Orientation of trimethylolethane cyclic phosphite in rhodium complexes: Structure of [Rh(CH3COCHCOCH3)(CO)(P(OCH2)3CCH3)

Abstract

Density functional theory calculations showed that rotation of the (P(OCH2)3CCH3) group in the rhodium–acetylacetonato complex [Rh(acac)(CO)(P(OCH2)3CCH3)] has a negligible influence on the energy of the complex. Density functional theory calculations further showed that the minimum energy orientation of the cyclic (P(OCH2)3CCH3) group in square planar rhodium–(P(OCH2)3CCH3)–(CO) complexes containing a bidentate ligand that is larger than the acetylacetonato ligand, is with one of the PO bonds near parallel (within 10°) to the plane defined by the four atoms coordinated to Rh. The three PO bonds of the rigid (P(OCH2)3CCH3) group adopt a C3-symmetrical conformation around the RhP axis. The lowest energy geometry of [Rh(BID)(CO)(P(OCH2)3CCH3)] (BID=bidentate ligand with two O donor atoms and charge −1) complexes is where one PO bond is aligned near parallel to the RhOBIDtransto CO bond, while the geometry with a PO bond orientated near parallel to the RhCCO bond, is slightly higher in energy, but still possible experimentally. The highest energy orientation of the (P(OCH2)3CCH3) group in square planar [Rh(BID)(CO)(P(OCH2)3CCH3)] complexes, is with one of the PO bonds near perpendicular to the plane described by the four atoms coordinated to Rh. The orientation of the cyclic (P(OCH2)3CCH3) group in available experimental structures of square planar [Rh(BID)(CO)(P(OCH2)3CCH3)] complexes, confirms this finding.