Sulfur–carbon bond formation and bond cleavage in alkynyl-bridged heterobinuclear complexes of rhodium and iridium

Abstract

The phenylacetylide-bridged heterobinuclear complexes [RhIr(CO)2(μ-η1:η2-C2Ph)(dppm)2][X] (X=BF4, SO3CF3; dppm=Ph2PCH2PPh2) (1) react with carbon disulfide to give several products. At temperatures between −60 and −80°C the first product, [RhIr(CO)(η2-CS2)(μ-CO)(μ-η1:η2-C2Ph)(dppm)2][X] (2), is the result of CS2 coordination at Ir. Upon warming, two products are formed as a result of condensation of two CS2 groups. In [RhIr(CO)(μ-η1:η3-CC(Ph)SCSCS2)(μ-CO)(dppm)2][X] (3), the resulting C2S4 fragment has also condensed at the β-carbon of the acetylide group to give a heteroatom-substituted vinylidene group. The other identified product, [RhIr(CO)(C2S4)(μ-C2Ph)(μ-CO)(dppm)2][X] (4), is very similar to 3 apart from the absence of coupling of the C2S4 moiety and the acetylide group. Compound 3 appears to be formed independently of 4, but also slowly transforms into 4 by cleavage of a C-S bond. The reaction of 1 with nBuNCS at −80°C yields [RhIr(CO)(η2-SCNnBu)(μ-CCPh)(μ-CO)(dppm)2][X] (5), analogous to 2, and upon warming this rearranges to the isothiocyanate-bridged product [RhIr(CCPh)(CO)2(μ-SCNnBu)(dppm)2][X] (6). Compound 6 undergoes S-C bond cleavage to yield [RhIr(CCPh)(CO)(CNnBu)(μ-S)(μ-CO)(dppm)2][X] (7), slowly at ambient temperature or within hours under reflux. Although no simple adducts analogous to 5 and 6 were observed with tBuNCS, refluxing 1 in the presence of an excess of this substrate yields [RhIr(CCPh)(CO)(CNtBu)2(μ-S)2(dppm)2][X] (9) as the major product along with smaller amounts of [RhIr(CCPh)(CO)(CNtBu)(μ-S)(μ-CO)(dppm)2][X] (8), analogous to compound 7. Refluxing 1 in the presence of excess nBuNCS also yields some of the bis-n-butylisocyanide product, analogous to 9. The X-ray structures of compounds 3 (SO3CF3− salt), 7 (BF4− salt) and 9 (BF4− salt) are reported.