Rhodium carbonyl complexes containing pyridine; crystal structure of an unusual octahedral rhodium(I) complex [Rh2(µ-CO)3Cl2(py)4]
Abstract
The products resulting from the progressive addition of pyridine (py) to a solution of [Rh2(µ-Cl)2(CO)4] 1 have been found to depend both upon the solvent and the atmosphere (CO or N2). In CH2Cl2 under N2, cis-[Rh(CO)2Cl(py)] 2, [Rh(CO)2Cl(py)2] 3 and [Rh2(µ-CO)3Cl2(py)4] 4 were obtained successively; under CO, 4 was converted into 3 and under N2 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 N2 to give the lightly solvent-stabilised complex [Rh(CO)2Cl(solv)] 6 (solv = thf a or MeOH b) and, in the presence of AgClO4, cis-[Rh(CO)2(solv)2]+ 7 (solv = thf a or MeOH b); additionally, when solv = MeOH there was spectroscopic evidence for the formation of [Rh2(µ-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 converted into 9. The stereochemistry of all the above complexes has been established through a combination of IR and multinuclear (13C, 15N, 103Rh) NMR measurements and X-ray crystallography for 2 and 4. Analogous reactions have been carried out using trans-[Rh2(µ-Cl)2(CO)2(CxHy)2] 11 (CxHy = C2H4 a or C8H14 b) under a nitrogen atmosphere and spectroscopic measurements on the reaction of 11a with pyridine were consistent with the successive formation of [Rh2(µ-Cl)2(CO)2(C2H4)2(py)2] 12, which lost ethylene and rearranged to give [Rh2(µ-CO)2Cl2(py)2] 13. Reaction of 11b with pyridine gave immediately trans-[Rh2(µ-Cl)2(CO)2(py)2] 14 and both 13 and 14 further reacted with pyridine to give 5.
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