Photoinduced oxidative addition to a quadruply bonded tungsten complex bis[bis(diphenylphosphino)methane]tetrachloroditungsten

Physical, Spectroscopic and Theoretical Results

“…289 In the photochemical reaction of W 2 Cl 4 (dppm) 2 with CH 3 I, this goal has been reached. 290 While thermal additions to quadruply-bonded molecules, which proceed by radical processes, give scrambling of ligands, the photoaddition of CH 3 I to W 2 Cl 4 (dppm) 2 gives a single pure product. It is believed 289 that the photoactivation occurs through a * or a * excitation (or both, since the two excited states are accidently almost degenerate).…”

Photoredox Chemistry of d4 Bimetallic Systems

“…Such similarities may be accounted for by the prediction of a small gap in the HOMO-LUMO manifold (49,(59)(60)(61)(62)(63). Inasmuch as the lowest energy transitions would be predicted to lie in the near-IR region, higher energy visible absorptions for these sys tems may have similar transitions that are not of HOMO^UMO paren tage.…”

“…Although CH 3 I (Mel) solutions of W 2 Cl 4 (dppm) 2 are indefinitely stable at room temperature in the absence of light, excitation with fre quencies energetically coincident with the metal-localized δπ* and πδ* transitions leads to the quantitative production of a single product. Chemical and spectroscopic analyses have shown that the product corresponds to the addition of Mel to the tungsten-tungsten bond to yield W 2 Cl 4 (dppm) 2 (CH 3 )(I) (62). Although the unequivocal determination of the coordination geometry about the tungsten-tungsten bond has been impeded by our inability to obtain single crystals for X-ray structural analysis, the electronic absorption spectrum of the photoproduct is similar to that of edge-sharing bioctahedral species, and * 3 C NMR spectroscopy indicates that the methyl group is more likely to be in a terminal rather than a bridging position.…”

“…In addition the parent ion cluster of W 2 Cl 5 (dppm) 2 I at 1441 amu is also observed in the FABMS of the photoproduct. This pentac^oro product is a signature of the free radical photoreactions of M^1 4 (P P) 2 complex^ We have accounted for the formation of M 2 C1 5 (P P) 2 X and^jj^Cl^P P) 2 X 2 products with a radical mechanism wherein the M 2 C1 4 (P P) 2 _çomplex photoreacts with substrate to produce a mixed-valence M 2 C1 4 (P P) 2 X primary photoproduct (eq 3) that disproportionates by either chlorine (eq 4) or X atom (eq 5) transfer (35,62).…”

Tungsten Compounds

“…109 The quantitative oxidative addition of CH 3 I to W 2 Cl 4 (µ-dppm) 2 has been achieved using visible irradiation ( > 435 nm), whereas the thermal reactions of this complex with alkyl iodides yield W 2 Cl 5 I(µ-dppm) 2 and W 2 Cl 4 I 2 (µ-dppm) 2 . 110 The susceptibility of W 2 Cl 4 (µ-dppm) 2 to oxidative addition is probably the explanation for why W 2 (µ-H)(µ-Cl)Cl 4 (µ-dppm) 2 was obtained during unsuccessful attempts to prepare W 2 Cl 4 (µ-dppm) 2 from the reaction between W 2 Cl 4 (PBu n 3 ) 4 with dppm in toluene for 12 h. 57 The target complex W 2 Cl 4 (µ-dppm) 2 was later prepared by a similar procedure using toluene:hexane solvent mixtures and a reduction in reaction time to 4 h. 34 Attempts to prepare W 2 Cl 4 (µ-dmpm) 2 4 , the H 2 formed as a by-product of the reduction oxidatively adds to the W 2 4+ core. 114 The W-W bond length of 2.3918(7) Å for W 2 (µ-H) 2 Cl 4 (µ-dppm) 2 is only 0.12 Å longer than W 2 Cl 4 (µ-dppm) 2 (2.269(1) Å).…”