(PiPr3)2}2] (7). The triflato complex 1 reacts with 1,4-C6H4(CCH)2 to give the dinuclear compound trans-[{μ-1,4-C6H4(CHC)2}{Rh(η1-OS(O)2CF3)(PiPr3)2}2] (3) which in the presence of KF undergoes a ligand exchange to give the corresponding difluoro derivative 4. From 4 and RCCSnPh3 (R=CH3, C6H5) the complexes 5 and 6, in which a C6H4 unit bridges two alkynyl(vinylidene)rhodium(I) fragments, are obtained. Both 6 and 7 react with CO by migratory insertion of the vinylidene units into the alkynyl-metal bonds to afford the dinuclear complexes 8 and 9, in which an unusual C8 or C4(C6H4)C4 chain bridges the two rhodium centers. The reactions of [RhCl(PiPr3)2]2 (10) with the functionalized diynes 1,1′,4,4′-C6H4(OH)2(CCH)2 and 1,4-C6H4[C(Ph)(OH)CCH]2 lead, via the corresponding diyne-metal species 11 and 12 as intermediates, to the formation of the bis(vinylidene) complexes 13 and 14, the latter of which reacts with acidic Al2O3 by elimination of water to give the novel phenylene-bridged bis(allenylidenerhodium) compound [{μ-1,4-C6H4(CPhCC)2}{RhCl(PiPr3)2}2] (15) in 80% yield.