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 P-O bonds near parallel (within 10°) to the plane defined by the four atoms coordinated to Rh. The three P-O bonds of the rigid (P(OCH2)3CCH3) group adopt a C3-symmetrical conformation around the Rh-P 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 P-O bond is aligned near parallel to the Rh-OBID trans to CO bond, while the geometry with a P-O bond orientated near parallel to the Rh-CCO 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 P-O 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.