COMPLEXES CONTAINING CIS-[(MOO2)-O-V](-[(MOO)-O-V(OH)](2+) CENTERS() AND CIS)

Cobaltocene reduction of LMo(VI)O(2)(SPh) complexes yielded extremely dioxygen-sensitive cobaltocenium salts of the cis-dioxo-Mo(V) radical anions cis-[LMo(V)O(2)(SPh)](-), while sodium acenaphthalenide reducti on of L(a)-Wo(VI)O(2)(SPh) yielded a complex sodium salt containing [L (a)Mo(V)O(2)(SPh)](-) [L = hydrotris(3,5-dimethylpyrazol-1-yl)borate ( L(a)), hydrotris(3-isopropylpyrazol-1-yl)borate (L(b)), or hydrotris(3 ,5-dimethyl-1,2,3-triazol-1-yl)borate (L(c))]. Crystals of [CoCp(2)][L (c)Mo(V)O(2)(SPh)]. toluene were orthorhombic, space group Pbca, with a = 17.695(3) Angstrom, b = 19.490(3) Angstrom, c = 21.925(4) Angstrom , V = 7561(2) Angstrom(3) for Z = 8. The structure, refined using a fu ll-matrix least-squares procedure and 2269 data, converged with R = 0. 067 (R(w) = 0.067). In the distorted octahedral anion, the metrical pa rameters of the cis-(MoO2)-O-V fragment [Mo-O = 1.742(9) Angstrom, O-M o-O = 112.1(4)degrees] are significantly larger than those of L(c)Mo(V I)O(2)(SPh) [average Mo-O = 1.700(6) Angstrom, O-Mo-O = 103.9(2)degree s]. O-18-Substitution of [CoCp(2)][L(ab)-(MoO2)-O-V(SPh)] permitted th e assignment of bands at ca. 870 and 770 cm(-1) to the nu(s), and nu,, modes, respectively, of the cis-(MoO2)-O-V fragment. Freshly prepared solutions of [CoCp(2)] [LMo(V)O(2)(SPh)] exhibited a broad EPR signal (g, 1.92; W-1/2, 20 G) characteristic of a Cis-[(MoO2)-O-V](+) comple x. The signal was stable when L = L(c) but when L = L(a) or L(b) it wa s replaced by a proton-coupled signal characteristic of a cis-[(MoO)-O -V(OH)](2+) center. The complex L(a)-MoVO(OH)(SPh) was isolated as a c oprecipitate with its conjugate base salt [CoCp(2)][L(a)Mo(V)O(2)(SPh) ]. It was characterized by infrared bands at 915 and 535 cm(-1), assig ned to nu(Mo=O) and nu(Mo-OH) modes, respectively. The anions were rea dily converted to air-stable LMo(V)O(OSiMe(3))(SPh) upon reaction with Me(3)SiCl and reacted with dioxygen to regenerate LMo(VI)O(2)(SPh). T he paper reports the first isolation in substance of compounds contain ing novel cis-[(MoO2)-O-V](+) and cis-[(MoO)-O-V(OH)](2+) centers and the first crystallographic characterization of a cis-dioxo-Mo(V) speci es.