Conformational analysis of triphenylphosphine in square planar [Rh(β-diketonato)(CO)(PPh3)] complexes. Crystal structure of [Rh(PhCOCHCO(CH2)3CH3)(CO)(PPh3)]

The crystal structure of [Rh(PhCOCHCO(CH2)3CH3)(CO)(PPh3)], 1, and the conformation analysis of PPh3 coordinated to 1 is presented. Two geometrical isomers are possible, which unexpectedly crystallized in the same space in the unit cell with an 89.7:10.3 ratio. Results from density functional theory calculations, in agreement with experimental structures, show that favored degenerate conformations of coordinated PPh3 in square planar [(PPh3)(ML1L2L3)], [M(acac)(L’)(PPh3)] and [Rh(β-diketonato)(CO)(PPh3)] complexes possess distinct features and can be obtained by applying the following principles (P helicity, view along P–M axis), (i) superimpose Co of the vertical ring A onto the nadir plane perpendicular to the square plane and allow ring A to tilt towards the smallest ligand, (ii) allow ring B to tilt in the space below the smallest ligand in the quadrant between the nadir plane below the complex and a horizontal plane through the SQP of the complex, (iii) tilt ring C over the largest ligand and (iv) allow correlated tilting of rings A, B and C to minimize inter ring–ring and inter ring–ligand interactions. The steric influence of Oβ-diketonato and CO is similar on the preferred orientation of the vertical phenyl ring A of PPh3 in [Rh(β-diketonato)(CO)(PPh3)] complexes. The size of the side groups R and R′ on the β-diketonato ligand (RCOCHCOR′)− does not influence the preferred conformation of coordinated PPh3 in [Rh(β-diketonato)(CO)(PPh3)].