SYNTHESIS AND CRYSTAL-STRUCTURE OF A DINUCLEAR RHODIUM COMPLEX - CATALYTIC ACTIVITY OF MONONUCLEAR AND DINUCLEAR RHODIUM PHOSPHITE COMPLEXES IN HYDROFORMYLATION

A new bidentate phosphite, 2-(diphenoxyphosphinoxy)-1-naphthyl]methyl} benzene L(1) and a tetradentate phosphite, 2-(diphenoxyphosphinoxy)-1- naphthyl]methyl}benzene L(2) were prepared in a facile two-step proced ure involving condensation of 2-naphthol with respectively benzaldehyd e or terephthalaldehyde, followed by treatment with chlorodiphenoxypho sphine. The corresponding monuclear rhodium(I) complex [RhL(1)(acac)] 1 (acac = acetylacetonate) and dinuclear complexes [Rh(2)L(2)(acac)(2) ] 2 and [Rh(2)L(2)Cl(2)(CO)(2)] 3 have been isolated. The fluxial beha viour of the ligand in the mono- and di-nuclear rhodium complexes in s olution was studied by dynamic H-1 and P-31 NMR spectroscopy, showing hindered rotation in the biarylmethane units. The crystal structure of complex 2, obtained by X-ray analysis, reveals its dinuclear nature a nd an 'unfolded' geometry. Complexes 1 and 2 catalyse the hydroformyla tion of cyclohexene with average turnover frequencies of 428 and 344 m m(-1) h(-1), respectively, over 4 h. A notable increase was observed i n turnover frequency during the course of reaction. High-pressure (20 bar H-2-CO) IR and H-1 and P-31 NMR studies with complex 1 revealed a single rhodium hydride species in solution.