Abstract:The [CpM(PH3)H(C2H4)]+, (M = Rh, Co), complexes have been investigated with electronic structure and
quantum dynamical methods. Stationary points, including transition states, have been found and characterized
with various methods and basis sets. The global minimum of the Rh complex is the ethylene structure, but
for the Co complex, it is the agostic structure, in agreement with experiment. A one-dimensional reaction-path profile was calculated and used for a wave packet propagation. The time-dependent wave fu… Show more
“…Our calculations even indicate a slightly higher energy (1.0 kcal mol -1 ) for this agostic intermediate. This is in marked contrast to related systems, where the agostic intermediate was always found at an energy much lower than that of the corresponding ethyl complex (without the β-agostic interaction). , The barrier between the agostic intermediate and the ethyl structure is also very low (0.40 kcal mol -1 ). 5 Energies Δ E of the stationary points (B3LYP/SDD) relative to structure 1D .…”
Section: Resultscontrasting
confidence: 62%
“…We used a standard DFT method (B3LYP) 40 with the Stuttgart−Dresden basis set (SDD) . This method/basis set combination has proven reliable by high-accuracy CCSD(T) calculations on related transition-metal complexes . The nature of the minima and transition states has been verified by frequency calculations (giving zero and one imaginary frequency, respectively).…”
The kinetics and energetics of -migratory insertion in the electron-rich cobalt ethylene hydride complex [(PMe 3 ) 3 Co(H)(C 2 H 4 )] (1) were studied with experimental and theoretical techniques. The activation parameters were established in toluene solution using 1 H magnetization transfer methods. Data obtained over the temperature range 265-290 K gave ∆H q ) 16.4 ( 0.6 kcal mol -1 and ∆S q ) 8 ( 2 cal mol -1 K -1 . The structural and energetic parameters have also been determined by DFT electronic structure calculations. The global minimum thus obtained is in agreement with the experimental findings. The same holds true for the activation energies for migratory insertion as well as for -elimination. Comparison of the activation parameters with those for other complexes suggests an increase of the barrier of migratory insertion with increasing electron richness of the metal center, which destabilizes species with agostic metal-H-C interactions. It is proposed that there may even be cases where an agostic structure is not an intermediate.
“…Our calculations even indicate a slightly higher energy (1.0 kcal mol -1 ) for this agostic intermediate. This is in marked contrast to related systems, where the agostic intermediate was always found at an energy much lower than that of the corresponding ethyl complex (without the β-agostic interaction). , The barrier between the agostic intermediate and the ethyl structure is also very low (0.40 kcal mol -1 ). 5 Energies Δ E of the stationary points (B3LYP/SDD) relative to structure 1D .…”
Section: Resultscontrasting
confidence: 62%
“…We used a standard DFT method (B3LYP) 40 with the Stuttgart−Dresden basis set (SDD) . This method/basis set combination has proven reliable by high-accuracy CCSD(T) calculations on related transition-metal complexes . The nature of the minima and transition states has been verified by frequency calculations (giving zero and one imaginary frequency, respectively).…”
The kinetics and energetics of -migratory insertion in the electron-rich cobalt ethylene hydride complex [(PMe 3 ) 3 Co(H)(C 2 H 4 )] (1) were studied with experimental and theoretical techniques. The activation parameters were established in toluene solution using 1 H magnetization transfer methods. Data obtained over the temperature range 265-290 K gave ∆H q ) 16.4 ( 0.6 kcal mol -1 and ∆S q ) 8 ( 2 cal mol -1 K -1 . The structural and energetic parameters have also been determined by DFT electronic structure calculations. The global minimum thus obtained is in agreement with the experimental findings. The same holds true for the activation energies for migratory insertion as well as for -elimination. Comparison of the activation parameters with those for other complexes suggests an increase of the barrier of migratory insertion with increasing electron richness of the metal center, which destabilizes species with agostic metal-H-C interactions. It is proposed that there may even be cases where an agostic structure is not an intermediate.
“…This energy barrier is quite low but lies within the range reported for related first-row transition metal complexes. For example, Δ E ⧧ was calculated to be 82 kJ mol –1 for [(PMe 3 ) 3 CoH(C 2 H 4 )] and less than 2 kJ mol –1 for [CpCoH(C 2 H 4 )(PMe 3 )] + . , …”
Section: Resultssupporting
confidence: 73%
“…However, no such energy minimum could be located; the energy of such a species was estimated by restraining the Mn–C α –C β angle to 109.5°, yielding a structure ( B 109.5 ) 49 kJ mol –1 higher in energy than B β‑agostic . This energy difference is consistent with the typical strength of a first-row transition metal β-agostic interaction. , However, it differs significantly from that calculated for the ethyl isomer of [(PMe 3 ) 3 CoH(C 2 H 4 )], where the nonagostic structure was reported to be 4 kJ mol –1 lower in energy than the β-agostic isomer.…”
Wilkinson’s
manganese(I) ethylene hydride complex trans-[(dmpe)2MnH(C2H4)]
(1) reacts as a source of a low-coordinate manganese(I)
ethyl complex. This is illustrated in the reactivity of 1 toward a variety of reagents. Reactions of 1 with primary
silanes RSiH3 (R = Ph,
n
Bu)
at 60 °C afforded ethane and the disilyl hydride manganese complexes
[(dmpe)2MnH(SiH2R)2] (4a, R = Ph; 4b, R =
n
Bu).
Additionally, reaction with H2 at 60 °C afforded ethane
and the dihydrogen hydride complex [(dmpe)2MnH(H2)] (5), which has previously been prepared by an alternate
route. The proposed low-coordinate intermediate, [(dmpe)2MnEt], was not observed spectroscopically but could be trapped using
isonitrile ligands; reaction of 1 with CNR (R =
t
Bu, o-xylyl) afforded the
manganese(I) ethyl complexes [(dmpe)2MnEt(CNR)] (6a, R =
t
Bu; 6b,
R = o-xylyl). Ethyl complex 6a did not
react further with CN
t
Bu at 80 °C.
In contrast, complex 6b reacted with excess o-xylyl isonitrile to form 1,1-insertion products, including the iminoacyl
complex [(dmpe)Mn(CNXyl)3{C(NXyl)CEt(NXyl)}]
(7, Xyl = o-xylyl). Complexes 4a, 6a,b, and 7, as
well as the previously reported 1 and 5,
have been crystallographically characterized, and DFT calculations
have been employed to probe the accessibility of cis ethylene hydride and ethyl isomers of 1.
The dynamics of migratory insertion and beta-hydrogen elimination in the cationic complex [CpRh(PH3)H(C2H4)]+ is studied from a quantal point of view. On the basis of DFT results for the relevant stationary points of the potential energy surface, three coordinates are identified that vary strongly during the reaction. A suitable three-dimensional grid, along with an appropriate kinetic energy operator, are constructed that are employed in the subsequent wave packet propagations. The latter are performed in the spirit of transition state spectroscopy and start from the various saddle points of the potential energy surface. Vibrational periods and lifetimes for these elementary processes, relevant to homogeneous catalysis, are obtained in this way for the first time. This work is considered to provide the basis for a subsequent treatment of equilibrium rate constants and to shed new light on the electronic factors governing these prototypical reaction steps.
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