104911-77-5Relevant academic research and scientific papers
Reversible intramolecular isomerization associated with the electron-transfer reactions of mixed-carbonyl-isocyanide-phosphine complexes of molybdenum of the type [Mo(CO)2(CNR)2(PR′3)2] +/0
Conner, Kay A.,Walton, Richard A.
, p. 4422 - 4430 (2008/10/08)
Neutral species of the type Mo(CO)2(CNR)2(PR′3)2 (R = methyl, isopropyl, tert-butyl, cyclohexyl, p-tolyl, xylyl, mesityl, 2,4,6-tri-tert-butylphenyl; PR′3 = PEt3, P-n-Pr3, PEt2Ph, PMePh2, PPh3) have been synthesized and found to exist as a single isomer with a trans disposition of phosphine ligands and cis arrangements of the pairs of CO and RNC groups in the case of R = alkyl and PR′3 = any phosphine except (in some instances) PPh3. For the analogous aryl isocyanide complexes, spectroscopic evidence (IR and 1H and 31P{1H} NMR) suggests that a mixture of isomers is present. In all instances (i.e., R = alkyl and aryl) electrochemical and chemical oxidations afford the paramagnetic 17-electron all-trans cations [Mo(CO)2(CNR)2(PR′3)2] +, which have been isolated as their PF6- salts in a few cases. The monocations have been characterized by IR and X-band ESR spectroscopies. Rereduction of these cations results in a very rapid reisomerization to the isomer or equilibrium mixture of isomers that are present in the parent neutral complexes, except in the cases of Mo(CO)2(CNXylyl)2(PEt2Ph)2, Mo(CO)2(CN(t-Bu3Ph))2(PMePh2) 2, and Mo(CO)2(CN(t-Bu3Ph))2(P-n-Pr3) 2. For these three complexes rereduction affords solutions of the neutral all-trans isomers, which can be characterized spectroscopically before they slowly reisomerize to the mixtures of isomers that contain cis CO groups. From cyclic voltammetric measurements on solutions of these complexes in 0.1 M n-Bu4NPF6/CH2Cl2, the equilibrium constants for the redox cross-reactions trans0 + cis+ ? trans+ + cis0 show that these equilibria lie far to the right; this is attributable to the high thermodynamic stability of the trans+ and cis0 species. The homogeneous chemical rate constants for the cis-trans isomerizations of Mo(CO)2(CNR)2(PR′3)2 have been evaluated. For the processes (Chemical Equation Presented) it is clear that k1 > k2. The intramolecular isomerizations can be interpreted in terms of sequential trigonal twists.
