The complex [ MoH,(dppe),] (1 ) (dppe = Ph,PCH,CH,PPh,) reacted with ally1 carboxylates RCO,CH,CH=CH, (R = H, Me, Et, Pr", But, CH,=CMe, or Ph) in benzene upon irradiation with a high-pressure mercury lamp to give [MoH(O,CR) (dppe),] (2), together with propene and H, .Reaction pathways comprising the oxidative addition of the ally1 carboxylates involving allyloxygen bond cleavage are proposed on the basis of the results obtained with substituted allylic esters. The complexes (2) were characterized spectroscopically as having pentagonal-bipyramidal structures in solution. The similar reaction of complex (1 ) with ally1 formate led t o selective cleavage of the formic C-H bond to give ultimately the known cis-[Mo(CO),(dppe),] via (2; R = H).
A theoretical study of the photosubstitution reactions of d6 metal carbonyls M(C0)5L, characterized by a high degree of cis stereospecificity, is reported. The possible excitedstate isomerization pathways of the five-coordinate species M(C0)4L (square pyramid (SP), with L basal or apical, trigonal bipyramid regular (TBP) or distorted (d-TBP)) have been considered on the basis of CASSCFICASPTB calculations of the relative stabilities of the different structures of Mn(C0)4Cl in the lowest excited states (singlet or triplet). The basis set effect on the relative stabilities of the various structures of Tc(C0)4C1 and Mo (C0)4NH3 have been ascertained a t the SCF level with double-g-quality basis sets. The results obtained for Mn(CO)&l have been used to generate a state correlation diagram that connects the ground state and lowest excited states of the reactant Mn(C0)&1 with those of the fivecoordinate species with different structures. On the basis of this diagram, we propose the following mechanism. (i) Excitation of Mn(C0)&1 occurs into the lE ligand field state followed by elimination of a carbonyl ligand with formation of Mn(C0)&1 either as a n SP apical in the lE state (axial elimination) or as a n SP basal in the lA' state (equatorial elimination). (ii) Through a Berry pseudorotation, followed by a lB2 -lA1 internal conversion, the SP structures evolve either to the AI ground state of the regular TBP or to the d-TBP in the ' A1 state. (iii) The molecule gets trapped in the potential well corresponding to the ' A1 ground state of the d-TBP (after a downhill rearrangement in the case of the regular TBP), until it reacts with a n incident nucleophile, leading to the cis derivatives.
Electronic spectra of RMn(CO)sub3(alpha-diimine) (R=H,CHsub3): a CASSCF/CCI comparative study of the lowest singlet excited states Daniel, C.; Matsubara, T.; Stor, G.J.
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