Cluster complexes [M2Rh(μ-PCy2)(μ-CO)2(CO)8] with triangular core of RhM2 (M = Re, Mn; M2= MnRe):: Synthesis, structure, ring opening reaction, and properties as catalysts for hydroformylation and isomerisation of 1-hexene

The salts PPh4[M-2(mu -H)(mu -PCy2)(CO)(8)] and Rh(COD)[ClO4] were in equimolar amounts reacted at -40 to -15 degreesC in the presence of CO(g) in CH2Cl2/methanol solution under release of PPh4[ClO4] to intermediates. Such species formed in a selective reaction the unifold unsaturated 46 valence electrons title compounds [M2Rh(mu -PCy2)(mu -CO)(2)(CO)(8)] (M = Re 1, Mn 2; M-2 = MnRe 3) in yields of > 90%; analogeous the derivatives with the PPh2 bridge could the obtained (M = Re 4, Mn 5). From these clusters the molecular structure of 2 was determined by a single crystal X-ray analysis. The exchange of the labil CO ligand attached at the rhodium ring atom in 1-3 against selected tertiary and secondary phosphanes in solution gave the substitution products [M2RhL(mu -PCy2)(mu -CO)(2)(CO)(7)] (M = Re: L = PMe3 6, P(n-Bu)(3) 7 P(n-C6H4SO3Na)(3) 8, HPCy2 9, HPPh2 10, HPMen(2) 11, M-2 = MnRe: L = NPCy2 12) nearly quantitative. Such dimanganese rhodium intermediates ligated with secondary phosphanes were converted in a subsequent reaction to the ring-opened complexes [MnRh-(mu -PCy2)(mu -H)(CO)(5)Mn(mu -PR2)(CO)(4)] (M = Mn: R = Cy 13, Ph 14, Mn 15). The molecular structure of 13, which showed in the time scale of the P-31 NMR method a fluxional behaviour, was determined by X-ray structure analysis. All products obtained were always characterized by means of upsilon (CO)Ir, H-1 and P-31 NMR measurements. From the reactants of hydroformylation process, CO(g) 1-2 in different solvents afforded at 20 degreesC under a reversible ring opening reaction the valence-saturated complexes [MRh(mu -PCy2)(CO)(7)M(CO)(5)] (M = Re 16, Mn 17), whereas the reaction of CO(g) and the ring-opened 13 to [MnRh(mu -PCy2)(mu -H)(CO)(6)Mn(mu -PCy2)(CO)(4)] (18) was as well reversible. The molecular structures of 17 and 18 were determined by X-ray analysis. The upsilon (CO)IR, H-1 and P-31 NMR measurements in pressure-resistant reaction vessels at 20 degreesC ascertained the heterolytic splitting of hydrogen in the reaction of 1-2 dissolved in CDCl3 or THF-d(8) under formation of product monoanions [M2Rh(mu -CO)(mu -H)(mu -PCy2)(CO)(9)](-) (M = Re, Mn), which also were formed by the reaction of NaBH4 and 1-2. Finally, the substrate 1-hexene and 1 and 3 gave under the release of the labil CO ligand an eta (2)-coordination pattern of hexene, which was weekened going from the Re to the Mn neighbor atoms. After the results of the catalytic experiments with 1 and 2 as catalysts, such change in the bonding property revealed an advantageous formation of hydroformylation products for the dirhenium rhodium catalyst 1 and that of isomerisation products of hexene for the dimanganese rhodium catalyst 2. Par example, 1 generated n-heptanal/2-methylhexanal in TOF values of 246 [h(-1)] (n/iso = 3.4) and the c,t-hexenes in that of 241 [h(-1)]. Opposotite to this, 2 achieved such values of 55 [h(-1)] (n/iso = 3.6) and 473 [h(-1)]. A triphenylphosphane substitution product of 1 increased the activity of the hydroformylation reaction about 20%, accompanied by an only gradually improved selectivity. The hydrogenation products like alcohols and saturated hydrocarbons known from industrial hydroformylation processes were not observed. The metals manganese and rhenium bound at the rhodium reaction center showed a cooperative effect.