15711-66-7Relevant academic research and scientific papers
What is the real steric impact of triphenylphosphite? Solid-state and solution structural studies of cis- and trans-isomers of M(CO) 4[P(OPh)3]2 (M = Mo and W)
Darensbourg, Donald J.,Andreatta, Jeremy R.,Stranahan, Sarah M.,Reibenspies, Joseph H.
, p. 6832 - 6838 (2007)
The steric requirements for the triphenylphosphite ligand in several molybdenum and tungsten carbonyl derivatives have been shown by X-ray crystallography to exceed the original Tolman's cone angle of 128°. That is, due to various accessible conformers possible for P(OPh)3, solid-state data predict a considerably larger cone angle for the ligand of between 140° and 160°. Importantly, the solution behavior of cis-M(CO)4[P(OPh)3]2 (M = Mo or W), coupled with similarly reported observations on a series of cis-Mo(CO) 4[PR3]2 derivatives, support this conclusion, for these molecules both undergo thermal rearrangement to the more stable trans-isomers. On the other hand, the electronically similar but sterically much smaller cis-Mo(CO)4[P(OCH2)3CEt]2 complex is thermally stable under much harsher conditions. Furthermore, a comprehensive survey of structural data for transition-metal-triphenylphosphite derivatives available in the Cambridge Crystallographic Database reveals that most molecules display conformations that dictate cone angles much greater than that originally suggested by Tolman.
Mechanism of the Low-Energy Photochemical Disproportionation Reactions of (η5-C5H5)2Mo2(CO)6
Stiegman, Albert E.,Stieglitz, Marc,Tyler, David R.
, p. 6032 - 6037 (2007/10/02)
The photochemical disproportionation reactions of the (RCp)2Mo2(CO)6 (R = H or CH3; Cp = η5-C5H4) complexes were investigated.The general disproportionation reaction can be written (RCp)2Mo2(CO)6 + 2L (RCp)Mo(CO)3- + (RCp)Mo(CO)2L2+ + CO.Control experiments showed that the previously reported analogous thermal disproportionation reactions are actually photochemical reactions.The properties of the ligand L are important in determining whether or nor the (RCp)2Mo2(CO)6 complex will disproportionate; the ligands cannot be sterically bulky and they must be good electron-donating ligands if disproportionation is to occur.If either of these criteria is not met, the irradiation of the (RCp)2Mo2CO)6 complex in the presence of the ligand leads only to substitution products of the type (RCp)2Mo2(CO)5L and/or (RCp)2Mo2(CO)4L2.The disproportionation reaction is wavelength dependent.For example, PPh3 will disproportionate the (RCp)2Mo2(CO)6 complex upon 290-nm irradiation but not upon 405-nm irradiation.Smaller ligands will disproportionate the dimer with 405-nm irradiation.The mechanism of lower energy pathway was investigated in detail, and it is proposed to be a radical chain pathway: (1) (RCp)2Mo2(CO)6->2(RCp)Mo(CO)3, (2) (RCp)Mo(CO)3+L->(RCp)Mo(CO)2L+CO, (3) (RCp)Mo(CO)2L+L->(RCp)Mo(CO)2L2, (4) (RCp)Mo(CO)2L2+(RCp)2Mo2(CO)6->(RCp)Mo(CO)2L2++(RCp)2Mo2(CO)6-, (5) (RCp)2Mo2(CO)6-->(RCp)2Mo2(CO)3-+(RCp)Mo(CO)3.The quantum yield data support this chain pathway; the quantum yields are greater than 1 and they are not reproducible from trial to trial.The key intermediate (CH3Cp)2Mo2(CO)6- was generated by reacting (CH3Cp)2Mo2(CO)6 with Na; in the presence of appropriate L the disproportionation resulted.The key to the mechanism is the formation of the 19-electron intermediate (RCp)Mo(CO)2L2.Electron transfer from this electron rich species is the driving force for the reaction.Evidence is presented for the formation of this intermediate.
Transition-metal Chemical Shifts in Complexes of Molybdenum(0) and Tungsten(0)
Andrews, Geoffrey T.,Colquhoun, Ian J.,McFarlane, William,Grim, Samuel O.
, p. 2353 - 2358 (2007/10/02)
Molybdenum-95 and tungsten-183 n.m.r. spectra have been measured by direct observation and by multiple-resonance methods respectively for 65 related derivatives of and with (mainly) phosphorus ligands.The chemical shifts of the two nuclei are remarkably parallel, those for (183)W being ca. 1.7 times more sensitive to changes in chemical environment than those for (95)Mo.The chemical shifts are temperature-dependent, and trends in them can be largely accounted for by variations in the mean electronic excitation energy.The metal-phosphorus spin-coupling constants are very predictable.Molybdenum-95 linewidths in many cases are quite small, and can be broadly explained by the use of a point-charge model.
