Reactions of the Unsaturated Ditungsten Complexes [W₂Cp₂(μ-PPh₂)₂(CO)_x] (x = 1, 2) with Nitric Oxide: Stereoselective Carbonyl Displacement and Oxygen-Transfer Reactions of a Nitrite Ligand

Abstract

The dicarbonyl complex trans-[W2Cp2(μ-PPh2)2(CO)2] (Cp = η(5)-C5H5) reacted rapidly with NO (5% in N2) at 273 K to give selectively cis-[W2Cp2(μ-PPh2)2(NO)2]. In contrast, the analogous reactions of monocarbonyl [W2Cp2(μ-PPh2)2(μ-CO)] yielded either trans-[W2Cp2(μ-PPh2)2(NO)2] or the nitrito complex [W2Cp2(μ-PPh2)2(ONO)(CO)(NO)] (W-W = 2.9797(4) Å), depending on experimental conditions, with the latter presumably arising from reaction with trace amounts of oxygen in the medium. The stereoselectivity of the above reactions can be rationalized by assuming the participation of 33-electron [W2Cp2(μ-PPh2)2(CO)(NO)] intermediates which rapidly add a second molecule of NO via η(2)-C5H5 intermediates to eventually yield the corresponding dinitrosyls with inversion of the stereochemistry at the dimetal center, as supported by density functional theory (DFT) calculations. The nitrito complex was thermally unstable and evolved through oxygen transfer either to the carbonyl ligand, to yield the above dinitrosyls with release of CO2, or to the phosphide ligand, to give the phosphinito derivative cis-[W2Cp2(μ-OPPh2)(μ-PPh2)(NO)2], depending on experimental conditions. According to DFT calculations, the first process would involve transient dissociation/recombination of the nitrite ligand followed by coupling to carbonyl to give an intermediate with a chelate W{C,N-C(O)ON(O)} ring. Indeed, the nitrite ligand could be easily removed upon reaction of the nitrito complex with Na(BAr'4), but immediate decomposition also took place to render the electron-precise dicarbonyl [W2Cp2(μ-PPh2)2(CO)2(NO)]BAr'4 (W-W = 2.9663(3) Å) as the unique product (Ar' = 3,5-C6H3(CF3)2). Attempts to decarbonylate the latter complex photochemically yielded instead the oxo derivatives cis- and trans-[W2Cp2(μ-PPh2)2(O)(NO)]BAr'4 as the only isolable products (W-W = 2.980(2) and 3.0077(3) Å, respectively).

N–O Bond Activation and Cleavage Reactions of the Nitrosyl-Bridged Complexes [M2Cp2(μ-PCy2)(μ-NO)(NO)2] (M = Mo, W)

“…Found: C,44.20;H,3.12;N,2.67. Data for isomer A: 1 H NMR:  7.72 (m, 8H, C6H2), 7.56 (m, 4H, C6H2), 6.04, 5.75 (2s, 2 x 5H, Cp), 4.00 (d, JPH = 2, 3H, NMe), 2.80-0.60 (m, 22H, Cy). 13 (10 mL) of compound 1a (0.050 g, 0.082 mmol) was stirred vigorously with Na(Hg) (1 mL of a 0.5% amalgam, 1.03 mmol) for 10 min to give a brown solution. The solvent was then removed from the solution under vacuum, the residue was extracted with dichloromethane/petroleum ether (1/2) and the extracts chromatographed on an alumina column at 288 K. Elution with dichloromethane/petroleum ether (2/1) gave a yellow fraction yielding, after removal of solvents, compound 5a as a yellow solid (0.015 g, 31%).…”

Mild N–O Bond Cleavage Reactions of a Pyramidalized Nitrosyl Ligand Bridging a Dimolybdenum Center

“…14 We note that no nitroxyl-bridged complexes have been characterized previously. (5); Mo2O3= 2.092(4); N3O3 = 1.348 (6).…”

“…5 Compound 1 is a 34-electron complex for which a single metalmetal bond should be formulated, and is devoid of any particularly chromogenic ligand; therefore, it would be expected to display a color in the red to yellow range, as it is the case of the isoelectronic dinitrosyl complexes [W 2 Cp 2 (-PPh 2 ) 2 (NO) 2 ], 6 and related molecules. 7 Surprisingly, however, compound 1 turned to be a dark blue material both in solution and in the solid state.…”

E–H Bond Activation and Insertion Processes in the Reactions of the Unsaturated Hydride [W2Cp2(μ-H)(μ-PPh2)(NO)2]

“…An overall analysis of the 31 P NMR parameters of compounds 4, 5, and 7 to 10, as well as those of related complexes of type trans-[W2Cp2(-PPh2)(-X)(NO)2] recently described by us, with ligands X = PPh2, 22 SMe and I, 6 Br and Cl, 43 reveal no clear trends concerning their chemical shifts. In contrast, their one-bond couplings to the tungsten atoms correlate quite well with the Pauling electronegativity (P) of the bridgehead atom of the ligand X ( Figure 7).…”

“…Spectroscopic data for the stannyl compound 3 are comparable to those of isomer B of the trihydride 2, notably those concerning the chemical shifts and couplings of the P and hydride atoms, which now also display couplings to the Sn atom, as expected. In particular, its 1 H NMR spectrum denotes the presence of a terminal hydride trans to the 6,22 There are, however, significant differences in the one-bond PW couplings when changing X in this family of compounds, a matter to be discussed later on. We also note that the pyramidal environment around the S and O atoms of the bridging ligands in 4 and 5 renders inequivalent W centers, which is reflected in the observation of two distinct NMR resonances for the cyclopentadienyl ligands in each case.…”