Synthesis, structure and reactivity of a novel bis(phosphite) tetrarhodium decacarbonyl hydroformylation catalyst precursor

Abstract

Abstract The tetranuclear Rh4(μ-bpnap)(CO)10 (1) was synthesized in 68% yield by the reaction of Rh2(CO)4C12 with bpnap (2,2′-bis[(1,1'-biphenyl-2,2′-diyl)phosphite]-1,1′-binaphthyl) (2) under CO. The crystal structure of 1, determined by X-ray diffraction, established that the bpnap ligand bridged two rhodium atoms of a tetrahedral metal framework. Recrystallization of 1 from CH2Cl2/THF led to its partial conversion to a structural isomer, la, which was characterized by solution spectroscopic methods. The reaction of Rh(acac)(CO)2 and bpnap under 1:1 CO/H2 led to a mixture of products consisting of 1, la and at least two hydridic compounds. The latter were also formed by the hydrogenation of Rh(acac)(CO)2 and bpnap. Rh4(μ-bpnap)(CO)10 was shown to be an effective catalyst precursor for the isomerization and hydroformylation of 1-octene, giving, for the latter reaction, moderate linear/branched selectivity for the product aldehydes. The hydroformylation of a-methylstyrene with Rh(acac)(CO)2 and R-(+)-bpnap gave essentially no enantiomeric excess of 3-phenylbutanal. The structural features of 1, along with comparison of its reactivity with other bis(phosphite) metal complexes are discussed. Crystal data for Rh4(bpnap)(CO)10 (1) (f.w. 1577.48): monoclinic, P21/c; a = 14.624(4), b = 18.974(6), c = 21.343(5)A; V= 5899(5)A; β = 95.06(2)°, Z= 4; R = 6.4%.