MOLYBDENUM-MEDIATED IMIDO GROUP TRANSFER - STOICHIOMETRIC AND CATALYTIC REACTIONS AND STRUCTURES

The isoelectronic relationship O2- = RN2- implies imido group transfer chemistry related to oxygen atom transfer reactivity, which is extensive for certain elements. This matter has been subjected to its first systematic examination, using the (V,A-diethyldithiocarbamate (Et2dtc)2complexes of molybdenum and the (V-tosylimido (NTs) group. The imido group transfer reactions to Mo, MoO(Et2dtc)2+ XNR and Mo(CO)2(Et2dtc)2+ XNR, afford MoO(NTs)(Et2dtc)2and Mo-(NTs)2(Et2dtc)2, respectively, in high yield with the imido group transfer reagents XNR = C5H5NNTs, PhMeSNTs, Ph3SbNTs, PhINTs, and TsN3. MoO(NTs)(Et2dtc)2-1/2PhMe crystallizes in triclinic space group P1 with a = 9.212 (2) Å, b- 12.080 (4) Å, c - 14.310 (4) Å, α = 115.02 (2)°, β = 95.51 (2)°, γ = 100.34 (2)°, and Z = 2; the structure was refined to R = 4.8%. Mo(NTs)2(Et2dtc)2was obtained in monoclinic space group P21/n with a = 10.632 (2) Å, b = 16.307 (3) Å, c = 19.023 (5) Å, β = 101.29 (2)°, and Z = 4; the structure was refined to R = 4.0%. The two compounds have a distorted octahedral structure with the multiply bonded groups O and NTs in cis positions. Comparison of these structures with that of MoO2(Et2dtc)2reveals that the NTs group is a nearly isostructural replacement for oxo. The imido group transfer reactions from Mo, MoO(NTs)(Et2dtc)2+ R3P, proceed but with the more basic phosphines favoring imido (R3PNTs) rather than oxo (R3PO) transfer. Imido transfers to and from Mo involve the purple intermediates Mo2O2(NTs)(Et2dtc)4and MoO(NTs)2(Et2dtc)4, respectively, which are in presumed equilibrium with Mo(IV,VI) complexes. The complex Mo(NTs)(Et2dtc)2, resulting from imido group transfer, was too unstable to be isolated. Group transfers to and from Mo were coupled to form the catalytic reactions XNTs + R3P → X + R3PNTs, which did not proceed at a measurable rate in the absence of Mo(NTs)2(Et2dtc)2. The system based on PhMeSNTs + Ph2MeP showed 28 turnovers in 7.5 h in chloroform at 35 °C. The reaction PhMeSNTs + 2PhSH → PhSMe + PhSSPh + TsNH2, in which benzenethiol acts as an electron donor, was also catalyzed by Mo-(NTs)2(Et2dtc)2. All known imidometal groups are tabulated, and oxo and imido group transfer reactions of Mo are schematically summarized. © 1990, American Chemical Society. All rights reserved.