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

Abstract

In this Article, we outline the synthesis of B(CF)-coordinated mono-, di-, and trivanadocene phosphorus oxide complexes, CpVOP(OB(CF))Ph (2), (CpVO)P(OB(CF))Ph (3), and (CpVO)P(OB(CF)) (4), respectively (Cp = η-cyclopentadienyl). The complexes were synthesized from the known reagents, CpVF and PhP(O)OSiMe (for 2) or PhP(O)(OSiMe) (for 3) or (MeSiO)PO (for 4), via MeSiF elimination and in the presence of B(CF). The multimetallic complexes (3 and 4) could not be synthesized without the capping B(CF) Lewis acid, whereas the uncapped version of 2, CpVOP(O)Ph (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 -OVCp 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(CF)] resulted in a ligand rearrangement reaction producing the V product, CpV(OP(OB(CF))Ph) (7). In contrast, the oxidation of 4 with the trityl salt, [PhC][B(CF)], resulted in the isolation of a mixed-valent V/V dimetallic species, (CpVOP(OB(CF))OVCp (9). Both oxidations likely produce the [CpV][B(CF)] byproduct and evidence for its formation is presented. The synthesis and characterization of the mono- and dimetallic species, CpVOP(OBPh)Ph (8) and (CpVO)P(OB(CF))OSiMe (5), is also reported.

Vanadium Pentafulvene Complexes: Synthon for Unprecedented VanadoceneIIIDerivatives

“…The vanadium centers are trigonally planar coordinated with bent vanadocenes ( 5 a : 142.9°; 5 b : 141.7°, 141.1°; 6 : 145.9°), and the C ispo −C exo bonds are elongated to single bonds ( 5 a : 1.513(2) Å; 5 b : 1.502(2) Å, 1.513(1) Å; 6 : 1.5248(8) Å) compared to the single to double bonds found in 2 a and 2 b and the double bonds in the free pentafulvenes [21,31,38] . The newly formed V−O bonds ( 5 a : 1.9729(9) Å; 5 b : 1.9822(9) Å, 1.9899(8) Å; 6 : 1.9361(5) Å) match those in known vanadium phenolate complexes, [40] and are similar to the bond length in recently reported vanadocene III phosphate complexes (1.96–2.03 Å) [41] …”

Mesoionic Carbenes in Low- to High-Valent Vanadium Chemistry

“…Among the early transition metals, vanadium chemistry has witnessed a remarkable activity over the past 50 years and has been applied in heterogeneous and homogeneous catalysis, small molecule activation, − molecular magnetism, − and spin qubits. − Narrowing down the field to NHC vanadium complexes, since the first two reports of vanadium NHC complexes in 1994 by Roesky et al. and 2003 by Abernethy et al , the utility of these complexes has mostly been explored in polymerization catalysis. − Beyond this, only a few other applications of vanadium-NHC complexes have been examined, including small molecule activation , and the neutralization of chemical warfare agents .…”

Redox-Controlled Reactivity at Boron: Parallels to Frustrated Lewis/Radical Pair Chemistry

“…Our group has been exploring new reactivity at main-group centers by tethering these to redox-active metal centers, such as V or Fe. − In a recent contribution, we uncovered how a typically unreactive P V O bond tethered to a neighboring V V center in the complexes (Ph 2 N) 3 VN–P­(O)­Ar 2 (Ar = Ph, C 6 F 5 ) can engage in H atom (H·) or silyl group (Me 3 Si·) transfer chemistry, resulting in the proposed protonation or isolated silylation of the P V O bond, respectively, with the concurrent reduction of V V to V IV . Similar reactivity was not observed in related all-main-group model compounds (ex.…”