SYNTHESIS, STRUCTURE AND REACTIVITY OF A NOVEL BIS(PHOSPHITE) TETRARHODIUM DECACARBONYL HYDROFORMYLATION CATALYST PRECURSOR

The tetranuclear Rh-4(mu-bpnap)(CO)(10) (1) was synthesized in 68% yie ld by the reaction of Rh-2(CO)(4)Cl-2 with bpnap ,1'-biphenyl-2,2'-diy l)phosphite]-1,1'-binaphthyl) (2) under CO. The crystal structure of 1 , determined by X-ray diffraction, established that the bpnap ligand b ridged two rhodium atoms of a tetrahedral metal framework. Recrystalli zation of 1 from CH2Cl2/THF led to its partial conversion to a structu ral isomer, 1a, which was characterized by solution spectroscopic meth ods. The reaction of Rh(acac)(CO)(2) and bpnap under 1:1 CO/H-2 led to a mixture of products consisting of 1, la and at least two hydridic c ompounds. The latter were also formed by the hydrogenation of Rh(acac) (CO)(2) and bpnap. Rh-4(mu-bpnap)(CO)(10) was shown to be an effective catalyst precursor for the isomerization and hydroformylation of 1-oc tene, giving, for the latter reaction, moderate linear/branched select ivity for the product aldehydes. The hydroformylation of a-methylstyre ne with Rh(acac)(CO)(2) and R-(+)-bpnap gave essentially no enantiomer ic excess of 3-phenylbutanal. The structural features of 1, along with comparison of its reactivity with other bis(phosphite) metal complexe s are discussed. Crystal data for Rh-4(bpnap)(CO)(10) (1) (f.w. 1577.4 8): monoclinic, P2(1)/c; a=14.624(4), b=18.974(6), c=21.343(5) Angstro m; V=5899(5) Angstrom(3); beta=95.06(2)degrees, Z=4; R=6.4%.