Steric effects associated with monosubstituted cyclopentadienyl transition-metal complexes. Synthesis and NMR spectroscopic and molecular mechanics study of [(.eta.5-C5H4Bu-tert)Fe(CO)(L)I] complexes and crystal structure determination of [(.eta.5-C5H4Bu-tert)Fe(CO)(PPh3)I]

Steric measurement of substituted cyclopentadiene ligands and the synthesis and proton NMR spectral analysis of [(.eta.5-C5H4R)Fe(CO)(L)I] complexes with variable R

“…VTNMR studies have, consequently, led to the measurement of ring rotational barriers through this interaction. 3,4,41,42 However, no systematic attempt to quantify the role of the steric effect on physical parameters associated with the complex type has been reported to date. for [(i?5-CsH4R)Fe(CO)(L)I] complexes.…”

“…However, no quantitative measure of the substituent size relative to the ring centroid as the apex (Figure lb) has been reported, although we did propose, earlier, that this would be a viable measure of the ligand size. 4 Herein, we report on the measurement of the size of a range of substituted cyclopentadienyl ligands using both the above methods.…”

Iron‐Mediated Coupling of Two Ethyl Anions to Form a 2‐Butyne Ligand

“…The iron–ring plane distance of 1.93 Å classifies 5 as another high‐spin cyclopentadienyliron(II) complex. The iron–iodine distances of 2.68 and 2.76 Å are longer than the Fe–I distances of 2.59 Å for the iodo bridge in the low‐spin Fe II complex [{CpFe(CO) 2 } 2 I][BF 4 ]23 or the value of 2.62 Å for the terminal iodo complex [( t BuC 5 H 4 )FeI(CO)(PPh 3 )] 24. Only slightly shorter is the iron–iodine distance of 2.67 Å for the trinuclear cluster [MeC(CH 2 NPh‐ o ‐NPh) 3 Fe 3 I(thf)], in which the high‐spin central Fe II atom has an approximately trigonal‐bipyramidal coordination geometry with a terminal iodo ligand 25.…”

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.…”