A Mono-, Di-, and Trivanadocene Phosphorus Oxide Series: Synthesis, Magnetism, and Chemical/Electrochemical Properties.

In this Article, we outline the synthesis of B(C6 F5 )3 -coordinated mono-, di-, and trivanadocene phosphorus oxide complexes, Cp2 VOP(OB(C6 F5 )3 )Ph2 (2), (Cp2 VO)2 P(OB(C6 F5 )3 )Ph (3), and (Cp2 VO)3 P(OB(C6 F5 )3 ) (4), respectively (Cp = η5 -cyclopentadienyl). The complexes were synthesized from the known reagents, Cp2 VF and Ph2 P(O)OSiMe3 (for 2) or PhP(O)(OSiMe3 )2 (for 3) or (Me3 SiO)3 PO (for 4), via Me3 SiF elimination and in the presence of B(C6 F5 )3 . The multimetallic complexes (3 and 4) could not be synthesized without the capping B(C6 F5 )3 Lewis acid, whereas the uncapped version of 2, Cp2 VOP(O)Ph2 (1), has previously been reported by us. Spectroscopic and crystallographic analyses of 2-4 support an increasingly Lewis basic P═O bond upon substitution of -Ph for -OVCp2 fragments (2-4). The increased metal nuclearity also results in increasingly reducing complexes as evidenced by cyclic voltammetry (CV). Magnetic measurements (SQUID) further revealed high-spin complexes with negligible magnetic exchange between V centers. Chemical oxidation of 2 with 0.5 equiv of [Ag][B(C6 F5 )4 ] resulted in a ligand rearrangement reaction producing the VIV product, Cp2 V(OP(OB(C6 F5 )3 )Ph2 )2 (7). In contrast, the oxidation of 4 with the trityl salt, [Ph3 C][B(C6 F5 )4 ], resulted in the isolation of a mixed-valent VIII /VIV dimetallic species, (Cp2 VO2 P(OB(C6 F5 )3 )OVCp2 (9). Both oxidations likely produce the [Cp2 V][B(C6 F5 )4 ] byproduct and evidence for its formation is presented. The synthesis and characterization of the mono- and dimetallic species, Cp2 VOP(OBPh3 )Ph2 (8) and (Cp2 VO)2 P(OB(C6 F5 )3 )OSiMe3 (5), is also reported.