Reactivity of 17-electron organometallic tungsten and molybdenum radicals: A laser flash photolysis study

Journal Article · Wed Mar 10 04:00:00 EST 1993 · Journal of the American Chemical Society; (United States)

DOI:https://doi.org/10.1021/ja00058a025· OSTI ID:6215217

Scott, S L; Espenson, J H; Zhu, Zuolin ^[1]

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1. Ames Lab., IA (United States)

Visible (460--490 nm) laser flash photolysis of [CpW(CO)[sub 3]][sub 2] or [CpMo(CO)[sub 3]][sub 2] induces homolysis of the metal-metal bond with formation of 17-electron radicals, CpM(CO)[sub 3]. Radical dimerization results in quantitative recovery of the parent dimer and can be followed by the time-resolved increase in dimer absorbance. The reaction follows clean second-order kinetics, -d[CpM(CO)[sub 3]]/dt = 2k[sub c][CpM(CO)[sub 3]][sup 2]; k[sub c](W) = 6.2 [times] 10[sup 9] and k[sub c](Mo) = 3.9 [times] 10[sup 9] L mol[sup [minus]1] s[sup [minus]1] in CH[sub 3]CN at 23[degrees]C. The CpM(CO)[sub 3] radicals react with organic and inorganic halides and pseudohalides by an atom-transfer mechanism. In the presence of a large excess of the halide-containing substrate, the rate of loss of the radical, -d[CpM(CO)[sub 3]]/dt, proceeds according to a mixed first- and second-order rate law. The pseudo-first-order rate constants for reactions with organic halides vary linearly with the concentration of the organic halide; bimolecular rate constants for CpW(CO)[sub 3] range from 3.9 [times] 10[sup 2] L mol[sup [minus]1] s[sup [minus]1] with CH[sub 2]Br[sub 2] to 1.34 [times] 10[sup 9] L mol[sup [minus]1] s[sup [minus]1] for CBr[sub 4]. The reactivity trends (RI > RBr > RCl) and (benzyl > allyl > 3[degrees] > 2[degrees] > 1[degrees] > CH[sub 3]) are observed. The 7 orders of magnitude variation in bimolecular rate constants is attributed to a highly selective atom abstraction process. The range of rate constants for atom abstraction from halo- and pseudohalopentaamminecobalt(III) and halobis(dimethylglyoximato)cobalt(III) complexes is smaller (2 orders of magnitude, from 1.6 1.6 [times] 10[sup 7] mol[sup [minus]1] s[sup [minus]1] for NCCo(NH[sub 3])[sub 5][sup 2+] to > 2 [times] 10[sup 9] L mol[sup [minus]1] s[sup [minus]1] for BrCo(dmgH)[sub 2]py), because of the upper limit imposed by diffusion. 97 refs., 6 figs., 3 tabs.

• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 6215217
• Journal Information: Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 115:5; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400500* -- Photochemistry
CHEMICAL REACTIONS
COBALT COMPLEXES
COMPLEXES
DATA
DECOMPOSITION
DIMERIZATION
ELECTROMAGNETIC RADIATION
ELEMENTS
EXPERIMENTAL DATA
HALOGEN COMPOUNDS
INFORMATION
KINETICS
LASER RADIATION
MOLYBDENUM COMPOUNDS
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
OXYGEN
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
POLYMERIZATION
RADIATIONS
RADICALS
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
SPECTROSCOPY
TIN COMPOUNDS
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS