Synthesis and protonation reactions of nitrosyl complexes [M2Cp (μ-K:115-C5H4)(μ-PR2)(CO)(NO)2] to give K : 11-NO-bridged derivatives (M = Mo, W; R = Cy, t Bu)

The title compounds were prepared upon reaction of BAr'4- salts of the known cations [M2Cp2(mu -PR2) (CO)2(NO)2]+ (M = Mo, W; R = Cy, tBu; Ar' = 3,5-C6H3(CF3)2), with commercial Me3NO & sdot;2H2O in fluorobenzene solution at 273 K, this promoting decarbonylation and cyclopentadienyl deprotonation to yield complexes with cyclopentadienylidene ligands bridging the metal centres (W-W = 2.9917(5) & Aring; when R = Cy). The use of dichloromethane as solvent, however, triggered a competitive chloride abstraction reaction by the Mo compounds that yielded the chloride complexes [Mo2Cp2Cl(mu -PR2)(CO)(NO)2], specifically formed with an anti disposition of the Cp ligands relative to the Mo2P plane, and cis positioning of carbonyl and chloride ligands relative to the P atom (Mo-Cl = 2.336(4) & Aring; when R = tBu). Protonation of the cyclopentadienylidene-bridged complexes with [H(OEt2)2](BAr'4) yielded the BAr'4- salts of the dicyclopentadienyl cations [M2Cp2(mu -K:11-NO) (mu -PR2)(CO)(NO)]+ (Mo-Mo = 3.1027(2) & Aring; when R = tBu; W- W = 3.0446(7) & Aring; when R = Cy), which display bridging nitrosyl ligands in the rare linear end-on:side-on coordination mode, and are kinetic rather than thermodynamic products, according to density functional theory calculations. When using HBF4 & sdot;OEt2 as protonation reagent on the PtBu2-bridged complexes, however, coordination of the external anion (in the K1-mode) also takes place, to yield the tetrafluoroborate complexes [M2Cp2(K1-BF4)(mu -PtBu2)(CO)(NO)2] as unique (Mo) or major (W) products. Methylation of the same cyclopentadienylidene complexes with [Me3O](BF4) was only observed for the tungsten cation, and took place specifically at the O atom of one nitrosyl ligand to give [W2Cp(mu -K:115-C5H4) (NOMe)(mu -PtBu2)(CO)(NO)](BF4), a complex displaying a linear methoxyimido ligand (W-N = 1.746(4) & Aring;; W-N-O = 163.5(4)o).