Cluster complexes [M2Rh(mu-PCy2)(mu-CO)(2)(CO)(8)] with triangular core ofRhM2 (M = Re, Mn; M-2= 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 equim olar amounts reacted at -40 to -15 degreesC in the presence of CO(g) in CH2 Cl2/methanol solution under release of PPh4[ClO4] to intermediates. Such sp ecies formed in a selective reaction the unifold unsaturated 46 valence ele ctrons 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 molecul ar structure of 2 was determined by a single crystal X-ray analysis. The ex change of the labil CO ligand attached at the rhodium ring atom in 1-3 agai nst selected tertiary and secondary phosphanes in solution gave the substit ution 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 l igated 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 s howed in the time scale of the P-31 NMR method a fluxional behaviour, was d etermined by X-ray structure analysis. All products obtained were always ch aracterized 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 valen ce-saturated complexes [MRh(mu -PCy2)(CO)(7)M(CO)(5)] (M = Re 16, Mn 17), w hereas 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 st ructures 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 2 0 degreesC ascertained the heterolytic splitting of hydrogen in the reactio n of 1-2 dissolved in CDCl3 or THF-d(8) under formation of product monoanio ns [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 an d 1 and 3 gave under the release of the labil CO ligand an eta (2)-coordina tion pattern of hexene, which was weekened going from the Re to the Mn neig hbor atoms. After the results of the catalytic experiments with 1 and 2 as catalysts, such change in the bonding property revealed an advantageous for mation of hydroformylation products for the dirhenium rhodium catalyst 1 an d that of isomerisation products of hexene for the dimanganese rhodium cata lyst 2. Par example, 1 generated n-heptanal/2-methylhexanal in TOF values o f 246 [h(-1)] (n/iso = 3.4) and the c,t-hexenes in that of 241 [h(-1)]. Opp osotite 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 acti vity of the hydroformylation reaction about 20%, accompanied by an only gra dually improved selectivity. The hydrogenation products like alcohols and saturated hydrocarbons known f rom industrial hydroformylation processes were not observed. The metals man ganese and rhenium bound at the rhodium reaction center showed a cooperativ e effect.