Application of molecular mechanics (MMX) calculations to an investigation of the conformations of coordinated triphenylphosphine in organometallic compounds of the types (.eta.6-C6R6)Cr(CO)2PPh3 and (.eta.5-C5H5)Fe(CO)(PPh3)R' (R = H, Me; R' = H, alkyl, acyl)

The conformational analysis of phosphine ligands in organometallic complexes. Part 1. Triphenylphosphine coordinated to an achiral metal centre 1

“…The enantiomeric complexes interconvert via rapid low energy intramolecular processes. 5 Although structural correlations 6,7 and molecular mechanics calculations 8 have been reported, limited success has been achieved in developing a general model 1 which includes an account of the intramolecular interactions associated with the propeller conformations of PPh 3 ligands attached to achiral metal centres. In organometallic complexes containing 1, the conformation of the three phenyl rings in the crystal is primarily determined by intramolecular steric interactions.…”

Alternative force field models for ansa-zirconocene complexes—vibrational and structural studies on Me 2 Si-bridged and tert -butyl-substituted representatives

“…Instead, the coordination geometry of such a complex has to be reproduced by mutual repulsions of the C 5 -ring ligands with each other and with the other ligands present. Van-der-Waals-interactions of this type are commonly used to describe coordination geometries [15][16][17][18][19][20][21][22][23] and have also been shown to afford satisfactory structural descriptions for complexes with cyclopentadienyl ligands [8][9][10][11][12][13][14][15][16][17][18].…”

“…In all of these studies, a force field is utilized where the metal center is connected to each of the C 5ring ligands by a pseudo-bond to the respective C 5ring centroid. This connectivity scheme has been shown to afford rather accurate descriptions of interring angles and of rotational conformations for a variety of cyclopentadienyl complexes [5][6][7][8][9][10][11][12][13][14][15][16][17]. Closer to chemical intuition, however, would appear to be a force field in which each cyclopentadienyl C atom is connected directly to the Zr center, such that distortions-caused for example by steric repulsions-are controlled by the "elasticity" of the individual Zr-C bonds rather than by that of the fictional metalcentroid-carbon "bond" angle.…”

Evidence for an intramolecular transition metal Arbuzov reaction

“…Starting structures for the cations 3, obtained from model compounds derived from crystallographic data, were minimized using the MMX (33) force field, which has been shown to be appropriate for related piano-stool molecules (34,35). GMMX searches of conformational space used a combined Monte Carlo internal -Cartesian randomization protocol that examined rotations about all specified bonds with less than 3-fold symmetry.…”