35039-06-6Relevant academic research and scientific papers
KINETICS AND MECHANISM OF DIENE EXCHANGE AT SIX-CO-ORDINATE CHROMIUM
Dixon, Denis T.,Burkinshaw, Philip M.,Howell, James A. S.
, p. 2237 - 2240 (1980)
The results of kinetic studies on the ligand-exchange and substitution reactions of (buta-1,3-diene)tetracarbonyl-chromium and tetracarbonyl(trans,trans-hexa-2,4-diene)chromium with cyclo-octa-1,5-diene (cod), norbornadiene (nbd), and P(OR')3 (R'=Me or Ph) to yield , , and are consistent with a mechanism involving a stepwise displacement of the diene ligand, which is SN1 in nature for the diene exchange but contains a ligand-dependent SN2 component in the case of substitution by phosphite.
Phosphorus chemical shift anisotropies in solid triphenyl phosphite and mer,trans-bis(triphenyl phosphite)tricarbonyl(thiocarbonyl)chromium(0), Cr(CO)3(CS)[P(OPh)3]2
Huang, Yining,Uhm, Haewon L.,Gilson, Denis F. R.,Butler, Ian S.
, p. 804 - 807 (2008/10/08)
The 31P chemical shift anisotropies have been measured for solid triphenyl phosphite, P(OPh)3 (at 128 K), and the complex with the tricarbonyl(thiocarbonyl)chromium(0) moiety, mer,trans-Cr(CO)3(CS) [P(OPh)3]2 (at 298 K). The shift tensor is axially symmetric in the phosphite ligand, and the major change upon complexation occurs for the components of the shift tensor perpendicular to the bond direction. The crystal structure of the chromium complex has been determined by single-crystal X-ray diffraction at 293 K. The complex crystallizes in the centric P21/n (No. 14) space group with cell constants (at 20°C) a = 8.166(3) A?, b = 11.530(2) A?, c = 20.183(2) A?, β = 96.43(1)°, and Z = 2. The molecule is disordered on a crystallographically imposed inversion center so that the thiocarbonyl ligand is superimposed on the trans carbonyl ligand (50:50).
Influence of atomic size on mechanism: Displacement of chelating ligands coordinating through sulfur from their chromium and molybdenum carbonyl complexes
Awad, Hani H.,Dobson, Charles B.,Dobson, Gerard R.,Leipoldt, Johann G.,Schneider, Karen,Van Eldik, Rudi,Wood, Helen Elizabeth
, p. 1654 - 1657 (2008/10/08)
Variable-pressure kinetics studies (to 150 MPa) at various temperatures for chelate ring displacement from cis-(S2)M(CO)4 complexes (S2 = dithiaalkane, dithiaalkene (2,5-dithiahexane, 3,6-dithiaoctane, and cis-2,2,7,7-tetramethyl-3,6-dithiaoct-4-ene); M = Cr, Mo) by L (=Lewis base (P(OR)3, R = Me, Et, i-Pr, Ph)) in chlorobenzene (CB) and 1,2-dichloroethane (DCE) have been carried out. All reactions obey the rate law -d[(S2)M(CO)4]/dt = k[(S2)M(CO)4][L]. However, calculated volumes of activation (ΔV≠) and thermal activation parameters (ΔH≠, ΔS≠) indicate that ligand displacement in the Cr complexes takes place via initial, reversible Cr-S bond fission, while for Mo and S2 = 2,5-dithiahexane and 3,6-dithiaoctane an associative pathway involving significant initial L-Mo bond making is operative. For S2 = cis-2,2,7,7-tetramethyl-3,6-dkhiaoct-4-ene and M = Mo, activation parameters (the thermal data were taken over a 70°C temperature range) are equivocal as to whether the mechanism is best described as an interchange process or in terms of competing dissociative and associative pathways. It is concluded that the mechanistic differences observed in the Cr and Mo systems result from the differing atomic sizes of these metals. The results are also discussed in terms of the properties of the chelating rings.
