Synthesis of dinuclear rhodium complexes with 1,3-butadiyndiyl bridges.: Coupling of the C4 and the two C2 units of a C2RhC4RhC2 chain

Compounds trans-[RhF(=C=CHR)(PiPr(3))(2)] (2-4), of which 2 (R = H) was prepared for the first time from [Rh{eta(2)-O2S(O)CF3}(PiPr(3))(2)], C2H2, and KF, reacted with Ph3SnC=C-C=CSnPh3 to give the dinuclear C-4-bridged rhodium(I) complexes trans,trans-[{Rh(=C=CHR)-(PiPr(3))(2)}(2)(mu-C=C-C=C)] (5-7) in 78-88% isolated yield. On a similar route, by using trans[RhF(CX)(PiPr(3))(2)] (8, CX = CNC6H3Me2-2,6; 9, CX = CO) and Ph3SnC=C-C=CSnPh3 in the molar ratio of 2:1 as the starting materials, the diisocyanidedirhodium and dicarbonyl-dirhodium derivatives trans,trans-[{Rh(CX)(PiPr(3))(2)}(2)(mu-C=C-C=C)] (12, 13) were obtained. The reactions of 8 and 9 with equimolar amounts of Ph3SnC=C-C=CSdPh(3) gave the mononuclear complexes trans-[Rh(C=C-C=CSnPh3)(CX)(PiPr(3))(2)] (10, 11), which on further treatment with 8 or 9 afforded the dinuclear compounds 12 and 13, respectively. The C-SnPh3 bond of 10 could be cleaved both by Al2O3/H2O and trans-[RhF(=C=CHPh)(PiPr(3))(2)] (3) to give the butadiynyl compound trans-[Rh(C=C-C=CH)(CNC6H3Me2-2,6)(PiPr(3))(2)] (14) and the unsymmetrical dirhodium complex trans,trans-[{Rh(=C=CHPh)(PiPr(3))(2)}{Rh-(CNC6H3Me2-2,6)(PiPr(3))(2)}(mu-C=C-C=C)] (15). Moreover, treatment of 5 and 6 with CNC6H3-Me-2-2,6 or CO led to a 2-fold migratory insertion reaction to yield the novel dinuclear compounds trans,trans-[{Rh(CX)(PiPr(3))(2)}2{mu-C(=CHR)C=C-C(=CHR)}] (16 - 18), which contain a highly unsaturated eight-membered C-8 chain as a bridge. The molecular structure of 17 (CX = CO; R = Ph) was determined by X-ray crystallography.