The square planar complex (BINAP)Rh(CO)Cl (BINAP = 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl) was synthesized from [Rh(COD)Cl]2 (COD = 1,5 cyclooctadiene) and BINAP
under a CO atmosphere. It reacts with oxygen to form the square planar (BINAP(O))Rh(CO)Cl in approximately 50% yield, along with molar equivalents of free BINAP dioxide
(BINAP(O)2) and CO2. The oxygen atom of the BINAP(O) was shown crystallographically to
be trans to the CO ligand. In the presence of excess BINAP under CO/O2 gas mixtures, the
reaction is catalytic with a TOF of 0.16 h-1 at ambient temperature in chloroform. The
kinetics of this transformation were investigated and conditions for optimum selectivity for
BINAP(O) formation suggested. A stoichiometric mechanism is proposed that involves initial
formation of an O2 adduct, followed by oxygen atom transfer to both phosphorus atoms of
BINAP or to one phosphorus atom and the CO ligand trans to it. These processes might be
concerted, or stepwise with intermediate RhO species. To the best of our knowledge, this
chemistry represents the first example of a reaction exhibiting oxygen atom addition from
O2 either to both phosphorus atoms in a bisphosphine ligand or to one phosphorus atom
and a CO ligand in the same complex.
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