Conformational analysis for the ligands CH2OR (R = Me, CH2Ph, and menthyl) and CH2SR (R = Me, Et, CH2Ph, and Ph) attached to the iron chiral auxiliary [(C5H5)Fe(CO)(PPh3)]

Isolation and Ring-Opening of New 1-Sila-3-metallacyclobutanes (η5-C5H4Fe)(CO)2CH2SiR2 Leading to A New Class of Organometallic Polymer

“…These latter complexes exhibit significant ring strain and a rich vein of ring-opened polymerization chemistry. , The ring Si−C bond distances of 5 , 1.840(3) and 1.874(3) Å, are in the range for such silacyclobutanes, while the C−Si−C angle of 94° is relatively small for such angles, and the C−Fe−C angle of 80° illustrates a degree of ring strain for this new structural arrangement. Further evidence for a level of ring strain is the Cp(centroid)−Fe−CH 2 angle of 115.6° in 5 , which is smaller than literature values for related (η 5 -C 5 H 5 )Fe(CO)(PPh 3 )CH 2 R systems (R = CH 3 , 118.7°;15a R = CH 2 OCH 3 , 120.4;15b R = CH 2 SCH 2 Ph, 121.6) 15b…”

Ir(2-Phenylpyridine)2(benzene-1,2-dithiolate) Anion as a Diastereoselective Metalloligand and Nucleophile: Stereoelectronic Effect, Spectroscopy, and Computational Study of the Methylated and Aurated Complexes and their Oxygenation Products

“…The diastereoselectivity observed is a kinetic discrimination arising from a combination of the steric effect of the ppy ligands and the orientation and nature of the HOMO, which is therefore a stereoelectronic effect. Stereoelectronic effects are common in organic reactions, but to date, fewer than 10 examples have been demonstrated in inorganic or organometallic reactions . Our result shows that filled dπ–pπ interactions in a trisbidentate dithiolate complex give rise to a HOMO that has its si or re face sterically hindered by the two auxiliary ligands.…”

Variable-Temperature NMR Determination of the Barriers to Rotation about the Ir−C σ-Bond in a Series of Primary Perfluoroalkyl Iridium Complexes [IrCp*{(CF2)nCF3}(PMe3)2]+X- [n = 1, 2, 3, 5, 7, 9, 11; X = I, OTf]

“…Many chemical reactions have a stereochemical requirement such that reaction cannot proceed directly from the ground state conformation, and the activation energy to achieve the required bond rotation must be part of the overall barrier for the chemical transformation . While conformational analysis and measurement of rotational barriers have been used mainly for C−C bonds, analogous studies of a variety of compounds containing transition metal−carbon σ-bonds have also proven useful in predicting ground state conformations, reactivity patterns, and reaction stereoselectivities. − While early vibrational spectroscopic studies were used to estimate the barrier to rotation of ∼3 kcal/mol for the Mn−C bond in CH 3 −Mn(CO) 5 , the most common techniques have been those of NMR spectroscopy. 13 C relaxation studies were used to define barriers for M−CH 3 rotation in a number of compounds, with sterically uncrowded CH 3 −Re(CO) 5 , CH 3 −Au(PPh 3 ), and (CH 3 ) 2 Os(CO) 4 having negligibly small barriers and more crowded systems like CpFe(CO) 2 (CH 3 ), CpMo(CO) 3 (CH 3 ), and Cp 2 Zr(CH 3 ) 2 having barriers of >6 kcal/mol …”

“…Rotational barriers for M−C bonds in fluoroalkyl complexes have been less easily achieved. Estimates of rotational barriers (between 5 and 10 kcal/mol) and conformational preferences in compounds of the type CpCo(L)(I)(R F ) and CpFe(L)(CO)(R F ) have been published. , These estimates were made on the basis of temperature dependence of chemical shift and coupling constant data and, as with analogous studies of corresponding alkyl analogues, have been subject to criticism, particularly in their predictions of conformational preferences. − …”

“…As with previously studied compounds CpCo(L)(I)(R F ) and CpFe(L)(CO)(R F ) (vide supra), , the presence of a stereocenter in compounds of type 1 means the α-CF 2 fluorines are diastereotopic in all conformations . Consequently, unless site exchange can be observed between two or more conformational populations, M−C bond rotation cannot unambiguously be defined as having a high or low energy barrier, and attempts to define it using temperature dependence of δ or J values 9,10 may be subject to other interpretations. − In most cases only a single conformer is populated to any observable extent so there is no chemical site exchange resulting from any rotation about the M−C bond, and no rotation barrier can be estimated using typical NMR coalescence methods.

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