Catalytic Production of Isocyanates via Orthogonal Atom and Group Transfers Employing a Shared Formal Group 6 M(II)/M(IV) Redox Cycle

Under
an atmosphere of CO, the Mo­(IV) imido complex Cp*Mo­[N­(iPr)­C­(Me)­N­(iPr)]­(NSiMe3) (Cp* = η5-C5Me5) (1) serves as a
catalyst for production of an isocyanate via metal-mediated nitrene
group transfer in benzene solution under mild conditions (55 °C,
10 psi) according to RN3 + CO → N2 +
RNCO. Mechanistic and structural studies support a catalytic cycle
for nitrene group transfer involving formal Mo­(II) monocarbonyl and
Mo­(IV) (κ2-C,N)-isocyanate intermediates.
These results complement an earlier finding that catalytic production
of isocyanates can alternatively proceed through oxygen-atom transfer
and an isomeric Mo­(IV) (κ2-C,O)-isocyanate
according to N2O + CNR → N2 + RNCO.

在一氧化碳(CO)气氛下，钼(IV)亚胺基配合物Cp*Mo[N(iPr)C(Me)N(iPr)](NSiMe3)（其中五甲基环戊二烯基(Cp*, η5-C5Me5)，编号为1）可作为催化剂，在温和条件（55℃、10 psi）下的苯溶液中，通过金属介导的氮宾基团转移反应催化异氰酸酯的生成，反应式为RN3 + CO → N2 + RNCO。机理与结构研究证实，该氮宾基团转移催化循环包含形式上的钼(II)单羰基配合物与钼(IV)(κ2-C,N)-异氰酸酯中间体。本研究结果与此前一项发现互为补充：异氰酸酯的催化生成也可通过氧原子转移途径进行，经由异构化的钼(IV)(κ2-C,O)-异氰酸酯中间体，对应反应式为N2O + CNR → N2 + RNCO。