Syntheses of Molybdenum(VI) Imido Alkylidene Complexes That Contain a Bidentate Dithiolate Ligand

Zn­(DCTC)
(DCTC = 3,6-dichlorodithiacatecholate) reacts with Mo­(NAd)­(CHCMe2Ph)­Cl2(PPh2Me) (Ad = 1-adamantyl) to
give Mo­(NAd)­(CHCMe2Ph)­(DCTC)­(PPh2Me). The reactions
between Zn­(DCTC) and Mo­(NAd)­(CH-t-Bu)­(OTf)2(dme) or Mo­(NAr)­(CHCMe2Ph)­(OTf)2(dme) (Ar =
2,6-i-Pr2C6H3; OTf
= triflate; dme = 1,2-dimethoxyethane) produce [Mo­(NAd)­(CH-t-Bu)­(DCTC)]2 and [Mo­(NAr)­(CHCMe2Ph)­(DCTC)]2, respectively. Complexes that contain a 3,3′,5,5′-tetrasubstituted
dithiabiphenolate were prepared in a reaction between Mo­(NAr)­(CHCMe2Ph)­(Me2pyr)2 (Me2pyr = 2,5-dimethylpyrrolide)
and the 3,3′,5,5′-tetrasubstituted dithiabiphenols,
(3,3′,5,5′-tetrachlorodithiabiphenol (H2Cl4S2), 3,3′,5,5′-tetrabromodithiabiphenol
(H2Br4S2), and 3,3′,5,5′-tetra-t-Bu-dithiabiphenol (H2Bu4S2)). The isolated complexes include Mo­(NAr)­(CHCMe2Ph)­(Cl4S2)­(pyridine), Mo­(NAr)­(CHCMe2Ph)­(Br4S2)­(pyridine), Mo­(NAr)­(CHCMe2Ph)­(Bu4S2)­(PMe3), and [Mo­(NAr)­(CHCMe2Ph)­(Cl4S2)]2. Only the dithiabiphenolate
derivatives (in the presence of B­(C6F5)3) show activity for the metathesis of 1-decene, and although
that reaction is limited by a sensitivity of the alkylidene complexes
to ethylene, as suggested by the reaction between ethylene and Mo­(NAr)­(CHCMe2Ph)­(Bu4S2) to give the ethylene complex,
Mo­(NAr)­(C2H4)­(Bu4S2).
Mo­(NAr)­(C2H4)­(Bu4S2) was
unstable with respect to loss of ethylene and formation of an ethylene-free
dimer. Mo­(NAd)­(CHCMe2Ph)­(DCTC)­(PPh2Me), [Mo­(NAr)­(CHCMe2Ph)­(DCTC)]2, and [Mo­(NAr)­(CHCMe2Ph)­(Cl4S2)]2 were characterized crystallographically.