RHODIUM CARBONYL-COMPLEXES CONTAINING PYRIDINE - CRYSTAL-STRUCTURE OFAN UNUSUAL OCTAHEDRAL RHODIUM(I) COMPLEX [RH-2(MU-CO)(3)CL-2(PY)(4)]

The products resulting from the progressive addition of pyridine (py) to a solution of [Rh-2(mu-Cl)(2)(CO)(4)] 1 have been found to depend b oth upon the solvent and the atmosphere (CO or N-2). In CH2Cl2 under N -2, cis-[Rh(CO)(2)Cl(py)] 2, [Rh(CO)(2)Cl(py)(2)] 3 and [Rh-2(mu-CO)(3 )Cl-2(py)(4)] 4 were obtained successively; under CO, 4 was converted into 3 and under N, disproportionation of 4 slowly occurred to give 3 and trans-[Rh(CO)Cl(py)(2)] 5 which reacted with CO to give 3. In more polar solvents (thf or MeOH), 1 reacted under N, to give the lightly solvent-stabilised complex [Rh(CO)(2)Cl(solv)] 6 (solv = thf a or MeOH b) and, in the presence of AgClO4, cis-[Rh(CO)(2)(solv)(2)](+) 7 (sol v = thf a or MeOH b); additionally, when solv = MeOH there was spectro scopic evidence for the formation of [Rh-2(mu-CO)(x)(MeOH)(y)](2+) 8 ( x = 2, y = 4 or x = 3, y = 6) which reacted with CO to give [Rh(CO)(2) (MeOH)(2)](+). Complex 7 reacted with py to give successively cis-[Rh( CO)(2)(py)(2)](+) 9 and [Rh(CO)(py)(3)](+) 10; under CO 10 was convert ed into 9. The stereochemistry of all the above complexes has been est ablished through a combination of IR and multinuclear (C-13, N-15, Rh- 103) NMR measurements and X-ray crystallography for 2 and 4. Analogous reactions have been carried out using trans-[Rh-2(mu-Cl)(2)(CO)(2)(Cx Hy)(2)] 11 (CxHy = C2H4 a or C8H14 b) under a nitrogen atmosphere and spectroscopic measurements on the reaction of 11a with pyridine were c onsistent with the successive formation of [Rh-2(mu-Cl)(2)(CO)(2)(C2H4 )(2)(py)(2)] 12, which lost ethylene and rearranged to give [Rh-2(mu-C O)(2)Cl-2(py)(2)] 13. Reaction of 11b with pyridine gave immediately t rans-[Rh-2(mu-Cl)(2)(CO)(2)(py)(2)] 14 and both 13 and 14 further reac ted with pyridine to give 5.