Cationic and Neutral Cp*M(NO)(κ2‑Ph2PCH2CH2PPh2) Complexes of Molybdenum and Tungsten: Lewis-Acid-Induced Intramolecular C–H Activation
Version 2 2017-03-02, 20:33
Version 1 2017-03-02, 17:12
journal contribution
posted on 2017-03-02, 00:00 authored by Rex C. Handford, Russell J. Wakeham, Brian O. Patrick, Peter LegzdinsTreatment
of CH2Cl2 solutions of Cp*M(NO)Cl2 (Cp* = η5-C5(CH3)5; M = Mo, W) first with 2 equiv of AgSbF6 in the presence
of PhCN and then with 1 equiv of Ph2PCH2CH2PPh2 affords the yellow–orange salts [Cp*M(NO)(PhCN)(κ2-Ph2PCH2CH2PPh2)](SbF6)2 in good yields (M = Mo, W).
Reduction of [Cp*M(NO)(PhCN)(κ2-Ph2PCH2CH2PPh2)](SbF6)2 with 2 equiv of Cp2Co in C6H6 at 80 °C produces the corresponding 18e neutral
compounds, Cp*M(NO)(κ2-Ph2PCH2CH2PPh2) which have been isolated as
analytically pure orange–red solids. The addition of 1 equiv
of the Lewis acid, Sc(OTf)3, to solutions of Cp*M(NO)(κ2-Ph2PCH2CH2PPh2) at room temperature results in the immediate formation of thermally
stable Cp*M(NO→Sc(OTf)3)(H)(κ3-(C6H4)PhPCH2CH2PPh2) complexes in which one of the phenyl substituents
of the Ph2PCH2CH2PPh2 ligands
has undergone intramolecular orthometalation. In a similar manner,
addition of BF3 produces the analogous Cp*M(NO→BF3)(H)(κ3-(C6H4)PhPCH2CH2PPh2) complexes. In contrast,
B(C6F5)3 forms the 1:1 Lewis acid–base
adducts, Cp*M(NO→B(C6F5)3)(κ2-Ph2PCH2CH2PPh2) in CH2Cl2 at room temperature. Upon warming
to 80 °C, Cp*Mo(NO→B(C6F5)3)(κ2-Ph2PCH2CH2PPh2) converts cleanly to the orthometalated product Cp*Mo(NO→B(C6F5)3)(H)(κ3-(C6H4)PhPCH2CH2PPh2), but Cp*W(NO→B(C6F5)3)(κ2-Ph2PCH2CH2PPh2) generates a mixture of products whose identities
remain to be ascertained. Attempts to extend this chemistry to include
related Ph2PCH2PPh2 compounds have
had only limited success. All new complexes have been characterized
by conventional spectroscopic and analytical methods, and the solid-state
molecular structures of most of them have been established by single-crystal
X-ray crystallographic analyses.