Redox reactions of chromium tetracarbonyl and tricarbonyl complexes: Thermodynamic, kinetic, and catalytic aspects of isomerization in the fac/mer-tricarbonyltris(trimethyl phosphite)chromium(1+/0) system
Bond,Colton,Kevekordes
, p. 749 - 756 (2008/10/08)
Electrochemical studies have been undertaken on mixtures of cis- and trans-[Cr(CO)4P2]+/0 systems (where P = P(m-tol)3, P(p-tol)3, P(OMe)3, P(OEt)3, P(OPh)3). In accordance with theoretical predictions, redox potentials for both cis- and trans-[Cr(CO)4P2]+/0 are similar and oxidation involves the formation of trans-[Cr(CO)4P2]+ via either direct electron transfer or cis-[Cr(CO)4P2]+ to trans-[Cr(CO)4P2]+ isomerization after electron transfer. The trans-[Cr(CO)4P2]+ species have all been identified by infrared spectroscopy. trans-[Cr(CO)4(P(OPh)3)2]+ is a very strong oxidant and can be used to oxidize all the other [Cr(CO)4P2] complexes: trans-[Cr(CO)4(P(OPh)3)2]+ + cis/trans-[Cr(CO)4P2] → cis/trans-[Cr(CO)4(P(OPh)3)2] + trans-[Cr(CO)4P2]+. Tricarbonyltris(phosphorus ligand)chromium complexes, Cr(CO)3P3, can exist in fac or mer isomeric forms. In contrast to those of the tetracarbonyl complexes, the oxidation potentials of the fac and mer isomers of the tricarbonyls occur at considerably different potentials, enabling detailed electrochemical studies to be made. In this work it is shown that isomerization of fac-[Cr(CO)3(P(OMe)3)3] → mer-[Cr(CO)3(P(OMe)3)3] occurs either slowly by an intramolecular twist mechanism or via art alternative redox-catalyzed pathway. Variable-temperature electrochemical studies at platinum electrodes (cyclic voltammetry and differential-pulse voltammetry at a stationary electrode, rotating-disk voltammetry, and controlled-potential electrolysis) of the redox properties of both fac- and mer-[Cr(CO)3(P(OMe)3)3] provide a complete thermodynamic and kinetic description of the catalytic scheme, which involves the following reactions: fac-[Cr(CO)3(P(OMe)3)3] →oxidant fac-[Cr(CO)3(P(OMe)3)3]+ (i) where oxidant = e-, NOPF6, or trans-[Cr(CO)4(P(OPh)3)2]+ fac-[Cr(CO)3(P(OMe)3)3]+ ? mer-[Cr(CO)3(P(OMe)3)3]+ (ii) mer-[Cr(CO)3(P(OMe)3)3]+ + fac-[Cr(CO)3(P(OMe)3)3] →fast fac-[Cr(CO)3(P(OMe)3)3]+ + mer-[Cr(CO)3(P(OMe)3)3] (iii) where fac/mer-[Cr(CO)3(P(OMe)3)3]+ is the catalyst. Data at 22°C in dichloromethane: fac-[Cr(CO)3(P(OMe)3)3] ?k-1k1 mer-[Cr(CO)3(P(OMe)3)3] k1 = (1.8 ± 0.3) × 10-4 s-1 k-1 = (4.5 ± 1.3) × 10-5 s-1 K1 = 4 ± 0.5 fac-[Cr(CO)3(P(OMe)3)3]+ →k-2k2 mer-[Cr(CO)3(P(OMe)3)3]+ k2 = 0.11 ± 0.01 k-2 = (1.7 ± 0.8) × 10-4 s-1 K2 = 640 ± 130 The activation parameters for fac-[Cr(CO)3(P(OMe)3)3]+ ? mer-[Cr(CO)3(P(OMe)3)3]+ are consistent with those expected for an intramolecular twist mechanism (EA = 15.9 ± 0.7 kJ/mol; ΔS* = -17.0 ± 1.0 J/(K mol)). The equilibrium constant, K3, for the redox cross-reaction fac-[Cr(CO)3(P(OMe)3)3]+ + mer-[Cr(CO)3(P(OMe)3)3] ?K3 fac-[Cr(CO)3(P(OMe)3)3] + mer-[Cr(CO)3(P(OMe)3)3]+ has a value of 160 ± 13. The electrochemical properties of fac/mer-[Cr(CO)3(P(OEt)3)3] are similar.
The Mechanism of Displacement of Diene from 4-diene)(CO)4> (M = Cr, Mo, or W, diene = norbornadiene; M = Mo, diene = cyclo-octa-1,5-diene) and the cis trans Isomerization of Complexes
Dixon, Denis T.,Kola, John C.,Howell, James A. S.
, p. 1307 - 1316 (2007/10/02)
Kinetic studies are reported of the displacement of the diene from 4-diene)(CO)4> by phosphorus ligands to give complexes .With the exception of , all reactions exhibit a bimolecular rate law of the type -d>/dt = Kobs.>, where A = which is interpreted mechanistically as a stepwise ligand-assisted dechelation of the diene; Kobs. may be seen to increase in the order Cr reflects the increasing order of ligand nucleophilicity. cis-trans Isomerization of (L = PBu3, P(OMe)3, or P(OPh)3; M = Cr, Mo, or W) has also been studied kinetically.With the exception of 2>, all isomerizations are intramolecular.Rates of isomerization increase in the order Mo eq (=/) increases in the order W ca.Mo Cr and in the order P(OPh)3 P(OMe)3 PBu3.These results are interpreted in terms of both steric and electronic factors.
Octahedral metal carbonyls: Reactions and bonding. VII. Kinetics of the substitution reactions of 2,5-dithiahexane complexes of chromium hexacarbonyl and molybdenum hexacarbonyl
Faber, Gary C.,Dobson, Gerard R.
, p. 584 - 588 (2008/10/08)
The complexes (DTH)Cr(CO)4 and (DTH)Mo(CO)4 (DTH = 2,5-dithiahexane) react with phosphites with the replacement of the bidentate ligand to yield cis- and trans-(phosphite)2M(CO)4 complexes according to a second-order rate law. Activation parameters and previous results suggest, however, that the reactions of the two complexes occur substantially through different mechanisms, the Cr reaction proceeding through a preequilibrium step involving the dissociation of one end of the bidentate ligand followed by attack on the resulting five-coordinate species, with the Mo reaction proceeding through the formation of a seven-coordinate intermediate. Reaction rates vary according to the steric nature of the various phosphite ligands employed; the results obtained are computed to those previously obtained for similar systems and are discussed in terms of σ- and π-bonding properties of the bidentate ligands.
